CO2 Partial Pressure as a bio-marker for the ovulation time. .
It has been known since 1951 that a few days before ovulation, alveolar CO2 waste occurs. This means that the pulmonary alveoli cause a drop in carbon dioxide
This effect is due to an excessive increase in respiration, the so-called hyperventilation. The cause of this is a change in the sensitivity of the respiratory centre to the CO2 concentration in the blood.
This hyperventilation is hormonal and occurs unnoticed in women. The high performance of the lungs leads to a lowering of carbon dioxide partial pressure (pCO2) in the blood-air barrier. At rest, the end of exhalation (end expiratory) corresponds to the pCO2 value of the respiratory gas very well to the alveolar blood value, so that an analysis via the respiratory air is possible.
This effect makes it possible to predict the time of ovulation over several days, because the CO2 value is significantly lower in the 1st phase of the cycle (luteal phase) than in the 2nd phase of the cycle (follicular phase).