Differential reflex control of forearm and calf resistance vessels by chemosensitive cardiac afferent activation

Abstract

The aim of this study was to determine whether chemosensitive ventricular afferent activation in humans evokes a diffuse pattern of reflex vasodilation involving the skeletal muscle circulation of all the extremities or a highly specified pattern of vasodilation that is limited to the rather small vascular bed of the forearm. In 10 patients with innervated ventricles and 7 patients with denervated ventricles resulting from heart transplantation, we performed simultaneous plethysmographic recordings of blood flow in the forearm and calf during chemosensitive ventricular afferent activation with intracoronary Renografin. In patients with innervated ventricles, intracoronary Renografin evoked directionally opposite vascular responses in the forearm and calf: forearm resistance decreased from 50 +/- 11 to 31 +/- 8 units, whereas calf resistance increased from 42 +/- 7 to 59 +/- 9 units (P < 0.05, calf vs. forearm). Forearm vasodilation was eliminated after heart transplantation, indicating that this is a reflex response caused by ventricular afferents. In contrast, calf vasoconstriction was well preserved despite ventricular deafferentation, indicating that this response is caused by mechanisms other than ventricular afferent activation, possibly the sinoaortic baroreceptors. Taken together, these findings document a remarkable degree of specificity in the effects of cardiac afferent activation on the reflex regulation of regional vasomotor tone in humans.

Angiotensin AT1 receptor blockade abolishes the reflex sympatho-excitatory response to adenosine.

“…Differences in sympathetic vasoconstrictor outflow to the arm and the leg in response to intraarterial adenosine might account for the dissociation between TBS, which increased, and NAR in the contralateral noninfused forearm, which did not. Similar discordance has been observed during mental stress (33), or on stimulation of chemosensitive cardiac afferents (34). However, Wallin and colleagues demonstrated that circulatory arrest, after handgrip, increases muscle sympathetic traffic in both the opposite radial, and in the peroneal nerve (35), leading us to anticipate an increase in NAR in the contralateral arm in these experiments.…”

Heterogeneous responses of human limbs to infused adrenergic agonists: a gravitational effect?

“…Several stimuli have been reported to produce heterogeneous regional vascular responses in skeletal muscle. For example, orthostatic stress (5,6), cold stress (13), and ventricular chemoreceptor activation (14) may elicit differential responses. Despite lower norepinephrine spillover from legs compared with arms (13,16), neural traffic to arm and leg skeletal muscle during orthostatic stress appears to be relatively uniform (22,29).…”