The Buffer Values and the Bohr Effect of Human Fetal and Adult Whole Blood in Vitro in an Acid Range

Abstract

ExtractThe buffering properties and the Bohr effect were studied in vitro on 10 human fetal and 9 adult whole blood samples. At the beginning of the experiments, the fetal and adult blood samples were similarly acidotic {BE = -9 mEq/liter).In order to obtain the respiratory and the metabolic buffer values, the blood was titrated either by varying the P CO2 at constant buffer base or by adding known amounts of base at constant Pco 2 -The mean fetal and adult in vitro apparent respiratory buffer values (/?') were 28.30 mEq HCOr/literpH unit ± 2.23 SEM and 23.66 mEq HCO 3~/ liter • pH unit ± 0.80 SEM, respectively. These values were not statistically different. The in vitro apparent metabolic buffer value (X) rose significantly when P C o 2 increased. At P CO2 of 30, 40, and 60 mm Hg, the mean values were, respectively, for fetal blood: 55 ± 1.75 SEM, 61.25 ± 1.41 SEM, and 71.25 ± 3.21 SEM mEq H+Aiter-pH un it; for adult blood: 61.94 ± 2.76 SEM, 65.83 ± 2.47 SEM, and 71.94 ± 2.97 SEM mEq H+/liter-pH unit. Only at a P C02 of 30 mm Hg was the difference between adult and fetal blood statistically significant. In order to determine the magnitude of the Bohr effect, the iso-P CO2 pH change (ApH ox ) associated with the oxygenation of a desaturated blood sample was measured and the O 2 contents were determined by Natelson's micromanometric method. Thus, by the following equation: AH+ = X> ApH, the ratio -AH + /AO 2 was calculated. The mean values obtained for P CO2 of 30, 40, and 60 mm Hg were, respectively, 0.330 ± 0.027 SEM, 0.365 ± 0.028 SEM, and 0.401 ± 0.032 SEM mEq H+/mM O 2 for fetal blood; and 0.391 ± 0.029 SEM, 0.414 ± 0.029 SEM and 0.445 ± 0.032 SEM mEq H+/mM O 2 for adult blood. No significant differences were found at each P cc . 2 between the adult and the fetal blood. SpeculationThese results show that the in vitro buffering properties and the Bohr effect were similar in the adult and the fetal whole blood. The observed difference between the adult and fetal blood for the metabolic buffer value at P C o 2 of 30 mm Hg could be explained by differences in hemoglobin (Hb) concentration or different carbamino reaction with fetal hemoglobin (HbF). However, the heterogeneity and the complexity of whole blood hinder simple interpretation. The practical implication of this study is that the use of the Siggaard-Andersen's nomogram for fetal blood is justified, at least in vitro. 126Blood buffer values and Bohr effect 127

A Further Study of the Metabolic Buffer Value and the Bohr Effect in Human Fetal Whole Blood

“…Two milliliters of the same solution were added in the same manner to 15 ml fetal blood in order to obtain a [BE] of +10 mEq/liter. After this alkalization, each blood sample was immediately handled as previously described [3]. All procedures were identical with those previously reported [2,3].…”

“…Figure 1 shows the relation between the mean A. and the pH at P c02 30, 40, and 60 mm Hg. The values obtained previously for adult and fetal blood [3] at [BE] = -9 mEq/liter are included on this graph together with the values of Table I. This diagram makes apparent the following.…”

“…A study of and adult blood [3]. However, it has been demonthese variables made in adult and fetal blood at the strated in adult whole blood that the \ and the -AH+/AO 2 ratio depend at any constant P co , on the pH, i.e., on the [BE]; a rise of pH at constant P 002 causes an increase of A and a decrease of the AH + /AO 2 ratio [6,10].…”

“…A study of and adult blood [3]. However, it has been demonthese variables made in adult and fetal blood at the strated in adult whole blood that the \ and the…”

“…

ExtractThe metabolic buffer value (X = AH+/liter • pH unit) and the Bohr effect (-AH+/ AO 2 ) were studied in vitro in fetal blood at a base excess concentration [BE] of 0 mEq/ liter and + 10 mEq/liter by the same method as in a previous study [3]. At a P C o 2 of 30, 40, and 60 mm Hg, the mean fetal X ( ±SEM) was, respectively, for [BE] [BE] = -9 mEq/liter were compared with the corresponding values obtained previously for adult blood with the same conditions and method.

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