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in Journal of the American Veterinary Medical Association

SUMMARY

Lumbosacral csf pressure was measured in 6 horses via a catheter inserted through the lumbosacral space. Heart rate, facial artery pressure, central venous pressure, and csf pressure were measured before iv injection of a saline solution control, for 15 minutes after saline solution injection, and for 60 minutes after the iv injection of 1.1 mg of xylazine/kg of body weight. Arterial pH and blood gases were analyzed before saline solution injection, 15 minutes after saline solution injection, and at 15, 30, and 60 minutes after xylazine injection. Constant craniocervical posture was maintained during sedation. Lumbosacral csf pressure was significantly decreased for 15 minutes after xylazine injection. Diastolic arterial pressure was significantly increased 4 minutes after xylazine administration and diastolic and mean arterial pressure were increased at 6 and 8 minutes after xylazine administration. Small increases in systolic arterial blood pressure and central venous pressure, and a small decrease in heart rate were observed. There were no significant differences in the arterial blood gas values. It was concluded that iv injection of xylazine causes a decrease in intracranial pressure in healthy conscious horses. The effects may be different in horses with neurologic disease or cerebral trauma.

Free access
in American Journal of Veterinary Research

Summary

Arthroscopy was performed in 1 carpal joint unilaterally in 27 horses and either in 2 carpal joints unilaterally or 1 carpal joint bilaterally in 7 horses. All horses were lame, but the cause of lameness could not be determined from radiographs. Twenty-seven carpi did not have radiographically visible abnormalities; the remaining 14 had only mild to moderate lucency or sclerosis of the radial facet of the third carpal bone. The primary abnormalities identified during arthroscopy included a crush fracture of the third carpal bone (7 carpi), an incomplete fracture of the third carpal bone in the frontal plane (13 carpi), an incomplete fracture of the third carpal bone in the sagittal plane (1 carpus), a crush fracture of the radial carpal bone (1 carpus), a chip fracture of the intermediate carpal bone (1 carpus), damage to the articular cartilage of the third carpal bone (12 carpi), tearing or fraying of the medial palmar intercarpal ligament (4 carpi), and synovitis (2 carpi).

All of the horses in this study were racehorses (29 Standardbreds and 5 Thoroughbreds), and race records were used to evaluate performance before and after surgery. Twenty-four of 34 horses raced preoperatively, and 25 of 34 raced postoperatively. Twenty-three of the 27 (85%) horses in which a single joint was examined raced postoperatively. Fifteen of these horses had an incomplete or crush fracture of the radial facet of the third carpal bone, and 13 raced postoperatively; 7 horses had full- or partial-thickness damage of cartilage of the third carpal bone, and all 7 raced postoperatively; 2 horses had partial or complete rupture of the medial palmar intercarpal ligament, and both raced postoperatively.

Fifteen horses with either a frontal plane incomplete fracture, crush fracture, or full-thickness damage of cartilage of the third carpal bone in 1 carpus were treated by removing bone and cartilage from the dorsoproximal margin of the third carpal bone; 13 of these horses raced postoperatively. Both horses with incomplete frontal plane fractures of the third carpal bone repaired with screws raced postoperatively.

Only 2 of 6 horses that underwent bilateral carpal arthroscopy raced postoperatively; 1 of these horses had bilateral partial tearing of the medial palmar intercarpal ligament; the other had bilateral frontal plane incomplete fractures of the radial facet of the third carpal bone. The remaining horse, in which both the radiocarpal and middle carpal joints were examined, did not race postoperatively

Our results suggest that horses with lameness, the cause of which has been localized to the carpus, in which radiographs are not diagnostic are likely to have an underlying abnormality that can be effectively diagnosed and treated via arthroscopy. Arthroscopy allows the examiner to thoroughly explore the joint, make an accurate diagnosis, and make the best decision regarding treatment.

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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Objective—

To evaluate clinical findings and response to treatment in horses in which cartilage lesions on the medial femoral condyle were a cause of lameness.

Design—

Retrospective case series.

Sample Population—

Medical records of 11 horses that had cartilage lesions on the medial femoral condyle detected during arthroscopy of the stifle.

Procedure—

Signalment, history, lameness examination, response to intra-articular anesthesia, radiographs of the stifle, observations during diagnostic arthroscopy, and treatment were extracted from the medical record of each horse. Follow-up examinations and outcome were available for all horses.

