Category Locality Theory: A unified account of locality effects in sentence comprehension

In real-time sentence comprehension, the comprehender is often required to establish syntactic dependencies between words that are linearly distant. Major models of sentence comprehension assume that longer dependencies are more difficult to process because of working memory limitations. While the expected effect of distance on reading times (locality effect) has been robustly observed in certain constructions, such as relative clauses in English, its generalizability to a wider range of constructions has been empirically questioned. The current study proposes a new metric of syntactic distance that capitalizes on the flexible constituency of Combinatory Categorial Grammar (CCG), and argues that it offers a unified account of the locality effects. It is shown that this metric correctly predicts both the presence of the locality effect in English relative clauses and its absence in verb-final languages, without assuming language- or dependency-specific differences in the sensitivity to the locality effect. It is further shown that the CCG-based distance is a significant predictor of the self-paced reading times from an English corpus, even when other known predictors such as dependency-based locality and surprisal are taken into account. These results suggest that human sentence comprehension involves rapid integration of input words into efficiently compressed syntactic representations, and CCG is a plausible theory of the grammar that subserves this process.

Impact of perioperative interruption of antithrombotic therapy on thrombotic and bleeding events in non-cardiac surgery

Funding Acknowledgements

Type of funding sources: None.

Introduction

Antithrombotic therapy including antiplatelet agents and anticoagulants are prescribed for secondary prevention in patients with established cardiovascular disease. Although antithrombotic therapy is often interrupted before non-cardiac surgery with or without perioperative bridging anticoagulation, the impact on thrombotic and bleeding events remains uncertain. 

Purpose

The aim of this study was to clarify the impact of perioperative interruption of anticoagulants on thrombotic and bleeding events in patients with established CVD undergoing elective non-cardiac surgery. 

Methods

A total of 330 patients chronically treated with antithrombotic therapy for secondary prevention underwent elective non-cardiac surgery under general anesthesia, with the complete interruption of antithrombotic agents. The study endpoints included all-cause death, thrombotic events, and major bleeding complications after surgical procedures. 

Results

Of 330 patients, 171 (51.8%) and 159 (48.2%) received antiplatelet agents and anticoagulants perioperatively. Atrial fibrillation (31.8%) and coronary artery disease (20.3%) were the major indications for antithrombotic regimens. Antithrombotic therapy was interrupted from 5 [2, 7] days before the surgery to 4 [2, 7] days postoperatively. Perioperative bridging therapy with unfractionated heparin was employed in 99 (30.0%) patients. During the hospitalization, 3 (0.9%) patients died due to non-cardiovascular causes. Thrombotic events and major bleeding occurred in 2 (0.6%) and 9 (2.7%) patients. Bridging therapy with heparin was non-significantly associated with an increased risk of bleeding events (5.1% vs. 1.7%, p = 0.09). In univariable and multivariable analyses, pre-operative hemoglobin level and operative duration were significantly associated with bleeding complications.

Conclusions

In the present study, complete interruption of antithrombotic therapy resulted in a few thrombotic events with a numerically higher rate of bleeding events in patients undergoing elective non-cardiac surgery. Pre-operative hemoglobin level and operative duration were significantly associated with post-operative bleeding complications.

Dynamic behaviour of the soft palate during nasal positive pressure ventilation under anaesthesia and paralysis: comparison between patients with and without obstructive sleep-disordered breathing

BACKGROUND

Difficult mask ventilation is common and is known to be associated with sleep-disordered breathing (SDB). It is our hypothesis that the incidence of expiratory retropalatal (RP) airway closure (primary outcome) during nasal positive pressure ventilation (PPV) is more frequent in patients with SDB (apnea hypopnea index ≥5 h^-1) than non-SDB subjects.

METHODS

The severity of SDB was assessed before surgery using a portable sleep monitor. In anaesthetized and paralysed patients with (n=11) and without SDB (n=9), we observed the behaviour of the RP airway endoscopically during nasal PPV with the mouth closed and determined the dynamic RP closing pressure, which was defined as the highest airway pressure above which the RP airway closure was reversed. The static RP closing pressure was obtained during cessation of mechanical ventilation in patients with dynamic RP closure during nasal PPV.

RESULTS

The expiratory RP airway closure accompanied by expiratory flow limitation occurred more frequently in SDB patients (9/11, 82%) than in non-SDB subjects (2/9, 22%; exact logistic regression analysis: P=0.022, odds ratio 3.6, 95% confidence interval 1.1-15.4). Receiver operating characteristic curve analyses indicated AHI >10h^-1 and presence of habitual snoring as clinically useful predictors for the occurrence of RP closure during PPV. Dynamic RP closing pressure was greater than the static RP closing pressure by approximately 4-5 cm H₂O.

CONCLUSIONS

Valve-like dynamic RP closure that limits expiratory flow during nasal PPV occurs more frequently in SDB patients.

Perioperative respiratory complications: current evidence and strategy discussed in 2017 JA symposium

Respiratory management during general anesthesia aims to safely secure the airway and maintain adequate ventilation to deliver oxygen to the vital organs, maintaining homeostasis even during surgery. Despite its clinical importance, anesthesiologists often encounter difficulties in properly managing respiration during the perioperative period, leading to severe respiratory complications. In this year's JA symposium, 5 editorial board members of Journal of Anesthesia (JA) who are experts in the field of respiratory management in anesthesia discussed the following topics: quitting smoking before surgery: exposure to passive smoke is damaging to children, ventilator-associated pneumonia, high inspiratory oxygen concentration and lung injury, aspiration pneumonia, and postoperative respiratory management strategy in patients with obstructive sleep apnea. We hope that this special article regarding this year's JA symposium may be useful for JA readers to manage clinical anesthesia on a daily basis.

Laryngeal inputs in defensive airway reflexes in humans

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.

Effects of minor surgery and endotracheal intubation on postoperative breathing patterns in patients anaesthetized with isoflurane or sevoflurane

We studied the effects of minor surgery and endotracheal intubation on postoperative breathing patterns. We measured breathing patterns and laryngeal resistance during the periods immediately before intubation (preoperative) and immediately after extubation following minor surgery (postoperative) in eight patients anaesthetized with sevoflurane and eight patients anaesthetized with isoflurane, breathing spontaneously through a laryngeal mask airway at a constant end-tidal anaesthetic concentration (1.0 MAC). In both sevoflurane-anaesthetized and isoflurane-anaesthetized patients, expiratory time was reduced and inspiratory and expiratory laryngeal resistance increased after surgery. In sevoflurane-anaesthetized patients, occlusion pressure (P0.1) increased without changes in inspiratory time (T(I)). Occlusion pressure did not change and T(I) was greater in isoflurane-anaesthetized patients after surgery. Minor surgery may have a small but significant influence on breathing and increased laryngeal resistance following endotracheal intubation may modulate these changes. The difference in breathing pattern between sevoflurane and isoflurane may be a result of different responses of the central nervous system to different anaesthetics in the presence of increased laryngeal resistance.

