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Intravenous magnesium sulfate as a rescue therapeutic for bronchoconstriction in equine pasture asthma
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Abstracts / Journal of Equine Veterinary Science 52 (2017) 49e63
32 Sedated versus nonsedated methacholine challenge for the diagnosis of airway hyper-responsiveness in horses A. Lack*, J. Bowser, C. Wenzel, R. Wilson, A. Tucker, E. Moyer, C. Swiderski Mississippi State College of Veterinary Medicine, Mississippi State, MS, USA Equine pasture asthma (EPA) is a chronic, progressive asthmalike condition affecting horses in the southeastern United States. Methacholine bronchoprovocation (MB) is a diagnostic test that elicits a hallmark feature of EPA, airway hyperresponsiveness (AHR), by quantifying measures of airway constriction in response to doubling doses of nebulized methacholine (0.0625e8 mg/mL). Most horses require extensive conditioning to accept MB instrumentation, limiting its clinical application. Also, commonly employed sedatives alter airway tone, making sedation problematic for measuring baseline pulmonary mechanics. Guidelines for MB in human asthmatics have determined that differences of up to 2 fold, in the quantity of methacholine to achieve a constant threshold increase in airway caliber, are not significantly different. Thus, we hypothesized that sedated MB would be similarly accurate to nonsedated MB for identifying AHR in EPA horses if the absolute quantities of methacholine required to achieve a set threshold (40%) increase in baseline lung resistance were within 1e2 fold. MB was performed, identifying the quantity of methacholine that induced a 40% increase in baseline lung resistance (ie friction) using a 2-min tidal breathing protocol (American Thoracic Society). Six horses with EPA were tested, with and without acepromazine sedation. Findings from 4 horses indicate that the quantity of methacholine eliciting a 40% increase in baseline lung resistance is within 2 doubling doses in the presence and absence of sedation for individual horses. Validation of a standard sedation protocol for use in MB, using conventional pulmonary mechanics, will expand the application of this diagnostic, allowing earlier disease identification and intervention. Key Words: equine asthma, methacholine challenge, pulmonary function testing
33 Intravenous magnesium sulfate as a rescue therapeutic for bronchoconstriction in equine pasture asthma C. Wenzel*, J. Bowser, R. Wills, N. Bondi, R. Wilson, R. Cobb, C. Swiderski Mississippi State University College of Veterinary Medicine, Mississippi State, MS, USA Horses with equine pasture asthma (EPA) exhibit exacerbations of acute airway obstruction elicited by warm season pasture aeroallergens in the southeastern US, resulting in respiratory distress from bronchospasm, mucus accumulation, and airway inflammation. Emergency therapeutic options for control and reversal of airway bronchoconstriction in horses are currently limited to parasympatholytic agents, b2-adrenoceptor agonists and corticosteroids. Meta-analysis of emergency intervention for asthmatics found adjunctive infusion of magnesium sulfate (MgSO4) improves lung function, reducing hospital admissions. This study examined utility and effectiveness of intravenous MgSO4 as a
novel, inexpensive, easily administered bronchodilatory agent for horses with EPA. Six EPA-affected horses exhibiting naturally occurring disease exacerbation were treated with 3 doubling dosages of MgSO4 by rapid IV infusion using 3 way crossover design with minimum 48 h wash-out. Conventional pulmonary mechanics including pulmonary resistance (RL), dynamic compliance (Cdyn) and maximum change in pleural pressure (DPplmax) along with thoracic (TA) and tracheal (TRA) auscultation were monitored at 5-min intervals for each infusion and 30 min following bolus completion. Serum magnesium was measured at 0, 20, 50 min, and 24 h. Mixed model analysis for percent change from baseline values for each outcome was used (SAS, SAS Institute. Cary, NC). Increase in serum magnesium levels paralleled dose-dependent significant (P 0.01) decreases in DPplmax, RL and increases in Cdyn. This was accompanied by improved TA and TRA. We conclude that intravenous MgSO4 has immediate bronchodilatory effects in horses, making this therapy a valuable adjunct in horses with signs of respiratory distress caused by bronchoconstriction. Key Words: equine asthma, magnesium, bronchoconstriction
