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A broad diversity in oxygen affinity to haemoglobin.

ABSTRACT: Oxygen affinity to haemoglobin is indicated by the p50 value (pO2 at 50% O2Hb) and critically determines cellular oxygen availability. Although high Hb-O2 affinity can cause tissue hypoxia under conditions of well O2 saturated blood, individual differences in p50 are commonly not considered in clinical routine. Here, we investigated the diversity in Hb-O2 affinity in the context of physiological relevance. Oxyhaemoglobin dissociation curves (ODCs) of 60 volunteers (18-40 years, both sexes, either endurance trained or untrained) were measured at rest and after maximum exercise (VO2max) test. At rest, p50 values of all participants ranged over 7 mmHg. For comparison, right shift of ODC after VO2max test, representing the maximal physiological range to release oxygen to the tissue, indicated a p50 difference of up to 10 mmHg. P50 at rest differs significantly between women and men, with women showing lower Hb-O2 affinity that is determined by higher 2,3-BPG and BPGM levels. Regular endurance exercise did not alter baseline Hb-O2 affinity. Thus, p50 diversity is already high at baseline level and needs to be considered under conditions of impaired tissue oxygenation. For fast prediction of Hb-O2 affinity by blood gas analysis, only venous but not capillary blood samples can be recommended.

SUBMITTER: Balcerek B

PROVIDER: S-EPMC7547706 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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A broad diversity in oxygen affinity to haemoglobin.

Balcerek Björn B Steinach Mathias M Lichti Julia J Maggioni Martina A MA Becker Philipp N PN Labes Robert R Gunga Hanns-Christian HC Persson Pontus B PB Fähling Michael M

Scientific reports 20201009 1

Oxygen affinity to haemoglobin is indicated by the p50 value (pO2 at 50% O2Hb) and critically determines cellular oxygen availability. Although high Hb-O2 affinity can cause tissue hypoxia under conditions of well O2 saturated blood, individual differences in p50 are commonly not considered in clinical routine. Here, we investigated the diversity in Hb-O2 affinity in the context of physiological relevance. Oxyhaemoglobin dissociation curves ...[more]

PMID: 33037242

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Project description:Key pointsTheoretical models suggest there is no benefit of high affinity haemoglobin to preserve maximal oxygen uptake in acute hypoxia but the comparative biology literature has many examples of species that are evolutionarily adapted to hypoxia and have high affinity haemoglobin. We studied humans with high affinity haemoglobin and compensatory polycythaemia. These subjects performed maximal exercise tests in normoxia and hypoxia to determine how their altered haemoglobin affinity impacts hypoxic exercise tolerance. The high affinity haemoglobin participants demonstrated an attenuated decline in maximal aerobic capacity in acute hypoxia. Those with high affinity haemoglobin had no worsening of pulmonary gas exchange during hypoxic exercise but had greater lactate and lower pH than controls for all exercise bouts. High affinity haemoglobin and compensatory polycythaemia mitigated the decline in exercise performance in acute hypoxia through a higher arterial oxygen content and an unchanged pulmonary gas exchange.AbstractThe longstanding dogma is that humans exhibit an acute reduction in haemoglobin (Hb) binding affinity for oxygen that facilitates adaptation to moderate hypoxia. However, many animals have adapted to high altitude through enhanced Hb binding affinity for oxygen. The objective of the study was to determine whether high affinity haemoglobin (HAH) affects maximal and submaximal exercise capacity. To accomplish this, we recruited individuals (n = 11, n = 8 females) with HAH (P50 = 16 ± 1 mmHg), had them perform normoxic and acute hypoxic (15% inspired oxygen) maximal exercise tests, and then compared their results to matched controls (P50 = 26 ± 1, n = 14, n = 8 females). Cardiorespiratory and arterial blood gases were collected throughout both exercise tests. Despite no difference in end-exercise arterial oxygen tension in hypoxia (59 ± 6 vs. 59 ± 9 mmHg for controls and HAH, respectively), the HAH subjects' oxyhaemoglobin saturation ( Sa,O2 ) was ∼7% higher. Those with HAH had an attenuated decline in maximal oxygen uptake ( V̇O2max ) (4 ± 5% vs. 12 ± %, p < 0.001) in hypoxia and the change in V̇O2max between trials was related to the change in SaO2 (r = -0.75, p < 0.0001). Compared to normoxia, the controls' alveolar-to-arterial oxygen gradient significantly increased during hypoxic exercise, whereas pulmonary gas exchange in HAH subjects was unchanged between the two exercise trials. However, arterial lactate was significantly higher and arterial pH significantly lower in the HAH subjects for both exercise trials. We conclude that HAH attenuates the decline in maximal aerobic capacity and preserves pulmonary gas exchange during acute hypoxic exercise. Our data support the comparative biology literature indicating that HAH is a positive adaptation to acute hypoxia.

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A broad diversity in oxygen affinity to haemoglobin.

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A broad diversity in oxygen affinity to haemoglobin.

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