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CTB Block 2 > B2 W2 - Basic Lung Function Testing > Flashcards

B2 W2 - Basic Lung Function Testing Flashcards

1
Q

What is the basic definition of lung function tests?

A

Lung function tests are investigations into a patient’s breathing to help diagnose and understand their lung condition.

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2
Q

What are the three main questions lung function tests aim to answer?

A

They aim to determine:

  • if the airways are narrowed
  • if the lungs are a normal size
  • if gas uptake is normal
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3
Q

Do lung function tests directly identify a specific lung condition?

A
  • No
  • Lung function tests generate patterns that are common to a number of conditions, but they don’t pinpoint a specific diagnosis.

* Clinical history and examination are needed alongside the test results

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4
Q

What is a primary reason for performing lung function tests?

A

Important for detecting the presence of lung disease and are a key part of diagnosis.

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5
Q

Besides diagnosis, how can lung function tests help assess the severity of a patient’s condition?

A

By evaluating the degree of lung impairment

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6
Q

How are lung function tests used in the assessment of asthma?

A
  • To assess the extent of airway reversibility in asthma

* Particularly those involving bronchodilators

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7
Q

What role do lung function tests play in long-term patient management?

A

They are useful for monitoring patients over time, tracking the progression of their condition and their response to therapy.

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8
Q

How are lung function tests utilised in pre-operative settings?

A

To determine a patient’s suitability for general anaesthesia and the level of support they might need during and after a procedure.

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9
Q

What is the definition of peak expiratory flow rate (PEFR)?

A

Themaximum flow rate generated during a forceful exhalation starting from full lung inhalation.

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10
Q

How is airflow related to airway resistance?

A
  • Airflow through the airways is determined by airway resistance
  • Factors like bronchoconstriction and mucus secretion increase resistance and reduce airflow.
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11
Q

Why is peak expiratory flow rate particularly useful in managing asthma?

A

PEFR is a valuable tool for assessing and monitoring asthma due to its sensitivity to changes in airway resistance, a key feature of asthma.

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12
Q

How is peak flow measured?

A
  • A peak flow meter is used
  • The patient takes a deep breath in and forcefully exhales into the meter, with the highest of three readings recorded.
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13
Q

What factors are considered when comparing a patient’s peak flow readings to predicted values?

A
  • Age
  • Sex
  • Height.
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14
Q

Why is proper training and consistent use of the same peak flow meter important?

A
  • It’s the trend in your peak flow readings that’s most important, not just a single reading.
  • There is significant variability in peak flow testing, so consistent technique and equipment are crucial for accurate and reliable monitoring.
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15
Q

What is diurnal variation in peak flow, and what causes it?

A
  • Diurnal variation refers to the pattern of lower peak flow readings in the morning compared to the afternoon.
  • It is caused by lower cortisol levels at night, which worsens lung inflammation and increases airway resistance.
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16
Q

What is spirometry?

A

Spirometry is an objective test that measures lung function by having a patient breathe into a mouthpiece connected to a machine that records and analyses their breathing patterns.

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17
Q

What are the different types of spirometers?

A

Spirometers range in complexity from portable devices used in GP practices to advanced machines found in hospital settings, offering varying levels of detail in the results.

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18
Q

What types of lung volumes can spirometry measure?

A

Spirometry measures both:

  • Dynamic lung volumes, which depend on airflow speed

and some

  • Static lung volumes, which are independent of airflow.
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19
Q

What are the two key dynamic lung volumes measured by spirometry?

A
  • Forced vital capacity (FVC)
  • Forced expiratory volume in one second (FEV1).
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20
Q

Describe the procedure for measuring FVC during spirometry.

A
  • The patient sits down, wears a nose clip, and takes the deepest breath they can.
  • They then exhale as forcefully and completely as possible into the spirometer mouthpiece
  • The total volume of air expelled is recorded as the FVC.
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21
Q

What does FEV1 represent?

A

FEV1 is the volume of air exhaled within the first second of the forced expiration, calculated from the FVC measurement.

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22
Q

Why are FVC and FEV1 considered dynamic lung volumes?

A

They depend on the speed of airflow, indicating how quickly the air is exhaled.

