Venoarteriolar reflex and heart rate variability

Abstract

The venoarteriolar reflex is a local vasomotor response to a gravitational stimulus depending on both myogenic and neural mechanisms. The neural component is considered to be mediated by an axon reflex and as such should have little central effects. The afferent sensory input however may still reach systemic vasomotor regulatory centers and eventually result in a more generalized response. To evaluate such a possibility we studied heart rate variability while inducing a venoarteriolar reflex in the right arm. The reflex was elicited by lowering the arm 40 cm below heart level while the subject was in supine position after initial rest. To document the reflex a photoplethysmography was continuously recorded from the index finger of the same arm. Precordial single channel ECG was also recorded. Both recordings were obtained by using MP100 system, PPG100C transducer, and TSD200 and ECG100C amplifiers (Biopac Systems Inc). To obtain time‐frequency analysis of the heart rate variability we used AcqKnowledge 4.0 software and Matlab based software (HRVAS). All our subjects were young healthy adults. The results showed changes in the heart rate variability similar to those obtained by standard orthostatic tests, although not as pronounced and more variable. We conclude that even though the venoarteriolar reflex is a local phenomenon it is integrated within the overall cardiovascular regulation.