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SUMMARY

The role of platelet-activating factor in mediating the cardiovascular and peripheral cellular responses to large-colon ischemia and reperfusion, was explored in anesthetized ponies. A specific platelet-activating factor (PAF) antagonist (WEB 2086) was administered to a group of 6 ponies, and another 6 ponies (controls) were given an equivalent volume of saline solution, prior to 1 hour of large-colon torsion. After correction of the torsion, ponies were monitored during the reperfusion period. Significant (P < 0.05) hypotension and metabolic acidosis developed in all ponies after correction of colonic torsion, cardiac index increased initially, but then decreased significantly (P < 0.05) over the study period. Mean times between correction of torsion and onset of cardiac failure and death were not different between groups. Significant (P < 0.05) thrombocytopenia developed during the reperfusion period in control ponies, but not in WEB-treated ponies. Blood leukocyte concentration in control ponies was more variable and significantly (P < 0.05) decreased immediately upon reperfusion, compared with that in WEB-treated ponies. We conclude that although the cardiovascular responses to colonic ischemia and reperfusion are not prevented by use of a specific paf-antagonist, specific peripheral cellular responses are mediated by paf.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the effect of bilateral blockade of the pharyngeal branch of the vagus nerve on soft palate function in horses.

Animals

5 Standardbreds.

Procedure

Peak tracheal inspiratory and expiratory pressures and airflow were measured while horses exercised at the speeds corresponding to 75 and 100% of the speed that resulted in maximal heart rate, with and without pharyngeal branch of the vagus nerve blockade. Respiratory frequency-to-stride frequency coupling ratio was measured by correlating foot fall measurements with respiratory frequency. The pharyngeal branch of the vagus nerve was blocked bilaterally as the nerve coursed through the auditory tube diverticulum (guttural pouch) across the longus capitus muscle.

Results

Persistent, reversible dorsal displacement of the soft palate (DDSP) occurred in all horses after nerve blockade, and lasted from 1 to 3 hours; normal nasopharyngeal function returned within 3 hours. Compared with control values, peak expiratory tracheal pressure increased (P = 0.001), expiratory impedance increased (P = 0.007), and minute ventilation decreased (P = 0.04). Respiratory frequency-to-stride frequency coupling ratio decreased (P = 0.009) so that horses took 1 breath/stride without the nerve block and, approximately, 1 breath/2 strides with the block.

Conclusion

DDSP creates flow-limiting expiratory obstruction and may be caused by neuromuscular dysfunction involving the pharyngeal branch of the vagus nerve. It may alter performance by causing expiratory obstruction and by altering breathing strategy in horses.

Clinical Relevance

A repeatable, reversible model of DDSP exists that allows further study of the disease. Dysfunction of the neuromuscular group, pharyngeal branch of the vagus nerve and palatinus and palatopharyngeus muscles, may be implicated in the pathogenesis of clinical DDSP. (Am J Vet Res 1998;59:504–508)

Free access
in American Journal of Veterinary Research

Summary

Flow-volume loops generated from 6 Standardbreds at rest and during treadmill exercise were evaluated for their use in detecting upper airway obstruction. Tidal breathing flow-volume loops (tbfvl) were obtained from horses at rest and exercising at speeds corresponding to 75% of maximal heart rate and at maximal heart rate. The tbfvl were evaluated, using a pulmonary function computer; calculated indices describing airflow rate and expiratory-to-inspiratory airflow ratio for individual loops were determined. In addition to tbfvl indices, standard variables of upper airway function also were measured: peak airflow, peak pressure, and calculated inspiratory and expiratory impedances. Measurements were recorded before left recurrent laryngeal neurectomy (lrln; baseline) and 14 days after surgically induced left laryngeal hemiplegia.

When horses were at rest, tbfvl shape and indices describing the loop were highly variable. In contrast, in exercising horses, tbfvl shape was consistent and coefficients of variation of loop indices were less during exercise than at rest. After lrln, tbfvl from exercising horses indicated marked inspiratory airflow limitation, while the expiratory airflow curve was preserved. Peak inspiratory flow rate and inspiratory flow at 50 and 25% of tidal volume decreased, and the ratio of peak expiratory to inspiratory airflow and that of midtidal volume expiratory and inspiratory airflow rates increased significantly (P < 0.05). Inspiratory impedance also increased after lrln.

Although in resting horses tbfvl were not a useful indicator of upper airway obstruction, examination of tbfvl from exercising horses allowed objective, specific, and repeatable detection of upper airway obstruction. The technique was noninvasive, rapid, and well tolerated by horses; thus, it is a potentially valuable clinical diagnostic test.

Free access
in American Journal of Veterinary Research

Summary

Effects of 1 hour of colonic volvulus and 3 hours of reperfusion on concentrations of thromboxane (txb 2) and prostacyclin (6-keto-PGF) in portal, pulmonary arterial, and jugular blood were determined by radioimmunoassay to assess the site of production and clearance of these eicosanoids from the circulation in 5 anesthetized ponies. Colonic volvulus had no significant effect on mean arterial pressure or txb 2 concentrations, but significantly (P < 0.05) increased 6-keto-PGF concentrations in all blood samples. Immediately after colonic reperfusion, all eicosanoid concentrations were significantly (P < 0.05) increased. Then, txb 2 returned to baseline values, whereas 6-keto-PGF concentrations remained significantly (P < 0.05) high for the remainder of the study. Eicosanoid concentrations were significantly (P < 0.05) greater in portal blood than in pulmonary arterial and jugular blood samples at all periods. This suggests that the splanchnic circulation is the primary site of eicosanoid production during and after colonic volvulus and the liver appears to provide most of the circulatory clearance of thromboxane and prostacyclin.

Free access
in American Journal of Veterinary Research