8-Cardiovascular System, Part-2 (Nursing, 11-2024) PDF

Physiology of Cardiovascular System (Part-2) Introductory Case A 77-year-old female. Palpitations & headache for previous 3 weeks. Blood pressure 180/100. Learning Objectives At the end of this lecture, you should be able to: Define cardiac output & explain its regulation. Define arter...

Physiology of Cardiovascular System (Part-2) Introductory Case A 77-year-old female. Palpitations & headache for previous 3 weeks. Blood pressure 180/100. Learning Objectives At the end of this lecture, you should be able to: Define cardiac output & explain its regulation. Define arterial blood pressure and describe its physiological variations. List 4 factors determine arterial blood pressure. Clarify regulation of arterial blood pressure. Describe factors affecting tissue fluid formation. Define edema & list its causes. Cardiac Output  Cardiac Output (COP) Definition Normal value Equation (In adult male) Volume of blood pumped by each ventricle per minute 5 L/min COP = Stroke Volume X Heart Rate Regulation  Important Definitions Stroke volume (SV) End diastolic End systolic volume (EDV) volume (ESV) Definition Normal value Definition Normal value Volume of blood 70 ml Definition Normal pumped by each Volume of blood 135 ml value ventricle per beat remained inside the ventricle at end of Volume of blood diastole remained inside the 65 ml ventricle at end of SV = EDV - ESV = 135 - 65 = 70 ml. systole  Regulation of Cardiac Output [COP= SV x HR= (EDV-ESV) x HR] (1) (2) (3) Effect of cardiac Effect of changes in Effect of venous return contractility & SV heart rate (HR) (VR, preload, EDV) I-Intrinsic regulation (autoregulation): ↑VR → ↑ COP by ↑ HR It occurs also in transplanted or Marked ↑ in HR (>160 & force of contraction. denervated heart. beat/min) or marked ↓ in Factors ↑ VR: It does not depend on either HR ( with age due to Less stress & (7) Respiration loss of elasticity cholesterol in ↑ Systolic ABP of arteries Due to diet & ↓diastolic Small fluctuations hormonal ABP of ABP changes Figure-2: Effect of gravity on arterial blood pressure.  Factors That Determine ABP & Pulse Pressure (ABP = COP X TPR = SV X HR X TPR) (1) (2) (3) (4) Stroke Heart rate Total peripheral Elasticity of volume (SV) (HR) resistance (TPR) aorta & arteries ↑ SBP > DBP ↑ DBP Atherosclerosis → ↑ DBP > SBP. It depends on diameter ↑ SBP & ↓ DBP of blood vessels. SBP= systolic blood pressure, DBP= diastolic blood pressure Big pulse pressure  Regulation of Arterial Blood Pressure (ABP) Nervous mechanism Capillary Fluid Role of Kidney (Rapid) (Hormonal regulation Shift mechanism of ABP, Slow) (Intermediate) ↓ABP ↑ ABP Kidney regulates ABP by regulating ↑ Sympathetic ↑ Parasympathetic plasma volume & extracellular fluid Vasoconstriction. volume. Vasodilatation. ↑ SV. It is the most important mechanism ↓ HR. ↑ HR. for ABP regulation. ↓ ABP ↑ ABP  Capillary Fluid Shift Mechanism (Intermediate ABP Regulation) ↑ Blood volume ↓ Blood volume ↑ ABP ↓ ABP ↑ Capillary hydrostatic pressure ↓ Capillary hydrostatic pressure ↑ Filtration of fluid from ↓ Filtration of fluid at arteriolar end of plasma to the tissue fluid capillaries & ↑ reabsorption at venular end ↓ Plasma volume ↑ Plasma volume ↓ ABP ↑ ABP Figure-3: Capillary fluid shift mechanism. Figure-4: Capillary fluid shift mechanism.  