Effects of hematocrit and erythrocyte deformability on pulmonary vascular pressures in perfused pony lungs.

This research investigates the contributions of hematocrit levels and red blood cell (RBC) deformability to pulmonary vascular pressures in racehorses, and the potential benefits of a medication called pentoxifylline in reducing these pressures.

Research Methodology

• The researchers conducted their experiments using the lungs of 11 healthy mixed-breed ponies.
• The ponies were anesthetized, and their blood was collected. They were then euthanized, and their lungs removed.
• Both the right and left lungs of each pony were separately perfused (i.e., the process of circulating blood) at a constant flow rate using the collected blood, enabling the researchers to study the changes in pulmonary vascular pressures brought about by modifications in hematocrit.
• The hematocrit level, which represents the proportion of blood volume that is occupied by RBCs, was varied between 35% to 65% during the experiments.
• Additionally, the potential effects of pentoxifylline treatment on these pressures were evaluated. Pentoxifylline is a medication used to improve blood flow in patients with peripheral artery disease.

Results

• Increasing the hematocrit from 35% to 65% led to increased pulmonary arterial pressure (by 53% and 45%), capillary shear stress (by 45% and 32%), and total vascular resistance (by 92% and 143%) at low and high flow rates, respectively.
• Interestingly, when the pony lungs were perfused with blood taken from ponies treated with pentoxifylline, the pulmonary artery pressures were lower, by about 10% and 11% compared to control ponies with low hematocrit and high hematocrit respectively. There were also decreases in capillary shear stress and total vascular resistance.

Conclusions

• The study found that changes in hematocrit equivalent to those occurring during competitive racing activities can significantly increase pulmonary vascular pressures in horses’ lungs.
• This highlights hematocrit as a potential key factor contributing to exercise-induced pulmonary hemorrhage, a common and performance-limiting issue in racehorses.
• Importantly, the study discovered that the administration of pentoxifylline to ponies reduced RBC deformability and mitigated the increases in pulmonary vascular pressures.
• Therefore, treating racehorses with pentoxifylline might help reduce the exercise-associated increases in pulmonary vascular pressure, thereby lessening the incidence of exercise-induced pulmonary hemorrhage.