Why the study?
The relative importance of cardiac output versus total peripheral resistance in mediating the pressor response to isometric exercise remains unclear.
Does total peripheral resistance or cardiac output primarily mediate the pressor response to isometric exercise during reduced preload in healthy volunteers?
Does total peripheral resistance or cardiac output primarily mediate the pressor response to isometric exercise during reduced preload in healthy volunteers?
In healthy individuals, the pressor response to isometric exercise during reduced cardiac output is primarily maintained by an increase in total peripheral resistance rather than cardiac output.
Pressor response preserved by increased TPR during reduced preload; extends physiological insight in healthy volunteers but leaves open clinical relevance.
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.
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Stens et al. (2020) studied this question.
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