磯野 史朗

The pharyngeal airway is surrounded by soft tissues that are also enclosed by bony structures such as the mandible, maxilla, and cervical spine. The passive pharyngeal airway is therefore structurally analogous to a collapsible tube within a rigid box. Cross-sectional area of the tube is determined by transmural pressure, the pressure difference between intraluminal and extraluminal pressures. Due to a lack of knowledge on the influence of extraluminal soft tissue pressure on the human pharyngeal airway patency, we hypothesized that application of negative external pressure to the submental region decreases collapsibility of the passive pharynx, and that obese individuals have less response to the intervention than nonobese individuals. Static mechanical properties of the passive pharynx were compared before and during application of submental negative pressure in 10 obese and 10 nonobese adult women under general anesthesia and paralysis. Negative pressure was applied through use of a silicone collar covering the entire submental region and a vacuum pump. In nonobese subjects, application of submental negative pressure (-25 and -50 cmH2O) significantly decreased closing pressures at the retropalatal airway by 2.3 ± 3.2 cmH2O and 2.0 ± 3.0 cmH2O, respectively, and at the retroglossal airway by 2.9 ± 2.7 cmH2O and 3.7 ± 2.6 cmH2O, respectively, and the intervention stiffened the retroglossal pharyngeal airway wall. No significant mechanical changes were observed during application of submental negative pressure in obese subjects. Conclusively, application of submental negative pressure was found to decreases collapsibility of the passive pharyngeal airway in nonobese Japanese women.

咽頭が様々な生理機能を遂行するためには閉塞性とその調節能力を有することが必要である。吸気相と吸気相からなる呼吸サイクルにおいても、気道開通性を維持するために様々な神経性調節機構が働いている。睡眠は、この調節機能を大きく抑制する。特に吸気時は咽頭狭窄が進行し、生体が想定した吸気流量が達成できず、呼吸流量が制限されるようになる。さらに生体の呼吸努力が強くなると咽頭壁が振動し、イビキ音が発生することとなる。閉塞性の高い咽頭気道を流れる呼吸流量と咽頭断面積、呼吸ドライブの相互作用を流体力学的に理解することは、睡眠呼吸障害に対する治療や研究の発展には重要である。(著者抄録)

BACKGROUND: Oral appliances are increasingly prescribed for patients with moderate obstructive sleep apnea (OSA) instead of nasal CPAP. However, the efficacy of oral appliances varies greatly. We hypothesized that oral appliances were not efficacious in patients with moderate OSA who were obese with oropharyngeal crowding. METHODS: Japanese patients with moderate OSA were prospectively and consecutively recruited. The Mallampati score (MS) was used as an estimate of oropharyngeal crowding. Follow-up polysomnography was performed with the adjusted oral appliance in place. Responders were defined as subjects who showed a follow-up apnea-hypopnea index (AHI) of < 5 with > 50% reduction in baseline AHI. RESULTS: The mean baseline AHI was reduced with an oral appliance from 21 ± 4 to 9.8 ± 8 in 95 subjects. Thirty-five patients were regarded as responders. Logistic regression analyses revealed that both MS and BMI could individually predict the treatment outcome. When the cutoff value of BMI was determined to be 24 kg/m2 based on a receiver operating characteristic curve, 53 obese patients (ie, BMI > 24 kg/m2) with an MS of class 4 were indicative of treatment failure with a high negative predictive value (92) and a low negative likelihood ratio (0.28). CONCLUSIONS: We conclude that patients with moderate OSA who are obese with oropharyngeal crowding are unlikely to respond to oral appliance treatment. This simple prediction can be applied without the need for any cumbersome tools immediately after the diagnosis of OSA.

Recent evidence suggests the possible development of difficult mask ventilation in patients with obstructive sleep apnea. Based on our current understanding of the pathophysiology of pharyngeal airway obstruction in obstructive sleep apnea patients, we conclude that anesthesiologists can decrease respiratory complications during anesthesia induction by conducting careful pre-induction preparations, including body and head positioning and sufficient preoxygenation, and by using the two-hand mask ventilation technique with effective airway maneuvers and appropriate ventilator settings while continuously assessing ventilation status with capnography.

Pleasantness associated with dyspnoea relief or 'respiratory pleasure' is considered as a particular sensory experience. The purpose of this study is to elucidate the mechanism of generation of this particular sensory experience. After taking deep breaths during normal breathing, 35 healthy subjects received three different magnitudes of inspiratory loads (light: 8.4; moderate: 23.4; severe: 70.5 cm H2O/L/s) to induce dyspnoeic sensation. We found that (1) deep breaths during normal breathing rarely induce 'respiratory pleasure', (2) a sudden removal of dyspnoea alone is not sufficient to produce 'respiratory pleasure', and (3) the generation of 'respiratory pleasure' can be observed when a sudden removal of dyspnoea accompanies a large increase in tidal volume (V(T)). In addition, qualitative assessment of 'respiratory pleasure' showed that this sensation is compatible with a strong, positively valenced sensation. These findings indicate that an increase in V(T) after removal of respiratory loading plays a crucial role in generation of 'respiratory pleasure' that is a specific sensory-emotional experience.

