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

We tested the hypothesis that intermittent apneas performed by awake subjec ts simulate obstructive sleep apnea (OSA) and change dynamic complexity of the cardiovascular control system by repetitive short time stimulation of a rterial chemoreceptors. Correlation dimension (CD) and reccurent plot quant ification 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 b y 1 min free breathing period. Systolic (SYS), diastolic (DIAS) arterial bl ood pressure was continuously recorded by finger volume clamp. Stroke volum e (SV) was estimated by pulse pressure analysis. Cardiac output (CO) and to tal peripheral resistance (TPR) were calculated by Portapress system. Cardi ac inter-beat interval (IBI) was measured from R-R intervals of EGG. Standa rd deviation (SD), an index of linear variability, was calculated in 1 min epoch. Dynamics of cardiovascular variables was computed in each subject du ring 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 perio d CD of all circulatory variables was significantly reduced and RDR augment ed. In 23 out of 33 subjects decreased nonlinear dynamics of TPR was carrie d over from A to R. In contrast, SD increased significantly in A. In conclu sion, intermittent brief chemoreflex stimulations by repetitive apneas incr ease blood pressure and TPR and decrease chaotic behaviour and complexity o f 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 ar terial hypertension linked with OSA.