Physiologic changes during maximal treadmill exercise of poorly performing Standardbred horses with or without tracheal blood post-exercise

From a group of 46 young racing Standardbreds presented for problems of decreased athletic performance, 8 with complete physiological data were found to have blood in the trachea (POS) within 1 h after a maximum exercise test on a high speed treadmill. This group was compared to those horses which had no tracheal blood after treadmill exercise (NEG). Parameters measured during the treadmill test included maximum speed (Vmax), heart rate (HRmax), respiratory and stride frequency (RF, SF, respectively) at maximum speed, aerobic capacity (VO2max/peak), and post-exercise plasma lactate concentration (Lac). Within 1 h of the exercise, bronchoscopy and bronchoalveolar lavage were also performed. There were no differences between the groups in Vmax, HRmax, SF, VO2 max/peak, or Lac, but there was a significant decrease in RF at end exercise (85±5.9 vs 96±10.9 breaths per minute) in the POS group of horses. The bronchoalveolar findings were suggestive of increased airway inflammation in more of the POS horses, whereas all horses had haemosiderophages present. It is suggested that some horses with blood in the trachea after exercise may have an associated decrease in respiratory rate at the point of fatigue during exercise. The validity of using tracheal blood as the sole criterion for sanctioned, yet empirical treatment of race horses for exercise-induced pulmonary haemorrhage is questioned.