Haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia

In order to evaluate the haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia (RCHV), 12 trotters with RCHV were com pared with 9 normovolaemic (NV) trotters. Haemodynamic data were recorded d uring exercise at 4 different speeds on a treadmill. Oxygen uptake was dete rmined with an open bias flow system. Pulmonary artery pressure (PAP), syst emic artery pressure (SAP), heart rate, packed cell volume (PCV) and plasma lactate and haemoglobin ([Hb]) concentrations were measured. Arteriovenous O-2 content difference, cardiac output, stroke volume, pulmonary vascular resistance (PVR) and total systemic resistance (TSR) were calculated. Oxyge n uptake, arteriovenous O-2 content difference, heart rate, cardiac output, stroke volume, TSR and lactate did not differ between groups. The RCHV-hor ses had significantly higher both mean diastolic and systolic PAP compared to NV horses and this difference increased with higher workload. Further, a higher SAP, PVR, PCV and [Hb] were found in RCHV horses during the course of exercise. Eleven of the RCHV horses, but none of the NV, showed exercise -induced pulmonary haemorrhage on endoscopic examination. The increase in r ed cell volume, resulting in a high PCV and high total blood volume, is sug gested to be;an important contributor to both the increased blood pressures in pulmonary and systemic circulation during exercise and to the developme nt of exercise-induced pulmonary haemorrhage in RCHV horses.