Ch 10 PFT

Question 1

What is the purpose of pulmonary function testing?

Answer 1

To assess lung function and diagnose/manage pulmonary or cardiac diseases.

These tests can also evaluate surgical fitness and assess disability.

Question 2

Define forced expiratory volume (FEV).

Answer 2

The volume of air that can be forcibly exhaled in one second.

FEV is often measured in conjunction with forced vital capacity (FVC).

Question 3

What does a flow-volume curve illustrate?

Answer 3

The relationship between airflow rate and lung volume during forced expiration.

It helps identify restrictive and obstructive lung diseases.

Question 4

In restrictive diseases, how is the forced vital capacity (FVC) typically affected?

Answer 4

FVC is reduced at its top or bottom end.

This is due to limited inspiration from decreased lung compliance.

Question 5

What is the significance of dynamic airway compression?

Answer 5

It affects flow rate during forced expiration, independent of downstream airway resistance.

This phenomenon is crucial in understanding FEV1.0.

Question 6

What measurement technique is used to determine functional residual capacity (FRC)?

Answer 6

Helium dilution and body plethysmography.

FRC can also be calculated using nitrogen washout methods.

Question 7

What is the main challenge in measuring the diffusing capacity for oxygen?

Answer 7

It is difficult to measure accurately and is generally reserved for research.

The diffusing capacity for carbon monoxide is more commonly measured.

Question 8

How can regional differences in ventilation and perfusion be assessed?

Answer 8

Using radioactive xenon.

This method allows for visualization of blood flow and ventilation in various lung regions.

Question 9

What does the inequality of ventilation refer to?

Answer 9

The uneven distribution of air in the lungs during breathing.

This can be evaluated using single-breath and multiple-breath methods.

Question 10

What is the alveolar-arterial Po2 difference?

Answer 10

The difference in oxygen partial pressure between alveolar gas and arterial blood.

It indicates ventilation-perfusion inequality in the lungs.

Question 11

True or False: Pulmonary function tests are the most definitive diagnostic tools for lung diseases.

Answer 11

False.

These tests are valuable, but various patterns of impaired function can overlap different diseases.

Question 12

Fill in the blank: The measurement of total pulmonary blood flow can be assessed using the _______ principle.

Answer 12

Fick

This principle is commonly used in clinical settings.

Question 13

What characterizes the flow rate in obstructive diseases?

Answer 13

It is very low in relation to lung volume, often with a scooped-out appearance on flow-volume curves.

This occurs due to increased airway resistance.

Question 14

What role does exercise play in pulmonary function testing?

Answer 14

It influences the control of ventilation and the assessment of lung function.

Understanding changes during exercise can provide insights into lung health.

Question 15

What is the effect of increased smooth muscle tone in the bronchi?

Answer 15

It can lead to early airway closure during expiration.

This is commonly seen in conditions like asthma.

Question 16

What is a physiological shunt?

Answer 16

The portion of blood that bypasses ventilation, contributing to hypoxemia.

It is calculated based on deviations from ideal gas exchange.

Question 17

What is the primary focus for medical students regarding pulmonary function tests?

Answer 17

Understanding the principles of respiratory physiology.

This foundational knowledge is more important than memorizing test details.

Question 18

What does physiologic shunt refer to?

Answer 18

Physiologic shunt (venous admixture) is the leftward movement of the arterial point away from the ideal point due to the addition of mixed venous blood to ideal blood.

Question 19

What is the formula for calculating physiologic shunt?

Answer 19

Q· PS = CiO2 - CaO2

Where Q· PS / Q· T refers to the ratio of the physiologic shunt to total flow.

Question 20

What is alveolar dead space?

Answer 20

Alveolar dead space is the movement of the alveolar point away from the ideal point caused by the addition of inspired gas to ideal gas.

Question 21

What is the Bohr equation for dead space?

Answer 21

VD alv = (PiCO2 - PACO2) / (VT * PiCO2)

Where A refers to expired alveolar gas.

Question 22

What is the normal value for physiologic dead space?

Answer 22

About 30% of the tidal volume at rest.

Question 23

How can blood gases (Po2, Pco2, and pH) be measured?

Answer 23

Blood gases can be measured using blood gas electrodes, including a glass electrode for pH, a Pco2 electrode, and an O2 polarograph.

Question 24

What are the four causes of low arterial Po2 (hypoxemia)?

Answer 24

• Hypoventilation
• Diffusion impairment
• Shunt
• Ventilation-perfusion inequality

Question 25

True or False: Hypoventilation is always associated with a raised arterial Pco2.

