Repetitive apneas reduce nonlinear dynamical complexity of the human cardiovascular control system

We tested the hypothesis that intermittent apneas performed by awake subjects simulate obstructive sleep apnea (OSA) and change dynamic complexity of the cardiovascular control system by repetitive short time stimulation of arterial chemoreceptors. Correlation dimension (CD) and reccurent plot quantification calculated as ratio % determinism versus % recurrence (RDR) were used as indices of chaotic dynamics. Thirty three normotensive subjects of mean age 21,58 +/-4,1 performed 10 voluntary apneas 1 min. each separated by 1 min free breathing period. Systolic (SYS), diastolic (DIAS) arterial blood pressure was continuously recorded by finger volume clamp. Stroke volume (SV) was estimated by pulse pressure analysis. Cardiac output (CO) and total peripheral resistance (TPR) were calculated by Portapress system. Cardiac inter-beat interval (IBI) was measured from R-R intervals of EGG. Standard deviation (SD), an index of linear variability, was calculated in 1 min epoch. Dynamics of cardiovascular variables was computed in each subject during 20 min, rest (C), 20 min. of 10 apneas, 1 min each, separated by 1 min free breathing (A), and in 20 min. recovery free breathing (R). In A period CD of all circulatory variables was significantly reduced and RDR augmented. In 23 out of 33 subjects decreased nonlinear dynamics of TPR was carried over from A to R. In contrast, SD increased significantly in A. In conclusion, intermittent brief chemoreflex stimulations by repetitive apneas increase blood pressure and TPR and decrease chaotic behaviour and complexity of the cardiovascular autonomic control system, presumably by inhibition of some regulatory loops such as baroreflex, less vital for survival at oxygen deprivation. Reduced complexity could be implicated in the mechanism of arterial hypertension linked with OSA.