BACKGROUND: Recent studies suggest advantages of muscle relaxants for facemask ventilation. However, direct effects of muscle relaxants on mask ventilation remain unclear because these studies did not control mechanical factors influencing ventilation. We tested a hypothesis that muscle relaxants, either rocuronium or succinylcholine, improve mask ventilation. METHODS: In anesthetized adult persons with normal upper airway anatomy, tidal volumes during facemask ventilation were measured while maintaining the neutral head and mandible positions and the airway pressures of a ventilator before and during muscle paralysis induced by either rocuronium (n=14) or succinylcholine (n=17). Tidal volumes of oral and nasal airway routes were separately measured with a custom-made oronasal portioning full facemask. Behavior of the oral airway was observed by an endoscope in six additional subjects receiving succinylcholine. RESULTS: Total, oral, and nasal tidal volumes did not significantly change at complete muscle paralysis with rocuronium. In contrast, succinylcholine significantly increased total tidal volumes at 60 s after its administration (mean±SD; 4.2±2.1 vs. 5.4±2.6 ml/kg, P=0.02) because of increases of ventilation through both airway routes. Abrupt tidal volume increase occurred more through oral airway route than nasal route. Dilation of the space at the isthmus of the fauces was endoscopically observed during pharyngeal fasciculation in all six subjects. CONCLUSIONS: Rocuronium did not deteriorate facemask ventilation, and it was improved after succinylcholine administration in association with airway dilation during pharyngeal fasciculation. This effect continued to a lesser degree after resolution of the fasciculation.

A large tongue is recognised as a factor that increases the collapsibility of the upper airway in obstructive sleep apnoea (OSA) patients. We hypothesised that the propensity to develop severe OSA could be minimised if the dental arches were enlarged in obese OSA people who are thought to have a large tongue. We therefore compared the size of the dental arches in obese and non-obese OSA patients. Using a lateral cephalogram and study models, we compared the sizes of the tongue and dental arches in 23 obese and 23 non-obese Japanese male OSA patients, who were matched for age, apnoea hypopnea index (AHI) and maxillomandibular size. The median age (years) and AHI (events per hour) for the obese and non-obese groups were 36·5 and 39·0, and 13·4 and 14·3, respectively. The maxillomandibular size was matched with regard to SNA, SNB and lower face cage obtained from cephalometric measurements. The parameters that were measured for the study model included dental arch width, dental arch length, overjet and overbite. Tongue size (P < 0·05) and both upper (P < 0·01) and lower (P < 0·05) dental arch widths were significantly larger in obese than in non-obese OSA patients, and there was no difference in the severity of OSA between the two groups. These findings suggest that the tongue was larger and dental arches were enlarged in obese patients compared with non-obese patients under the same disease severity. Wider dental arches in obese OSA patients may help to offset the impact of the enlarged tongue on upper airway patency.

Epidemiological evidence suggests there are significant links between obesity and obstructive sleep apnoea (OSA), with a particular emphasis on the importance of fat distribution in the development of OSA. In patients with OSA, the structure of the pharyngeal airway collapses. A collapsible tube within a rigid box collapses either due to decreased intraluminal pressure or increased external tissue pressure (i.e. reduction in transmural pressure), or due to reduction in the longitudinal tension of the tube. Accordingly, obesity should structurally increase the collapsibility of the pharyngeal airway due to excessive fat deposition at two distinct locations. In the pharyngeal airway region, excessive soft tissue for a given maxillomandibular enclosure size (upper airway anatomical imbalance) can increase tissue pressure surrounding the pharyngeal airway, thereby narrowing the airway. Even mild obesity may cause anatomical imbalance in individuals with a small maxilla and mandible. Lung volume reduction due to excessive central fat deposition may decrease longitudinal tracheal traction forces and pharyngeal wall tension, changing the 'tube law' in the pharyngeal airway (lung volume dependence of the upper airway). The lung volume dependence of pharyngeal airway patency appears to contribute more significantly to the development of OSA in morbidly obese, apnoeic patients. Neurostructural interactions required for stable breathing may be influenced by obesity-related hormones and cytokines. Accumulating evidence strongly supports these speculations, but further intensive research is needed.

We highlight the areas we think important for future development of the subspeciality. The ultimate goal is to improve patient care and safety and to do this, we need to identify how and where episodes of harm arise. Simply continuing with current practice does not represent the best path towards our ultimate goal; objective evidence is needed to inform changes in practice.

Although dyspnoea has been shown to attenuate pain, whether different forms of dyspnoea exert a similar inhibitory effect on pain has never been tested. We examined the effects of two different forms of dyspnoea, i.e., "air hunger" sensation (AIR HUNGER) and "work/effort" sensation (WORK/EFFORT), on pain induced by a cold-pressor test. Dyspnoea was induced by two different dyspnoea stimuli (i.e., AIR HUNGER and WORK/EFFORT stimuli) and the magnitudes of both sensations were evaluated by using a visual analogue scale (VAS). At equi-dyspneic VAS levels of two different forms of dyspnoea, pain was induced and the unpleasantness of pain was assessed by pain VAS, pain threshold time (PTT) and pain endurance time (PET). Both AIR HUNGER and WORK/EFFORT caused an increase in PTT and an increase in PET or a decrease in maximal pain VAS. Our findings suggest that AIR HUNGER and WORK/EFFORT exert a similar analgesic effect although the WORK/EFFORT-induced analgesia was slightly more effective.

