The contribution of neuromechanical mechanisms to the pathogenesis of upper airway obstruction during sleep

Background. The relative contributions of passive mechanical loads and dynamic compensatory neuromuscular responses to pharyngeal collapsibility in obstructive sleep apnea (OSA) are largely unknown. The overall objective of the dissertation was to determine the contribution of passive mechanical loads and dynamic neuromuscular responses to the pathogenesis of OSA. Specific objectives of the dissertation were: (1) To review the pathogenesis of OSA, (2) To develop a standardized approach to the acquisition and analysis of pressure-flow data used to measure pharyngeal collapsibility, and (3) To determine the relative contributions of passive mechanical loads and active compensatory neuromuscular responses to pharyngeal collapsibility during sleep. Methods. (1) Summary of the literature concerning the pathogenesis of OSA, (2) Development of a standardized approach to the acquisition and analysis of upper airway pressure-flow relationships in a consecutive sample of OSA patients, (3) Measurements of passive mechanical loads and active compensatory neuromuscular responses and their contributions to pharyngeal collapsibility (PCRIT) were assessed in a sample of normal subjects and OSA patients matched on age, gender, and body-mass index. Results. Two series of measurements acquired at varying nasal pressure levels with two or more breaths per level were comparable to three series in determining the PCRIT. OSA patients demonstrated elevated mechanical loads as demonstrated by a higher passive PCRIT (-0.05 cm H2O (SD 2.4) vs. -4.5 cm H 2O (SD 3.0), P = 0.0003) and reduced dynamic responses to upper airway obstruction as suggested by failure to lower their active PCRIT (-1.6 cm H 2O (SD 3.5) vs. -11.1 cm H2O (SD 5.3), P < 0.0001) compared to normal subjects. Moreover, a subset of normal subjects at risk for OSA due to elevations in mechanical loads similar to OSA patients was identified that maintained airway patency by lowering the active PCRIT. Conclusions. Ascertainment of PCRIT can be performed in a standardized fashion. Patients with OSA demonstrate both increased upper airway mechanical loads and blunted neuromuscular responses during sleep. Normal subjects with passive mechanical loads in a range similar to patients with OSA are protected from the disorder due to the presence of vigorous compensatory neuromuscular responses during sleep

Portable Sleep Monitoring for Diagnosing Sleep Apnea in Hospitalized Patients With Heart Failure

Sleep apnea is an underdiagnosed condition in patients with heart failure. Efficient identification of sleep apnea is needed, as treatment may improve heart failure-related outcomes. Currently, use of portable sleep monitoring in hospitalized patients and those at risk for central sleep apnea is discouraged. This study examined whether portable sleep monitoring with respiratory polygraphy can accurately diagnose sleep apnea in patients hospitalized with decompensated heart failure. Hospitalized patients with decompensated heart failure underwent concurrent respiratory polygraphy and polysomnography. Both recordings were scored for obstructive and central disordered breathing events in a blinded fashion, using standard criteria, and the apnea-hypopnea index (AHI) was determined. Pearson's correlation coefficients and Bland-Altman plots were used to examine the concordance among the overall, obstructive, and central AHI values derived by respiratory polygraphy and polysomnography. The sample consisted of 53 patients (47% women) with a mean age of 59.0 years. The correlation coefficient for the overall AHI from the two diagnostic methods was 0.94 (95% CI, 0.89-0.96). The average difference in AHI between the two methods was 3.6 events/h. Analyses of the central and obstructive AHI values showed strong concordance between the two methods, with correlation coefficients of 0.98 (95% CI, 0.96-0.99) and 0.91 (95% CI, 0.84-0.95), respectively. Complete agreement in the classification of sleep apnea severity between the two methods was seen in 89% of the sample. Portable sleep monitoring can accurately diagnose sleep apnea in hospitalized patients with heart failure and may promote early initiation of treatment

Variability and Misclassification of Sleep Apnea Severity Based on Multi-Night Testing

BACKGROUND: Portable monitoring is a convenient means for diagnosing sleep apnea. However, data on whether one night of monitoring is sufficiently precise for the diagnosis of sleep apnea are limited. RESEARCH QUESTION: The current study sought to determine the variability and misclassification in disease severity over three consecutive nights in a large sample of patients referred for sleep apnea. METHODS: A sample of 10,340 adults referred for sleep apnea testing was assessed. A self-applied type III monitor was used for three consecutive nights. The apnea-hypopnea index (AHI) was determined for each night, and a reference AHI was computed by using data from all 3 nights. Pairwise correlations and the proportion misclassified regarding disease severity were computed for each of the three AHI values against the reference AHI. RESULTS: Strong correlations were observed between the AHI from each of the 3 nights (r = 0.87-0.89). However, substantial within-patient variability in the AHI and significant misclassification in sleep apnea severity were observed based on any 1 night of monitoring. Approximately 93% of the patients with a normal study on the first night and 87% of those with severe sleep apnea on the first night were correctly classified compared with the reference derived from all three nights. However, approximately 20% of the patients with mild and moderate sleep apnea on the first night were misdiagnosed either as not having sleep apnea or as having mild disease, respectively. CONCLUSIONS: In patients with mild to moderate sleep apnea, one night of portable testing can lead to misclassification of disease severity given the substantial night-to-night variability in the AHI