Blood Pressure and Exercise

Blood Pressure and Exercise

• Systolic Blood Pressure (SBP): Increases during exercise.
• Diastolic Blood Pressure (DBP): No change or slightly decreases during exercise.
• Mean Arterial Blood Pressure (MAP): Increases during exercise.
• Baroreceptors do not decrease blood pressure during exercise because they reset to a higher limit and work to maintain the blood pressure.
• Blood Pressure Changes with Exercise:
  • Increased SBP is due to increased cardiac output and total peripheral resistance (TPR).
  • Unchanged or slightly decreased DBP is due to the slight decrease in cardiac output and TPR.
  • Increased MAP is due to its dependence on both SBP and DBP, with SBP increasing during exercise which heavily influences MAP.
• Arm vs. Leg Exercise
  • Similar workloads require the same amount of oxygen.
  • Arm exercise causes higher blood pressure because of vasoconstriction in the lower body and vasodilation in the arms.
  • Leg exercise causes lower blood pressure because of vasodilation in the legs and vasoconstriction in the arms.
• Baroreceptor Location: Carotid arteries and aortic arch
• Baroreceptor Response to Increased Blood Pressure: ↑ Parasympathetic nerve activity, ↓ Sympathetic nerve activity, ↓ Blood Pressure.

Cardiac Output

• Equation: CO = HR x SV
• Resting Cardiac Output:
  • Females: 4.5 L/min
  • Males: 5 L/min
• Cardiac Output during Exercise: Increases to meet oxygen demands for working muscles.
• Why Increase CO during Exercise? To deliver more oxygenated blood to skeletal muscles, increase ATP production, and increase oxygen extraction by muscle cells.

Heart Rate

• Resting Heart Rate: 60-70 bpm (untrained individuals)
• Maximal Heart Rate: 220 - age
• Heart Rate Response to Exercise: Increases linearly with exercise intensity.
• Mechanisms for Increased Heart Rate: Sympathetic nervous system and parasympathetic withdrawal.
• Parasympathetic Withdrawal: Decreases ACh release, slowing down the SA node, resulting in a faster heart rate.
• Sympathetic Stimulation: Cardiac accelerator nerve interacts with the SA node, increasing heart rate above 100 bpm.

Stroke Volume

• Stroke Volume: Amount of blood ejected from the heart in one contraction.
• Stroke Volume Response to Exercise: Increases during exercise.
• Stroke Volume in Untrained Individuals: Peaks and plateaus at 40% of VO2max, further increases are driven by heart rate.
• Resting Stroke Volume:
  • Males: 70 ml per beat
  • Females: 60 ml per beat
• Exercise Stroke Volume:
  • Males: 110 ml per beat
  • Females: 90 ml per beat
• Factors Influencing Stroke Volume:
  • Preload: Increased blood volume in the ventricle prior to contraction.
  • Contractility: Strength of the ventricle contraction.
  • Afterload: Aortic blood pressure.

Factors Affecting Stroke Volume

• Preload:
  • Venoconstriction: Increases blood return to the heart.
  • Skeletal Muscle Pump: Muscle contraction pushes blood towards the heart.
  • Respiratory Pump: Diaphragm movement creates negative pressure in the thoracic cavity, aiding blood return.
• Contractility:
  • Sympathetic Stimulation: Increased contractility.
  • Circulating Epinephrine: Increases contractility.
• Afterload: Increases in afterload decrease stroke volume.

Cardiac Drift

• Cardiac Drift: During prolonged exercise, despite constant exercise intensity:
  • Heart rate increases.
  • Cardiac output remains relatively constant.
  • Stroke volume decreases.
  • Plasma volume decreases due to sweating.

Endurance Exercise Training

• Impact on Cardiac Output: No change in cardiac output with exercise.
• Impact on Heart Rate and Stroke Volume: Heart rate decreases, stroke volume remains constant during exercise.
• Endurance Exercise Training and Stroke Volume: Increase in left ventricle chamber size, thicker wall (hypertrophy), increased preload, increased contractility, and decreased afterload.