Oral Presentations 34 Comparison of processed and unprocessed digital images for the determination of radiographic bone aluminum equivalent (RBAE) values in equine bone
J.D. Pagan*, P. Kazakevicius, A. Swanhall, E. Ford, A. Pritchard Kentucky Equine Research, Versailles, Kentucky, USA Radiographic photodensitometry to estimate bone density in horses was originally developed using conventional analog film radiography. Today, most researchers have switched to digital radiography (DR) to make these measurements. One important feature of DR is that the raw data are processed after acquisition. Processing algorithms are generally proprietary and specific to the DR vendor, but they encompass manipulations to optimize image quality parameters such as contrast and noise. These processing steps have a profound effect on the final appearance of the radiograph, and they can also lead to artifacts unique to digital systems that may affect density measurements. This study measured radiographic bone aluminum equivalent (RBAE) values in the left third metacarpal (MCIII) of 16 Thoroughbred horses (3.2 ± 0.4 y) using raw (unprocessed) and processed images acquired using a portable x-ray unit and read by a DR system (Sound NEXT Equine DR). Radiographs of the dorsal-palmar (n ¼ 16) and lateral-medial views (n ¼ 16) of MCIII were taken. An aluminum step wedge placed in the same plane as the MCIII was exposed simultaneously to calculate RBAE values. Unprocessed and processed images were analyzed using ImageJ image-processing software. An optical density calibration curve was created for each image using the known thicknesses of the step wedge. This relationship was best described using a natural log equation in the unprocessed images and a 4th degree polynomial equation in the processed images. Differences between image types were analyzed using a paired t-test. Image processing had a large, inconsistent effect on RBAE values. Peak densities were 32e68% greater in the processed images and many were greater than the density of the thickest step of the step wedge. In lower density areas, the processed images had lesser densities than the unprocessed images, demonstrating the nonlinear nature of the processing algorithm. RBAE values obtained from unprocessed
Abstracts / Journal of Equine Veterinary Science 52 (2017) 49e63
32 Sedated versus nonsedated methacholine challenge for the diagnosis of airway hyper-responsiveness in horses A. Lack*, J. Bowser, C. Wenzel, R. Wilson, A. Tucker, E. Moyer, C. Swiderski Mississippi State College of Veterinary Medicine, Mississippi State, MS, USA Equine pasture asthma (EPA) is a chronic, progressive asthmalike condition affecting horses in the southeastern United States. Methacholine bronchoprovocation (MB) is a diagnostic test that elicits a hallmark feature of EPA, airway hyperresponsiveness (AHR), by quantifying measures of airway constriction in response to doubling doses of nebulized methacholine (0.0625e8 mg/mL). Most horses require extensive conditioning to accept MB instrumentation, limiting its clinical application. Also, commonly employed sedatives alter airway tone, making sedation problematic for measuring baseline pulmonary mechanics. Guidelines for MB in human asthmatics have determined that differences of up to 2 fold, in the quantity of methacholine to achieve a constant threshold increase in airway caliber, are not significantly different. Thus, we hypothesized that sedated MB would be similarly accurate to nonsedated MB for identifying AHR in EPA horses if the absolute quantities of methacholine required to achieve a set threshold (40%) increase in baseline lung resistance were within 1e2 fold. MB was performed, identifying the quantity of methacholine that induced a 40% increase in baseline lung resistance (ie friction) using a 2-min tidal breathing protocol (American Thoracic Society). Six horses with EPA were tested, with and without acepromazine sedation. Findings from 4 horses indicate that the quantity of methacholine eliciting a 40% increase in baseline lung resistance is within 2 doubling doses in the presence and absence of sedation for individual horses. Validation of a standard sedation protocol for use in MB, using conventional pulmonary mechanics, will expand the application of this diagnostic, allowing earlier disease identification and intervention. Key Words: equine asthma, methacholine challenge, pulmonary function testing
