Whole‐body heat stress and exercise stimulate the appearance of platelet microvesicles in plasma with limited influence of vascular shear stress

Figure 1. Effect of passive heat stress with single‐leg cooling and dynamic knee extensor exercise with the cooled and heated leg on arterial and venous plasma platelet microvesicle (PMV) concentrations and in femoral artery mean shear rate. [PMV] increased systemically during heat stress with cooled leg knee extensor exercise, and remained elevated thereafter in all sampling sites. Mean vascular shear rate and estimated shear rate (gray bars) increased throughout the protocol in the heated leg femoral artery, whereas with less pronounced changes in the cooled leg. Data are mean ± SEM for five participants. *Significant difference from baseline (P < 0.05).

Figure 2. Effect of passive heat stress with single‐leg cooling and dynamic knee extensor exercise on arterial venous endothelial microvesicles (EMV) concentrations. Neither heat stress nor single‐leg knee extensor exercise affected the [EMV]. Data are mean ± SEM for five participants.

Figure 3. Effect of whole‐body heat stress and cycling under heat stress and thermoneutral conditions upon platelet microvesicle (PMV) and leg vascular shear rate. Arterial [PMV] increased with whole‐body heat stress and remained elevated during exercise, while venous PMVs only increased during cycling. Mean femoral artery shear rate was slightly elevated by passive heat stress, with large increases observed in estimates of vascular shear rate (gray bars) during exercise. Mean ± SEM for 6–7 participants. *Significant difference from baseline (P < 0.05).

Figure 4. Effect of whole‐body heat stress and cycling on endothelial microvesicle (EMV) concentration sampled at the radial artery and femoral vein before (A and B) and after (C and D) correction for changes in plasma volume. No increase in venous EMV content was observed with whole‐body heat stress combined with large muscle mass exercise when changes in plasma volume were taken into consideration. Mean ± SEM for seven participants. *Significant difference from baseline (P < 0.05).

Figure 5. Relationship between platelet microvesicle (PMV) concentrations and femoral artery shear rate in the Cycling Study (A and B), and Knee Extensor Study (C and D). Vascular shear rate was estimated during passive heat stress and cycling exercise from individual within‐subject multiple regressions (A) or calculated during passive heat stress with simultaneous cooling of one leg and during single‐limb knee extensor (KE) exercise (C). Group averages (B and D) are displayed for illustration purposes. Compared with the cycling study, a reduction in the PMV explained variance is observed when data from active and contralateral inactive limbs are analyzed.

Figure 6. Representation of PMV and shear rate fold change in both experiments. The dotted line represents where the data should fall if there were a close relationship between shear rate and circulating PMV concentrations across a wide range (line slope 10:1).