RELATIONSHIP BETWEEN INDICES OF HEART RATE VARIABILITY, FOREARM VASOREACTIVITY AND EXERCISE TOLERANCE

Abstract

The importance of autonomic control on cardiovascular performance is well established. However, the relationship between autonomic modulation of the heart, peripheral vasoreactivity and exercise tolerance is not clearly defined. This study examined the relationship between indices of heart rate variability, forearm vasoreactivity, and exercise tolerance in 17 individuals (age = 51 ± 15). Subjects ranged from apparently healthy (n = 5) to those with moderate (n = 6) to severe cardiovascular disease (n = 6). Following a 10-min rest period, standard EKG's were collected in a supine position for 5-min and evaluated for the standard deviation of normal RR intervals (SDnn). Non-dominant forearm blood flow (FBF), vascular resistance (FVR), venous capacitance (FVCap) and venous outflow (FVO) were evaluated at rest and following 5-min upper arm occlusion (OCC) using plethysmography. Exercise tolerance was measured as the maximum distance (MWD) achieved on a 6-min- walk test. Results revealed a graded reduction in SDnn, vasoreactivity, and MWD from apparently healthy to moderate and severe disease. Univariate analysis revealed associations between MWD and SDnn (r = 0.44, p = 0.04), and MWD and vasoreactivity after OCC (FBF: r = 0.51, p = 0.02; FVR: r = −0.58, p = 0.01; FVCap: r = 0.60, p = 0.009; FVO: r = 0.49, p = 0.04). In addition, SDnn was correlated with vasoreactivity after OCC (FBF: r = 0.62, p = 0.008; FVR: r = −0.51, p = 0.04; FVCap: r = 0.53, p = 0.03; FVO: r = 0.37, p = 0.15). These data confirm previous literature regarding independent influences of SDnn and vasoreactivity on exercise tolerance. Uniquely, they also suggest an important relationship between SDnn and forearm vasoreactivity.