Transcript As Pa is greater then Pv atrial contraction adds to the diastolic

Twelfth lecture
Pressure pulses in the cardiac chamber and
related vessels.
The heart beat in a rate of about 72 -75 /min.
At the beginning of the cardiac cycle both atria
and ventricle are relaxed and filled with blood.
Atrium and ventricle on each side are in continuity
as the A-V valves are open and the pressure in
each cavity is almost identical. Following the
impulse generation of SA node , the atrial muscle
contract with Pa rises with Pv following .
As Pa is greater then Pv atrial contraction
adds to the diastolic volume of the
ventricle . The atrial contraction was lasts
about 0.1 sec. in a cardiac cycle of 0.8 sec.
As it passes off, the pressure in both atrium and
ventricle falls, and the ventricle has meanwhile
been invaded by the excitation process which has
spread from SA node across the atrial muscle to
the AV node and hence via bundle of His and the
purkinje tissues .
Ventricular contraction begin and
promptly Pv exceed Pa and the A-V valve
close (causing first heart sound).
The ventricle is now a closed chamber and the
pressure rises promptly during the isometric
phase which lasts about 0.05 sec. The
ventricular pressure then rapidly exceeds than
that of the artery and Semilunar valve open.
The arterial pressure rises because blood enters the
vessels faster than it can escape via the peripheral
arterial brandies . The pressure decline as the
ventricular contraction begins to subside which follow
from the artery to its peripheral branches continues to
be high.
The total period of ventricular systol is 0.3 sec. and
when this ends the ventricular pressure drops
sharply .
The arterial pressure is better sustained however
owing to elastic recoil of the vessels and almost
immidiately the arterial pressure exceeds that in the
ventricle , thereby causing closure of the semilunar
valve and the sharp second heart sound .
The initial part of ventricular diastole which
follow is isometric lasting some 0.08 sec. ending
in opening of the A-V valve because the arterial
pressure exceeds that in the ventricle .
Rapid filling of the ventricle then occur for 0.1 - 0.12
sec. , although the pressure in both chambers still
falls' owing to continued rapid relaxation of the
ventricle .
Finally the phase of slow filling or Diastasis lasting
0.19 sec. terminates the cardiac cycle
This slow filling is due to continued venous return
filling both atrium and ventricle and the
readjusting the diastolic volume of the ventricle .
ventricular diastole lasts 0.5 sec.
(0.08 sec. isomctic relaxation ; 0.12 sec. rapid filing ; 0.2 sec.
diastasis ; 0.1 sec. atrial cystol) The atrial pressure curve shows
three well marked waves :
1 - Is due to atrial cystol.
2 - With the onset of vetricular cystol, there is a rise of pressure
due to bulging of the A-V valve into the atrium .
This is soon succeded by a sharp fall in pressure which
attributed to the pressure lengthening of the atrium caused by
the downword movement of the A-V as the ventricular
.contraction proceedes
3 - the rising phase of this wave is due to venous return .
The EGG waves P, Q RS,and T depict the sequential
events in the cardiac cycle:
P is the electrical activity associated with atrial systol.
Its duration 0.1 sec.
It is some guide to the functional activity of the atrial
muscle. QRS is the electrical activity aroused by
invasion of the ventricle. ts duration in man 0.08 sec.
The P - R interval 0.13 - 0.16 sec It represent the stage
of ventricular deplarization .. The time interval from the
begining of P to the commencement of R Is a guide to
the conduction of the bundle of His and ,T is a wave
caused by the repolarization of the ventricle . Its
duration is about 0.27 sec.