title: Hemodilution does not alter the aortic-to-femoral arterial pressure difference in dogs.
abstract: BACKGROUND
  Distal arterial pressure normally differs from aortic pressure. 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 could be altered as well. We investigated whether acute hemodilution affected this difference in dogs.
  
  
  METHODS
  Eleven mongrel dogs weighing 16.6 +/- 4.4 kg were anesthetized with pentobarbital and sufentanyl and mechanically ventilated. Arterial presssure was recorded using Millar catheter-tipped pressure transducers in the proximal aorta and in the distal femoral artery. An electromagnetic flowmeter probe was placed around the aorta. Effective downstream pressure 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 saline. In addition, the effects of 1 microg/kg phenylephrine and 4 microg/kg of sodium nitroprusside were measured before and after hemodilution.
  
  
  RESULTS
  Hemodilution decreased hematocrit from 39 +/- 11.2% to 25.6 +/- 4.95%. Systolic and mean pressures were unchanged but aortic diastolic pressure decreased significantly, from 86 +/- 17 to 79 +/- 15 mmHg (p < 0.005). Peak systolic 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). Nitroprusside 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 14.3 +/- 8.8 to 2.5 +/- 11 mmHg, p < 0.005 afterwards. Hemodilution significantly 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 the distal femoral artery (p < 0.05).
  
  
  CONCLUSIONS
  Acute hemodilution did not alter the aortic-to-distal arterial pressure difference in dogs.
authors.affiliation: Department of Anesthesiology, Catholic University of Chile Medical School, Santiago de Chile. jurzua@med.puc.cl
authors.forename: J
authors.initials: J
authors.lastname: Urzua
authors.forename: G
authors.initials: G
authors.lastname: Nunez
authors.forename: G
authors.initials: G
authors.lastname: Lema
authors.forename: R
authors.initials: R
authors.lastname: Canessa
authors.forename: C
authors.initials: C
authors.lastname: Sacco
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002316:Cardiotonic Agents / Q000008:administration & dosage / Q000494:pharmacology; D004285:Dogs; D006438:Hemodilution; D009599:Nitroprusside / Q000008:administration & dosage / Q000494:pharmacology; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology; D012039:Regional Blood Flow; D012965:Sodium Chloride / Q000008:administration & dosage; D014655:Vascular Resistance; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D002316:Cardiotonic Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine; D012965:Sodium Chloride