Cardiovascular System Physiology PDF

# Cardiovascular System ## Physiology ### Structure of the heart * The heart consists of four chambers: * Two upper chambers (atria) * Two lower chambers (ventricles) * The heart also has four valves that open and close to let blood flow in only one direction when the heart beats. * The f...

# Cardiovascular System ## Physiology ### Structure of the heart * The heart consists of four chambers: * Two upper chambers (atria) * Two lower chambers (ventricles) * The heart also has four valves that open and close to let blood flow in only one direction when the heart beats. * The four heart valves are: * **Tricuspid Valve:** Located between the right atrium and right ventricle. * **Pulmonary Valve:** Between the right ventricle and the pulmonary artery. * **Mitral Valve:** Between the left atrium and left ventricle. * **Aortic Valve:** Between the left ventricle and the aorta. * Blood flow occurs only when there's a difference in pressure across the valves, which causes them to open. Under normal conditions, the valves permit blood to flow in only one direction. ## Important Definitions: | Term | Definition | |:---:|:---:| | **Preload** | The load on the cardiac muscle at the end of diastole (at the end of the relaxation phase) | | **Afterload** | The load on the cardiac muscle at the end of systole | | **Cardiac Output** | The amount of blood pumped from the heart per unit time | | **Stroke Volume** | The volume of blood ejected from the heart in each beat | | **Heart Rate** | The number of heart beats per unit time | | **Positive Inotropy** | Increased heart force of contraction | | **Positive Chonotropy** | Increased heart rate | | **Positive Dromotropy** | Increased conduction velocity between the auricle and ventricle | | **Stroke Volume** | Volume of blood pumped from the heart in each beat | | **Heart Rate** | Number of heart beats per minute | | **Pre-load on the Cardiac Muscles** | Load on the Cardiac muscles at the end of diastole | | **After-load on the Cardiac Muscles** | Load on the cardiac muscles at the end of systole | | **Cardiac Output** | Amount of blood pumped from the heart per unit time | ## Hypertension * Hypertension means elevated blood pressure to a degree high enough to perfuse tissues and organs. * Blood pressure is considered high when its systolic reading exceeds **140 mmHg** and diastolic reading exceeds **90 mmHg.** * Normal blood pressure is blood pressure which is not exceeding **120/80 mmHg.** * Pre-hypertension is considered in patients with blood pressure not exceeding **140/90 mmHg.** * **Stage 1 Hypertension** is not exceeding **160/100 mmHg.** * **Stage 2 Hypertension** is exceeding **160/100 mmHg** ### Hypertension is the most common cardiovascular disorder. * Incidence of hypertension is highly associated with age (about 60-70 % of persons exceeding 60 years of age have hypertension). * The usual incidence of hypertension is between 30 and 50 years of age. ### Elevated untreated hypertension is associated with higher incidence of: * Myocardial infarction * Stroke * Heart failure * Retinal damage * Cerebrovascular bleeding * Headache * Neurological symptoms * Kidney Disease ### Cardiovascular Findings * Angina pain (due to insufficient blood supply to the constricted coronary vasculature) * Left ventricular hypertrophy * Dyspnea (due to increased preload and afterload causing heart failure) * Peripheral edema (due to increased aldosterone secretion) ### Neurological Findings * Severe occipital headache with nausea, vomiting, drowsiness, anxiety, mental impairment, and stroke. * These are caused by vessel damage within the brain (due to weakened blood vessel wall) causing transient ischemic attacks. ### Renal Findings * Polyuria * Nocturia * Proteinuria * Red blood cells in urine * Elevated serum creatinine * Mostly related to arteriolar nephrosclerosis (hardening of renal arterioles). ### Ocular Findings * Retinal hemorrhage and exudates. * These are due to damage of arterioles that supply the retina. ### Types of Hypertension * **Primary (Essential)** Hypertension: This type has no specific cause. It constitutes more than 95% of all cases of systemic hypertension. * **Secondary Hypertension:** This results from an identifiable