Role of Kidney in Regulation of ABP When it is Decreased (Hormonal regulation of ABP) ↑ Secretion of antidiuretic Stimulation of renin - hormone (ADH) & angiotensin system aldosterone hormones ↑ Renin release & Salt & H2O retention increasing angiotensin II formation extracellular fluid volume ↑ Venous return, COP & ABP  Renin is secreted from the kidney. Angiotensinogen is formed by the liver. Angiotensin converting enzyme (ACE) is secreted by the blood vessels of the lungs. Figure-5: Renin-angiotensin system. Capillary Circulation  Exchange of Materials Across Capillary Wall (Function of blood capillaries) Function Mechanism Maintains equilibrium Filtration Diffusion between the blood & (Bulk flow) interstitial fluids  Diffusion Characters Factors affecting diffusion rate Passive. (A) (B) Occurs in both directions. In substance In capillary wall permeability Concerned with H2O & dissolved substances. Concentration difference: direct. Liver capillaries: high permeability. Solubility: H2O soluble or lipid Muscle, skin, heart & lung soluble. capillaries: low permeability. Molecular weight: inverse. Kidney & intestine capillaries: moderate permeability.  Filtration (Bulk Flow) Across Capillary Wall Characters Factors affecting tissue fluid formation (A) (B) Passive. Occurs in one direction. Main forces tending to Main forces tending It is the bulk transport move fluid outwards to move fluid inwards of H2O & electrolytes. Hydrostatic capillary pressure (at Colloidal osmotic pressure of arterial end= 37 mmHg & at plasma proteins (25 mmHg). venous end 17 mmHg). Hydrostatic pressure of Interstitial fluid colloidal osmotic interstitial fluid (1 mmHg). pressure (0 mmHg).  Summation of Main Forces Affecting Filtration At arteriolar end At venular end 11 mmHg outwards [37-(25+1)]. 9 mmHg inwards [(25+1)- 17]. Filtration of fluid from blood to Reabsorption of a nearly equal the interstitial fluid as a bulk. amount of fluid into blood (the remaining is taken by lymphatics) Figure-6: Bulk flow. Pc=capillary hydrostatic pressure c=capillary osmotic pressure Pi = hydrostatic tissue pressure Figure-7: Capillary filtration, reabsorption & lymph flow.  Edema Definition Causes Effect (1) (2) (3) (4) (5) (6) (7) Cardiac Hepatic Accumulation of ↑Capillary Pregnancy fluid in Excess permeability Due to ↓ Due to compression of formation of It is very dangerous e.g., allergy veins of the lower limbs plasma proteins if it occurs in brain by pregnant uterus or lung Nutritional Renal Lymphatic e.g., in heart failure due to obstruction ↑ venous pressure → more Due to ↑ loss of Due to ↓ intake fluids leave capillaries to plasma proteins of proteins tissues Figure-8: Causes of edema. Summary At the end of this lecture, you should be able to: Define cardiac output & explain its regulation. Define arterial blood pressure and describe its physiological variations. List 4 factors determine arterial blood pressure. Clarify regulation of arterial blood pressure. Describe factors affecting tissue fluid formation. Define edema & list its causes. Examples of Self-Assessment Questions Single Best Answer (SBAs) 1-If end diastolic volume is 140 ml, end systolic volume is 70 ml and heart rate is 70 beats/min, which of the following represents cardiac output? 4.9 L/minute. 5.2 L/minute. 5.8 L/minute. 6.3 L/minute. 2-A 20-year-old male has a blood pressure of 130/60. Which one of the following values represents his pulse pressure? 190 mm Hg. 100 mmHg. 70 mmHg. 40 mmHg. 3-In newborn, the blood pressure is represented by which of the following values normally? 40/20 mmHg. 80/40 mmHg. 120/80 mmHg. 160/120 mmHg. 4-A 20-year-old male has a blood pressure of 130/60. Which one of the following values represents his diastolic blood pressure? 190 mm Hg. 130 mmHg. 70 mmHg. 60 mmHg. 5-Arterial blood pressure (ABP) is calculated from which of the following equations? ABP= Systolic blood pressure- diastolic blood pressure ABP= Diastolic blood pressure- 1/3 pulse pressure ABP= Cardiac output x heart rate ABP= Cardiac output x total peripheral resistance 6-Renin is secreted from which organ? Brain. Heart. Kidney. Liver. 7-Angiotensin II increases secretion of which hormone? Aldosterone. Glucagon. Insulin. Somatostatin. 8-Capillary wall permeability is high in which structure? Brain. Kidney. Liver. Stomach. 9-Which one of the following organs secretes angiotensinogen? Brain. Heart. Kidney. Liver. 