Cytologic and endoscopic findings after intrapulmonary blood inoculation in horses

The bronchial trees of 8 horses were inoculated with citrated autologous blood, and subsequent observations were compared with those from 3 controls. Free blood was observed at the external nares of six of the eight horses after inoculation. Changes in the appearance of the trachea and changes in the cytologic properties of tracheal wash aspirates, stained using a rapid Papanicolaou method, were followed over time. The cell types found after blood inoculation included free red blood cells, erythrophages, and siderophages. Erythrophages were found only in the few days after inoculation while siderophages persisted until at least 4 weeks. Finely stippled "early" siderophages were distinguished from granular "aged" siderophages. Direct visual assessment ceased to detect blood after 7 days. Ten percent of the tracheal wash samples contained insufficient cells to permit interpretation. In the 4 weeks after blood inoculation, cytologic evaluation was diagnostic of intrapulmonary blood in 20 out of 21 tracheal washes with sufficient cells for evaluation; that is a false negative rate of 1 in 21. Cytologic interpretation gave 1 false positive diagnosis in 20 tracheal washes in the period up to 4 weeks. This protocol could be modified to study the effects of exercise, drug administration or other variables on the clearance of blood from the pulmonary tree. Comparison of such studies with results from horses with exercise-induced pulmonary hemorrhage (EIPH) may improve our understanding, diagnosis, treatment and monitoring of naturally occurring EIPH in horses.