Oxygen Consumption (VO2)

• Endurance Exercise Training Impacts on VO2:
  • VO2max: Increases.
  • VO2rest: Remains the same.
  • VO2submax: Remains the same.
• Increased VO2max: Due to an increase in both cardiac output and arterio-venous oxygen difference (a-vO2 differ).
• Equal Contributions to Increased VO2max: Cardiac output and arterio-venous oxygen difference contribute equally.

Cardiac Muscle Characteristics

• Endocardium: Composed of endothelial cells, not cardiac muscle.
• Left Ventricle Wall: Thicker than the right ventricular wall.
• Cardiac Myocyte Characteristics:
  • Single nuclei.
  • Fibres branching.
  • Single fiber type.
  • Not: Multiple satellite cells

Total Peripheral Resistance (TPR)

• TPR: Resistance to blood flow in the circulatory system.
• Factors Affecting TPR:
  • Viscosity: Thick blood (e.g., high RBC count) increases TPR.
  • Diameter/Radius: A smaller radius increases TPR.
  • Length of Vessel: A longer vessel increases TPR.
• Variable Most Affected by Exercise: Radius.
• TPR and Blood Vessels: Arterioles contribute the most to TPR regulation.
• TPR during Exercise: Can increase or decrease depending on exercise type, muscle mass activation, and intensity.

Mean Arterial Pressure

• MAP: Average blood pressure over the cardiac cycle.
• Equation: MAP = (SBP + 2DBP) / 3
• Important: MAP is not the simple average of SBP and DBP during exercise due to variations in the cardiac cycle duration.

Blood Pressure Regulation

• Resting Blood Pressure: 120/80 mmHg
• Blood Pressure Regulators:
  • Slow-acting: Kidney (renin-angiotensin system).
  • Fast-acting: Baroreceptors.
• Baroreceptors: Pressure sensors located in the carotid arteries and aortic arch that detect blood pressure changes.
• High Blood Pressure Response: Decreased sympathetic activity, increased parasympathetic activity, decreased heart rate, and vasodilation.
• Low Blood Pressure Response: Increased sympathetic activity, decreased parasympathetic activity, increased heart rate, and vasoconstriction.

Blood Pressure and Exercise

• Sympathetic activity increases heart rate and decreases artery dilation.
• Parasympathetic activity decreases heart rate and increases artery dilation.

Blood Pressure Changes During Exercise

• Systolic blood pressure increases during exercise.
• Diastolic blood pressure remains unchanged or decreases slightly during exercise.
• Mean arterial blood pressure increases during exercise.
• Baroreceptors reset to a higher limit during exercise, so they do not decrease blood pressure.

Calculating Blood Pressure

• SBP (Systolic Blood Pressure) increases during exercise because of increased Cardiac Output (Q) and Total Peripheral Resistance (TPR).
• DBP (Diastolic Blood Pressure) remains the same or decreases slightly during exercise as Q increases and TPR stays the same.
• Cardiac Output (Q) refers to the amount of blood pumped by the heart per minute.
• Total Peripheral Resistance (TPR) refers to the resistance that blood faces as it flows through the blood vessels

Blood Pressure Changes in Arm vs. Leg Exercise

• Arm exercise results in a larger increase in blood pressure compared to leg exercise at the same workload because it leads to constriction in larger portion of the body (⅔ of the lower body) compared to leg exercise (½ of the body).
• Leg exercise requires dilation of more muscle mass and only constricts half of the body.
• Oxygen consumption remains the same for the same workload, regardless of which limb is being exercised.

Baroreceptors

• Baroreceptors located in the carotid arteries and aortic arch detect changes in blood pressure.
• When stretched due to increased blood pressure, baroreceptors increase parasympathetic and decrease sympathetic nerve activity, leading to decreased blood pressure.

Blood Pressure Regulation During Rest and Exercise

• Baroreceptors primarily regulate blood pressure changes during rest and exercise by altering vascular conductance (TPR), with minimal contribution from cardiac output (CO).

Cardiac Output

• Cardiac Output (CO) is the amount of blood pumped by the heart per minute.
• Equation: CO = HR x SV (Heart Rate x Stroke Volume)
• Resting Cardiac Output: 4.5 L/min for females, 5 L/min for males.
• Cardiac Output increases during exercise to meet the increased oxygen demand of working skeletal muscle.