Pathogenesis of laryngeal narrowing in patients with multiple system atrophy

1. We do not fully understand the pathogenesis of nocturnal laryngeal stridor in patients with multiple system atrophy (MSA). Recent studies suggest that inspiratory thyroarytenoid (TA) muscle activation has a role in the development of the stridor. 2. The breathing pattern and firing timing of TA muscle activation were determined in ten MSA patients, anaesthetized with propofol and breathing through the laryngeal mask airway, while the behaviour of the laryngeal aperture was being observed endoscopically. 3. Two distinct breathing patterns, i.e. no inspiratory flow limitation (no-IFL) and IFL, were identified during the measurements. During IFL, significant laryngeal narrowing was observed leading to an increase in laryngeal resistance and end-tidal carbon dioxide concentration. Development of IFL was significantly associated with the presence of phasic inspiratory activation of TA muscle. Application of continuous positive airway pressure suppressed the TA muscle activation. 4. The results indicate that contraction of laryngeal adductors during inspiration narrows the larynx leading to development of inspiratory flow limitation accompanied by stridor in patients with MSA under general anaesthesia.

Modulation of swallowing reflex by lung volume changes

We investigated the effects of changes in lung volume on coordination of respiration and swallowing in 11 healthy subjects. Swallowing reflexes were elicited by bolus injections of a small amount of distilled water (1 ml) and by continuous infusion of distilled water (3 ml/min) into the pharynx at three different levels of lung volume. The lung volume was changed by application of negative extrathoracic pressure (0, -20, and -40 cm H(2)O). We found that increases in lung volume prolonged the latency of swallows elicited by bolus injection of water and decreased the number of swallows during continuous infusion of water. In addition, the preponderant coupling of swallows with the expiratory phase observed before application of negative extrathoracic pressure was lost during application of negative extrathoracic pressure. These results may indicate that lung inflation has an inhibitory influence on the swallowing reflex, and modulates the timing of swallowing in reference to the respiratory cycle.

Developmental changes in collapsibility of the passive pharynx during infancy

The upper airway configuration significantly changes during the first year of life in humans, possibly leading to alteration of collapsibility of the pharyngeal airway. The present study evaluated developmental changes of passive pharyngeal mechanics in nine normal infants ranging in age from 2 to 12 mo. The static pressure-area relationship of the passive pharynx was quantified under general anesthesia with complete paralysis. We found a direct association between age and maximal velopharyngeal area (r = 0.840, p = 0.005). Velopharyngeal closing pressure progressively decreased with increasing age (r = -0.809, p = 0.008) and the closing pressures were below atmospheric pressure in all infants (range: -0.7 to -9.8 cm H(2)O; mean +/- SD: -3.6 +/- 2.7 cm H(2)O). Shape of the pressure-area curves became steeper in slope with maturation, indicating increased pharyngeal wall stiffness during development. Accordingly, we conclude that anatomic properties of the pharynx gain stability in favor of maintaining patent airway during development in normal infants.

[Long-term result after UPPP for OSAS by evaluation of nocturnal oxygenation]

The nocturnal oxygenation of 45 patients with OSAS who had UPPP at our hospital were evaluated by pulse oximetry before and after surgery and at the time more than one year after UPPP. "Successful case" is defined as the case that showed more than 50% reduced oxygen desaturation index(ODI) after UPPP. Twenty seven cases including 15 severe cases(ODI > or = 40) have showed continuously successful ODI for more than one year. We could not get good result in 8 cases, which kept high ODI. Four of them are now using dental appliance. We have recognized the recurrence of sleep apnea in 10 cases that once got successful results just after UPPP. Our report strongly suggests the importance of long-term follow-up after surgery.

[Diagnosis of sites of upper airway obstruction in patients with obstructive sleep apnea]

Precise determination of the site of obstruction is mandatory for improvement of surgical outcome. The size of the upper airway depends on the balance between the upper airway(UA) muscle activity and intraluminal pressure. Structural property of the UA is considered to be a fulcrum of the balance model. Our final goal is to identify structural abnormalities within the UA. State-dependent and individual variability of the UA muscle activity and luminal pressure makes interpretation of UA size difficult. Measurements of UA size and evaluation of UA collapsibility may be less valuable during wakefulness and sleep without controlling the variability. Two unique approaches to identify the anatomic abnormalities while controlling the UA muscle activity and luminal pressure were reviewed.

Usefulness of continuous oxygen insufflation into trachea for management of upper airway obstruction during anesthesia

BACKGROUND

Severe complications associated with upper airway obstruction often occur during the perioperative period. Development of a simple and reliable technique for reversing the impaired airway patency may improve airway management. The purpose of the current study is to evaluate the usefulness of transtracheal oxygen insufflation (TTI) for management of upper airway obstruction during anesthesia and to explore the mechanisms of TTI in detail.

METHODS

During propofol anesthesia in eight spontaneously breathing patients, the upper airway cross-sectional area and pressure-flow measurements during neck flexion with TTI were compared with those during triple airway maneuvers (TAM) without TTI. Blood gas analyses assessed efficacy of CO2 elimination during TTI in an additional nine patients.

RESULTS

TTI achieved adequate PaCO2 and PaO2 levels equivalent to those during TAM. In addition to a significantly smaller cross-sectional area during TTI, the location and slope of the pressure-flow relation during TTI completely differed from those during TAM, indicating that upper airway resistance was much higher during TTI. Notably, minute ventilation during TTI was significantly smaller than that during TAM, suggesting reduced dead space or other mechanisms for CO2 elimination.

CONCLUSIONS

TTI is capable of maintaining adequate blood gases through mechanisms different from those of conventional airway support in anesthetized subjects with upper airway obstruction.

Dose-dependent effects of mandibular advancement on pharyngeal mechanics and nocturnal oxygenation in patients with sleep-disordered breathing

STUDY OBJECTIVES

To examine dose-dependent effects of mandibular advancement on collapsibility of the passive pharynx and sleep-disordered breathing (SDB).

DESIGN

Prospective, randomized study.

SETTING

University hospital.

PATIENTS

Thirty-seven adult patients with SDB.

INTERVENTIONS

Oral appliances with 2-, 4-, and 6-mm advancement of the mandible.

MEASUREMENTS AND RESULTS

Overnight oximetry was performed with and without oral appliances. Each 2-mm mandibular advancement coincided with approximately 20% improvement in number and severity of nocturnal desaturations. Percentages of patients producing a > 50% improvement rate of the number of desaturations were 25%, 48%, and 65% with use of oral appliances with 2-, 4-, and 6-mm mandibular advancement, respectively. Static pharyngeal mechanics were evaluated in six completely paralyzed patients with SDB under general anesthesia with and without the oral appliances. Advancement of mandibular position was found to produce dose-dependent closing pressure reduction of all pharyngeal segments. Normalization of nocturnal oxygenation was associated with negative closing pressure, especially at the velopharynx.

CONCLUSIONS

We conclude that improvement of both nocturnal oxygenation and pharyngeal collapsibility significantly depends on the mandibular position.

Pre-and post-operative respiratory assessment of acromegalics with sleep apnea--bedside oximetric study for transsphenoidal approach

PURPOSE

Although routine mechanical nasal packing after transsphenoidal surgery (TS) is thought to increase respiratory disorders during sleep, there has been little in the literature about the pre- and post-operative airway assessment of acromegalics with sleep apnea (SA). We describe 4 acromegalic patients with SA, who underwent transsphenoidal surgery. METHODS AND CASES: The patients were all men, aged from 47 to 59 years. The pre- and post-operative sleep study consisted with a computer calculated oximetry parameter of oxygen desaturation index (ODI), which was defined as the number/hour of oxygen desaturation episodes exceeding 4% from the base line (normal range < 15). The postoperative (postop.) sleep study was carried out from the 1st postop. day to the 8th day, for 1 to 8 days, varying for each patient.