10-Which one of the following organs is excluded to be required in the steps of formation of angiotensin II? Heart. Kidney. Lung. Liver. 11-Which one of the following values is the colloidal osmotic pressure of plasma proteins? 10 mmHg. 25 mmHg. 37 mmHg. 44 mmHg. 12-Which one of the following values represents the normal cardiac output in a normal adult male? 5 L/min. 4 L/min. 3 L/min. 2 L/min. 13-Which one of the following equations used to calculate cardiac output? Cardiac output= stroke volume x peripheral resistance. Cardiac output= stroke volume + peripheral resistance. Cardiac output= stroke volume x heart rate. Cardiac output= stroke volume + heart rate. 14-Which of the following represents volume of blood pumped by each ventricle per beat? Cardiac output. Stroke volume. End diastolic volume. End systolic volume. 15-Which of the following represents volume of blood remained inside the ventricle at the end of systole? Cardiac output. Stroke volume. End diastolic volume. End systolic volume. 16-Which of the following represents volume of blood remained inside the ventricle at the end of diastole? Cardiac output. Stroke volume. End diastolic volume. End systolic volume. 17-Regulation of cardiac output in transplanted heart occurs by which mechanism? Hormones. Autoregulation. Sympathetic nervous system. Parasympathetic nervous system. 18-Which of the following increases venous return? Decreased blood volume. Relaxation of muscle. Venoconstriction. Expiration. 19-Which of the following is a feature of arterial blood pressure? Decreases with age. Orientals have higher pressure than Europeans. Parasympathetic nervous system increases systolic blood pressure. Each 1 cm below heart increases arterial blood pressure by 0.77 mmHg. 20-Which blood capillaries have low permeability? Liver capillaries. Skin capillaries. Kidney capillaries. Intestine capillaries. 21-Edema is caused by which of the following? Lymphatic obstruction. Decreased capillary permeability. Increased capillary oncotic pressure. Decreased capillary hydrostatic pressure. 22-Hepatic edema is caused by which of the following? Increased venous pressure. Decreased formation of plasma proteins. Increased loss of plasma proteins. Compression of veins of lower limbs. 23-True (T) or false (F): Arterial blood pressure is higher in young adult male than that in young adult female during childbearing period. Normally, colloidal osmotic pressure of plasma proteins is 47 mmHg. At venous end of capillary, there is filtration of fluid from blood to the interstitial fluid as a bulk. Stroke volume (SV) = End systolic volume (ESV) – End diastolic volume (EDV). Cardiac output is volume of blood pumped by each ventricle per minute. Parasympathetic nervous system has a negative chronotropic effect. Thyroxine decreases cardiac output. Marked increase in heart rate decreases cardiac output. Normal systolic blood pressure in adult male is 180 mmHg. Arterial blood pressure (ABP) = cardiac output (COP) x peripheral resistance. Capillary fluid shift mechanism is an intermediate regulation of arterial blood pressure. Angiotensin converting enzyme (ACE) is secreted by the blood vessels of the liver. Sympathetic stimulation decreases arterial blood pressure. Kidney is important for slow regulation of blood pressure. Normal end diastolic volume is 140 ml. Pulse pressure is 100 mmHg when arterial blood pressure is 180/80. Angiotensin II decreases secretion of antidiuretic hormone (ADH). Diffusion of water across capillary wall occurs in both directions. Capillary hydrostatic pressure decreases tissue fluid formation. Kidney edema occurs due to increased loss of plasma proteins. Answer Key SBAs SBAs Answer Key: 1-A. 2-C. 3-B. 4-D. 5-D. 6-C. 7-A. 8-C. 9-D. 10-A. 11-B. 12-A. 13-C. 14-B. 15-D. 16-C. 17-B. 18-C. 19-D. 20-B. 21-A. 22-B. Case Discussion A 77-year-old female. Palpitations & headache for previous 3 weeks. Blood pressure 180/100. References