BACKGROUND: Obstructive sleep apnea (OSA) is an independent risk factor for difficult and/or impossible mask ventilation during anesthesia induction. Postural change from supine to sitting improves nocturnal breathing in patients with OSA. The purpose of this study was to evaluate the effect of patient position on collapsibility of the pharyngeal airway in anesthetized and paralyzed patients with OSA. The authors tested the hypothesis that the passive pharynx is structurally less collapsible during sitting than during supine posture. METHOD: Total muscle paralysis was induced with general anesthesia in nine patients with OSA, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plots between the supine and sitting (62° head-up) allowed assessment of the postural differences of the mechanical properties of the pharynx. RESULTS: : Maximum cross-sectional area was greater during sitting than during supine posture at both retropalatal (median (10th-90th percentile): 1.91 (1.52-3.40) versus 1.25 (0.65-1.97) cm) and retroglossal (2.42 (1.72-3.84) versus 1.75 (0.47-2.35) cm) airways. Closing pressure of the passive pharynx was significantly lower during sitting than supine posture. Differences of the closing pressures between the postures are 5.89 (3.73-11.6) and 6.74 (4.16-9.87) cm H2O, at retropalatal and retroglossal airways, respectively, and did not differ between the pharyngeal segments. CONCLUSIONS: Postural change from supine to sitting significantly improves collapsibility of pharyngeal airway in anesthetized and paralyzed patients with OSA.

STUDY DESIGN: Case series. OBJECTIVE: To analyze factors that contribute to the development of sleep apnea in patients with rheumatoid arthritis (RA) and upper cervical lesions. SUMMARY OF BACKGROUND DATA: No large prospective study has analyzed the association between sleep apnea and upper cervical involvement resulting from RA. Furthermore, only 1 report in the literature describes a case of sleep apnea accompanying rheumatoid vertical subluxation of the odontoid process. METHODS: The authors analyzed 8 consecutive RA patients with upper cervical lesions who underwent occipitocervical (O-C) fusion. The patients were examined with all-night polysomnography before and after surgery. Patients with apnea-hypopnea index values>or=5 were diagnosed to have sleep apnea. O-C2 angles were calculated from cervical radiographs. RESULTS: All 8 patients were diagnosed as having sleep apnea, and most of their apneic episodes were obstructive in origin. Among the 4 patients with medullary compression, central apneic episodes comprised<or=5% of their respiratory events. Two patients with severe sleep apnea had negative O-C2 angles. Six patients who showed postoperative improvements in their sleep apnea all had positive changes in their O-C2 angles exceeding 5 degrees after surgery. The differences between preoperative and postoperative O-C2 angles were significantly greater in the patients with improvement of sleep apnea than in the patients with worsening sleep apnea. CONCLUSION: All our study patients with RA and upper cervical lesions had obstructive-dominant sleep apnea. Negative O-C2 angles may result in upper airway narrowing, increasing the severity of sleep apnea. O-C fusion with correction of kyphosis at the craniovertebral junction has the potential to improve sleep apnea in RA patients.

Dyspnea and pain have a number of similarities. Recent brain imaging experiments showed that similar cortical regions are activated by the perceptions of dyspnea and pain. We tested the hypothesis that an individual's pain sensitivity might parallel the individual's dyspnea sensitivity. Studies were carried out in 52 young healthy subjects. Each subject experienced experimentally induced pain and dyspnea. Pain was induced by a cold-pressor test and dyspnea was induced by breathholding while the unpleasant experience of pain and dyspnea was assessed by using a Visual Analogue Scale (VAS). The times from the start of cold stimulation and breathholding to the onset of uncomfortable sensation (pain threshold time and the period of no respiratory sensation, respectively) and to the limit of tolerance (pain endurance time and total breathholding time, respectively) were also measured. In response to cold pain stimulation, a behavioral dichotomy (pain-tolerant and pain-sensitive) was observed. The period of no respiratory sensation was significantly shorter in the PS (pain-sensitive) group than in the PT (pain-tolerant) group (16.9+/-3.8 vs. 19.6+/-5.3 s: P<0.05), whereas no significant difference in the total breathholding time was found between the PT and PS groups. A significant correlation was observed between the pain threshold time and the period of no respiratory sensation in both the PT and PS groups. However, no significant association was observed between pain and dyspnea tolerance in both groups. In conclusion, an individual's pain threshold is correlated to the individual's dyspnea threshold, but the individual's pain tolerance is not consistently correlated to the individual's dyspnea tolerance.

Collapsible pharyngeal airway size is determined by interaction between structural properties of the pharyngeal airway and neural regulation of the pharyngeal dilating muscles. Obesity seems to have two distinct mechanical influences on the pharyngeal airway collapsibility. First, obesity increases soft tissue surrounding the pharyngeal airway within limited maxillomandible enclosure occupying and narrowing its space (pharyngeal anatomical imbalance). Second, obesity, particularly central obesity, increases visceral fat volume decreasing lung volume. Pharyngeal wall collapsibility is increased by the lung volume reduction, possibly through decreased longitudinal tracheal traction (lung volume hypothesis). Neural compensation for functioning structural abnormalities operating during wakefulness is lost during sleep, leading to pharyngeal obstruction. Instability of the negative feedback of the respiratory system may accelerate cycling of pharyngeal closure and opening. Improvement of the pharyngeal anatomical imbalance and maintenance of lung volume are the keys for safe perioperative airway managements of obese patients with obstructive sleep apnea.

