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Topic:Respiratory Health
Respiratory health in horses encompasses the study of the equine respiratory system, its function, and the various conditions that can affect it. The respiratory system in horses includes the upper airways, lungs, and associated structures, which facilitate gas exchange and are vital for maintaining physiological homeostasis during rest and exercise. Common respiratory conditions in horses include equine asthma, infectious diseases like strangles, and exercise-induced pulmonary hemorrhage (EIPH). These conditions can impact a horse's performance and overall health. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, pathophysiology, and management of respiratory health in horses.
Removal of inspissated purulent exudate from the ventral conchal sinus of three standing horses. Primary paranasal sinusitis, complicated by inspissated purulent exudate in a ventral conchal sinus, was diagnosed in 3 horses. Partial nasal obstruction, caused by axial deviation of the ventral concha, was detected endoscopically in 2 of the horses. A mass, dorsal to the maxillary molars, was detected via a lateral radiographic view of the skull of 3 horses and on the dorsoventral view of 1 of the horses. Inspissated purulent exudate was removed from the ventral conchal sinus of the horses via trephination of the conchofrontal sinus and penetration of the caudal wall of the ventral conchal s...
Sevoflurane and oxygen anaesthesia following administration of atropine-xylazine-guaifenesin-thiopental in spontaneously breathing horses. The effects of sevoflurane-oxygen anaesthesia at a light-surgical depth on clinically important features were evaluated in spontaneously breathing horses that received atropine, xylazine, and guaifenesin-thiopental. Mean end-tidal concentrations of sevoflurane ranged from 1.6 to 2.3% during 90 min maintenance. Recovery from anaesthesia was extremely rapid and smooth. Heart rates did not significantly change after anaesthesia. Arrhythmia was not observed. Mean arterial pressure (mean +/- SD) ranged from 86 +/- 17 to 98 +/- 5 mmHg during anaesthesia. Minute ventilation was low due to decreased r...
PGE2 inhibits acetylcholine release from cholinergic nerves in canine but not equine airways. The effects of exogenous prostaglandin E2 (PGE2) and endogenous prostanoids on cholinergic neurotransmission were determined by measurement of acetylcholine (ACh) release from canine and equine airway tissues. Trachealis strips and bronchial segments were suspended in 2 ml tissue baths. ACh release was induced by electrical field stimulation (EFS), and its content in tissue bath liquid was measured by high pressure liquid chromatography (HPLC) with electrochemical detection. In canine airways, exogenous PGE2 (10(-9) to 10(-7) M) inhibited ACh release concentration-dependently, whereas inhibiti...
Effect of increasing work rate on metabolic responses of the donkey (Equus asinus). Oxygen consumption (VO2) and concentration of venous blood metabolites were measured in donkeys trained to run and to pull loads on a treadmill. VO2 in two donkeys running at maximal speed on a 9.8% slope was 110 +/- 2 ml.min-1.kg-1, approximately 22 times preexercise VO2. Average heart rate at maximal VO2 (VO2max) was 223 +/- 2 beats/min, five times the preexercise heart rate. Blood lactate increased 14-fold, and blood glucose did not change (P > 0.05). Animals running up a 4% incline and incremental draft loading of five donkeys walking on the level were also studied. The total energy cost o...
Quantitation of alpha-1 proteinase inhibitor in the pulmonary epithelial lining fluid of horses with chronic obstructive pulmonary disease. The concentration of alpha-1 proteinase inhibitor (API) was measured in the pulmonary epithelial lining fluid (PELF) of horses with chronic obstructive pulmonary disease (COPD) while they had clinical signs and while they had none. The concentrations of total protein, albumin and API were significantly higher in the PELF of animals with clinical signs of COPD. The correlation between albumin and API in the PELF suggested that most of the API was derived from the serum.
Surgical treatment for epiglottic entrapment in horses: 51 cases (1981-1992). Medical records of 51 horses with epiglottic entrapment were reviewed, and the outcome after surgical treatment was evaluated by use of results from a survey of owners and from race records. Horses with epiglottic entrapment and no additional problem (uncomplicated) of the nares, nasal passages, pharynx, or larynx (upper airway) that were treated by transoral axial division (group 1) or resection via laryngotomy (group 2), and horses with epiglottic entrapment complicated by an additional upper airway abnormality (group 3) were compared. The cost of treatment, duration of hospitalization, time...
