Predicting obstructive sleep apnoea and perioperative respiratory adverse events in children: role of upper airway collapsibility measurements.

BACKGROUND: Obstructive sleep apnoea (OSA) and perioperative respiratory adverse events are significant risks for anaesthesia in children undergoing adenotonsillectomy. Upper airway collapse is a crucial feature of OSA that contributes to respiratory adverse events. A measure of upper airway collapsibility to identify undiagnosed OSA can help guide perioperative management. We investigated the utility of pharyngeal closing pressure (PCLOSE) for predicting OSA and respiratory adverse events. METHODS: Children scheduled for elective adenotonsillectomy underwent in-laboratory polysomnography 2-12 weeks before surgery. PCLOSE measurements were obtained while the child was anaesthetised and breathing spontaneously just before surgery. Logistic regression was used to assess the predictive performance of PCLOSE for detecting OSA and perioperative respiratory adverse events after adjusting for potential covariates. RESULTS: In 52 children (age, mean [standard deviation] 5.7 [1.8] yr; 20 [38%] females), airway collapse during PCLOSE was observed in 42 (81%). Of these, 19 of 42 (45%) patients did not have OSA, 15 (36%) had mild OSA, and eight (19%) had moderate-to-severe OSA. All 10 children with no evidence of airway collapse during the PCLOSE measurements did not have OSA. PCLOSE predicted moderate-to-severe OSA (odds ratio [OR] 1.71; 95% confidence interval [CI]: 1.2-2.8; P=0.011). All children with moderate-to-severe OSA could be identified at a PCLOSE threshold of -4.0 cm H2O (100% sensitivity), and most with no or mild OSA were ruled out (64.7% specificity; receiver operating characteristic/area under the curve=0.857). However, there was no significant association between respiratory adverse events and PCLOSE (OR 1.0; 95% CI: 0.8-1.1; P=0.641). CONCLUSIONS: Measurement of PCLOSE after induction of anaesthesia can reliably identify moderate or severe OSA but not perioperative respiratory adverse events in children before adenotonsillectomy. CLINICAL TRIAL REGISTRATION: ANZCTR ACTRN 12617001503314.

Bilateral hypoglossal nerve stimulation for treatment of adult obstructive sleep apnoea.

BACKGROUND AND AIM: Hypoglossal nerve stimulation (HNS) decreases obstructive sleep apnoea (OSA) severity via genioglossus muscle activation and decreased upper airway collapsibility. This study assessed the safety and effectiveness at 6 months post-implantation of a novel device delivering bilateral HNS via a small implanted electrode activated by a unit worn externally, to treat OSA: the Genio™ system. METHODS: This prospective, open-label, non-randomised, single-arm treatment study was conducted at eight centres in three countries (Australia, France and the UK). Primary outcomes were incidence of device-related serious adverse events and change in the apnoea-hypopnoea index (AHI). The secondary outcome was the change in the 4% oxygen desaturation index (ODI). Additional outcomes included measures of sleepiness, quality of life, snoring and device use. This trial was registered with ClinicalTrials.gov, number NCT03048604. RESULTS: 22 out of 27 implanted participants (63% male, aged 55.9±12.0 years, body mass index (BMI) 27.4±3.0 kg·m-2) completed the protocol. At 6 months BMI was unchanged (p=0.85); AHI decreased from 23.7±12.2 to 12.9±10.1 events·h-1, a mean change of 10.8 events·h-1 (p<0.001); and ODI decreased from 19.1±11.2 to 9.8±6.9 events·h-1, a mean change of 9.3 events·h-1 (p<0.001). Daytime sleepiness (Epworth Sleepiness Scale; p=0.01) and sleep-related quality of life (Functional Outcomes of Sleep Questionnaire-10; p=0.02) both improved significantly. The number of bed partners reporting loud, very intense snoring, or leaving the bedroom due to participant snoring decreased from 96% to 35%. 91% of participants reported device use >5 days per week, and 77% reported use for >5 h per night. No device-related serious adverse events occurred during the 6-month post-implantation period. CONCLUSIONS: Bilateral HNS using the Genio™ system reduces OSA severity and improves quality of life without device-related complications. The results are comparable with previously published HNS systems despite minimal implanted components and a simple stimulation algorithm.