Inhibition of ventilatory drive may improve the sensation of dyspnea, because heightened ventilatory demand contributes to dyspnea. Tris-hydroxymethyl aminomethane (THAM) is an alkalizing agent that does not increase CO(2) production and exerts a depressant effect on respiration. The purpose of this study was to clarify the effect of THAM on dyspnea associated with increases in respiratory drive. We investigated the effects of THAM on dyspneic sensation produced by a combination of hypercapnia (mean PaCO(2)=52 mm Hg) and elastic loading (30 cm H(2)O/L) in 14 healthy subjects. The subjects were asked to rate their dyspneic sensation using a visual analogue scale (VAS) during the loaded breathing while monitoring ventilation using a pneumotachograph. THAM was infused at a rate of 0.4 mL/kg/minute for 10 minutes, and the effects of THAM on dyspnea and ventilation were evaluated by comparing the steady-state values of ventilatory variables and VAS score obtained before and after THAM administration. Administration of THAM corrected respiratory acidosis and was associated with significant improvements in VAS score and significant decreases in minute ventilation, respiratory frequency, and ventilatory drive. THAM administration greatly alleviates dyspneic sensation associated with the increase in respiratory drive and could be an effective therapy for treating severe dyspnea in patients with hypercapnia.

BACKGROUND: Previous study has demonstrated that dyspnea exerts inhibitory influence on pain, and empirical research supports the existence of sex differences in pain. To test the hypothesis that the inhibitory influence of dyspnea on the pain sensation may be less in females than in males, the authors investigated the sex differences in the responses of thermal pain threshold to dyspnea in healthy young subjects. METHODS: The authors measured changes in thermal pain threshold in 30 female subjects and 30 male subjects before and during dyspnea produced by a combination of hypercapnia and elastic loading, and compared the difference between males and females. RESULTS: The thermal pain threshold significantly increased during loaded breathing in male subjects (46.0 degrees +/- 1.3 degrees vs. 47.2 degrees +/- 1.2 degrees C; P < 0.01, baseline vs. loaded breathing), whereas no change was observed in female subjects (46.1 degrees +/- 1.3 degrees vs. 46.0 degrees +/- 1.4 degrees C; P > 0.1). No significant correlation was observed between the values of dyspneic visual analog scale and changes in thermal pain threshold. Comparison of the different phases of the menstrual cycle in female subjects also showed that there was no consistent effect of the particular phase on thermal pain threshold (45.7 degrees +/- 1.0 degrees vs. 46.1 degrees +/- 1.4 degrees C; P > 0.1, follicular phase vs. luteal phase during baseline; and 45.9 degrees +/- 1.1 degrees vs. 46.0 degrees +/- 1.7 degrees C; P > 0.1, follicular phase vs. luteal phase during loaded breathing). CONCLUSION: The inhibitory influence of dyspnea on the pain sensation is less in females than in males, but the sex difference may not be explained by female reproductive hormones alone.

BACKGROUND: Obesity and craniofacial abnormalities such as small maxilla and mandible are common features of patients with obstructive sleep apnea (OSA). The authors hypothesized that anatomical imbalance between the upper airway soft-tissue volume and the craniofacial size (rather than each alone) may result in pharyngeal airway obstruction during sleep, and therefore development of OSA. METHODS: Blind measurements of tongue cross-sectional area and craniofacial dimensions were performed through lateral cephalograms in 50 adult male patients with OSA and 55 adult male non-OSA subjects with various craniofacial dimensions. RESULTS: Maxillomandibular dimensions were matched between OSA and non-OSA groups. While the tongue was significantly larger in subjects with larger maxillomandible dimensions, OSA patients had a significantly larger tongue for a given maxillomandible size than non-OSA subjects. The hypothesis was also supported in subgroups matched for both body mass index and maxillomandible dimensions. CONCLUSIONS: Upper airway anatomical imbalance is involved in the pathogenesis of OSA.

The aim of this study was to clarify whether coughing elicited by airway irritation can modulate the sensation of air hunger. Using a visual analog scale (VAS), we measured air hunger for 30 s following breakpoint of a breath-hold in healthy young subjects who were asked to resume their breathing according to four patterns (free breathing, citric acid inhalation, voluntary cough, and panting) before and/or after airway anaesthesia. We also measured air hunger for citric acid-induced coughing and voluntary coughing without the preceding breath-holding. The free breathing after breakpoint of breath-holding causes an immediate relief of air hunger (VAS median values at 5, 15 and 25 s after breath-hold: 39, 0 and 0), whereas voluntary coughing causes a delay in the relief of air hunger (67, P < 0.05; 17, P < 0.05; and 0, NS) and a slower relief occurred during citric acid-induced coughing (81, P < 0.01; 49, P < 0.05; and 12, P < 0.05). Conversely, the voluntary coughing and citric acid-induced coughing per se failed to induce air hunger. Inhalation of lidocaine aerosol completely abolished the cough response to citric acid inhalation causing an immediate relief of air hunger, whereas airway anaesthesia alleviated only slightly the air hunger during voluntary coughing. The changes in air hunger during the panting were similar to those during the voluntary coughing observed before airway anaesthesia and were not affected by airway anaesthesia (VAS at 15 s point before versus after anaesthesia: 18 versus 15; NS). Coughing induced by airway irritation per se does not generate the sensation of air hunger but can aggravate it, presumably by vagally mediated mechanisms and/or central mechanisms.