RESULTS

Only the worst postop. result is shown. Patient 1 had 2 operations, 2 years apart. ODI was 39.6 before the 1st operation and 45.9 postop.. In the second operation ODI was 21.8 preoperatively (preop.) and 57.9 postop.. Preop. and postop. ODI was 18.1 and 22.2 in patient 2, 21.6 and 22.5 in patient 3 and 45.5 and 18.9 in patient 4, respectively. ODI of patient 4 was 39.6, 3 weeks later.

CONCLUSION

Our data showed that the postop. oxymetric study commonly showed worse results in acromegalics with nasal packing. The better result of patient 4 was probably due to a postop. sleepless state. REM sleep usually increases in the first several postop. days, when cardiopulmonary complications are more likely to occur. Since acromegalics with severe SA and postop. nasal packing may more readily suffer from cardiopulmonary complications, postoperative meticulous respiratory monitoring and care should be mandatory.

Bone CT evaluation of nasal cavity of acromegalics--its morphological and surgical implication in comparison to non-acromegalics

PURPOSE

In order to numerically compare the morphological differences of the nasal cavity and nasal sinus between acromegalics and non-acromegalics, bone window CT scans sliced parallel to the transsphenoidal surgical route were performed. MATERIAL AND CASES: Acromegalic patients had small or large macroadenomas and were 13 (7 men and 6 women) in number, aged 53.2 +/- 16.1 years. Non-acromegalic patients had pituitary tumors and were 44 (21 men and 23 women) in number, aged 52.1 +/- 12.5 years.

RESULTS

The results of acromegalics are described in comparison to non-acromegalics in parentheses. a) The width of the surgical corridor: piriform aperture, 27.6 +/- 2.7 (25.9 +/- 2.6) mm; origin of inferior nasal concha, 29.4 +/- 9.4 (26.6 +/- 4.0) mm; and origin of middle nasal concha, 29.8 +/- 3.2 (26.2 +/- 4.2) mm. b) The depth of the surgical corridor: the upper lip thickness, 18.1 +/- 2.7 (13.3 +/- 1.4) mm; the distances between piriform aperture and sphenoid wall, 52.9 +/- 4.6 (49 +/- 4.2) mm; sphenoid wall and sellar floor, 17.3 +/- 4.1 (18.7 +/- 4.1) mm; and sellar floor to dorsum sellae, 17.6 +/- 3.4 (15.6 +/- 4.0) mm. c) Marked carotid prominence: 7/13=53.4% (8/44=18.25%). d) Sinusitis: 8/13=61.5% (12/44=27.3%).

DISCUSSION & CONCLUSION

The data presented above show that morphological differences in bony nasal cavity and soft tissue may be responsible for a deeper and narrower surgical field for acromegalics. Acromegalics had a marked carotid prominence more frequently, which needs special attention to avoid carotid injury, when enlarging the surgical field. Knowing these morphological differences will provide useful information for peri- and intra-operative care.

Effects of tongue electrical stimulation on pharyngeal mechanics in anaesthetized patients with obstructive sleep apnoea

The tongue plays a significant role in the maintenance of a patent airway. The purpose of this study was to examine the effects of tongue musculature contraction on the static mechanical properties of the pharynx in patients with obstructive sleep apnoea (OSA). During hyperventilation-induced apnoea in seven OSA patients anaesthetized with sevoflurane, the static pressure/area relationships of the oropharynx were obtained by means of step changes in airway pressure while endoscopically measuring cross-sectional area. At each airway pressure, the tongue was electrically stimulated via electrodes placed bilaterally. Tongue electrical stimulation (TES) did not further dilate the oropharyngeal area at higher airway pressure (3.2+/-1.9 versus 3.0+/-2.1 cm2), although the narrowed oropharyngeal area at lower airway pressures increased during TES (0.8+/-9.0) versus 1.7+/-1.8 cm2, p<0.05). Accordingly, the slope of the pressure/area relationship decreased during TES (0.24+/-0.20 versus 0.12+/-0.09 cm2 x cm H2O(-1), p<0.05). In conclusion, electrical stimulation of the tongue stiffens the retroglossal airway wall in patients with obstructive sleep apnoea.

Experimental pain augments experimental dyspnea, but not vice versa in human volunteers

BACKGROUND

Pain and dyspnea frequently coexist in many clinical situations. However, whether the two different symptoms interact with each other has not been elucidated. To elucidate the interaction between pain and dyspneic sensations, the authors investigated separately the effects of pain on dyspnea and the effects of dyspnea on pain in 15 healthy subjects.

METHODS

Subjects were asked to rate their sensation of pain or dyspnea using a visual analog scale (VAS) during pain stimulation produced by tourniquet inflation (inflation cuff pressure: 350 mmHg) around the calf, and/or the respiratory loading consisted of a combination of resistive load (77 cm H2O x l(-1) x s(-1)) and hypercapnia induced by extra mechanical dead space (255 ml). In addition to changes in VAS scores, changes in ventilatory airflow and airway pressure were continuously measured.

RESULTS

Pain stimulation and loaded breathing increased VAS scores, ventilation, and occlusion pressure (P0.1). The addition of a pain stimulus during loaded breathing increased the dyspneic VAS score (median 56 [interquartile range 50-62] vs. 64 [55-77]: before vs. after addition of pain stimulus, P < 0.05) with concomitant increases in minute ventilation (10.8 [10.1-13.3] vs. 12.4 [11.0-14.8] l/min, P < 0.05) and P0.1 (5.5 [4.9-7.2] vs. 6.8 [5.8-9.0] cm H2O, P < 0.05). The addition of respiratory loading during pain stimulation did not cause a significant change in pain VAS score (40 [33-55] vs. 31 [30-44]: before vs. after addition of respiratory loading), although both additional burdens increased further minute ventilation (10.0 [8.8-10.9] vs. 12.0 [10.6-13.2] l/min, P < 0.05) and P0.1 (2.5 [2.0-3.0] vs. 6.2 [4.9-7.0] cm H2O, P < 0.05).

CONCLUSION

The authors' findings suggest that pain intensifies the dyspneic sensation, presumably by increasing the respiratory drive, whereas dyspnea may not intensify the pain sensation.

MRI of growth hormone-secreting pituitary adenomas: factors determining pretreatment hormone levels

Preoperative serum growth hormone (GH) level is one of the most important determinants of outcome. Our aim was to assess MRI findings which may correlate with pretreatment GH levels in GH-secreting adenomas. We retrospectively studied 29 patients with acromegaly caused by a pituitary adenoma. Tumor size (height, width, thickness and volume), suprasellar extension, sphenoid or cavernous sinus invasion, signal intensity and contrast enhancement were studied. Linear regression analysis or Fisher's exact probability test was used for statistical analysis. Factors related to high GH levels were the maximum dimension of the tumour (r = 0.496, P < 0. 01), its volume (r = 0.439, P < 0.05), spenoid sinus invasion (P < 0. 01) and intracavernous carotid artery (encasement (P < 0.01). The other items were not related to serum GH levels. Since we believe surgery is the first choice of treatment and the cavernous sinus is difficult of access with a conventional surgical approach, preoperative assessment of invasion into the cavernous sinus is critical for predicting the surgical outcome. Low GH levels (5-50 ng/ml) were found with tumours medial to the intercarotid line and high levels (more than 101 ng/ml) with invasive tumours with carotid artery encasement. Variable GH levels were noted with tumours extending beyond the intercarotid line. Because functioning adenomas invading the cavernous sinus tend to have markedly high hormone levels, and only patients with carotid artery encasement showed markedly elevated GH levels, we believe carotid artery encasement a reliable MRI indicator of cavernous sinus invasion.