Comparison of Collapsibility of the Human Upper Airway During Anesthesia and During Sleep.

BACKGROUND: The propensities for the upper airway to collapse during anesthesia and sleep are related, although much of our understanding of this relationship has been inferred from clinical observation and indirect measures such as the apnea-hypopnea index. The aim of this study was to use an identical, rigorous, direct measure of upper airway collapsibility (critical closing pressure of the upper airway) under both conditions to allow the magnitude of upper airway collapsibility in each state to be precisely compared. METHODS: Ten subjects (8 men and 2 women; mean ± SD: age, 40.4 ± 12.1 years; body mass index, 28.5 ± 4.0 kg/m) were studied. Critical closing pressure of the upper airway was measured in each subject on separate days during (1) propofol anesthesia and (2) sleep. RESULTS: Critical closing pressure of the upper airway measurements were obtained in all 10 subjects during nonrapid eye movement sleep and, in 4 of these 10 subjects, also during rapid eye movement sleep. Critical closing pressure of the upper airway during anesthesia was linearly related to critical closing pressure of the upper airway during nonrapid eye movement sleep (r = 0.64 [95% CI, 0.02-0.91]; n = 10; P = .046) with a similar tendency in rapid eye movement sleep (r = 0.80 [95% CI, -0.70 to 0.99]; n = 4; P = .200). However, critical closing pressure of the upper airway during anesthesia was systematically greater (indicating increased collapsibility) than during nonrapid eye movement sleep (2.1 ± 2.2 vs -2.0 ± 3.2 cm H2O, respectively, n = 10; within-subject mean difference, 4.1 cm H2O [95% CI, 2.32-5.87]; P < .001) with a similar tendency during rapid eye movement sleep (1.6 ± 2.4 vs -1.9 ± 4.3 cm H2O, respectively, n = 4; unadjusted difference, 3.5 cm H2O [95% CI, -0.95 to 7.96]; P = .087). CONCLUSIONS: These results demonstrate that the magnitude of upper airway collapsibility during anesthesia and sleep is directly related. However, the upper airway is systematically more collapsible during anesthesia than sleep, suggesting greater vulnerability to upper airway obstruction in the anesthetized state.

Upper Airway Collapsibility during Dexmedetomidine and Propofol Sedation in Healthy Volunteers: A Nonblinded Randomized Crossover Study.

BACKGROUND: Dexmedetomidine is a sedative promoted as having minimal impact on ventilatory drive or upper airway muscle activity. However, a trial recently demonstrated impaired ventilatory drive and induction of apneas in sedated volunteers. The present study measured upper airway collapsibility during dexmedetomidine sedation and related it to propofol. METHODS: Twelve volunteers (seven female) entered this nonblinded, randomized crossover study. Upper airway collapsibility (pharyngeal critical pressure) was measured during low and moderate infusion rates of propofol or dexmedetomidine. A bolus dose was followed by low (0.5 µg · kg · h or 42 µg · kg · min) and moderate (1.5 µg · kg · h or 83 µg · kg · min) rates of infusion of dexmedetomidine and propofol, respectively. RESULTS: Complete data sets were obtained from nine volunteers (median age [range], 46 [23 to 66] yr; body mass index, 25.4 [20.3 to 32.4] kg/m). The Bispectral Index score at time of pharyngeal critical pressure measurements was 74 ± 10 and 65 ± 13 (mean difference, 9; 95% CI, 3 to 16; P = 0.011) during low infusion rates versus 57 ± 16 and 39 ± 12 (mean difference, 18; 95% CI, 8 to 28; P = 0.003) during moderate infusion rates of dexmedetomidine and propofol, respectively. A difference in pharyngeal critical pressure during sedation with dexmedetomidine or propofol could not be shown at either the low or moderate infusion rate. Median (interquartile range) pharyngeal critical pressure was -2.0 (less than -15 to 2.3) and 0.9 (less than -15 to 1.5) cm H2O (mean difference, 0.9; 95% CI, -4.7 to 3.1) during low infusion rates (P = 0. 595) versus 0.3 (-9.2 to 1.4) and -0.6 (-7.7 to 1.3) cm H2O (mean difference, 0.0; 95% CI, -2.1 to 2.1; P = 0.980) during moderate infusion of dexmedetomidine and propofol, respectively. A strong linear relationship between pharyngeal critical pressure during dexmedetomidine and propofol sedation was evident at low (r = 0.82; P = 0.007) and moderate (r = 0.90; P < 0.001) infusion rates. CONCLUSIONS: These observations suggest that dexmedetomidine sedation does not inherently protect against upper airway obstruction.

