Acute adaptation of skin microcirculatory perfusion does not involve local responses
Authors: Monteiro Rodrigues Luis , Rocha Clemente , Gregorio Joao , Florindo Margarida , Granja Tiago , Andrade Sergio 
Published: May 2023

Effective cardio-circulatory adaptation is central to managing acute physiological challenges (e.g., posture change) as in chronic pathological processes (e.g., hypertension or heart failure) to continuously harmonize hemodynamics with cell needs. Acute responses such as sudden venous and capillary flow and pressure changes are believed to be linked to tissue-related intervenients (neuro-humoral, metabolic, endocrine) converging to a “local reflex” thought to protect capillary integrity in the absence of disease (the veno-arteriolar reflex VAR). Similar observations were produced in healthy individuals with increasing pressure using an inflated cuff applied in one limb – the post-occlusive reactive hyperemia (POHR). Our group has been involved in the quest to identify players and mechanisms in acute adaptive circulatory responses to in vivo perfusion changes. Recently we studied microcirculatory responses to hyperemia (produced by massage and by occlusion) and to a standard VAR maneuver. Protocols were independently applied to each participant to ensure full hemodynamicalrecovery. Sixty-six healthy participants of both sexes (mean age 31,3 + 3,6 years old) were selected. Distal perfusion was measured in both feet by laser Doppler flowmetry following massage and VAR (n=56). The PORH in one (randomly chosen) brachial artery was followed by optoacoustic tomography (OAT) in the ventral forearm (n=10).Reactive hyperaemia has been referred to be governed by local endothelial vasodilators sensory nerves and myogenic activities, while VAR is regarded as a regional reflex resulting from local interactions between myogenic fibers and non-adrenergic vasoconstrictive neurons. Massage and PORH are very different stressors (in intensity, duration, and extension) but both produced a significant perfusion increase in both limbs detected by LDF. VAR consistently evoked an opposite perfusion decrease in both limbs. Our results clearly indicate that these responses are not local. With the cuff applied to the arm, OAT functional imaging analysis of the PORH response in the ventral forearm revealed a sequential movement of blood from the skin superficial plexus to the deeper vascular structures with occlusion and returning with cuff deflation that confirms a centrally mediated response. An equivalent circuit is present with VAR with reverse effect. This response, which we named the Prompt Adaptive Hemodynamical Response (PAHR), appears to be independent of sex or age. No matter the involved receptors, different intensity spinal-supraspinal inflow produce proportional somatic and autonomous outflow, which also suggests that PAHR might be used as an endpoint with clinical relevance to characterize in vivo vascular function. This research is funded by Fundação Ciência Tecnologia (FCT) by grant UIDB/04567/2020. J Gregório is supported by FCT by the SES contract CEEC/CBIOS/EPH/2018. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.