61.2 Friday, Jan. 6 Limits of the blood oxygen carrying capacity in the deer mouse, Peromyscus maniculatus VAN SANT, M.J.*; HAMMOND, K.A.; Univ. of California, Riverside; Univ. of California, Riverside email@example.com
Animals have evolved physiological systems capable of dealing with certain loads experienced in nature. It has often been shown to be beneficial for an animal to have physiological systems with an “excess capacity” for dealing with higher loads that may be encountered due to natural variation in the load. It is not known exactly how costly it is to have excess capacities; however, if the cost is low and the benefit is high we should find physiological systems with excess capacities. During exercise, respiration and heart rate increase in an effort to deliver oxygen to muscles at a faster rate. Although previous work has shown a large surplus of pulmonary diffusive capacity in some mammals, VO2max sets an upper limit to the exercise intensity that can be maintained for prolonged periods and has therefore presumably been a target of natural selection. If lung capacity is not limiting, we asked if, perhaps, blood oxygen carrying capacity was a limit to further increases in exercise performance. As exercise intensity increases, the amount of oxygen consumed and delivered to tissues increases; however, the blood never completely releases all of its oxygen. As an initial effort to understand limits to blood oxygen carrying capacity during intense activity, we measured VO2max of deer mice before and after taking blood. We found that after removal of 10-20% of blood volume (typical for blood chemistry) VO2max declines by up to 12%. Immediately following blood loss the blood volume can be replaced (by water), but it takes over a week to recover the lost red blood cells and VO2max. From these data we can estimate the excess carrying capacity of oxygen in the deer mouse. We also provide a note of caution on measuring performance too soon after blood measurements.