Sleep-disordered breathing in acromegalics--relation of hormonal levels and quantitative sleep study by means of bedside oximeter

Sleep-disordered breathing (SDB) is common in patients with growth hormone (GH) secreting pituitary adenomas. Since long-term untreated SDB aggravates systemic conditions (hypertension and arrhythmia etc.), the therapeutic outcome of SDB is important in reducing morbidity and mortality rates. But the results of a quantitative analysis of the lowered GH and IGF-1 levels in SDB in a relatively large number of patients are not detailed. Ten consecutive acromegalic patients were studied with a bedside oximeter. Preoperatively they were divided into two groups based on the presence (SDB group = 6 patients) or absence (non-SDB group = 4 patients) of clinical symptoms of SDB such as habitual snoring, excessive daytime somnolence and nocturnal apneic episodes. The serum IGF-1 averaged 931.7 ng/ml in SDB group and 898.3 ng/ml in non-SDB group. The oxygen desaturation index (ODI) (the number of oxygen desaturations exceeding 4% from the base line) was 29.1+/-15.4 in the SDB group and 2.5+/-1.8 in the non-SDB group (P=0.01). Other oximeter parameters such as the percent of the time spent at O2 saturation < 90% and the mean and the lowest O2 saturations closely correlated with the degree of the clinical symptoms. A postoperative sleep study was conducted in 5 patients in the preoperative SDB group, 4 months or more after the surgery. The serum GH and IGF-1 levels normalized in 3 patients but remained slightly high in 2. ODI became 9.1+/-5.6, which was significantly lower than the preoperative value (P=0.026). One patient had a complete clinical resolution. The other 4 obtained slight to moderate improvement clinically and oximetrically despite normalized or decreased hormonal levels. This study clarified that the response of SDB to lowering of the GH level varies from one patient to another and persisting SDB despite the normalization of the hormonal levels suggests the involvement of other factors in the production of SDB.

Collapsibility of passive pharynx in patients with acromegaly

Sleep-disordered breathing (SDB), either central or obstructive in nature, is common in patients with acromegaly. However, no study has systematically examined the collapsibility of the pharynx in acromegaly to date. We evaluated intrinsic mechanical properties of passive pharynx in 10 anesthetized and paralyzed patients with active acromegaly before transsphenoidal adenomectomy for their pituitary adenoma. Static pressure-area relationships of the velopharynx and oropharynx were obtained by step changes in airway pressure during endoscopic cross-sectional area measurement of each segment. Moreover, curve fitting analysis by an exponential function estimated the closing pressure (P'close) of each segment. Preoperative nocturnal oximetry identified five acromegalic patients with an oxygen desaturation index (ODI) greater than 10 h-1 and clinical symptoms suggesting presence of SDB. The pharyngeal airway of all five acromegalic patients with SDB was highly collapsible at both velopharynx and oropharynx with positive P'close. Compared with age-, body mass index (BMI)-, and ODI-matched SDB patients without acromegaly, SDB patients with acromegaly had a higher P'close of the oropharynx, indicating that the etiology of SDB in acromegaly appears to differ from that of ordinary sleep apnea. Our results suggest that anatomic abnormality, especially at the base of the tongue, appears to play a significant role in development of SDB in acromegaly.

Coordination of swallowing and phases of respiration during added respiratory loads in awake subjects

In order to test the hypothesis that different types of respiratory mechanical loads may differently modify the coordination of respiration and swallowing, we investigated the coordination of respiration and swallowing during resistive and elastic loads in 14 healthy subjects. Ventilation was monitored with a pneumotachograph and reflex swallowing was elicited by continuous infusion of distilled water into the pharynx (3 ml/min) and recorded on a submental electromyogram while the subject breathed through a device with a flow-resistive load (180 cm H2O/L/s), an elastic load (70 cm H2O/L), or without any external load. We found that addition of a flow-resistive load did not influence the frequency of swallowing, whereas addition of an elastic load caused a significant increase in swallowing frequency during continuous infusion of water. Analysis of the timing of swallowing in relation to respiratory cycle phase revealed that with flow-resistive loading, swallows occurred preferentially during the inspiratory-expiratory (I-E) transition, whereas with elastic loading, swallows occurred preferentially during the expiratory-inspiratory (E-I) transition. Signs of laryngeal irritation were observed most often during the elastic loading following E-I swallows. These results indicate that different types of respiratory mechanical loads can differently modify this coordination of respiration and swallowing, and suggest that the coordination may be compromised more with elastic loading than with flow-resistive loading.

Efficacy of endoscopic static pressure/area assessment of the passive pharynx in predicting uvulopalatopharyngoplasty outcomes

OBJECTIVES/HYPOTHESIS

Although uvulopalatopharyngoplasty (UPPP) is an attractive surgical treatment for obstructive sleep apnea (OSA), the unpredictable outcome limits application of the procedure. Since UPPP corrects only retropalatal airway (RP) patency, we hypothesized that response to UPPP is determined by collapsibility of the retroglossal airway (RG), where UPPP does not correct.

METHODS

We estimated closing pressure (Pclose) for each pharyngeal segment by endoscopically obtaining the static pressure/area relationship of the passive pharynx in completely paralyzed and anesthetized patients with sleep-disordered breathing (n = 41) before UPPP. Preferable response to UPPP was defined as the number of oxygen dips (ODI), obtained by nocturnal oximetry, less than 10 h(-1) after UPPP.

RESULTS

Patients with negative Pclose at RG responded to UPPP significantly better than those with positive Pclose at RG (22/30 [73%] vs. 3/11 [27%], P<.05). ODI after UPPP was significantly correlated with age, Pclose at RP, and Pclose at RG.

CONCLUSIONS

Endoscopic assessment of anatomic abnormality of the pharynx in paralyzed patients with sleep-disordered breathing under general anesthesia has clinical value for the improvement of UPPP outcome.

A low concentration of nitrous oxide reduces dyspnoea produced by a combination of hypercapnia and severe elastic load

We have measured how a low concentration of nitrous oxide affected respiratory sensation and ventilation. Severe dyspnoea was induced in nine normal subjects by a combination of hypercapnia and inspiratory elastic load (50 cm H2O litre-1). Subjects were asked to rate their sensation of respiratory discomfort using a visual analogue scale (VAS) while breathing either 20% nitrous oxide or 20% nitrogen gas mixture. We compared the effects of each gas mixture on respiratory sensation and ventilation using steady-state values of ventilatory variables and VAS scores obtained before, during and after inhalation of each gas mixture. Inhalation of 20% nitrous oxide reduced the sensation of respiratory discomfort from a median VAS score of 6.5 (range 5.0-8.1) before inhalation to 3.6 (2.4-5.9) during inhalation (P < 0.05). There was no significant change in minute ventilation but tidal volume increased during inhalation of 20% nitrogen did not alter VAS scores or ventilatory variables. We found that a low concentration of nitrous oxide greatly alleviated the intensity of dyspnoea without changing respiratory load compensation.