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23
Q

What does the FEV1/FVC ratio tell us about lung function?

A
  • This ratio reflects the proportion of the FVC exhaled in the first second.
  • It’s a key indicator of airway limitation.
  • In healthy lungs, this ratio is typically around 80%.
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24
Q

How is the spirometry procedure performed to ensure accurate results?

A
  • Repeated at least three times to ensure consistent measurements.
  • The best values are then compared to predicted values based on the patient’s age, sex, and height.
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25
Q

In what formats are spirometry results typically presented?

A
  • Usually provided numerically and graphically - allowing for a comprehensive understanding of the patient’s lung function.
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26
Q

What information does a volume-time graph display in spirometry?

A

The volume-time graph in spirometry plots the volume of air exhaled against time, clearly showing the FVC, FEV1, and peak flow, which is represented by the steepest part of the curve.

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27
Q

What is a flow-volume loop?

A
  • A flow-volume loop is a graphical representation of airflow through the airways plotted against the volume of air in the lungs.
  • It shows both the expiration and inspiration phases.
  • Expiration is often displayed as a triangular shape above the x-axis
  • Inspiration is shown as a semi-circular curve below.
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28
Q

Explain total lung capacity (TLC) in the context of a flow-volume loop.

A

On a flow-volume loop, TLC marks the total volume of air within the lungs at the very beginning of the exhalation, when the lungs are at their fullest.

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29
Q

What is residual volume (RV) in relation to a flow-volume loop?

A

RV, shown on the flow-volume loop, represents the volume of air that remains in the lungs after a complete and full exhalation.

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30
Q

Are TLC and RV precisely measured from a flow-volume loop?

A
  • No
  • A flow-volume loop only provides estimates of TLC and RV.
  • The only directly measurable value on the loop is the FVC, which is the difference between TLC and RV.
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31
Q

How are the effort-dependent and effort-independent phases of the expiratory curve distinguished on a flow-volume loop?

A
  • The expiratory curve on the flow-volume loop has two distinct phases.
  • The initial, steeper part of the curve is effort-dependent, meaning a stronger effort from the respiratory muscles results in a faster airflow.
  • As lung volume decreases, the curve becomes effort-independent.
  • In this phase, airflow is primarily determined by the decreasing lung volume and the phenomenon of dynamic compression.
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32
Q

What is dynamic compression, and when does it occur during breathing?

A
  • Dynamic compression happens during a forced exhalation.
  • The increased pressure in the chest cavity (intrapleural pressure) compresses the smaller airways that lack cartilage, leading to increased resistance and reduced airflow.
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33
Q

How does a flow-volume loop depict tidal breathing compared to a forced expiration?

A

On a flow-volume loop, tidal breathing (normal breaths) appears as a much smaller loop since the lungs are not being completely filled or emptied, unlike during a forced expiration.

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34
Q

Define functional residual capacity (FRC).

A

FRC is the volume of air remaining in the lungs at the end of a normal, relaxed exhalation (tidal expiration).

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35
Q

What does a flow-volume loop reveal about peak expiratory flow rate (FEF max)?

A

The FEF max is easily identified on a flow-volume loop as the highest point reached on the expiratory curve.

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36
Q

Besides peak flow and FVC, what additional information can be gathered from the shape of a flow-volume loop?

A
  • Potential lung abnormalities.
  • Different patterns in the loop can suggest specific lung conditions, aiding in diagnosis.
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37
Q

Do changes observed solely in the inspiratory portion of a flow-volume loop always point towards problems in the lower airways?

A
  • No
  • Changes that are limited to the inspiratory part of the flow-volume loop are typically caused by issues in the upper airways rather than the lower airways.
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38
Q

What are the two common patterns of abnormalities that can be detected using spirometry?

A

Spirometry can reveal two primary patterns:

  • obstructive, indicating difficulty exhaling air

and

  • restrictive, signifying limited lung expansion.
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39
Q

What is an obstructive defect? How does it impact FEV1, FVC, and the FEV1/FVC ratio?

