In patients with cystic fibrosis lung damages cause arterial hypoxia. As a typical compensatory reaction one might expect changes in oxygen affinity of hemoglobin. Therefore position (standard half saturation pressure P50st) and slope (Hill’s n) of the O2 dissociation curve as well as the Bohr coefficients (BC) for CO2 and lactic acid were determined in blood of 14 adult patients (8 males, 6 females) and 14 healthy controls (6 males, 8 females). While Hill’s n amounted to approximately 2.6 in all subjects, P50st was slightly increased by 1mmHg in both patient groups (controls male 26.7±0.2, controls female 27.0±0.1, patients male 27.7±0.5, patients female 28.0±0.3 mmHg; mean and standard error, overall p<0.01). Main cause was a rise of 1–2 µmol/g hemoglobin in erythrocytic 2,3-biphosphoglycerate concentration. One patient only, clearly identified as an outlier and with the mutation G551D, showed a reduction of both P50st (24.5 mmHg) and [2,3-biphosphoglycerate] (9.8 µmol/g hemoglobin). There were no differences in BCCO2, but small sex differences in the BC for lactic acid in the controls which were not detectable in the patients. Causes for the right shift of the O2 dissociation curve might be hypoxic stimulation of erythrocytic glycolysis and an increased red cell turnover both causing increased [2,3-biphosphoglycerate]. However, for situations with additional hypercapnia as observed in exercising patients a left shift seems to be a more favourable adaptation in cystic fibrosis. Additionally when in vivo PO2 values were corrected to the standard conditions they mostly lay left of the in vitro O2 dissociation curve in both patients and controls. This hints to unknown fugitive factors influencing oxygen affinity.

The use of the OSM3 oximeter for measurement of the fraction of carboxyhaemoglobin (FCOHb) in blood allows for estimation of total circulating haemoglobin mass (Hb(tot)) by using the carbon monoxide rebreathing method. To ensure high accuracy of Hb(tot) estimation, potential sources of analytical errors should be identified and adjusted for. Based on observed differences in results of measured FCOHb between simultaneously sampled, arterialized and venous blood samples we investigated the influence of haemoglobin oxygen saturation (sO2) on results of measured FCOHb. Blood from nine healthy non-smokers was tonometered with gas mixtures containing 94% N2 or air and 6% CO2. The resulting oxygenated and deoxygenated specimens were mixed in different proportions to obtain varying sO2 values in the same blood. sO2, fractions of dyshaemoglobins, pO2, pCO2 and pH were measured at each step. FCOHb was significantly (p<0.001) higher in oxygenated (median, range: 0.6%, 0.4-0.9%) compared to deoxygenated (-0.2%, -0.5-0.0%) blood. Regression analysis identified the sO2 as the most important factor explaining 86% of the variance in observed changes in FCOHb. The observed sO2 effect has important implications on calibration procedure of OSM3, accuracy of measured FCOHb, and FCOHb dependent calculations such as estimation of Hb(tot) and related quantities. If the highest accuracy of FCOHb measurement is needed, an sO2 effect on results of measured FCOHb has to be considered and adjusted for.