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: Separate real differences from a look alike difference.
Three of the four choices describe things that are truly different in a newborn compared with an adult. The fourth choice sounds like a difference but is not, once you correct for the newborn's small size.

Step 2: Oxygen demand.
Because a newborn's tissues are metabolically busier per kilogram of body weight than an adult's, its oxygen use rate per kilogram is nearly double that of an adult. This is a real, true difference.

Step 3: Haemoglobin type.
A newborn still carries mostly fetal haemoglobin, which grabs oxygen more tightly than the adult type. So compared with fetal Hb, adult Hb genuinely does have a lower pull on oxygen. This too is a real difference.

Step 4: Lung size.
A newborn's lungs, alveoli, and airways are all smaller in absolute size than an adult's, simply because the whole newborn body is smaller. Total lung volume is genuinely smaller.

Step 5: FRC, the odd one out.
FRC looks reduced in the newborn only if you compare raw numbers without adjusting for size. Once FRC is expressed per kilogram of body weight, it comes out close to the adult figure. What makes newborns vulnerable is not a truly reduced FRC, but that their oxygen use per kilogram is so high relative to that near normal FRC, so their oxygen reserve runs out fast.

Step 6: Conclude.
The option that is not a genuine difference is the FRC one.
\[ \boxed{\text{Decreased FRC in the newborn}} \]