Is P₅₀ the most representative P(So₂) to evaluate HbO₂ affinity?

Abstract

Off-line computer assistance allowed a correct visualization of the actual data included in any experimental whole oxygen-hemoglobin association curve.

The affinity of hemoglobin for oxygen (characterized by the successive Po₂ corresponding to any saturation value: P(So₂)), the shape of the association curve (Hill's curve and Hill's numbers) and the Bohr coefficients all along the oxygenation process, were determined with great accuracy. Results agreed with literature values obtained for successive steps of oxygenation. A batch of 78 computerized curves was divided into 3 groups (normal: NL, right deviated: RD and left deviated: LD) to which the principal component (P.C.) method was applied. It was therefore possible not only to study correlations between any curve summarized by its P.C. and any external variable but also to define for any association curve, whatever its eventual shift, the most representative value of P(So₂). For all mixed groups, the most significant parameter would be P₄₄. If the characterization of the HbO₂ dissociation curve is to be represented by a single point, then it should be P₄₈ for the NL curves, P₅₂ for the LD group, and P₂₄ for the RD group. Then, the common use of P₅₀, appeared to be illegitimate and inadequate for the right shifted curves, a very frequent circumstance in clinical practice.

Key Words:

• HbO₂ affinity curves
• Hill curves
• computerization
• principal component method.