Hemodilution causes decreased compliance in puppies.

Cardiopulmonary bypass and hemodilution in the newborn have been associated with increased myocardial edema, which may be due to immature connective tissue formation. Five adult and four puppy dogs were placed on bypass while compliance and ventricular function (intraventricular balloon) were measured during normohemoconcentration (NH) (hematocrit 45.1, osmolality 307) and hemodilution with normal saline (hematocrit 24.7, osmolality 307). Compared with NH, the adult group showed no change in compliance or function after 90 min of hemodilution. The puppy group showed a marked decrease in compliance with hemodilution compared to NH (P < 0.001) without change in ventricular function when peak systolic pressure was plotted against end-diastolic volume. Electron micrographs confirmed greater edema formation in the puppy group than the adult group with hemodilution. These changes demonstrate that the newborn heart is more sensitive to edema formation than the adult during hemodilution and that filling pressures do not necessarily reflect ventricular performance during the early post-perfusion period when compliance is decreased.