Examination of the intrarenal hematocrit ratio with the techinque of circulatory stop-flow in dogs.

Estimates of the intrarenal hematocrit ratio vary widely, depending on the techniques used for its determination. Computation of blood volume from the product of mean transit time of labeled erythrocytes and albumin, and minute volume blood flow, yields values averaging approximately 90% of the systemic vessel hematocrit. To the other extreme are values that are slightly less than half of the systemic hematocrit ratio based on the determination of total renal blood volume by labeled red cells and albumin. Intermediate values are obtained by methods involving draining the blood from the kidney and measuring its hematocrit ratio. The current investigation, by a technique of circulatory stop-flow, has shown that a substantial fluid shift occurs in the kidney within 2 minutes of circulatory arrest, so that interstitial fluid, supplemented by fluid reabsorbed by the nephrons, dilutes the erythrocytes within the peritubular capillaries to reduce the hematocrit ratio to almost half of the systemic figure. The drainage methods are subject to error as a result of this mechanism, but if such fluid shifts are taken into account, values for the intrarenal hematocrit closer to the ratio of systemic blood can be anticipated. ADDITIONAL