CARDIOVASCULAR CONTROL DURING EXERCISE

CARDIOVASCULAR CONTROL DURING EXERCISE

CHAPTER 7CHAPTER 7

Major Cardiovascular Functions

Delivery

Removal

Transport

Maintenance

Prevention

THE HEART

Myocardium—The Cardiac Muscle

Thickness varies directly with stress placed on chamber walls.

Left ventricle is the most powerful of chambers and thus, the largest.

With vigorous exercise, the left ventricle size increases.

Impulses travel quickly in cardiac muscle and allow it to act as one large muscle fiber; all fibers contract together.

THE INTRINSIC CONDUCTION SYSTEM

Extrinsic Control of the Heart

ParasympatheticPNS acts through the vagus nerve to decrease heart rate and force of contraction.

SympatheticSNS is stimulated by stress to increase heart rate and force

of contraction.

Resting heart rates in adults tend to be between 60 and 85 beats per min. However, extended endurance training can lower resting heart rate to 35 beats or less. This lower heart rate is thought to be due to decreased intrinsic heart rate and increased parasympathetic stimulation.

Did You Know…?

The decrease in resting heart rate that occurs as an adaptation to endurance training is different from pathological bradycardia, an abnormal disturbance in the resting heart rate.

Did You Know…?

Electrocardiogram (ECG)

Records the heart's electrical activity and monitors cardiac changes

The P wave—atrial depolarization

The QRS complex—ventricular depolarization and atrial repolarization

The T wave—ventricular repolarization

PHASES OF THE RESTING ECG

Cardiac Cycle

Events that occur between two consecutive heartbeats (systole to systole)

Diastole—relaxation phase during which the chambers fill with blood (T wave to QRS)

Systole—contraction phase during which the chambers expel blood (QRS to T wave)

Stroke Volume and Cardiac Output

Stroke Volume (SV)

End-diastolic volume (EDV)—volume of blood in ventricle before contraction

End-systolic volume (ESV)—volume of blood in ventricle after contraction

SV = EDV – ESV

Volume of blood pumped per contraction

Total volume of blood pumped by the ventricle per minute

Cardiac Output (Q).

Q = HR SV.

Ejection Fraction (EF)

Proportion of blood pumped out of the left ventricle each beat

EF = SV/EDV

Averages 60% at rest

The Vascular System

Arteries

Arterioles

Capillaries

Venules

Veins

Arteries always carry blood away from the heart; veins always carry blood back to the heart with the help of breathing, the muscle pump, and valves.

Do arteries always carry oxygenated blood and veins always carry deoxygenaed blood?

Did You Know…?

THE MUSCLE PUMP

BLOOD DISTRIBUTION AT REST

BP

• A measure of the pressure exerted by the blood on the arteries– systolic BP - the pressure in the arteries during

systole (the contractile phase of the cardiac cycle)

– diastolic BP - the pressure in the arteries during diastole (the relaxation phase of the cardiac cycle)

Methods of Assessing BP

• Auscultation using a stethoscope and sphygmomanometer– 1. Seated for at least 5 minutes with arm the

level of the heart (no caffeine or smoking 30 min prior)

– 2. Align cuff with brachial artery (the bladder should encircle 80% of an adults arm and 100% of a child’s arm)

Methods of Assessing BP

– 3. Place stethoscope bell over the brachial artery beneath the cuff

– 4. Inflate cuff quickly to 20 mmHg above estimated systolic

– 5. Slowly release valve (2-3mmHg/s) noting first Korotkoff sound)

Methods of Assessing BP

– 6. Continue releasing until sound becomes muffled (4th) and then disappears (5th)

– 7. Wait 30s and repeat (use the average)

What causes the sounds you here?

BP Sounds

• The sound of blood moving through the vessels is normally silent.

• Smooth laminar blood flow - blood in center of vessels moves faster than blood closest to vessel walls (produces little sound)

BP Sounds

• Pinching the artery causes turbulence and is noisy

• The tendency of the cuff pressure to constrict the artery is opposed by blood pressure

• If cuff pressure is greater than systolic pressure the artery is completely constricted and no sounds are heard.

