Br. vet. j (1992) . 148, 3
GUEST EDITORIAL PULMONARY FUNCTION TESTING IN LARGE ANIMAL MEDICINE
C . A. ROBERTS Department of Comparative Physiology, Animal Health Trust, P .O. Box 5, Newmarket, Suffolk CB8 7DW
Respiratory diseases represent a major cause of loss of production in agricultural animals and loss of performance in species trained for their athletic prowess . Whilst cases of overt respiratory disease may be relatively easily detected, subclinical disorders present the clinician with a major diagnostic challenge . Additionally, the consistency with which the effects of pulmonary dysfunction may be quantified clinically is hampered by `observer variation' which may be quite considerable (Stradling, 1973) . The use of pulmonary function testing to facilitate the diagnosis and monitoring of respiratory conditions in human medicine is well established (West, 1987) . A wide variety of tests are available, some of which may be carried out quickly and simply by the medical practitioner as `bed side' tests . Whilst not replacing the need for a thorough clinical assessment of the patient, such tests provide useful data for the objective assessment of lung function and responses to therapy . Unfortunately, many of the clinically useful tests in man, such as the commonly used FEV, (forced expiratory volume over one second) and PEFR (peak expiratory flow rate), require patient cooperation and are therefore of little value to the veterinary clinician . Other tests may be difficult to apply in veterinary practice due to considerations of scale and economics . However, despite the limitations placed on the large animal clinician or researcher wishing to measure pulmonary function, many procedures are applicable to the domestic species and in the last 20 years or so there has been a progressive increase in the use of pulmonary function tests in the contexts of both research and diagnosis . Although a range of tests have been used in large animals for the investigation of normal and abnormal respiratory function, the techniques which have gained the greatest popularity for in-field use are blood gas analysis and measurement of oesophageal pressures as an estimate of intrapleural pressure . Clinically these have been widely applied in the horse, in which species Sasse (1971) and McPherson et al. (1978) found them useful in the identification of chronic obstructive pulmonary disease . The application of these techniques to measure pulmonary function in calves with naturally occurring chronic respiratory disease as reported in this issue (Collie, 1992h) is therefore of considerable interest . The respiratory system has a great reserve capacity to allow for the demands of
4
BRITISH VETERINARY JOURNAL, 148, 1
exercise so that significant abnormalities can be present which are not apparent at rest . The use of exercise testing to force utilization of this reserve to reveal such abnormalities is a well accepted procedure in man (Godfrey, 1974) . In large animal medicine, clinical applications of exercise testing have chiefly centred on the horse and there have been many studies on the cardiorespiratory response to exercise in healthy horses (Rose & Evans, 1987) and in animals with upper or lower respiratory tract disorders (Shappell et al., 1988 ; Pollman & Hörnicke, 1987) . For obvious reasons, this approach to clinical diagnosis has been little used in the ruminant although there is now increasing interest in the exercise physiology of the racing camel . It is likely, however, that clinical applications of pulmonary function testing in the non-athletic species will remain in the realm of resting studies . Also in this issue, Collie (1992a), reporting measurements of pulmonary mechanics in normal calves, draws attention to the large variability of some pulmonary function tests in both man and ruminants . Derksen et al. (1982) found similar variability in a number of pulmonary function tests in ponies and concluded that this precluded the use of those tests for the detection of mild or moderate lung disease in individual horses . In the clinical sphere, however, the object must be the development of tests which will aid in the detection of low-grade or subclinical disease which is not demonstrable by other means . Studies of naturally occurring respiratory disease present further problems due to the wide range of severity and the variations in the pathology of individual cases . Investigations are further complicated by varied responses of animals unaccustomed to examination and, in the case of in-field testing, the differences in conditions between farms . In production animals, it would be helpful to develop prognostic indicators which might aid in deciding the likelihood of successful treatment, as this may be difficult to predict (Vestweber et al., 1977) . In view of the correlation between clinical score and arterial blood gas measurements described in field cases of chronic respiratory disease (Collie, 1992b), it may be of value to attempt to correlate such measurements with responsiveness to treatment and pathological findings to determine whether they have a prognostic role .
REFERENCES
COLLIE, D . D . S.
(1992a) . Pulmonary mechanics measurements in normal calves . Br. vet . J.
