Regional brain blood flow and O 2 delivery during severe exertion in the pony

Abstract

Regional distribution of brain blood flow (radionuclide labelled 15 μm diameter microspheres) and O 2 supply were studied in 11 healthy adult grade ponies at rest and during severe exercise (SE) performed on a treadmill ( heart rate = 220 ± 4 beats· min −1; V dot O 2 = 126 ± 9 ml· min −1· kg −1 ). During SE, the mean aortic pressure increased to 169±4 mm Hg and the pHa, Pa CO 2 and Pa O 2 were 7.213 ± 0.010, 30 ± 1 mm Hg and 85 ± 4 mm Hg, respectively. The hemoglobin concentration increased by 59.6% with SE. Whereas blood flow increased in the cerebellar gray matter (96%), pons (39.5%) and medulla (55.6%), in none of the other brain regions blood flow was different from rest. However, vascular resistance decreased only in the cerebellar cortex. Due to a 58% increment in arterial O 2 content with SE, the O 2 supply to all regions of the brain increased ( P < 0.01). The latter may be suggestive of an overall increase in brain metabolism during heavy exertion in ponies.