Hemodynamic responses to metaboreflex activation: insights from spinal cord-injured humans

Abstract

This investigation was conducted to study the hemodynamic consequences of spinal cord injury (SCI) during post-exercise muscle metaboreflex activation in SCI subjects. The hemodynamic response to metaboreflex recruitment was assessed in ten SCI patients and nine healthy controls (CTL) by means of impedance cardiography. The main results were (1) the metaboreflex-induced blood pressure rise was blunted in SCI subjects compared with normals, (2) the CTL group achieved the blood pressure response via cardiac output increase, while the SCI subjects could not use this mechanism, (3) the CTL group was able to enhance stroke volume and ventricular filling rate in response to the metaboreflex, whereas the SCI group could not. It was concluded that in healthy individuals, the hemodynamic response to the metaboreflex is an integrated phenomenon that depends mainly on a flow-mediated mechanism, whereas in SCI individuals the reduced venous return impairs this mechanism.

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.…”

“…From recent and early findings, it appears that the capacity to centralize blood volume and to increase venous return plays a pivotal role during the metaboreflex, and altered hemodynamic responses have been described where this capacity is impaired (4,13,33,53). In the present investigation, VFR was used to investigate venous return.…”

“…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).…”

“…The possibility to modulate SV has been defined crucial in the metaboreflex activation by means of PEMI, since in this setting HR does not normally have an evident response because of the elevated vagal tone, which counteracts the sympathetic activation (25,38). Thus, to increase/or to maintain stable CO values, cardiovascular regulatory mechanisms can only rely on the SV reserve, which can be recruited by enhancing cardiac performance and/or cardiac preload (11,13,29,33). In the present study, the OMS group showed a tendency to decrease SV response during the metaboreflex, whereas normal subjects increased this parameter.…”

Cardiovascular responses to forearm muscle metaboreflex activation during hypercapnia in humans

“…However, the local circulatory occlusion used to trap metabolites that activate metaboreflex prevents venous dilation, which is a major component of metaboreflex activation (10,25). To avoid this obstacle, we chose to use a 1-min 50% MVC handgrip model, which is known to evoke the muscle metaboreflex without increasing HR, SV, or CO.…”