Determinants of heart rate variability during deep breathing: Basic findings and clinical applications

Abstract

The measurement of heart rate variation during forced breathing (HR_DB) is a well-known clinical test of parasympathetic function. It is known that normal values of HR_DB are strongly dependent on age. However, little is known about other physiological factors that may lead to reduced HR_DB values that may mimic parasympathetic failure. Thirty-two normal subjects (age 56.7±12.4 years) and 32 neurological patients with pathological autonomic test findings (age 57.9±10.2) were studied. Oscillations in heart rate and in mean arterial blood pressure were recorded in the supine position during forced breathing (6 cycles/min) using the Finapres monitor. Amplitudes of heart rate and blood pressure waves at 6 cycles/min (HR₆ and ABP₆) as well as gain values (Gain₆=HR₆/ABP₆) and phase differences ({ie131-1}) between HR and ABP waves were calculated by means of spectral analysis. The mean (±SD) HR₆ in normal subjects was 6.34±3.36 cycles/min with a mean ABP₆ of 5.11±2.49 mmHg. HR₆ correlated significantly with age (r=−0.426) and with ABP₆ (r=0.602). No significant correlation was found between HR₆ and mean blood pressure, mean heart rate or sex. From 24 patients with pathological findings in the classical HR_DB value, only nine could be classified as pathological when the effect of ABP₆ was considered. In conclusion, ABP variations significantly influence the amplitude of heart rate variations during forced breathing. We interpret these findings in terms of a baroreflex mechanism of HR_DB including both vagal and sympathetic efferents. Normal reference value tables for clinical HR_DB studies should not only consider age but also the amplitude of blood pressure variations.