BACKGROUND: We lack fundamental knowledge of the mechanisms of difficult laryngoscopy despite its clinical significance. The aim of this study was to examine how head positioning and direct laryngoscopy alter arrangements of craniofacial structures. METHODS: Digital photographs of the lateral view of the head and neck were taken at each step of head positioning and direct laryngoscopy in age- and body mass index-matched patients with (n = 13) and without (n = 13) difficult laryngoscopy during general anesthesia with muscle paralysis. The images were used for measurements of various craniofacial dimensions. RESULTS: Both simple neck extension and the sniffing position produced a caudal shift of the mandible and a downward shift of the larynx, resulting in an increase of the submandibular space. Direct laryngoscopy during the sniffing position displaced the mandible and tongue base upward and caudally, and the larynx downward and caudally, increasing the submandibular space and facilitating vertical arrangement of the mandible, tongue base, and larynx to the facial line. These structural arrangements in response to direct laryngoscopy were not observed in patients with difficult laryngoscopy, whereas head positioning produced similar structural arrangements in patients with and without difficult laryngoscopy. CONCLUSION: Increase in the submandibular space and a vertical arrangement of the mandible, tongue base, and larynx to the facial line seem to be important mechanisms for improving the laryngeal view during head positioning and direct laryngoscopy. Failure of these structural arrangements in response to direct laryngoscopy may result in difficult laryngoscopy.

Lung volume dependence of pharyngeal airway patency suggests involvement of lung volume in pathogenesis of obstructive sleep apnea. We examined the structural interaction between passive pharyngeal airway and lung volume independent of neuromuscular factors. Static mechanical properties of the passive pharynx were compared before and during lung inflation in eight anesthetized and paralyzed patients with sleep-disordered breathing. The respiratory system volume was increased by applying negative extrathoracic pressure, thereby leaving the transpharyngeal pressure unchanged. Application of -50-cmH(2)O negative extrathoracic pressure produced an increase in lung volume of 0.72 (0.63-0.91) liter [median (25-75 percentile)], resulting in a significant reduction of velopharyngeal closing pressure of 1.22 (0.14-2.03) cmH(2)O without significantly changing collapsibility of the oropharyngeal airway. Improvement of the velopharyngeal closing pressure was directly associated with body mass index. We conclude that increase in lung volume structurally improves velopharyngeal collapsibility particularly in obese patients with sleep-disordered breathing.

BACKGROUND: Although functional immobility of craniofacial structures during direct laryngoscopy may cause difficult tracheal intubation (DTI), there may be an unfavorable specific craniofacial feature for successful tracheal intubation. The aim of this study was to identify the specific craniofacial features associated with DTI. METHODS: Digital photographs of nonobese patients with DTI (23 males and 18 females) and age- and body mass index-matched patients with easy tracheal intubation (ETI) (16 males and 16 females) were taken and used for measurements of various craniofacial dimensions. Composite facial pictures of each patient group were constructed for visualization of differences of the craniofacial features. RESULTS: Mandible position angle was significantly smaller in DTI males than in male patients with ETI. Submandible angle was significantly larger in both male and female DTI patients than in patients with ETI. Logistic regression analysis revealed that the submandible angle was a significant and independent variable associated with DTI among the craniofacial dimensions for both sexes. The specific craniofacial features were visually more evident in the profile in than frontal composites. CONCLUSION: Increased submandible angle characterizes craniofacial features of patients with DTI.

We evaluated the sensation of dyspnea induced by hypercapnia alone and a combination of hypercapnia and flow-resistive loading by the use of visual analogue scale (VAS) and the use of 13 listed descriptors in 23 healthy subjects. Hypercapnia alone caused a modest degree of dyspnea characterized by both air hunger and work/effort sensations. An addition of inspiratory flow-resistive loading (IRL) caused an increase in inspiratory difficulty and some attenuation of 'work/effort.' The addition of expiratory flow-resistive loading (ERL) caused an increase in expiratory difficulty and attenuation of 'air hunger.' The addition of both IRL and ERL caused a marked increase in dyspnea, the amount of which was close to the sum of the increases obtained individually by IRL and by ERL, while the quality of dyspnea was characterized predominantly by work/effort. These results suggest that despite the difference in quality of sensations, the intensity of dyspnea would sum linearly when the two kinds of loads are presented at the same time.

Majority of severe anesthetic complications result from airway difficulties. Among the airway difficulties, difficult mask ventilation is a key critical condition in the currently proposed difficult airway algorithms, and is probably the most life-threatening event. Presence of severe obstructive sleep apnea may indicate potential difficulty in mask ventilation during anesthesia induction. Lateral neck radiographs for patients with suspected airway difficulties may provide useful information for identification of potential patients with difficult mask ventilation. Among the parameters measured by the radiographs, I recommend anesthesiologists to measure distance between the hyoid bone and mandibular plane, which possibly reflects anatomical balance of the upper airway maintenance.

To investigate how sevoflurane modifies airway protective reflexes in anesthetized children, we recruited patients younger than 12-yr-old for our study. Anesthesia was induced with inhaled sevoflurane in oxygen. The airway was managed with a laryngeal mask airway and the patient breathing spontaneously. Depending on the depth of anesthesia, the subjects were divided into two groups: Group 1 and Group 2 (1% and 2% of end-tidal sevoflurane concentration, respectively). Behaviors of the larynx were assessed mainly by the fiberscopic images of the larynx as well as respiratory flow and esophageal pressure. A small dose, 0.02 mL/kg of distilled water (minimum 0.2 mL) was instilled to the larynx through a channel of the scope to evoke an airway protective reflex from the larynx. The responses were categorized into passive (laryngeal closure, laryngospasm, and apnea) and active (cough, expiration reflex, and swallowing reflex) responses. Ten subjects were included in each group. In both groups, the primary responses were passive; however, in Group 1, active reflexes were also observed in 8 of 10 subjects; no subjects in Group 2 had active reflexes (P < 0.01). We concluded that, in children, the depth of general anesthesia with sevoflurane modified airway protective reflexes.

