Hemodilution mediates hemodynamic changes during acute expansion in unanesthetized rats

Abstract

Studies were carried out to determine the relative importance of volume and hemodilution on hemodynamic adjustments to acute volume expansion. Systemic and renal hemodynamics were monitored in unanesthetized and unrestrained rats during progressive and equivalent blood volume expansion with saline (Sal; 1, 2, and 4% body wt), 7% BSA solution (0.35, 0.7, and 1.4% body wt), and reconstituted whole blood from donor rats (WBL; 0.35, 0.7, and 1.4% body wt). Mean arterial pressure remained unchanged in Sal and BSA but increased progressively in WBL-expanded rats (from 92 to 106 mmHg after maximal expansion). In Sal and BSA-expanded rats, cardiac output (CO) and renal blood flow (RBF) increased (CO: Sal from 19 to 20, 22, and 25; BSA from 21 to 23, 27, and 31; RBF: Sal from 1.6 to 1.8, 2.2, and 2.5; BSA from 2 to 2.4, 2.7, and 3.1 ml. min(-1). 100 g body wt(-1)), whereas total peripheral (TPR) and renal vascular (RVR) resistance decreased in parallel with the expansions. After expansion with WBL, CO increased progressively but less extensively than in cell-free expanded rats (21 to 22, 24, and 26 ml. min(-1). 100 g body wt(-1)), whereas TPR and RVR remained unchanged. Systemic hematocrit (Hct) decreased approximately the same after expansion with Sal or BSA solutions but remained unchanged after expansion with WBL. Isovolemic hemodilution to Hct levels comparable to those seen after maximal expansion with cell-free solutions also reduced SVR and RVR, although less extensively. These findings suggest that in unanesthetized rats hemodilution plays a major role in the systemic and renal hemodynamics during expansion.

Blood transfusion improves renal oxygenation and renal function in sepsis-induced acute kidney injury in rats

“…Renal oxygen consumption was calculated as follows: VO 2ren (ml/min/g) = renal blood flow × (CaO 2 – CvO 2 ), where renal venous oxygen content (CvO 2 ) is calculated as (1.31 × hemoglobin × renal venous oxygen saturation) + (0.003 × renal venous partial pressure of oxygen (rvPO 2 )) [12]. An estimation of the renal vascular resistance was made as follows: renal vascular resistance (dynes·sec·cm –5 ) = (MAP/renal blood flow) × 100 [13]. …”

Acute decrease in renal microvascular Po2 during acute normovolemic hemodilution

“…The renal oxygen extraction ratio was calculated as O2ERren (%) ϭ V O2ren/DO2ren. The vascular resistance of the renal artery flow region was calculated as MAP Ϫ RBF ratio (U) ϭ [MAP/RBF] * 100 (13).…”

Influence of fluid resuscitation on renal microvascular PO2 in a normotensive rat model of endotoxemia

“…Since values of renal venous pressure were not available, an estimation of the vascular resistance of the renal artery flow region was made: MAP – RBF ratio ( U ) = (MAP/RBF) × 100 [ 31 ].…”