Am. J. Respir. Crit. Care Med., Vol 150, No. 3, 09 1994, 752-758.
Effects of continuous positive airway pressure on cardiac output in normal and hypervolemic unanesthetized pigs
J Genovese, M Moskowitz, A Tarasiuk, LM Graver and SM Scharf
Division of Pulmonary and Critical Care Medicine, Long Island Jewish Medical Center, Albert Einstein College of Medicine, New Hyde Park, New York.
Continuous positive airway pressure (CPAP) has been used to increase
cardiac index (CI) in patients with congestive cardiomyopathy in the
presence of elevated pulmonary wedge pressure. We hypothesized that with
normovolemia, CPAP would decrease CI because of decreased left ventricular
(LV) preload, whereas in hypervolemia CPAP would increase CI because of a
decrease in afterload. We tested this hypothesis on nine sedated,
unanesthetized pigs instrumented 5 to 10 d before study. We measured CI,
heart rate, stroke volume, LV end-diastolic and end- systolic pressures,
and LV dimensions at CPAP levels 0, 5, 10, 15, and 20 cm H2O before and
after volume expansion with hetastarch (35 ml/kg). From LV dimensions, LV
end-diastolic (LVEDV) and LV end-systolic volumes (LVESV) and LV ejection
fraction (LVEF) were calculated. With normovolemia, CI and LVEDV decreased
with increased CPAP. Volume infusion produced mild cardiac dysfunction as
evidenced by increased LV volumes, decreased LVEF, and decreased
contractility. With hypervolemia, CPAP produced an increase in CI, decrease
in LVEDV and LVESV, and an increase in LVEF. At higher values of CPAP, we
observed decreased CI and LVEDV as with normovolemia. We conclude that with
normovolemia, CPAP's effects are mainly related to changes in preload.
Hypervolemia produced mild cardiac dysfunction. The improvement in CI with
CPAP appears predominantly to be secondary to decrease in LV afterload, but
a mild preload effect, which parallels the effect seen with normovolemia,
was superimposed on afterload changes at higher CPAP values.
