Role of heart rate and stroke volume during muscle metaboreflex-induced cardiac output increase: differences between activation during and after exercise

Abstract

We hypothesized that the role of stroke volume (SV) in the metaboreflex-induced cardiac output (CO) increase was blunted when the metaboreflex was stimulated by exercise muscle ischemia (EMI) compared with post-exercise muscle ischemia (PEMI), because during EMI heart rate (HR) increases and limits diastolic filling. Twelve healthy volunteers were recruited and their hemodynamic responses to the metaboreflex evoked by EMI, PEMI, and by a control dynamic exercise were assessed. The main finding was that the blood pressure increment was very similar in the EMI and PEMI settings. In both conditions the main mechanism used to raise blood pressure was a CO elevation. However, during the EMI test CO was increased as a result of HR elevation whereas during the PEMI test CO was increased as a result of an increase in SV. These results were explainable on the basis of the different HR behavior between the two settings, which in turn led to different diastolic time and myocardial performance.

Differences in hemodynamic response to metaboreflex activation between obese patients with metabolic syndrome and healthy subjects with obese phenotype

“…The response in this parameter was higher in the CTL than in the OMS group, whereas no difference was present between the two groups with obesity, with the MHO group showing a behavior in the medium between those of the CTL and of the OMS group. The increase in VFR occurring in the CTL and in the MHO group is similar to what has been reported in previous human research with similar experimental settings (13,14,29) and confirms that an increase in diastolic flow takes place during the metaboreflex in normal individuals, probably because of a sympathetic-mediated venous and splanchnic constriction (32,53,54). The lack of VFR response in the OMS group appears to suggest that, in subjects with complicated obesity, certain phenomena likely prevented the normal increase in venous return and cardiac preload.…”

“…These substances can trigger cardiovascular reflexes (i.e., the so called "metaboreflex"), thereby activating the sympathetic nervous system, which in turn increases blood pressure to guarantee sufficient metabolite wash-out from the contracting muscle (19,39). In normal individuals, this task is accomplished with a complex hemodynamic response that encompasses complex interplay between myocardial performance, cardiac preload, afterload, and HR (3,6,9,13,14,24,33,40,51,56). Recent evidence suggests that, at least in healthy subjects, when the metaboreflex is activated by PEMI, a central role in the described metaboreflex-induced blood pressure response is played by the possibility to keep constant or to increase SV, thereby maintaining or increasing CO, since HR is not usually involved in the phenomenon (3, 9 -11, 25, 38).…”

“…MEAN BLOOD PRESSURE RESPONSE (MBP) to metaboreflex activation in healthy individuals is normally the consequence of increases in both systemic vascular resistance (SVR) and cardiac output (CO) (3,9,10,12,14,24,29,31,54,56). This response is achieved as the result of an elevation in sympathetic tone, which produces arteriolar constriction and enhancement in myocardial performance and in cardiac preload (18,35,39).…”

Attenuated muscle metaboreflex-induced pressor response during postexercise muscle ischemia in renovascular hypertension

“…Muscle metaboreflex activation results in a reflex increase in sympathetic outflow (9, 28 -30, 36 -38, 62). During submaximal dynamic exercise, metaboreflex activation markedly increases heart rate (HR), cardiac output (CO) and left ventricular dP/dt max , with little effect on the peripheral vasculature (5,16,17,26,27,55,60,65). Therefore, the substantial metaboreflex-mediated pressor response observed during mild dynamic exercise is virtually solely the result of the increase in CO.…”

Individual differences in cardiac and vascular components of the pressor response to isometric handgrip exercise in humans

“…When the reflex is selectively activated in humans by postexercise muscle ischemia (PEMI) after isometric handgrip exercise, the pressor response occurs mainly via peripheral vasoconstriction; CO remains at the resting level (16,27,31,44,57). However, humans can also reportedly show an increase in CO during PEMI after leg cycling (5), dynamic knee extension (10), and dynamic handgrip exercise (9,11). Although differences in the type of exercise and muscle mass used in the exercise could potentially affect the results, an alternative explanation for this inconsistency is that the components of the muscle metaboreflex-mediated pressor response vary widely among human subjects.…”