P: cardiac cycle Flashcards
Semilunar valves
At origin of pulmonary artery + aorta. Open during ventricular contraction and allow blood to flow only from ventricles into arteries. Closure of semilunar valves generates 2nd heart sound.
Sinoatrial node
location: right atrium near opening of superior vena cava.
Spontaneous depolarizations here pass into surrounding myocardial cells + generate contraction:
1. Atrial myocardial cells
2. Pause (fibrous layer)
Ventricular myocardial cells
Atrial systole
- At t=0 sec, both atria and ventricles are in diastole
- Atrial pressure > ventricular pressure, AV valves open and semilunar valves are closed –> ventricles become 80% filled.
- Wave of depolarization spreads through both atria (P wave)
Pressure in atria increases, remaining 20% blood flows into ventricles.
Ventricular systole
- T=100msec, depolarization wave spreads into ventricles QRS wave
- Ventricle pressure > atrial pressure, so AV valves closed
- Ventricular contraction strength + pressure increases
- Below 80mmHg, left ventricular pressure is not strong enough to open SL valves into aorta
- Below 8mmHg, right ventricular pressure is not strong enough to open SL valves into pulmonary artery
- Isovolumetric contraction.
- Atrial pressure increases slightly as upward pressure of ventricles causes AV valves to bulge into atria.
- At t=130msec, pressure LV> aorta + pressure RV> pressure pulmonary artery so both SL valves open.
- Total volume of blood ejected = stroke volume.
- End systolic volume = residual blood remaining in ventricles.
Ventricular diastole
- T=300msec, repolarization of ventricles begins (T wave)
- T=350 msec, LV pressure < aortic pressure, RV pressure < pulmonary artery pressure, backflow closes SL valves and generates 2nd heart sounds.
- Atrial pressure increasing (filling)
- Short period of backflow prior to closing of aortic valve
Tachycardia
- Diastasis is shortened + contribution of atrial contraction is significant
- Intense exercise: ventricular contraction can begin during rapid filling, contribution of atrial contraction is more important. There is a reduction in stroke volume.
- Syncope (fainting) can result if inadequate ventricular filling occurs.
Pressure changes: ACV wave
A: rise in pressure caused by atrial contraction. Pressure increases by 4-mm Hg in RA and by 7-8mm Hg in left atrium.
C: Increasing ventricular pressure causes bulging of AV valves into atria.
V: Rise in pressure associated with atrial filling.
Atrial fibrillation
- Arrhythmia causing uncoordinated contractions of atrial fibres
- No P waves on ECG
- Irregular fluctuations: f waves
- AV node activation is irregular: ventricular contractions irregular.
Normal interval between successive ventricular contractions
0.35-0.95 sec (0.8sec)
Aortic pressure curve
- Ejection of blood from left ventricle into arteries increases pressure to -120mm Hg
- Immediately before closure of aortic valve, short period of backflow into ventricle - causing incisura/ dicrotic notch
- Pressure in aorta decreases slowly throughout diastole as elastic recoil pushes blood continually to peripheral vessels
- Before ventricle contracts again, aortic pressure falls to -80mm Hg
Heart sound 1
- Upon systole, sudden backflow of blood against AV valves causes their closure
- Bulges into atria until chordae tendineae abruptly stop back bulging.
- Tautness of valves/ chordae tendineae causes blood to bounce forward again into each ventricle
- Vibration of valves + turbulent blood transmitted to ventricular walls & surrounding blood vessels
- Loudest + longest (0.14 sec) heart sound.
Heart sound 2
- Upon diastole, SL valves close + bulge back into ventricles
- Elastic stretch recoils blood back into arteries
- Reverberation of blood between the walls of arterial walls and valves and between valves and ventricular walls
- Duration (0.11 sec)
Phonocardiography
detection of 2 further heart sounds with a microphone.
S3: caused by inrushing blood from atria during middle 1/3 of diastole. Typically only heard in younger individuals –> heard in older individuals can be a sign of a heart murmur
S4: Inflow of blood into ventricles following atrial contraction.
Left ventricle pressure-volume loop
A: opening of mitral valve + beginning of filling
A-B: pressure falls as diastole progresses, blood volume increasing
B-C: pressure and volume increase as filling progresses, small increase in pressure before C (atrial contraction)
C: mitral valve closes, EDV (end diastolic volume).
C-D: systole begins, isovolumetric contraction.
D: aortic valve opens (80mmHg)
D-E: pressure rises (120mmHg), volume falls, rapid ejection
E-F: pressure + volume fall, reduced ejection
D-F: stroke volume
F: aortic valve closes, ESV
A-F: Diastole begins, isovolumetric relaxation.
Preload
degree of tension on the muscle when it begins to contract. Magnitude of EDV and corresponding end diastolic pressure. Point C on pressure-volume loop