Relationship between prevalence and severity of exercise-induced pulmonary hemorrhage and environmental factors

Environmental risk factors could contribute to the development of exercise-induced pulmonary hemorrhage (EIPH) in racing Thoroughbreds.

To identify environmental risk factors that might contribute to differences in EIPH prevalence and severity across 12 Thoroughbred racetracks in the United States.

Eight hundred fifteen 2-year-old and 122 >2-year-old Thoroughbred racehorses.

Prospective blinded observational study. Videoendoscopy was performed 30-60 min post-race. Three observers independently assigned an EIPH grade to each videorecording, and prevalence and severity of EIPH were determined. Multivariable logistic regression assessed relationships between EIPH prevalence and severity, respectively, and independent variables including furosemide administration, race distance and surface, and lifetime race number (LRN). P ≤ .05 was considered significant.

One thousand one hundred ninety-two videorecordings received EIPH severity grades from 12 racetracks in 10 different states and 3 time zones. Ambient temperature (AT) was negatively associated with EIPH prevalence (OR = 0.82, 95% CI, 0.69-0.98; P = .03) and severity (OR = 0.79, 95% CI, 0.63-0.99; P = .04). Furosemide administration (OR = 0.04, 95% CI, 0.006-0.33; P = .002), turf (OR = 0.64, 95% CI, 0.43-0.95; P = .027) and all weather (OR = 0.03, 95% CI, 0.004-0.26; P = .001) track surfaces, and LRN (OR = 1.07, 95% CI, 1.01-1.12; P = .012) were associated with occurrence of EIPH. Two-year-olds racing in bad air (air quality index [AQI] > 100) had more severe EIPH than those racing in AQI < 50 (OR = 2.78, 95% CI, 1.06-7.29; P = .04).

AT, AQI, LRN, and surface type might be associated with EIPH prevalence and severity between American racetracks.