lecture 8 Cardiac Performance Basics
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Questions and Answers

What physiological change is primarily responsible for postural hypotension when moving from lying to standing?

  • Decreased sympathetic activity
  • Increased cardiac output
  • Increased venous return
  • Shift of blood from thoracic cavity to lower extremities (correct)

    • Which mechanism compensates almost immediately for the decrease in blood pressure during postural hypotension?

  • Atrial natriuretic peptide release
  • Antidiuretic hormone secretion
  • Baroreceptor reflex (correct)
  • Atrial volume receptor reflex

    • What role does atrial natriuretic peptide (ANP) play in blood pressure regulation?

  • Decreases sodium excretion
  • Increases sodium excretion (correct)
  • Promotes vasoconstriction
  • Increases sodium retention

    • What effect does the release of renin have on blood pressure?

    <p>Increases synthesis of angiotensin II</p> Signup and view all the answers

    Which component of the autonomic nervous system is activated to counteract low blood pressure as a response to decreased baroreceptor firing?

    <p>Increased sympathetic activity</p> Signup and view all the answers

    What primarily influences vascular resistance in the body?

    <p>Arteriolar diameter</p> Signup and view all the answers

    Which mechanism helps to regulate blood flow specifically to critical organs?

    <p>Autoregulation</p> Signup and view all the answers

    Which of the following substances primarily causes vasodilatory effects during parasympathetic stimulation?

    <p>Nitric oxide</p> Signup and view all the answers

    What is the primary function of baroreceptors in the cardiovascular system?

    <p>Sensing stretching of arterial walls</p> Signup and view all the answers

    Which factor is least effective in influencing cardiac output?

    <p>Total peripheral resistance</p> Signup and view all the answers

    How does metabolic regulation affect blood vessel diameter?

    <p>Increases with higher levels of NO</p> Signup and view all the answers

    What happens to venous pressure when blood enters the venous system?

    <p>It remains constant at 10 mm Hg</p> Signup and view all the answers

    Which of the following statements about arterioles is true?

    <p>Their contraction can alter blood flow significantly.</p> Signup and view all the answers

    What physiological change assists venous blood flow back to the heart during inspiration?

    <p>Decreased thoracic pressure</p> Signup and view all the answers

    Which factor is NOT a role of the cardiovascular (vasomotor) center in the medulla oblongata?

    <p>Monitoring blood pH levels</p> Signup and view all the answers

    What is the primary determinant of preload in cardiac performance?

    <p>Venous return</p> Signup and view all the answers

    Which phase of the cardiac cycle includes both atrial contraction and ventricular filling?

    <p>Refilling</p> Signup and view all the answers

    How does increasing end-diastolic volume (EDV) affect stroke volume (SV)?

    <p>It increases stroke volume</p> Signup and view all the answers

    What effect does higher arterial resistance have on blood pressure during systole?

    <p>It increases blood pressure</p> Signup and view all the answers

    What primarily influences the afterload during rest?

    <p>Total Peripheral Resistance (TPR)</p> Signup and view all the answers

    What happens to blood flow during aortic valve closure?

    <p>Flow stops temporarily from the ventricle</p> Signup and view all the answers

    Which of the following factors does NOT directly affect preload?

    <p>Contractility of the heart</p> Signup and view all the answers

    In which phase of the cardiac cycle does ventricular contraction occur?

    <p>Ventricular contraction</p> Signup and view all the answers

    What is the primary factor that reduces resistance to blood flow in a vessel?

    <p>Radius of the vessel</p> Signup and view all the answers

    What role does the sympathetic nervous system play in cardiovascular regulation?

    <p>Increases heart rate and contractility</p> Signup and view all the answers

    What outcome results from an increase in blood volume?

    <p>Increased venous return</p> Signup and view all the answers

    What is the term for the difference between systolic and diastolic pressure?

