Lung Function Testing Flashcards
Measured values for lung function testing
FEV1
FVC
flow volume curve
Peak expiratory flow (PEF)
Lung volumes
Transfer factor estimates
[compliance]
FEV1
the maximal volume of air that a subject can expel in one second from a point of maximal inspiration.
FVC
Forced vital capacity
Total volume of air breathed out
Forced breathing out
the maximal volume of air that a subject can expel in one maximal expiration from a point of maximal inspiration.
Forced expiration
Volume/time plot AND flow/volume plot
Breathe in to total lung capacity (TLC)
Exhale as fast as possible to residual volume (RV)
Volume produced is the vital capacity (FVC)
Flow/volume plot
Re-plot the data showing flow as a function of volume
PEF: peak flow
FEF25: flow at point when 25% of total volume to be exhaled has been exhaled
FEF25
flow at point when 25% of total volume to be exhaled has been exhaled
PEF (peak expiratory flow)- rate
Single measure of highest flow during expiration
Peak flow meter, spirometer
Gives reading in litres/minute (L/min)
Very effort dependent
May be measured over time, by giving a patient a PEF meter and chart
Other ways to measure RV and TLC
Gas dilution
Body box (total body plethysmography)
What do expiratory procedures measure
VC
FRC
Functional residual capacity
Tidal volume average value at rest in warmth
500 ml
Gas dilution
Get patient to breathe in a known volume of gas
Then measure volume of dilution
Gives total lung volume
Measurement of all air in the lungs that communicates with the airways
Does not measure air in non-communicating bullae
Gas dilution techniques use either closed-circuit helium dilution or open-circuit nitrogen washout
How long does it take for the majority of the air to leave the lungs
1s
Which gas is used in closed-circuit dilution
Helium
Which gas is used in open-circuit washout
Nitrogen
Total body plethysmography
Alternative method of measuring lung volume (Boule’s law), including gas trapped in bullae
From the FRC, patient ‘pants’ with an open glottis against a closed shutter to produce changes on the box pressure proportionate to the volume of air in the chest
The volume measured (TGV) represents the lung volume at which the shutter was closed
Vital capacity
Total volume breathed out to residual capacity
Volume that can be exhaled after maximum inspiration (ie. maximum inspiration to maximum expiration)-
average 4.5L
• Inspiratory reserve volume + tidal volume + expiratory reserve volume
• Often changes in disease
• Requires adequate compliance, muscle strength and low airway resistance
In young = similar to FVC
In older = higher the FVC due to reduced elastic recoil of lungs and closure of respiratory bronchioles
What is measured by total body plethysmography
FRC (functional residual capacity)
Inspiratory capacity
Expiratory reserve volume
Vital capacity
Total lung capacity
Vital capacity + residual volume
Transfer estimates
Carbon monoxide used to estimate TLCO, as has high affinity for haemoglobin
What is TLCO the overall measure interaction of
alveolar surface area
alveolar capillary perfusion
physical properties of the alveolar capillary interface
capillary volume
haemoglobin concentration, and the reaction rate of carbon monoxide and hemoglobin.
Transfer estimates - single 10s breath-holding technique
10% helium, 0.3% carbon monoxide, 21% oxygen, remainder nitrogen.
DLCO - known conc. inhaled —> hold breath for 10s —> expired conc. measured
Transfer estimates- alveolar sample obtained
DLCO is calculated from the total volume of the lung, breath-hold time, and the initial and final alveolar concentrations of carbon monoxide.
What value can you not directly measure
Residual volume
Compliance of the lung
Change in volume per unit change in pressure gradient between the pleura and the alveoli; (transpulmonary pressure)
Static compliance
Can be measured during breath-hold
A measure of distensibility
A lung of high compliance expands more than one of low compliance when exposed to same trans-pulmonary pressure
Disadvantages of gas dilution
Doesn’t show parts of diseased lungs
Dynamic compliance
Can be measured during regular breathing
Measured during tidal breathing at end of inspiration and expiration when lung is apparently stationary
Similar to static compliance in normal lungs
Reduced compared to static compliance in airway obstruction
What is the affinity of CO for haemoglobin compared to O2
x400 higher affinity
Abnormal values - FEV1
Compare with predicted value
80% or greater “normal”
Above the lower limit of normal for that patient (LLN)
Above mean minus 1.645 SD
Abnormal values - FVC
Compare with predicted value
80% or greater “normal”
Above the lower limit of normal for that patient (LLN)
Above mean minus 1.645 SD
Low value indicates likely Airways Restriction
FVC <80% predicted
Low value indicates airways restriction
Abnormal values FEV1/FVC ratio
Abnormal ratio <0.7 = airways obstruction
Asthma
Asthma is a variable condition