BACKGROUND: Appropriate bag-and-mask ventilation with patent airway is mandatory during induction of general anesthesia. Although the sniffing neck position is a traditionally recommended head and neck position during this critical period, knowledge of the influences of this position on the pharyngeal airway patency is still inadequate. METHODS: Total muscle paralysis was induced with general anesthesia in 12 patients with obstructive sleep apnea, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plot between the neutral and sniffing neck positions allowed assessment of the influence of the neck position change on the mechanical properties of the pharynx. RESULTS: The static pressure-area curves of the sniffing position were above those of neutral neck position, with increasing maximum cross-sectional area and decreasing the closing pressure at both retropalatal and retroglossal airways. The beneficial effects of the sniffing position were greater in obstructive sleep apnea patients with higher closing pressure and smaller body mass index. CONCLUSIONS: Sniffing position structurally improves maintenance of the passive pharyngeal airway in patients with obstructive sleep apnea and may be beneficial for both mask ventilation and tracheal intubation during anesthesia induction.

Severe respiratory stress causes dyspnea, and a sudden release of this stress frequently accompanies a euphoric sensation. We hypothesized that acute severe respiratory stress may result in an elaboration of endogenous opioids within the central nervous system, and that these opioids may play significant roles in relieving dyspnea and generating euphoric sensation after a sudden removal of the stress. To test this hypothesis, we examined the effects of naloxone (0.04 mg/kg, I.V.) and the placebo (normal saline) on changes in respiratory sensation before and after the release of severe respiratory stress in a double-blind, randomized, crossover study in 14 healthy adults. Acute severe respiratory stress was induced by loaded breathing with a combination of resistive loading and hypercapnia. The subjects rated their changes in sensation by using a bidirectional visual analogue scale. Naloxone pretreatment affected neither the ventilation nor the development of dyspneic sensation during loaded breathing. Naloxone pretreatment only slightly attentuated the euphoric sensation developed after the release of severe respiratory stress. These findings suggest a small role of opioids in relieving dyspnea and in generating euphoria before and after a sudden removal of stress.

BACKGROUND: Previous reports indicate that detrimental laryngeal function persists over several hours after tracheal extubation even in patients who have regained full consciousness from anesthesia. The authors hypothesize that even after minor surgery, the presence of an endotracheal tube (ETT) impairs the receptors at the vocal cord and diminishes the defensive laryngeal function. The hypothesis was tested by comparing types of experimentally induced laryngeal airway reflexes before and after surgery in anesthetized patients with use of either an ETT or a Laryngeal Mask Airway. METHODS: Twenty adult patients undergoing elective minor surgeries were randomly allocated into two groups, the ETT and Laryngeal Mask Airway groups, depending on the airway management method used during surgery. While maintaining sevoflurane at 1 minimum alveolar concentration, laryngeal and respiratory responses were elicited by instillation of distilled water on the vocal cords immediately before and after surgery. Furthermore, the vocal cord angles were endoscopically measured under complete paralysis. RESULTS: Some laryngeal reflex responses of both groups, particularly the cough reflex, were significantly attenuated after minor surgery. Significant narrowing of the glottic aperture was evident in patients with ETT placement but not in patients with Laryngeal Mask Airway placement. CONCLUSIONS: With either airway intervention, laryngeal defensive reflexes are depressed immediately after surgery even without visible laryngeal swelling. The sensory impairment attributable to the presence of an ETT cannot be the solo factor responsible for the modification of the defensive airway reflexes elicited from the larynx.

Infantile tracheomalacia is a potentially life-threatening disease requiring prolonged artificial respiratory support. Diagnosis and management of this disease may be further improved by establishing a suitable objective and quantitative assessment protocol for tracheal collapsibility. It is our hypothesis that tracheal collapsibility can be represented by the relationship between intraluminal pressure and the cross-sectional area of the trachea. To test this hypothesis, static pressure/area relationships of the trachea were obtained from anesthetized and paralyzed infants, who were diagnosed as having tracheomalacia by endoscopic observation. These relationships were fitted on a linear regression model, followed by calculation of the estimated closing pressure. The tracheal closing pressure ranged from -8 to -27 cm H(2)O, suggesting easy collapsibility of the trachea during crying or coughing and noncollapsibility during the spontaneous respiratory cycle, which coincided with the infants' symptoms. It is our conclusion that tracheal collapsibility of infants with tracheomalacia can be quantitatively assessed by the static pressure/area relationship of the trachea obtained under general anesthesia and paralysis.

A collapsible tube surrounded by soft material within a rigid box was proposed as a two-dimensional mechanical model for the pharyngeal airway. This model predicts that changes in the box size (pharyngeal bony enclosure size anatomically defined as cross-sectional area bounded by the inside edge of bony structures such as the mandible, maxilla, and spine, and being perpendicular to the airway) influence patency of the tube. We examined whether changes in the bony enclosure size either with head positioning or bite opening influence collapsibility of the pharyngeal airway. Static mechanical properties of the passive pharynx were evaluated in anesthetized, paralyzed patients with sleep-disordered breathing before and during neck extension with bite closure (n = 11), neck flexion with bite closure (n = 9), and neutral neck position with bite opening (n = 11). Neck extension significantly increased maximum oropharyngeal airway size and decreased closing pressures of the velopharynx and oropharynx. Notably, neck extension significantly decreased compliance of the oropharyngeal airway wall. Neck flexion and bite opening decreased maximum oropharyngeal airway size and increased closing pressure of the velopharynx and oropharynx. Our results indicate the importance of neck and mandibular position for determining patency and collapsibility of the passive pharynx.