148,23-32 . (1992b) . Pulmonary function changes and clinical findings associated with respiratory disease in calves. Br. vet . J. 148, 33-40 . DERKSEN, F . J ., ROBINSON, N . E ., SLOCOMBE, R . F ., RIEBOLD, T . W. & BRUNSON, D . B . (1982) . Pulmonary function tests in standing ponies : reproducibility and effect of vagal blockade . Am . J. vet . Res . 43, 598 . GODFREY, S. (1974) . Exercise Testing in Children . London : W. B . Saunders . MCPHERSON, E . A., LAWSON . G . H . K., MURPHY, J . R., et al. (1978) . Chronic obstructive pulmonary disease (COPD) : identification of affected horses . Equine vet. J. 10, 47-53 . POLLMAN, U . & HÖRNIcICE, H . (1987) . Characteristics of respiratory airflow during exercise in horses with reduced performance due to pulmonary emphysema or bronchitis . In Equine COLLIE, D . D . S .
GUEST EDITORIAL
Exercise Physiology 2, eds J . R. Gillespie & N . E . Robinson, pp . 760-71 . Davis, USA : ICEEP Publications. ROSE, R . J . & EVANS, D . L . (1987) . Cardiovascular and respiratory function in the athletic horse . In Equine Exercise Physiology 2, eds . J . R. Gillespie & N . E . Robinson, pp . 1-24 . Davis, USA: ICEEP Publications . SASSE, H . H . L . (1971) . Some pulmonary function tests in horses . PhD thesis, State University of Utrecht . Cited by McPherson, E . A ., Lawson, G . H . K ., Murphy, J . R., et al. (1978) . Equine vet. j 10, 47-53 . SHAPPELL, K. K ., DERKSEN, F . J ., STICK, J . A. & ROBINSON, N . E . (1988) . Effects of ventriculectomy, prosthetic laryngoplasty, and exercise on upper airway function in horses with induced left laryngeal hemiplegia . Am. j vet. Res . 49, 1760-5 . STRAHI.i«c, P . (1973) . Discussion . In Gerber, 1-1 . Chronic pulmonary disease in the horse . Equine vet . j 5, 26-33 . WEST, J . B . (1987) . Pulmonary Pathophysiology-the Essentials, 3rd edn . Baltimore, USA : Williams and Wilkins . VESTWEBER, G . E ., GUFFY, M ., KELLY, B . & LEIPOLD, H . W . (1977) . Chronic bronchopneumonia in cattle . Bovine Practit . 55, 5 .5-62 .
GUEST EDITORIAL PULMONARY FUNCTION TESTING IN LARGE ANIMAL MEDICINE
C . A. ROBERTS Department of Comparative Physiology, Animal Health Trust, P .O. Box 5, Newmarket, Suffolk CB8 7DW
Respiratory diseases represent a major cause of loss of production in agricultural animals and loss of performance in species trained for their athletic prowess . Whilst cases of overt respiratory disease may be relatively easily detected, subclinical disorders present the clinician with a major diagnostic challenge . Additionally, the consistency with which the effects of pulmonary dysfunction may be quantified clinically is hampered by `observer variation' which may be quite considerable (Stradling, 1973) . The use of pulmonary function testing to facilitate the diagnosis and monitoring of respiratory conditions in human medicine is well established (West, 1987) . A wide variety of tests are available, some of which may be carried out quickly and simply by the medical practitioner as `bed side' tests . Whilst not replacing the need for a thorough clinical assessment of the patient, such tests provide useful data for the objective assessment of lung function and responses to therapy . Unfortunately, many of the clinically useful tests in man, such as the commonly used FEV, (forced expiratory volume over one second) and PEFR (peak expiratory flow rate), require patient cooperation and are therefore of little value to the veterinary clinician . Other tests may be difficult to apply in veterinary practice due to considerations of scale and economics . However, despite the limitations placed on the large animal clinician or researcher wishing to measure pulmonary function, many procedures are applicable to the domestic species and in the last 20 years or so there has been a progressive increase in the use of pulmonary function tests in the contexts of both research and diagnosis . Although a range of tests have been used in large animals for the investigation of normal and abnormal respiratory function, the techniques which have gained the greatest popularity for in-field use are blood gas analysis and measurement of oesophageal pressures as an estimate of intrapleural pressure . Clinically these have been widely applied in the horse, in which species Sasse (1971) and McPherson et al. (1978) found them useful in the identification of chronic obstructive pulmonary disease . The application of these techniques to measure pulmonary function in calves with naturally occurring chronic respiratory disease as reported in this issue (Collie, 1992h) is therefore of considerable interest . The respiratory system has a great reserve capacity to allow for the demands of