Answer 25

True

Question 26

What causes increased arterial Pco2?

Answer 26

* Hypoventilation * Ventilation-perfusion inequality

Question 27

What is lung compliance?

Answer 27

Compliance is defined as the volume change per unit of pressure change across the lung.

Question 28

How is lung compliance measured?

Answer 28

By measuring the volume difference divided by the pressure difference at no-flow points during breathing.

Question 29

What is airway resistance?

Answer 29

Airway resistance is the pressure difference between the alveoli and the mouth per unit of airflow.

Question 30

How can airway resistance be measured?

Answer 30

Using a body plethysmograph or during normal breathing from an intrapleural pressure record.

Question 31

What does closing volume indicate?

Answer 31

Closing volume indicates the volume of the lung at which dependent airways begin to close.

Question 32

What is the typical closing volume in young normal subjects?

Answer 32

About 10% of the vital capacity (VC).

Question 33

How does exercise affect pulmonary function tests?

Answer 33

Exercise can reveal pulmonary function abnormalities that may be normal at rest.

Question 34

What is the most useful and simplest test in the clinical setting for lung function?

Answer 34

Forced expiration with indices such as FEV1.0 and FVC.

Question 35

What is the significance of arterial blood gas measurement?

Answer 35

It is essential for managing patients with acute or chronic respiratory failure.

Question 36

What additional tests can be performed in a well-equipped pulmonary function laboratory?

Answer 36

* Lung volumes * Inequality of ventilation * Alveolar-arterial Po2 difference * Physiologic dead space and shunt * Diffusing capacity for carbon monoxide * Airway resistance * Lung compliance * Ventilatory response to CO2 and hypoxia * Patient's response to exercise

Question 37

What can a well-equipped pulmonary function laboratory measure?

Answer 37

* Lung volumes * Inequality of ventilation * Alveolar-arterial Po2 difference * Physiologic dead space and shunt * Diffusing capacity for carbon monoxide * Airway resistance * Lung compliance * Ventilatory response to CO2 and hypoxia * Patient’s response to exercise ## Footnote Specialized measurements such as the topographical distribution of ventilation and blood flow may also be available in large laboratories.

Question 38

What is a simple and informative test for lung function?

Answer 38

The measurement of a single forced expiration

Question 39

How can arterial blood gases be measured?

Answer 39

With blood-gas electrodes

Question 40

What can the alveolar-arterial Po2 difference help assess?

Answer 40

The degree of ventilation-perfusion inequality in a diseased lung

Question 41

What equipment can measure lung volumes and airway resistance easily?

Answer 41

Body plethysmograph

Question 42

What is the value of exercise testing in pulmonary function assessment?

Answer 42

Identifying the cause of the patient’s exercise limitation

Question 43

True or False: The 1-s forced expiratory volume (FEV1) is unaffected by dynamic compression of the airways.

Answer 43

False

Question 44

Which condition can reduce the FEV1 in a patient with chronic obstructive pulmonary disease?

Answer 44

* Loss of radial traction on the airways * Increased elastic recoil of the lung ## Footnote Other options like hypertrophy of the diaphragm and administration of a bronchodilator drug may not reduce FEV1.

Question 45

What characterizes the slope of the alveolar plateau in chronic bronchitis?

Answer 45

It is reduced compared to normal

Question 46

Fill in the blank: The last exhaled gas in the single-breath nitrogen test comes from the _______.

Answer 46

base of the lung

Question 47

What does V· A / Q· inequality do to the alveolar-arterial Po2 difference?

Answer 47

Reduces it

Question 48

What happens to the Pco2 of expired gas when a subject exhales to residual volume (RV)?

Answer 48

Falls just before the end of expiration

Question 49

Fill in the blank: If the mouthpiece is closed at residual volume (RV) and the subject relaxes, the pressure in the airways is _______.

Answer 49

greater than atmospheric pressure

Question 50

True or False: All small airways in the lung are closed at residual volume (RV).

Answer 50

False

Question 51

What could explain a significantly lower FEV1.0 in a 66-year-old woman with worsening dyspnea?

Answer 51

* Decreased lung elastic recoil * Fibrotic changes in the interstitial space ## Footnote Other factors like decreased number of pulmonary capillaries and thickening of the blood-gas barrier may also contribute.

Question 52

What conclusion can be drawn from a multiple-breath nitrogen washout test showing two distinct phases?

Answer 52

The patient has nonuniform ventilation

Question 53

What mechanism is likely responsible for hypoxemia in a patient with severe hypoxemic respiratory failure treated with mechanical ventilation?

Answer 53

Ventilation-perfusion inequality