Cardiorespiratory System and Blood Flow

• The cardiorespiratory system transports oxygen and nutrients to tissues.
• The cardiorespiratory system removes carbon dioxide wastes from tissues.
• The cardiorespiratory system regulates body temperature.
• Two major adjustments of blood flow during exercise are increased cardiac output and redistribution of blood flow.

Circulatory System Components

• Heart: Creates pressure to pump blood.
• Arteries and arterioles: Carry blood away from the heart.
• Capillaries: Facilitate the exchange of oxygen, carbon dioxide, and nutrients with tissues.
• Veins and venules: Carry blood toward the heart.

Heart Structure

• The heart has a right atrium, right ventricle, left atrium, and left ventricle.
• The right atrium receives deoxygenated blood from the body.
• The right ventricle pumps deoxygenated blood to the lungs.
• The left atrium receives oxygenated blood from the lungs.
• The left ventricle pumps oxygenated blood to the body.
• The heart contains the aorta, pulmonary artery, and vena cava.

Pulmonary and Systemic Circuits

• The pulmonary circuit involves the right side of the heart pumping deoxygenated blood to the lungs.
• In the pulmonary circuit, oxygenated blood returns to the left side of the heart via pulmonary veins.
• The systemic circuit involves the left side of the heart pumping oxygenated blood to the body via arteries.
• In the systemic circuit, deoxygenated blood returns to the right side of the heart via veins.

Heart Function Summary

• The cardiovascular system transports oxygen and nutrients to body tissues while removing waste.
• The cardiovascular system serves to regulate body temperature.
• The right side of the heart pumps blood through the pulmonary circulation.
• The left side of the heart delivers blood to systemic circulation.

Myocardium

• The heart wall consists of the epicardium, myocardium, and endocardium.
• The myocardium receives its blood supply via coronary arteries.
• The myocardium has a high demand for oxygen and nutrients.
• Myocardial infarction (MI) occurs when a blockage in coronary blood flow results in cell damage.
• Exercise training protects against heart damage during MI.

Heart Wall Layers

• Epicardium: A serous membrane that serves as a lubricative outer covering, including blood, lymph capillaries, and nerve fibers.
• Myocardium: Cardiac muscle tissue that provides muscular contractions to eject blood from the heart chambers, including capillaries, connective tissues, lymph capillaries, and nerve fibers.
• Endocardium: Endothelial tissue with a thick subendothelial layer of elastic and collagenous fibers, serving as a protective inner lining for heart chambers and valves.

Cardioprotective Benefits of Exercise

• Regular exercise reduces the incidence of heart attacks and improves survival after a heart attack.
• Exercise reduces the amount of myocardial damage from heart attacks, and improves the heart’s antioxidant capacity.
• Exercise improves the function of ATP-sensitive potassium channels.

Cardiac Cycle: Systole and Diastole

• Systole: The contraction phase resulting in blood ejection.
• Diastole: The relaxation phase allowing the heart to fill with blood.
• At rest, diastole is longer than systole.
• During exercise, both systole and diastole are shorter.

Pressure Changes During the Cardiac Cycle

• During diastole, pressure in the ventricles is low, and the heart fills with blood from the atria.
• AV valves open when ventricular pressure is lower than atrial pressure.
• During systole, pressure in the ventricles rises, and blood is ejected into pulmonary and systemic circulation.
• Semilunar valves open when ventricular pressure is greater than aortic pressure.
• Heart sounds: The first heart sound is the closing of AV valves, and the second is the closing of aortic and pulmonary valves.

Arterial Blood Pressure

• Arterial blood pressure is expressed as systolic/diastolic, with a normal value of 120/80 mmHg.
• Systolic pressure: The pressure generated during ventricular contraction.
• Diastolic pressure: The pressure in the arteries during cardiac relaxation.
• Pulse pressure: The difference between systolic and diastolic pressure.
• Mean arterial pressure (MAP): The average pressure in the arteries, calculated as DBP + 0.33(SBP – DBP).

Hypertension

• Hypertension: Blood pressure above 140/90 mmHg.
• Primary (essential) hypertension: Unknown cause, accounting for 90% of hypertension cases.
• Secondary hypertension: Results from another disease process.
• Hypertension Risk factors include left ventricular hypertrophy, atherosclerosis and heart attack, kidney damage, and stroke.

Influences on Arterial Blood Pressure

• Determinants of mean arterial pressure: cardiac output and total vascular resistance.
  • MAP = cardiac output x total vascular resistance.
• Short-term regulation: sympathetic nervous system and baroreceptors in the aorta and carotid arteries.
  • BP increase = SNS activity decrease
  • BP decrease = SNS activity increase
• Long-term regulation: by kidneys via control of blood volume.

