Myocardium – Cardiac Muscle Thickness varies directly with stress placed on chamber walls. With vigorous exercise, the left ventricle size increases.
Heart Function At rest, the heart spends most of its time filling (60% - diastole) than expelling (40% - systole) Following systole, the AV valves rapidly open and fill the ventricles up to 70-80% The middle 1/3 of diastole has little filling and is known as diastasis
Stroke Volume & Cardiac Output Stroke Volume (SV) End-systolic volume (ESV)—volume of blood in ventricle after contraction SV = EDV – ESV Volume of blood pumped per contraction Cardiac Output (Q). Q = HR SV Varies considerably between people Trained athletes have lower resting HR and higher SV (Table 4.1).
Ejection Fraction Proportion of blood pumped out of the left ventricle each beat Averages 60% at rest
Vascular System Arteries Arterioles Capillaries Creates a large surface area ideal for gas exchange Venules Veins Blood Flow controlled by the autonomic nervous system During REST During EXERCISE
Muscle Pump Blood distribution matched to overall metabolic demands Autoregulation— Extrinsic neural control— sympathetic nerves within walls of vessels are stimulated causing vessels to constrict
Blood Pressure Systolic blood pressure (SBP: s=squeeze) is the highest pressure and diastolic blood pressure (DBP) is the lowest pressure MAP = DBP + [0.333 (SBP – DBP)]
Review Blood returns to the heart with the help of breathing, the muscle pump, and valves in the veins. Vascular System Autoregulation controls blood flow by vasodilation in response to local chemical changes in an area. (continued)
Review (continued) Extrinsic neural factors control blood flow primarily by vasoconstriction. Mean arterial pressure (MAP) is the average pressure on the arterial walls.
Blood Functions Transports gas, nutrients, and wastes Buffers and balances acid base
Blood Formed Elements & Hematocrit Blood formed elements White blood cells—protect body from disease organisms Red blood cells—carry oxygen to tissues with the help of hemoglobin Hematocrit Ratio of formed elements to the total blood volume
Oxygen Transport Oxygen transported in blood combined to hemoglobin (98%) or dissolved in plasma (2%) Oxygen saturation affected by: 1.) 2.) 3.)
Erythropoietin (EPO) Protein hormone produced by kidney Medically used to treat anemia (chronic kidney failure) Increase oxygen carrying capacity of blood “Sludging” of blood VERY dangerous
Cardiovascular Response to Acute Exercise All result in allowing the body to efficiently meet the increased demands placed on it. Heart rate (HR) increases as exercise intensity increases up to maximal heart rate.. Increases in HR and SV during exercise cause cardiac output (Q) to increase..
Heart Rate During Exercise Initial increase b/c of withdrawal of parasympathetic input Feedback from peripheral mechanical and chemical receptors
Stroke Volume During Exercise Stroke volume changes are because of an increase in EDV Suctioning Mechanism: Frank-Starling Mechanism : with a greater volume of blood returning to the heart the ventricles become stretched and respond with a more powerful contraction
Cardiac Drift Increase in HR and decrease in SV Reason: greater % of blood flowing to skin to dissipate heat lower EDV causes an increased HR
Arteriovenous Oxygen Difference Rest 25% of O 2 extracted from blood Exercise up to 75% of O 2 extracted from blood (used by exercising muscles) Fick Equation:
Cardiovascular Response to Training Cardiac Output Heart Rate Cardiac Morphology Table 4.2 (p. 52)
Cardiac Output VO 2 max increases due to 1.) Improved oxygen extraction 2.) Increased cardiac output 3.) Max HR NOT affected from training
Stroke Volume Endurance-trained athletes have 60% greater SV Enlarged left ventricular chamber (eccentric hypertrophy)
Blood Pressure In hypertensive individuals, endurance exercise reduces both systolic and diastolic blood pressure (3-5x week; 30 min) Conflicting results from the result of resistance training
Blood Flow Increases With Training Increased capillarization of trained muscles (higher capillary-to-fiber ratio) More effective blood redistribution—blood goes where it is needed
Blood Volume and Training Endurance training, especially intense training, increases blood volume. Red blood cell volume increases, but increase in plasma volume is higher; thus, hematocrit decreases. Changes in plasma volume are highly correlated with changes in SV and VO 2 max..
Cardiac Morphology Law of LaPlace: ventricular wall pressure is proportional to pressure and the radius of curvature (Ford 1976) Adaptations from Exercise Programs Endurance Athletes Greater than normal left ventricular internal diameter Resistance Athletes Left ventricular mass 45% greater than age-matched sedentary controls (Fleck 1988)
Differences in Heart Size Intraventricular septal thickness
The effect of acute aerobic exercise on stress related blood pressure responses: A systematic review and meta-analysis Hamer et al. (2005) Left Ventricular Mass Index and Sports: the influence of different sports activities and arterial blood pressure Cubero et al. (2000)