title: Mathematical modeling of buffers used in myocardial preservation.
abstract: OBJECTIVE
  Buffers added to myocardial preservation solutions are considered to be critical for resisting myocardium pH changes from the accumulation of protons (H+). Our hypothesis is that mathematical modeling of three clinically used buffers will define their individual buffering capacities under simulated clinical conditions.
  
  
  METHODS
  The buffers, tromethamine (THAM), sodium bicarbonate (HCO3-), and L-histidine, were compared in terms of their buffering capacity (beta) under specific temperatures and concentrations, using a mathematical model.
  
  
  RESULTS
  At 37 degrees C, the maximal beta (betamax) occurred at pH 7.75 for THAM, pH 6.10 for HCO3-, and pH 5.89 for L-histidine at equimolar concentrations. A decrease in temperature moved betamax to a higher pH value for each buffer. At clinical concentrations, L-histidine provided the greatest buffering capacity followed by HCO3- and THAM, respectively.
  
  
  CONCLUSIONS
  This model permitted comparison of the above buffers under simulated clinical conditions. The assumption was that the magnitude of betamax at a given temperature determines which buffer(s) could be most effective for myocardial preservation. Also, the assumption was taken that these buffers are used in a closed system--where there is no continuous blood flow--and that the buffering ability of THAM and L-histidine were not influenced by the accumulation of CO2 as is HCO3-. THAM and L-histidine were more effective at hypothermic temperatures compared with HCO3-; however, HCO3- provided buffering at normothermic temperatures. Through the theoretical considerations of this study, we propose that combining HCO3- with THAM or L-histidine could be most efficacious for myocardial preservation during open heart surgery or organ transplantation.
authors.affiliation: Sarver Heart Center, College of Medicine, The University of Arizona, Tucson, AZ 85724, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Triana
authors.forename: Mark
authors.initials: M
authors.lastname: Yanagihashi
authors.forename: Douglas F
authors.initials: DF
authors.lastname: Larson
mesh_terms: D000143:Acids / Q000737:chemistry; D002021:Buffers; D002315:Cardiopulmonary Bypass; D016027:Heart Transplantation; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D009206:Myocardium; D019188:Organ Preservation Solutions / Q000737:chemistry*; D015427:Reperfusion Injury / Q000517:prevention & control; D017693:Sodium Bicarbonate / Q000737:chemistry; D014325:Tromethamine / Q000737:chemistry
chemical_list: D000143:Acids; D002021:Buffers; D019188:Organ Preservation Solutions; D014325:Tromethamine; D006639:Histidine; D017693:Sodium Bicarbonate