Exercise science: cardio

3 purposes of the cardiorespiratory system?

-Transporting O2 and nutrients to tissues

-Removal of CO2 wastes from tissues

-Regulation of body temperature

Heart

Creates pressure to pump blood

Arteries and arterioles

Carry blood away from the heart

Capillaries

Exchange of O2, CO2, and nutrients with tissues

Veins and venules

Carry blood towards the heart

Where is the pulmonary circuit located?

Located on the right side of the heart

Functions of pulmonary circuit

Pumps deoxygenated blood to the lungs via pulmonary arteries and returns oxygenated blood to the left side of the heart via pulmonary veins

Where is the systemic circuit located?

Located on the left side of the heart

Functions of the systemic circuit

Pumps oxygenated blood to the whole body via arteries and returns deoxygenated blood to the right side of the heart via veins

3 layers of the heart wall

Epicardium, myocardium and endocardium

What does the myocardium receive?

Receives blood supply via coronary arteries because there is a high demand for oxygen and nutrients

What is a Myocardial Infarction?

A blockage in coronary blood flow results in cell damage

How is regular exercise cardio-protective?

It reduces incidence of heart attacks and improves survival from heart attack

What are the 4 ways in which exercise reduces the amount of myocardial damage from a heart attack?

-Increase endogenous antioxidant defense

-Increased expression of Heat Shock Proteins

-Improves ATP-sensitive potassium channel functions

-Increases endothelial nitric oxide (eNO)

What is systole?

The contraction phase where 2/3rds blood is ejected from ventricles per beat

What is diastole?

The relaxation phase where the heart is filling with blood

When is diastole longer than systole?

When the body is at rest

When is pressure in the ventricles low?

During diastole

When do the atrioventricular valves open?

When ventricular pressure is less than atrial pressure

When does pressure in the ventricles rise?

During systole

When is blood ejected in pulmonary and systemic circulation?

During systole where the semilunar valves open because ventricular pressure is greater than aortic pressure

First heart sound

The closing of the AV valves

Second heart sound

The closing of the aortic and pulmonary valves

Systolic pressure

Pressure generated during ventricular contraction

Diastolic pressure

Pressure in the arteries during cardiac relaxation

Pulse pressure

The difference between systolic and diastolic pressure

Mean arterial pressure (MAP)

Average pressure in the arteries and determines the rate of blood flow through the systemic circuit

What are the 3 factors that influence arterial blood pressure?

-Determinants of mean arterial pressure (MAP)

-Short-term regulation

-Long term regulation

What are the determinants of MAP?

Cardiac output and total vascular resistance

What are the 5 ways in which blood pressure can be increased?

-Increase in blood volume

-Increase in heart rate

-Increased blood viscosity

-Increase in stroke volume

-Increased peripheral resistance

What is classified hypertension?

A blood pressure of 140/90

What is primary hypertension?

It has unknown causes which make up 90% of the cases of hypertension

What is secondary hypertension?

It results of some other disease process

What is hypertension a risk factor for?

-Left ventricular hypertrophy

-Atherosclerosis and MI

-Kidney damage

-Stroke

What does contraction of the heart depend on?

Depends on the electrical stimulation of the myocardium (muscular tissue of the heart)

What are the 4 parts of the conduction system?

-Sinoatrial node (SA node)

-Atrioventricular node (AV node)

-Bundle branches

-Purkinje fibers

Sinoatrial node (SA node)

The pacemaker of the heart which initiates depolarization

Atrioventricular node (AV node)

The part that passes depolarization to ventricles where there is a brief delay to allow for ventricular filling

Bundle branches

Extend to the left and right ventricle

Purkinje fibers

Found throughout ventricles

What is the P wave of an EKG?

It resembles atrial depolarization (contraction)

What is the QRS complex of an EKG?

It resembles ventricular depolarization (contraction) and atrial repolarization (resting)

What is the T wave of an EKG?

It resembles ventricular repolarization (resting)

What are some diagnostic uses of the EKG during exercise?

-Graded exercise test to evaluate cardiac function

-Detect atherosclerosis

-Detect S-T segment depression

What is atherosclerosis?

The fatty plaque that narrows coronary arteries which reduces blood flow to myocardium resulting in myocardial ischemia (less blood flow)

What does S-T segment depression suggest?

A MI

Is a wide variation in HRV considered healthy?

Yes because arrythmias have physiological factors which cause HRV

Is low HRV a predictor of cardiovascular morbidity and mortality?

Yes especially in patients with existing cardiovascular disease

How does the PNS regulate HR?

By inhibiting SA and AV node via the vagus nerve

How does the SNS regulate HR?

Stimulates SA and AV node via cardiac accelerator nerves

Why is there an increase in HR at onset of exercise?

Because of parasympathetic withdrawal which then is later increased due to increased SNS stimulation

Why would someone have a low resting HR?

Due to parasympathetic tone

How do beta-adrenergic blocking drugs reduce heart rate and contractility?

Drugs compete with epinephrine and norepinephrine for beta adrenergic receptors in the heart which lowers the myocardial oxygen demand

When would beta-blockers be prescribed?

When patients have coronary artery disease and hypertension

Cardiac output

The amount of blood pumped by the heart each minute

What is CO the product of?

Heart rate and stroke volume (amount of blood ejected in each beat)

What is cardiac output dependent on?

Training state and gender

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) (MAP)

What is the strength of the ventricular contraction enhanced by?

-Circulating epinephrine and norepinephrine

-Direct sympathetic stimulation of heart

What is the Frank-Starling mechanism for EDV?

Greater EDV results in a more forceful contraction

Does EDV depend on venous return?

Yes

How can we increase venous return?

-Venoconstriction via SNS

-Skeletal muscle pump (contractions force blood in the extremities towards heart) (one way valves)

-Respiratory pump changing thoracic pressure pull towards heart

What two things control cardiac rate?

Parasympathetic nerves and sympathetic nerves

What control stroke volume?

Contraction strength and end diastolic volume

What are the 3 physical characteristics of blood?

Plasma, cells and hematocrit

Plasma

The liquid portion of blood which contains ions, proteins, hormones

Red blood cells

Cells that contains hemoglobin to carry oxygen

White blood cells

Cells that are important in preventing infection

Platelets (megakaryocytes)

Cells that are important in blood clotting

Hematocrit

Percentage of blood composed of red blood cells

What is the oxygen demand of muscles during exercise?

It is 15-25x greater than at rest

How can we increase O2 delivery during exercise?

-Increase cardiac output

-Redistribution of blood flow from inactive organs to working skeletal muscle

How does cardiac output increase during exercise?

Increased heart rate causes increase

How does stroke volume increase during exercise?

There is an initial increase and then a plateu at 40-60% VO2 but there is no plateau in highly trained subjects

Does stroke volume plateau in endurance athletes?

No

Higher arteriovenous difference (a-VO2 difference)

The amount of O2 that is taken up from 100ml of blood which can increase due to higher amount of O2 taken up (used for ATP)

What is the redistribution of blood flow during exercise?

-Increased blood flow to working skeletal muscle (15-20% during rest and 80-85 during exercise)

-Decreased splanchnic blood flow (liver, kidneys, GI)

Does the redistribution of blood flow during exercise depend on metabolic rate?

Yes

How does the body regulate local blood flow during exercise?

Skeletal muscle vasodilation and vasoconstriction to visceral organs and inactive tissues

Skeletal muscle vasodilation

Helps to regulate blood flow during exercise by autoregulation where blood flow increased to meet metabolic demands of tissue

Vasoconstriction to visceral organs and inactive tissues

Helps to regulate blood flow during exercise by SNS vasoconstriction

Is nitric oxide an important vasodilator?

Yes

Where is nitric oxide produced?

Produced in the endothelium or arterioles

What does nitric oxide cause?

Promotes smooth muscle relaxation resulting in vasodilation and increased blood flow

What do circulatory changes in response to exercise depend on?

-type, intensity and duration of exercise

-environmental conditions

-emotional influence

How does emotions influence exercise?

There is an elevated HR and BP in emotionally charged environments (SNS) which increases pre-exercise BP and HY but does not increase the peak during exercise

What happens at the onset of exercise?

There is a rapid increase in HR, SV and cardiac output where there is a plateau in submaximal exercise

What happens during recovery?

There is a decrease in HR, SV, and cardiac output towards resting

What happens with HR and CO during incremental exercise?

HR and CO increase linearly with increasing work rate and reaches at plateau at 100% VO2 max

What happens to blood pressure during incremental exercise?

MAP increases linearly where systolic increases but diastolic remains constant

Does arm workouts result in higher HR and BP?

Yes. HR due to higher SNS stimulation and BP due to vasoconstriction of large inactive muscles in legs

Does recovery of heart rate and blood pressure vary during intermittent exercise?

Yes, recovery depends on fitness level, temperature and humidity, and during/intensity of exercise

What happens during prolonged exercise?

-Cardiac output is maintained

-Gradual decrease in stroke volume because of dehydration

-Gradual increase in HR