Ventilation-perfusion relationships during exercise in standardbred trotters with red cell hypervolaemia.

This research evaluates the effects of red cell hypervolaemia (RCHV) on pulmonary gas exchange during exercise in Standardbred trotters. The study found that horses with RCHV show more pronounced hypoxaemia, primarily due to increased ventilation-perfusion mismatch during heavy exercise.

Introduction and Methodology

• A comparative study was conducted involving two groups of Standardbred trotters – one group consisted of 12 horses with Red Cell Hypervolaemia (RCHV) and the other consisted of 9 normovolaemic (NV) horses.
• The experiment was designed to examine how RCHV affects the pulmonary gas exchange during exercise in these trotters. This was done by determining VO2 and VCO2 using an open bias flow system.
• The horses underwent exercise at four different speeds on a treadmill while their cardiovascular and haemodynamic data were recorded.
• The examination of pulmonary gas exchange was done through traditional blood gas variables (arterial and mixed venous blood gas tensions).
• The researches also evaluated the distribution of ventilation-perfusion, also known as VA/Q, using the multiple inert gas elimination technique. VA and AaDO2 were calculated.
• The dispersions of perfusion and ventilation distribution, represented as SDQ and SDV, were also determined.

Key Findings

• Measures like heart rate (HR), respiratory rate (RR), cardiac output (Qt), oxygen consumption (VO2), ventilation (VA), log SDV, arterial-venous oxygen difference (C(a-åv)O2), and lactate levels were observed to be similar in both the groups.
• However, the extent of hypoxia, a condition characterized by an inadequate supply of oxygen, was found to be higher in the RCHV group than in the NV group at the highest workload.
• Further, there were differences in pH, the partial pressure of carbon dioxide (PaCO2), and carbon dioxide production (VCO2). All of those were found to be higher in the RCHV group during exercise.
• The actual measured partial pressure of oxygen (PaO2) in the blood during heavy exercise was found to be lesser than what was predicted from the VA/Q distribution, suggesting potential diffusion limitations across the alveolar-capillary membranes in both of the groups.
• The more significant hypoxia observed in RCHV trotters was mainly due to a substantial increase in the VA/Q mismatch, represented by an increased log SDQ.

Thus, the research reveals that RCHV in Standardbred trotters significantly affects the pulmonary gas exchange, primarily causing increased hypoxia during heavy exercise due to the enhanced ventilation-perfusion mismatch.