AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 5 1286-R1293, Copyright © 1991 by American Physiological Society
Cardiovascular and pulmonary effects of morphine in conscious pigs
J. P. Hannon and C. A. Bossone
Division of Military Trauma Research, Letterman Army Institute of Research, Presidio of San Francisco, California 94129.
Cardiovascular and pulmonary effects of morphine (1 mg/kg bolus iv) were
investigated in conscious chronically instrumented pigs, a species
exhibiting an excitable response. Control animals received an equivalent
volume (less than 2 ml) of normal saline. Morphine induced an immediate but
small increase in cardiac output and substantial increases in heart rate,
mean systemic and pulmonary arterial pressure, left and right ventricular
work, hematocrit, and hemoglobin concentration, but did not change stroke
volume or systemic vascular resistance. Morphine administration also led to
a gradual increase in ventilatory rate and rapid increases in tidal volume,
expired and alveolar ventilation, ventilation-perfusion ratio, and shunt
fraction. In addition, morphine administration produced substantial
decrements in arterial and mixed venous PO2, hemoglobin saturation and
mixed venous O2 content; no change in arterial O2 content; and a widening
of the arteriovenous O2 difference. Arterial O2 transport was increased
slightly. Finally, it produced substantial increments in arterial and mixed
venous PCO2 and substantial decrements in arterial and mixed venous pH. It
was concluded that arterial O2 delivery did not adequately rise to meet
tissue O2 demand, in part because an appropriate increase in cardiac output
was attenuated by morphine, and in part because morphine impaired pulmonary
gas exchange.