Effects of negative pressure assisted ventilation on dyspnoeic sensation and breathing pattern

Although negative pressure assisted ventilation with an assist-control mode may have a potential therapeutic role in the treatment of severe dyspnoea, the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns have not been examined. We examined the effects of negative pressure assisted ventilation with the assist-control mode on dyspnoea and breathing patterns produced by a combination of resistive loading and hypercapnia in nine healthy subjects breathing spontaneously. Subjects were asked to rate their sensation of respiratory discomfort using a visual analogue scale. Negative pressure assisted ventilation caused a significant reduction in sensation of respiratory discomfort from a visual analogue scale score of 74 (55-91) (median (range)) before negative pressure assisted ventilation to 34 (15-53) during negative pressure assisted ventilation (p<0.01). During negative pressure assisted ventilation, there were significant changes in breathing patterns characterized by an increase in tidal volume and a decrease in respiratory frequency, while neither minute ventilation nor end-tidal carbon dioxide tension changed. Our results indicate that negative pressure assisted ventilation with the assist-control mode is effective in relief of dyspnoea and that negative pressure assisted ventilation influences the control of breathing to minimize respiratory discomfort.

[Influence of sevoflurane on renal medullary blood flow in humans]

Proper anesthetic management is necessary to preserve renal function during anesthesia and surgery. Using ultra-sound color Doppler, we examined the influence of sevoflurane on renal medullary blood flow in 20 adult patients without renal dysfunction. After identifying an interlobar artery in the outer medulla, we measured the velocity of the arterial blood flow before induction of anesthesia, and during sevoflurane anesthesia (1 MAC, 1.5 MAC). The minimum velocity of the interlobar arterial blood flow (Vmin) during wakefulness correlated significantly with creatinine clearance measured preoperatively. We did not find any significant change in Vmin after induction of sevoflurane anesthesia, despite significant decreases in mean arterial blood pressure.

Upper airway reflexes during a combination of propofol and fentanyl anesthesia

BACKGROUND

The effects of intravenous anesthetics on airway protective reflexes have not been fully explored. The purpose of the present study was to characterize respiratory and laryngeal responses to laryngeal irritation during increasing doses of fentanyl under propofol anesthesia.

METHODS

Twenty-two female patients anesthetized with propofol and breathing through the laryngeal mask airway were randomly allocated to three groups: (1) eight patients who received cumulative total doses of 200 microg fentanyl given in the form of two doses of 50 microg and one dose of 100 microg spaced 6 min under mechanical controlled ventilation while end-tidal carbon dioxide tension (PCO2) was maintained at 38 mmHg (fentanyl-controlled ventilation group), (2) eight patients who received cumulative total doses of 200 microg fentanyl while breathing spontaneously while end-tidal PCO2 was allowed to increase spontaneously (fentanyl-spontaneous ventilation group), and (3) six spontaneously breathing patients who were anesthetized with propofol alone (propofol group). The laryngeal mucosa of each patient was stimulated by spraying the cord with distilled water, and the evoked responses were assessed by analyzing the respiratory variables and endoscopic images.

RESULTS

Before administration of fentanyl, laryngeal stimulation caused vigorous reflex responses, such as expiration reflex spasmodic panting, cough reflex, and apnea with laryngospasm. Increasing doses of fentanyl reduced the incidences of all these responses, except for apnea with laryngospasm, in a dose-related manner in both the fentanyl-controlled ventilation and the fentanyl-spontaneous ventilation groups. Detailed analysis of endoscopic images revealed several characteristics of laryngeal behavior during the airway reflex responses.

CONCLUSION

Incremental doses of fentanyl depress airway reflex responses in a dose-related manner, except for apnea with laryngospasm.

Preoperative nocturnal desaturations as a risk factor for late postoperative nocturnal desaturations

Severe postoperative hypoxaemia during sleep may increase the risk of postoperative cardiovascular complications. We hypothesized that the severity of hypoxic episodes after surgery are related to the presence of preoperative sleep-disordered breathing (SDB). We tested this hypothesis in a multicentre study designed to elucidate the major risk factors for development of postoperative nocturnal desaturations. We performed overnight oximetry before operation and for one night between the second and fourth day after operation in 80 patients undergoing major surgery. We calculated oximetry variables such as oxygen desaturation index (ODI), defined as the number of oxygen desaturations exceeding 4% below baseline, percentage time spent at SpO2 < 90% (CT90, %) and lowest SpO2 value. After operation, although the change in ODI was not significant (P = 0.34), deterioration in CT90 and lowest SpO2 values were significant (P = 0.036 and P = 0.007, respectively). Multivariate analysis of possible risk factors for postoperative desaturations revealed that preoperative hypoxaemia and apnoea witnessed by others were highly correlated with postoperative hypoxaemia.

Comparison of static mechanical properties of the passive pharynx between normal children and children with sleep-disordered breathing

Collapsibility of the active pharynx, where active contraction of the upper airway muscles is evident, was previously reported to be higher in children with obstructive sleep apnea (OSA) than in those with primary snoring during sleep. Contribution of neuromuscular and anatomic factors to the increased collapsibility, however, was not estimated. We therefore evaluated collapsibility of the passive pharynx, in which upper airway muscle activities were eliminated. Our aim in the present study was to test the hypothesis that children with sleep-disordered breathing (SDB) have a structurally narrowed and a more collapsible pharynx compared with normal children. The static pressure/area relationship of the passive pharynx was endoscopically quantified in 14 children with SDB and in 13 normal children under general anesthesia with complete paralysis. The majority of children with SDB primarily closed their airways at levels of enlarged adenoids and tonsils with positive closing pressure (Pclose) (3.5+/-4.3 cm H2O), whereas half of the normal children closed their airways at the soft palate edges and the other half at the tongue bases with subatmospheric Pclose (-7.4+/-4.9 cm H2O). Cross-sectional area of the narrowest segment was significantly smaller in SDB children than in normal children. Interestingly, collapsibility of the retropalatal and retroglossal segments significantly increased in SDB children, compared with the normal subjects. We conclude that anatomic factors play a significant role in the pathogenesis of pediatric OSA and that predisposing structural abnormalities of the entire pharynx are likely to contribute to manifestation of OSA in addition to enlarged adenoids and tonsils.

Hypercapnia enhances the development of coughing during continuous infusion of water into the pharynx

We investigated the effects of increasing CO2 ventilatory drive on the coordination of respiration and reflex swallowing elicited by continuous infusion of distilled water into the pharynx (2.5 ml/min) in 11 normal subjects. Ventilation was monitored using a pneumotachograph and swallowing was recorded by submental electromyogram. The CO2 ventilatory drive was increased by addition of external dead space, while ventilation, the frequency of swallows, and the timing of swallows in relation to the phases of the respiratory cycle were measured at steady-state conditions. We found that the CO2 ventilatory response is not influenced by continuous reflex swallowing but that hypercapnia influences the timing and frequency of these swallows. Signs of aspiration were never observed during continuous infusion of water at eucapnia, but seven of 11 subjects showed laryngeal irritation and/or pending aspiration during hypercapnia, and the incidence of laryngeal irritation was higher the greater the PCO2. Detailed analysis of laryngeal irritations consisting of single coughs in seven subjects revealed that the majority of laryngeal irritations occurred when swallows coincided with expiratory-inspiratory transition or when swallows coincided with inspiration, whereas laryngeal irritation after an expiratory swallow was never observed. These results suggest that the automatic respiratory control system is not influenced by continuous swallowing but that the coordination of swallowing and respiration may be compromised during hypercapnia.

