(10 points) A young patient arrives in your clinic exhibiting classic symptoms o

Question

(10 points) A young patient arrives in your clinic exhibiting classic symptoms of respiratory failure including Cheyne-Stokes breathing (abnormal irregular pattern punctuated by periods of apnea). In the ensuing workup, you note that the patient has low arterial PO2. Moreover, further blood work demonstrates that the blood exhibits no evidence of a Bohr effect. What kind of measurements are taken on a blood sample to test the Bohr effect and what would the results of those measurements be to cause low PO2.

Explanation / Answer

Determination of oxygen affinity in blood sample:

Measurement of Partial pressure of oxygen helps determine the amount of dissolved oxygen in blood. The oxygen affinity of RBCs can be measured by common blood gas analyzers. These are designed to give haemoglobin fractional saturation (p50) with oxygen and the calculations can be made by the oxygen dissociation curve provided. Using this curve, Hill coefficient can also be estimated which is the measure of cooperative binging of oxygen to Hb. Hemox analyser or hemoximeters can be employed for such measurements using blood samples.

Microfluidic single cell assays are also recently available, and is a high throughput technique to estimate oxygen saturation of individual RBCs. Cellular oxygen affinity is determined by scanning the partial pressure of oxygen (considered from 0% to 21%) and finding the mean and standard deviation of single-cell saturation distribution. This is an indirect method of understanding oxygen affinity by means of cooperative interaction of Hb and Oxygen. The pH, temperature, type of Hb (mixed wit CO2 etc) and 2,3-DPG:Hb ratio, all of these affects oxygen binding to Hb.

If a sample at low pH shows lower oxygen affinity, it is due to Bohr’s effect.

In patient with Cheyne-Stokes respiration:

Oxygen in the blood will be reduced and CO2 is easy to be found in bodies of these patients. CO2 is known to trigger Bohr’s effect. The increase in partial pressure of CO2 as is a common observation in people with CSR condition, the pH drops. pH drop affects the binding of oxygen to Hb and thus leads to Bohr’s effect.

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