A
  • An obstructive defect refers to a limitation in airflow out of the lungs, often due to narrowed or blocked airways.
  • This leads to a reduced FEV1 because less air can be exhaled forcefully in the first second.
  • The FVC might be preserved or even increased due to air trapping in the lungs.
  • Consequently, the FEV1/FVC ratio decreases, usually below 70%, reflecting the difficulty in rapidly emptying the lungs.
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40
Q

Describe the typical appearance of a flow-volume loop in an obstructive defect.

A
  • The expiratory portion of the flow-volume loop exhibits a characteristic “scooped-out” appearance.
  • This concavity results from the reduced and prolonged expiratory airflow caused by the obstruction.
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41
Q

Provide examples of conditions commonly associated with an obstructive pattern on spirometry.

A

Common obstructive lung diseases include:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Bronchiectasis.
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42
Q

What is a restrictive defect, and how does it affect lung volumes and spirometry measurements?

A
  • A restrictive defect occurs when lung expansion is restricted, leading to reduced lung volumes.
  • This results in a decreased FVC, as the total amount of air that can be inhaled and exhaled is diminished.
  • However, the FEV1 might remain relatively normal because the airways themselves are not significantly obstructed.
  • As a result, the FEV1/FVC ratio is often normal or even increased.
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43
Q

How does a flow-volume loop typically appear in a restrictive defect?

A

The flow-volume loop in a restrictive defect appears narrower and smaller compared to a normal loop, reflecting the overall reduction in lung volumes.

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44
Q

Name some conditions that can cause a restrictive pattern on spirometry.

A

Restrictive patterns can be seen in conditions like:

  • Interstitial lung disease
  • Pulmonary fibrosis
  • Neuromuscular disorders that impair the respiratory muscles.
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45
Q

Can spirometry definitively diagnose a specific lung condition solely based on the observed pattern?

A
  • No
  • Spirometry is a tool that helps identify patterns of lung dysfunction, but it doesn’t offer a definitive diagnosis on its own.
46
Q

Why are spirometry results interpreted in the context of predicted values?

A
  • Predicted values for FEV1, FVC, and other spirometry parameters are calculated based on the patient’s age, sex, and height.
  • These predicted values serve as a reference point to compare the patient’s actual measurements and determine how much they deviate from what would be expected for someone of similar characteristics.
  • This helps assess the severity of lung dysfunction.
47
Q

Why is it essential to maintain good quality and reproducibility when performing spirometry?

A
  • Achieving accurate and reliable spirometry results is crucial for proper interpretation.
  • Factors like the patient’s effort, adequate coaching by the technician, and strict adherence to standardised procedures significantly influence the accuracy of the measurements.
48
Q

What is reversibility testing, and in what condition is it particularly useful?

A
  • Reversibility testing in spirometry involves measuring lung function before and after administering a bronchodilator, a medication that relaxes and widens the airways.
  • It is particularly useful in assessing asthma, as a significant improvement in FEV1 after the bronchodilator suggests reversible airflow obstruction, a hallmark of asthma.
49
Q

Explain the concept of dynamic compression in detail and its relevance to flow-volume loops.

A
  • Dynamic compression occurs during a forced exhalation.
  • As the patient forcefully exhales, the pressure within the chest cavity (intrapleural pressure) increases.
  • This increased pressure compresses the smaller airways, particularly those lacking cartilaginous support.
  • As a result, the resistance to airflow increases, and the flow rate decreases.
  • This phenomenon explains why the later part of the expiratory curve on a flow-volume loop becomes effort-independent.
50
Q

Describe the characteristic visual features of flow-volume loops in obstructive and restrictive patterns.

A
  • In an obstructive pattern, the flow-volume loop displays a “scooped-out” appearance in the expiratory curve, reflecting the reduced and prolonged airflow.
  • In a restrictive pattern, the loop appears narrower and smaller overall, indicating the reduced lung volumes.
51
Q

What are the two basic ways in which breathing can be impaired?

A
  • Narrowed airways, leading to obstructive disorders
  • Reduced lung expansion, resulting in restrictive disorders.
52
Q

What is the key characteristic of obstructive disorders?

A

Airway narrowing, which increases resistance to airflow.

53
Q

What are the two most common obstructive disorders?