BACKGROUND: When oral or nasal fiberoptic laryngoscopy is attempted, mandibular advancement has been reported to improve the laryngeal view. The authors hypothesized that mandibular advancement may also improve the laryngeal view during direct laryngoscopy. METHODS: Forty patients undergoing elective surgery under general anesthesia were included in this study. After establishment of an adequate level of anesthesia and muscle relaxation, direct laryngoscopy was performed by inexperienced physicians. Four different maneuvers--simple direct laryngoscopy without any assistance (C), simple direct laryngoscopy with mandibular advancement (M), simple direct laryngoscopy with the BURP maneuver (backward, upward, rightward pressure maneuver of the larynx; B), and simple direct laryngoscopy with both mandibular advancement and the BURP maneuver (BM)--were attempted in each subject, and the laryngeal aperture was videotaped with each procedure. An instructor in anesthesiology who was blinded to the procedure evaluated the visualization by reviewing videotape off-line, using the Cormack-Lehane classification system (grades I-IV) and a rating score within each subject (1 = best view; 4 = poorest view). The Friedman test followed by the Student-Newman-Keuls test was performed for statistical comparison. P < 0.05 was considered significant. RESULTS: The laryngeal view was improved with M and B when compared with C (P < 0.05 by both rating and Cormack-Lehane evaluation). BM was the most effective method to visualize the laryngeal aperture (P < 0.05, vs. B and M by rating evaluation), whereas B and M were the second and the third most effective methods, respectively. No statistical difference was observed between B and M with the Cormack-Lehane classification. CONCLUSION: Mandibular advancement improves the laryngeal view during direct laryngoscopy performed by inexperienced physicians.

PURPOSE: This study was done to test the hypothesis that hypercapnia has a direct, inhibitory effect on swallowing. METHODS: We investigated changes in the frequency and timing of repeated swallows induced by continuous infusion of water into the pharynx before, during, and after transient airway occlusion at normocapnia and hypercapnia in 12 healthy volunteers. Hypercapnia was induced by adding a dead space. Ventilation was monitored using a pneumotachograph, and swallowing was identified by submental electromyogram. RESULTS: We found that hypercapnia decreased the frequency of swallows (8.2 +/- 3.7 vs 11.4 +/- 5.3 swallows.min-1 [mean +/- SD]: hypercapnia vs normocapnia; P < 0.05), together with a loss of the preponderant coupling of swallows with expiratory phase observed at normocapnia. We also found that the withdrawal of phasic lung inflation produced by airway occlusion at end-expiration suddenly increased the swallowing frequency, both at normocapnia (from 11.4 +/- 5.3 to 16.7 +/- 3.7 swallows.min-1; P < 0.01) and at hypercapnia (from 8.2 +/- 3.7 to 22.0 +/- 6.7 swallows.min-1; P < 0.01). Although the degree of increased swallowing frequency during airway occlusion was more prominent at hypercapnia than at normocapnia ( P < 0.05), the distribution of the timing of swallows in relation to the phase of the respiratory cycle during airway occlusion at hypercapnia was similar to that during airway occlusion at normocapnia. CONCLUSION: The results of our study strongly suggest that the attenuation of the swallowing reflex during hypercapnia is not due to the direct, inhibitory effect of CO2 on the swallowing center, but, rather, is due to the increased inhibitory influence of a lung-volume-related reflex.

Stimulation of laryngeal receptors is the natural starting point of defensive airway reflexes including the cough reflex, expiration reflex, spasmodic panting, and apnoea with laryngospasm. Although several different types of laryngeal receptors have been reported, the laryngeal irritant receptors are considered to play the most essential role in elicitation of defensive airway reflexes. Based on the knowledge that the laryngeal irritant receptors are stimulated by water solutions lacking chloride anions, we have developed an experimental method to elicit defensive airway reflexes with a direct instillation of distilled water onto the laryngeal mucosa in humans. Using this experimental method, we studied the characteristics of defensive airway reflexes in lightly anaesthetized patients with multiple system atrophy (MSA). The reflex responses to water stimulation observed in these patients were characterized by apnoea with laryngospasm while the cough reflex was never elicited. Endoscopic images of the larynx in these patients were also characterized by laryngeal oedema. Considering the pathological changes occurring in the central nervous system and the laryngeal mucosa, it is possible that the defensive airway reflexes may be modified by central and/or peripheral mechanisms in patients with MSA.

Little is known about the mechanisms of persistence of obstructive apnea. Structurally, the dorsum of the tongue locates anterior to the soft palate. On the basis of the observation of posterior displacement of the tongue during obstructive apnea, we hypothesized that the dorsum of the tongue pushes the anterior wall of the soft palate posteriorly during inspiratory efforts, maintaining closure at the retropalatal airway. To test this hypothesis, we measured the pressure between dorsum of the tongue and anterior wall of the soft palate (PT&P) during experimentally induced obstructive apneas in anesthetized patients with sleep-disordered breathing. P(T&P) changes during the obstruction significantly depended on collapsibility of the retroglossal airway. Progressive increase in the P(T&P) during obstructive apnea was observed only in patients with highly collapsible retroglossal airways. Significant increase in the P(T&P) during inspiratory effort in accordance with positive deflection pattern of P(T&P) tracing was evident in the patients with highly collapsible retroglossal airways. The results indicate significant dynamic interaction between the tongue and soft palate during both obstructive apnea and each inspiratory effort, possibly maintaining closure at the retropalatal airway.

