Question

A 23-year old female has generalized skeletal muscles weakness but is otherwise normal. Which of the following lung volume or lung capacity most likely would be normal?

a. Inspiratory reserve volume

b. Functional residual capacity

c. Residual volume

d. Total lung capacity

e. Vital capacity

Defend your answer by describing why each of the other answers are not correct

Answer 1

Answer

C) Residual volume because it is the volume of air still remaining in lungs after expiratory reserve volume is exhaled. expiratory reserve volume is additional air that can be forcibly exhaled after the expiration of a nomal tidal volume which is 500ml and the amount of air inhaled in relaxed normal breathing. Therefore in Residual volume(RV) no function of muscles are necessary. hence it will be normal compared to a healthy person.

see image below:-

CW L RS TLC Healthy Muscular dystrophy CW LRS :Pimax . FRC RV Pressure Pressure

Comaprision of size of Chest wall(CW) Lung(L) Respiratory System(RS) Total Lung Capacity(TLC) Functional Residual Capacity(FRC) and Residual Volume(RV) of a healthy person and a peson with muscular dystrophy.

RV of a healthy person and of a person with muscular dystrophy remains the same

Inspiratory reserve volume is the amount of air that can be forcibly inhaled after inspiration of a normal tidal volume. therefore for forcibly inhalation there is a requirement of healthy diaphragm and other respiratory muscles. hence option A is wrong.

Functional residual capacity---as shown in above graph its value is affected when muscles are weak.

Total lung capacity--It is also affected because of need of well functioning healthy and conditioned respiratory muscles.also referred in Graph.

Vital Capacity is the total amount of air that can be expired after fully inhaling(VC=TV+IRV+ERV approx 80% of TLC) so it will be affected if any of IRV,ERV,TLC is affected.

C is the correct answer