The inhaled smoke and air containing cocaine molecules arrive in the alveoli, the air sacs of the lungs. The cocaine molecules can penetrate the cell membranes of the air sacs and enter the capillaries.
When chasing the dragon, the user inhales and exhales several times. The cocaine molecules enter the blood in waves. When freebasing or smoking cocaine, the cocaine molecules are absorbed into the blood all at once via the lungs.
At the same time, the blood is absorbing oxygen from the inhaled air. Some of the inhaled cocaine molecules are exhaled with the air from the lungs without entering the bloodstream.