4. Lung function and measurements _ static and dynamic volumes

Question 1

What are pulmonary function tests (PFTs)?

Answer 1

They are tests that assess lung volumes, flow rates, and diffusion capacity :
- spirometry
- body plethysmography
- single breath diffusion capacity

Question 2

What is the difference between dynamic and static lung volumes?

Answer 2

Dynamic lung volumes are related to the rate at which air flows in/out of the lungs, while static lung volumes are not affected by the rate of airflow into/out of the lungs.

Question 3

What is residual volume (RV)?

Answer 3

Residual volume is the air remaining in the lungs after complete exhalation, which is 1200mL / 1000mL

Question 4

What is the functional residual capacity (FRC)?

Answer 4

Functional residual capacity is the volume after normal expiration, which is RV + ERV, or 2400mL /1800mL

Question 5

What is the total lung capacity (TLC)?

Answer 5

Total lung capacity is all of the air in the lungs, which is VC + RV, or 6000mL / 4200mL

Question 6

What is the definition of Vital Capacity (VC)?

Answer 6

The entire volume of air that can be maximally inhaled and exhaled, which is 4800mL / 3200mL

Question 7

What is the definition of Forced Vital Capacity (FVC)?

Answer 7

The maximum volume of air that can be exhaled after maximum inspiration, which is greater than 80% of total capacity.

Question 8

What is the definition of Forced Expiratory Volume (FEV)?

Answer 8

The volume of air exhaled during a forced breath.

Question 9

What is the definition of Peak Expiratory Flow (PEF)?

Answer 9

The maximal airflow rate during forced exhalation.

Question 10

What is the definition of Forced Expiratory Flow (FEF)?

Answer 10

The rate of airflow during the middle portion of the forced vital capacity maneuver.

Question 11

What is the difference between obstructive and restrictive lung diseases?

Answer 11

Obstructive lung diseases are caused by increased airway resistance due to narrowing of airways, while restrictive lung diseases are caused by impaired ability of lungs to expand due to decreased compliance and decreased diffusion capacity.

Question 12

What is spirometry?

Answer 12

It is the best initial test for evaluation of pulmonary function.

Question 13

What are flow-volume loops?

Answer 13

They are graphical representations of spirometry findings that demonstrate inspiratory + expiratory airflow (y-axis) against lung volume (x-axis).

Question 14

What is body plethysmography?

Answer 14

It is the gold standard test for measuring lung volumes and, unlike spirometry, it can also measure TLC and RV.

Question 15

What are the indications for body plethysmography?

Answer 15

• Patients who cannot actively participate in spirometry
• obstructive lung disease on spirometry → evaluate for air trapping (e.g. in emphysema)
• restrictive lung disease → distinguish between extrinsic VS intrinsic causes.

Question 16

What is the procedure for measuring lung volumes in body plethysmography?

Answer 16

Lung volumes are measured in a sealed chamber, and the air pressure in the cabin is inversely proportional to the air pressure in the lungs.

Question 17

What are the parameters measured in body plethysmography?

Answer 17

• Includes spirometry parameters, plus:
• airway resistance (Raw) → resistance to airflow from mouth to alveoli during inspiration/exhalation,
• residual volume (RV) → volume of air remaining in the lungs after maximal expiration.

Question 18

What parameters are included in lung function tests besides spirometry?

Answer 18

• Airway resistance (Raw),
• residual volume (RV),
• total lung capacity (TLC),
• thoracic gas volume (TGV),
• lung compliance.

Question 19

What is the purpose of a single-breath diffusion capacity test?

Answer 19

To measure the ability of the alveoli to transfer gases to the pulmonary capillaries.

Question 20

What are the indications for a single-breath diffusion capacity test?

Answer 20

To differentiate between intrapulmonary and extrapulmonary causes of restrictive lung disease, and to investigate unexplained hypoxemia after spirometry.

Question 21

What is the procedure for a single-breath diffusion capacity test?

Answer 21

The patient inhales an inert gas and a low concentration of carbon monoxide (CO), holds their breath for about 10 seconds, and then exhales while the concentration of CO in the breath is measured.

Question 22

What parameters are measured in a single-breath diffusion capacity test?

Answer 22

Carbon monoxide transfer coefficient (KCO) and diffusion capacity of the lung for CO (DLCO).