Hill-equation Hb saturation vs pO2 with effective P50 shifts from pH, CO2, and temperature; arterial/venous points, Bohr effect, and O2 content.
This is a teaching model for adult hemoglobin. It omits fetal hemoglobin, dyshemoglobins, 2,3-BPG details, acid-base buffering, and full blood gas physiology.
Live graphs
About this model
This simulator plots the oxygen-hemoglobin dissociation curve using the Hill equation S = pO₂ⁿ/(P50ⁿ+pO₂ⁿ), where S is fractional hemoglobin saturation, n controls cooperativity, and P50 is the oxygen partial pressure at 50% saturation. The sliders shift the effective P50 with a teaching approximation of the Bohr effect: lower pH, higher CO₂, and higher temperature increase P50 and shift the curve right, making unloading easier in active tissue. Higher affinity conditions shift the curve left. The second plot converts saturation into blood oxygen content C_O₂ = 1.34·Hb·S + 0.003·pO₂, separating the large hemoglobin-bound reservoir from the small dissolved oxygen contribution. Arterial and venous points show how changes in pO₂ and curve position affect saturation, content, and extracted oxygen.
Who it's for: Students in physiology, medicine, biophysics, or biomedical engineering learning blood gas transport, cooperative binding, and the Bohr effect.
Key terms
Hemoglobin saturation
Hill equation
P50
Bohr effect
Oxygen content
pO2
Cooperative binding
Oxygen extraction
How it works
Interactive oxygen-hemoglobin dissociation curve: Hill saturation, P50 shifts from pH/CO2/temperature, arterial and venous points, Bohr effect, and oxygen content.
Key equations
S = pO₂ⁿ/(P50ⁿ + pO₂ⁿ), C_O₂ = 1.34 Hb S + 0.003 pO₂. Lower pH / higher CO₂ / higher T raises P50 (right shift).
Frequently asked questions
What does P50 mean?
P50 is the pO₂ at which hemoglobin is 50% saturated. A higher P50 means lower affinity and a right-shifted curve; a lower P50 means higher affinity and a left-shifted curve.
Why does active tissue shift the curve right?
Active tissue tends to be warmer, more acidic, and richer in CO₂. These conditions stabilize the deoxygenated form of hemoglobin, raising P50 and helping oxygen unload where metabolism is high.
Why include oxygen content, not only saturation?
Saturation alone ignores hemoglobin concentration. An anemic patient can have high SaO₂ but low total oxygen content because there is less hemoglobin available to carry oxygen.