BP Sounds

• When pressure is released from the cuff the first sound you hear (1st Kortokoff sound) is when the cuff pressure reaches the systolic pressure

• Blood is passing turbulently as the artery becomes unconstricted

BP Sounds

• You continue to hear sounds at every systole (contraction of the heart) as long as the cuff pressure remains above diastolic pressure

• When sound becomes muffled is called the 4th Kortokoff sound (7-10 mmHg higher than 5th Kortokoff sound)

BP Sounds

• When cuff pressure reaches diastolic pressure the sounds disappear (5th Kortokoff sound) since the artery opens and laminar blood flow begins

• Use 5th sound as an index of diastolic pressure

Functions of the Blood

Transports gas, nutrients, and wastes

Regulates temperature

Buffers and balances acid base

THE COMPOSITION OF TOTAL BLOOD VOLUME

Hematocrit

Ratio of formed elements to the total blood volume

White blood cells—protect body from disease organisms

Blood platelets—cell fragments that help blood coagulation

Red blood cells—carry oxygen to tissues with the help of hemoglobin

Blood Viscosity

Thickness of the blood

The more viscous, the more resistant to flow

Higher hematocrits result in higher blood viscosity

Cardiovascular Response to Acute Exercise

Blood flow and blood pressure change.

All result in allowing the body to meet the increased demands placed on it efficiently.

Heart rate (HR), stroke volume (SV), and cardiac output (Q) increase.

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Resting Heart Rate

Averages 60 to 80 beats per minute (bpm); can range from 28 bpm to above 100 bpm

Tends to decrease with age and with increased cardiovascular fitness

Is affected by environmental conditions such as altitude and temperature

Maximum Heart Rate

The highest heart rate value one can achieve in an all-out effort to the point of exhaustion

Remains constant day to day and changes slightly from year to year

Can be estimated: HRmax = 220 – age in years

Steady-State Heart Rate

Heart rate plateau reached during constant rate of submaximal work

Optimal heart rate for meeting circulatory demands at that rate of work

The lower the steady-state heart rate, the more efficient the heart

Stroke Volume

Determinant of cardiorespiratory endurance capacity at maximal rates of work

May increase with increasing rates of work up to intensities of 40% to 60% of max

May continue to increase up through maximal exercise intensity

Depends on position of body during exercise

Stroke Volume Increases During Exercise

Frank Starling mechanism—more blood in the ventricle causes it to stretch more and contract with more force.

Increased ventricular contractility (without end-diastolic volume increases).

Decreased total peripheral resistance due to increased vasodilation of blood vessels to active muscles.

Cardiac Output

Resting value is approximately 5.0 L/min.

Increases directly with increasing exercise intensity to between 20 to 40 L/min.

Value of increase varies with body size and endurance conditioning.

When exercise intensity exceeds 40% to 60%, further increases in Q are more a result of increases in HR than SV.

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Changes in Heart Rate, Stroke Volume, and Cardiac Output

Resting (supine) 55 95 5.2

Resting (standing 60 70 4.2 and sitting)

Running 190 130 24.7

Cycling 185 120 22.2

Swimming 170 135 22.9

Heart rate Stroke volume Cardiac outputActivity (beats/min) (ml/beat) (L/min)

Cardiovascular Drift

Gradual decrease in stroke volume and systemic and pulmonary arterial pressures and an increase in heart rate.

Occurs with steady-state prolonged exercise or exercise in a hot environment.

Blood Pressure

Cardiovascular Endurance Exercise

Systolic BP increases in direct proportion to increased exercise intensity

Diastolic BP changes little if any during endurance exercise, regardless of intensity

Resistance Exercise

Exaggerates BP responses to as high as 480/350 mmHg

Some BP increases are attributed to the Valsalva maneuver

Arterial-Venous Oxygen Difference

Amount of oxygen extracted from the blood as it travels through the body

Calculated as the difference between the oxygen content of arterial blood and venous blood

Increases with increasing rates of exercise as more oxygen is taken from blood

The Fick equation represents the relationship of the body’s oxygen consumption (VO2), to the arterial-venous oxygen difference (a-vO2 diff) and cardiac output (Q); VO2 = Q a-vO2 diff.

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Blood Plasma Volume

Reduced with onset of exercise (goes to interstitial fluid space)

More is lost if exercise results in sweating

Excessive loss can result in impaired performance

Reduction in blood plasma volume results in hemoconcentration