The effect of repeated hot water immersion on vascular function, blood pressure and central haemodynamics in individuals with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterised by endothelial dysfunction, leading to increased risk of cardiovascular disease. Emerging evidence suggest that HWI may favourably improve vascular function but data are limited in individual with T2DM. The aim was to investigate whether repeated hot water immersion (HWI) improved macrovascular, microvascular and central haemodynamic function in individuals with T2DM. Fourteen individuals completed a pre-post experimental study where participants were assessed pre- and post-8-10 × 1 h HWI sessions (40 °C water) undertaken within a 14-day period. During HWIs, body position was adjusted to clamp rectal temperature at 38.5-39.0 °C for the duration of the immersion. Stroke volume index (SVi), cardiac index (Q˙ i), resting heart rate (HR), systolic blood pressure (SBP), diastolic BP (DBP), brachial flow-mediated dilation (FMD) and cutaneous microvascular endothelial function (via transdermal iontophoresis) and plasma [nitrate] and [nitrite] (NOX; via ozone chemiluminescence) were assessed pre- and post HWI. Neither brachial FMD measures of macrovascular endothelial function (p = 0.43) or forearm microvascular function (ACh max, p = 0.63; ACh area under curve (AUC), p = 0.63; insulin max, p = 0.51; insulin AUC, p = 0.86) or NOX (p = 0.38) were changed. Q˙ i (p < 0.01), SVi (p < 0.02) and resting HR (p < 0.01) were all significantly reduced following the 10-days HWI intervention. SBP was reduced (p = 0.03), whereas DBP was unchanged (p = 0.56). HWI may represent an appropriate intervention to improve Q˙ I, SVi and BP in individuals with T2DM, but not macrovascular endothelial or cutaneous microvascular function.