Factors mediating the pressor response to isometric muscle contraction: An experimental study in healthy volunteers during lower body negative pressure

Abstract

Whilst both cardiac output (CO) and total peripheral resistance (TPR) determine mean arterial blood pressure (MAP), their relative importance in the pressor response to isometric exercise remains unclear. This study aimed to elucidate the relative importance of these two different factors by examining pressor responses during cardiopulmonary unloading leading to step-wise reductions in CO. Hemodynamics were investigated in 11 healthy individuals before, during and after two-minute isometric exercise during lower body negative pressure (LBNP; -20mmHg and -40mmHg). The blood pressure response to isometric exercise was similar during normal and reduced preload, despite a step-wise reduction in CO during LBNP (-20mmHg and -40mmHg). During -20mmHg LBNP, the decreased stroke volume, and consequently CO, was counteracted by an increased TPR, while heart rate (HR) was unaffected. HR was increased during -40 mmHg LBNP, although insufficient to maintain CO; the drop in CO was perfectly compensated by an increased TPR to maintain MAP. Likewise, transient application of LBNP (-20mmHg and -40mmHg) resulted in a short transient drop in MAP, caused by a decrease in CO, which was compensated by an increase in TPR. This study suggests that, in case of reductions of CO, changes in TPR are primarily responsible for maintaining the pressor response during isometric exercise. This highlights the relative importance of TPR compared to CO in mediating the pressor response during isometric exercise.

Effects of experimental hypovolemia and pain on pre‐ejection period and pulse transit time in healthy volunteers

“…Cold pressor test (CPT) is a model of acute pain, where typically a hand is immersed in ice-cold water (Wolf & Hardy, 1941). CPT stimulates thermoreceptors and nociceptors (Patapoutian et al, 2003), causing increased sympathetic nervous activity (Victor et al, 1987) and a rise in arterial pressure, peripheral resistance, HR, and cardiac output (Stens et al, 2020;Stocks et al, 2004).…”

Isometric Exercise Training and Arterial Hypertension: An Updated Review

“…TPR has been previously suggested to provide a less active contribution to this BP rise, although the limited previous data have been largely based on transitory measures as opposed to continuous recording which may not be sufficient to effectively capture the true pressor response [130,147,149,150]. Examining the current continuous data, handgrip research has demonstrated a small increase in TPR that remains above baseline when measured throughout a single contraction [151], as well as when measured throughout a 4 × 2-min protocol session [62]. Conversely, the wall squat appears to produce an initial rise in TPR, followed by a stepwise reduction throughout each interval [96,97].…”

Cerebral blood flow velocity during simultaneous changes in mean arterial pressure and cardiac output in healthy volunteers

“…Although LBNP mainly affects and reduces cardiac output, small changes in MAP may be seen. Conversely, IHG mainly increases MAP but may also slightly increases cardiac output (Stens et al 2020 ). The regression models therefore attempt to describe the effect of one variable, controlling for the other.…”