    <p>Pulse pressure</p> Signup and view all the answers

    Which mechanism assists in promoting venous return during inspiration?

    <p>Decrease in abdominal cavity pressure</p> Signup and view all the answers

    Cardiac output is calculated by multiplying heart rate and which other factor?

    <p>Stroke volume</p> Signup and view all the answers

    Which of the following statements correctly describes the function of baroreceptors?

    <p>They sense stretching of the arterial wall.</p> Signup and view all the answers

    What is primarily influenced by myogenic tone in arterioles?

    <p>Resistance to blood flow</p> Signup and view all the answers

    What role does metabolic regulation play in blood vessel function?

    <p>It increases vessel diameter in response to heightened metabolic activity.</p> Signup and view all the answers

    How do extrinsic control factors primarily affect vascular resistance?

    <p>By impacting sympathetic nerve stimulation on adrenergic receptors.</p> Signup and view all the answers

    What happens to blood flow when venous pressure is too high?

    <p>Fluid leaks out, leading to edema.</p> Signup and view all the answers

    Which factor does NOT serve as an influence on total peripheral resistance (TPR)?

    <p>Heart rate</p> Signup and view all the answers

    Which of the following best describes the role of the cardiovascular center in the brain?

    <p>It integrates sensory input and manages both heart and vascular function.</p> Signup and view all the answers

    What is the primary physiological response when arterial pressure stretches baroreceptors?

    <p>Increased frequency of action potentials</p> Signup and view all the answers

    Why is autoregulation considered a protective mechanism in critical organs?

    <p>It ensures constant blood flow despite systemic pressure changes.</p> Signup and view all the answers

    Which of the following correctly describes the influence of vascular resistance on blood pressure?

    <p>Higher resistance typically results in higher blood pressure.</p> Signup and view all the answers

    What is the relationship between end-diastolic volume (EDV) and stroke volume (SV)?

    <p>An increase in EDV increases stroke volume.</p> Signup and view all the answers

    What primarily determines afterload in the cardiovascular system?

    <p>The vascular resistance during blood ejection.</p> Signup and view all the answers

    Which factor does NOT influence venous return?

    <p>Diameter of arterioles.</p> Signup and view all the answers

    During which phase of the cardiac cycle does isovolumic contraction occur?

    <p>Ventricular contraction.</p> Signup and view all the answers

    What accounts for the changes in arterial pressure during a cardiac cycle?

    <p>Elasticity of arteries absorbing pulsatile flow.</p> Signup and view all the answers

    Which statement correctly describes the determinants of cardiac output?

    <p>Cardiac output is the product of heart rate and stroke volume.</p> Signup and view all the answers

    How does total peripheral resistance (TPR) affect blood pressure?

    <p>Increased TPR increases blood pressure.</p> Signup and view all the answers

    Which mechanism assists in maintaining adequate arterial pressure during inspiration?

    <p>Contraction of diaphragm causing increased pressure in veins.</p> Signup and view all the answers

    What is the effect of the sympathetic nervous system on heart rate?

    <p>Increases heart rate by enhancing the intrinsic rhythm.</p> Signup and view all the answers

    Which factor influences blood flow resistance the most?

    <p>Radius of the blood vessel.</p> Signup and view all the answers

    What term describes the pressure difference between systolic and diastolic pressures?

    <p>Pulse pressure.</p> Signup and view all the answers

    Which condition occurs if the cardiac output increases while afterload decreases?

    <p>Increased stroke volume.</p> Signup and view all the answers

    What is the contribution of baroreceptor reflexes to cardiovascular regulation?

    <p>They regulate blood pressure changes.</p> Signup and view all the answers

    During which phase of the heart's cycle does blood refill the ventricles?

    <p>Refilling phase.</p> Signup and view all the answers

    What is the primary result of a change from a lying to a standing position in terms of blood distribution?

    <p>Shift of 500-700 ml of blood to lower extremities</p> Signup and view all the answers

    What immediate physiological response occurs due to decreased baroreceptor firing?

