Given an oxygen saturation curve, how would you calculate the dissociation constant (Kd) for fetal hemoglobin, and what does a lower Kd signify?

• A. Calculate Kd from the curve's trough; a lower Kd signifies weaker oxygen affinity.
• B. Calculate Kd from the curve's midpoint; a lower Kd signifies stronger oxygen affinity.
• C. Calculate Kd from the curve's peak; a lower Kd signifies stronger oxygen affinity.
• D. Calculate Kd from the curve's endpoint; a lower Kd signifies weaker oxygen affinity.

Answer: (B)