Cardiovascular System

Cheatsheet Content

### Learning Objectives - Define Cardiac Output (CO) and factors affecting it. - Understand blood pressure regulation. - Differentiate between hypertension and hypotension. - Understand Cardiac Tamponade. - Understand the two types of heart failure (CHF). - Comprehend valvular dysfunction and its complications. ### Heart: Quick Summary - **4-chamber muscular pump** located in the center of the thorax. - Requires a **continuous supply of oxygenated blood** to its cardiac muscle fibers. - Powers the circulatory system by distributing nutrients and removing metabolic waste products. - Consists of **2 separate pumps**: Right (pulmonary circulation) & Left (systemic circulation). - A normal, healthy adult heart beats **60-80 bpm**. - Each ventricle ejects approximately **70mL per heartbeat**. - **Total Output (CO) = ~5L/min**. ### Pumping Action of the Heart - **Systole (Contraction):** - Heart chambers contract. - Blood is ejected from the Left Ventricle (LV) into the aorta. - **Diastole (Relaxation):** - Heart chambers relax. - Chambers fill with blood. ### Cardiac Output (CO) - **Definition:** The amount of blood pumped by each ventricle during a given period. - Usually 5 L/min. - Varies according to metabolic demand. - **Frank-Starling's Law of the Heart:** CO = Stroke Volume (SV) x Heart Rate (HR). - **Stroke Volume (SV):** Amount of blood ejected from the LV per contraction (heartbeat). - Average resting SV is ~70 mL. ### Factors Determining Stroke Volume SV is primarily determined by 3 factors: 1. **Preload:** The degree of stretch of the cardiac muscle fibers at the end of diastole. - **Factors affecting preload:** - Diuresis (fluid loss) - Nitrates (vasodilation) - Loss of blood (fluid loss) - Vomiting (fluid loss) - Diarrhea (fluid loss) 2. **Afterload:** The pressure the ventricular myocardium must overcome to eject blood during systole. - **Factors affecting afterload:** - **Systemic Vascular Resistance (SVR):** - Arterial Vasoconstriction (increases SVR) - Arterial Vasodilation (decreases SVR) - **Pulmonary Vascular Resistance (PVR)** 3. **Contractility:** The force generated by the contracting myocardium. - **Factors affecting contractility:** - **Beta-1 Adrenergic receptors:** - Circulating Catecholamines (e.g., epinephrine & norepinephrine) - SNS stimulation (e.g., hypothalamus) - Medications (e.g., Levophed, Digoxin) - **Increases in HR & Contractility --> increases Stroke Volume.** #### CO Response to Metabolic Demands - CO responds to metabolic demands of the body's tissues (e.g., exercise can increase CO by 4x, up to 20 L/min). - **How the heart achieves this:** - By increasing Preload - By increasing Contractility - By decreasing Afterload #### Ejection Fraction (EF) - **Definition:** The percentage of the end-diastolic volume that is ejected with each contraction. - Healthy human EF: - ~42% Right Ventricle (RV) or more - ~50% Left Ventricle (LV) or more - EF% is an index of myocardial contractility. - **The EF% decreases if contractility decreases.** ### Congestive Heart Failure (CHF) - **Definition:** A condition resulting from cardiac disease where the heart is unable to pump enough blood to meet the body's needs. - The heart fails to pump out all the blood that enters the ventricles. - **Causes of CHF:** - Damage to heart muscle or mechanisms controlling blood inflow/outflow. - Coronary Artery Disease (CAD) - Damage post Myocardial Infarction (MI) - Hypertension (HTN) - Diabetes - Valve disease - Viruses - Chemotherapy - Chronic alcohol use - Drug abuse - Amyloidosis #### Types of CHF - **2 types:** Left-sided or Right-sided CHF. - Measured by ECHO or MUGA exam. #### Left-sided Heart Failure (Ls-CHF) - Causes fluid to **back up and accumulate in the lungs**. - **Signs/Symptoms:** - Shortness of Breath (SOB) (even without exercise) - Waking up in the middle of the night gasping for breath (paroxysmal nocturnal dyspnea) - Inability to catch breath while at rest - Coughing / gurgling with frothy sputum (severe cases) - **Sign of Chronic Ls-CHF:** Clubbing of the fingers (tissue growth extended in fingertips), related to hypoxia/hypoxemia. #### Right-sided Heart Failure (Rs-CHF) - Causes blood entering the heart from systemic circulation to **back up in the venous system**. - **Key Signs/Symptoms:** Peripheral Edema. - **Important:** Since heart chambers are interconnected, CHF is often a combination of both left and right heart failure. #### Manifestations of Heart Failure - **Right Ventricular Failure:** Congestion of peripheral tissues - Dependent edema and ascites - GI tract congestion (anorexia, GI distress, weight loss) - Liver congestion (signs related to impaired liver function) - **Left Ventricular Failure:** Decreased cardiac output & Pulmonary congestion - Activity intolerance and signs of decreased tissue perfusion - Impaired gas exchange - Pulmonary edema - Cyanosis and signs of hypoxia - Cough with frothy sputum #### Management of CHF - **Lifestyle Changes:** Diet & Exercise - **Medications (Optimize Cardiac Function):** - Correct fluid retention (e.g., diuretics) - Increase contractility - Reduce workload - Anxiety reducers (e.g., tranquilizers) - **Surgery:** - Bypass blocked arteries - Repair valves - Ventricular Assist Device (VAD) - Heart Transplant (last resort) ### Controlling Heart Rate (HR) & Blood Pressure (BP) - **Accomplished by:** - Reflex controls mediated by the **Autonomic Nervous System**. - Circulating Catecholamines. - Excess thyroid hormone. - Controls mediated by the **Central Nervous System (CNS)** & **Baroreceptors**. #### Cardiac Control: Baroreceptors - **Definition:** Specialized nerve cells located in the aortic arch and both Right (R) & Left (L) internal carotid arteries. - **Function:** Monitor changes in BP. - When BP rises: Transmit a signal to the medulla, which increases parasympathetic drive and decreases sympathetic drive. - When BP decreases: The reverse occurs (decreases parasympathetic, increases sympathetic drive). ### Hypotension - **Definition:** Blood pressure ### Hypertension - **Definition:** Consistently high blood pressure measurements. - **Chronic Hypertension:** Receptor sensitivity changed (baroreceptors adapt). #### Types of Chronic Hypertension - **Primary (Essential) Hypertension:** - Most common type. - Heart malfunction. - Unknown cause. - **Secondary Hypertension:** - External factors. - Kidney disease. - Hormonal disorder. - Medications. #### Hypertension: Damages Blood Vessels - **If uncontrolled, injury occurs:** - Kidney damage - Heart Failure - Stroke - Atherosclerosis #### Hypertension: Diagnoses - **Normal Ranges:** ### Heart Tissue Layers - The heart tissue is made of **3 layers**: 1. **Epicardium (Visceral pericardium):** Outermost layer. 2. **Myocardium:** Middle muscular layer, responsible for pumping. 3. **Endocardium:** Innermost layer, lining the chambers and valves. - **Encased in a thin fibrous sac (pericardium):** Has 2 layers. - **Pericardial Cavity (space):** Located between the visceral and parietal pericardium, filled with ~30mL of lubricant. - Can hold up to 2L of fluid. - Reduces friction. - **If fluid accumulates rapidly, it is a life-threatening situation!** ### Cardiac Tamponade - **Definition:** Impairs normal diastolic filling of the heart due to compression of cardiac chambers, thereby reducing CO. - Occurs when fluid fills the pericardial space rapidly – a life-threatening situation. - **May result from:** - **Effusion:** Cancer, infections, TB. - **Hemorrhage:** Trauma, Gunshot Wounds (GSW), stab wounds, surgery. - **Pericarditis** - **Acute MI** - **Rx Reaction** - **Connective Tissue Disorders:** Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), Rheumatic Fever (RF). - Other causes. #### Signs & Symptoms of Cardiac Tamponade - Chest pain/discomfort - SOB - Tachycardia - Fainting/lightheadedness - Swelling in arms/legs - Upset stomach - Pain in right upper abdomen - Hypotension (shock) #### Treatment for Cardiac Tamponade - **Pericardiocentesis:** Needle aspiration of the pericardial cavity. - **Pericardial Window:** Surgical creation of an opening. - **Insertion of a drain** into the pericardial space to drain the effusion. ### Heart Valves - **4 valves** within the heart permit blood to flow only in one direction. - Made of thin leaflets of fibrous tissue. - Open & close in response to blood movement and pressure changes within chambers. - **Types of Valves:** - **Tricuspid valve:** Separates Right Atrium (RA) / Right Ventricle (RV). - **Mitral (bicuspid) valve:** Separates Left Atrium (LA) / Left Ventricle (LV). - **Pulmonic semilunar valve:** Separates RV / Pulmonary Artery. - **Aortic semilunar valve:** Separates LV / Aorta. ### Valvular Disease - **Major cause of low blood flow.** - **Inefficient heart valve** allows **REGURGITATION** (blood flowing backward). - Regurgitation forces the heart to pump more blood, increasing cardiac workload. - Over time, the heart may fail to meet the tissue's metabolic requirements for blood and fail to function as an effective pump. - **Example:** Failure of the aortic valve to close tightly causes backflow of blood into the left ventricle. #### Treatment: Valvular Replacement - Valves may be repaired or replaced. - **2 types of replacement valves:** - **Natural valves (biological):** - Human donors (cadavers). - Modified natural valves (animal donors, e.g., porcine) placed in synthetic rings. - Rarely require anticoagulation therapy. - **Artificial valves (mechanical):** - Made of metal or plastic. - **Will require anticoagulation therapy.**