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 years) (5 female) underwent 30 minutes of whole body passive heating (42 °C bath), followed on a separate day by 30 minutes of semi-recumbent stepping exercise performed at two workloads corresponding to the increase in cardiac output (Qc) (Δ3.72 l∙min-1) and heart rate (HR) (Δ38 bpm) recorded at the end of passive heating. Results: At the same Qc (Δ3.72 l∙min-1 vs 3.78 l∙min-1), femoral artery blood flow (1599 ml/min vs 1947 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 HR matched intensity, femoral blood flow (1599 ml·min-1 vs 2588 ml·min-1) and shear rate (161s-1 vs 271s-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% VO2max), however exercise performed at a higher intensity (53% VO2max) results in significantly larger shear rates towards the active skeletal muscle.