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

2. 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

3. 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

4. Hematocrit

5. 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

6. 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

7. 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

8. Changes in Cardiovascular Variables During Exercise

9. 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

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

11. Changes in Muscle and Splanchnic Blood Flow During Exercise

12. Redistribution of Blood Flow During Exercise

13. HR, SV, and CO During Prolonged Exercise

14. 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) .

15. Heat Exchange Mechanisms during Exercise

16. 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

20. Changes in Heat Production and Loss during Exercise

21. 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

22. 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

23. 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

24. Exercise in Hot/Humid vs. Cool Environment

25. 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

26. 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

27. 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

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

29. 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