What are the events that occur during one heart beat?    Oxygen-poor blood (shown in blue) flows from the body into the right atrium.    Blood flows through the right atrium into the right ventricle.                                     Cardiac Cycle: one complete heartbeat, consisting of the contraction/relaxation of both atria, followed by the contraction/relaxation of both ventricles. The average duration is 0.8 sec.                                  file:/// What are the events that occur during one heart beat?

The Cardiac Cycle: Definitions Systole: phase of myocardial contraction (atrial systole, ventricular systole); during systole, the pressure in a chamber is elevated and blood is ejected Diastole: phase of myocardial relaxation; during diastole, the pressure in a chamber falls and the chamber fills with blood Systole Diastole

Cardiac cycle points to remember: 1. The purpose of the myocardium is to contract to provide pressure for the ejection of blood (systole) and to relax to reduce pressure and allow filling (diastole). 2. Blood moves from regions of high pressure to regions of low pressure. 3. The contraction of the myocardium is coordinated by the cardiac conduction system. 4. The valves of the heart (atrioventricular and semilunar) ensure that blood moves in a forward, not backward, direction. The cardiac cycle

75 Event Value # cardiac cycles/minute Duration of one cardiac cycle 0.8 second Duration of 0.1 sec Duration of atrial diastole Duration of ventricular systole Duration of 0.5 sec. Duration of cardiac quiescence (the atria and ventricles are in diastole at the same time) 75 atrial systole 0.7 second 0.3 second ventricular diastole 0.4 second Note: the events of the cardiac cycle are traditionally described in terms of the left heart. Pressure changes occurring in the right heart are 1/5th as great as the changes in the left heart

The Cardiac Pressure Curve End Diastolic Volume (EDV) The volume of blood received by a ventricle during the period of ventricular filling End Systolic Volume (ESV) The volume of blood remaining in a ventricle after the period of ventricular ejection

Early Ventricular diastole Ventricle Diastole Ventricular Systole Early Ventricular diastole Passive ventricular filling Active ventricular filling Period of isovolumetric contraction Period of ejection Period of isovolumetric relaxation Blood flow From atrium into ventricle Contraction of atrium pumps additional 20-25% of blood Ventricles begin to contract – no volume change Ventricle continue to contract – blood ejected into aorta Pressures Atrial>ventricular Ventricular >aorta Atrial starting to rise Valve state A-V open (pressure in atrium greater than pressure in ventricle Semilunar closed (pressure in aorta > pressure in ventricle A-V open Semilunar - A-V closes (pressure in ventricle is greater than atrium) A-V closed (pressure in ventricle>pressure in atrium Semilunar opens– why? ECG Pre-P wave P-wave QRS T-wave Heart Sound Comments End Diastolic volume Period of isovolumetric contraction – all valves closed, ventricular volume does not change (an isometric contraction?) End-systolic Volume Ventricular pressure > atrial Why? Atrial systole Why? Atrial pressure > than ventricular pressure Closed -pressure in aorta is still > than ventricle Closed -pressure in aorta > than ventricle Pressure in ventricle is now > than aorta none none 1st heart sound none The volume of blood received by a ventricle during the period of ventricular filling The volume of blood remaining in a ventricle after the period of ventricular ejection

Mid Ventricular Diastole a. The atria and ventricles are in diastole b. Atrial pressure is ventricular pressure Thus, blood moves from atria into ventricles through open AV valves Note: the ventricles receives about of its final blood volume during this time Late Ventricular Diastole the atria contract and eject the remaining volume of blood into the ventricles Note: the ventricles receive the remaining blood during atrial systole greater than 75% 25% The arteries during this entire time period are pressure as blood circulates to smaller vessels losing

Ventricular Systole Ventricular pressure as the ventricles contract When ventricular pressure is greater than atrial pressure, the AV valves When ventricular pressure is greater than arterial pressure, the semilunar valves and blood is ejected into the arteries close open Isovolumetric Period of Contraction: period of time, during ventricular systole, after the AV valves close but before the semilunar valves open, when ventricular volume remains unchanged

Early Ventricular Disatole Ventricular pressure falls during ventricular diastole When ventricular pressure is less than arterial pressure, the semilunar valves close When ventricular pressure is less than atrial pressure, the atrioventricular valves open ; the ventricles begin to fill Isovolumetric Period of Relaxation Period of time, during ventricular diastole, after the semilunar valve closes but before the AV valve opens, when ventricular volume remains unchanged

A Few Other Things .. Dicrotic Notch: A brief rise in arterial pressure that results from arterial blood rebounding off of newly closed semilunar valves End Diastolic Volume (EDV) The total volume of blood that a ventricle receives during its filling period End Systolic Volume (ESV) The total volume of blood left in a ventricle after ventricular contraction Stroke Volume (SV) The total volume of blood that ejected into arteries as a result of ventricular contraction

There are two easily and consistently heard heart sounds: Normal valves have two characteristcs: 1. Unimpeded flow 2. Unidirectional flow First Sound (S1) Second Sound (S2) Generated By closure of the closure of the Sounds like “lub” “dup” When heard at the beginning of ventricular at the beginning of ventricular semilunar valves AV valves systole diastole

Valve Abnormalities Stenosis: a significant amount of pressure must be generated to eject blood though a narrowed valve this can lead to: 1. Increased residual volume of blood in a chamber 2. Cardiac cell hypertrophy 3. Low pulse pressure A narrowed valve Rheumatic mitral stenosis: note thickened leaflets and shortened chordae Calcification of the aortic semilunar valve

Note the turbulance (red spirals) of the blood as it flows through the stenotic aortic semilunar valve It is the turbulance that creates the mumur

At which point in the cardiac cycle would you expect to hear a murmur associated with Stenosis of the mitral valve? b. Stenosis of the aortic semilunar valve? Answer choices are: Ventricular diastole Ventricular systole Ventricular diastole Ventricular systole

Insufficiency (Incontinence): This can lead to: 1. The backward flow of blood 2. Increased volume of blood in the affected chamber 3. Cardiac cell hypertrophy 4. Low pulse pressure A valve that does not close properly Ruptured chords – mitral valve prolapse secondary to a Haemophilus infection

At which point in the cardiac cycle would you expect to hear a murmur associated with Insufficient mitral valve? Insufficient aortic semilunar valve? Answer choices are: Ventricular diastole Ventricular systole Ventricular systole Ventricular diastole

Causes of valve abnormalities include: Coronary atherosclerosis (papillary muscle dysfunction) Rheumatic fever (most common cause, mitral valve) Autoimmune diseases Congenital malformations of valves Connective tissue defects (eg, Marfan’s syndrome) Aging (calcification)