Final answer:
The fractional saturation of hemoglobin at 20 torr is typically below 50%, at 40 torr it is often between 50-75%, and at 60 torr it is usually above 80-90%, as determined by the oxygen-hemoglobin dissociation curve, although other factors like pH and temperature can affect these values.
Step-by-step explanation:
The question pertains to the estimate of the fractional saturation of haemoglobin at different partial pressures of oxygen (Po2). This concept is crucial in understanding how oxygen is transported in the blood. To estimate the fractional saturation for each of the given Po2 values (20 torr, 40 torrs, and 60 torrs), we would utilize the oxygen-haemoglobin dissociation curve, which is typically represented as an S-shaped graph showing the relationship between Po2 and haemoglobin saturation. At 20 torr Po2, haemoglobin is relatively less saturated because this is on the lower, steeper part of the S-shaped curve, indicating a lower affinity for oxygen. Typically this would correspond to less than 50% saturation. At 40 torr Po2, the curve starts to level off, suggesting that haemoglobin's affinity for oxygen is increasing; thus, saturation would be higher, often between 50-75%. Finally, at 60 torr Po2, the curve begins to level off, approaching a plateau that indicates higher saturation levels, usually above 80-90%. It should be noted that this graph and resulting estimates can be affected by factors such as pH and temperature, which can cause a rightward or leftward shift in the curve, known as the Bohr effect and the temperature effect, respectively.