the cardiac cycle Flashcards

1
Q

what is the cardiac cycle?

A
  • diastole = ventricles relax and fill with blood
  • systole = ventricles contract and pump blood into the aorta (LV) and pulmonary artery (RV)
  • at a HR of 75bpm, diastole is 0.5 sec and systole is 0.3 sec
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2
Q

what events occur during the cardiac cycle?

A
  1. passive filling
  2. atrial contraction
  3. isovolumetric ventricular contraction
  4. ventricular ejection
  5. isovolumetric ventricular relaxation
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3
Q

what happens during passive filling?

A
  • pressure in the atria and ventricles close to zero
  • AV valves open so venous return flows into the ventricles
  • aortic pressure = 80mmHg, and aortic valve is closed
  • same happens in right side but pressure is lower
  • ventricles become 80% full
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4
Q

what happens during atrial contraction?

A
  • the P-wave in the ECG signals atrial depolarisation
  • the atria contracts between the P-wave and the QRS
  • atrial contraction complete the EDV
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5
Q

what happens during isovolumetric ventricular contraction?

A
  • starts after the QRS in the ECG
  • ventricular pressure rises
  • when the VP exceeds atrial pressure, the AV valves shut
  • this produces the first heart sounds (LUB)
  • the aortic valve is still shut
  • the tension rises around a closed volume “isovolumetric”
  • the ventricular pressure rises very steeply
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6
Q

what is ventricular ejection?

A
  • when the ventriuclar pressure exceeds aorta/pulmonary artery pressure
  • aortic/pulmonary valve open (silent event)
  • SV is ejected by each ventricle, leaving behind the ESV
  • aortic pressure rises
  • T-wave in ECG signals ventricular repolarisation
  • ventricles relax and ventricular pressure starts to fall
  • when the VP falls below aortic/pulmonary, the valves shut
  • this produces DUB
  • the valve vibration produced the dicrotic notch in aortic pressure curve
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7
Q

what is isovolumetric ventricular relaxation?

A
  • closure of aortic/pulmonary valves signals the start of the isovolmumetric ventricular relaxation
  • ventricle is again a closed box, as the AV valve is shut
  • the tension falls around a closed volume
  • when the ventricular pressure falls below atrial pressure, AV valves ioen (silent) and a new cycle will start
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8
Q

when is S1 heard?

A
  • S1 - caused by closure of nitral and tricuspid valves “lub”, heard in the beginning of systole
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9
Q

when is S2 heard?

A
  • S2 - caused by closure of aortic and pulomnary valves “dub”, heard at the beginning of diastole
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10
Q

what are the jugular venous pressures?

A
  • JVP occurs after right atrial pressure waves
  • a = atrial contraction
  • c = bulging of tricuspic valve into atrium during ventricular contraction
  • v = rise of atrial pressure during atrial filling: release as AV vales open
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