Pharyngeal patency in response to advancement of the mandible in obese anesthetized persons

BACKGROUND

During anesthesia in humans, anterior displacement of the mandible is often helpful to relieve airway obstruction. However, it appears to be less useful in obese patients. The authors tested the possibility that obesity limits the effectiveness of the maneuver.

METHODS

Total muscle paralysis was induced under general anesthesia in a group of obese persons (n = 9; body mass index, 32 +/- 3 kg[-2]) and in a group of nonobese persons (n = 9; body mas index, 21 +/- 2 kg[-2]). Nocturnal oximetry confirmed that none of them had sleep-disordered breathing. The cross-sectional area of the pharynx was measured endoscopically at different static airway pressures. A static pressure-area plot allowed assessment of the mechanical properties of the pharynx. The influence of mandibular advancement on airway patency was assessed by comparing the static pressure-area relation with and without the maneuver in obese and nonobese persons.

RESULTS

Mandibular advancement increased the retroglossal area at a given pharyngeal pressure, and mandibular advancement increased the retropalatal area in nonobese but not in obese persons at a given pharyngeal pressure.

CONCLUSION

Mandibular advancement did not improve the retropalatal airway in obese persons.

Interaction of cross-sectional area, driving pressure, and airflow of passive velopharynx

Previous studies have shown that, when the pharyngeal muscles are relaxed, the velopharynx is a highly compliant segment of the pharynx. Thus, under these circumstances, cross-sectional area of the velopharynx (AVP), driving pressure across the velopharynx (DeltaP), and inspiratory airflow (VI) will be mutually interdependent variables. The purpose of the present investigation was to describe the interrelation among these three variables during inspiration. We studied 15 sleeping patients with obstructive sleep apnea/hypopnea when the pharyngeal muscles were rendered hypotonic by applying continuous positive airway pressure to the nasal airway. AVP, determined by endoscopic imaging, was significantly greater at onset of VI limitation than at minimum oropharyngeal pressure (P < 0. 01). Snoring was never observed during VI limitation. In a subgroup of six patients, values for DeltaP, VI, and AVP were obtained at 0. 1-s intervals at various levels of mask pressure. For these six patients, the mathematical expression VI = 0.657(AVP/Amax) . DeltaP0. 332, where Amax is maximal AVP, described the relationship among the three variables (R2 = 0.962) for flow-limited and non-flow-limited inspirations. The impedance of the passive velopharynx, defined as DeltaP0.33/V, was inversely related to AVP and increased dramatically when AVP was <0.3 cm2. In summary, we observed a progressive decrease in AVP during flow-limited inspiration in patients with obstructive sleep apnea. This constriction of the velopharynx contributes to an increase in velopharyngeal impedance that, in turn, counterbalances the increase in DeltaP during flow limitation.

Anatomy of pharynx in patients with obstructive sleep apnea and in normal subjects

Anatomic abnormalities of the pharynx are thought to play a role in the pathogenesis of obstructive sleep apnea (OSA), but their contribution has never been conclusively proven. The present study tested this anatomic hypothesis by comparing the mechanics of the paralyzed pharynx in OSA patients and in normal subjects. According to evaluation of sleep-disordered breathing (SDB) by nocturnal oximetry, subjects were divided into three groups: normal group (n = 17), SDB-1 (n = 18), and SDB-2 (n = 22). The static pressure-area relationship of the passive pharynx was quantified under general anesthesia with complete paralysis. Age and body mass index were matched among the three groups. The site of the primary closure was the velopharynx in 49 subjects and the oropharynx in only 8 subjects. Distribution of the location of the primary closure did not differ among the groups. Closing pressure (PC) of the velopharynx for SDB-1 and SDB-2 groups (0.90 +/- 1.34 and 2.78 +/- 2.78 cmH2O, respectively) was significantly higher than that for the normal group (-3.77 +/- 3.44 cmH2O; P < 0.01). Maximal velopharyngeal area for the normal group (2.10 +/- 0.85 cm2) was significantly greater than for SDB-1 and SDB-2 groups (1.15 +/- 0.46 and 1.06 +/- 0.75 cm2, respectively). The shape of the pressure-area curve for the velopharynx differed between normal subjects and patients with SDB, being steeper in slope near Pc in patients with SDB. Multivariate analysis of mechanical parameters and oxygen desaturation index (ODI) revealed that velopharyngeal Pc was the only variable highly correlated with ODI. Velopharyngeal Pc was associated with oropharyngeal Pc, suggesting mechanical interdependence of these segments. We conclude that the passive pharynx is more narrow and collapsible in sleep-apneic patients than in matched controls and that velopharyngeal Pc is the principal correlate of the frequency of nocturnal desaturations.

Static properties of the passive pharynx in sleep apnea

Complete paralysis under general anesthesia allowed separating anatomic factors from neural factors which influence pharyngeal patency. We compared static mechanical properties of the passive pharynx in normals and sleep apneics. The passive pharynx was narrower and more collapsible in sleep apneics than normal controls indicating significance of anatomic factors in the pathogenesis of obstructive sleep apnea.

Cough and other reflexes on irritation of airway mucosa in man

Both human and animal studies show that irritation of airway mucosa elicits a variety of reflex responses such as coughing, apnoea, and laryngeal closure. Most of the information concerning these reflex responses were obtained in anesthetized conditions with little applicability to awake conditions. Various aspects of cough and other reflexes on irritation of the airway mucosa are discussed. Studies on awake humans showed that stimulation of the laryngeal mucosa with a small amount of distilled water during wakefulness causes elicitation of the expiration reflex, cough reflex, and swallowing reflex while other types of responses are scarcely observed. In addition, the duration of these responses is remarkably short. In contrast, the same stimulation causes more variant, prolonged, and exaggerated responses during a light depth of anesthesia. An increase in depth of anesthesia abolishes expiratory efforts such as coughing and the expiration reflex whereas the apnoeic reflex and laryngeal closure reflex are resistant to the depressant effect of anesthesia. Also, the respiratory reflex responses to airway irritation varied, depending on the site of stimulation: both laryngeal and tracheal stimulation cause vigorous respiratory responses whereas bronchial stimulation causes little or no respiratory responses. These results indicate not only that the types and magnitude of reflex responses is greatly modified by the central nervous state but also that the site of stimulation is crucial for determining the pattern of respiratory responses elicited by airway stimulation in humans.