The effect of temazepam on assessment of severity of obstructive sleep apnea by polysomnography.

PURPOSE: To determine the effect of temazepam on assessment of the severity of obstructive sleep apnea (OSA) by polysomnography (PSG). METHODS: Analysis of diagnostic laboratory-PSG studies was performed in OSA patients who were administered temazepam (10 mg) to facilitate sleep ("temazepam group", n = 73) and in OSA patients (matched for age, gender, body mass index and study date) in whom temazepam was not administered ("control group", n = 73). Sleep- and respiratory-related variables were compared between the groups for the (i) first 3 h of study following temazepam in the temazepam group (when peak blood concentration is expected) or following lights out in the control group, and (ii) entire study duration. RESULTS: Within the first 3 h, no differences in sleep-related variables were observed between the groups. Over the entire study duration, the temazepam group had a reduced total sleep time compared to the control group, likely due to the overnight sleep difficulties that led to its use. Whether measured during the first 3 h of study or over the entire study duration, no significant differences were detected between the groups for any respiratory-related variable, including apnea hypopnea index, arousal index, oxygen desaturation, apnea index, hypopnea index, and event duration. When patients were considered in terms of OSA severity, decreased arousal index was noted in the temazepam group over the entire study duration, but only in those with severe OSA. CONCLUSION: Oral administration of 10 mg of temazepam during the course of PSG does not systematically affect assessment of the severity of OSA by PSG.

Effects on upper airway collapsibility of presence of a pharyngeal catheter.

Catheters that traverse the pharynx are often in place during clinical or research evaluations of upper airway function. The purpose of this study was to determine whether the presence of such catheters affects measures of upper airway collapsibility itself. To do so, pharyngeal critical closing pressure (Pcrit) and resistance upstream of the site of collapse Rus) were assessed in 24 propofol-anaesthetized subjects (14 men) with and without a multi-sensor oesophageal catheter (external diameter 2.7 mm) in place. Anaesthetic depth and posture were maintained constant throughout each study. Six subjects had polysomnography(PSG)-defined obstructive sleep apnea (OSA) and 18 either did not have or were at low risk of OSA. Airway patency was maintained with positive airway pressure. At intervals, pressure was reduced by varying amounts to induce varying degrees of inspiratory flow limitation. The slope of the pressure flow relationship for flow-limited breaths defined Rus. Pcrit was similar with the catheter in and out (-1.5 ± 5.4 cmH2 O and -2.1 ± 5.6 cmH2O, respectively, P = 0.14, n = 24). This remained the case both for those with PSG-defined OSA (3.9 ± 2.2 cmH2O and 2.6 ± 1.4 cmH2O, n = 6) and those at low risk/without OSA (-3.3 ± 4.9 cmH2O and -3.7 ± 5.6 cmH2O, respectively, n = 18). Rus was similar with the catheter in and out (20.0 ± 12.3 cmH2O mL(-1) s(-1) and 16.8 ± 10.1 cmH2O mL(-1) s(-1), P = 0.22, n = 24). In conclusion, the presence of a small catheter traversing the pharynx had no significant effect on upper airway collapsibility in these anaesthestized subjects, providing reassurance that such measures can be made reliably in their presence.

