Cardiac Physiology Fundamentals Lecture Notes (Western Sydney University)

CARDIAC PHYSIOLOGY FUNDAMENTALS Lecture 2 Cardiovascular Circulation Paul Stoodley Contents 1 Cardiovascular System Components 2 Normal Circulation 3 Altered Circulation 4 Conclusion 2 Learning Outcomes Follo...

CARDIAC PHYSIOLOGY FUNDAMENTALS Lecture 2 Cardiovascular Circulation Paul Stoodley Contents 1 Cardiovascular System Components 2 Normal Circulation 3 Altered Circulation 4 Conclusion 2 Learning Outcomes Following this lecture, you will be able to: 1. Define the components of the cardiovascular system 2. Describe elements essential to maintaining normal circulation 3. Describe specific alterations to the circulation 3 Cardiovascular System Components The Cardiovascular System Closed loop system with two loops (circulations) Pulmonary circulation Carries blood between the heart and the lungs Systemic circulation Carries blood from the heart to the rest of the body 4 Cardiovascular System Components Pulmonary Systemic RV LV Arteries Arteries Arterioles Arterioles Capillaries Capillaries Venules Venules Veins Veins LA RA 5 Cardiovascular System Components Pulmonary Systemic RV LV RV Stroke Volume LV Stroke Volume = = LV Stroke Volume RV Stroke Volume Total [P] Volume Total [P] Volume < > Total [S] Volume Total [S] Volume 6 Circulation Normal Cardiac Function Synchronous (rhythmic) contraction and relaxation of myocytes. Rhythm Contraction and relaxation occurs as a result of coordinated electrical stimulus starting at the sino-atrial node (sinus rhythm). Ante-grade Blood Flow When pressure within a chamber forces one of the heart valves to close, and another to open, blood can flow forwards. 7 Circulation Cardiac Cycle Systole Diastole Events that occur from one Myocardial Contraction Myocardial Relaxation heart beat to the next. I. Atria II. Ventricles. I. Atria II. Ventricles. 8 Circulation Circulation RA LA The heart provides the driving force for the circulation of blood. RV LV Ventricular contraction: dramatic (fast [Systole 15 - 30] [Systole100-140] Systole & large) increase in chamber pressure [Diastole 0 - 8] [Diastole 3 -12] & results in the ejection of blood Ventricular relaxation: reduction in Diastole chamber pressure Cardiac valves - open & close Ante-grade (passively) in response to pressure blood flow changes. 9 Circulation Systole - Most often, the point of reference is contraction of the ventricles - From MV closure to AV closure. 1 Isovolumetric Contraction I. MV closes II. Contraction begins III. LV P < Systemic P 2 Ejection I. AV opens II. LV P > Systemic P III. Rapid IV. Reduced 10 Circulation Cardiac Output (CO) Cardiac output is the volume of blood ejected by the heart per minute. CO Calculation CO = HR x SV. If HR is 57bpm & SV 94mL/beat CO = (57 x 94) = 5,358mL/min = 5.4L/min 11 Circulation Cardiac State Output Rest ~5 - 6 L / min Exercise >20 L / min 12 Circulation Diastole - Most often, the point of reference is relaxation of the ventricles - From AV closure to MV closure. 1 Isovolumetric Relaxation I. MV closes II. Relaxation begins III. LV P > LA P 2 Filling I. MV opens II. LA P > LV P [‘E’ Early filling] III. Atrial contraction [‘A’ Active / late filling] 13 Circulation Chamber / vessel Mean pressure (mmHg) Pressure range (mmHg) Right atrium 4 1-8 Left atrium 7 4 - 12 Right ventricle Systolic | End-diastolic 24 | 4 15 - 28 | 0 - 8 Left ventricle Systolic | End-diastolic 130 | 7 90 - 140 | 4 - 12 Pulmonary artery 24 |10 15 - 28 | 5 - 16 Systolic | End-diastolic [10 - 22] [Mean] Aorta 130 | 70 90 - 140 | 60 - 90 Systolic | End-diastolic [70 - 105] [Mean] 14 Circulation Blood Flow Blood flow throughout the circulation is ante- grade (forward flowing). This helps to ensure a balanced pressure within the circulation and promotes gas exchange within the capillaries. Ante-grade flow is aided by: Synchronous contraction and relaxation of the heart (and pressure differences that result) Four one-way valves within the heart (and valves within the large leg veins) Higher pressure within the arterial circulation compared to venous circulation. 15 Altered Circulation Next: So far: Altered Circulation Components of CV System Introduce what happens when there (Normal) Circulation is an alteration (disease) Stenosis | Reduced O2 | Thrombus 16 Altered Circulation Pressure Gradients Blood flow throughout the circulation is determined by differences in pressure. Like all fluid, blood flow occurs ‘down’ the pressure gradient: that is, from high to low. Normally, the highest velocity that blood reaches within the heart is ~1.0 m/s (as it exits the left ventricle - the chamber which generates the highest pressure). Flow is inversely proportional to cross-sectional area. Thus, the velocity of flow can be altered, if the cross- sectional area through which blood is flowing is reduced. Altered Circulation Higher Velocity Stenosis Valve stenosis is the most common cause of reduced cross-sectional area of structures within the heart. In this case, the cross sectional area of a valve is reduced: to compensate, the velocity of blood must increase. Higher velocity occurs via increases contractile cvphysiology.com force (& increased chamber pressure) from the ventricle. Altered Circulation Supply and Demand In order to pump blood, the heart needs its own blood supply (via coronary arteries). Even at rest, the heart needs a constant supply of oxygen: at rest approximately 70% of available oxygen is extracted from the coronary supply. Unlike the heart valves, stenosis in coronary arteries (and other arteries in the circulation) is not overcome via increased ventricular contractile force. The result is reduced blood flow. Even minor reductions in blood supply (ischaemia) cause an imbalance in oxygen supply and demand. This causes pain (angina), ECG changes & reduced regional function. Prolonged imbalance in oxygen supply and demand result in infarction - myocardial tissue death. ResearchGate 19 Altered Circulation Plaque & Thrombus ResearchGate Clotting is a normal defence mechanism to prevent blood loss. ‘Thrombus’ is the term used to define an abnormal clot within the cardiovascular system The most common cause of myocardial infarction is due to a ruptured plaque within a coronary with a resultant thrombus (clot) at the site of the plaque (which prevents blood flow) Less commonly, myocardial infarction is due to a fixed plaque within a coronary, which completely prevents blood flow. 20  shutterstock.c om Altered Circulation Plaque & Thrombus Thrombus can effect other parts of the cardiopulmonary circulation. For example, a thrombus can become lodged in the lungs. In this case, clots most often start in the legs (DVT) and travel through the right heart and into the lungs. Plaque accumulation that limits blood supply and plaque rupture which blocks blood supply can occur in other parts of the cardiovascular system. For example, a plaque within a carotid artery may limit supply to the brain. Or, a carotid plaque that ruptures will cause an embolic stroke. 21 Conclusions Circulation Cardiovascular System Heart Pulmonary Circulation Cardiac Cycle: Systole & Diastole Systemic Circulation Pressure Gradients CO | Blood Flow 22 Altered Circulation Altered Circulation Introduce what happens when there is an alteration (disease) Stenosis | Reduced O2 | Thrombus 23 Cardiac Physiology Fundamentals