Cardiac Output Q = HR x SV Q = cardiac output HR = heart rate SV = stroke volume

Regulation of Stroke Volume end diastolic volume (EDV) - volume of blood in ventricles at the end of diastole Frank-Starling Law increase in contractility increases volume pumped per beat venous return average aortic blood pressure strength of ventricular contraction

Components of Blood Plasma Cells Hematocrit Liquid portion of blood Contains ions, proteins, hormones Cells Red blood cells Contain hemoglobin to carry oxygen White blood cells Platelets Important in blood clotting Hematocrit Percent of blood composed of cells

Hematocrit

the blood is composed primarily of water (~55 %) called plasma hematocrit is the percentage of whole blood which is composed of solid material cells, platelets etc the blood is composed primarily of water (~55 %) called plasma the hematocrit would be 45 can vary between 40 and 50

Cardiac Output during Exercise Q increases in direct proportion to the metabolic rate required to perform task linear relationship between Q and VO2 remember... Q = HR x SV

Stroke Volume and Heart Rate during Exercise in untrained or moderately trained individuals stroke volume plateaus ~ 40% VO2 max at work rates > 40% VO2 max, Q increases by HR alone See fig 9.17

Changes in Cardiovascular Variables During Exercise

The Fick Equation VO2 = Q x (a-vO2 diff) VO2 is equal to the product of cardiac output and arterial-mixed venous difference an increase in either Q or a-vO2 difference will result in an increase in VO2max

Redistribution of Blood Flow Increased blood flow to working skeletal muscle Reduced blood flow to less active organs Liver, kidneys, GI tract

Changes in Muscle and Splanchnic Blood Flow During Exercise

Redistribution of Blood Flow During Exercise

HR, SV, and CO During Prolonged Exercise

Prolonged Exercise Cardiac output is maintained Cardiovascular drift Gradual decrease in stroke volume Gradual increase in heart rate Cardiovascular drift Due to dehydration and increased skin blood flow (rising body temperature) .

Heat Exchange Mechanisms during Exercise

Increases in Temperature Receptors on skin first sense changes receptors also located in spinal cord and hypothalamus respond to core temp changes Stimulates sweat glands - increases evaporation Increases skin blood flow - vasodilation

Changes in Heat Production and Loss during Exercise

Take Home Message During exercise, evaporation is the most important method of heat loss Heat production must be matched with heat dissipation or hyperthermia will ensue

Metabolic heat production increases in proportion to the exercise intensity Convective and radiative heat loss do not increase with intensity as temp gradient between body and environment does not change significantly

Hyperthermia Increased core temperature to the point that physiological functions are impaired Contributing factors dehydration electrolyte loss failure of cooling mechanisms to match heat production

Exercise in Hot/Humid vs. Cool Environment

Other factors related to hydration Water as a solvent Ionic concentration Neuro-muscular coordination Contractile function Reactions Macronutrient formation Glycogen Proper digestion and waste removal

Amount of fluids ingested Small amounts of fluid ingestion do not entirely attenuate Elevation in core temperature Elevation in heart rate Rating of perceived exertion

Moderate and Large fluid intake resulted in significantly different responses than No or Small fluid intake Small = 300 ml/hr Moderate=700 ml/hr Large=1200 ml/hr From Coyle SSE #50 GSSI

Effects of dehydration on cardiovascular parameters versus % body weight loss From Coyle SSE #50 GSSI

Recommendations Drink as much as can be tolerated up to 1250 ml/h for 68 kg/150 lb individual Drink should contain 4-8 % CHO to optimize absorption Adjust volume per body weight as ratio of 68 kg E.g. 50 kg> 50/68 * 1250 = 925 ml/hr