Hypoglossal nerve stimulation improves obstructive sleep apnea: 12-month outcomes.

Reduced upper airway muscle activity during sleep is a key contributor to obstructive sleep apnea pathogenesis. Hypoglossal nerve stimulation activates upper airway dilator muscles, including the genioglossus, and has the potential to reduce obstructive sleep apnea severity. The objective of this study was to examine the safety, feasibility and efficacy of a novel hypoglossal nerve stimulation system (HGNS; Apnex Medical, St Paul, MN, USA) in treating obstructive sleep apnea at 12 months following implantation. Thirty-one subjects (35% female, age 52.4 ± 9.4 years) with moderate to severe obstructive sleep apnea and unable to tolerate positive airway pressure underwent surgical implantation and activation of the hypoglossal nerve stimulation system in a prospective single-arm interventional trial. Primary outcomes were changes in obstructive sleep apnea severity (apnea-hypopnea index, from in-laboratory polysomnogram) and sleep-related quality of life [Functional Outcomes of Sleep Questionnaire (FOSQ)]. Hypoglossal nerve stimulation was used on 86 ± 16% of nights for 5.4 ± 1.4 h per night. There was a significant improvement (P < 0.001) from baseline to 12 months in apnea-hypopnea index (45.4 ± 17.5 to 25.3 ± 20.6 events h(-1) ) and Functional Outcomes of Sleep Questionnaire score (14.2 ± 2.0 to 17.0 ± 2.4), as well as other polysomnogram and symptom measures. Outcomes were stable compared with 6 months following implantation. Three serious device-related adverse events occurred: an infection requiring device removal; and two stimulation lead cuff dislodgements requiring replacement. There were no significant adverse events with onset later than 6 months following implantation. Hypoglossal nerve stimulation demonstrated favourable safety, feasibility and efficacy.

Early life predictors of obstructive sleep apnoea in young adults: Insights from a longitudinal community cohort (Raine study).

OBJECTIVE: Early-life obstructive sleep apnoea (OSA) predictors are unavailable for young adults. This study identifies early-life factors predisposing young adults to OSA. METHODS: This retrospective study included 923 young adults and their mothers from the Western Australian Pregnancy Raine Study Cohort. OSA at 22 years was determined from in-laboratory polysomnography. Logistic regression was used to identify maternal and neonatal factors associated with OSA in young adulthood. RESULTS: OSA was observed in 20.8% (192) participants. Maternal predictors of OSA included gestational diabetes mellitus (odds ratio (OR) 9.54, 95% confidence interval (CI) 1.7, 58.5, P = 0.011), preterm delivery (OR 3.18, 95%CI 1.1,10.5, P = 0.043), preeclampsia (OR 2.95, 95%CI 1.1,8.0, P = 0.034), premature rupture of membranes (OR 2.46, 95%CI 1.2, 5.2, P = 0.015), age ≥35 years (OR 2.28, 95%CI 1.2,4.4, P = 0.011), overweight and obesity (pregnancy BMI≥25 kg/m2) (OR 2.00, 95%CI 1.2,3.2, P = 0.004), pregnancy-induced hypertension (OR 1.89, 95%CI 1.1,3.2, P = 0.019), and Chinese ethnicity (OR 2.36,95%CI 1.01,5.5, P = 0.047). Neonatal predictors included male child (OR 2.10, 95%CI 1.5,3.0, P < 0.0001), presence of meconium-stained liquor during delivery (OR 1.60, 95%CI 1.0,2.5, P = 0.044) and admission to special care nursery (OR 1.51 95%CI 1.0,2.2, P = 0.040). Higher birth lengths reduced OSA odds by 7% for each centimetre (OR 0.93, 95%CI 0.87, 0.99, P = 0.033). CONCLUSIONS: A range of maternal and neonatal factors predict OSA in young adults, including those related to poor maternal metabolic health, high-risk pregnancy and stressful perinatal events. This information could assist in the early identification and management of at-risk individuals and indicates that better maternal health may reduce the likelihood of young adults developing OSA.

