Question

Describe how arterial pCO₂ changes during a) hyperventilation, and b) breathing into a paper bag. How would you expect your body to compensate for these changes in pCO2 through breathing afterward?

Answer 1

Introduction

pCO2 (partial pressure of carbon dioxide) reflects the the amount of carbon dioxide gas dissolved in the blood.Its normal values are in the range 35–45 mmHg. is less than 35 mmHg, the patient is hyperventilating, and if the pH (potential hydrogen) is greater than 7.45, corresponding to a respiratory alkalosis.

Indirectly, the pCO2 reflects the exchange of this gas through the lungs to the outside air. Two factors each have a significant impact on the pCO2. The first is how rapidly and deeply the individual is breathing:

• Someone who is hyperventilating will blow off more CO2, leading to lower pCO2 levels
• Someone who is holding their breath will retain CO2, leading to increased pCO2 levels

Arterial pCO₂ changes in Hyperventilation and Breathing from a bag.

Hyperventilation, sustained abnormal increase in breathing. During hyperventilation the rate of removal of carbon dioxide from the blood is increased. As the partial pressure of carbon dioxide in the blood decreases, respiratory alkalosis, characterized by decreased acidity or increased alkalinity of the blood, ensues. In turn, alkalosis causes constriction of the small blood vessels that supply the brain. Reduced blood supply to the brain can cause a variety of symptoms, including light-headedness and tingling of the fingertips. Severe hyperventilation can cause transient loss of consciousness.

The idea behind breathing into a paper bag or mask is that rebreathing exhaled air helps your body put CO2 back into your blood. While breathing into a paper bag to treat hyperventilation can work in theory, many doctors (and patients) don't find it to be a particularly quick or effective method.

Compensatory mechanism of the body for changes in pCO₂

Respiratory alkalosis is a disturbance in acid and base balance due to alveolar hyperventilation. Alveolar hyperventilation leads to a decreased partial pressure of arterial carbon dioxide (PaCO₂). In turn, the decrease in PaCO₂ increases the ratio of bicarbonate concentration to PaCO₂ and, thereby, increases the pH level; thus the descriptive term respiratory alkalosis. The decrease in PaCO₂ (hypocapnia) develops when a strong respiratory stimulus causes the respiratory system to remove more carbon dioxide than is produced metabolically in the tissues.Respiratory alkalosis is treated by having the hyperventilating person breathe into a paper bag.In chronic respiratory alkalosis, the kidneys decrease H+ secretion, which produces a decrease in the serum HCO3− concentration. Metabolic compensation for a respiratory alkalosis develops gradually and takes 2-3 days. In chronic compensation, plasma bicarbonate falls by 4 for each 10 mm Hg decrease in the Pco2.