The Venoarteriolar Reflex Significantly Reduces Contralateral Perfusion as Part of the Lower Limb Circulatory Homeostasis in vivo

Abstract

Perfusion at microvascular level involves the contribution of both local and central regulators, under a complex vascular signaling frame. The venoarteriolar reflex (VAR) is one of such regulatory responses, of particular relevance in the lower limb to prevent edema. Although known for quite some time, many of the complex interactions involving all of these regulatory mechanisms still need clarification. Our objective was to look deeper into VAR through modern photoplethymography (PPG). Twelve healthy subjects (both sexes, 26.0 ± 5.0 y.o.) were enrolled in this study after informed written consent. Subjects were submitted to a leg lowering maneuver while lying supine to evoke the VAR, involving three phases–10 min baseline register, both legs extended, 10 min challenge, with one randomly chosen leg (test) pending 50 cm below heart level, while the contralateral (control) remained in place, and 10 minutes recovery, resuming the initial position. PPG signals were collected from both feet and treated by the wavelet transform (WT) revealing six spectral bands in frequency intervals comprising the cardiac [1.6–0.7 Hz], respiratory [0.4–0.26 Hz], myogenic [0.26–0.1 Hz], neurogenic/sympathetic [0.1–0.045 Hz], endothelial NO-dependent (NOd) [0.045–0.015 Hz], and NO-independent (NOi) [0.015–0.007 Hz] activities. For the first time, this approach revealed that, with VAR, perfusion significantly decreased in both limbs, although the change was more pronounced in the test foot. Here, a significant decrease in myogenic, neurogenic and NOd, were noted, while the control foot recorded a decrease in neurogenic and an increase in NOd. These results confirm the utility of WT spectral analysis for flowmotion. Further, it strongly suggests that VAR results from a complex cooperation between local myogenic-endothelial responses, where a central neurogenic reflex might also be involved.

Texture Analysis is a Useful Tool to Assess the Complexity Profile of Microcirculatory Blood Flow

“…As previously published, during the postural challenge, perfusion decreased significantly on both the test and control feet [4]. The mean and standard deviation (SD) of the entropy parameter (CI) calculated with MSE is presented in Table 1.…”

“…Their coordination is highly complex, depending on the continuous feedback and cross-talk between effector organs and controlling systems [1]. The heart pump and respiration are the most notorious "central" processes governing the performance of the cardiovascular system, while on a more "peripheral" level, the phenomena that control vascular tone, such as the myogenic activity of the vessel wall, the sympathetic activity and the endothelial release of vasoactive substances, play crucial roles [2][3][4]. Microcirculation signals are composed of both these central and peripheral components and therefore provide an "integrated" view of cardiovascular function [4,5].…”

“…Although currently underexplored in vascular physiology, the complexity assessment of microcirculation signals, both raw and decomposed, may deepen our knowledge of the mechanisms underlying perfusion regulation. Microcirculation signals are easily decomposed into their frequency components by the wavelet transform (WT) [4]. One of the WT main outputs is a scalogram, i.e., a multi-patterned image representation of the time evolution of all components of the decomposed signal.…”

Exploring the perfusion modifications occurring with massage in the human lower limbs by non-contact polarized spectroscopy

“…An identical phenomenom was referred some years ago in human patients as part of a long-term vascular adaptation to ischemia due to peripheral arterial occlusive disease 13 . More recently, we also detected that the postural vasoconstriction in the human foot obtained with the so-called venoarterial reflex (VAR) also significantly reduced the perfusion in the contralateral foot 14 . In both cases this cooperation seems to reveal other intervenients in the distal limb cir-Introdução A natureza complexa da regulação da circulação periférica é conhecida há muito tempo e ainda assim continua a ser um assunto em aberto 1,2 .…”

“…The experimental design involved two protocols -I, an upward massage (upM) applied during 5 minutes on the ascending direction in one randomly selected leg and foot, from the middle of the foot until below the knee, and a second protocol, II, involving an identical procedure in a downward massage (dwM), that is, in the opposite direction. Both protocols involved three phases, Phase I, with perfusion recording in rest, in supine, for 5 minutes; Phase II with leg and foot massage for 5 minutes and, Phase III, recording for 5 minutes during bém foi detetado que a vasoconstrição postural no pé humano obtida a partir do assim chamado reflexo venoarterial (RVA) também reduziu, significativamente, a perfusão no pé contralateral 14 . Em ambos os casos esta cooperação parece revelar outros intervenientes na homeostase circulatória na zona distal do membro, envolvendo provavelmente alguma comunicação entre os componentes centrais dos mecanismos neurogénicos e miogénicos locais, através de eferentes simpáticos.…”