    <p>Increased heart rate and vasoconstriction</p> Signup and view all the answers

    Which hormone is responsible for increasing sodium excretion in response to high blood volume?

    <p>Atrial natriuretic peptide (ANP)</p> Signup and view all the answers

    What effect does renin have on blood pressure regulation?

    <p>Enhances the secretion of aldosterone</p> Signup and view all the answers

    What mechanism regulates blood volume through neural input and hormone secretion in response to atrial stretch?

    <p>Atrial volume receptor reflex</p> Signup and view all the answers

    Study Notes

    Cardiac Performance

    • Cardiac Output (CO) is the amount of blood the heart pumps per minute.
    • CO is calculated by multiplying Heart Rate (HR) by Stroke Volume (SV).
    • CO = HR x SV
    • HR can be influenced by sympathetic and parasympathetic nervous systems, as well as adrenal medulla.
    • SV is the amount of blood ejected by the ventricle during each contraction.
    • SV is determined by preload (EDV) and afterload (ESV).
    • EDV is the volume of blood in the ventricle at the end of diastole (relaxation).
    • ESV is the volume of blood remaining in the ventricle after systole (contraction).
    • Frank-Starling Law of the Heart: Increased preload leads to increased contractility and increased SV.

    Preload (EDV)

    • Venous return is the primary factor impacting EDV.
    • Increased venous return increases EDV.
    • Decreased venous return decreases EDV.
    • Venous return is influenced by:
      • Skeletal muscle pump: Muscle contractions squeeze blood through veins, pushing it towards the heart.
      • Respiratory pump: During inspiration, abdominal pressure increases and thoracic pressure decreases, promoting venous return.
      • Blood volume: Increased blood volume leads to increased venous return.
      • Autonomic nervous system: Sympathetic stimulation causes vasoconstriction in veins, increasing pressure and venous return.

    Afterload (ESV)

    • Afterload is the resistance the ventricles encounter during ejection.
    • During exercise, afterload is indirectly controlled by heart contractility.
    • During rest, afterload is primarily determined by arterial vasomotor tone (Total Peripheral Resistance - TPR).
    • Blood pressure is a surrogate indicator of afterload.
    • BP = CO x Arterial Resistance

    Blood Vessels and Blood Pressure

    • Blood vessel diameter, elasticity, and contractility are important factors influencing pressure and flow.
    • Flow (Q) = Pressure Difference (P) / Resistance (R)
    • Arterioles are the “bottlenecks” of the circulation, controlling pressure and flow due to significant smooth muscle content.

    Arterial Blood Pressure

    • Arterial pressure fluctuates between systolic and diastolic pressure.
    • Systolic pressure is the peak pressure during ventricular contraction.
    • Diastolic pressure is the minimum pressure during ventricular relaxation.
    • Mean Blood Pressure (MBP) is the average pressure over a cardiac cycle.
    • Pulse Pressure is the difference between systolic and diastolic pressure.

    Factors Influencing Arterial Pressure

    • Elasticity of the artery: Low elasticity leads to high pressure.
    • Cardiac output: Higher CO leads to increased pressure.
    • Respiration: Inspiration lowers thoracic pressure and increases abdominal pressure, promoting venous return. Expiration reverses these effects.
    • Resistance to blood flow (TPR): TPR, determined by vasoconstriction of arterioles, significantly influences blood pressure. Increased TPR leads to increased pressure.
    • Blood volume: Influences CO, but has a minimal effect on blood pressure due to veins absorbing the major impact.

    Control of Arteriolar Diameter

    • Myogenic tone: A basal level of constriction in arterioles, allowing for vasoconstriction and dilation to regulate resistance.
    • Autoregulation (local): Regulates blood flow within organs/tissues, overriding extrinsic control.
      • Metabolic regulation: Responds to changes in metabolic demands, increasing diameter in response to increased CO2, decreased pH, increased K+, and increased NO.
      • Myogenic (pressure) autoregulation: Vessels respond to changes in pressure, maintaining blood supply even with pressure changes.