Results—

All horses in the study had lameness, but their gait improved after intra-articular injection of anesthetic. Abnormalities were not observed on radiography of the stifle. Diagnostic arthroscopy was performed on 12 affected joints in 11 horses. Cartilage was dimpled, wrinkled, and infolded, and a blunt arthroscopic probe could be inserted into the subchondral bone. In addition to focal lesions, 4 horses had generalized damage to cartilage on the medial femoral condyle. Focal cartilage lesions on the femoral condyle were debrided. In 2 horses. debridement was not performed because of extensive generalized damage to the cartilage. Six of 7 horses with focal cartilage lesions treated by debridement recovered completely and resumed previous activities.

Clinical Implications—

Cartilage lesions on the medial femoral condyle can cause lameness in performance horses. Diagnostic arthroscopy is necessary to make an accurate diagnosis. Debridement of focal cartilage lesions may allow some horses to successfully resume performance activities. (J Am Vet Med Assoc 1997;210:1649–1652)

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in Journal of the American Veterinary Medical Association

Abstract

Objective

To measure colonic arterial (CA) and colonic venous (CV) plasma neuropeptide concentrations during low-flow ischemia and reperfusion of the large colon in horses.

Animals

10 adult horses.

Procedure

CA and CV plasma samples collected from anesthetized horses during experimentally induced low-flow colonic ischemia and reperfusion were assayed for vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and substance P (SP), using radioimmunoassays. In 6 anesthetized horses, colonic ischemia (20% of baseline [BL]) was maintained for 3 hours, then blood flow was restored and monitored for 3 hours. Hemodynamic variables were monitored continuously and recorded at 30-minute intervals. CA resistance was calculated from colonic blood flow (Qcolon) and mean CA pressure values at each time. Blood was obtained from CA and CV catheters at 0, 1, 2, 3, 3.25, 3.5, 4, 5, and 6 hours; plasma VIP, CGRP, and SP concentrations were quantified, using radioimmunoassays. In 4 additional horses, VIP and CGRP were measured in CA and CV blood at 0, 0.25, 0.5, 0.75, and 1 hour.

Results

Heart rate was significantly increased at 5.5 and 6 hours; other alterations in systemic hemodynamic variables were not significant. Decrease in Qcolon during ischemia was significant; Qcolon rebounded to a value significantly greater than BL value within 5 minutes of reperfusion and was maintained above the BL value during 3 hours of reperfusion. Mean CA pressure was significantly decreased during ischemia, but returned to a value not different from the BL value by 3.25 hours. Mean CV pressure remained unchanged from the BL value during ischemia, but increased to a value significantly greater than the BL value by 3.25 hours and remained increased through 6 hours. CA resistance began to decrease during early ischemia and was significantly less than the BL value by 3.25 hours; it remained less than the BL value through 4 hours. Increase in CV VIP concentration was significant by 0.25 hour of ischemia, but decreased to a value not different from BL value by 3.25 hours. Increase in CV CGRP was significant at 3.25 hours, but this variable returned to a value not different from BL value by 3.5 hours.

Conclusions

CV VIP concentration increases during low-flow colonic ischemia, and CV and CA CGRP and CA SP concentrations increase during early reperfusion. (Am J Vet Res 1996;57:1200-1205)

