TYK35
All of the following concerning cardiac physiology are true EXCEPT:
A. Cardiac output is INVERSELY proportional to afterload
B. The right ventricular output is more sensitive to increases in afterload when compared to the left ventricle
C. When using a pulmonary artery catheter, SVR can be directly measured
D. Arteriolar tone is the primary determinant of SVR
Answer
The answer is C. SVR (and SVRI) are calculated based on measured cardiac output, MAP and CVP. This is why some people don't care what the SVR and SVRI are as long as they know the BP and CO. The right ventricle is more sensitive to increases in afterload due to its relatively thin wall compared to the LV. This is a similar concept as why single RV will usually do worse long term than single LV patients. The equation for SVR is: SVR= 80 x (MAP-CVP/CO)
Notes
Pappenheimer, J. R., et al. "Role of cerebral fluids in control of respiration as studied in unanesthetized goats." American Journal of Physiology--Legacy Content 208.3 (1965): 436-450.[1]