Question

If alveolar ventilation is \[4200mL.{\min ^{ - 1}}\] , respiratory frequency is $12$ breaths per minute, and tidal volume is$500$ , What is the anatomical-dead space ventilation?
$A)$ \[1800mL.{\min ^{ - 1}}\]
$B)$ \[6000mL.{\min ^{ - 1}}\]
$C)$ \[350mL.{\min ^{ - 1}}\]
$D)$ \[1200mL.{\min ^{ - 1}}\]

Answer 1

Hint: The amount of air found in the respiratory tract segments responsible for conducting air to the alveoli and respiratory bronchioles but do not participate in the gas exchange process itself is referred to as anatomic dead space.

Complete answer:
The total volume of gas entering (or exiting) the lung per minute is known as minute ventilation $\left( {VE} \right)$ . It is obtained by multiplying the tidal volume $\left( {TV} \right)$ and the respiratory rate (also known as respiratory frequency) $\left( f \right)$ . The quantity of air that flows in and out of the lungs during each respiratory cycle is referred to as tidal volume. The number of breaths inhaled per minute is referred to as the respiration rate.

From the question, we know that $TV = $ Tidal Volume $ = 500mL$ per breath and $f = $ respiratory frequency $ = 12$ breaths per minute
$
  \Rightarrow VE = TV \times f \\
  \Rightarrow 500 \times 12 \\
  \Rightarrow 6000mL.{\min ^{ - 1}} \\
 $

Total minute ventilation $\left( {VE} \right)$ is made up of anatomical-dead space ventilation and alveolar ventilation $\left( {AV} \right)$. The quantity of air entering and exiting the alveoli per minute is known as alveolar ventilation. Therefore, we can find the volume of anatomical-dead space ventilation by subtracting alveolar ventilation from total minute ventilation.

Anatomical-dead space ventilation
 $
  \Rightarrow VE - AV \\
  \Rightarrow 6000 - 4200 \\
  \Rightarrow 1800mL.{\min ^{ - 1}} \\
 $


Therefore, the correct option is $A)$ \[1800mL.{\min ^{ - 1}}\]

Note: Minute ventilation is usually between $5$ and $8$ litres a minute $(Lpm)$ . For example, tidal volumes of $500$ to $600$ mL at $12 - 14$ breaths per minute result in minute ventilations of $6.0$ to $8.4L$ . With moderate exercise, minute ventilation can double, and with hard exercise, it can reach $40Lpm$ .