Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema

Recentclinical observations of a high incidence of preexisting respiratoryinfections in pediatric cases of high-altitude pulmonary edema promptedus to ask whether such infections would increase the susceptibility tohypoxia-induced pulmonary edema in young rats. We infected weanlingrats with Sendai virus, thus causing a mild respiratory infection.Within 7 days of infection, Sendai virus was essentially undetectableby using viral culture and immunohistochemical techniques. Animals atday 7 of Sendai virus infection werethen exposed to normobaric hypoxia (fraction of inspiredO₂ = 0.1) for 24 h and examinedfor increases in gravimetric lung water and in vascular permeability,as well as for histological evidence of increased lung water.Bronchoalveolar lavage was performed on a separate series of animals.Compared with control groups, infected hypoxic animals showedsignificant increases in perivascular cuffing, gravimetric lung water,and lung protein leak. In addition, infected hypoxic animals hadincreases in lavage fluid cell counts and protein content compared withcontrols. We conclude that young rats, exposed to moderate hypoxiawhile recovering from a mild viral respiratory infection, maydemonstrate evidence of early pulmonary edema formation, a finding ofpotential relevance to human high-altitude pulmonary edema.