Circulatory Adaptations to Exercise

Chapter 9

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

Systemic circuit– 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

MAP = Diastolic + 1/3(Systolic - Diastolic)

Mean arterial pressure (MAP)– Average pressure in the arteries

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– 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– 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– 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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