Cardiovascular and pulmonary effects of recumbency in two conscious ponies

Respiratory dead-space, tidal volume, respiratory rate, blood gases, cardiac output, heart rate and arterial and pulmonary arterial blood pressures were measured in two conscious, trained ponies in the standing position and in left lateral recumbency. The ponies were reluctant to remain lying down for more than about 20 mins but the reason for this did not become apparent. Tidal volume was reduced during recumbency but the respiratory rate increased, tending to maintain the minute volume at about that of the standing animal. Arterial carbon dioxide tension did not change significantly from standing values but the mean arterial oxygen tension values tended to decrease in both ponies during recumbency because of a slight increase in pulmonary venous admixture. Venous admixture in these two laterally recumbent conscious animals was considerably less than previously reported for anaesthetised subjects.