cause such as renal disease or adrenal hyperfunction. It constitutes about 2-5% of all cases of systemic hypertension. ### Blood Pressure Equation Blood pressure = cardiac output (heart rate x stroke volume) x peripheral resistance Therefore, elevation of any of these values increases blood pressure. For example: * **Increased Sympathetic Nervous System Activity:** Baroreceptors (pressure receptors) in carotid and aortic arch respond to changes in blood pressure by inducing reflex changes in cardiac output (through cardiac accelerator centre and cardiac inhibitory centre) and peripheral resistance (through vasomotor centre). In case of sustained untreated hypertension, resetting of baroreceptors to a higher level takes place, making blood pressure sustained at a higher value. * **Increased Renin-Angiotensin System Activity:** Renin is produced in the kidneys in response to both decreased intra renal blood pressure at the juxtaglomerular cells, or decreased delivery of Na and Cl to the macula densa. It is also secreted in response to sympathetic stimulation. Angiotensin I (a weak vasoconstrictor) is formed by the action of renin on angiotensinogen (a peptide produced constitutively by the liver and released into circulation). Angiotensin I is converted to angiotensin II by the enzyme angiotensin-converting enzyme (ACE, or kinase), which is found predominantly in the capillaries of the lung. Angiotensin II actions are mediated by binding to what is known as angiotensin AT1 receptors. Angiotensin II acts on the adrenal cortex, causing it to release aldosterone, a hormone that causes the kidneys to retain sodium and lose potassium. Increased activity of renin-angiotensin system is therefore associated with elevated blood pressure. ## Congestive Heart Failure * Heart Failure (HF) is generally defined as inability of the heart to supply sufficient blood flow to meet the body's needs. * It is a common, costly, disabling and potentially deadly condition. * Heart failure may be **left-sided** or **right-sided**. * Failure of the left ventricle causes congestion of the pulmonary vasculature, and so the symptoms are predominantly respiratory in nature. The patient will have dyspnea (shortness of breath) on exertion and, in severe cases, dyspnea at rest. * Increasing breathlessness on lying flat, called orthopnea, occurs. * Failure of the right ventricle leads to congestion of systemic capillaries. This generates excess fluid accumulation in the body. This causes swelling under the skin (termed peripheral edema) and usually affects the dependent parts of the body first (causing foot and ankle swelling in people who are standing up, and sacral edema in people who are predominantly lying down). Nocturia (frequent nighttime urination) may occur when fluid from the legs is returned to the bloodstream while lying down at night. In progressively severe cases, ascites (fluid accumulation in the abdominal cavity causing swelling) and hepatomegaly (enlargement of the liver) may develop. ### Causes of Heart Failure * Ischemic heart disease (62%) * Cigarette smoking (16%) * Hypertension (10%) * Obesity (8%) * Diabetes (3%) * Valvular heart disease (2%) ### Heart Failure Progresses as Follows: 1. **Reduced Contractility:** Reduced force of contraction due to overloading of the ventricle. 2. **Reduced Stroke Volume:** As a result of a failure of systole, diastole or both 3. **Reduced Spare Capacity:** The heart works harder to meet normal metabolic demands, and the cardiac reserve is reduced, thus increasing exercise intolerance. 4. **Increased Heart Rate:** This helps compensate for heart failure by maintaining blood pressure and perfusion, but places further strain on the myocardium 5. **Hypertrophy** (enlargement of the myocardium): The muscle fibers increasing in size in an attempt to improve contractility, which may contribute to increased stiffness and decreased ability to relax during diastole. 6. **Enlargement of the Ventricles:** Contributing to the enlargement and spherical shape of the failing heart. 7. **Increased Preload and Afterload:** Increases the load on the cardiac muscle while ejecting blood during systole. 8. **Increased Activation of Renin-Angiotensin System:** Due to the decreased renal blood flow.