Whole body passive heating versus dynamic lower body exercise: A comparison of peripheral hemodynamic profiles

Passive heating has emerged as a therapeutic intervention for the treatment and prevention of cardiovascular disease. Like exercise, heating increases peripheral artery blood flow and shear rate, which is thought to be a primary mechanism underpinning endothelium-mediated vascular adaptation. However, few studies have compared the increase in arterial blood flow and shear rate between dynamic exercise and passive heating. In a fixed crossover design study, 15 moderately trained healthy participants (25.6 ± 3.4 yr) (5 female) underwent 30 min of whole body passive heating (42°C bath), followed on a separate day by 30 min of semi-recumbent stepping exercise performed at two workloads corresponding to the increase in cardiac output (Qc) (D3.72 L min-1) and heart rate (HR) (D40 beats/min) recorded at the end of passive heating. At the same Qc (D3.72 L min-1 vs. 3.78 L min-1), femoral artery blood flow (1,599 mL/min vs. 1,947 mL/min) (P = 0.596) and shear rate (162 s-1 vs. 192 s-1) (P = 0.471) measured by ultrasonography were similar between passive heating and stepping exercise. However, for the same HRMATCHED intensity, femoral blood flow (1,599 mL min-1 vs. 2,588 mL min-1) and shear rate (161 s-1 vs. 271 s-1) were significantly greater during exercise, compared with heating (both P = <0.001). The results indicate that, for moderately trained individuals, passive heating increases common femoral artery blood flow and shear rate similar to low-intensity continuous dynamic exercise (29% V O2max); however, exercise performed at a higher intensity (53% V O2max) results in significantly larger shear rates toward the active skeletal muscle.