Plasma volume expansion as a primary adaptation to heat acclimation

Introduction

Heat acclimation, also known as acclimatization, affects the body’s physiological sensations and overall capacity to handle the heat. Heat acclimation is a general phrase that refers to a complicated series of changes or adjustments that happen in a contained way over 7 to 14 days concerning heat treatment. These changes help the body to manage heat stress and enable it to function in the heat (Vricella, 2017). Considering the deficits in the physiological role and physical activity that happen when body water supplies are insufficient to meet simultaneous demands, plasma volume expansion is one of many adaptive responses (Lorenzo, et al., 2010).

Following heat acclimation, Taylor (2011) argued that the earliest adaptations are highlighted by plasma volume expansion, which is supported by enhanced aldosterone production and tolerance, as well as intra-vascular albumin inflow. These coupled actions enhance sodium and chloride reabsorption in sweat glands and collecting ducts, decreasing sweat electrolyte percentage and boosting ionic fluid retention; with continuous heat stress, red cell size may also rise (Taylor, 2011). The rise in myocardial efficacy may help to enhance stroke volume, decrease heart rate at a constant work rate, and boost maximum cardiac output (Garrett, et al., 2014). Bass and Henschel  (1956) were the first to report the kinetics of changes in plasma volume in people who were sitting peacefully in the heat.  Hemodilution is relatively mild (less than 5% rise in plasma levels) and transitory. It goes away after around 30-45 minutes if there isn’t any fluid replenishment. It may not manifest in patients who have been exhausted before to heat exposure (Kenney, Craighead, & Alexander, 2014), or in individuals who have been anesthetized or who have had a vertebral artery dissection of the spinal cord underneath the area of the medulla (Kenney, Craighead, & Alexander, 2014). The transient gain in plasma volume gives a fluid reserve for sweat formation and controls the loss in central blood volume as sweating continues and blood flow is diverted from the core to the epidermis. Body temperature would rise more quickly without this immediate rise in plasma volume, and heat sensitivity would be diminished. The increase of plasma volume remains with proper water and electrolyte restoration, and it also aids in the reduction of cardiovascular stress during the early stages of heat adaptation (Patterson, Stocks & Taylor, 2014)…..