Haemodynamic response to exercise in Standardbred trotters with red cell hypervolaemia.

This study compares the hemodynamic response to exercise in Standardbred trotters with an excess of red blood cells (red cell hypervolaemia) to normovolaemic trotters. The findings suggest that an increased red blood cell volume contributes to increased blood pressures during exercise and could cause exercise-induced pulmonary hemorrhage.

Methodology

• The study is based on a comparison between 12 Standardbred trotters diagnosed with Red Cell Hypervolaemia (RCHV) and 9 normovolaemic (NV) trotters.
• It involved recording haemodynamic data from the horses during exercise at four different speeds on a treadmill.
• Methods such as an open bias flow system were used to determine the oxygen uptake of the horses.
• Various metrics were measured during the study, including Pulmonary Artery Pressure (PAP), Systemic Artery Pressure (SAP), heart rate, Packed Cell Volume (PCV), plasma lactate and haemoglobin ([Hb]) concentration.
• Additional parameters calculated included arteriovenous O2 content difference, cardiac output, stroke volume, Pulmonary Vascular Resistance (PVR) and Total Systemic Resistance (TSR).

Findings

• The results show no significant difference between the RCHV and NV groups in multiple parameters such as oxygen uptake, arteriovenous O2 content difference, heart rate, cardiac output, stroke volume, TSR and lactate.
• However, horses with RCHV displayed significantly higher diastolic and systolic PAP when compared to NV horses. This difference increased with a higher workload.
• Furthermore, higher SAP, PVR, PCV, and [Hb] were observed in RCHV horses during exercise.
• Of the 12 RCHV horses, 11 showed signs of exercise-induced pulmonary haemorrhage upon endoscopic examination. In contrast, none of the NV horses showed such symptoms.
• The researchers suggest the increased red cell volume, leading to high PCV and total blood volume, could be a critical contributor to the rise in blood pressure in both pulmonary and systemic circulation during exercise and the occurrence of exercise-induced pulmonary hemorrhage in RCHV horses.