Diaphragmatic O2 and lactate extraction during submaximal and maximal exertion in ponies.

This study examines how oxygen and lactate levels in the diaphragm of ponies change during rest and varying intensities of exercise. It shows that as exertion levels increase, oxygen saturation in the diaphragm significantly decreases, while its extraction significantly increases.

Methodology

• The study observed 10 healthy ponies through various periods of rest and exercise on a treadmill.
• The ponies’ phrenic vein, part of the diaphragm, was catheterized through a procedure called lateral thoracotomy executed 8 to 35 days before the study.
• Both arterial and phrenic venous blood samples were taken concurrently at rest and at 30-second intervals during four minutes of exercise.
• Three levels of exertion were analyzed: moderate (10 mi/h), heavy (15 mi/h), and maximal (20 mi/h). Each exertion level was separated by rest periods of at least 90 minutes.
• Each pony was studied twice, with an interval of 2-3 days between studies.

Results

• At rest, the levels of oxygen and oxygen saturation in the diaphragmatic venous were 43.2 Torr and 76.1%, respectively, while the arteriovenous O2 content difference and oxygen extraction were 3.14 ml/dl and 23.60%, respectively.
• Once exercise commenced, a significant decrease in both phrenic venous PO2 and O2 saturation occurred within 30 seconds. Inversely, diaphragmatic arteriovenous O2 content difference (the difference in oxygen content between the arterial and venous blood) and oxygen extraction increased significantly.
• During heavy and maximal exercise, the diaphragmatic venous lactate concentration (an indicator of anaerobic metabolism or lack of oxygen) remained similar to the arterial concentration. This suggests that the diaphragm was functioning at its anaerobic threshold, i.e., it was already stressed to its maximum capacity.

Conclusion

• Findings indicate that with increasing exercise intensity, there’s a decrease in oxygen saturation in the diaphragm, while its extraction and arteriovenous O2 content difference surge significantly.