Mathematical modeling of buffers used in myocardial preservation.
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.
Triana
Jonathan R
JR
Sarver Heart Center, College of Medicine, The University of Arizona, Tucson, AZ 85724, USA.
Yanagihashi
Mark
M
Larson
Douglas F
DF
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
D000143:Acids; D002021:Buffers; D019188:Organ Preservation Solutions; D014325:Tromethamine; D006639:Histidine; D017693:Sodium Bicarbonate