Examining the impact of multilevel upper airway surgery on the obstructive sleep apnoea endotypes and their utility in predicting surgical outcomes.

BACKGROUND AND OBJECTIVE: Upper airway surgery for obstructive sleep apnoea (OSA) is an alternative treatment for patients who are intolerant of continuous positive airway pressure (CPAP). However, upper airway surgery has variable treatment efficacy with no reliable predictors of response. While we now know that there are several endotypes contributing to OSA (i.e., upper airway collapsibility, airway muscle response/compensation, respiratory arousal threshold and loop gain), no study to date has examined: (i) how upper airway surgery affects all four OSA endotypes, (ii) whether knowledge of baseline OSA endotypes predicts response to surgery and (iii) whether there are any differences when OSA endotypes are measured using the CPAP dial-down or clinical polysomnographic (PSG) methods. METHODS: We prospectively studied 23 OSA patients before and ≥3 months after multilevel upper airway surgery. Participants underwent clinical and research PSG to measure OSA severity (apnoea-hypopnoea index [AHI]) and endotypes (measured in supine non-rapid eye movement [NREM]). Values are presented as mean ± SD or median (interquartile range). RESULTS: Surgery reduced the AHITotal (38.7 [23.4 to 79.2] vs. 22.0 [13.3 to 53.5] events/h; p = 0.009). There were no significant changes in OSA endotypes, however, large but variable improvements in collapsibility were observed (CPAP dial-down method: ∆1.9 ± 4.9 L/min, p = 0.09, n = 21; PSG method: ∆3.4 [-2.8 to 49.0]%Veupnoea , p = 0.06, n = 20). Improvement in collapsibility strongly correlated with improvement in AHI (%∆AHISupineNREM vs. ∆collapsibility: p < 0.005; R2  = 0.46-0.48). None of the baseline OSA endotypes predicted response to surgery. CONCLUSION: Surgery unpredictably alters upper airway collapsibility but does not alter the non-anatomical endotypes. There are no baseline predictors of response to surgery.

Ventilatory control sensitivity in patients with obstructive sleep apnea is sleep stage dependent.

Study Objectives: The severity of obstructive sleep apnea (OSA) is known to vary according to sleep stage; however, the pathophysiology responsible for this robust observation is incompletely understood. The objective of the present work was to examine how ventilatory control system sensitivity (i.e. loop gain) varies during sleep in patients with OSA. Methods: Loop gain was estimated using signals collected from standard diagnostic polysomnographic recordings performed in 44 patients with OSA. Loop gain measurements associated with nonrapid eye movement (NREM) stage 2 (N2), stage 3 (N3), and REM sleep were calculated and compared. The sleep period was also split into three equal duration tertiles to investigate how loop gain changes over the course of sleep. Results: Loop gain was significantly lower (i.e. ventilatory control more stable) in REM (Mean ± SEM: 0.51 ± 0.04) compared with N2 sleep (0.63 ± 0.04; p = 0.001). Differences in loop gain between REM and N3 (p = 0.095), and N2 and N3 (p = 0.247) sleep were not significant. Furthermore, N2 loop gain was significantly lower in the first third (0.57 ± 0.03) of the sleep period compared with later second (0.64 ± 0.03, p = 0.012) and third (0.64 ± 0.03, p = 0.015) tertiles. REM loop gain also tended to increase across the night; however, this trend was not statistically significant [F(2, 12) = 3.49, p = 0.09]. Conclusions: These data suggest that loop gain varies between REM and NREM sleep and modestly increases over the course of sleep. Lower loop gain in REM is unlikely to contribute to the worsened OSA severity typically observed in REM sleep, but may explain the reduced propensity for central sleep apnea in this sleep stage.

Dynamic loop gain increases upon adopting the supine body position during sleep in patients with obstructive sleep apnoea.

BACKGROUND AND OBJECTIVE: Obstructive sleep apnoea (OSA) is typically worse in the supine versus lateral sleeping position. One potential factor driving this observation is a decrease in lung volume in the supine position which is expected by theory to increase a key OSA pathogenic factor: dynamic ventilatory control instability (i.e. loop gain). We aimed to quantify dynamic loop gain in OSA patients in the lateral and supine positions, and to explore the relationship between change in dynamic loop gain and change in lung volume with position. METHODS: Data from 20 patients enrolled in previous studies on the effect of body position on OSA pathogenesis were retrospectively analysed. Dynamic loop gain was calculated from routinely collected polysomnographic signals using a previously validated mathematical model. Lung volumes were measured in the awake state with a nitrogen washout technique. RESULTS: Dynamic loop gain was significantly higher in the supine than in the lateral position (0.77 ± 0.15 vs 0.68 ± 0.14, P = 0.012). Supine functional residual capacity (FRC) was significantly lower than lateral FRC (81.0 ± 15.4% vs 87.3 ± 18.4% of the seated FRC, P = 0.021). The reduced FRC we observed on moving to the supine position was predicted by theory to increase loop gain by 10.2 (0.6, 17.1)%, a value similar to the observed increase of 8.4 (-1.5, 31.0)%. CONCLUSION: Dynamic loop gain increased by a small but statistically significant amount when moving from the lateral to supine position and this may, in part, contribute to the worsening of OSA in the supine sleeping position.

