Hemodilution does not alter the aortic-to-femoral arterial pressure difference in dogs

Introduction. Distal arterial pressure normally differs from aortic pressur e. This difference is modified by changes of vascular resistance. Hemodilut ion, due to decreased viscosity, decreases vascular resistance. Therefore, the difference between aortic and distal arterial pressures could be altere d as well. We investigated whether acute hemodilution affected this differe nce in dogs. Methods. Eleven mongrel dogs weighing 16.6 +/- 4.4 kg were ane sthetized with pentobarbital and sufentanyl and mechanically ventilated. Ar terial presssure was recorded using Millar catheter-tipped pressure transdu cers in the proximal aorta and in the distal femoral artery. An electromagn etic flowmeter probe was placed around the aorta. Effective downstream pres sure was estimated by extrapolation of exponential arterial pressure decay during 3-second occlusion of the proximal aorta. Hemodilution was effected by removal of 30 ml/kg of blood and replacement with 60 ml/kg of warmed sal ine. In addition, the effects of 1 mu g/kg phenylephrine and 4 mu g/kg of s odium nitroprusside were measured before and after hemodilution. Results. H emodilution decreased hematocrit from 39 +/- 11.2% to 25.6 +/- 4.95%. Systo lic and mean pressures were unchanged but aortic diastolic pressure decreas ed significantly, from 86 +/- 17 to 79 +/- 15 mmHg (p < 0.005). Peak systol ic pressure was 13.5 +/- 7.2 mmHg higher in the femoral artery than in the aorta before, and 16 +/- 8.7 mmHg after, hemodilution (p > 0.05). Nitroprus side decreased the femoral to aortic peak systolic pressure difference from 14.3 +/- 6.3 to 7.7 +/- 15.3 mmHg, p = 0.05 before hemodilution and from 1 4.3 +/- 8.8 to 2.5 +/- 11 mmHg, p < 0.005 afterwards. Hemodilution signific antly decreased the effective downstream pressure, from 44 +/- 9 to 36 +/- 6.8 mmHg in the aorta (p < 0.05), and from 51 +/- 2 to 37 +/- 3.1 mmHg in t he distal femoral artery (p < 0.05). Conclusion.Acute hemodilution did not alter the aortic-to-distal arterial pressure difference in dogs.