Beta-glucuronidase and trypsin inhibitor capacity of tracheal lavage fluid as indicators of seasonal airway irritation in the horse. The health of the respiratory tracts of 19 horses was studied for 11 months. The horses were placed into 3 groups (healthy, periodically diseased and continuously diseased) based on the measurements of blood gases, intrapleural pressure and on neutrophil content of tracheal mucus. Lysosomal enzymes (N-acetyl-beta-D-glucosaminidase and beta-glucuronidase) and reflectors of the proteolytic system (plasmin, plasminogen, trypsin inhibitor capacity) were determined. beta-glucuronidase appeared to be a good indicator of the presence of disease of the respiratory system. High beta-glucuronidase value...
Differential artificial ventilation in anesthetized horses positioned in lateral recumbency. Effects of differential ventilation on gas exchange were studied in 7 isoflurane-anesthetized, laterally recumbent horses, and were compared with effects of conventional ventilation, using similar minute volume. A tracheal tube-in-tube intubation technique allowed each lung to be connected separately to an anesthetic circle system with a ventilator. Two distribution patterns of tidal volume were investigated; half the tidal volume was distributed to each lung and two-thirds the tidal volume was distributed to the dependent lung. Effects of the combination of these patterns with positive end-ex...
Gait and respiration in standardbred horses when pacing and galloping. The relationship between gait and the respiratory response to exercise was examined in five standardbred racehorses which exercised on a treadmill at a pace and a gallop. After an initial warm-up, respiratory rate and stride frequency were measured after one and two minutes of treadmill exercise at 80 per cent of maximal oxygen consumption (VO2max), after one minute at 100 per cent VO2max and after two minutes at 100 per cent VO2max (galloping horses only). Exercise at 100 per cent VO2max continued until the horses showed signs of fatigue. Arterial blood was collected during exercise and when ...
Transnasal incision of restrictive nasopharyngeal cicatrix in three horses. Three horses were found to have an extensive nasopharyngeal cicatrix that was responsible for respiratory impairment. The cicatrization was diagnosed by use of endoscopy during evaluations of the horses for inspiratory stridor. All 3 horses were treated by endoscope-guided transnasal incision of the cicatrix and were able to resume their previous activities.
Temperature and pH effects on the oxygen equilibrium curve of the thoroughbred horse. A new oxygen equilibrium curve is defined for the Thoroughbred horse under standard conditions of 37 degrees C, pH = 7.4 and PCO2 = 5.33 kPa. The "standard" P50 for the Thoroughbred is, at 2.83 +/- 0.04 (SE of mean) kPa, significantly lower than that found for the Hanoverian horse (3.17 +/- 0.03 kPa) by Clerbaux et al. (Can. J. Vet. Res. 50: 188-192, 1986), and lower than other values for horses in the literature. Using data from Butler et al. (J. Exp. Biol. 179: 159-180, 1993), curves were also constructed, in vitro, under simulated conditions of intense exercise to examine the individual eff...
Substance P and calcitonin gene-related peptide-like immunoreactive nerve fibers in lungs from adult equids. Distribution of pulmonary nerves immunoreactive for either substance P or calcitonin gene-related peptide was determined, using immunohistochemical methods on healthy lungs from adult equids. The overall patterns of distribution of substance P and calcitonin gene-related peptide-like immunoreactivity were similar. Distribution of immunoreactive nerves was not uniform throughout the lungs; nerve fibers immunoreactive for these peptides were more frequently observed near the hilus of the lung than in the caudal lobes or in the periphery of the lung. Nerve fibers immunoreactive for substance P or...
The trigeminal ganglion is a location for equine herpesvirus 1 latency and reactivation in the horse. Four specific pathogen-free ponies were infected intranasally with equine herpesvirus 1 (EHV-1) and two were similarly infected with an EHV-1 thymidine kinase deletion mutant. The primary infections were characterized by a transient fever accompanied by virus shedding into nasal mucus and viraemia. No virus was detected in clinical specimens after 15 days post-infection. Two months later a reactivation stimulus was administered to all six ponies and only the four that had been previously inoculated with wild-type EHV-1 shed virus into nasal mucus (for 10 days), proving the presence of a latent...
Endoscopic anatomy and map of the equine bronchial tree. To develop a bronchoscopic map of the equine respiratory tree, the major airways of the lungs of 6 healthy Thoroughbred horses were systematically explored with a flexible fibreoptic endoscope through a tracheostomy while the horses were sedated in stocks. With the carina as the reference point, measurements were made of distances to the branches of the major airways using markers on the shaft of the endoscope. All branches were explored until the narrowing of their diameters prevented further advancement of the endoscope. Positions of origins of branches from the parent bronchus were recorded...
Comparative aspects of the strength of pulmonary capillaries in rabbit, dog, and horse. In previous studies of rabbit and dog lung, we demonstrated stress failure of pulmonary capillaries at high transmural pressures (Ptm). The Ptm necessary to elicit stress failure was 40 cmH2O higher in dog than rabbit, and the total blood-gas barrier (BGB) thickness was greater in dog than rabbit. This suggests that stress failure may be related to BGB thickness, and is consistent with the Laplace relationship which states that wall stress is proportional to capillary radius but inversely proportional to wall thickness. In the present studies, we compared BGB thickness and an index of capillar...
Tidal breathing flow-volume loops in horses with recurrent airway obstruction (heaves). Tidal breathing flow-volume (TBFV) loops were determined in a group of control horses and in horses affected with recurrent airway obstruction (heaves). The latter group was studied when the condition was in remission and under increasing amounts of airway obstruction as reflected by measurements of change in pleural pressure, pulmonary resistance, and dynamic compliance. The TBFV loops of control horses had biphasic inspiratory and expiratory patterns; peak inspiratory and peak expiratory flows were detected early in inspiration and expiration, respectively. Tidal volume was unaffected by hea...
Evaluation of a technique for detection of pulmonary hemorrhage in horses, using carbon monoxide uptake. The diffusing capacity for carbon monoxide (DLCO) and the functional residual capacity (FRC) of the lung were measured in 5 healthy Thoroughbreds before and after instillation of autologous blood into their lungs, in an attempt to develop a method to quantitate extravascular blood in the lungs of horses with exercise-induced pulmonary hemorrhage. Mean (+/- SD) baseline values of DLCO and FRC were 333.8 +/- 61.9 ml/min/mm of Hg and 21.464 +/- 4.156 L, respectively. Blood instillation resulted in decreases in DLCO and FRC. The paradoxic decrease in DLCO (we were expecting to find an increase owi...
Effect of helium-induced ventilatory unloading on breathing and diaphragm EMG in awake ponies. Two questions were addressed in this study: 1) Does respiratory resistive unloading (inspired O2 fraction = 0.21, inspired He fraction = 0.79) elicit a compensatory reduction in stimulation of the diaphragm? 2) Do diaphragm and lung afferents contribute to compensatory responses to unloading? Ten intact (I), five diaphragm-deafferented (DD), four hilar nerve-denervated (HND), and seven DD+HND adult ponies were studied at rest and during mild and moderate treadmill exercise. During steady-state unloading at rest, duration of the diaphragm electromyogram (EMGdi) was less (P < 0.05) than contr...
[Prognostic parameters in equine colic]. A retrospective study was performed on 271 horses with colic referred to the I. Medizinische Tierklinik within a period of 2 years, to examine the prognostic value of different clinical and diagnostic laboratory parameters by Student's t-test and the Chi-quadratic test. The following quantitative parameters presented a highly significant prognostic value (P < 0.0001): capillary refill time, pulse rate, heart rate, respiratory rate, hematocrit, hemoglobin concentration, blood lactate, base excess and anion gap. The intensity of colic signs, the degree of disturbance of the patient's gen...
Mechanism of reduction in alveolar-arterial PO2 difference by helium breathing in the exercising horse. Previous work has shown that replacing N2 in air with He at the same inspired O2 fraction reduces the exercise-induced alveolar-arterial PO2 difference (AaPO2) in horses but has provided no mechanism explaining this effect. We sought to distinguish among possible causes by using the multiple inert gas elimination technique. Six horses were studied on a high-speed treadmill while they breathed either ambient air or normoxic He-O2. O2 uptake reached 138.0 ml.min-1.kg-1 and was not affected by He-O2. Temperature-corrected arterial PO2 was 76.7 Torr (air) and 86.9 Torr (He-O2) (P < 0.01). Corre...
Effect of hypoxia on metabolic rate in awake ponies. To determine the effect of hypoxia on metabolic rate (VO2) of ponies, on 2 days we studied ponies that were breathing room air for 1 h followed by 5 h of either hypoxic hypoxia (fractional concn of inspired O2 = 0.126) or 5 h of CO hypoxia. Control arterial PO2 was 103 +/- 1.2 Torr, and at 5 min and 5 h of hypoxic hypoxia, arterial PO2 was 53.1 +/- 1.8 and 41.0 +/- 1.8 Torr, respectively. There was a time-dependent hypocapnia and alkalosis during hypoxic hypoxia. During CO hypoxia, carboxyhemoglobin increased to 25% after 30 min and remained constant thereafter. With increased carboxyhemoglobi...
Respiratory mechanics of horses measured by conventional and forced oscillation techniques. Respiratory mechanics were compared using conventional and forced oscillation techniques in six conscious horses and a mechanical model of the equine respiratory system. The parameters calculated from conventional airflow and esophageal pressure measurements were pulmonary resistance and dynamic compliance. The impedance of the respiratory system was measured at 1, 2, and 3 Hz with the forced oscillation technique, and respiratory system resistance, compliance, inertance, and resonant frequency were calculated. Pulmonary resistance was 1.0 +/- 0.3 cmH2O.l-1.s, and pulmonary dynamic compliance ...
