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- Author or Editor: Tatiana Art x
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SUMMARY
Five healthy, fit Standardbreds (mean ± sem, 490.4 ± 15.0 kg, 4.0 ± 0.5 years) were studied during a standardized test carried out on a treadmill. The test consisted of an 8-minute warm-up and a 9-minute exercise period (1 minute at 1.7, 4, 7, 8, 9, and 10 m/s; 2 minutes at 4 m/s; and a 1-minute walk at a 6% slope). Respiratory airflow, tidal volume (Vt), and respiratory frequency (f) were continuously recorded, using 2 ultrasonic pneumotachographs connected to a face mask and mass spectrometer. Oxygen uptake, carbon dioxide output, and expired minute volume (V˙e) were obtained on a breath-by-breath basis. Arterial blood was tested at the end of each step for O2 and CO2 partial pressures. Heart rate was continuously recorded, using a heart rate recording system. Stride frequency was measured at each step, and the stride frequency-to-f ratio was calculated. Venous blood was tested for plasma lactate concentration before and 2 minutes after completion of the test.
Some horses had a locomotion-respiration coupling (lrc), but this coupling was occasional and intermittent. The f was lower and Vt was higher than values reported for Thoroughbreds working under similar experimental conditions. Nevertheless, maximal V˙e did not overshoot maximal V˙e reported in Thoroughbreds. All horses were hypoxemic and hypercapnic, but there was wide variability between subjects. The horses with the highest oxygen uptake and the lowest plasma lactate concentration were more hypoxemic and hypercapnic.
The Standardbreds, studied under our laboratory conditions, did not have constant lrc and had lower f with higher Vt than did Thoroughbreds under similar experimental conditions. Despite these differences in breathing strategy, the Standardbreds did not have higher V˙e than did Thoroughbreds, and they were hypoxemic and hypercapnic. The fact that these Standardbreds, which obviously freely selected their breathing strategy, were unable or unwilling to adopt compensatory hyperventilation reinforces the hypothesis that, in strenuous exercising horses, there could be a physiologic limit to ventilation, most probably related to mechanical factors, but independent of any lrc.
Abstract
Objective—To compare sensitivity of the impulse oscillometry system (IOS) with that of the conventional reference technique (CRT; ie, esophageal balloon method) for pulmonary function testing in horses.
Animals—10 horses (4 healthy; 6 with recurrent airway obstruction [heaves] in remission).
Procedure—Healthy horses (group-A horses) and heaves-affected horses (group-B horses) were housed in a controlled environment. At each step of a methacholine bronchoprovocation test, threshold concentration (TC2SD; results in a 2-fold increase in SD of a value) and sensitivity index (SI) were determined for respiratory tract system resistance (Rrs) and respiratory tract system reactance (Xrs) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (RL) and dynamic lung compliance (Cdyn), by use of CRT.
Results—Bronchoconstriction resulted in an increase in Rrs at 5 Hz (R5Hz) and a decrease in Xrs at all frequencies. Most sensitive parameters were Xrs at 5 Hz (X5Hz), R5Hz, and R5Hz:R10Hz ratio; RL and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC35Cdyn) were significantly less sensitive than these IOS parameters. The TC2SD for Xrs at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC2SD was obtained for X5Hz in group-B horses and R5Hz in group-A horses.
Conclusions and Clinical Relevance—In contrast to CRT parameters, IOS parameters were significantly more sensitive for testing pulmonary function. The IOS provides a practical and noninvasive pulmonary function test that may be useful in assessing subclinical changes in horses. (Am J Vet Res 2003;64:1414–1420)
Abstract
Objective
To assess sensitivity of scintigraphic alveolar clearance rate as an indicator of alveolar epithelium damage in horses.
Animals
5 healthy horses (group A) and 5 with chronic obstructive pulmonary disease (COPD; group B).
Procedure
Horses underwent clearance rate (k [%/min]) determination. Clearance rate of group-B horses was determined after remission of the disease following 2 months at pasture (remission 1), stabling in a controlled environment (remission 2), and during crisis induced by exposure to moldy hay and straw. Methacholine challenge test was performed at each investigation period to determine nonspecific pulmonary airway hyperresponsiveness. Pulmonary function tests (PFT) also were performed, and cell populations in bronchoalveolar lavage (BAL) fluid were determined on another occasion.
Results
Group-B horses had significantly faster mean clearance rate during crisis (k = 4.30 ± 0.95%/min), compared with that for remission 1 (k = 1.98 ± 0.55%/min), which did not differ from the rate in group-A horses (k = 1.95 ± 0.33%/min). Despite lack of clinical signs of COPD during remission when stabled in a controlled environment, an intermediate value was found (k = 3.20 ± 0.72%/min).
Conclusions
This technique allowed grading of lung damage induced by COPD, whereas use of PFT and determination of BAL fluid cell populations failed to differentiate between remission 1 and remission 2.
Clinical Relevance
Determination of alveolar clearance rate by use of scintigraphy is a sensitive indicator of lung damage. A modified clearance rate was found despite the lack of clinical and functional changes. (Am J Vet Res 1999;60:495-500)