Advancement of the mandible improves velopharyngeal airway patency

The velopharynx is the most common site of obstruction in patients with obstructive sleep apnea (OSA). Advancement of the mandible effectively reverses the pharyngeal obstruction. Accordingly, we hypothesized that mandibular advancement increases cross-sectional area of several segments of the upper airway, including the velopharynx and the oropharynx. We examined the pressure-area properties of the pharyngeal airway in 13 patients with OSA. Under general anesthesia and total muscle paralysis, the pharynx was visualized with an endoscope connected to a video-recording system. During an experimentally induced apnea, we manipulated the nasal pressure from 20 cmH2O to the point of total closure at the velopharynx. The procedure was repeated after maximal forward displacement of the mandible. Measurements of the cross-sectional area at different levels of nasal pressure allowed construction of a static pressure-area relationship of the "passive pharynx," where active neuromuscular factors are suppressed. In 12 of 13 patients with OSA, advancement of the mandible stabilized the airway by reducing the closing pressure and increasing the area at any airway pressure. Thus the maneuver shifted the static pressure-area curve of the velopharynx and the oropharynx upward in these patients. We conclude that anterior movement of the mandible widens the retropalatal airway as well as that at the base of the tongue in the passive pharynx of OSA patients.

Upper airway obstruction during midazolam sedation: modification by nasal CPAP

We examined the depressant effect of midazolam on respiration in 21 healthy women undergoing lower abdominal surgery with spinal anaesthesia. Airway gas flow, airway pressure, and the sound of snoring were recorded together with arterial oxygen saturation (SpO2). After spinal anaesthesia was established, subjects were deeply sedated with pentazocine 15 mg followed by incremental doses of midazolam 1 mg i.v. up to 0.1 mg.kg-1. When SpO2 decreased to < 90% or snoring and/or apnoea was observed, continuous positive airway pressure applied through the nose (nasal CPAP) was increased until the respiratory deterioration was reversed. While one patient remained free of respiratory events, the other 20 patients were successfully treated with nasal CPAP restoring normal SpO2 (95.5 +/- 1.7%) without snoring. Stepwise reduction of nasal CPAP determined the minimally effective CPAP to prevent snoring to be 5.1 +/- 2.1 cm H2O. Further reduction of nasal CPAP induced snoring in 15 patients and obstructive apnoea in five patients with the latter accompanied by a severe reduction of SpO2 (87.4 +/- 6.1%). Patients with apnoea were older than those who snored (P < 0.05. We conclude that upper airway obstruction contributes considerably to decreases in SpO2 during midazolam sedation for spinal anaesthesia.

Pharyngeal narrowing and closing pressures in patients with obstructive sleep apnea

Based on previous studies, we hypothesized that the pharynx collapses at multiple sites in most patients with obstructive sleep apnea (OSA). The purpose of this study was to document, in a population of apneic subjects, the site(s) of narrowing and closing pressure of the hypotonic pharynx. We endoscopically examined the pharynx in 45 OSA patients during sleep while they received nasal continuous positive airway pressure (CPAP), which produces hypotonia of pharyngeal muscles. Intrapharyngeal images and pressures were obtained at the end of expiration during single-breath tests (SBT). The fractional narrowing (FN) of each pharyngeal segment (nasopharynx, oropharynx, and hypopharynx) was calculated as the relative change in area when nasal airway pressure was reduced from a pressure that held the pharynx fully distended to the pressure at which the airway closed. The frequency distribution of FN for the nasopharynx was skewed toward larger values, and the frequency was relatively evenly distributed for the oropharynx and hypopharynx. A site having FN greater than 0.75 was defined as a site of primary narrowing, and a site showing FN 0.25 to 0.75 was defined as a site of secondary narrowing. The nasopharynx was a site of primary narrowing in 80% of patients, and two or more sites of narrowing were commonly observed (82%). Four categories of combined narrowing were identified: (1) primary narrowing only at the nasopharynx (18%); (2) primary narrowing at the nasopharynx plus other sites of secondary narrowing (40%); (3) primary narrowing at the nasopharynx plus other sites of primary narrowing (22%); and (4) other patterns (20%).(ABSTRACT TRUNCATED AT 250 WORDS)

Partial monosomy 5p and partial trisomy 5q due to paternal pericentric inversion of chromosome 5

A male infant with partial monosomy 5p and partial trisomy 5q due to paternal pericentric inversion of chromosome 5 (46,XY,rec(5), dup q,inv(5)(p15.1q35.1)pat) is reported together with the oral findings. The phenotype was chiefly the cri-du-chat syndrome. Severe retardation of mental and motor development, microencephaly, cardiac malformation, crying and facial appearance unique to the cri-du-chat syndrome were observed. Perioral and intraoral findings included thin upper lip, down-turning corners of mouth, micrognathia, shallow palate, and cleft of soft palate. Anterior deciduous teeth were small and canine deciduous teeth were conic. The row of deciduous teeth showed a flat arch-like shape that was very wide but short in length. No abnormality was noted in the number of deciduous teeth or the timing of eruption.

Static mechanics of the velopharynx of patients with obstructive sleep apnea

The static mechanics of the hypotonic pharynx were endoscopically evaluated in nine sleeping patients with obstructive sleep apnea, having a primary narrowing only at the velopharynx. The velopharynx closed completely at a mean pressure of 0.18 +/- 1.21 cmH2O, and the mean half-dilation pressure was 1.93 cmH2O above closing pressure. The dependence of area on pressure was distinctly curvilinear, being steep near closing pressure and asymptotically approaching maximum area (mean = 1.32 cm2). The data for each patient were satisfactorily fitted by an exponential function (mean R2 = 0.98), and a single exponential relationship usefully represented the dependence of relative area on pressure above closing pressure for the population (R2 = 0.85). During the test inspiration, flow limitation was consistently observed when mask pressure exceeded closing pressure by 0.5-3.0 cmH2O. In summary, the static mechanics of the hypotonic velopharynx of patients with obstructive sleep apnea can be described by an exponential pressure-area relationship, with a closing pressure near atmospheric pressure and a high compliance in the range of airway pressure 0-3 cmH2O above closing pressure.

Diaphragmatic activity during isoflurane anaesthesia in dogs

The effect of isoflurane administration on diaphragmatic activity was investigated in six anaesthetized mechanically ventilated dogs. Diaphragmatic strength was assessed by measuring the transdiaphragmatic pressure (Pdi) generated during supramaximal stimulation of both cervical phrenic nerves at frequencies of 0.5, 10, 20, 50 and 100 Hz under partially isometric conditions at 1, 1.5 and 2 minimum alveolar anaesthetic concentrations (MAC), after maintaining 1 h of stable conditions. Pdi measurements were made at the start of the stimulation (initial) and at the end of a 2-s period (2-s). The force-frequency relationship was compared at each anaesthetic level. For single twitch (0.5 Hz) stimulation, the time constant of diaphragmatic relaxation was also assessed. The sequence of changing anaesthetic depth was altered in random fashion between animals. Pdi amplitude at single twitch stimulation was unchanged at the three anaesthetic concentrations. There was no significant difference in initial Pdi at various stimulus frequencies with increasing depth of isoflurane anaesthesia. In addition, no change in 2-s Pdi during low frequency stimulation (10 and 20 Hz) was noted during any of the three levels of anaesthesia. By contrast, 2-s Pdi with 50 Hz stimulation during 2 MAC isoflurane exposure decreased significantly below Pdi levels seen at 1 and 1.5 MAC (P < 0.01). Furthermore, 2-s Pdi at 100 Hz stimulation decreased significantly in a dose-dependent fashion. From these results, we conclude that isoflurane reduces diaphragmatic activity at higher stimulation frequencies of 50 and 100 Hz.

