Journal of Applied Physiology, Vol 66, Issue 2 863-869, Copyright © 1989 by American Physiological Society
Effect of increased afterload on right ventricular function in newborn pigs
J. Belik and R. B. Light
Department of Pediatrics, University of Manitoba, Winnipeg, Canada.
The effect of a progressive increase in right ventricular (RV) afterload
was studied in pigs less than 24 h (group I) and 3-5 days old (group III).
RV load was applied to increase mean pulmonary arterial pressure (Ppa)
until right to left shunt was observed. Initially, pigs in group I had a
significantly lower systemic arterial pressure (Psa = 63 +/- 2 vs. 82 +/- 5
mmHg) and higher Ppa (30 +/- 1 vs. 23 +/- 2 mmHg) even though the RV stroke
work (RVSW) was similar (54.3 +/- 10.8 vs. 32.4 +/- 2.1 mmHg/ml) to group
II. After a progressive rise in afterload, pigs in group I could maintain a
higher RV stroke volume than those in group II (1.3 +/- 0.3 vs. 0.4 +/- 0.1
ml; P less than 0.05). At shunt condition, the RVSW was increased by 21 +/-
14% of the initial value in group I vs. a 32 +/- 8% decrease in group II (P
less than 0.05). The ductus arteriosus was constricted and right-to-left
shunt was observed in all animals at the foramen ovale level even though
Ppa exceeded Psa before the rise in the right atrial pressure in group I.
Thus, as RV afterload is increased in the pig, the older animals' right
ventricle is progressively less capable of maintaining pulmonary blood flow
than animals within 24 h of birth.
