circulatory adaptations to exercise
DESCRIPTION
Chapter 9. Circulatory Adaptations to Exercise. The Cardiovascular System. Components Circulatory system Pulmonary system Purposes Transport O 2 to tissues and removal of other products (“waste”) Transport of nutrients to tissues Regulation of body temperature. The Circulatory System. - PowerPoint PPT PresentationTRANSCRIPT
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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