Cardiac cycle phases, pressure-volume loops, and baroreceptor reflex mechanisms tested on USMLE Step 1.
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- What event marks the beginning of isovolumetric contraction in the cardiac cycle?
- Closure of the mitral (and tricuspid) valve, marked by the first heart sound (S1)
- Why is isovolumetric contraction called 'isovolumetric'?
- Ventricular volume stays constant because both the atrioventricular and semilunar valves are closed while pressure rises
- What event ends isovolumetric contraction and begins ventricular ejection?
- Opening of the aortic (and pulmonic) valve, when ventricular pressure exceeds aortic pressure
- What event marks the beginning of isovolumetric relaxation?
- Closure of the aortic (and pulmonic) valve, marked by the second heart sound (S2)
- Why is isovolumetric relaxation called 'isovolumetric'?
- Ventricular volume stays constant because both the semilunar and atrioventricular valves are closed while pressure falls
- What event ends isovolumetric relaxation and begins rapid ventricular filling?
- Opening of the mitral (and tricuspid) valve, when atrial pressure exceeds ventricular pressure
- What heart sound, when present, corresponds to rapid ventricular filling and is often a normal finding in children?
- The third heart sound (S3)
- What heart sound corresponds to atrial contraction (the atrial 'kick') late in diastole?
- The fourth heart sound (S4)
- What is the a wave on the jugular venous pulse (or atrial pressure tracing) caused by?
- Atrial contraction
- What is the c wave on the jugular venous pulse caused by?
- Bulging of the tricuspid valve into the right atrium during isovolumetric ventricular contraction
- What is the v wave on the jugular venous pulse caused by?
- Atrial filling against a closed tricuspid valve during ventricular systole
- What is the x descent on the jugular venous pulse caused by?
- Atrial relaxation and downward pulling of the tricuspid valve during ventricular systole
- What is the y descent on the jugular venous pulse caused by?
- Opening of the tricuspid valve and rapid early ventricular filling
- What does the width of a pressure-volume loop along the x-axis represent?
- Stroke volume
- What does the area enclosed within a pressure-volume loop represent?
- Stroke work performed by the ventricle
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