BACKGROUND: The placement of an endotracheal tube (ETT) may promote laryngeal swelling, which is an important cause of upper airway obstruction after extubation. The authors hypothesized that laryngeal swelling after ETT placement increases laryngeal resistance and tested that hypothesis by comparing postoperative laryngeal patency between patients with ETT placement and those with a Laryngeal Mask Airway trade mark (LMA). METHODS: Fourteen adult patients who underwent elective minor surgeries were randomly allocated to two groups whose airway would be managed through ETTs (the ETT group) or LMAs (the LMA group) during the surgery. While maintaining at sevoflurane 1 minimum alveolar concentration, the authors measured laryngeal resistance before and after surgery, during both spontaneous breathing and mechanical ventilation under complete paralysis. In addition, they endoscopically measured the vocal cord angle under complete paralysis. RESULTS: In association with marked swelling of the vocal cords, the vocal cord angle significantly decreased after surgery in the ETT group, whereas the angle did not change in the LMA group. Laryngeal resistance during mechanical ventilation significantly increased only in the ETT group. Laryngeal resistance during spontaneous breathing significantly increased after surgeries in both groups. CONCLUSIONS: Postoperative laryngeal resistance increases at least in part because of laryngeal swelling in patients with ETT placement, whereas alteration of laryngeal neural control mechanisms has been also indicated. The use of the LMA trade mark has an advantage over ETT placement in order to avoid postoperative laryngeal swelling.

Short-term chest compression has been shown to decrease tidal volume and increase respiratory frequency. The present study was designed to assess and characterize the effect of long-term chest compression on breathing pattern and blood gases in awake rats. Chest compression was carried out by inflating a pneumatic cuff placed around the chest to a pressure of 25 mmHg and the pressure was maintained for 28 days. Respiratory frequency increased progressively until 14 days after chest compression whereas a decrease in tidal volume was stabilized within 3 days after chest compression. Although the changes in minute ventilation were small and no substantial change in Pa(CO2) was observed, an impairment of weight gain and a decrease in body temperature with a concomitant hypoxemia were evident during sustained chest compression. These observations suggest that the ventilatory response to chest compression may involve not only neural reflex mechanisms but also other non-reflex mechanisms. Sustained chest compression possibly impairs growth and metabolism.

OBJECTIVES/HYPOTHESIS: Uvulopalatopharyngoplasty improves sleep-disordered breathing, particularly in patients with sleep-disordered breathing with abnormally high collapsible airway exclusively at the retropalatal airway, as was previously reported. The present study examined the direct and long-term effects of uvulopalatopharyngoplasty on retropalatal airway collapsibility. STUDY DESIGN: Prospective longitudinal study of 18 patients with abnormally high collapsible airway exclusively at the retropalatal airway. METHODS: Closing pressure of the retropalatal airway was estimated by endoscopically obtaining static pressure/area relationship of the passive pharynx in completely paralyzed and anesthetized patients with sleep-disordered breathing (n = 18) before and 3 months after uvulopalatopharyngoplasty. The measurements were repeated 1 year after uvulopalatopharyngoplasty in eight of these patients. RESULTS: Uvulopalatopharyngoplasty decreased retropalatal airway closing pressure by 3.5 cm H2O; furthermore, a direct correlation between the severity of sleep-disordered breathing (as determined by nocturnal oximetry) and retropalatal airway closing pressure was revealed. Uvulopalatopharyngoplasty failures revealed retropalatal airway closing pressure greater than atmospheric pressure. Reduced retropalatal airway collapsibility was maintained up to 1 year after uvulopalatopharyngoplasty. Two patients developed marked stenosis of the retropalatal airway with aggravation of sleep-disordered breathing after initial improvement of sleep-disordered breathing and retropalatal airway collapsibility. CONCLUSIONS: Uvulopalatopharyngoplasty decreases the retropalatal airway collapsibility. The effect is maintained for at least 1 year after uvulopalatopharyngoplasty, whereas a few patients develop retropalatal airway stenosis leading to recurrence of sleep-disordered breathing.

BACKGROUND: Reduction of nocturnal obstructive events during lateral position in patients with obstructive sleep apnea was previously reported. However, little information is available regarding mechanisms of the improvement and the precise pharyngeal site influenced by the lateral position. The authors tested the hypothesis that structural properties of the passive pharynx change by changing the body position from supine to lateral. METHOD: Total muscle paralysis was induced with general anesthesia in eight patients with obstructive sleep apnea, eliminating neuromuscular factors contributing to pharyngeal patency. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. Comparison of static pressure-area plot between the positions allowed assessment of the influence of the position change on the mechanical properties of the pharynx. RESULTS: The static pressure-area curves of the lateral position were above those of the supine position, with increasing maximum cross-sectional area and decreasing the closing pressure at both retropalatal and retroglossal airways. CONCLUSIONS: Lateral position structurally improves maintenance of the passive pharyngeal airway in patients with obstructive sleep apnea.