A

Asthma & COPD

54
Q

What happens during forced exhalation in individuals with obstructive lung disease?

A

High intrathoracic pressures during forced exhalation cause premature closure of the airways, termed small airway obstruction.

55
Q

Name a condition in which stiffening of lung tissue leads to breathing impairment.

A
  • Pulmonary fibrosis

  • A restrictive disorder characterised by stiffening of lung tissue.
56
Q

How could a restrictive disorder be caused by a neuromuscluar disorder?

A

A neuromuscular disorder can cause weakness of the respiratory muscles, limiting lung expansion and leading to a restrictive disorder.

57
Q

Besides lung-specific conditions, what other factors can contribute to restrictive disorders?

A

Conditions that limit chest expansion, such as scoliosis or obesity, can also cause restrictive disorders.

58
Q

Is it possible for a patient to exhibit characteristics of both obstructive and restrictive lung diseases?

A
  • Yes
  • Mixed obstructive and restrictive patterns can occur, for example, in severe obstruction or when two diseases coexist.
59
Q

How does spirometry help in investigating lung disease?

A

Spirometry measures characteristic patterns of lung function that differentiate obstructive and restrictive disorders.

60
Q

In spirometry, what does the acronym FEV1 stand for?

A
  • FEV1 stands for Forced Expiratory Volume in 1 second.
  • It is the volume of air a person can forcibly exhale in the first second of a forced breath.
61
Q

In spirometry, what does FVC stand for?

A
  • FVC stands for Forced Vital Capacity.
  • It represents the total volume of air a person can forcibly exhale after taking a maximal inhalation.
62
Q

What is a key spirometry finding in obstructive disorders, and why does it occur?

A
  • A reduced FEV1/FVC ratio is characteristic of obstructive disorders.
  • This is because premature airway closure during forced expiration limits airflow and the volume exhaled in the first second.
63
Q

According to many guidelines, what FEV1/FVC ratio is used as the cut-off to indicate obstruction?

A

An FEV1/FVC ratio below 0.7 is often used to indicate obstruction.

64
Q

Why might using 0.7 as the FEV1/FVC cut-off be problematic in older adults?

A

Older adults may have an FEV1/FVC ratio below 0.7 without actual airway obstruction.

65
Q

Besides diagnosing obstruction, how else is the FEV1 value used in spirometry?

A

The FEV1 percentage predicted helps categorise the severity of airflow obstruction in COPD.

66
Q

What might cause underestimation of FVC in patients with severe obstruction?

A

Patients with severe obstruction may not be able to exhale for long enough to expel all the air from their lungs, leading to underestimation of FVC.

67
Q

What alternative measurement can be used when FVC may be underestimated?

A

Some spirometers can measure FEV6 (volume exhaled in 6 seconds) to address potential FVC underestimation in severe obstruction.

68
Q

How does the expiratory flow rate appear on a flow-volume loop in obstructive disorders?

A

The peak expiratory flow rate is reduced, and the effort-independent part of the curve displays a concave dip, which becomes more pronounced with increasing obstruction.

69
Q

What is the “steeple pattern” seen in flow-volume loops, and when does it occur?

A
  • The steeple pattern is a sudden, rapid decrease in flow rate during expiration
  • Occurs in severe airway obstruction due to premature airway collapse in conditions such as severe emphysema
70
Q

What is air trapping, and how does it relate to obstructive lung disease?

A
  • Air trapping is the retention of air in the lungs at the end of expiration due to the inability to exhale fully.
  • It worsens with increasing severity of obstructive disease.
71
Q

What is the purpose of bronchodilator reversibility testing?

A

It helps determine if airway narrowing is fixed or reversible with medication by comparing lung function before and after a bronchodilator.

72
Q

In what condition is bronchodilator reversibility testing particularly important?

A
  • Asthma
  • To assess if bronchodilators can improve lung function by relaxing airway smooth muscle.
73
Q

Why is the degree of reversibility after bronchodilator administration less useful in COPD assessment?

A

Some COPD patients may show FEV1 improvement after bronchodilators, even though their airway narrowing is largely irreversible.

74
Q

How is the FVC affected in restrictive disorders, and why?

