CARDIOVASCULAR CONTROL DURING EXERCISE

Major Cardiovascular Functions w Delivery (e.g., oxygen and nutrients) w Removal (e.g., carbon dioxide and waste products) w Transportation (e.g., hormones) w Maintenance (e.g., body temperature, pH) w Prevention (e.g., infection—immune function)

The Cardiovascular System w A pump (the heart) w A system of channels (the blood vessels) w A fluid medium (blood)

THE HEART

Did You Know…? 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. Pulmonary “veins” carry oxygenated blood from the lungs to the heart and pulmonary “arteries” carry blood with lower oxygen levels to the lungs for oxygenation.

Myocardium—The Cardiac Muscle w Thickness varies directly with stress placed on chamber walls. w Left ventricle is the most powerful of chambers and thus, the largest. w With vigorous exercise, the left ventricle size increases. w Due to intercalated disks—impulses travel quickly in cardiac muscle and allow it to act as one large muscle fiber; all fibers contract together.

Resting Heart Rate w Averages 60 to 80 beats per minute (bpm); can range from 28 bpm to above 100 bpm w Tends to decrease with age and with increased cardiovascular fitness w Is affected by environmental conditions such as altitude and temperature

Maximum Heart Rate w The highest heart rate value one can achieve in an all-out effort to the point of exhaustion w Remains constant day to day and changes slightly from year to year w Can be estimated: HRmax = 220 – age in years

THE INTRINSIC CONDUCTION SYSTEM

The Cardiac Conduction System w Sinoatrial (SA) node—pacemaker (60-80 beats/min intrinsic heart rate) w Atrioventricular (AV) node—built-in delay of 0.13 sec. w AV bundle (bundle of His) wPurkinje fibers—6 times faster transmission

Did You Know…? 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 per minute or less.

Electrocardiogram (ECG) Records the heart's electrical activity and monitors cardiac changes Cardiac conduction system

PHASES OF THE RESTING ECG

Cardiac Cycle w Events that occur between two consecutive heartbeats (systole to systole) w Diastole—relaxation phase during which the chambers fill with blood (T wave to QRS)—62% of cycle duration w Systole—contraction phase during which the chambers expel blood (QRS to T wave)—38% of cycle duration

Stroke Volume and Cardiac Output Stroke Volume (SV) w End-diastolic volume (EDV)—volume of blood in ventricle before contraction w End-systolic volume (ESV)—volume of blood in ventricle after contraction w SV = EDV – ESV w Volume of blood pumped per contraction w Total volume of blood pumped by the ventricle per minute Cardiac Output (Q) . w Q = HR ´ SV

BLOOD DISTRIBUTION AT REST

Functions of the Blood w Transports gas, nutrients, and wastes w Regulates temperature w Buffers and balances acid base

THE COMPOSITION OF TOTAL BLOOD VOLUME

Blood Plasma Volume w Reduced with onset of exercise (goes to interstitial fluid space) w More is lost if exercise results in sweating w Excessive loss can result in impaired performance w Reduction in blood plasma volume results in hemoconcentration

Hematocrit and Blood Formed Elements Ratio of formed elements to the total blood volume w White blood cells—protect body from disease organisms w Blood platelets—cell fragments that help blood coagulation w Red blood cells—carry oxygen to tissues with the help of hemoglobin

Blood Viscosity w Thickness of the blood w The more viscous, the more resistant to flow w Higher hematocrits result in higher blood viscosity

Steady-State Heart Rate w Heart rate plateau reached during constant rate of submaximal work w Optimal heart rate for meeting circulatory demands at that rate of work w The lower the steady-state heart rate, the more efficient the heart

Cardiovascular Response to Acute Exercise w Heart rate (HR), stroke volume (SV), and cardiac output (Q) increase. . w Blood flow and blood pressure change. w All result in allowing the body to meet the increased demands placed on it efficiently.

Stroke Volume w Determinant of cardiorespiratory endurance capacity at maximal rates of work w May increase with increasing rates of work up to intensities of 40% to 60% of max w May continue to increase up through maximal exercise intensity, generally in highly trained athletes Depends on position of body during exercise stroke volume video

STROKE VOLUME

STROKE VOLUME INCREASES IN CYCLISTS

Cardiac Output w Resting value is approximately 5.0 L/min. w Increases directly with increasing exercise intensity to between 20 to 40 L/min. wThe magnitude of increase varies with body size and endurance conditioning. w When exercise intensity exceeds 40% to 60%, further increases in Q are more a result of increases in HR than SV since SV tends to plateau at higher work rates. .

CARDIAC OUTPUT DURING EXERCISE

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 output Activity (beats/min) (ml/beat) (L/min)

Blood Pressure Cardiovascular Endurance Exercise w Systolic BP increases in direct proportion to increased exercise intensity w Diastolic BP changes little if any during endurance exercise, regardless of intensity Resistance Exercise w Exaggerates BP responses to as high as 480/350 mmHg w Some BP increases are attributed to the Valsalva maneuver

Key Points Cardiovascular Response to Exercise (continued) w As exercise intensity increases, heart rate, stroke volume, and cardiac output increase to get more blood to the tissues. w More blood pumped from the heart per minute during exercise allows for more oxygen and nutrients to get to the muscles and for waste to be removed more quickly. w Blood flow distribution changes from rest to exercise as blood is redirected to the muscles and systems that need it. (continued)

Key Points Cardiovascular Response to Exercise w Cardiovascular drift is the result of decreased stroke volume, increased heart rate, and decreased systemic and pulmonary arterial pressure due to prolonged steady-state exercise or exercise in the heat. w Systolic blood pressure increases directly with increased exercise intensity while diastolic blood pressure remains constant. w Blood pressure tends to increase during high-intensity resistance training, due in part to the Valsalva maneuver.