Is There a Place for Medicinal Cannabis in Treating Patients with Sleep Disorders? What We Know so Far.

The legalization of cannabis for medicinal, and in some countries, recreational, purposes in addition to growth in the cannabis industry has meant that cannabis use and interest in the area has increased rapidly over the past 20 years. Treatment of poor sleep and sleep disorders are two of the most common reasons for the current use of medicinal cannabis. However, evidence for the role of medical cannabis in the treatment of sleep disorders has not been clearly established, thus making it challenging for clinicians to make evidence-based decisions regarding efficacy and safety. This narrative review summarizes the highest quality clinical evidence currently available in relation to the use of medicinal cannabis for the treatment of sleep disorders including insomnia, obstructive sleep apnea, restless legs syndrome, rapid eye movement sleep behavior disorder, nightmare disorder and narcolepsy. A summary of the effect of cannabis on sleep quality and architecture is also presented. Currently, there is insufficient evidence to support the routine use of medicinal cannabis as an effective and safe treatment option for any sleep disorder. Nevertheless, emerging evidence is promising and warrants further investigation using standardized cannabinoid products and validated quantitative measurement techniques.

Shift work, clinically significant sleep disorders and mental health in a representative, cross-sectional sample of young working adults.

Mental health conditions confer considerable global disease burden in young adults, who are also the highest demographic to work shifts, and of whom 20% meet criteria for a sleep disorder. We aimed to establish the relationship between the combined effect of shift work and sleep disorders, and mental health. The Raine Study is the only longitudinal, population-based birth cohort in the world with gold-standard, Level 1 measurement of sleep (polysomnography, PSG) collected in early adulthood. Participants (aged 22y) underwent in-laboratory PSG and completed detailed sleep questionnaires. Multivariable adjusted robust linear regression models were conducted to explore associations with anxiety (GAD7) and depression (PHQ9), adjusted for sex, health comorbidities, and work hours/week. Data were from 660 employed young adults (27.3% shift workers). At least one clinically significant sleep disorder was present in 18% of shift workers (day, evening and night shifts) and 21% of non-shift workers (p = 0.51); 80% were undiagnosed. Scores for anxiety and depression were not different between shift and non-shift workers (p = 0.29 and p = 0.82); but were higher in those with a sleep disorder than those without (Md(IQR) anxiety: 7.0(4.0-10.0) vs 4.0(1.0-6.0)), and depression: (9.0(5.0-13.0) vs 4.0(2.0-6.0)). Considering evening and night shift workers only (i.e. excluding day shift workers) revealed an interaction between shift work and sleep disorder status for anxiety (p = 0.021), but not depression (p = 0.96), with anxiety scores being highest in those shift workers with a sleep disorder (Md(IQR) 8.5(4.0-12.2). We have shown that clinical sleep disorders are common in young workers and are largely undiagnosed. Measures of mental health do not appear be different between shift and non-shift workers. These findings indicate that the identification and treatment of clinical sleep disorders should be prioritised for young workers as these sleep disorders, rather than shift work per se, are associated with poorer mental health. These negative mental health effects appear to be greatest in those who work evening and/or night shift and have a sleep disorder.

Variability of human upper airway collapsibility during sleep and the influence of body posture and sleep stage.

