Circulatory Adaptations to Exercise Chapter 9 Circulatory Adaptations to Exercise

The Cardiovascular System Components Circulatory system Pulmonary system Purposes Transport O2 to tissues and removal of other products (“waste”) Transport of nutrients to tissues Regulation of body temperature

The Circulatory System Heart Pumps blood Arteries and arterioles Carry blood away from the heart Capillaries Exchange of materials with tissues Veins and venules Carry blood toward the heart

Structure of the Heart

Pulmonary and Systemic Circuits Left side of the heart Pumps oxygenated blood to the whole body via arteries Returns “deoxygenated” blood to the right heart via veins Pulmonary circuit Right side of the heart Pumps “deoxygen-ated” blood to the lungs via pulmonary arteries Returns oxygenated blood to the left heart via pulmonary veins

The Myocardium

The Cardiac Cycle Systole Contraction phase Diastole Relaxation phase

Pressure Changes During the Cardiac Cycle

Arterial Blood Pressure Expressed as systolic/diastolic Normal is 120/80 mmHg High is 140/90 mmHg Systolic pressure (top number) Arterial pressure during systole Diastolic pressure Arterial Pressure during diastole

Arterial Blood Pressure Pulse pressure Difference between systolic and diastolic Pulse Pressure = Systolic - Diastolic Mean arterial pressure (MAP) Average pressure in the arteries MAP = Diastolic + 1/3(Systolic - Diastolic)

Measurement of Blood Pressure

Factors That Influence Arterial Blood Pressure

Electrical Activity of the Heart Contraction of the heart depends on electrical stimulation of the myocardium Impulse is initiated by the SA node and spreads throughout entire heart May be recorded on an electrocardiogram (ECG or EKG)

Conduction System of the Heart

Electrocardiogram

Electrocardiogram Records the electrical activity of the heart P-wave Atrial depolarization QRS complex Ventricular depolarization T-wave Ventricular repolarization

Diagnostic Use of the ECG ECG abnormalities may indicate coronary heart disease ST-segment depression can indicate myocardial ischemia (reduced blood flow)

Abnormal ECG Response to Exercise

Cardiac Output The amount of blood pumped by the heart each minute Product of heart rate and stroke volume Heart rate = number of beats per minute Stroke volume = amount of blood ejected from the heart in each beat . Q = HR x SV

Regulation of Heart Rate Decrease in HR Parasympathetic nervous system Via vagus nerve Slows HR by inhibiting SA node Increase in HR Sympathetic nervous system Via cardiac accelerator nerves Increases HR by stimulating SA node

A Summary of Cardiovascular Control During Exercise: Fine Tuning

Nervous System Regulation of HR

Regulation of Stroke Volume End-diastolic volume (EDV) Volume of blood in the ventricles at the end of diastole (“preload”) Average aortic blood pressure Pressure the heart must pump against to eject blood (“afterload”) Contractility Strength of the ventricular contraction

Incremental Exercise Heart rate and cardiac output Increases linearly with increasing work rate Reaches plateau at 100% VO2max Systolic blood pressure Increases with increasing work rate Double product Increases linearly with exercise intensity Indicates the work of the heart Double product = heart rate x systolic BP

End-Diastolic Volume Frank-Starling mechanism Affected by: Greater preload results in stretch of ventricles and in a more forceful contraction Affected by: Venoconstriction Skeletal muscle pump Respiratory pump

The Skeletal Muscle Pump Rhythmic skeletal muscle contractions force blood in the extremities toward the heart One-way valves in veins prevent backflow of blood

The Skeletal Muscle Pump

Average Aortic Pressure Aortic pressure is inversely related to stroke volume High after load results in a decreased stroke volume Requires greater force generation by the myocardium to eject blood into the aorta Reducing after load results in higher stroke volume

Ventricular Contractility Increased contractility results in higher stroke volume Causes: Circulating epinephrine and norepinephrine Direct sympathetic stimulation of heart

Hemodynamics Flow of blood through the circulatory system Based on interrelationships between: Pressure Resistance Flow

Components of Blood

Hemodynamics: Resistance Resistance depends upon: Length of the vessel Viscosity of the blood Radius of the vessel A small change in vessel diameter can have a dramatic impact on resistance! Resistance = Length x viscosity Radius4

Hemodynamics: Blood Flow Directly proportional to the pressure difference between the two ends of the system Inversely proportional to resistance Flow =  Pressure Resistance

Sources of Vascular Resistance MAP decreases throughout the systemic circulation Largest drop occurs across the arterioles Arterioles are called “resistance vessels”

Pressure Changes Across the Systemic Circulation

Oxygen Delivery During Exercise Oxygen demand by muscles during exercise is many times greater than at rest Increased O2 delivery accomplished by: Increased cardiac output Redistribution of blood flow to skeletal muscle

Changes in Cardiac Output Cardiac output increases due to: Increased HR Linear increase to max after 120 bpm Increased SV Plateau at ~40% VO2max Max HR = 220 - Age (years) .

Changes in Cardiovascular Variables During Exercise

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

Circulatory Responses to Exercise Heart rate and blood pressure Depend on: Type, intensity, and duration of exercise Environmental conditions Emotional influence

Transition From Rest  Exercise and Exercise  Recovery Increase in HR, SV, cardiac output Plateau in sub maximal exercise Recovery depends on: Duration and intensity of exercise Training state of subject

Transition From Rest  Exercise  Recovery

Incremental Exercise Heart rate and cardiac output Systolic BP Increases linearly with increasing work rate Reaches plateau at 100% VO2max Systolic BP Increases with increasing work rate Diastolic BP Decreases slightly then remains even .

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)

HR, SV, and CO During Prolonged Exercise

Summary of Cardiovascular Adjustments to Exercise

Chronic Endurance Training Stronger/ thicker/ larger left ventricle Lower resting and working HR Greater resting and working SV Lower resting and working blood pressure Greater capillarization which decreases TPR – total peripheral resistance

Questions?

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