Echocardiographic changes following active heat acclimation. (October 2020)

• Record Type: Journal Article
• Authors: Parsons, Iain T.; Snape, Daniel; O'Hara, John; Holdsworth, David A.; Stacey, Michael J.; Gall, Nick; Chowienczyk, Phil; Wainwright, Barney; Woods, David R.
• Is Part Of: Journal of thermal biology. Volume 93(2020)
• Publication Date: 2020-10
• Subjects: Heat adaptation -- Heat acclimation -- Plasma volume -- Stroke volume -- Diastolic function -- Echocardiography -- Preload; Thermobiology -- Periodicals; Temperature -- Periodicals; Biology -- Periodicals; Thermobiologie -- Périodiques; Thermobiology; Periodicals; 571.46
• DOI: 10.1016/j.jtherbio.2020.102705
• Languages: English
• ISSNs: 0306-4565

Abstract

Abstract: Heat adaption through acclimatisation or acclimation improves cardiovascular stability by maintaining cardiac output due to compensatory increases in stroke volume. The main aim of this study was to assess whether 2D transthoracic echocardiography (TTE) could be used to confirm differences in resting echocardiographic parameters, before and after active heat acclimation (HA). Thirteen male endurance trained cyclists underwent a resting blinded TTE before and after randomisation to either 5 consecutive daily exertional heat exposures of controlled hyperthermia at 32 °C with 70% relative humidity (RH) (HOT) or 5-days of exercise in temperate (21 °C with 36% RH) environmental conditions (TEMP). Measures of HA included heart rate, gastrointestinal temperature, skin temperature, sweat loss, total non-urinary fluid loss (TNUFL), plasma volume and participant's ratings of perceived exertion (RPE). Following HA, the HOT group demonstrated increased sweat loss (p = 0.01) and TNUFL (p = 0.01) in comparison to the TEMP group with a significantly decreased RPE (p = 0.01). On TTE, post exposure, there was a significant comparative increase in the HOT group in left ventricular end diastolic volume (p = 0.029), SV (p = 0.009), left atrial volume (p = 0.005), inferior vena cava diameter (p = 0.041), and a significant difference in mean peak diastolic mitral annular velocity (e') (p = 0.044). Cardiovascular adaptations to HA appear to be predominantly mediated by improvements in increased preload and ventricular compliance. TTE is a useful tool to demonstrate and quantify cardiac HA. Highlights: There are echocardiographic differences in comparing an isothermic heat acclimation regime to equivalent temperate exercise. Heat acclimation results in an increased LA volume, LVEDV, stroke volume, IVC diameter and LV diastolic function (e'). The increase in LA volume and IVC diameter would suggest an increase in preload secondary to increased plasma volume. The rise in the speed of early LV relaxation (e') during diastole reflects increased LV compliance or reduced LV stiffness. This gives further insight into the cardiovascular adaptations to heat acclimation.