Why the study?
Acute hypoxia induces sympathetic activation and pulmonary edema; investigators sought to determine whether adrenergic blockade and reduced fluid load attenuate hypoxic cardiopulmonary injury.
Does reduced fluid load or adrenergic blockade prevent left ventricular depression and pulmonary edema in rats exposed to acute normobaric hypoxia?
Does reduced fluid load or adrenergic blockade prevent left ventricular depression and pulmonary edema in rats exposed to acute normobaric hypoxia?
In a rat model of acute hypoxia, reduced fluid load had a protective effect on cardiopulmonary function, whereas increased fluid load promoted pulmonary edema and impaired left ventricular inotropic function.
Reduced fluid load attenuates hypoxic lung injury in rats while adrenergic blockade does not; leaves open relevance to clinical hypoxia management.
Acute normobaric hypoxia may induce pulmonary injury with edema (PE) and inflammation. Hypoxia is accompanied by sympathetic activation. As both acute hypoxia and high plasma catecholamine levels may elicit PE, we had originally expected that adrenergic blockade may attenuate the severity of hypoxic pulmonary injury. In particular, we investigated whether administration of drugs with reduced fluid load would be beneficial with respect to both cardiocirculatory and pulmonary functions in acute hypoxia. Rats were exposed to normobaric hypoxia (10% O2) over 1.5 or 6 h and received 0.9% NaCl or adrenergic blockers either as infusion (1 ml/h, increased fluid load) or injection (0.5 ml, reduced fluid load). Control animals were kept in normoxia and received infusions or injections of 0.9% NaCl. After 6 h of hypoxia, LV inotropic function was maintained with NaCl injection but decreased significantly with NaCl infusion. Adrenergic blockade induced a similar LV depression when fluid load was low, but did not further deteriorate LV depression after 6 h of infusion. Reduced fluid load also attenuated pulmonary injury after 6 h of hypoxia. This might be due to an effective fluid drainage into the pleural space. Adrenergic blockade could not prevent PE. In general, increased fluid load and impaired LV inotropic function promote the development of PE in acute hypoxia. The main physiologic conclusion from this study is that fluid reduction under hypoxic conditions has a protective effect on cardiopulmonary function. Consequently, appropriate fluid management has particular importance to subjects in hypoxic conditions.
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Appelt et al. (2021) studied this question.
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