The critical pressure at which the pharynx collapses (Pcrit) is an objective measurement of upper airway collapsibility, an important pathogenetic factor in obstructive sleep apnoea. This study examined the inherent variability of passive Pcrit measurement during sleep and evaluated the effects of sleep stage and body posture on Pcrit. Repeated measurements of Pcrit were assessed in 23 individuals (15 male) with diagnosed obstructive sleep apnoea throughout a single overnight sleep study. Body posture and sleep stage were unrestricted. Applied upper airway pressure was repetitively reduced to obtain multiple measurements of Pcrit. In 20 subjects multiple measurements of Pcrit were obtained. The overall coefficient of repeatability for Pcrit measurement was 4.1 cm H2O. Considering only the lateral posture, the coefficient was 4.8 cm H2O. It was 3.3 cm H2O in the supine posture. Pcrit decreased from the supine to lateral posture [supine mean 2.5 cm H2O, 95% confidence interval (CI) 1.4-3.6; lateral mean 0.3 cm H2O, 95% CI -0.8-1.4, P = 0.007] but did not vary with sleep stage (P = 0.91). This study has shown that the overall coefficient of repeatability was 4.1 cm H2O, implying that the minimum detectable difference, with 95% probability, between two repeated Pcrit measurements in an individual is 4.1 cm H2O. Such variability in overnight measures of Pcrit indicates that a single unqualified value of Pcrit cannot be used to characterize an individual's overall collapsibility during sleep. When within-subject variability is accounted for, change in body posture from supine to lateral significantly decreases passive pharyngeal collapsibility.

Comment on Gratwicke et al. Nutritional Interventions to Improve Sleep in Team-Sport Athletes: A Narrative Review. Nutrients 2021, 13, 1586.

We recently read with great interest the recent paper by Gratwicke, M et al. (2021) [...].

Treating insomnia symptoms with medicinal cannabis: a randomized, crossover trial of the efficacy of a cannabinoid medicine compared with placebo.

STUDY OBJECTIVES: This randomized, double-blind, placebo-controlled, crossover study was conducted to evaluate the safety and efficacy of 2 weeks of nightly sublingual cannabinoid extract (ZTL-101) in treating chronic insomnia (symptoms ≥3 months). METHODS: Co-primary study endpoints were safety of the medication based on adverse event reporting and global insomnia symptoms (Insomnia Severity Index [ISI]). Secondary endpoints included: self-reported (sleep diary), actigraphy-derived, and polysomnography measurements of sleep onset latency (SOL), wake after sleep onset (WASO), total sleep time (TST), sleep efficiency (SE); and self-reported assessments of sleep quality (sSQ) and feeling rested upon waking. Adjusted mean differences between placebo and ZTL-101 were calculated. RESULTS: Twenty-three of 24 randomized participants (n = 20 female, mean age 53 ± 9 years) completed the protocol. No serious adverse events were reported. Forty mild, nonserious, adverse events were reported (36 during ZTL-101) with all but one resolving overnight or soon after waking. Compared to placebo, ZTL-101 decreased ISI (-5.07 units [95% CI: -7.28 to -2.86]; p = 0.0001) and self-reported SOL (-8.45 min [95% CI: -16.33 to -0.57]; p = 0.04) and increased self-reported TST (64.6 min [95% CI: 41.70 to 87.46]; p < 0.0001), sSQ (0.74 units [95% CI: 0.51 to 0.97]; p < 0.0001), and feeling of being rested on waking (0.51 units [95% CI: 0.24 to 0.78]; p = 0.0007). ZTL-101 also decreased actigraphy-derived WASO (-10.2 min [95% CI: -16.2 to -4.2]; p = 0.002), and increased actigraphy-derived TST (33.4 min [95% CI: 23.07 to 43.76]; p < 0.001) and SE (2.9% [95% CI: 2.0 to 3.8]; p = 0.005). CONCLUSIONS: Two weeks of nightly sublingual administration of a cannabinoid extract (ZTL-101) is well tolerated and improves insomnia symptoms and sleep quality in individuals with chronic insomnia symptoms. CLINICAL TRIAL: ANZCTR; anzctr.org.au; ACTRN12618000078257.

Respiratory gating of anatomical optical coherence tomography images of the human airway.

