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Characteristics and Consequences of Non-apneic Respiratory Events during Sleep.

RATIONALE
Current scoring criteria of non-apneic events (i.e. hypopnea) require the presence of oxyhemoglobin de-saturation and/or arousal. However, other sleep study parameters may help to identify abnormal respiratory events and assist in making more accurate diagnosis.


OBJECTIVES
To investigate whether non-apneic respiratory events without de-saturation or cortical arousal are associated with respiratory and cardiac consequences.


METHODS
Thirteen participants with sleep disturbances (snoring and/or excessive day time sleepiness), were screened using attended in laboratory polysomnography (PSG) while monitoring pressure and airflow via a nasal mask with an attached pneumotach. To separate the contribution of the upper airway resistance (RUA) and total pulmonary resistance (RL), supraglottic and esophageal pressures were measured using Millar® pressure catheters. RL and RUA were calculated during baseline and hypopneas. RL was defined as the resistive pressure divided by the maximal flow during inspiration and expiration. Hypopnea was defined 30% decrease in flow with 3% de-saturation and /or cortical arousal. Respiratory events (RE): was defined as 30% decrease in the flow without de-saturation and/or cortical arousal. In 8 subjects CPAP was titrated to optimal pressure. R-R interval (RRI) was defined as consecutive beat-to-beat RR interval on single lead ECG during baseline, RE/hypopnea and on optimal CPAP.


RESULTS
REs associated with increased expiratory RUA (14.6±11.3 vs.7.5±4.5 cmH2O/L/s; p<0.05), and increased expiratory RL relative to baseline (29.2 14.6 vs. 20.9 11.0 and 23.7±12.1 vs. 14.3±5.6 cmH2O/L/s during inspiration and expiration, respectively; p<0.05). RRI decreased significantly following RE and hypopnea relative to baseline (804.8±33.1 vs. 806.4±36.3 vs. 934.3±45.8 ms; p<0.05). Optimal CPAP decreased expiratory RUA (4.0±2.5 vs.7.5±4.5 cmH2O/L/s; p<0.05), inspiratory RL decreased (12.6±14.1 vs.7.5±4.5 cmH2O/L/s; p<0.05), and RRI returned to baseline (p<0.05). RRI dips index was an independent predictor of SDB in symptomatic patients (p<0.05).


CONCLUSIONS
Non-apneic respiratory events without cortical arousal or de-saturation are associated with significant respiratory and heart rate changes. Optimal CPAP and the reduction of resistive load are associated with the normalization of heart rate indicating potential clinical benefit.