Renal O<inf>2</inf> consumption during progressive hemorrhage

Most mammalian tissues regulate O2 utilization such that O2 consumption (V̇O2) is relatively constant at O2 delivery (ḊO2) higher than a critical value (ḊO(2 c)). We studied the relationship between V̇O2 and ḊO2 of kidney and whole body during graded progressive exsanguination. The relationship between whole body V̇O2 and ḊO2 was biphasic, and whole body V̇O2 decreased by 5.6 ± 14.4% (P = NS) from the initial value to the value nearest whole body ḊO(2 c). Kidney ḊO2 decreased in direct proportion to whole body ḊO2 such that the average R2 value describing the linear regression of kidney ḊO2 vs. whole body ḊO2 was 0.94 ± 0.02. The relationship between kidney, like whole body, V̇O2 and ḊO2 appeared biphasic; however, kidney V̇O2 decreased by 63.3 ± 10.4% (P < 0.0001) from the initial value to the value nearest kidney ḊO(2 c). Renal O2 extraction ratio was relatively constant over a wide range of kidney ḊO2, whereas whole body O2 extraction ratio increased progressively at all whole body ḊO2 values as whole body ḊO2 decreased. However, final values of O2 extraction ratio were indistinguishable for whole body (0.86 ± 0.1) and kidney (0.86 ± 0.06) (P = NS). We conclude that the pattern of kidney and whole body V̇O2 response to decreasing ḊO2 differs during hemorrhage, particularly in the range of ḊO2 normally associated with tissue wellness