    Extrinsic Regulation of Blood Pressure

    • Regulates peripheral pressure as a whole.
    • Vasoconstrictive influences:
      • Sympathetic stimulation: Activates α-adrenergic receptors, causing constriction.
      • Angiotensin II: Increases vasoconstriction.
      • Arginine vasopressin (AVP): Promotes vasoconstriction.
    • Vasodilatory influences:
      • Parasympathetic stimulation: Primarily in penis and clitoris.

    Veins and Venous Pressure

    • Venous pressure is low, around 10 mm Hg.
    • Heart acts as a pump, pulling blood upward.
    • Venous smooth muscle contributes to pressure regulation.
    • Excessive pressure in veins can lead to edema (fluid accumulation in tissues).

    Blood Pressure Control

    • Baroreceptor reflex: A critical mechanism for maintaining blood pressure.
      • Baroreceptors: Stretch receptors in aortic arch and carotid sinus, sense changes in arterial wall stretching.
      • Sensory fibers: Transmit signals via the vagus nerve, increasing APs frequency with increased stretch.
      • Integration center: Cardiovascular center in the medulla oblongata, compares sensory information to reference values.
      • Motor fibers: Autonomic nervous system, modulating heart rate and vasoconstriction.
      • Effectors: Heart (rate and SV) and arterioles/veins (TPR).
    • Postural hypotension: A decrease in blood pressure upon standing due to blood pooling in lower extremities. The baroreceptor reflex compensates by increasing heart rate and vasoconstriction.

    Other Blood Pressure Control Mechanisms

    • Atrial volume receptor reflex:
      • Stretch receptors in atrial walls sense changes in blood volume.
      • Regulates blood volume via the autonomic nervous system and hormone secretion (affecting sodium and water handling in kidneys).
    • Hormones:
      • Atrial natriuretic peptide (ANP): Increases sodium excretion.
      • Renin: From kidneys, activates angiotensin II and aldosterone.
        • Angiotensin II: Vasoconstriction.
        • Aldosterone: Decreases sodium excretion.
      • Antidiuretic hormone (ADH) or vasopressin: Decreases water excretion.

    Cardiac Performance

    • Cardiac Output (CO) is the amount of blood pumped by the heart per minute.
    • CO is determined by the heart rate (HR) and stroke volume (SV).
    • CO = HR x SV
    • The autonomic nervous system modulates HR. Increased sympathetic activity increases HR, while increased parasympathetic activity decreases HR.
    • SV is the volume of blood ejected from the ventricle with each contraction. It is determined by preload and afterload.
    • Preload: the volume of blood present in the ventricles at the end of diastole. It is influenced by venous return, which is dependent on factors like the skeletal muscle pump, respiratory activity, and blood volume. Increased preload results in increased SV due to the Frank-Starling Law of the Heart, which states that increased stretch of cardiac muscle fibers at the end of diastole enhances contractility.
    • Afterload: the resistance the ventricles encounter during ejection. It is primarily determined by arterial vasomotor tone, which is a measure of the total peripheral resistance (TPR). Factors that affect afterload include sympathetic stimulation (which increases contractility and decreases ESV), and increased arterial resistance (which increases TPR).
    • Blood pressure (BP) is a surrogate measure of afterload. It is calculated as BP = cardiac output x arterial resistance.

