Hemodynamic and Vascular Effects of Different Durations of Lower-Leg Hot-Water Immersion

A footbath may be an accessible form of passive heat therapy (PHT) to improve cardiovascular health. As a localized PHT stimulus, it is unclear if longer durations are superior for promoting adaptive hemodynamic and vascular adjustments. Fourteen older adults (7 female; mean±SD; age:68±6 years) performed 30, 45 and 60-min lower-leg hot-water (42°C) immersions as well as a 60-min thermoneutral (36°C) sham immersion on four separate days. Superficial femoral artery blood flow and flow-mediated dilation (FMD) were assessed pre- and post-immersion, and the time course of recovery was characterized over the 60-min following immersion. Twenty-four-hour ambulatory blood pressure was monitored over each experimental day. Femoral artery blood flow increased following immersion in all PHT conditions (mean of all PHT conditions: +345±211%; P<0.001) but was unchanged in sham. The 30 and 45-min PHT conditions sustained a higher leg blood flow than sham for the full hour following immersion (all post-hoc comparisons: P<0.01) while the 60-min condition was not different from sham by 30 minutes into recovery. FMD was greater following 45-min PHT than sham over the hour of recovery (mean of recovery timepoints: 2.5±0.9% FMD vs. 1.7±1.0%; P=0.002). Twenty-four-hour mean arterial pressure was lower with 45-min and 60-min PHT compared to sham (both -4±4mmHg; P<0.05). A 45-min footbath results in comparable hemodynamic adjustments as 60 minutes of immersion and led to the largest acute improvement in vascular function. As such, a 45-min footbath may be the preferred dose of PHT to use in future interventions seeking to improve vascular health and blood pressure.