Ch 10 PFT Flashcards
What is the purpose of pulmonary function testing?
To assess lung function and diagnose/manage pulmonary or cardiac diseases.
These tests can also evaluate surgical fitness and assess disability.
Define forced expiratory volume (FEV).
The volume of air that can be forcibly exhaled in one second.
FEV is often measured in conjunction with forced vital capacity (FVC).
What does a flow-volume curve illustrate?
The relationship between airflow rate and lung volume during forced expiration.
It helps identify restrictive and obstructive lung diseases.
In restrictive diseases, how is the forced vital capacity (FVC) typically affected?
FVC is reduced at its top or bottom end.
This is due to limited inspiration from decreased lung compliance.
What is the significance of dynamic airway compression?
It affects flow rate during forced expiration, independent of downstream airway resistance.
This phenomenon is crucial in understanding FEV1.0.
What measurement technique is used to determine functional residual capacity (FRC)?
Helium dilution and body plethysmography.
FRC can also be calculated using nitrogen washout methods.
What is the main challenge in measuring the diffusing capacity for oxygen?
It is difficult to measure accurately and is generally reserved for research.
The diffusing capacity for carbon monoxide is more commonly measured.
How can regional differences in ventilation and perfusion be assessed?
Using radioactive xenon.
This method allows for visualization of blood flow and ventilation in various lung regions.
What does the inequality of ventilation refer to?
The uneven distribution of air in the lungs during breathing.
This can be evaluated using single-breath and multiple-breath methods.
What is the alveolar-arterial Po2 difference?
The difference in oxygen partial pressure between alveolar gas and arterial blood.
It indicates ventilation-perfusion inequality in the lungs.
True or False: Pulmonary function tests are the most definitive diagnostic tools for lung diseases.
False.
These tests are valuable, but various patterns of impaired function can overlap different diseases.
Fill in the blank: The measurement of total pulmonary blood flow can be assessed using the _______ principle.
Fick
This principle is commonly used in clinical settings.
What characterizes the flow rate in obstructive diseases?
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.
What role does exercise play in pulmonary function testing?
It influences the control of ventilation and the assessment of lung function.
Understanding changes during exercise can provide insights into lung health.
What is the effect of increased smooth muscle tone in the bronchi?
It can lead to early airway closure during expiration.
This is commonly seen in conditions like asthma.
What is a physiological shunt?
The portion of blood that bypasses ventilation, contributing to hypoxemia.
It is calculated based on deviations from ideal gas exchange.
What is the primary focus for medical students regarding pulmonary function tests?
Understanding the principles of respiratory physiology.
This foundational knowledge is more important than memorizing test details.
What does physiologic shunt refer to?
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.
What is the formula for calculating physiologic shunt?
Q· PS = CiO2 - CaO2
Where Q· PS / Q· T refers to the ratio of the physiologic shunt to total flow.
What is alveolar dead space?
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.
What is the Bohr equation for dead space?
VD alv = (PiCO2 - PACO2) / (VT * PiCO2)
Where A refers to expired alveolar gas.
What is the normal value for physiologic dead space?
About 30% of the tidal volume at rest.
How can blood gases (Po2, Pco2, and pH) be measured?
Blood gases can be measured using blood gas electrodes, including a glass electrode for pH, a Pco2 electrode, and an O2 polarograph.
What are the four causes of low arterial Po2 (hypoxemia)?
- Hypoventilation
- Diffusion impairment
- Shunt
- Ventilation-perfusion inequality
True or False: Hypoventilation is always associated with a raised arterial Pco2.
True
What causes increased arterial Pco2?
- Hypoventilation
- Ventilation-perfusion inequality
What is lung compliance?
Compliance is defined as the volume change per unit of pressure change across the lung.
How is lung compliance measured?
By measuring the volume difference divided by the pressure difference at no-flow points during breathing.
What is airway resistance?
Airway resistance is the pressure difference between the alveoli and the mouth per unit of airflow.
How can airway resistance be measured?
Using a body plethysmograph or during normal breathing from an intrapleural pressure record.
What does closing volume indicate?
Closing volume indicates the volume of the lung at which dependent airways begin to close.
What is the typical closing volume in young normal subjects?
About 10% of the vital capacity (VC).
How does exercise affect pulmonary function tests?
Exercise can reveal pulmonary function abnormalities that may be normal at rest.
What is the most useful and simplest test in the clinical setting for lung function?
Forced expiration with indices such as FEV1.0 and FVC.
What is the significance of arterial blood gas measurement?
It is essential for managing patients with acute or chronic respiratory failure.
What additional tests can be performed in a well-equipped pulmonary function laboratory?
- 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
What can a well-equipped pulmonary function laboratory measure?
- 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
Specialized measurements such as the topographical distribution of ventilation and blood flow may also be available in large laboratories.
What is a simple and informative test for lung function?
The measurement of a single forced expiration
How can arterial blood gases be measured?
With blood-gas electrodes
What can the alveolar-arterial Po2 difference help assess?
The degree of ventilation-perfusion inequality in a diseased lung
What equipment can measure lung volumes and airway resistance easily?
Body plethysmograph
What is the value of exercise testing in pulmonary function assessment?
Identifying the cause of the patient’s exercise limitation
True or False: The 1-s forced expiratory volume (FEV1) is unaffected by dynamic compression of the airways.
False
Which condition can reduce the FEV1 in a patient with chronic obstructive pulmonary disease?
- Loss of radial traction on the airways
- Increased elastic recoil of the lung
Other options like hypertrophy of the diaphragm and administration of a bronchodilator drug may not reduce FEV1.
What characterizes the slope of the alveolar plateau in chronic bronchitis?
It is reduced compared to normal
Fill in the blank: The last exhaled gas in the single-breath nitrogen test comes from the _______.
base of the lung
What does V· A / Q· inequality do to the alveolar-arterial Po2 difference?
Reduces it
What happens to the Pco2 of expired gas when a subject exhales to residual volume (RV)?
Falls just before the end of expiration
Fill in the blank: If the mouthpiece is closed at residual volume (RV) and the subject relaxes, the pressure in the airways is _______.
greater than atmospheric pressure
True or False: All small airways in the lung are closed at residual volume (RV).
False
What could explain a significantly lower FEV1.0 in a 66-year-old woman with worsening dyspnea?
- Decreased lung elastic recoil
- Fibrotic changes in the interstitial space
Other factors like decreased number of pulmonary capillaries and thickening of the blood-gas barrier may also contribute.
What conclusion can be drawn from a multiple-breath nitrogen washout test showing two distinct phases?
The patient has nonuniform ventilation
What mechanism is likely responsible for hypoxemia in a patient with severe hypoxemic respiratory failure treated with mechanical ventilation?
Ventilation-perfusion inequality
