Effect of oscillatory lower body negative pressure and isometric handgrip exercise on cardioautonomic tone of healthy individuals

The influence of the autonomic nervous system on the heart can be quantified by assessing changes in the heart rate variability (HRV) during orthostatic challenge and exercise. However, the combination of oscillatory lower body negative pressure (oLBNP) and isometric handgrip exercise (IHE) on HRV has not been previously investigated. Therefore, the present study aimed to assess the effects of (oLBNP) at sympathetic (0.1 Hz) and parasympathetic (0.25 Hz) frequencies and IHE at 30% of maximum voluntary contraction (MVC) on HRV in normal healthy individuals. We conducted a cross-sectional study on 18 healthy male subjects. Beat-to-beat blood pressure, lead-II electrocardiogram, and oLBNP chamber pressure were recorded continuously during oLBNP at 0.1 and 0.25 Hz for 3 min each and IHE at 30% of MVC (for 4 min) along with oLBNP at 0.1 or 0.25 Hz (oLBNP was added in last 3 min) each followed by HRV analysis. The oLBNP at 0.25 Hz reduced the root mean square of successive inter-beat (RR) interval differences significantly as compared to baseline values and came to normal during the recovery phase (P = 0.008). The absolute power of the high-frequency band (HF power), Poincaré plot standard deviation perpendicular to the line of identity (SD1), and percentage of successive RR intervals that differ by more than 50 ms (pNN50) were also reduced significantly during oLBNP at 0.25 Hz and when IHE at 30% of MVC (IHE) was added to oLBNP at 0.25 Hz as compared to baseline (P < 0.05). oLBNP and IHE could be used as a non-invasive haemodynamic stressor to assess the neurocardiac axis and its mechanism of action during orthostatic stresses.