In the pressure-volume loop shown, movement from point 3 to point 4 corresponds to the stroke volume. Stroke volume is the total amount of blood that is ejected from the left ventricle (LV) during left ventricle contraction. At the end of isovolumetric contraction (point 3) the aorta opens and blood leaves the left ventricle until it closes (point 4) and isovolumetric relaxation begins.
Stroke volume (SV) can be calculated using the following equation:
SV = End Diastolic Volume - End Systolic Volume
Therefore, SV is dependent on diastolic filling (point 1 to point 2) and systolic ejection (point 3 to point 4). During ventricular filling, the mitral valve is open, while the aortic valve is closed. During ejection, the mitral valve is closed, while the aortic valve is open. See Illustration A.
Kagawa et al. state that diastolic filling of the LV is dependent on passive filling of blood into the LV during early diastole, and active filling during late diastole when the atria contract. The authors go on to note that left atrial (LA) contraction volume increases as atrial volume increases. This follows the Frank-Starling principle that increased stretch leads to increased contraction so long as it does not exceed a certain point of stretch at which point atrial contractility would begin to decrease.
Cheitlin notes that during chronic aortic regurgitation the regurgitant leak increases gradually so that the end-diastolic left ventricular volume becomes greater. To compensate for the increased amount of volume the left ventricle responds with dilatation and hypertrophy (eccentric hypertrophy) and stroke volume increases enough to keep the forward effective stroke volume normal.
Answer 1: 4 => 1 corresponds to isovolumetric relaxation.
Answer 2: 1 => 2 corresponds to ventricular filling. The mitral valve is open at this time.
Answer 4: 2 => 3 corresponds to the period isovolumetric contraction of the ventricle while all valves are closed.
Answer 5: The stroke volume can be calculated from this exam and is demonstrated by movement from 3 to 4.
Kagawa K, Arakawa M, Miwa H, Noda T, Nishigaki K, Ito Y, Hirakawa S. [Left atrial function during left ventricular diastole evaluated by left atrial angiography and left ventriculography]. J Cardiol. 1994 Jul-Aug;24(4):317-25
PMID:8057244 (Link to Abstract)
Cheitlin MD. Surgery for chronic aortic regurgitation: when should it be considered? Am Fam Physician. 2001 Nov 15;64(10):1709-14
PMID:11759077 (Link to Abstract)
USMLE World Step 1 QBank Question #1530. Copyright © USMLEWorld, LLC 2012