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pressure1

  • -Real time measurement of pressure & volume within left ventricle
  • -It gives information on stroke volume, cardiac output, ejection fraction, and myocardial contractility
  • -The LV pressure is plotted against the LV volume at multiple points during a single cardiac cycle

1 → 2 (isovolumetric contraction). The cycle begins at the end of diastole at point 1. Ventricular pressure is low because the ventricular muscle is relaxed. On excitation, the ventricle contracts and ventricular pressure increases. The mitral valve closes when left ventricular pressure is greater than left atrial pressure. Because all valves are closed, no blood can be ejected from the ventricle (isovolumetric).

2 → 3 (ventricular ejection). The aortic valve opens at point 2 when pressure in the left ventricle exceeds pressure in the aorta. Blood is ejected into the aorta, and ventricular volume decreases. The volume that is ejected in this phase is the stroke volume. Thus, stroke volume can be measured graphically by the width of the pressure–volume loop. The volume remaining in the left ventricle at point 3 is end-systolic volume.

3 → 4 (isovolumetric relaxation). At point 3, the ventricle relaxes. When ventricular pressure decreases to less than aortic pressure, the aortic valve closes. Because all of the valves are closed again, ventricular volume is constant (isovolumetric) during this phase.

4 → 1 (ventricular filling). Once left ventricular pressure decreases to less than left atrial pressure, the mitral valve opens and filling of the ventricle begins. During this phase, ventricular volume increases to about 140 mL (the end-diastolic volume).

Loops Based off Drugs

Increased Preload/ Intravenous Fluids

  • -Increases end diastolic volume and increases stroke volume
  • -Increases width of pressure-volume loop

Decreased Afterload – ACE-inhibitors, ARB’s

  • -Increased stroke volume because ventricle ejects blood against a lower pressure in the systemic vasculature
  • -Causes increased width of pressure-volume loop
  • -Decreases end systolic volume

Increased Contractility/Positive Inotropes – Dobutamine, Dopamine

  • -Ventricle develops more tension during systole, leads to an increase in stroke volume
  • -Decreases end systolic volume

pressure2

 

pressure3

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