Polysomnographic monitoring of difficult-to-control asthma patients

BACKGROUND Difficult-to-Control Asthma (DCA) is associated with sleep disturbances. Polysomnography allows for a continuous monitoring of sleep quality, and it also enables to carry out mathematical analyses of cardiorespiratory signals, useful to gain insight into the mechanisms of heart rate variability (HRV). OBJECTIVES The goal of this study was to integrate standard polysomnographic indices with HRV indices for a comprehensive description of sleep of DCA patients. MATERIALS AND METHODS Twenty-one DCA patients were screened at the Santa Casa de Misericordia de Sao Paulo’s Pulmonary Outpatient Clinic and polysomnographic exams were conducted at the sleep laboratory of Universidade Nove de Julho in Sao Paulo. Signals from polysomnography which were analyzed included O2 saturation and electrocardiogram (ECG). Sleep stages were identified from the hypnogram. HRV analysis was performed on a subset of patients by means of spectral analysis of RR series extracted from ECG. Standard spectral indices were computed to determine the contribution of the sympathetic nervous system and of respiration to the beat-to-beat variability of heart rate. RESULTS Sleep efficiency displayed an average of 72.9%. The distribution of sleep time showed a predominance of non-REM (NREM) sleep (85.5%). Oxygen saturation was 93.8% in NREM sleep, 83% during REM sleep, and 83.2% in micro-arousals. Preliminary results of HRV analysis showed an association between an abnormal cardiorespiratory coupling and an inferior quality of sleep. CONCLUSIONS The quality of sleep in DCA patients was affected by the occurrence of microarousals, which may depend on desaturation episodes in association with slower breathing, as suggested also by HRV analysis.