Post-Exercise Hyperemic Response Adds to Muscle Microvascular Flow Changes during Lower Body Pressure

Abstract

Exercise increases muscle microvascular flow via vasodilation from both endothelial dependent and independent mechanisms. Altered transmural pressure also affects blood flow in muscle. For example, lower body negative pressure decreases and lower body positive pressure increases blood flow. PURPOSE: To determine muscle microvascular blood flow (MBF) during post-exercise hyperemia at negative and positive lower body pressure (LBP). It was hypothesized that the post-exercise hyperemic response would not be present at increased levels of positive LBP. METHODS: Eight healthy subjects (6 male, 2 female; ages 21–41) were placed supine in a LBP chamber that was sealed at the waist. Photoplethysmography was used to noninvasively measure MBF of the tibialis anterior muscle and skin microvascular blood flow (SBF) of overlying skin during exposure to a series of LBP levels (−30, −20, −10, 0, 10, 20, 30mmHg) with and without dorsiflexion exercise. At each pressure level MBF was allowed to stabilize for one minute prior to a one minute baseline data collection. Subjects then performed a one minute isometric dorsiflexion at a resistance of 41N and MBF was recorded for one minute following dorsiflexion. Subjects were given a 5 minute rest period between pressure levels to ensure MBF return to baseline. All microvascular flow data were normalized to the control value obtained at ambient pressure without exercise and presented as percentages (mean±SE) to compare between conditions. Data were analyzed using two-way repeated measures ANOVA to determine exercise effect and pressure effect on MBF. RESULTS: MBF and SBF increased at all LBP levels with exercise compared to no exercise (p=0.001 and p=0.005). MBF significantly decreased with negative pressure and increased with positive pressure (p=0.003 and p<0.001). The lowest MBF was at −30mmHg (52±9% w/o exercise, 61±9% w/ exercise) and the highest was at 10mmHg (137±15% w/o exercise, 145±12% w/ exercise). CONCLUSION: Post exercise hyperemia occurs at all lower body pressure levels studied. Elevation of microvascular flow after isometric exercise adds to changes measured at different levels of LBP. Regimens for exercise training and post-injury rehabilitation may benefit from exercise at low levels of positive LBP. Supported by NIH Training Grant 2 T32AR07484-22 to GCM.