Electrical Activity of the Heart

• Contraction relies on electrical stimulation of the myocardium.
• Sinoatrial (SA) node, acts as a pacemaker, initiating depolarization.
• Atrioventricular (AV) node passes depolarization to ventricles with a brief delay for ventricular filling.
• Bundle Branches carry impulses to the left and right ventricles.
• Purkinje fibers distribute impulses throughout the ventricles.
• The electrical impulse starts at the SA node and travels through the wall of the atria.
• After the right atrium fills with blood, the electrical impulse spreads across the cells in both atria causing a contraction.
• The atria pushes blood through the open valves into the ventricles.
• The P wave on the ECG represents the contraction of the atria.
• The electrical impulse gets to the AV node.
• AV node is between the two atria.
• There is a slight slowdown for the ventricles to fill with blood.
• The line between the P and Q wave represents the impulse slowdown on an ECG reading.
• The electrical impulse goes down the bundle of His in the ventricles.
• The bundle of His branches down left and right bundle branches
• A Q wave measures the bundle of his impulse on an ECG.
• The purkinje fibers cause the ventricles to contract slightly separated from each other in time
• Contraction of the left ventricle is measured by the R wave.
• Contraction of the right ventricle is measured by the S wave.
• Once the impulse is complete, the ventricles relax and prepare for the next electrical impulse.
• The T wave represents on a ECG is the ventricles relaxing.

Diagnostic Uses of ECG

• Graded exercise tests assess cardiac function by monitoring ECG and blood pressure changes during exercise.
• Atherosclerosis involves fatty plaque that narrows the coronary arteries, reducing blood flow and causing myocardial ischemia.
• S-T segment depression suggests myocardial ischemia.

Cardiac Cycle Summary

• Systole is the contraction phase.
• Diastole is the relaxation phase.
• The SA node is the heart's pacemaker.
• The mean arterial pressure is the average blood pressure during a cardiac cycle.
• Blood pressure can be increased by increases in blood volume, heart rate, blood viscosity, stroke volume, or peripheral resistance.
• An electrocardiogram (ECG) records the heart's electrical activity during the cardiac cycle.

Cardiac output

• Cardiac output is the amount of blood ejected from the heart every minute
• Q = HR x SV (cardiac output = heart rate X stroke volume
• Cardiac output is dependent on training state and gender

Regulation of Heart Rate

• The parasympathetic nervous system slows heart rate by inhibiting the SA and AV nodes via the vagus nerve.
• The sympathetic nervous system increases heart rate by stimulating the SA and AV nodes via cardiac accelerator nerves.
• Resting heart rate is low due to parasympathetic tone.
• Heart rate increases at the onset of exercise due to parasympathetic withdrawal.
  • The increase in heart rate is due to an increased sympathetic stimulation up to ~100 beats/min.

Factors Influencing Stroke Volume

• End-diastolic volume (EDV): The volume of blood before contraction.
• Average aortic blood pressure: Pressure the heart pumps against.
• Increased strength of ventricular contraction is enhanced by:
  • Circulating epinephrine and norepinephrine
  • Direct sympathetic stimulation of heart

Frank-Starling Mechanism

• Greater EDV leads to more forceful contraction because of ventricles stretching.
• Venous return increased by SNS, skeletal muscle pump pulling blood towards the heart, and respiratory pump

Hemodynamics

• The physical characteristics of blood are defined by the plasma and cells
  • Plasma:Liquid portion of blood, contains ions, proteins, and hormones.
  • Cells: Red blood cells contain hemoglobin and white blood cells help prevent infections
  • Platelets help in blood clotting
• Hematocrit: A percentage of blood that is composed of cells
• The blood flow is directly proportional to the pressure and inversely proportional to resistance.
  • Blood flow = Pressure/Resistance
• Influenced by blood vessel length, blood radius, and viscosity which dictates resistance
• MAP decreases throughout the vascular system due to resistance
• Arterioles are the resistance vessels

Oxygen Delivery

• Oxygen demand is 15-25x greater during exercise
• Increased delivery accomplished by redistribution of blood flow and cardiac output
• Cardiac output=Linear increase -> HR = 220-age and SV = Plateau around 40%VO2

Oxygen Content Levels

• VO2 = Cardiac output x a-VO2 difference
• Higher arteriovenous (a-vO2) difference, the great the amount of oxygen being extracted into a 100 ml sample during exercise.

Vasodilation and Vasoconstriction

• Skeletal muscles cause vasodilation: Autoregulation, and increased blood flow due to metabolic needs.
• Visceral organs/tissues cause vasoconstriction: SNS vasoconstriction.

Vasodilation Factors:

• Nitric oxide is one of several factors and promotes muscle blood flow.
• It promotes smooth muscle muscle relaxation.
• Autoregulation

Exercise Blood Flow Summary

• An increased cardiac output and redistibution of blood flow causes increased oxygen delivery during exercise.
• There are other regulations primarily regulated by local factors

Circulatory exercise resposnes

• Type, duration, and intensity of exercise as well as environmental conditions dictates changes in heart rate and blood pressure.

Heart Rate, SV, and Cardiac Output for Recovery

• At onset, there is an increase in Heart Rate, SV and Cardiac output.
• During recovery they're all decreased.

Double Product During Exercise

• Increases linearly with exercise
• Indicates and is the measurement of the work the heart does during exercise

Arm and Leg Work

• Higher heart rate occurs during arm exercises more than leg
• Vasoconstriction occurs more duirng arm exercises than leg