Acute effects of the application of bi-level positive airway pressure on heart rate variability in healthy young men

Objective

To evaluate the acute effects of noninvasive ventilation through bi-level positive airway pressure (BiPAP) on heart rate variability (HRV) in young and healthy men.

Methods

Eleven young and healthy men, aged 22 ± 2 years, were studied. The heart rate and R–R intervals (ms) were collected on a beat-to-beat basis from an electrocardiogram recording in the CM5 derivation with an electrocardiography monitor (Ecafix TC500). The signal was converted by an analogical/digital conversor (Lab.PC+; National Instruments) and processed by a specific routine. The record was collected in two situations: 10 min at rest in the sitting position during spontaneous breathing; and 10 min at the same position with BiPAP (BiPAP^®; Tranquility Respironics) application through a nasal mask. The BiPAP pressures slowly increased the inspiratory pressure up to 15 cmH₂O and the expiratory pressure to 8 cmH₂O, allowing voluntary adaptation. The heart rate and its variability were analyzed by the time domain (TD), through RMSSD (ms) and RMSM (ms) indexes, and by the frequency domain (FD), which was expressed as normalized units of low frequency (LF), high frequency (HF) and the LF/HF ratio. In addition, the respiratory rate (RR), the arterial oxygen saturation (oxymeter Emai OX-P-10), the end-tidal carbon dioxide (capnometer BCI-1050) and the blood pressure (indirect auscultatory methods) were measured. The statistical analysis was performed by the Wilcoxon test with P < 0.05.

Results

In the TD the RMSSD index was significantly lower during BiPAP application when compared with the situation without the ventilatory support. In the FD, only the LF/HF ratio increased significantly during BiPAP application. In relation to physiologic variables, lower end-tidal carbon dioxide values (P = 0.001) and higher SaO₂ (P = 0.04) were observed during BiPAP application.

Conclusion

The results suggest that the acute application of positive pressure in the airway can promote a decrease of HRV and change the autonomic balance, with predominance of the sympathetic system over the parasympathetic system on heart rate modulation.