{Reference Type}: Journal Article
{Title}: Heated environment increases blood pressure drop and postural sway during initial orthostasis in healthy subjects.
{Author}: Ferreira FC;Padilha MCSV;Araujo-Leite MA;da Silva Soares PP;Rodrigues GD;
{Journal}: Eur J Appl Physiol
{Volume}: 0
{Issue}: 0
{Year}: 2024 Jun 27
{Factor}: 3.346
{DOI}: 10.1007/s00421-024-05546-8
{Abstract}: <B>OBJECTIVE: </B>We tested the hypothesis that heat stress influences the closed-loop cardio-postural control by an increased blood pressure (BP) drop and postural sway.<BR><B>METHODS: </B>Fourteen healthy individuals (eight women) performed two orthostatic tests under thermal reference (TC; ~ 24 ºC) and HOT (~ 38 ºC) conditions. The center-of-pressure (COP) displacements and the electromyography (EMG) activity of the calf muscles (medial gastrocnemius and tibialis anterior) were recorded during the initial orthostasis (ORT onset) after the supine-to-stand challenge. At the same period, BP (beat-to-beat) was continuously monitored, and supine-to-stand variations (∆%) were calculated. Sublingual temperature (Tsl) was measured as a surrogate of internal temperature.<BR><B>RESULTS: </B>Tsl increased in HOT compared to TC (TC 36.5 ± 0.3 vs. HOT 36.7 ± 0.3 ºC; p < 0.01). COP distance was greater in HOT compared to TC condition (TC 596.6 ± 242.4 vs. HOT 680.2 ± 249.1 mm; p < 0.01). EMG activity of the gastrocnemius decreased in HOT compared to TC condition (TC 95.5 ± 19.8 vs. HOT 78.4 ± 22.8%mV; p = 0.02). EMG of tibialis did not change between TC and HOT (TC 83.5 ± 42.9 vs. HOT 66.1 ± 31.9% mV; p = 0.29). BP showed a greater fall in HOT compared to TC condition (∆%TC - 24.5 ± 13.2 vs. ∆%HOT - 33.2 ± 20.2%; p = 0.01).<BR><B>CONCLUSIONS: </B>Heat stress causes a greater fall in blood pressure and a reduction in musculoskeletal pump activity during orthostatic onset. These effects could be potential mechanisms that underlie augmented postural instability under a heated environment.