Cytologic evaluation of BAL fluid is commonly used in clinical and research settings for the diagnosis and monitoring of diffuse lung diseases such as RAO (ie, heaves).1,2 Despite the fact there are guidelines on BAL techniques in horses with RAO3 and inflammatory airway disease,4 there is no general consensus on BAL technique, with wide variations in lavage volume and methods used by various research groups. It is assumed that a single sample of BAL fluid collected from any site is representative of an entire lung.
However, 1 study5 in healthy ponies and ponies with RAO in remission revealed variations in results of cytologic counts performed on BAL fluid obtained from the same animals at various times during a 4-week period. We suspect that some variations may be observed in cell populations in consecutive BAL samples obtained over time.
Controversy persists on the necessity to analyze 1 or several BAL aliquots for the diagnosis of lung diseases. In humans with bronchitis, the first aliquot is most representative of bronchial material (ie, contains concentrated numbers of neutrophils), whereas subsequent aliquots contain more bronchoalveolar secretions.6 Whether the same is true in horses remains controversial. For instance, investigators in 1 study7 found no significant difference in results of cytologic counts of BAL fluid for 3 sequential 100-mL lavages, compared with those of a single 300-mL lavage. In contrast, investigators in another study1 reported that sequential lavages increased the volume of BAL fluid recovered and the proportion of macrophages in healthy horses. In that study,1 BAL fluid from 3 sequential 100-mL lavages was compared with BAL fluid from a single 300-mL lavage. Investigators in a third study8 reported that although variations were observed, there was no significant difference in nucleated cell counts, differential cell counts, and results of CBCs among sequential and pooled BAL fluid aliquots in clinically normal horses and horses with RAO. In that study,8 300 mL of isotonic saline (0.9% NaCl) solution was introduced into a bronchus, and 3 sequential BAL fluid aliquots of 20 mL were collected and compared with pooled BAL fluid. Therefore, it was concluded that all aliquots were representative of the cell population of the lavaged lung segment.8
It has been assumed that cell populations are similar in BAL fluid recovered from sites throughout the lungs in clinically normal horses. Investigators in an aforementioned study1 reported that there was no significant difference in cellular composition of BAL fluid between the right and left lungs in healthy horses, except for the number of mast cells, which was significantly higher in the left lung. Because RAO is a diffuse pulmonary disease, we postulated that cell populations in BAL fluid should be uniform in both lungs.
To our knowledge, cytologic analysis of BAL fluid collected repeatedly over time and comparison of results between the right and left lungs of horses with clinical RAO stabled in conditions with constant mold exposure have not been reported. Thus, the objectives of the study reported here were to examine variations in cell populations in BAL fluid collected at various times (February, March, and April) in healthy horses and horses with RAO, effects of repeated sample collections (first and second aliquots) on results of BAL fluid analysis, and differences in the cellular composition of BAL fluid between the right and left lungs. Our hypotheses were that temporal variations in cell populations in BAL fluid would be detected in horses with RAO, the second aliquot would have a lower neutrophil concentration than would the first aliquot, and no significant differences would be detected in samples of BAL fluid obtained from the right and left lungs.
Recurrent airway obstruction
Fleisch No. 4, Oem Medical, Richmond, Va.
Model 143PC03D, Micro switch, Honeywell, Scarborough, ON, Canada.
Model HCXPM005D6V, Sensor Technics, Newport News, Va.
Anadat, RHT Infodat, Montreal, QC, Canada.
Labdat 5.1, RHT Infodat, Montreal, QC, Canada.
Rompun, Bayvet, Etobicoke, ON, Canada.
Torbugesic, Ayerst Laboratories, Montreal, QC, Canada.
Lurocaine, Vetoquinol, Lavaltrie, QC, Canada.
Cytospin, Shandon Southern Instruments Corp, Pittsburgh, Pa.
HEMA 3 stain set, Fisher Scientific Co, Kalamazoo, Mich.
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