Effect of sodium cromoglycate on light racehorses with elevated metachromatic cell numbers on bronchoalveolar lavage and reduced exercise tolerance. Some young horses with clinical signs of small airway disease demonstrate increased metachromatic cell numbers on bronchoalveolar lavage. The purpose of this study was to determine the effect of sodium cromoglycate treatment on clinical signs, bronchoalveolar lavage cytology and bronchoalveolar lavage histamine parameters in these horses. Twelve racehorses (age: 3.4 +/- 1.6 years) with a history of respiratory embarrassment at exercise, clinical signs of obstructive airway disease and bronchoalveolar lavage metachromatic cell differential greater than 2% were selected. Horses were randomly ass...
Structural and functional characterization of elastases from horse neutrophils. In order better to understand the pathophysiology of the equine form of emphysema, two elastinolytic enzymes from horse neutrophils, referred to as proteinases 2A and 2B, have been extensively characterized and compared with the human neutrophil proteinases, proteinase-3 and elastase. Specificity studies using both the oxidized insulin B-chain and synthetic peptides revealed that cleavage of peptide bonds with P1 alanine or valine residues was preferred. Further characterization of the two horse elastases by N-terminal sequence and reactive-site analyses indicated that proteinases 2A and 2B ha...
Cardiorespiratory and metabolic responses to exercise in horses with various abnormalities of the upper respiratory tract. A standardised incremental exercise test was performed by 9 racehorses with idiopathic laryngeal hemiplegia (ILH), 1 horse with maxillary sinus cysts, 1 horse with epiglottic entrapment, 1 horse with a lesion on the vocal folds, and 1 horse with pharyngitis. Two of the horses with ILH were retested after laryngoplasty and ventriculectomy. The findings were compared with those from 20 normal racehorses. Heart rate, plasma lactate concentration, arterial blood gases, stride frequency, oxygen uptake (VO2) and carbon dioxide production were assessed during treadmill exercise on a +10% slope. The g...
Pleuropneumonia associated with pulmonary hydatidosis in a horse. Hydatid cysts (metacestode of Echinococcus grunulosus) are a
common incidental post-mortem finding in horses in the United
Kingdom (Cranley 1982), being found most frequently in the liver
and the lungs (Schwabe 1986). However, hydatid cysts are well
tolerated by horses and clinical hydatidosis is rare, even in
heavily infected animals (Thompson and Smyth 1975; Thompson
and Allsopp 1988). Clinical disease has been attributed to hydatid
cysts in the equine retrobulbar region (Bamett et ul. 1988), brain
(Gordon 1974, quoted by Thompson 1977) and liver (Barvaux
and Derzelle 1947). This is...
Caudal analgesia induced by epidural or subarachnoid administration of detomidine hydrochloride solution in mares. Seven adult mares were used to determine the analgesic, CNS, and cardiopulmonary effects of detomidine hydrochloride solution after epidural or subarachnoid administration, using both regimens in random sequence. At least 1 week elapsed between experiments. A 17-gauge Huber point (Tuohy) directional needle was used to place a catheter with stylet into either the epidural space at the first coccygeal interspace or the subarachnoid space at the lumbosacral intervertebral junction. Catheters were advanced so that the tips lay at the caudal sacral (S5 to S4) epidural space or at the midsacral (S3 ...
The mechanical coupling of lung ventilation to locomotion in the horse. The phase relationship between the periods of the respiratory and limb cycles is demonstrated in the horse ridden in the field at the canter and gallop. Changes in intra-abdominal pressure, respiratory sounds, periods of ground contact of each foot and volume changes of the rib cage were measured in the normal horse exercised at the walk, trot, canter and gallop in the field. Correlation of these parameters identifies the major mechanical link establishing the coupling of lung ventilation and locomotion in the horse. The force and extent of contraction of the abdominal muscles couples the resp...
Comparison of ventilatory responses to sustained reduction in arterial oxygen tension vs. content in awake ponies. To gain insight into central and peripheral contributions to changes in breathing during hypoxia, we compared effects on breathing of reducing inspired PO2 (hypoxic hypoxia) with reducing arterial O2 content (CaO2) through elevation of carboxy-hemoglobin (COHb) (CO hypoxia). Twelve awake ponies were studied during 1 h of breathing room air followed by 6 h when COHb was increased to 25% and CaO2 was decreased by 17%. When COHb was increased, arterial PCO2 (PaCO2) increased gradually to 1.3 Torr above (P < 0.05) control level between 30 and 45 min of CO exposure. Pulmonary ventilation (VE) de...
