30 - Dynamics of heart contraction- the cardiac cycle. Opening and closing of the heart valves during the cardiac cycle.

sections

7 phases of cardiac cycle

times for atrial systole, diastole, isovolumetric relaxation, ventricular systole and diastole

PQRST

7 phases of cardiac cycle

1. Isovolumetric ventricular relaxation - as ventricles relax pressure in ventricles drop, blood flows back into cups of semilunar valves and snaps them close

2. late diastole - both sets of chambers relaxed. passive ventricular filling

3. Atrial systole - atrial contraction forces a small amount of additional blood into ventricles

4. EDV= end-diastolic volume - the maximum amount of blood in ventricles occurs at end of ventricular relaxation. EDV= 135 mL

5. Isovolumetric ventricular contraction - first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves

6. Ventricular ejection - as ventricular pressure rises and exceeds pressure in arteries, semilunar valves open and blood is ejected

7. ESV= end-systolic volume - or minimum amount of blood in ventricles. ESV = 65 mL

times for:

• atrial systole

• atrial diastole

• isovolumetric relaxation

• ventricular systole

• volumetric diastole

• Atrial systole- 0.1s

• Atrial diastole-0.7s

• Isovolumetric relaxation- 0.08s

• Ventricular systole- 0.3 s

• Ventricular diastole- 0.5 s

PQRST

1. P - wave = depolarisation of atria in response to SA node triggering

2. PR interval = delay of AV node to allow filling of ventricles

3. QRS complex = deploarisation of ventricles, triggers main pumping contractions

4. ST segments = beginning of ventricle replarisation should be flat

5. T wave = Ventricular repolarisation