Discuss the relation of ECG to cardiac cycle?
1-Atrial systole starts after the P wave of the electrocardiogram (ECG).
2-Ventricular systole starts near the end of the R wave and ends just after the T wave. Define: systolic blood pressure - diastolic blood pressure
• Systolic blood pressure: is the peak pressure reached during systole (not the mean pressure).
• Diastolic blood pressure: refers to the lowest pressure during diastole.Mention phases of cardiac cycle?
1. Isomeric contraction phase.
2. Maximal ejection phase.
3. Reduced ejection phase.
1. Early ventricular diastole:
a. protodiastolic phase
b. isometric relaxation phase
c. maximum filling phase.
2. Mid ventricular diastole: reduced filling phase.
3. Late ventricular diastole: atrial systole.Discuss the state of cardiac valves during cardiac cycle?
1. Isometric phases (contraction and relaxation): all valves are closed.
2. Filling phases and atrial systole: AV valves are open while semilunar valves are closed.
3. Ejection phases: AV valves are closed while semilunar valves are open.
4. No phase in the cardiac cycle during which all cardiac valves are open simultaneously. Define: SV, EDV, ESV and ejection phase.
• Stroke volume: the amount of blood ejected by each ventricle per beat (at rest is 70 to 90 ml).
• End diastolic volume (EDV): volume of blood in the ventricle at the end of diastole (130 ml).
• End systolic volume (ESV): volume of blood in the ventricle at the end of systole (50 ml).
• Ejection fraction: the percent of the end diastolic volume that is ejected with each beat i.e. SV/EDV (about 65%). It is a valuable index of ventricular function. What is the effect of respiration on semilunar valve closure (2nd heart sound)?
Contraction of the right ventricle starts after that of the left. However, since pulmonary arterial pressure is lower than aortic pressure, right ventricular ejection begins before that of the left. During expiration, the pulmonary and aortic valves close at the same time; but during inspiration, the aortic valve closes slightly before the pulmonary (with splitting of 2nd heart sound). The slower closure of the pulmonary valve is due to lower impedance of the pulmonary vascular tree. Mention the functions of ventricular diastole?
During diastole, the heart muscle rests, and coronary blood flow to the subendocardial portions of the left ventricle occurs only during diastole. Furthermore, most of the ventricular filling occurs in diastole. Why the cardiac muscle cannot be tetanized?
Because it has a prolonged action potential, cardiac muscle cannot contract in response to a second stimulus until near the end of the initial contraction. Therefore, cardiac muscle cannot be tetanized like skeletal muscle. What is the highest rate at which the ventricles can contract? Significance?
The highest rate at which the ventricles can contract is theoretically about 400/min, but in adults the AV node will not conduct more than about 230 impulses/min because of its long refractory period. A ventricular rate of more than 230 is seen only in paroxysmal ventricular tachycardia.Define: total electromechanical systole, left ventricular ejection time and pre-ejection period? Significance?
• Total electromechanical systole (QS2):
is the period from the onset of the QRS complex to the closure of the aortic valves (as determined by the onset of the second heart sound).
• Left ventricular ejection time (LVET):
is the period from the beginning of the carotid pressure rise to the dicrotic notch.
• Pre-ejection period (PEP):
is the difference between QS2 and LVET and represents the time for the electrical as well as the mechanical events that precede systolic ejection.
: the ratio PEP/LVET is normally about 0.35 and it increases without a change in QS2 when left ventricular performance is compromised in a variety of cardiac diseases.Discuss briefly normal heart sounds?
• The first
is a low, slightly prolonged "lub" (first sound), caused by vibrations set up by the sudden closure of the AV valves at the start of ventricular systole.
• The second
is a shorter, high-pitched "dup" (second sound), caused by vibrations associated with closure of the aortic and pulmonary valves just after the end of ventricular systole.
• A soft, low-pitched third
sound is heard about one third of the way through diastole in many normal young individuals. It coincides with the period of rapid ventricular filling and is probably due to vibrations set up by the inrush of blood.
• A fourth
sound can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hypertrophy. It is due to ventricular filling and is rarely heard in normal adults.
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