Autonomic cardiovascular effects of brief exposure to chronic intermittent hypoxia detected using analysis of heart rate variability and spontaneous baroreflex sensitivity

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Obstructive sleep apnea patients and chronic intermittent hypoxia (CIH) animal models present increased cardiovascular responses. Therefore, it is possible that increased chemoreflexes and decreased baroreflex sensitivity (BRS) would elicit sympathetic overactivity, inducing hypertension. We previously showed that exposure of cats to CIH for 4 days increases the carotid body chemosensory and ventilatory responses to hypoxia. Thus, we studied the effect of brief exposure to CIH in cats for 4 days on sympathetic tone and BRS, using spectral analysis of heart rate variability (HRV), blood pressure variability (BPV) and BRS determination with the sequence method. In anesthetized cats we evaluated the effect of acute hypoxia on heart rate and blood pressure. Data was digitized with a PowerLab 8SP A/D interface and stored in a PC computer. For HRV and BPV analysis, we used autoregressive methods for estimation of the spectral density at the low-frequency (LF, 0.025–0.15) and high-frequency (HF, 0.15–0.833) bands. We compared control (normoxic) cats with animals exposed to sham-CIH and CIH. We found that CIH-treated cats showed enhanced tachycardic responses to acute severe hypoxia, with reduced HRV and BRS. Our data suggests that CIH exposure for 4 days induced early autonomic changes that favor an enhanced sympathetic outflow and decreased baroreflex control on blood pressure. Supported by FONDECYT 1030330.