Effects of Passive Heating on Perfusive and Diffusive Microvascular Oxygen Delivery

Abstract

Previous studies have demonstrated that passive heating has led to increases in endothelial function and vasodilation of the brachial artery. The increase in vasodilation is thought to originate from increased nitric oxide bioavailability, thus increasing blood flow into the limb. However, the different aspects of the downstream microvascular oxygen delivery (i.e. perfusive and diffusive) to the exercising muscle have yet to be described. PURPOSE: The purpose of this study was to determine the effect of seven days of passive heating on oxygen delivery during handgrip exercise. We tested the hypothesis that, 7 days of passive heating would result in a decrease in the diffusive oxygen delivery (total-[heme]) and an increase in the perfusive oxygen delivery (deoxy-[heme]) in the exercising muscle. METHODS: Three participants (2 women, 23.0 ± 1.0 yrs, 70.9 ± 15.7 kg, 171 ± 10.1 cm) participated in this study. Peak power was determined by an incremental two-hand handgrip exercise test. Subjects performed 10 minutes of dynamic handgrip exercise at 40% peak power pre and post 7 days of passive heating. Absolute concentrations of deoxy-[heme] and total-[heme] of the flexor digitorum superficialis muscle were measured continuously via frequency-domain multi-distance near-infrared spectroscopy (OxiplexTS, ISS). The passive heating protocol consisted of immersion up to the shoulder in a 40°C hot tub until rectal temperature reached 38.5°C or increased by 1°C for 60 minutes. Data reported as mean ± SE. RESULTS: From baseline to the last 30 seconds of exercise there was no significant difference in the ∆ deoxy-[heme] (perfusive oxygen delivery) for pre (52.3 ± 2.2 μM) and post passive heating (47.6 ± 16.4 μM; p=0.822). However, the ∆ total-[heme] (diffusive oxygen delivery) was significantly lower following passive heating (p<0.001). Pre and post passive heating ∆ total-[heme] was 75.1 ± 13.8 μM and 30.7 ± 13.3 μM, respectively. CONCLUSION: The significant decrease in∆ total-[heme] after passive heating suggests that the diffusion of oxygen into the exercising muscle was reduced. This finding, along with no change in the perfusive oxygen delivery as represented by the ∆ deoxy-[heme], suggests that the oxygen uptake of the exercising muscle was decreased.