A definitive diagnosis of exercise-induced pulmonary hemorrhage is provided by postexercise endoscopy and visualization of blood in the trachea. The classification of a horse as exercise-induced pulmonary hemorrhage positive or negative has for the past 20 to 30 years been based primarily on the presence or absence of blood in the trachea after exercise. Simply recording exercise-induced pulmonary hemorrhage as positive or negative is not particularly informative, especially if comparing a horse before and after treatment over time as the amount of blood may vary from as little as a single fleck to the trachea being completely covered with a film of blood. Various scoring systems have been described, for example the following:
- Grade 1: flecks of blood
- Grade 2: more than flecks, but less than a continuous stream
- Grade 3: continuous stream less than half the tracheal width
- Grade 4: continuous stream greater than half the tracheal width
- Grade 5: airways awash with blood
The timing of endoscopic examination may be critical in cases of milder exercise-induced pulmonary hemorrhage. If endoscopy is performed immediately postexercise, hemorrhage in the distal airways may not have progressed to the trachea. Similarly, if endoscopy is undertaken too long after exercise, blood may have been removed by the mucociliary escalator and swallowed. On the basis of most reports in the literature, endoscopy 30 to 60 minutes after exercise is recommended.
Relatively infrequently, blood in the trachea may not originate from the lung but from the upper airway and can be inhaled. In this instance the pattern is usually different to that seen in typical exercise-induced pulmonary hemorrhage, with more blood seen in the proximal trachea and decreasing amounts of blood observed moving toward the carina.
The presence of free red blood cells and hemosiderophages in tracheal wash fluid indicates a previous episode of hemorrhage. In horses undertaking a canter or gallop this most likely suggests a history of exercise-induced pulmonary hemorrhage. Although the numbers of free red blood cells are likely to be highest immediately after exercise, peak numbers of hemosiderophages may not be seen until 7 to 21 days after an episode of exercise-induced pulmonary hemorrhage. It is difficult to relate numbers of hemosiderophages to the severity of a previous episode of exercise-induced pulmonary hemorrhage.
More recently the concentration of red blood cells (RBCs) in bronchoalveolar lavage (bronchoalveolar lavage) has been used to quantify exercise-induced pulmonary hemorrhage. This is performed using an endoscope and has the advantage that a scoring of blood in the trachea and tracheal wash can be performed before bronchoalveolar lavage. The left and right lungs also can be selectively lavaged. bronchoalveolar lavage is performed around 30 to 60 minutes after exercise with a volume of 300 ml per lung, in one or two aliquots (i.e., 300 ml infused and aspirated or 150 ml infused, aspirated, and repeated). bronchoalveolar lavage may be performed conveniently without an endoscope, using a bronchoalveolar lavage tube (see “Bronchoalveolar Lavage”). This has the advantage of sometimes allowing a better wedge to be obtained as a result of the balloon cuff, but the disadvantage of lacking the opportunity for direct visual inspection of blood and secretions in the airways.
The use of bronchoalveolar lavage allows better quantification of exercise-induced pulmonary hemorrhage and detects exercise-induced pulmonary hemorrhage at a level below that which results in visible blood in the trachea. Some reports say blood is seen in the trachea only when the sum of bronchoalveolar lavage red blood cell counts for the left and right lung exceed approximately 13,000 red blood cell/μl (13 x 106 red blood cell/ml) of bronchoalveolar lavage fluid. At this concentration of red blood cell, bronchoalveolar lavage fluid appears clearly red rather than simply orange tinged or pink.
In this author’s laboratory sequential selective bronchoalveolar lavage in horses performed using an endoscope (as opposed to a blindly passed bronchoalveolar lavage tube) in both the left and right dorsocaudal lung has demonstrated that hemorrhage based on red blood cell counts is almost always greater in one lung than the other. No consistent side produces more hemorrhage between horses, but within a horse one side almost always shows more hemorrhage than the other.
Chest radiography appears to be of limited value in diagnosis of exercise-induced pulmonary hemorrhage or even for detecting structural alterations in the lung as a result of many repeated episodes, even over a number of years. Pulmonary scintigraphy may detect moderate to severe alterations in the perfusion and possibly ventilation of the dorsocaudal lung. The use of radiolabeled red blood cells and scintigraphy to localize and or quantify hemorrhage is not useful because of general sequestration of labeled red blood cell by the lung, even in the absence of hemorrhage.
Ultrasound may be used to detect changes in the dorsocaudal lung fields associated with exercise-induced pulmonary hemorrhage. The efficacy of this method to diagnose exercise-induced pulmonary hemorrhage is unknown.