Question

Respiratory physiology of a newborn is different from that of an adult by all of the following EXCEPT

• A. Increased oxygen demand of the newborn
• B. Decreased FRC in the newborn
• C. Adult Hb has decreased affinity for oxygen
• D. Total lung volume is small/decreased in the newborn

Hint:

Three options are true differences; FRC per kg body weight is actually similar in newborns and adults.

Answer 1

The Correct Option is B

Step 1: Read the question type.
This is an EXCEPT question, so three options are real differences between newborn and adult respiratory physiology, and one option is actually a similarity, not a difference. We need to find that one similarity.

Step 2: Check oxygen demand.
A newborn's resting oxygen consumption is about 6 to 8 mL/kg/min, roughly twice the adult value of 3 to 4 mL/kg/min. This is a true and well known difference, driven by the newborn's higher metabolic rate per kilogram.

Step 3: Check functional residual capacity (FRC).
On a per kilogram basis, a newborn's FRC (about 25-30 mL/kg) is close to the adult value. What actually differs is the ratio of FRC to oxygen consumption: because oxygen demand per kilogram is so much higher in the newborn while the oxygen reserve stored in the lungs (FRC) stays about the same per kilogram, a newborn desaturates far faster during any pause in breathing. The FRC itself is not meaningfully decreased, it is the FRC-to-demand ratio that is unfavourable.

Step 4: Check haemoglobin oxygen affinity.
A newborn's blood is still rich in fetal haemoglobin (HbF), which binds oxygen more tightly than adult haemoglobin (HbA) because HbF binds 2,3-DPG poorly. Adult Hb, in comparison, does have a lower (decreased) affinity for oxygen, which shifts its dissociation curve to the right of the fetal curve. This is a genuine, true difference.

Step 5: Check total lung volume.
A newborn's lungs are anatomically much smaller than an adult's, simply because the newborn's whole body is smaller, with fewer and smaller alveoli. This too is a genuine difference.

Step 6: Pick the option that is NOT a true difference.
Out of the four, oxygen demand, haemoglobin affinity, and total lung volume are all genuinely different between a newborn and an adult. FRC, once corrected for body weight, is actually similar in the two groups, so calling it simply "decreased" is not accurate.

Final Answer:
\[ \boxed{\text{Decreased FRC in the newborn}} \]
Note: the source paper for this question did not print a marked answer key for this item. The answer above was worked out from first principles of neonatal respiratory physiology, since a newborn's FRC per kilogram body weight is close to the adult value, while oxygen demand, haemoglobin affinity, and total lung volume are all genuinely different.