Impact of the isometric contraction of the calf on the local microcirculation

Abstract

The muscle pump activity is an important component of venous return. Muscle weakness in the lower limb can decrease the efficacy of the calf muscle pump and compromise adequate venous return. The aim of this study was to propose an experimental model to evaluate the impact of the calf muscular pump influence on peripheral microcirculation. We studied the local microvascular response to isometric calf contraction in the standing position. Six healthy subjects (31± 9 years old) participated in this study after giving informed consent. After standing for 5 minutes, subjects performed 1 minute of maintained isometric plantar flexion with both feet before resuming the original position for another 5 minutes. Local (foot) perfusion was evaluated with photoplethysmography (PPG) and laser Doppler flowmetry (LDF), pulse rate (PR) obtained from the PPG, and calf muscle activity was followed by electromyography (EMG). Nonparametric statistics were used for phase comparisons. During calf pump activity we observed significant differences of wave PPG and LDF amplitude with a rapid replacement after calf muscle contraction stopped. Pulse rate did not change during the three protocol phases. Thus, this proposed model appears suitable to further explore the role of the muscular pump activity on the peripheral microcirculation.

The march in place activity – a view from the local concentration of red blood cells (CRBC) in the human foot dorsum

“…In Phase 2 CRBC significantly decreased (p=0.016) when compared to Phase 1 ( Table 1). This result is in line with previous studies regarding the foot microcirculation using PPG, suggesting that the calf muscle activity in the standing position decreases the blood perfusion at the foot region [15]. Other studies indicate that this response is due to the venoarterial reflex (or oedema protection reflex) that reacts to the vasodilator response starting in the upright position [18].…”

“…Na fase 2, os CCVS diminuíram significativamente (p = 0,016) quando comparados à fase 1 (tabela 1). Este resultado está de acordo com estudos anteriores sobre a microcirculação do pé utilizando FPG, sugerindo que a atividade muscular da região posterior da perna na posição em pé, diminui a perfusão sanguínea na região do pé [15]. Outros estudos indicam que essa resposta é devida ao reflexo venoarterial (ou reflexo de proteção do edema) que reage à resposta vasodilatadora a partir da posição ereta [18].…”

“…PPG detects blood volume changes in the capillary bed, generating a pulsatile wave in cardiac synchrony, allowing the identification of the Pulse Rate (PR) and variations in the amount of local blood perfusion [14]. To minimize the occurrence of probe-tissue movement artefacts, a double-sided adhesive strip was used to hold the probe adhering to the skin [15]. The influence organização vascular muito particular.…”

“…A FPG é uma técnica simples e prática que apresenta uma onda pulsátil aparecendo em sincronia cardíaca, o que permite a identificação da frequência de pulso (FP) [14]. Para minimizar a ocorrência de artefactos de movimento do tecido cutâneo na sonda, uma fita adesiva de dupla face foi usada para manter a sonda bem aderente à pele [15]. A influência da luz ambiente no FPG foi mínima porque a sala esteve escura durante a recolha de dados.…”

Studying the human lower limb perfusion dynamics with the step in place model

“…Comparing the EMG values between Phases 1 and 3 we find that the muscle is still activated, suggesting same muscle activity in the recovery phase that can influence the microcirculation. The calf muscle, the gastrocnemius in particular, is important for the lower limb microcirculation homeostasis triggering a complex regulatory feedforward mechanism that changes local blood flow according with task [18][19][20]. Our results suggest that this simple task can induce a similar effect to walking, and for that it might be also interesting as a rehabilitation exercise.…”