TITLE:
Morphine has latent deleterious effects on the ventilatory responses to a hypoxic-hypercapnic challenge
AUTHORS:
Walter J. May, Fraser Henderson Jr., Ryan B. Gruber, Joseph F. Discala, Alex P. Young, James N. Bates, Lisa A. Palmer, Stephen J. Lewis
KEYWORDS:
Morphine; Hypoxia-Hypercapnia; Minute Ventilation; Arterial Blood Gases; Conscious Rats
JOURNAL NAME:
Open Journal of Molecular and Integrative Physiology,
Vol.3 No.3,
August
28,
2013
ABSTRACT: This study explored the concept that morphine has
latent deleterious actions on the ventilatory control systems that respond to a
hypoxic-hypercapnic challenge. In this study, we examined the ventilatory responses elicited by hypoxic-hypercapnic challenge in conscious rats at a time
when the effects of morphine (10 mg/kg) on arterial blood-gas chemistry and minute ventilation had subsided. Morphine induced pronounced changes in arterial
blood-gas chemistry (e.g., an increase in pCO2, decreases in pO2 and sO2) and decreases in minute ventilation. Despite the complete
resolution of the morphine-induced changes in arterial blood-gas chemistry
and minute ventilation and almost complete resolution of the effects on peak inspiratory flow and peak expiratory flow, subsequent exposure to hypoxic-hypercapnic challenge elicited markedly
blunted increases in minute ventilation and in peak inspiratory and expiratory
flows. These findings demonstrate that 1)
the changes in arterial blood-gas chemistry elicited by morphine
parallel changes in minute ventilation
rather than PIF and PEF, and 2) morphine has latent untoward effects on
the ventilatory responses to
hypoxic-hypercapnic challenge. These novel
findings raise the possibility that patients deemed to have recovered
from the acute ventilatory depresssant effects of morphine may still be
susceptible to the latent effects of this opioid analgesic. The mechanisms
underlying these latent effects remain to be elucidated.