Shiroh Isono

Obstructive sleep apnea of obese adults: pathophysiology and perioperative airway management.

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.

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 [micro sign]g fentanyl given in the form of two doses of 50 [micro sign]g and one dose of 100 [micro sign]g 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 [micro sign]g 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.

Lateral Position Decreases Collapsibility of the Passive Pharynx in Patients with Obstructive Sleep Apnea

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.

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 sup ‐2) and in a group of nonobese persons (n = 9; body mas index, 21 +/‐ 2 kg sup ‐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.

Obesity and obstructive sleep apnoea: Mechanisms for increased collapsibility of the passive pharyngeal airway

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.

Anatomical balance of the upper airway and obstructive sleep apnea.

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.

Laryngeal resistance before and after minor surgery: endotracheal tube versus Laryngeal Mask 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™ (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™ has an advantage over ETT placement in order to avoid postoperative laryngeal swelling.

Sniffing Position Improves Pharyngeal Airway Patency in Anesthetized Patients with Obstructive Sleep Apnea

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.

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.

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.