Some blood pressure studies in normal horses and in horses affected with chronic obstructive pulmonary disease

Abstract

The literature indicated that the main obstacle to indirect peripheral blood pressure measurements (sphygmomanometry) in horses, is the lack of a large superficial artery capable of being temporarily occluded. Consequently, the standard human sphygmomanometric techniques employing palpatory and auscultatory methods are unsatisfactory in horses. Some other sphygmomanometric techniques including the xylol bead modified palpatory, the photoelectric and the modified auscultatory methods were assessed by trials on horses. The latter method was shown to be the only potentially useful technique.Blood pressure measurements using this technique showed that the blood pressure of resting horses shows continuous short term cyclic variations, an observation which was supported by direct peripheral blood pressure measurements. Peripheral blood pressure was shown to significantly increase in horses during excitement and also following submaximal exercise. During longer term studies, many technical difficulties were encountered with the modified auscultatory technique and it was concluded that it would be unlikely to become acceptable for general clinical use.The literature concerning right heart blood pressure measurements in horses indicated that very little information was available concerning the right heart blood pressure alterations that occur in chronic pulmonary disease. Angiographic studies indicated that the use of a single hydrostatic baseline for all right heart blood pressure as is currently used by all authors, causes estimation of right ventricular pressure. measurements, an under- A separate hydrostatic baseline was therefore established for right ventricular blood pressure measurements.It was shown that horses clinically affected with chronic obstructive pulmonary disease (COPD), had pulmonary and systolic right ventricular hypertension and that this hypertension became reversed during remission stages of the disease. Further studies showed that a close relationship existed between carotid arterial hypoxaemia and pulmonary hypertension in COPD affected horses.This relationship between arterial hypoxaemia and pulmonary hypertension in COPD was substantiated by inducing partial remission of pulmonary hypertension in clinically affected horses, by oxygen administration. In contrast, normal pulmonary hypertension was induced by rendering temporarily hypoxaemic, by administration of nitrogen enriched air.Marked pulmonary hypertension was also induced during experimental hypercapnia or acidosis production. Bicarbonate, atropine or furosemide administered intravenously had no significant short term effects on pulmonary arterial pressure. No clinical or cardiac catheterisation evidence of right heart failure was observed in any COPD affected horses. These observations were substantiated by the relative in frequency of right ventricular hypertrophy that was observed on post mortem examinations of horses affected with chronic pulmonary disease.