title: Hemodilution does not alter arterial baroreflex control of heart rate in anesthetized dogs.
abstract: The cardiovascular effects of acute normovolemic hemodilution (ANH) are characterized by increased cardiac output and decreased systemic vascular resistance. However, whether arterial baroreflex function is altered by ANH remains undetermined. We assigned 23 anesthetized, mechanically ventilated dogs to mild ANH (hemoglobin, 7-8 g/dL; n = 11) or profound ANH (hemoglobin, 4-5 g/dL; n = 12) achieved by phlebotomy and simultaneous exchange with lactated Ringer's solution at 1:3 ratio to maintain constant central venous pressure and pulmonary artery occluded pressure. Baroreflex sensitivity was assessed by measurements of RR intervals of the electrocardiogram and mean arterial blood pressure (MAP) through a femoral artery catheter. Baroreflex responses were triggered by bolus IV injections of phenylephrine (25-75 micro g) and nitroprusside (50-100 micro g). The linear portion of the baroreflex curves relating RR intervals and MAP were used to determine baroreflex sensitivities. Compared with the predilution period, both ANH groups had significant increases in cardiac output and decreases in systemic vascular resistance (P < 0.01), whereas MAP and heart rate (HR) remained unchanged. However, no significant difference was detected between pre-ANH and post-ANH baroreflex sensitivities in either group. Our results indicate that arterial baroreflex control of HR is preserved during ANH to a hemoglobin concentration of 4-5 g/dL in anesthetized dogs.
  
  
  CONCLUSIONS
  Acute normovolemic hemodilution may be preoperatively used to minimize the requirement of allogeneic blood products during major surgery. We found that baroreflex function is preserved during mild (hemoglobin concentration, 7-8 g/dL) and profound hemodilution (hemoglobin concentration, 4-5 g/dL) in pentobarbital-anesthetized dogs.
authors.affiliation: Department of Anesthesia, Akita University School of Medicine, Japan. mtanaka@med.akita-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Tanaka
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Nishikawa
mesh_terms: D000758:Anesthesia; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology; D001158:Arteries / Q000187:drug effects / Q000502:physiology*; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006438:Hemodilution / Q000009:adverse effects*; D006454:Hemoglobins / Q000378:metabolism; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects / Q000502:physiology; D013617:Tachycardia, Supraventricular / Q000209:etiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D006454:Hemoglobins; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine