Oxygen consumption and hemodynamic responses during graded treadmill exercise in the dog

A description is given of a technique that provides a relatively simple means by which O₂ consumption and hemodynamic variables can be measured in exercising dogs. We used a multistage submaximal treadmill test to study the responses of 10 foxhounds to dynamic exercise. They were also studied during maximal treadmill exercise. O₂ consumption increased from 16.3 ± 1.7 ml O₂·min^-1·kg^-1 at rest to 92.9 ± 9.7 ml O₂·min^-1·kg^-1 at a work load of 6.4 km/h, 20% grade and to 111.9 ± 9.6 ml O₂·min^-1·kg^-1 during maximal exercise. Cardiac output (CO) increased from 6.11 ± 0.45 1/min at rest to 16.91 ± 1.46 and 17.66 ± 0.60 1/min at 6.4 km/h, 20% grade and maximal exercise, respectively. Arteriovenous O₂ difference increased from 5.8 ± 0.3 vol% at rest to 12.0 ± 0.4 and 13.2 ± 0.7 vol% at 6.4 km/h, 20% grade and maximal exercise, respectively. Heart rate (HR) increased from 116 ± 7 beats/min at rest to 250 ± 8 beats/min at 6.4 km/h, 20% grade and to 278 ± 6 beats/min during maximal exercise. O₂ uptake, CO, and arteriovenous O₂ difference increased with the onset of exercise, appeared to level at lower work intensities (6.4 km/h, 4 and 8% grade), and increased significantly at each of the higher work intensities (6.4 km/h, 12, 16, and 20% grade). Additionally, we observed linear relationships between O₂ consumption and HR (HR = 1.35 x VO₂ + 120.5; r = 0.87; P < 0.001) and between O₂ consumption and CO (CO = 5.91 x VO₂ + 216.6; r = 0.96; P < 0.001). Further, the linear relationship between O₂ consumption and CO demonstrated in the present study is similar to that observed in humans.