Experimental mild pulmonary inflammation promotes the development of exercise-induced pulmonary haemorrhage



Reasons for performing study: Histological studies of exercise-induced pulmonary haemorrhage (EIPH) reveals inflammatory infiltrates within areas of lung that contain haemorrhage. This has resulted in the hypothesis that pulmonary inflammation could cause EIPH or contribute to an increased risk or severity of EIPH.

Objectives: To determine whether experimentally-induced pulmonary inflammation predisposes the lung to haemorrhage during exercise, by evaluating the bronchoalveolar lavage (BAL) cytology of normal and inflamed regions of lung following high speed treadmill exercise.

Materials and methods: Transendoscopic airway inoculations of 0.01% acetic acid were used to induce mild localised inflammation within bronchopulmonary segments. Horses underwent high speed exercise 24 h after inoculation. Following exercise, inoculated sites and corresponding segments in the opposite lung underwent BAL. The cytology results from inflamed and control bronchopulmonary segments were compared, using paired t tests.

Results: Erythrocytes were present in BAL samples from 12.5% (1/8) control segments compared with 75% (6/8) inoculated segments following exercise, indicating a significant increase (P = 0.04) in the relative risk of EIPH following the development of pulmonary inflammation. Samples from inoculated segments had significantly higher percentages and numbers of neutrophils (12.1 ± 1.0% and 601 ± 98 cells/μl) than control samples (4.3 ± 0.3% and 214 ± 52 cells/μl). Significantly higher erythrocyte numbers were observed in samples from inoculated segments (14,304 ± 6862 cells/μl) compared with control samples (3.5 ± 3.5 cells/μl).

Conclusions: The results showed inflammation increased the risk of developing pulmonary haemorrhage during exercise. These findings do not conflict with current theories on the common causes of EIPH, but suggest that care should be taken when recommending exercise in horses suspected to be suffering from pulmonary inflammatory disease. In addition, specific therapy to reduce pulmonary inflammation may benefit horses prone to the development of EIPH.