The important thing is the relationship between gases – between carbon dioxide and oxygen. Too much oxygen (relative to the level of carbon dioxide) and we feel agitated and jumpy. Too much carbon dioxide (again, relative to the level of oxygen) and we feel sluggish and sleepy and tired.
A natural misconception most doctors maintain is that oxygen and carbon dioxide are antagonistic that a gain of one in the blood necessarily involves a corresponding loss of the other. This is not correct; although each tends to raise the pressure and thus promote the diffusion of the other, the two gases are held and transported in the blood by different means; the hemoglobin in the corpuscles carry oxygen, while carbon dioxide is combined with alkali in the plasma.
A sample of blood may be high in both gases, or low in both gases. Under clinical conditions, low oxygen and low carbon dioxide generally occur together. Therapeutic increase of carbon dioxide, by inhalation of this gas diluted in air, is often an effective means of improving the oxygenation of the blood and tissue.