Costal diaphragmatic O2 and lactate extraction in laryngeal hemiplegic ponies during exercise

Ultrasonographic measurement of diaphragm muscle activity for assessment of respiratory function in horses

Ultrasonographic imaging of the diaphragm is a non-invasive alternative for respiratory function evaluation in horses. This study aimed to measure diaphragm thickness, thickening (change in thickness with contraction) and thickening fraction in healthy adult horses during tidal breathing and forced vital capacity. Correlation between body weight (≤400 kg and >400 kg) and diaphragm thickness was investigated. To that purpose, 20 adult horses, weight 409±50 kg, height 1.47±0.05 m, and age 16±6 years were included in the study. Diaphragm thickness was measured at end-inspiration and end-expiration using B-mode and M-mode. The transducer was placed in the 10th, 11th and 12th intercostal spaces of both hemithoraces. Measurements obtained at end inspiration using M-mode during forced vital capacity were greater than for tidal breathing for diaphragm thickness (P=0.006), diaphragm thickening (P<0.001) and thickening fraction (P<0.001). The same was found for thickening (P<0.001) and thickening fraction (P<0.001). Diaphragm thickness at end-inspiration was greater in horses weighing >400kg than those ≤400kg at the inspiration (0.93±0.2 cm and 0.74±0 0.02 cm, P<0.001) and at the end of expiration (0.77±0.02 cm and 0.63±0, 02 cm, P<0.001). There was no difference in thickening fraction between horses weighing ≤400kg and >400kg (tidal breathing: 18±2 % and 16±2 %, P=0.609; forced vital capacity: 39±6 % and 31±5 %, P=0.301). Diaphragm assessment in horses is possible using both B-mode and M-mode. Breathing workload has a positive correlation between breathing workload and diaphragm contraction. Due to the relationship demonstrated between diaphragm thickness and weight, it is recommended that diaphragm thickening fraction is used to compare diaphragm measurements between horses.

Blood gas tensions, acid-base status, heart rates, and venous profiles in exercising horses with laryngeal hemiplegia before and after corrective surgery

The physiologic effects of exercise were studied in four horses with complete laryngeal hemiplegia. Right carotid arteries were surgically elevated to a subcutaneous position for percutaneous catheterization. Each horse was fitted with a device designed to obtain multiple arterial samples while the horse was exercised over a 1.6-km course. After each horse completed 10 test gallops, the laryngeal hemiplegia was treated using a laryngeal prothesis and ventriculectomy. The horses were then reconditioned, and the exercise test and sampling were repeated. Horses with laryngeal hemiplegia became acidotic, hypoxic, and hypercapnic compared to normal horses. Surgical treatment improved blood gas and acid-base status, but the values were not equivalent to those in normal horses similarly tested.