Free access
in American Journal of Veterinary Research

SUMMARY

Six horses were subjected to 3 hours of low-flow ischemia and 3 hours of reperfusion of the large colon. After induction of anesthesia, the large colon was exteriorized through a ventral midline celiotomy. Colonic blood flow was measured continuously, using Doppler ultrasonic flow probes placed on the colonic arteries supplying the dorsal and ventral colons and was allowed to stabilize for 15 to 30 minutes after instrumentation. Low-flow ischemia was induced by reducing colonic arterial blood flow to 20% of baseline (bl) flow. Colonic mucosal, seromuscular, and full-thickness blood flow were determined on a tissue-weight basis by injecting colored microspheres proximally into the colonic artery supplying the ventral colon. Reference blood samples were obtained at a known flow rate from the colonic artery and vein at a site more distal to the site of injection. Left ventral colon biopsy specimens were harvested at bl, 3 hours of ischemia, and 15 minutes of reperfusion. Blood and tissue samples were digested and filtered to collect the microspheres, and dimethylformamide was added to release the colored dyes. Dye concentration in blood and tissue samples was measured by use of spectrophotometry, and tissue-blood flow was calculated. Data were analyzed, using two-way anova for repeated measures; statistical significance was set at P < 0.05. Doppler blood flow decreased to approximately 20% of BL, whereas microsphere blood flow ranged between 13.7 and 15.5% of bl at 3 hours of ischemia. Doppler-determined blood flow increased immediately on restoration of blood flow, reached 183% of bl at 15 minutes of reperfusion, and remained at or above bl throughout 3 hours of reperfusion. This reactive hyperemia was also detected, using the colored microspheres; blood flow increased to 242 and 327% of bl at 15 minutes of reperfusion in the mucosal and seromuscular layers, respectively. Mucosal blood flow was not different from seromuscular blood flow at any time, indicating relatively equal distribution of blood flow between these 2 layers. As determined from the venous reference samples, there was no evidence of arteriovenous anastomoses.

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in American Journal of Veterinary Research

Abstract

Objective—To examine the secretory response (in the presence and absence of prostaglandin inhibition) in vitro and structural alterations of colonic mucosa in horses after intragastric administration of black walnut extract (BWE).

Animals—14 adult horses.

Procedure—Seven horses were administered BWE intragastrically and monitored for 11 hours. Tissue samples were obtained from the right ventral, left ventral, and right dorsal colons (RVC, LVC, and RDC, respectively) of the 7 BWE-treated and 7 control horses. Tissue samples were examined via light microscopy, and the extent of hemorrhage, edema, and granulocytic cellular infiltration (neutrophils and eosinophils) was graded. Colonic mucosal segments were incubated with or without flunixin meglumine (FLM) for 240 minutes; spontaneous electrical potential difference and short-circuit current (Isc) were recorded and used to calculate mucosal resistance.

Results—Colonic tissues from BWE-treated horses (with or without FLM exposure) had an overall greater Isc during the 240-minute incubation period, compared with tissues from control horses. The resistance pattern in RVC, LVC, and RDC samples (with or without FLM exposure) from BWE-treated horses was decreased overall, compared with control tissues (with or without FLM exposure). Histologically, colonic mucosal tissues from BWE-treated horses had more severe inflammation (involving primarily eosinophils), edema, and hemorrhage, compared with tissue from control horses.

Conclusions and Clinical Relevance—In horses, BWE administration appears to cause an inflammatory response in colonic mucosal epithelium that results in mucosal barrier compromise as indicated by decreased mucosal resistance with presumed concomitant electrogenic chloride secretory response, which is not associated with prostaglandin mediation. (Am J Vet Res 2005;66:443–449)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate changes in digital vascular function in horses with carbohydrate overload (CHO)-induced laminitis and determine the effects of an endothelin (ET) receptor antagonist and nitroglycerin on laminitis-associated vascular dysfunction.

Animals—20 adult horses without abnormalities of the digit.

Procedures—Hemodynamic variables were recorded before (baseline) and hourly after all horses were administered a CHO ration via nasogastric tube. In 4 groups of 5 horses each, saline (0.9% NaCl) solution or ET receptor antagonist (10−5M in digital blood) was administered into the digital arterial circulation according to 1 of 2 schedules. During anesthesia, blood flow; arterial, venous, and capillary pressures; and total, precapillary, and postcapillary resistances were measured in an isolated perfused digit of each horse. In all groups, nitroglycerin was infused (10−5M in digital blood), and digital microvascular assessments were repeated.

Results—The CHO caused a significant decrease in right atrial pressure by 14 hours that was not affected by administration of saline solution or ET receptor antagonist. In isolated digits of anesthetized horses, CHO resulted in a significant decrease in digital blood flow associated with a significant increase in total and postcapillary resistances. Treatment with the ET receptor antagonist and nitroglycerin caused a significant decrease in total resistance. Postcapillary resistance was significantly decreased following treatment with the ET receptor antagonist but was not altered by treatment with nitroglycerin.

Conclusions and Clinical Relevance—Treatment with an ET receptor antagonist and nitroglycerin resulted in significant improvement in vascular resistance in isolated perfused digits of anesthetized horses with CHO-induced laminitis.

Full access
in American Journal of Veterinary Research