Reallocation of cutaneous and global blood circulation during sauna bathing through a closed-loop model

Time-continuous analysis of muscle and cerebral oxygenation during repeated treadmill sprints under heat stress: a statistical parametric mapping study

PURPOSE

We examined how heat exposure affects muscle and cerebral oxygenation kinetics using statistical parametric mapping (SPM) during repeated treadmill sprints.

METHODS

Eleven recreationally active males performed three sets of five 5-s sprints with 25 s of recovery and 3 min between sets in hot (38 °C) and temperate (25 °C) conditions. Continuous measurements of muscle (vastus lateralis) and cerebral (prefrontal cortex) tissue oxygenation were obtained using near-infrared spectroscopy. One-way ANOVA SPM{F} statistics were applied to pooled sprint data, with each condition including 15 time-series (three sets of five sprints) combined. Each time-series included the sprint and subsequent recovery phases.

RESULTS

Muscle tissue saturation index further decreased in hot compared to temperate condition, from the middle of the 5-s sprint phase (~ 2.9 s) until the end of the recovery period (p < 0.001), while total hemoglobin concentration was significantly higher in the early phase of recovery (from 5.1 to 11.8 s, p = 0.003). Cerebral tissue saturation index decreased from 0.7 s to 13.0 s (p < 0.001) in the heat. Total hemoglobin concentration was lower in hot condition during both the sprint phase and the initial third of the recovery (from 0 to 11.7 s, p < 0.001), as well as during the recovery (from 20.5 to 24.8 s, p = 0.007).

CONCLUSION

Adding heat stress to repeating treadmill sprints further lowered muscle oxygenation levels during both the sprint and recovery phases, and limited cerebral tissue perfusion during the sprint and the initial recovery phases. The use of SPM for continuous analysis of near-infrared spectroscopy data provides new insights beyond summary statistics.

Remodeling of the cardiovascular hemodynamic environment by lower limb heat exposure: A computational fluid dynamic study

BACKGROUND

Lower limb heat exposure (LLHE) is a promising strategy for the daily management of cardiovascular health because of its non-pharmaceutical advantages. To support the application of this strategy in cardiovascular protection, we examined its impact on the global hemodynamic environment.

METHODS

Skin blood flow (SBF) of eight locations on the lower limbs was measured before and after LLHE (40 °C and 44 °C) in ten healthy subjects by using a laser Doppler flowmeter. A closed-loop model of circulation uses changes in SBF to quantify the influence of LLHE on the blood flow of the arterial trunk (from ascending aorta to the femoral artery) and visceral branches (coronary, celiac, renal, and mesenteric arteries).

RESULTS

The SBF in all locations tested on the lower limbs increased significantly (p<0.001) with LLHE and a 3.39-fold and 7.40-fold increase in mean SBF were observed under 40 °C and 44 °C conditions, respectively. In the model, the peak (3.9-25.1%), end-diastolic (13.7-107.3%), and mean blood flow (8.5-86.5%) in the arterial trunk increased with the increase in temperature, but the retrograde flow in the thoracic aorta and abdominal aorta Ⅰ increased at least twice in the diastolic period. Furthermore, LLHE also increased the blood flow of the visceral branches (2.5-20.7%).

CONCLUSION

These findings suggest that LLHE is expected to be a daily strategy for enhancing the functions of both the arterial trunk and visceral arteries, but the increased blood flow reversal in the thoracic and abdominal aortas warrants further investigation.