In vivo, RBC are exposed to high (lung) and low (tissues) oxygen tensions. The transport from the lung to tissues and back is rapid.  These short cycles of high and low oxygen tension can be mimicked in vitro in the sicklomat.  When sickle RBC are exposed to low oxygen they change their shape due to hemoglobin polymerization and the percentage of deformed (sickled) RBC in the population increases. Oxygenation rapidly drops the percentage of abnormal shaped cells. This cycle of deoxygenation and re-oxygenation and the resulting repeated polymerization and depolymerization of hemoglobin increases the number of cells that do not change back to a normal biconcave morphology (ISC). In sickle cell patients, the formation of such cells (ISC’s) outpaces the normal programmed removal.  In vitro those cells are not removed and the increase in the percentage of ISC after a set number of cycles provides information on this process in vivo. 

In the current version of this assay, cells are deoxygenated for 1 minute followed by oxygenation for 1 minute. These cycles are repeated for 3 hours (90 cycles). More than 90% of the change from air (20% oxygen) to nitrogen (0% oxygen) is reached after 30 seconds.