Hemodilution does not Alter the Aortic-to-Femoral Arterial Pressure Difference in Dogs

Abstract

Introduction.Distal arterial pressure normally differs from aorticpressure. This difference is modified by changes of vascular resistance.Hemodilution, due to decreased viscosity, decreases vascular resistance.Therefore, the difference between aortic and distal arterial pressures couldbe altered as well. We investigated whether acute hemodilution affected thisdifference in dogs. Methods.Eleven mongrel dogs weighing 16.6 ±4.4 kg were anesthetized with pentobarbital and sufentanyl and mechanicallyventilated. Arterial presssure was recorded using Millar catheter-tippedpressure transducers in the proximal aorta and in the distal femoral artery.An electromagnetic flowmeter probe was placed around the aorta. Effectivedownstream pressure was estimated by extrapolation of exponential arterialpressure decay during 3-second occlusion of the proximal aorta. Hemodilutionwas effected by removal of 30 ml/kg of blood and replacement with 60 ml/kg ofwarmed saline. In addition, the effects of 1 µg/kg phenylephrine and 4µg/kg of sodium nitroprusside were measured before and afterhemodilution. Results.Hemodilution decreased hematocrit from 39± 11.2% to 25.6 ± 4.95%. Systolic and mean pressures wereunchanged but aortic diastolic pressure decreased significantly, from 86± 17 to 79 ± 15 mmHg (p < 0.005). Peak systolicpressure was 13.5 ± 7.2 mmHg higher in the femoral artery than in theaorta before, and 16 ± 8.7 mmHg after, hemodilution (p >0.05). Nitroprusside decreased the femoral to aortic peak systolic pressuredifference from 14.3 ± 6.3 to 7.7 ± 15.3 mmHg, p = 0.05before hemodilution and from 14.3 ± 8.8 to 2.5 ± 11 mmHg,p < 0.005 afterwards. Hemodilution significantly decreased theeffective downstream pressure, from 44 ± 9 to 36 ± 6.8 mmHg inthe aorta (p< 0.05), and from 51 ± 2 to 37 ± 3.1mmHg in the distal femoral artery (p< 0.05). Conclusion.Acute hemodilution did not alter the aortic-to-distal arterial pressuredifference in dogs.