Cardiovascular Regulation during Water Immersion.

Abstract

Abstract. Head-out water immersion at thermoneutral temperature (34-35 C) increases cardiac output for a given O2 consumption, leading to a relative hyperperfusion of peripheral tissues. To determine if subjects immersed in water at a colder temperature show similar responses and to explore the significance of the hyperperfusion, cardiovascular functions were investigated (impedance cardiography) on 10 men at rest and while performing exercise on a leg cycle ergometer (DM = ~95 W·m -2 ) in air and in water at 34.5 C and 30 C, respectively. In subjects resting in water, the cardiac output increased by ~50% compared to that in air, mainly due to a rise in stroke volume. The stroke volume change tended to be greater in 30 C water than in 34.5 C water, and this was due to a greater increase in cardiac preload, as indicated by a significantly greater left ventricular end-diastolic volume. Arterial systolic pressure rose slightly during water immersion. Arterial diastolic pressure remained unchanged in 34.5 C water, but it rose in 30 C water. The total peripheral resistance fell 37% in 34.5 C water and 32% in 30 C water. Both in air and in water, mild exercise increased the cardiac output, and this was mainly due to an increase in heart rate. Since, however, the stroke volume increased with water immersion, cardiac output at a given work load appeared to be significantly higher in water than in air. The arterial pressures did not decrease with water immersion, despite a marked reduction in total peripheral resistance. These results suggest that 1) during cold water immersion, peripheral vasoconstriction provides an additional increase in cardiac preload, leading to a further increase in the stroke volume compared to that of the thermoneutral water immersion, 2) the mechanism of cardiovascular adjustment during dynamic exercise is not changed by the persistent increase in cardiac preload in water immersion, and 3) a relatively high cardiac output during water immersion is to maintain a proper arterial pressure in the face of reduced vascular resistance.(Appl Human Sci,

Postexercise cooling interventions and the effects on exercise-induced heat stress in a temperate environment

“…Hornery et al (2005) also observed a trend towards lower _ VO 2 and HR values following V during a constant cycling exercise at 75% _ VO 2max in a similar environment (21°C vs. 20°C in the present study). Lower relative changes in exercise-induced responses, i.e., Ex1 to Ex2 for submaximal HR and _ VO 2 values after V exposition, may suggest a cold-related peripheral vasoconstriction and a greater central blood volume; often reported to enhance O 2 perfusion to active muscles, removal of waste substances, and assist exercise tolerance (Hessemer et al 1984;Hornery et al 2005;Park et al 1999;Vaile et al 2008). However, the sudden and greater change in T skin when entering water probably caused more severe vasoconstriction than V, along with potential increases in catecholamine release (Kozyreva et al 1999) and BP (Janský et al 1996).…”

“…Interestingly, in addition to convective heat loss, the effect of hydrostatic pressure during water immersion techniques may be an important aspect of the effectiveness of water immersion interventions (Park et al 1999). The pressure applied to the body during water immersion may cause displacement of fluids from the extremities, thus increasing the central blood volume, and leading to an increased stroke volume during immersion (Bonde-Petersen et al 1992;Gabrielsen et al 2002;Stocks et al 2004).…”

“…The pressure applied to the body during water immersion may cause displacement of fluids from the extremities, thus increasing the central blood volume, and leading to an increased stroke volume during immersion (Bonde-Petersen et al 1992;Gabrielsen et al 2002;Stocks et al 2004). As an example, HR has been shown to decrease by 15% in water at 30°C (Park et al 1999). It is proposed that hemodynamic changes are mediated through increased venous return to the thorax because of the hydrostatic pressure gradient (Ernst 1986).…”

VO2 Kinetics during Different Forms of Cycling Exercise on Land and in Water

“…ANP acts as a vasodilator via endothelial cells and promotes baroreflex-mediated activation. The pronounced sympatholytic effect of ANP leads to a reduced vasoconstriction in W compared to L. 17 The sympathicolysis corresponds well with lowered plasma noradrenalin concentrations. 33,34 Furthermore, larger ANP blood concentrations constrain the RAA-system by reducing the release of renine and aldosterone.…”

“…The physical properties of water change hemodynamic and metabolic responses: stroke volume increases by 30-50% and cardiac output at a given work load also increases about 25% through the Frank Starling mechanism. 15,16 From increased cardiac output as a result of increased cardiac filling pressure and lowered total peripheral resistance 17 it can be assumed that O 2 extraction in working muscles is more efficient in W than on L. However at present the effect is discussed controversial. Blood flow to oxidative muscles can also be affected if muscle pump generates a greater pressure gradient across the capillary bed and increases blood flow.…”