4
BRITISH VETERINARY JOURNAL, 148, 1
exercise so that significant abnormalities can be present which are not apparent at rest . The use of exercise testing to force utilization of this reserve to reveal such abnormalities is a well accepted procedure in man (Godfrey, 1974) . In large animal medicine, clinical applications of exercise testing have chiefly centred on the horse and there have been many studies on the cardiorespiratory response to exercise in healthy horses (Rose & Evans, 1987) and in animals with upper or lower respiratory tract disorders (Shappell et al., 1988 ; Pollman & Hörnicke, 1987) . For obvious reasons, this approach to clinical diagnosis has been little used in the ruminant although there is now increasing interest in the exercise physiology of the racing camel . It is likely, however, that clinical applications of pulmonary function testing in the non-athletic species will remain in the realm of resting studies . Also in this issue, Collie (1992a), reporting measurements of pulmonary mechanics in normal calves, draws attention to the large variability of some pulmonary function tests in both man and ruminants . Derksen et al. (1982) found similar variability in a number of pulmonary function tests in ponies and concluded that this precluded the use of those tests for the detection of mild or moderate lung disease in individual horses . In the clinical sphere, however, the object must be the development of tests which will aid in the detection of low-grade or subclinical disease which is not demonstrable by other means . Studies of naturally occurring respiratory disease present further problems due to the wide range of severity and the variations in the pathology of individual cases . Investigations are further complicated by varied responses of animals unaccustomed to examination and, in the case of in-field testing, the differences in conditions between farms . In production animals, it would be helpful to develop prognostic indicators which might aid in deciding the likelihood of successful treatment, as this may be difficult to predict (Vestweber et al., 1977) . In view of the correlation between clinical score and arterial blood gas measurements described in field cases of chronic respiratory disease (Collie, 1992b), it may be of value to attempt to correlate such measurements with responsiveness to treatment and pathological findings to determine whether they have a prognostic role .
REFERENCES
COLLIE, D . D . S.
(1992a) . Pulmonary mechanics measurements in normal calves . Br. vet . J.
148,23-32 . (1992b) . Pulmonary function changes and clinical findings associated with respiratory disease in calves. Br. vet . J. 148, 33-40 . DERKSEN, F . J ., ROBINSON, N . E ., SLOCOMBE, R . F ., RIEBOLD, T . W. & BRUNSON, D . B . (1982) . Pulmonary function tests in standing ponies : reproducibility and effect of vagal blockade . Am . J. vet . Res . 43, 598 . GODFREY, S. (1974) . Exercise Testing in Children . London : W. B . Saunders . MCPHERSON, E . A., LAWSON . G . H . K., MURPHY, J . R., et al. (1978) . Chronic obstructive pulmonary disease (COPD) : identification of affected horses . Equine vet. J. 10, 47-53 . POLLMAN, U . & HÖRNIcICE, H . (1987) . Characteristics of respiratory airflow during exercise in horses with reduced performance due to pulmonary emphysema or bronchitis . In Equine COLLIE, D . D . S .
GUEST EDITORIAL
Exercise Physiology 2, eds J . R. Gillespie & N . E . Robinson, pp . 760-71 . Davis, USA : ICEEP Publications. ROSE, R . J . & EVANS, D . L . (1987) . Cardiovascular and respiratory function in the athletic horse . In Equine Exercise Physiology 2, eds . J . R. Gillespie & N . E . Robinson, pp . 1-24 . Davis, USA: ICEEP Publications . SASSE, H . H . L . (1971) . Some pulmonary function tests in horses . PhD thesis, State University of Utrecht . Cited by McPherson, E . A ., Lawson, G . H . K ., Murphy, J . R., et al. (1978) . Equine vet. j 10, 47-53 . SHAPPELL, K. K ., DERKSEN, F . J ., STICK, J . A. & ROBINSON, N . E . (1988) . Effects of ventriculectomy, prosthetic laryngoplasty, and exercise on upper airway function in horses with induced left laryngeal hemiplegia . Am. j vet. Res . 49, 1760-5 . STRAHI.i«c, P . (1973) . Discussion . In Gerber, 1-1 . Chronic pulmonary disease in the horse . Equine vet . j 5, 26-33 . WEST, J . B . (1987) . Pulmonary Pathophysiology-the Essentials, 3rd edn . Baltimore, USA : Williams and Wilkins . VESTWEBER, G . E ., GUFFY, M ., KELLY, B . & LEIPOLD, H . W . (1977) . Chronic bronchopneumonia in cattle . Bovine Practit . 55, 5 .5-62 .