Heart Rate

• Heart rate increases linearly with increasing exercise intensity.
• Average resting heart rate: 60-70 bpm for untrained individuals.
• Maximal heart rate: 220 - age.
• Increased sympathetic activity and decreased parasympathetic activity drive heart rate increases during exercise.
• The vagus nerve releases Acetylcholine (ACh) to slow down heart rate.
• Cardiac accelerator nerve interacts with the SA node to increase heart rate.

Stroke Volume

• Stroke Volume (SV) is the amount of blood ejected from the heart in one contraction.
• Stroke volume increases during exercise.
• Average resting stroke volume: 70 ml/beat for males, 60 ml/beat for females.
• Average stroke volume during exercise: 110 ml/beat for males, 90 ml/beat for females.

Stroke Volume Regulation During Exercise

• Preload: The amount of blood in the ventricle prior to contraction.
• Contractility: The strength of the ventricular contraction.
• Afterload: Aortic blood pressure, the pressure the heart must overcome to eject blood.

Preload Factors Affecting Stroke Volume

• Venoconstriction: Constriction of veins, pushing blood towards the heart.
• Skeletal muscle pump: Contraction of skeletal muscles pushes blood towards the heart.
• Respiratory pump: Diaphragmatic movement creates negative pressure in the thoracic cavity, aiding blood flow to the heart.

Contractility Factors Affecting Stroke Volume

• Sympathetic stimulation: Increased sympathetic activity enhances ventricular contractility.
• Circulating epinephrine: Epinephrine released from the adrenal glands increases contractility.

Afterload Factors Affecting Stroke Volume

• Increased afterload decreases stroke volume by working against the heart's ability to eject blood.

Cardiac Output Response to Exercise Duration

• Cardiac drift: A phenomenon during prolonged exercise where heart rate increases, while stroke volume and cardiac output remain relatively unchanged. This is explained by a decrease in plasma volume due to sweating, leading to less preload.

Endurance Exercise Training

• Endurance training does not change cardiac output at rest or during submaximal exercise.
• Heart rate decreases and stroke volume does not change in trained individuals compared to untrained individuals.
• Training increases stroke volume due to increased left ventricular chamber size, thicker walls (hypertrophy), and increased preload, contractility, and decreased afterload.

Oxygen Consumption (VO2)

• Endurance training increases VO2 max (maximum oxygen consumption) by increasing both cardiac output (CO) and a-vO2 difference (the difference in oxygen content between arterial and venous blood).

Heart and its Structure

• The endocardium is not comprised of cardiac muscle, but of endothelial cells.
• The left ventricular wall is thicker than the right ventricular wall due to its role in pumping blood to the systemic circulation.
• Cardiac myocytes are characterized by single nuclei, branching fibers, and a single fiber type.
• Cardiac myocytes do not have multiple satellite cells.

Total Peripheral Resistance (TPR)

• TPR is the opposition to blood flow in the peripheral blood vessels.
• Arterioles contribute the most to TPR regulation.

Exercise and TPR

• TPR changes during exercise depending on the muscle mass activated and intensity, making it difficult to predict a steady-state change in TPR.
• Exercise primarily affects the radius of blood vessels by dilating working muscles and constricting non-working muscles (visceral).

Mean Arterial Pressure (MAP)

• MAP is the average arterial blood pressure throughout the cardiac cycle.
• MAP = DBP + ⅓(SBP-DBP)
• The equation for MAP is not accurate during exercise because the ratio of systole to diastole changes.

Blood Pressure Regulation at Rest

• Baroreceptors are the primary regulators of blood pressure at rest.

Blood Pressure Control Mechanisms

• Slow-acting: Renal control through the renin-angiotensin system.
• Fast-acting: Baroreceptors.

Blood Pressure Regulation

• Increased blood pressure: Baroreceptors stimulate increased parasympathetic and decreased sympathetic activity, leading to decreased heart rate and dilation of blood vessels.
• Decreased blood pressure: Baroreceptors stimulate increased sympathetic and decreased parasympathetic activity, leading to increased heart rate and constriction of blood vessels.

This quiz covers the relationship between blood pressure and exercise, including the changes in systolic and diastolic blood pressure during physical activity. It also addresses baroreceptor function and differences between arm and leg exercises. Test your understanding of these crucial physiological responses!