    Blood Vessels & Blood Pressure

    • Arterioles are considered the “bottlenecks” of circulation, with a larger number of smooth muscle fibers making them the main site of pressure/flow regulation in the body.
    • Blood flow (Q) is determined by the pressure difference (ΔP) between two points and the resistance (R) to fluid flow.
    • Q = ΔP / R
    • The initial pressure in arteries is generated from the heart contraction. Pressure progressively decreases as blood flows through the circulatory system.
    • Arterial pressure changes throughout the cardiac cycle:
      • During ventricular contraction, the aortic valve opens resulting in rapid blood flow, increased arterial pressure and some pressure absorption by the aorta.
      • During diastole, the aortic valve closes, there is no blood flow from the ventricle, and energy stored during the aorta’s stretch is released, allowing for continuous blood flow.
    • Mean blood pressure (MBP) is a measurement of the average pressure in the arteries. It is closer to diastolic pressure during rest, and closer to systolic pressure during exercise.
    • The difference between systolic and diastolic pressure is the pulse pressure, which is a measure of pressure exerted by the heart on the artery wall during systole.

    Control of Vascular Resistance

    • Arterioles have a basal level of constriction called the "myogenic tone." This tone provides a mechanism for increasing and decreasing vascular contraction and diameter.
    • Vasomotor tone is controlled by:
      • Autoregulation: a local mechanism that controls flow to critical organs, such as the heart, brain, liver, kidneys, and working skeletal muscles.
        • Metabolic autoregulation: responds to changes in metabolism, thus blood requirement. Increase in CO2, decrease in pH, increase in K+, and increase in NO all result in vasodilation.
        • Myogenic (pressure) autoregulation: vessels respond to changes in tone or stretch to maintain blood supply even when pressure changes.
      • Extrinsic control factor (neuro-hormonal): regulates the peripheral pressure as a whole.
        • Vasoconstrictive influences: sympathetic stimulation on α-adrenergic receptors, angiotensin II, and arginin vasopressin.
        • Vasodilatory influences: parasympathetic stimulation (vagus nerve, mainly in penis and clitoris).

    Control of Blood Pressure

    • Blood pressure is regulated by the baroreceptor reflex, a negative feedback loop.
    • Baroreceptors: Stretch receptors located in the aortic arch and carotid sinus that sense stretching of the artery wall.
    • Sensory fibers: Transmit information about stretching to the cardiovascular (vasomotor) center in the medulla oblongata via the vagus nerve. Increase in stretch results in an increase in APs frequency, while decrease in stretch results in decrease in APs frequency.
    • Integration center: The cardiovascular center compares the information to a reference value and sends appropriate signals to the effectors.
    • Motor fibers: Consists of the autonomic nervous system (both branches - sympathetic and parasympathetic).
    • Effectors: Heart (modifies rate and stroke volume, thus cardiac output) and arterioles and veins (modifies TPR).
    • Postural hypotension: the drop in BP that occurs when moving from a lying to standing position. It occurs due to the shift of blood from the thoracic cavity to the lower extremities resulting in decreased venous return and decreased BP. The baroreceptor reflex compensates for postural hypotension by decreasing parasympathetic activity (increasing heart rate) and increasing sympathetic activity (increasing heart rate, stroke volume, and vasoconstriction).

    Other BP Control Mechanisms

    • Atrial volume receptor reflex: Stretch receptors in the wall of atria sense volume changes and control blood volume via autonomic nervous system activity (similar to baroreflex responses) and neural input to the hypothalamus regulating thirst and hormone secretion that influences renal handling of sodium and water.
    • Hormones:
      • Atrial natriuretic peptide (ANP): synthesized in the atrial wall and increases sodium excretion.
      • Renin: synthesized in the kidney and increases the synthesis of angiotensin II and aldosterone.
        • Angiotensin II: vasoconstriction.
        • Aldosterone: decreases sodium excretion.
      • Antidiuretic hormone (ADH) / Vasopressin: synthesized in the posterior pituitary and decreases water excretion in the kidneys.

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    Description

    This quiz covers fundamental concepts of cardiac performance, including cardiac output, heart rate, stroke volume, and the factors affecting them. It also highlights the importance of preload and the Frank-Starling law of the heart. Test your knowledge on how the heart functions and the factors influencing its efficiency.

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