Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA340

Poster Communications

Isometric flexor muscle activity alters microcirculatory perfusion in the human lower limb

M. M. Florindo1,3, H. Silva1,2, S. Nuno1, L. Monteiro Rodrigues1,2

1. CBiOS (Research Center for Biosciences and Health Technologies), U Lusófona, School of Health Sc & Technologies, Lisboa, Portugal. 2. Pharmacol. Sciences Departm., U Lisboa, Faculty of Pharmacy, Lisboa, Portugal. 3. Portuguese Red Cross Health School, Avenida de Ceuta, Edifício Urbiceuta, 1300-125 Lisboa, Portugal, Lisboa, Portugal.

The ‘muscle pump' is a known determinant of vascular physiology, particularly in regard to venous return. Only a few studies to date have addressed the impact of the muscle pump on microcirculation. Our objective was to compare the effect of the isometric activity of two antagonistic muscle groups (plantar flexors and dorsal flexors) on the lower limb microcirculation. Six healthy volunteers (31 ± 9 years old) both genres (three female and three male) were selected after informed written consent. All procedures complied with the Helsinki Declaration and subsequent amendments. Two sequential postural changes in the standing position were requested, plantar flexion (PF) and dorsal flexion (DF), with a 10 minutes washout period in between, each consisting of three phases - 5 minutes baseline (Phase 1), 1 minute isometric muscle activity (Phase 2) and 5 minutes recovery at the initial position (Phase 3). Blood perfusion was assessed in both feet in the medial arch by photoplethysmography (PPG) and laser Doppler flowmetry (LDF). Pulse rate (PR) was also obtained from the PPG signal. Descriptive and comparative statistics were applied (p<0.05). PPG and LDF registered opposite perfusion responses during Phase 2 of both protocols. The LDF signal increased significantly (p=0.028 for both DF and PF), while PPG showed a significant decrease (p=0.028 for DF and p=0.027 for PF) for the same movements. PR did not change significantly in any of the posture changes. Additionally, the PPG signal was significantly higher in PF (p=0.002) during Phase 2 but no differences could be observed with LDF and PR. These opposite responses obtained with LDF and PPG, which share the same optical principle, suggest that they detect different perfusion phenomena, likely because they operate at different depths. Therefore, the selection of the appropriate technology for these purposes is a critical experimental issue. Our results also suggest that, in the present experimental conditions, both PF and DF impact microvascular perfusion, pointing to the role of muscular activity in local vascular regulation during motion.

Where applicable, experiments conform with Society ethical requirements