33 Intravenous magnesium sulfate as a rescue therapeutic for bronchoconstriction in equine pasture asthma C. Wenzel*, J. Bowser, R. Wills, N. Bondi, R. Wilson, R. Cobb, C. Swiderski Mississippi State University College of Veterinary Medicine, Mississippi State, MS, USA Horses with equine pasture asthma (EPA) exhibit exacerbations of acute airway obstruction elicited by warm season pasture aeroallergens in the southeastern US, resulting in respiratory distress from bronchospasm, mucus accumulation, and airway inflammation. Emergency therapeutic options for control and reversal of airway bronchoconstriction in horses are currently limited to parasympatholytic agents, b2-adrenoceptor agonists and corticosteroids. Meta-analysis of emergency intervention for asthmatics found adjunctive infusion of magnesium sulfate (MgSO4) improves lung function, reducing hospital admissions. This study examined utility and effectiveness of intravenous MgSO4 as a
novel, inexpensive, easily administered bronchodilatory agent for horses with EPA. Six EPA-affected horses exhibiting naturally occurring disease exacerbation were treated with 3 doubling dosages of MgSO4 by rapid IV infusion using 3 way crossover design with minimum 48 h wash-out. Conventional pulmonary mechanics including pulmonary resistance (RL), dynamic compliance (Cdyn) and maximum change in pleural pressure (DPplmax) along with thoracic (TA) and tracheal (TRA) auscultation were monitored at 5-min intervals for each infusion and 30 min following bolus completion. Serum magnesium was measured at 0, 20, 50 min, and 24 h. Mixed model analysis for percent change from baseline values for each outcome was used (SAS, SAS Institute. Cary, NC). Increase in serum magnesium levels paralleled dose-dependent significant (P 0.01) decreases in DPplmax, RL and increases in Cdyn. This was accompanied by improved TA and TRA. We conclude that intravenous MgSO4 has immediate bronchodilatory effects in horses, making this therapy a valuable adjunct in horses with signs of respiratory distress caused by bronchoconstriction. Key Words: equine asthma, magnesium, bronchoconstriction
Oral Presentations 34 Comparison of processed and unprocessed digital images for the determination of radiographic bone aluminum equivalent (RBAE) values in equine bone
J.D. Pagan*, P. Kazakevicius, A. Swanhall, E. Ford, A. Pritchard Kentucky Equine Research, Versailles, Kentucky, USA Radiographic photodensitometry to estimate bone density in horses was originally developed using conventional analog film radiography. Today, most researchers have switched to digital radiography (DR) to make these measurements. One important feature of DR is that the raw data are processed after acquisition. Processing algorithms are generally proprietary and specific to the DR vendor, but they encompass manipulations to optimize image quality parameters such as contrast and noise. These processing steps have a profound effect on the final appearance of the radiograph, and they can also lead to artifacts unique to digital systems that may affect density measurements. This study measured radiographic bone aluminum equivalent (RBAE) values in the left third metacarpal (MCIII) of 16 Thoroughbred horses (3.2 ± 0.4 y) using raw (unprocessed) and processed images acquired using a portable x-ray unit and read by a DR system (Sound NEXT Equine DR). Radiographs of the dorsal-palmar (n ¼ 16) and lateral-medial views (n ¼ 16) of MCIII were taken. An aluminum step wedge placed in the same plane as the MCIII was exposed simultaneously to calculate RBAE values. Unprocessed and processed images were analyzed using ImageJ image-processing software. An optical density calibration curve was created for each image using the known thicknesses of the step wedge. This relationship was best described using a natural log equation in the unprocessed images and a 4th degree polynomial equation in the processed images. Differences between image types were analyzed using a paired t-test. Image processing had a large, inconsistent effect on RBAE values. Peak densities were 32e68% greater in the processed images and many were greater than the density of the thickest step of the step wedge. In lower density areas, the processed images had lesser densities than the unprocessed images, demonstrating the nonlinear nature of the processing algorithm. RBAE values obtained from unprocessed