Blood
About 98.5% of the oxygen in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the hemoglobin. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O per gram hemoglobin, which increases the total blood oxygen capacity seventyfold, compared to if oxygen solely were carried by its solubility of 0.03 ml O per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries).
Suicide bag
Inhalation of oxygen deficient or oxygen free gas not only fails to replenish oxygen used in normal metabolism, but causes the blood passing through the capillaries of the gas exchange regions of the lungs to lose residual oxygen in relation to the concentration difference between the oxygen in the alveolar air and in the blood in the alveolar capillaries. This causes a far quicker drop in blood oxygen level than holding the breath. The deoxygenated blood then passes through the systemic circulation to the vital organs, including the brain, and rapidly lowers oxygen concentrations below the level required to sustain consciousness, and when it is insufficient to keep the heart functioning, cardiac arrest will occur. For the most people, an alveolar oxygen tension of less than or 4% by volume at atmospheric pressure is not sufficient to support consciousness.