Modification of the Oxyhemoglobin Dissociation Curve

‭Modification of the oxyhemoglobin dissociation curve.‬ ‭ ertain‬ ‭pathophysiological‬ ‭or‬ ‭physiological‬ ‭situations‬ ‭can‬ ‭modify‬ ‭this‬ C ‭oxyhemoglobin‬ ‭dissociation‬ ‭curve‬ ‭(modification‬ ‭of‬ ‭the‬ ‭affinity‬ ‭of‬ ‭oxyhemoglobin).‬‭These‬‭situations‬‭are‬‭the‬‭variation‬‭of‬‭pH‬‭and‬‭the‬‭variation‬ ‭of temperature. This is called the BOHR effect (1904).‬ ‭ hen‬ ‭this‬ ‭oxyhemoglobin‬ ‭dissociation‬ ‭curve‬ ‭approaches‬ ‭a‬ ‭linear‬ ‭model‬ W ‭(deviation‬‭of‬‭the‬‭curve‬‭to‬‭the‬‭right‬‭and‬‭downwards),‬‭there‬‭is‬‭a‬‭decrease‬‭in‬ ‭the affinity of Hb for O2 for the same pressure. (lower %SaO2).‬ ‭ hen‬ ‭this‬ ‭curve‬ ‭moves‬ ‭away‬ ‭from‬ ‭a‬ ‭linear‬ ‭model‬ ‭(deviation‬ ‭to‬‭the‬‭left),‬ W ‭there‬ ‭is‬ ‭an‬ ‭increase‬ ‭in‬ ‭the‬ ‭affinity‬ ‭of‬ ‭Hb‬ ‭for‬ ‭O2‬ ‭for‬ ‭the‬ ‭same‬ ‭pressure‬ ‭(higher %SaO2).‬ ‭1.1.‬‭pH‬ ‭ hen‬‭pH‬‭(blood‬‭acidity)‬‭falls,‬‭the‬‭oxyhemoglobin‬‭dissociation‬‭curve‬‭shifts‬ W ‭to‬‭the‬‭right‬‭and‬‭down.‬‭Conversely,‬‭if‬‭the‬‭pH‬‭increases,‬‭the‬‭curve‬‭moves‬‭to‬ ‭the‬ ‭left‬ ‭and‬ ‭up.‬ ‭If‬ ‭we‬ ‭look‬ ‭at‬ ‭the‬ ‭same‬ ‭pressure‬ ‭we‬ ‭see‬ ‭that,‬ ‭if‬ ‭the‬ ‭pH‬ ‭falls,‬ ‭the‬ ‭O2‬ ‭saturation‬ ‭decreases‬ ‭and‬ ‭if‬ ‭the‬ ‭pH‬ ‭increases‬ ‭the‬ ‭saturation‬ ‭becomes more important.‬ ‭ uring‬ ‭exercise,‬ ‭we‬ ‭note‬ ‭an‬ ‭increase‬ ‭in‬ ‭the‬ ‭number‬ ‭of‬ ‭H+‬ ‭ions,‬ ‭we‬ D ‭observe‬‭a‬‭drop‬‭in‬‭pH‬‭and‬‭therefore‬‭blood‬‭acidity.‬‭We‬‭therefore‬‭observe‬‭an‬ ‭increase‬ ‭in‬ ‭CO2‬ ‭production.‬ ‭The‬ ‭oxyhemoglobin‬ ‭dissociation‬ ‭curve‬ ‭therefore‬ ‭shifts‬ ‭downward‬ ‭and‬ ‭to‬ ‭the‬ ‭right‬ ‭(so‬ ‭oxygen‬ ‭saturation‬ ‭decreases).‬ ‭There‬ ‭is‬ ‭therefore‬ ‭a‬ ‭desaturation‬ ‭of‬ ‭oxyhemoglobin‬ ‭to‬ ‭facilitate‬ ‭the‬ ‭delivery‬ ‭of‬ ‭O2‬ ‭to‬ ‭the‬ ‭tissues‬ ‭in‬ ‭an‬ ‭attempt‬ ‭to‬ ‭limit‬ ‭blood‬ ‭acidity.‬ ‭The‬ ‭Hb‬ ‭then‬ ‭binds‬ ‭to‬ ‭the‬ ‭CO2‬ ‭which‬ ‭is‬ ‭produced‬ ‭by‬ ‭the‬ ‭tissues‬ ‭and which increases due to exercise.‬ ‭1.2.‬‭Temperature.‬ ‭ ny‬ ‭increase‬ ‭in‬ ‭temperature‬ ‭will‬ ‭cause‬‭the‬‭curve‬‭to‬‭shift‬‭to‬‭the‬‭right‬‭and‬ A ‭downwards‬‭(lower‬‭%SaO2‬‭for‬‭the‬‭same‬‭pressure).‬‭Conversely,‬‭any‬‭drop‬‭in‬ ‭temperature‬ ‭will‬ ‭cause‬ ‭this‬ ‭curve‬ ‭to‬ ‭shift‬‭upwards‬‭and‬‭to‬‭the‬‭left‬‭(higher‬ ‭%SaCO2 for the same pressure).‬ ‭ uring‬ ‭exercise,‬ ‭there‬ ‭is‬ ‭an‬ ‭increase‬ ‭in‬ ‭temperature‬ ‭(can‬ ‭increase‬ ‭up‬ ‭to‬ D ‭39°C).‬ ‭This‬ ‭causes‬ ‭the‬ ‭curve‬ ‭to‬ ‭shift‬ ‭downward‬ ‭and‬ ‭to‬ ‭the‬ ‭right.‬ ‭So,‬ ‭as‬ ‭with‬‭the‬‭pH,‬‭this‬‭will‬‭cause‬‭a‬‭desaturation‬‭of‬‭oxyhemoglobin,‬‭facilitate‬‭the‬ ‭delivery of O2 to the tissues and fix the CO2 on the hemoglobin.‬