The Cardiac Cycle

CARDIAC CYCLE Various events occur in the heart during on beat. These events are repeated in a cyclic manner. This cyclic repetition of events is called cardiac cycle. Duration of cardiac cycle 0.8 sec z z z z

ATRIAL SYSTOLE 0.1 sec VENTICULAR SYSTOLE 0.3 sec VENTICULAR DIASTOLE 0.5sec ATRIAL DIASTOLE 0.7 sec

1. ATRIAL SYSTOLE DURATION 0.1 SEC • Contraction of the atrium and atrial pressure rises. • Expulsion of blood into ventricles. 2. VENTRICULAR SYSTOLE DURATION 0.3 sec i. ISOVOLUMETRIC CONTRACTION ii. RAPID EJECTION iii. SLOW EJECTION I. ISOVOLUMETRIC CONTRACTION • Atrial systole ceases and pressure in atrium and ventricle falls. • Ventricular contraction starts and then ventricular pressure rises above atrial pressure, AV valve closes • FIRST HEART SOUND occurs with closure of AV valve • Isovolumetric contraction – ventricles are closed and pressure is rising in ventricles. No emptying. • Ventricular systole – Left ventricle pressure rises above aorta pressure 80 mm hg and RV ventricle pressure rises above pulmonary artery pressure 10 mm Hg, aortic and pulmonary valves open. II. RAPID EJECTION • Opening of semilunar valves. • Ejection of blood from ventricles to aorta and pulmonary artery.

III. SLOW EJECTION • Ventricular pressure declines. • Ejection of blood slows down.

3. VENTRICULAR DIASTOLE DURATION 0.5 seconds z Ventricular pressure drops after ventricular systole ends. z Closure of semilunar valves causes second heart sound. I. Isovolumetric relaxation • After closure of semilunar valves, ventricular pressure drops rapidly. • NO CHANGE in ventricular volume. • ENDS as ventricular pressure falls below atrial pressure. II. Rapid filling phase • AV valves open. • Rapid Ventricular filling occurs. • Slow ventricular filling. • Last Rapid ventricular filling due to atrial systole. 4. ATRIAL DIASTOLE DURATION 0.7 seconds • Atrial relaxation. • Venous return fills the right atrium. NOTE RA systole precedes LA systole. RV contraction starts after LV contraction.

DIAGRAM AND GRAPH

Pulmonary artery

mmHg 25/10

Aorta

120/80

Left atrium

5

Left ventricle

120/0

Right ventricle

25/0

NOTE Atrial systole starts after P wave. Ventricular systole starts near the end of R WAVE.

JUGULAR VENOUS PRESSURE (JVP) Right atrial pressure changes are transmitted to the jugular veins in the neck producing, characteristic waves. z A wave due to atrial systole. z C wave during isovolumetric contraction, there is bulge in right atrium due to tricuspid valve. z V wave rise in atrial pressure before tricuspid valve opens. APPLIED CANNON WAVES – GIANT a waves – seen in complete heart block TR --GIANT c waves

HEART SOUNDS 1. FIRST HEART SOUND

Occurs with closure of AV valves Denotes onset of ventricular systole. Low pitched. Loud sound. Coincide with R wave of ECG. 2. SECOND HEART SOUND Occurs with closure of semilunar valves. Signifies onset of ventricular diastole. High pitched. Sharp sound. Coincide with T wave of ECG. 3. THIRD HEART SOUND Occurs during rapid filling phase of the ventricles Low pitched Duration 0.1 sec 4. FOURTH HEART SOUND Occurs due to atrial systole Low frequency

Vessels Type of blood vessels Type 1. Wind Kessel vessels 2. Resistance vessels 3. Precapillary sphincters 4. Exchange vessels 5. Capacitance vessels

Features eg. Aorta, major arteries ,have a lot of elastic tissue ;show elastic recoil effect eg. Arteries, have some elastic tissue. Have lot of smooth muscle No innervation ,respond to local metabolites Capillaries. No innervations. Controlled by precapillary sphincters Veins. Have some innervations

6. Shunt vessels

A-V anastomoses. They have thick muscular wall very richly innervated

NOTE- 1. Cross sectional area area: is minimum for aorta and maximum for capillaries. 2. % of blood volume: is maximum in capacitance vessels and minimum in arterioles. Capillaries 3 Types a) Continous eg. Brain, skin b) Fenestrated eg. GIT , glomeruli of kidney, endocrine glands, circum ventricular organs c) Discontinous (Sinusoids) eg. Liver , bone marrow The least permeability of capillaries is that is the brain. Pericytes: These are associated with capillaries and post capillary venules. They are similar to the mesangial cells in the renal glomeruli. I. They are contractile II. They release vasoactive agents III. They synthesise and release constituents o bone marrow and extracellular matrix. One of their functions is to regulate the flow through the junction between the endothelial cells , especially during inflammation. BIOPHYSICAL PRINCIPLES 1. F= P/R (WHERE F= flow, P = effective perfusion pressure,R = resistance) R=P/F If P is expressed in mm Hg and flow is expressed in ml/sec , then resistance will be expressed in 'R' units. Flow can be laminar or turbulent Laminar flow Turbulent flow a) Eletcro magnetic flow meters a) Fick method b) Doppler flow meter b) Indicator method c)More efficient (less energy consumption) c) Plethysmography

The probability of turbulence in a given flo can be determined by Reynold's number. Re= PDV/n (where Re = Reynold number, P= Density of fluid, D = diameter of the vessel, V = velocity of the flow and n = Viscosity) More the Reynold number , more the chances of the turbulence. If D is measured in cms, Vin cm/sec, n in poises, then Re is < 2000 there is usually no turbulence ; if Re is > 3000, turbulence is almost always there. 2. Average velocity of flow V= Q/A (Where V = velocity , Q = Quantity/amount of fluid and A = area) So, if area is more, velocity is less. Therefore the flow is least in the capillaries (maximum cross sectional area) and maximum in the aorta (least cross sectional area)