Shared and Simple Effects of Determinants of Mean Arterial Pressure During Handgrip and Mirror Tracing Tasks

Abstract

Abstract Hierarchical linear regression (HLR) can be used to quantify the relative contribution specific cardiovascular (CV) mechanisms make to blood-pressure responses. The impact particular mechanisms exert varies depending on the nature of situational demands and the length of time these demands have been imposed. Theoretically, the determinants of blood-pressure changes may exercise their influence independently as simple effects, or they might evidence a relationship that is correlated or shared with other mechanisms. Following a procedure Lindenberger and Potter (1998) outlined, we used HLR and computations of shared versus simple effect ratios to quantify the portions of variance several cardiovascular parameters accounted for independently in mean arterial pressure (MAP) reactivity during isometric handgrip and mirror tracing. The predictor variables included heart rate (HR), total peripheral resistance (TPR), and cardiac output (CO). CV activity of 50 college-aged males was measured during adjacent 30-s periods using impedance cardiography and a Dinamap blood pressure monitor. HR reactivity predicted MAP changes during all measurement periods. However, for mirror tracing, a substantial portion of the variance in MAP accounted for by HR was shared with CO reactivity (39% for period 1; 13% for period 2). For handgrip, 5% and 20% of variance HR accounted for in MAP during periods 1 and 2, respectively, were shared with changes in TPR. CO shared trivial amounts of variance in MAP changes with HR during handgrip. Finally, CO changes were correlated with TPR changes and uncorrelated with MAP reactivity when handgrip was performed. However, adding CO to the equation improved TPR's predictive utility, suggesting that suppressor effects were present.