Anatomical optical coherence tomography (aOCT) is a long-range endoscopic imaging modality capable of quantifying size and shape of the human airway. A challenge to its in vivo application is motion artifact due to respiratory-related movement of the airway walls. This paper represents the first demonstration of respiratory gating of aOCT airway data, and introduces a novel error measure to guide appropriate parameter selection. Results indicate that at least four gates per respiratory cycle should be used, with only minor improvements as the number of gates is further increased. It is shown that respiratory gating can substantially improve the quality of aOCT images and reveal events and features that are otherwise obscured by blurring.

Evolution of changes in upper airway collapsibility during slow induction of anesthesia with propofol.

BACKGROUND: Upper airway collapsibility is known to increase under anesthesia. This study assessed how this increase in collapsibility evolves during slow Propofol induction and how it relates to anesthesia-induced changes in upper airway muscle activity and conscious state. METHODS: Nine healthy volunteers were studied. Anesthesia was induced with Propofol in a step-wise manner (effect-site concentration steps of 0.5 microg x ml(-1) from 0 to 3 microg x ml(-1) and thereafter to 4 microg x ml(-1) and 6 microg x ml(-1) [target-controlled infusion]). Airway patency was maintained with continuous positive airway pressure. Pharyngeal collapsibility was assessed at each concentration by measuring critical pressure. Intramuscular genioglossus electromyogram and anesthetic depth (bispectral index score) were monitored throughout. Loss of consciousness was defined as failure to respond to loud verbal command. RESULTS: Loss of consciousness occurred at varying Propofol effect-site concentrations between 1.5 and 4.0 microg x ml(-1). Initially genioglossus electromyographic activity was sustained with increases in Propofol concentration, increasing in some individuals. At or approaching loss of consciousness, it decreased, often abruptly, to minimal values with an accompanying increase in critical pressure. In most subjects, bispectral index score decreased alinearly with increasing Propofol concentration with greatest rate of change coinciding with loss of consciousness. CONCLUSIONS: Slow stepwise induction of Propofol anesthesia is associated with an alinear increase in upper airway collapsibility. Disproportionate decreases in genioglossus electromyogram activity and increases in pharyngeal critical closing pressure were observed proximate to loss of consciousness, suggesting that particular vulnerability exists after transition from conscious to unconscious sedation. Such changes may have parallels with upper airway behavior at sleep onset.

Influence of head extension, flexion, and rotation on collapsibility of the passive upper airway.

STUDY OBJECTIVES: To determine the effect of head posture on upper airway collapsibility and site of collapse of the passive human upper airway. DESIGN: Pharyngeal critical closing pressure (Pcrit) and site of airway collapse were assessed during head flexion, extension and rotation in individuals undergoing propofol anesthesia. SETTING: Operating theatre of major teaching hospital. PARTICIPANTS: Fifteen healthy volunteers (8 male), including 7 who were undergoing surgery unrelated to the head or neck. MEASUREMENTS AND RESULTS: Applied upper airway pressure was progressively decreased to induce variable degrees of inspiratory flow limitation and to define Pcrit. Upper airway and oesophageal pressure transducers identified the site of collapse. Genioglossus muscle activity (EMGgg) was assessed using intramuscular fine wire electrodes inserted percutaneously. Data from 3 subjects were excluded from analysis due to persistent EMGgg. In the neutral posture Pcrit was -0.4 +/- 4.4 cm H2O and collapsed most frequently in the velopharyngeal region. Relative to neutral, Pcrit increased to 3.7 +/- 2.9 cm H2O (P < 0.01) and decreased to -9.4 +/- 3.8 cm H2O (P < 0.01) when the head was flexed and extended, respectively but was unchanged by rotation (-2.6 +/- 3.3 cm H2O; n = 10; P = 0.44). The site of collapse varied, in no consistent pattern, with change in head posture in 5 subjects. CONCLUSIONS: Head posture has a marked effect on the collapsibility and site of collapse of the passive upper airway (measured by EMGgg) indicating that controlling head posture during sleep or recovery from anesthesia may alter the propensity for airway obstruction. Further, manipulating head posture during propofol sedation may assist with identification of pharyngeal regions vulnerable to collapse during sleep and may be useful for guiding surgical intervention.

