Final answer:
The estimated PvO2 for a venous oxygen saturation of 70% is approximately 30 mmHg, based on the oxygen-hemoglobin dissociation curve which shows a steep relationship between oxygen saturation levels and partial pressure at this range.
Step-by-step explanation:
The correct answer is b:
This is because the normal range for mixed venous oxygen saturation (SvO2) is typically between 70-75%, which corresponds to a mixed venous oxygen partial pressure (PvO2) of approximately 30-40 mmHg. To estimate the PvO2 from a given SvO2, we utilize the standard oxygen-hemoglobin dissociation curve, which describes the relationship between oxygen saturation and partial pressure of oxygen in the blood.
A SvO2 of 70% is near the steep part of the oxygen-hemoglobin dissociation curve, where small changes in the partial pressure of oxygen can result in significant changes in saturation levels. The steep slope of the curve at this point indicates that the PvO2 would be in the lower range, thus closer to 30 mmHg than to 40 mmHg or higher values. The relationship between SvO2 and PvO2 is predictable based on the shape of the dissociation curve. However, individual variations can occur, and different conditions, like changes in body temperature, pH, or levels of carbon dioxide (Pco2), can shift the curve, altering the PvO2 at a given saturation level.