Cloning and nucleotide sequencing of the genes, rpIU and rpmA, for ribosomal proteins L21 and L27 of Escherichia coli

The rpIU and rpmA genes that encode ribosomal proteins (r-proteins) L21 and L27 of Escherichia coli K-12 have been isolated from the ordered clone bank of this bacterium. They were found to be located at coordinates 3,351.7-3,352.3 kb on the physical map of E. coli. The nucleotide sequence of the cloned genes and their flanking regions indicated that the two r-protein genes compose an operon. Upstream of the two genes there is an open reading frame (ORF) in the opposite direction. The deduced polypeptide encoded by this ORF has a molecular weight of 35,215 and shows a significant degree of sequence similarity to the enzyme that is involved in the carotenoid biosynthesis and encoded by the crtE gene of carotenogenic bacteria and to prenyltransferases found in various organisms.

Site of pharyngeal narrowing predicts outcome of surgery for obstructive sleep apnea

Uvulopalatopharyngoplasty (UPPP), an operation that enlarges the pharyngeal airway at the level of the soft palate, improves respiratory status during sleep in only 50% of patients with obstructive sleep apnea (OSA). This poor outcome suggests that narrowing of the pharyngeal airway at nonpalatal sites contributes to the obstructive process in many patients with OSA. We have used a novel endoscopic method to identify regions of the passive pharyngeal airway most susceptible to narrowing or complete closure. In order to test the hypothesis that narrowing of the passive airway at the nasopharynx predicts a favorable surgical outcome, we have preoperatively assessed the local mechanics of the passive pharyngeal airway in 18 patients with OSA undergoing UPPP. The patient population was prospectively divided into two groups: an exclusively nasopharyngeal (ENP) group, consisting of patients exhibiting narrowing only in the nasopharynx, and a not exclusively nasopharyngeal (NENP) group, consisting of patients having at least one site of narrowing outside the nasopharynx. The frequency of respiratory disturbances and arousals and the cumulative time in apnea-hypopnea were significantly reduced after surgery for the ENP group, but not for the NENP group. Improvement rate for the ENP group (86%) exceeded that for the NENP group (18%) (p < 0.01). These differences became even greater when selection criteria for the ENP group were made more restrictive (i.e., restricted to the velopharynx) or more liberal (i.e., including secondary narrowing of the oropharynx). Our results show that evaluation of passive pharyngeal mechanics identifies patients with OSA likely to improve after UPPP.

Efficient large-scale sequencing of the Escherichia coli genome: implementation of a transposon- and PCR-based strategy for the analysis of ordered lambda phage clones

We have developed a strategy for efficient sequence analysis of the genome of E. coli K-12 using insertions of a Tn5-derived mini-transposon into overlapping ordered lambda phage clones to provide universal primer-binding sites, and PCR amplification of DNA segments adjacent to the insertions. Transposon-containing clones were selected by blue plaque formation on a dnaBamber lacZamber E. coli strain. Insertion points every 0.5-1 kb were identified by 'analytical PCR' and segments between the transposon inserts and phage arms were amplified by 'preparative PCR' using one biotinylated and one non-biotinylated primer. Single strands of amplified DNA fragments were coupled to Streptoavidin-coated paramagnetic beads (Dynabeads M280) through their biotin tails, purified magnetically, and used as templates for fluorescence-based automatic nucleotide sequencing.

Lack of the mechanoreceptor influences on ventilatory control during halothane anesthesia in humans

Mechanical influences independent of chemoreceptor function on ventilatory control were studied in halothane-anesthetized, artificially ventilated patients using the technique reported by Altose et al. (Respir Physiol 66: 171-180, 1986). Contribution of mechanical factor was indirectly assessed by comparing the values of arterial carbon dioxide tension at which the subjects started breathing efforts during CO(2) loading induced by the following two methods. 1) Partial rebreathing of expired gas and 2) Mechanical hypoventilation (successive decrease in inflation volume). These two maneuvers resulted in a similar rate of increase in end-expiratory carbon dioxide tension. However, contrary to the observation made by Altose et al. in awake volunteers, we found comparable values of ventilatory recruitment threshold for Pa(CO)(2). Thus, we speculate that halothane anesthesia and/or loss of consciousness impair transmission of afferent information from the lung and/or chest wall musculature. Such effects may be responsible for the depression of load compensatory mechanism during anesthesia.

Effect of sevoflurane on diaphragmatic contractility in dogs

The effect of sevoflurane on diaphragmatic contractility was investigated in 12 anesthetized, mechanically ventilated dogs with the thorax opened. Animals were divided into two groups of six each: the sevoflurane and time control groups. We assessed contractility by the transdiaphragmatic pressure (Pdi) during supramaximal stimulation of the phrenic nerve at frequencies of 0.5, 10, 20, 50, and 100 Hz under quasiisometric conditions. The integrated electrical activity (Edi) of the crural and costal parts of the diaphragm (Edi cru, Edi cost) was also measured. In the sevoflurane group, diaphragmatic contractility was determined during three levels of anesthesia, specifically 0, 1.0, and 1.5 minimum alveolar anesthetic concentration (MAC). Measurements were made at the start of the stimulation (initial) and at the end of the 2-s period (2-s). Increasing the depth of sevoflurane anesthesia did not cause any significant differences in Pdi and Edi at 0.5-, 10-, and 20-Hz stimulation. By contrast, at 50- and 100-Hz stimulation, initial Pdi during 1.0 and 1.5 MAC sevoflurane exposure decreased significantly compared with the 0 MAC value (P less than 0.05). In addition, there was a statistical difference in 2-s Pdi between 1.0 and 1.5 MAC at 100-Hz stimulation (P less than 0.05). The Edi cru showed similar changes in Pdi at both measurements, whereas there was no remarkable change in Edi cost. There was no significant change either in Pdi or in Edi with respect to time in the time control group. We conclude from these results that sevoflurane impairs diaphragmatic contractility through its inhibitory effect on neuromuscular transmission, predominantly of the crural part.

DIFFERENTIAL EFFECTS OF VECURONIUM ON DIAPHRAGM AND GENIOHYOID MUSCLE IN ANAESTHETIZED DOGS

We have examined the sensitivity of the geniohyoid, an upper airway dilating muscle, to vecuronium in 12 anaesthetized dogs undergoing mechanical ventilation of the lungs and compared it with that of the diaphragm. Dogs were allocated randomly to two groups: pentobarbitone alone (group 1, n = 7); pentobarbitone combined with 0.2 MAC (0.44%) of enflurane anaesthesia (group 2, n = 5). Supramaximal single twitch stimulations (0.1 Hz) were applied to the phrenic nerves in the upper thorax and the geniohyoid branches of the hypoglossal nerves at the neck. The evoked responses were assessed by the transdiaphragmatic pressure (Pdi) and the isometric force of the geniohyoid muscles (Tgh) until complete recovery of these variables after i.v. administration of vecuronium 0.02 mg kg-1. In both groups, the magnitude of the depression of twitch response was greater and time required to reach control amplitude was longer in the geniohyoid than the diaphragm. The depression of Tgh was significantly greater in group 2 than in group 1, whereas no change was observed in Pdi between the two groups. We conclude that the geniohyoid is more sensitive to vecuronium than the diaphragm and the differential effects of vecuronium are facilitated by a low concentration of enflurane.