Effect of body posture on pharyngeal shape and size in adults with and without obstructive sleep apnea.

STUDY OBJECTIVES: In patients with obstructive sleep apnea (OSA), the severity and frequency of respiratory events is increased in the supine body posture compared with the lateral recumbent posture. The mechanism responsible is not clear but may relate to the effect of posture on upper airway shape and size. This study compared the effect of body posture on upper airway shape and size in individuals with OSA with control subjects matched for age, BMI, and gender. PARTICIPANTS: 11 males with OSA and 11 age- and BMI-matched male control subjects. RESULTS: Anatomical optical coherence tomography was used to scan the upper airway of all subjects while awake and breathing quietly, initially when supine, and then in the lateral recumbent posture. A standard head, neck, and tongue position was maintained during scanning. Airway cross-sectional area (CSA) and anteroposterior (A-P) and lateral diameters were obtained in the oropharyngeal and velopharyngeal regions in both postures. A-P to lateral diameter ratios provided an index of regional airway shape. In equivalent postures, the ratio of A-P to lateral diameter in the velopharynx was similar in OSA and control subjects. In both groups, this ratio was significantly less for the supine than for the lateral recumbent posture. CSA was smaller in OSA subjects than in controls but was unaffected by posture. CONCLUSIONS: The upper airway changes from a more transversely oriented elliptical shape when supine to a more circular shape when in the lateral recumbent posture but without altering CSA. Increased circularity decreases propensity to tube collapse and may account for the postural dependency of OSA.

Evaluation of pharyngeal shape and size using anatomical optical coherence tomography in individuals with and without obstructive sleep apnoea.

This study compared shape, size and length of the pharyngeal airway in individuals with and without obstructive sleep apnoea (OSA) using a novel endoscopic imaging technique, anatomical optical coherence tomography (aOCT). The study population comprised a preliminary study group of 20 OSA patients and a subsequent controlled study group of 10 OSA patients and 10 body mass index (BMI)-, gender- and age-matched control subjects without OSA. All subjects were scanned using aOCT while awake, supine and breathing quietly. Measurements of airway cross-sectional area (CSA) and anteroposterior (A-P) and lateral diameters were obtained from the hypo-, oro- and velopharyngeal regions. A-P : lateral diameter ratios were calculated to provide an index of regional airway shape. In all subjects, pharyngeal CSA was lowest in the velopharynx. Patients with OSA had a smaller velopharyngeal CSA than controls (maximum CSA 91 +/- 40 versus 153 +/- 84 mm(2); P < 0.05) but comparable oro- (318 +/- 80 versus 279 +/- 129 mm(2); P = 0.48) and hypopharyngeal CSA (250 +/- 105 versus 303 +/- 112 mm(2); P = 0.36). In each pharyngeal region, the long axis of the airway was oriented in the lateral diameter. Airway shape was not different between the groups. Pharyngeal airway length was similar in both groups, although the OSA group had longer uvulae than the control group (16.8 +/- 6.2 versus 11.2 +/- 5.2 mm; P < 0.05). This study has shown that individuals with OSA have a smaller velopharyngeal CSA than BMI-, gender- and age-matched control volunteers, but comparable shape: a laterally oriented ellipse. These findings suggest that it is an abnormality in size rather than shape that is the more important anatomical predictor of OSA.

Anatomical optical coherence tomography for long-term, portable, quantitative endoscopy.

In this paper, we report on anatomical optical coherence tomography, a catheter-based optical modality designed to provide quantitative sectional images of internal hollow organ anatomy over extended observational periods. We consider the design and performance of an instrument and its initial intended application in the human upper airway for the characterization of obstructive sleep apnea (OSA). Compared with current modalities, the technique uniquely combines quantitative imaging, bedside operation, and safety for use over extended periods of time with no cumulative dose limit. Our experiments show that the instrument is capable of imaging subjects during sleep, and that it can record dynamic changes in airway size and shape.