A

The FVC is reduced in restrictive disorders because lung expansion is limited, resulting in less air being inhaled and exhaled.

75
Q

What happens to the FEV1 and FEV1/FVC ratio in restrictive disorders?

A
  • The FEV1 may be reduced, but proportionally to the FVC.
  • Consequently, the FEV1/FVC ratio is either normal or increased.
76
Q

Describe the appearance of the expiratory flow-volume curve in restrictive disorders.

A

The expiratory flow-volume curve is narrowed due to the reduced total volume exhaled.

77
Q

What happens to the peak expiratory flow rate in restrictive disorders?

A

Flow rates are usually maintained until late in the disease process, at which point the peak expiratory flow rate may decrease due to factors like respiratory muscle weakness rather than airway issues.

78
Q

Why is the effort-independent part of the expiratory flow-volume curve linear in restrictive disorders?

A

The linear shape indicates that the airways themselves are not the primary problem in restrictive disorders, unlike in obstructive disorders.

79
Q

Can spirometry definitively diagnose a restrictive disorder?

A
  • No
  • Spirometry only shows patterns.

Confirmation requires measurements of static lung volumes, typically done in secondary care.

80
Q

What is the difference between lung volumes and lung capacities?

A
  • Lung volumes are directly measurable amounts of air in the lungs.
  • Lung capacities are calculated values derived from two or more lung volumes.
81
Q

What is tidal volume (TV)?

A

Tidal volume is the amount of air inhaled or exhaled during a normal, quiet breath.

82
Q

What is Inspiratory Reserve Volume (IRV)?

A

Inspiratory reserve volume is the extra amount of air that can be inhaled from the end of a normal tidal inspiration to maximal inspiration.

83
Q

What is Expiratory Reserve Volume (ERV)?

A

Expiratory reserve volume is the extra volume that can be forcefully exhaled after the end of a normal tidal expiration.

84
Q

What is Residual Volume (RV)?

A

Residual volume is the amount of air that remains in the lungs even after a maximal exhalation.

85
Q

Define Vital Capacity (VC).

A
  • Vital capacity is the maximum amount of air that can be exhaled after a maximal inhalation (or vice-versa).
  • It is the sum of IRV, TV, and ERV.
86
Q

Define inspiratory capacity (IC).

A
  • Inspiratory capacity is the maximum volume of air that can be inhaled from the end of a normal tidal expiration.
  • It is the sum of IRV and TV.
87
Q

What is Functional Residual Capacity (FRC)?

A
  • Functional residual capacity is the volume of air remaining in the lungs at the end of a normal tidal expiration.
  • It represents the balance point between the inward elastic recoil of the lungs and the outward recoil of the chest wall.
88
Q

How is total lung capacity (TLC) calculated?

A
  • Total lung capacity is the total volume of air in the lungs at the end of a maximal inspiration.
  • It can be calculated by adding VC and RV.
89
Q

Which lung volume cannot be measured by spirometry?

A
  • Residual volume (RV) because it represents the air that cannot be forcefully exhaled.
90
Q

What alternative methods are used to measure lung volumes that cannot be measured by spirometry?

A
  • Helium dilution
  • Nitrogen washout
  • Body plethysmography
91
Q

What are the three main reasons why it is important for some air to remain in the lungs at the end of expiration (FRC)?

A

FRC:

  • Provides an oxygen reservoir for gas exchange between breaths
  • Helps keep alveoli open
  • Ensures the lungs are at their optimal compliance for easy expansion.
92
Q

At FRC, describe the state of the respiratory muscles and the balance of forces within the respiratory system.

A
  • At FRC, the respiratory muscles are at rest, and the alveolar pressure equals the atmospheric pressure.
  • The outward elastic recoil force of the chest wall is balanced by the inward elastic recoil force of the lungs.
93
Q

How does emphysema, an obstructive disease, affect FRC?

A
  • Emphysema, characterised by the destruction of lung elastic tissue, reduces the inward recoil of the lungs.
  • To maintain the balance of forces, FRC increases, leading to hyperinflation.
94
Q

How does pulmonary fibrosis, a restrictive disease, affect FRC?

