Reactive Hyperemia can be used to quantify cardiocirculatory homeostasis in vivo

Recent studies on reactive hyperemia (RH) have shown that RH involves centrally mediated adaptive responses that cannot be simply regarded as a marker of endothelial function. Our research has shown that a classical approach such as the post-occlusive reactive hyperemia (PORH) typically involves two sequential mechanisms of adaptation – one appearing immediately during occlusion involving a strong vasoconstriction, most likely sympathetic to adapt to the sudden drop of blood flow and pressure. The second appears immediately after ceasing the occlusion, triggered by the immediate hyper-reperfusion after the pressure cuff removal. This evokes a progressive vasodilation involving multiple neuro-humoral components (not only local) intending to restore the normal perfusion conditions. Therefore, our study aims to characterize RH through the quantification of those two reflex components, expecting to identify new dynamic outcomes with clinical interest. Data was obtained from two cohorts of young healthy participants, both sexes, recruited within our university and submitted to a standard PORH maneuver. Group 1 (n=34) were regular smokers (> one year), without any related clinical manifestations. Group 2 (n=52) were nonsmokers. Perfusion changes were measured in both upper limb extremities using laser Doppler flowmetry in baseline (phase 1, 10 min) during occlusion of brachial artery (phase 2, 2 min), and after occlusion (phase 3, 10 min). The first reflex was characterized as the level of synchrony between signals in both hands during occlusion. This adaptive synchrony was computed by subtracting each limb’s signal’s mean baseline value, segmenting the occlusion period, and calculating the normalized correlation between those segments from both limbs. The second reflex assessed the time-to-basal, that is, the time required for the occluded limb to recover baseline perfusion levels after the occlusion. Time-to-basal was defined as the time in seconds elapsed between removing the occlusion and observing two consecutive seconds of signal where the moving average (with one-second window) is consistently within a 10% relative margin of the average perfusion value measured at rest. Considering the nature of these reflexes we hypothesize that synchrony is linked to the efficiency of this first adaptive response meant to maintain a proper circulatory homeostasis triggered by a sudden perfusion (flow and pressure) drop. A high correlation in the observed perfusion signals in the occluded and non-occluded limbs over time will correspond to a high efficiency of the mechanism. The time-to-basal outcome involves many other components, neural as endocrine, central as local, and should be linked to the recovery efficiency in this homeostatic loop. This means that significant changes should be present when some effector(s) is impaired by disease or by an ongoing pathophysiological process, with wider time lapses in these cases. This approach, while exploratory, already allowed us to clearly discriminate between the smoking and non-smoking groups in the studied population. Although participants were all young and healthy, significantly higher values of synchrony and faster time-to-basal were identified for the non-smoking population. Through the quantification of this perfusion adaptation effectiveness, we expect these outcomes might be further used as a measure of cardiocirculatory homeostasis. FCT—Foundation for Science and Technology, I.P. (Portugal), under the [UIDB/04567/2020] and [UIDP/04567/2020] and ALIES-COFAC. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.