O sub(2) Delivery and the Venous P sub(O2)-O sub(2) Uptake Relationship in Pump-Perfused Canine Muscle

• Published in: Experimental physiology 2002-01, Vol.87 (1), p.53-61
• Main Authors: Kohzuki, H, Sakata, S, Misawa, H, Takaki, M
• Format: Article
• Language: English
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/eph8702249

Under the conditions of both an increased red cell affinity for O sub(2) at a constant rate of O sub(2) delivery (arterial O sub(2) content flow) and a decrease in the rate of O sub(2) delivery induced by hypoxic hypoxia at constant blood flow, we have obtained a linear relationship between the partial pressure of O sub(2) in the muscle venous effluent (P sub(v,) sub(O2)) and O sub(2) uptake (V sub(O2)). The relationship is described by the equation V sub(O2)= D sub(a) P sub(v,) sub(O2)+V sub(O2) sub(,conv) where D sub(a) is the apparent O sub(2) diffusion capacity and V sub(O2) sub(,conv) is O sub(2) delivery-limited V sub(O2), and D sub(a) P sub(v,) sub(O2) represents the O sub(2) diffusion-limited V sub(O2) (V sub(O2) sub(,diff)). From these observations, we propose the hypothesis that V sub(O2) consists of two additive values, V sub(O2) sub(,conv) and V sub(O2) sub(,diff). The mechanism underlying the reduction in V sub(O2) that is induced by reducing O sub(2) delivery to markedly below the V sub(O2) sub(,conv) value has only been investigated using a model based on the single compartment of diffusion-limited V sub(O2) sub(,) and has not been investigated in terms of this additive V sub(O2) model. The single compartment analysis appears to overestimate the role of O sub(2) diffusion in limiting the reduction of V sub(O2) that occurs in response to a decrease in O sub(2) diffusion capacity, as reflected by the V sub(O2)/P sub(v,) sub(O2) ratio. To gain better insight into the mechanism involved, we altered the rate of O sub(2) delivery by changing arterial P sub(O2) from normoxia (with inhalation of air) to hypoxia (by inhalation of 10-11% O sub(2)) and blood flow (with high and low flow rates (n = 7 for both groups), and very low and ischaemic flow rates (n = 4 for both groups)) in pump-perfused dog gastrocnemius preparations during tetanic isometric contractions at 1 Hz. As rates of O sub(2) delivery were reduced from 23.2 to 10.9 ml min super(-1) (100 g) super(-1), significant decreases in P sub(v,) sub(O2) and V sub(O2) were observed (P < 0.05). From the data of P sub(v,) sub(O2) and V sub(O2) values within this range of O sub(2) delivery rates, we obtained the regression equation V sub(O2)= 0.22 P sub(v,) sub(O2)+ 8.14 (r = 0.58). From the equation, the intercept of the V sub(O2)-axis was significantly different from zero (P < 0.05), in accordance with the observation that the V sub(O2)/P sub(v,) sub(O2) ratio (ml min super(-1) (100 g) super(-1) To