A
  • Pulmonary fibrosis increases lung stiffness and inward elastic recoil
  • FRC is decreased as a result, as the balance of forces is shifted towards a lower lung volume.
95
Q

In obstructive lung diseases, what changes are observed in RV, TLC, and VC?

A
  • RV and potentially TLC are increased as a result of air trapping and hyperinflation caused by obstructive diseases
  • VC decreases because a larger proportion of TLC is occupied by the increased RV.
96
Q

What is the significance of the residual volume/total lung capacity (RV/TLC) ratio?

A
  • The RV/TLC ratio reflects the proportion of the total lung capacity that is occupied by residual volume.
  • In healthy lungs, this should be less than 40%.
  • It is often increased in obstructive lung diseases.
97
Q

How are TLC, VC, and RV typically affected in restrictive lung diseases?

A
  • Restrictive diseases limit lung expansion, decreasing TLC and VC.
  • RV is also reduced, but often to a lesser extent than TLC, so the RV/TLC ratio may be normal or increased.
98
Q

What does diffusing capacity measure?

A

It measures the lungs’ ability to transfer gas between inhaled air and capillary blood, and for that gas to combine with haemoglobin.

99
Q

What is the most common test used to measure diffusing capacity?

A

The single-breath test using carbon monoxide (CO).

100
Q

Briefly describe the process of the single-breath test for diffusing capacity.

A
  • The patient inhales a gas mixture containing a known concentration of carbon monoxide and helium, holds their breath for about 10 seconds, and then exhales.
  • The concentration of gases in the exhaled breath is measured.
101
Q

Why is carbon monoxide used in diffusing capacity tests?

A
  • Carbon monoxide has a very high affinity for haemoglobin and does not dissolve in plasma, making its transfer across the alveolar-capillary membrane diffusion-limited.
  • This means the amount of CO transferred is directly related to the efficiency of diffusion.
102
Q

Why is helium used in the single-breath test?

A

Helium does not cross the alveolar-capillary membrane and is therefore used to estimate the total lung capacity in a single breath.

103
Q

What is TLCO (or DLCO)?

A

TLCO (transfer factor of the lungs for carbon monoxide) or DLCO (diffusing capacity of the lungs for carbon monoxide) represents the total amount of carbon monoxide transferred across the alveolar-capillary membrane per unit time per unit driving pressure.

104
Q

What is KCO?

A
  • KCO is the transfer coefficient for carbon monoxide, representing the efficiency of CO transfer in the alveoli.
  • It is calculated as TLCO divided by alveolar volume.
105
Q

Why is KCO particularly useful in patients with reduced alveolar volume?

A

KCO corrects for the loss of alveolar volume, such as after a pneumonectomy, allowing assessment of diffusing capacity in the remaining functioning alveoli.

106
Q

Why is it important to know the patient’s haemoglobin concentration before conducting a diffusing capacity test?

A

Carbon monoxide binds to haemoglobin, so the patient’s haemoglobin concentration can affect the amount of CO transferred and needs to be factored into the calculations.

107
Q

According to Fick’s law, what factors can affect the rate of gas diffusion across the alveolar-capillary membrane?

A
  • Surface area
  • Partial pressure difference
  • Membrane thickness.
108
Q

How can emphysema affect diffusing capacity?

A

Emphysema, which involves destruction of alveoli, reduces the surface area available for gas exchange, leading to a decreased diffusing capacity.

109
Q

How does pulmonary fibrosis affect diffusing capacity?

A

Pulmonary fibrosis increases the thickness of the alveolar-capillary membrane due to scarring, slowing the rate of gas diffusion and decreasing diffusing capacity.

110
Q

Give an example of an acute condition that can increase the thickness of the alveolar-capillary membrane and therefore affect diffusing capacity.

A

Pulmonary oedema, where fluid builds up in the lungs, increasing membrane thickness and reducing diffusing capacity.

111
Q

Give an example of a condition that can reduce diffusing capacity due to a loss of blood flow to parts of the lungs.

A

Pulmonary embolism, which blocks blood flow to sections of the lung, leading to reduced gas exchange and decreased diffusing capacity.

CTB Block 2 (19 decks)

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