Evaluation of equine digital Starling forces and hemodynamics during early laminitis.

This research study investigated the forces and blood flow behaviour, known as Starling forces and hemodynamics, in the feet of horses during the early stages of a disease called laminitis. This was done through a model that involved giving horses an excess of carbohydrates and examining various physiological factors in their feet.

Methods

To do this, eight horses were subjected to a carbohydrate overload model, which is a method used to trigger laminitis. A complex medical setup known as a pump-perfused extracorporeal digital preparation was used to study the horses’ feet, or ‘digit’. This setup allowed for measurements of various factors in the horses’ feet, including:

• Blood flow
• Arterial pressure
• Venous pressure
• Capillary pressure
• Isogravimetric capillary filtration coefficient
• Osmotic reflection coefficient
• Vascular compliance

Using this data, the researchers determined the resistance in the blood vessels before and after the capillaries, and the ratio of these resistances. They also estimated the pressures in the blood vessels and tissues based on protein concentrations in the plasma and lymph.

Key Findings

Using a technique called the lymph protein wash-down technique, the team was able to estimate the capillary permeability, and from this and the other measurements, they used the Starling equation to calculate the pressure in the tissues of the horses’ feet.

• The average capillary pressure was found to be 55.13 mm of Hg.
• The average plasma and lymph pressures based on protein concentrations were 22.29 mm of Hg and 7.2 mm of Hg respectively.
• The average osmotic reflection coefficient, which is a measure of how well the capillaries were holding onto water, was 0.66.
• The average capillary filtration coefficient, a measure of capillary leakiness, was 0.003 ml/min/mm of Hg/100 g.
• The average pressure of the fluid in the spaces between the tissues was 44.82 mm of Hg.

Conclusions

The researchers concluded that the high capillary pressure seemed to be due to high resistance in the blood vessels on the venous side, the side where blood returns to the heart. This high resistance may increase the chance of capillary filtration, which can lead to build-up of fluid in the tissues, a symptom characteristic of laminitis. The low osmotic reflection coefficient suggests increased capillary permeability, also pointing towards a risk of laminitis. These findings highlight the mechanisms that might underlie the development of laminitis during periods of carbohydrate overload in horses.