Errors in First Aid for the USMLE (2007): Pulmonary System

February 13, 2007

As always, this comes from an email sent to the First Aid Team.


  1. P.428, Oxygen-hemoglobin dissociation curve
    1. High altitude decreases P02 and decreases Hb saturation. This results in a decrease (or down-shift) in the dissociation curve, not a right shift as described.
  2. P.428, Pulmonary circulation
    1. While exercise does decrease the perfusion limitation, it never reaches the point of diffusion limitation i.e., the SaO2 on an athlete will almost never be lower than it is at rest.
  3. P.431, Obstructive lung disease (COPD)
    1. “[up arrow] FVC” is incorrect. RV increases, FVC is decreased or normal, FEV is decreased, TLC is increased.
    2. Emphysema and Asthma are both listed as having decreased I/E ratios. I assume this means Inspiration/Expiration ratio. This seems impossible as a ratio other than 1 would lead to progressive deflation and collapse of the lungs or the opposite expansion. What this should instead indicate is that in both cases, the breathing is shallow. In any steady state of respiration (including shallow breathing), I/E = 1 and the tidal volume (Vt) is lowered.
  4. P.431, Restrictive lung disease
    1. “([down arrow] VC and TLC)” should say “([down arrow] FVC and TLC)”
  5. P.431, Neonatal respiratory distress syndrome
    1. The opening description describes “lecithin” as the important surfactant. The surfactant is then described as “dipalmitoyl phosphatidylcholine .” I think everyone might benefit if this was changed to:
      1. Surfactant–dipalmitoyl phosphatidylcholine (DPPC, lecithin)
  6. P.432, Obstructive vs restrictive lung disease
    1. The FEV1/FVC ratios are listed for Normal and Obstructive, but not Restrictive even though “>80%” was listed on the previous page. For consistency, I think it should be included here.
    2. The curve for “Normal” is not drawn correctly, listing a ratio of 80% but showing a ratio of 60%.

Return to First Aid Errors page.