General Pathophysiology – Circulatory Function

Normal Function of the Heart

• Cardiac Output: The amount of blood the heart pumps into the aorta during one ventricular contraction. Normal value is 60 ml.

• Cardiac Output: The volume of blood pumped by the left ventricle into the aorta in one minute.

Cardiac output = Cardiac work x Heart rate

Cardiac Work

• Contractile work: Opening of the heart valves.

• Work of ejection: Pushing blood out of the heart during systole.

• Wasted work: Overcoming friction and resistance to blood flow.

Blood Pressure

• Blood Pressure Formula: Blood pressure P = Cardiac output CO x Peripheral resistance R.

Factors Affecting Blood Pressure and Cardiac Output

• Venous Return: The amount of blood returning from the venous system to the right heart.

• When venous return is high, CO increases.

• When there is venous stasis, CO decreases.

• Contractility of the Heart: The stronger the contraction, the more blood is ejected.

Factors Affecting Blood Pressure – Peripheral Resistance

• Blood Viscosity:

• Increase in red blood cells → Increase in blood pressure.

• Decrease in red blood cells → Decrease in blood pressure.

• Elasticity of the Vessel Walls:

• Vasoconstriction, arteriosclerosis → Increase in resistance.

• Vasodilation → Decrease in resistance.

Heart Failure

• Definition: A pathophysiological state in which the heart’s function is abnormal, and the heart is unable to pump blood out of the heart adequately to meet the body’s needs.

Causes of Heart Failure

• Diseases that decrease circulatory output → The heart works harder to meet oxygen demands, gradually leading to heart failure.

• Diseases that increase the workload of the heart → Heart failure.

Cardiac Hypertrophy in Heart Failure

• Basic compensatory mechanism when workload increases.

• Insufficient blood supply to the heart muscle causes angina.

Increased Sympathetic Nervous System Activity in Heart Failure

• Consequences:

• Increased heart rate.

• Increased heart contractility.

• Peripheral vasoconstriction.

• Tachycardia, cold skin, sweating.

Increased Blood Volume in Heart Failure

• Consequences:

• Heart failure → Decreased blood flow to the kidneys → Increased renin secretion → Increased aldosterone secretion causing retention of salt and water → Increased blood volume.

• Increased left atrial and right atrial pressure, leading to pulmonary congestion causing dyspnea.

Decreased Circulation Rate in Heart Failure

• Consequences:

• When the heart fails, contractility decreases, blood flow slows down, especially in the venous system.

• Pulmonary congestion in left heart failure.

• Venous congestion in right heart failure.

Blood Pressure Changes in Heart Failure

• Decreased Arterial Blood Pressure: Due to decreased cardiac output.

• Increased Venous Blood Pressure: Due to decreased heart contractility causing blood stasis.

Left Heart Failure

• Dyspnea: Poor left ventricular contraction → Increased pressure in the left atrium, pulmonary veins, and pulmonary capillaries → Pulmonary congestion.

• Dyspnea on exertion, orthopnea.

• Acute Pulmonary Edema: Pulmonary congestion, hydrostatic pressure exceeds oncotic pressure → Plasma and red blood cells leak into the alveoli, preventing gas exchange → Death due to hypoxia.

• Pink frothy sputum, crackles rising from the lung bases.

Right Heart Failure

• Consequences:

• Liver dysfunction: Congestion causes hepatomegaly and pain. Prolonged congestion leads to liver cell hypoxia, fatty degeneration, and necrosis.

• Decreased urine output: Decreased blood flow to the kidneys, reducing glomerular filtration rate.

• Edema:

• Increased hydrostatic pressure (blood stasis).

• Decreased oncotic pressure.

• Increased capillary permeability.

• Retention of water and salt.

Hypertension

• Definition: Blood pressure reaches a level at which the patient is at high risk of damage to target organs (eyes, brain, heart, kidneys, and major arteries).

• Normal blood pressure in adults: 140/90 mmHg.

• Hypertension: Systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg.

Symptoms of Hypertension

• Due to the heart compensating for the excessive workload caused by hypertension → Left ventricular hypertrophy, thickened walls → Eventually left ventricular function is impaired, dilation occurs → Symptoms of heart failure appear.

• Most deaths are caused by myocardial infarction or congestive heart failure.

Causes of Hypertension

• Renal Artery Stenosis: Poor blood flow to the kidneys, the juxtaglomerular apparatus secretes renin.

• Kidney Parenchymal Damage: In acute glomerulonephritis, hypertension is caused by increased circulating blood volume → Increased cardiac output.

• Lipid Metabolism Disorders:

• Elderly people due to lipid metabolism disorders lead to atherosclerosis, narrowing of blood vessels → Increased resistance → Hypertension.

• Blood vessel damage and thrombus formation are the two main pathophysiological factors in the formation and progression of atherosclerosis.

• Mechanism: Increased cholesterol, diabetes, abnormal LDL receptor.

• Atherosclerosis is the main cause of coronary artery disease and cerebrovascular disease.

• Endocrine Disorders:

• Adrenal medulla tumor: Contains large amounts of epinephrine and norepinephrine, causing episodic or persistent hypertension.

• Adrenal cortex tumor (Conn’s syndrome): More common. Tumor secretes increased aldosterone → Water and salt retention → Increased cardiac output → Hypertension.

• Cushing’s syndrome: Increased ACTH → Increased desoxycorticosterone → Increased water and salt retention.

• Pathogenesis of Essential Hypertension:

• Under the influence of stimuli (fear, anxiety, psychological trauma,…) → The intensity exceeds the limit of the cerebral cortex → The cerebral cortex enters a state of inhibition → The subcortical region generates chaotic excitation → Disorder of organ function, especially causing vasoconstriction, leading to hypertension.

• Vasoconstriction reduces blood flow to the kidneys, activating the RAA system, further increasing blood pressure.