INCREASED VO2MAX WITH RIGHT-SHIFTED HB-O-2 DISSOCIATION CURVE AT A CONSTANT O-2 DELIVERY IN DOG MUSCLE IN-SITU

If the diffusive component of O-2 transport in muscle is important in determining exercise capacity, an increased capillary-to-tissue Po-2 d ifference should enhance gas exchange from blood to skeletal muscle du ring exercise. Thus a rightward shift in the O-2 dissociation curve sh ould theoretically increase O-2 extraction and improve maximal O-2 upt ake (Vo(2max)). To test this hypothesis, we used the canine gastrocnem ius muscle to study maximal exercise in eight dogs at a normal P-50 (3 3.1 +/- 0.4 Torr) and with the O-2 dissociation curve shifted to the r ight by an allosteric modifier of hemoglobin (Kb) (methylpropionic aci d, RSR-13; P-50 = 53.2 +/- 5.0 Torr). Four control dogs were also stud ied before and after infusion of vehicle. O-2 (100%) was inspired duri ng exercise to maintain arterial saturation in both conditions. The mu scle was surgically isolated and electrically stimulated (tetanic trai n: 0.2-ms stimuli for 200-ms duration at 50 Hz, once per s). To mainta in O-2 delivery (pre-RSR-13 = 19.1 +/- 2.9; RSR-13 = 19.6 +/- 2.5 ml . 100 g(-1).min(-1)), the muscle was pump perfused. At a constant Oa de livery, RSR-13 significantly increased percent O-2 extraction (pre-RSR -13 = 61 +/- 4.0; RSR-13 = 75.5 +/- 4.7) and muscle Vo(2max) (pre-RSR- 13 = 11.8 +/- 2.1; RSR-13 = 14.2 +/- 1.5 ml . 100 g(-1). min(-1)). Thi s improvement in Vo(2max) with increased P-50 demonstrates its O-2 sup ply dependence when P-50 is normal and the importance of O-2 diffusive transport to muscle at maximal exercise.