BSCC Physiology 008
Haemoglobin-oxygen dissociation curve
- The shape of the Hb-Oxygen dissociation curve is “S” shaped.
- The reason for the “S” shape is to provide a double buffering effect
- The first buffering effect occurs at the top flat portion of the curve (point), a high Hb-O2 saturation is maintained despite a significant drop in PaO2.
- (e.g. 150mmhg=98% and a drop to 100mmHg=97.5%)
- This is useful in the lungs to maintain arterial Hb saturation
- The second buffering effect occurs at the steep portion of the curve. At this portion, high levels of oxygen are extracted from the Hb despite a small drop/ change in PaO2.
- (e.g. 40mmHg=75% and a small drop to 27mmHg will result in a large drop of Hb saturation of 50%)
- This means that the PARTIAL PRESSURE (PaO2) is maintained and that this pressure gradient required for diffusion of oxygen from the capillaries to the cells is preserved despite the increased oxygen extraction.
- Resting muscles have a PaO2 40mmHg, this pressure is found along the steep part of the curve so that oxygen can be extracted without a large change in the partial pressure of oxygen, thus maintaining the required pressure gradient for oxygen diffusion.
- Exercising muscle becomes hot, acidic and hypercarbic- shifting the curve to the right. This allows for a greater OFF loading of oxygen into the muscles for a given PaO2