Loop Gain Predicts the Response to Upper Airway Surgery in Patients With Obstructive Sleep Apnea.

Study Objectives: Upper airway surgery is often recommended to treat patients with obstructive sleep apnea (OSA) who cannot tolerate continuous positive airways pressure. However, the response to surgery is variable, potentially because it does not improve the nonanatomical factors (ie, loop gain [LG] and arousal threshold) causing OSA. Measuring these traits clinically might predict responses to surgery. Our primary objective was to test the value of LG and arousal threshold to predict surgical success defined as 50% reduction in apnea-hypopnea index (AHI) and AHI <10 events/hour post surgery. Methods: We retrospectively analyzed data from patients who underwent upper airway surgery for OSA (n = 46). Clinical estimates of LG and arousal threshold were calculated from routine polysomnographic recordings presurgery and postsurgery (median of 124 [91-170] days follow-up). Results: Surgery reduced both the AHI (39.1 ± 4.2 vs. 26.5 ± 3.6 events/hour; p < .005) and estimated arousal threshold (-14.8 [-22.9 to -10.2] vs. -9.4 [-14.5 to -6.0] cmH2O) but did not alter LG (0.45 ± 0.08 vs. 0.45 ± 0.12; p = .278). Responders to surgery had a lower baseline LG (0.38 ± 0.02 vs. 0.48 ± 0.01, p < .05) and were younger (31.0 [27.3-42.5] vs. 43.0 [33.0-55.3] years, p < .05) than nonresponders. Lower LG remained a significant predictor of surgical success after controlling for covariates (logistic regression p = .018; receiver operating characteristic area under curve = 0.80). Conclusions: Our study provides proof-of-principle that upper airway surgery most effectively resolves OSA in patients with lower LG. Predicting the failure of surgical treatment, consequent to less stable ventilatory control (elevated LG), can be achieved in the clinic and may facilitate avoidance of surgical failures.

Upper-Airway Collapsibility and Loop Gain Predict the Response to Oral Appliance Therapy in Patients with Obstructive Sleep Apnea.

RATIONALE: Oral appliances (OAs) are commonly used as an alternative treatment to continuous positive airway pressure for patients with obstructive sleep apnea (OSA). However, OAs have variable success at reducing the apnea-hypopnea index (AHI), and predicting responders is challenging. Understanding this variability may lie with the recognition that OSA is a multifactorial disorder and that OAs may affect more than just upper-airway anatomy/collapsibility. OBJECTIVES: The objectives of this study were to determine how OA alters AHI and four phenotypic traits (upper-airway anatomy/collapsibility and muscle function, loop gain, and arousal threshold), and baseline predictors of which patients gain the greatest benefit from therapy. METHODS: In a randomized crossover study, 14 patients with OSA attended two sleep studies with and without their OA. Under each condition, AHI and the phenotypic traits were assessed. Multiple linear regression was used to determine independent predictors of the reduction in AHI. MEASUREMENTS AND MAIN RESULTS: OA therapy reduced the AHI (30 ± 5 vs. 11 ± 2 events/h; P < 0.05), which was driven by improvements in upper-airway anatomy/collapsibility under passive (1.9 ± 0.7 vs. 4.7 ± 0.6 L/min; P < 0.005) and active conditions (2.4 ± 0.9 vs. 6.2 ± 0.4 L/min; P < 0.001). No changes were seen in muscle function, loop gain, or the arousal threshold. Using multivariate analysis, baseline passive upper-airway collapsibility and loop gain were independent predictors of the reduction in AHI (r2 = 0.70; P = 0.001). CONCLUSIONS: Our findings suggest that OA therapy improves the upper-airway collapsibility under passive and active conditions. Importantly, a greater response to therapy occurred in those patients with a mild anatomic compromise and a lower loop gain.

Derivación ventrículo-cava para hidrocefalia en casos extremos. Una alternativa viable / Ventriculocaval shunt for hydrocephalus in extreme cases. A viable alternative

Introducción. El manejo de la hidrocefalia habitualmente comprende la derivación del líquido cefalorraquídeo hacia alguna cavidad corporal. En circunstancias especiales, los pacientes requieren de abordajes alternos y el cirujano se enfrenta al empleo de opciones extremas. Caso clínico. En este estudio se presentan dos pacientes que se sometieron quirúrgicamente a una derivación ventrículo-cava a través de un acceso vascular periférico. Conclusiones. La técnica representó un abordaje de fácil aplicación y con mínimas complicaciones que nos brinda una opción de rescate en aquellos pacientes complicados. En los casos presentados, el empleo de esta técnica fue exitoso.

Background. Hydrocephalus management usually involves cerebrospinal fluid shunting into some corporal cavity. Under special circumstances, patients require alternate approaches, and the surgeon faces the use of extreme options. Case report. In this study we present two patients who were surgically approached with ventriculocaval shunt through peripheral vascular access. Conclusions. The technique represented an easy application with minimal complications, an approach that provides a rescue option in cases of complicated hydrocephalus. In our case, this technique was successful.