The Effect of Exercise on the Cardiovascular System

Effect during rhythmic exercise (jogging) Blood vessels dilate in active muscles Muscles pump (push) the blood to circulate faster Increased blood flow increases the systolic blood pressure initially, then the systolic pressure will level off (approx 140-160) The diastolic pressure does not increase significantly This response is similar for conditioned and unconditioned individuals

Response to sub-maximal exercise unconditioned 140 mmHg conditioned 120 mmHg 2-3 hours after exercise Jogging time recovery Initial minutes

Effect during resistance exercise (lifting) More dramatic changes are seen Strained muscle activity compresses peripheral arteries causing significant resistance to blood flow and an increase in blood pressure This is dangerous to individuals with HTN (high blood pressure) or heart disease

Response to resistive exercise 190 mmHg 170 mmHg unconditioned 140 mmHg conditioned 120 mmHg

Blood pressure changes are more dramatic with resistance exercise to the upper extremities (compared to the lower extremities) Upper extremity muscles cause greater resistance to blood flow in the smaller arterioles in the upper extremities Lower extremity muscles cause less resistance to blood flow in the larger arterioles of the lower extremities

Recovery After sustained sub-maximal exercise, systolic blood pressure is reduced below pre-exercise levels for 2 – 3 hours in all subjects (normal or individuals with high blood pressure) Blood pressure (diastolic and systolic) appear to be lower with a regular exercise program

AFTER 4 -6 WEEKS of SUB- MAXIMAL EXERCISE TRAINING BEFORE TRAINING AFTER 4 -6 WEEKS of SUB- MAXIMAL EXERCISE TRAINING at rest during exercise 139/78 133/73 173/92 155/79

Why does regular exercise decrease blood pressure?

Not fully understood May be an effect on the sympathetic nervous system May be the increased elimination of Na (sodium) which decreases blood volume which decreases blood pressure

Resistance training causes a short term increase in blood pressure during the exercise, but no long term rise in blood pressure noted

Oxygen supply to the heart Normal tissues use 25% of oxygen in the blood Heart muscle uses 70-80% of oxygen in the blood Exercise can increase coronary blood flow 4-6 times Exercise increases myocardial metabolism If blood flow is restricted (due to coronary disease) chest pain results Stress tests are done during exercise to measure the demand on the heart

Energy for the heart Myocardium (heart muscle) has the greatest number of mitochondria per cell (compared to all muscles in the body) Myocardium uses glucose, fatty acids, and lactic acid (from skeletal muscle activity) for energy During sub-maximal exercise, the heart muscle may get up to 50% of its energy from lactic acid

Cardiovascular regulation and integration Nerves and chemicals regulate vasodilation (opening of blood vessels) Nerves and chemicals regulate heart rate The heart, at rest, regulates itself at rate of 60-80 b/m (beats per minute) Nerves and chemicals can reduce that rate as low as 30 b/m in a conditioned athlete Nerves and chemicals can increase that rate as high as 220 b/m during maximum exercise

Athletes have a high heart rate before events called an anticipatory response Sprinters increase the most – up to 148 b/m (74% of the entire increase in the event) Heart rate increase is progressively less with longer distance events (long distance runners have a higher anticipatory heart rate than the highest heart rate of the whole event)

Distribution of blood (arterial) Vasodilatation in active muscles will increase blood flow significantly At rest, only 1 of 30-40 capillaries in muscle tissue are open Exercise will open these capillaries This increases the exchange surface area between blood and muscle cells This is stimulated mostly by sensors in the tissue that sense an increased demand for oxygen Increased circulation is also stimulated by tissue’s increased temperature, and increased carbon dioxide levels

Distribution of blood (venous) Adequate venous return is also important for regulating distribution of blood This is achieved by action of muscles (pushing blood along) Also achieved by venous valves (prevention of back flow)

Distribution of blood At rest During Exercise Muscles = 20% increases significantly in active muscles Brain = 14% increases Skin = 6% increases especially in hot weather in order to lose heat Heart = 4% increases blood flow proportionately with increased cardiac output Kidneys = 22% decreases to about 1%

Kidney, at rest, receives 1100 ml/min of blood (20% of cardiac output) Kidney, during heavy exercise, receives only 250 ml/min (less than 1%)

Cardiac output (CO) Measures the functional capacity of the circulation to meet the demands of physical activity CO is equal to HR (heart rate or rate of pumping) times SV (stroke volume or quantity of blood ejected in each ventricular contraction) CO = HR X SV

Let’s try these problems!

