Describe the cardiovascular effects of a sudden increase in afterload.
It was expected the answer would start with a definition of afterload and then proceeded to
indicate what effects this increase in afterload would have on ventricular end-systolic pressure,
ventricular end-diastolic pressure, left atrial pressure, cardiac output, myocardial oxygen
demand and myocardial work, coronary blood flow and systemic blood pressure.
Most candidates who failed to pass this question submitted answers that were just too brief,
only including a small subset of the material required. Very few candidates included any
mention of myocardial oxygen demand or myocardial work or the impact upon the cardiac
output. A number of candidates included a detailed description of the Sympathetic Nervous
System and the Renin-Angiotensin system, material which was not asked for. There were
quite a number of incorrect perceptions about what effect a sudden increase in afterload would
have on the systemic blood pressure. Candidates who mentioned the baroreceptor response
and the stretch receptor response where rewarded with additional credit.
Afterload can be defined as the resistance to ventricular ejection - the "load" that the heart must eject blood against. It consists of two main sets of determinant factors:
- Myocardial wall stress, which represents intracardiac factors
- Input impedance, which represents extracardiac factors
|Cardiovascular variable||How it changes with increased afterload, and why|
Ideally, remains stable if all the compensatory reflexes work as they are supposed to.
Ideally, remains stable. Or:
Decreases; because of:
Increases, because of:
Increases, because of the acute increase in preload (as above)
|Myocardial oxygen consumption||
|Coronary blood flow||
Freeman, GREGORY L. "Effects of increased afterload on left ventricular function in closed-chest dogs." American Journal of Physiology-Heart and Circulatory Physiology 259.2 (1990): H619-H625.
Norton, James M. "Toward consistent definitions for preload and afterload."Advances in physiology education 25.1 (2001): 53-61.
ROTHE, CARL. "Toward consistent definitions for preload and afterload—revisited." Advances in physiology education 27.1 (2003): 44-45.
Vest, Amanda R. "Afterload." Cardiovascular Hemodynamics. Humana, Cham, 2019. 23-40.
Milnor, William R. "Arterial impedance as ventricular afterload." Circulation Research 36.5 (1975): 565-570.