At rest (untrained individual) Entire blood volume (5000 ml) is pumped out of the left ventricle each minute - this is the same for trained and untrained individuals (males) CO = 5000ml/min Untrained person at rest average HR is 70 b/m Now substitute the values in the equation below to solve for the stroke volume (SV) CO = HR x SV

(the average stroke volume for an untrained individual) CO = HR x SV 5000 ml/min = 70 b/m x SV SV = 71 ml/beat (the average stroke volume for an untrained individual)

At rest (trained individual) Remember, CO stays constant CO = 5000ml/min Endurance athletes at rest average HR = 50 b/m Now substitute the values in the equation below to solve for the stroke volume (SV) CO = HR x SV

(the average stroke volume for a trained individual) CO = HR x SV 5000 ml/min = 50 b/min x SV SV = 100 ml/beat (the average stroke volume for a trained individual)

AT REST CARDIAC OUTPUT HEART RATE STROKE VOLUME UNTRAINED 5000 ml/min 70 b/min 71 ml/b TRAINED 50 b/min 100 ml/b

In conclusion: CO (cardiac output) stays the same at rest for trained and untrained individuals The heart rate (HR) decreases with training. WHY?

Why? Endurance training strengthens heart muscle and allows the heart to pump with more force pushing out more blood per stroke (ventricular contraction) Because the stroke volume is greater in conditioned persons, the heart rate can be lower, the heart does not have to beat as many times/minute to maintain the necessary cardiac output.

Is this same effect seen during exercise? Blood flow increases rapidly at first, then rises gradually until it reaches a plateau

During exercise in an untrained person CO increases to ~22,000 ml/min HR increases to ~195 b/min What is the stroke volume? CO = HR x SV 22,000 ml/min = 195 b/min x SV SV = 113 ml/beat

An Olympic athlete exercising (at the same level as the previous individual) CO increases to 22,000 ml/min HR will increase to ~150 b/min What is the stroke volume? CO = HR x SV 22,000 ml/min = 150 b/min x SV SV = 147 ml/beat

DURING EXERCISE CARDIAC OUTPUT HEART RATE STROKE VOLUME UNTRAINED 22,000 ml/min 195 b/min 113 ml/b TRAINED 150 b/min 147 ml/b

What happens when both individuals perform maximum exercise? ** We will have both individuals work up to a pulse of 195 b/min **

MAXIMUM EXERCISE CARDIAC OUTPUT HEART RATE STROKE VOLUME UNTRAINED 22,000 ml/min 195 b/min 113 ml/b TRAINED 35,000 ml/min 179 ml/b

In conclusion: The untrained person increases his cardiac output mainly due to an increased pulse *The trained athlete increases his cardiac output mainly due to an increased stroke volume *Stroke volumes are larger in athletes at rest and during exercise, therefore the HR (pulse) does not need to rise as much in either case

Oxygen transport in the blood remains constant The blood carries about 200 ml of oxygen per liter of blood The hemoglobin is about 100% saturated and can not increase what it carries The body tissues use about 25% of circulating oxygen from the blood at rest Increased demands of the tissues during exercise is met by increased cardiac out put, not more oxygen in the blood

Oxygen up-take increases with exercise At rest - tissues use 25% of oxygen in the blood (~50 ml per liter of blood) During exercise – tissues may use up to 75% of oxygen in the blood(~150 ml/l of blood) After 55 days of training – tissues may use up to 85% of oxygen in the blood (~175 ml/l of blood)

How does oxygen uptake increase with exercise? This increased oxygen up-take is due primarily to increased blood flow in the tissues also training increases the muscle cell’s ability to metabolize oxygen (with greater numbers of mitochondria)

Patients with heart disease can improve oxygen use (by improving the tissue’s oxygen up-take) even if heart rate and stroke volume are unable to improve