Typified by variable wheeze and shortness of breath, and normal periods in-between
Typified by airways obstruction and PEF variation (in later stages)
Typified by reduced mid expiratory flows
Typified by good response to treatments
Airways restriction
FVC < 0.8
Volume problem: pulmonary fibrosis —> decreased lung compliance —> decreased expansion
Airways obstruction
FEV1/FVC ratio< 0.7
Flow problem: COPD, asthma —> decreased airflow—> hyperinflation
FEV1 asthma
Normal or reduced
FVC asthma
Normal
TLCO and KCO asthma
Normal or elevated
Amplitude % maximum asthma
Normal up to 8%
Asthma > 15-20%
Amplitude % mean asthma
> 20%
Asthma typical blood gases
PaO2 = normal
PaCO2 = low
pH - normal or elevated
HCO3- = normal
PEF asthma
Typically variable, increased diurnal variation of 20%
MEF asthma
Low, typically ‘scalloped’ shape to the flow-volume curve
eNO
High
R(AW)
High when airway narrowing present
COPD
COPD is a progressive condition
Typified by wheeze and shortness of breath on exercise, progressively worse with time
Intermittent exacerbations
Typified by airways obstruction and lack of significant PEF variation
Typified by reduced mid expiratory flows
Typified by partial or poor response to treatments
FEV1 COPD
Reduced significantly
FVC COPD
May be normal or reduced
PEF COPD
Typically not variable
PEF
Peak flow measurements
MEF
Maximal expiratory flow
MEF COPD
Low, typical ‘scalloped’ shape to the flow-volume curve
TLC COPD
High or normal
DLCO and KCO COPD
Low
eNO COPD
Normal
R(AW) COPD
High
R(AW)
Airway resistance
COPD typical blood gases
PaO2 = low
PaCO2 = high in type 2 respiratory failure
Low in type 1 respiratory failure
pH = normal
HCO3- = may be elevated if chronic acidosis
1 pack year
1 packet of cigarettes per day for a year
eNO
Exhale of nitrous oxide
Dynamic hyperinflation
increase in end-expiratory lung volume (EELV) that may occur in patients with airflow limitation when minute ventilation increases (e.g. during exercise, hypoxia, anxiety etc.)
Dynamic hyperinflation occurs when end expiratory lung volume (EELV) or FRC is unable to return to the resting volume, resulting in a positive end-expiratory pressure (PEEP).
Asbestosis
Pulmonary fibrosis due to asbestos
FEV1 asbestosis
Reduced significantly
FVC asbestosis
Reduced significantly
PEF asbestosis
Typically not variable
MEF asbestosis
Low or normal
TLC asbestosis
Reduced
DLCO and KCO asbestosis
Low
eNO asbestosis
Normal
R(AW) asbestosis
No typical change
Typical blood gases of asbestosis
PaO2 = low
PaCO2 = low
pH - normal
HCO3- = low
Mixed airways obstruction and restriction
FEV1/FVC ratio < 0.7 AND low FVC
Tidal volume
Volume that enters and leaves with each breath, from a normal quiet inspiration to a normal quiet expiration
Average 0.5L
Changes with pattern of breathing e.g. shallow breaths vs deep breaths
Increased in pregnancy
Inspiratory reserve volume
Extra volume that can be inspired above tidal volume, from normal quiet inspiration to maximum inspiration
Average is 2.5 L
Relies on muscle strength, lung compliance (elastic recoil) and a normal starting point (end of tidal volume)
Expiratory reserve volume
Extra volume that can be expired below tidal volume, from normal quiet expiration to maximum expiration
Average 1.5L
Relies on muscle strength and low airway resistance
Reduced in pregnancy, obesity, severe obstruction or proximal (of trachea/bronchi obstruction)
Residual volume
Volume remaining after maximum expiration
Average 1.5L
Cannot be measured using spirometry
Inspiratory capacity
Volume breathed in from quiet expiration to maximum inspiration
Average 3L
Tidal volume + Inspiratory reserve volume
Functional residual capacity
volume remaining after quiet expiration
- average 3L
• Expiratory reserve volume + residual volume
• Affected by height, gender, posture, changes in lung compliance. Height has the greatest influence.
Prevents lung collapse
Total lung capacity
Volume of air in lungs after maximum inspiration-
average 6L
• sum of all volumes
• Restriction < 80% predicted
• Hyperinflation > 120% predicted
• Measured with helium dilution
Anatomical (serial) dead space
the volume of air that never reaches alveoli and so never participates in respiration. It includes volume in upper and lower respiratory tract up to and including the terminal bronchioles
Alveolar (distributive) dead space
the volume of air that reaches alveoli but never participates in respiration. This can reflect alveoli that are ventilated but not perfused, for example secondary to a pulmonary embolus.
Helium dilution
measure total lung capacity. However, it is only accurate if the lungs are not obstructed. If there is a point of obstruction, helium may not reach all areas of the lung during a ventilation, producing an underestimate as only ventilated lung volumes are measured.
Helium dilution process
After quiet expiration, the subject breathes in a gas with a known concentration of helium (an inert gas). They hold their breath for 10 seconds, allowing helium to mix with air in the lungs, diluting the concentration of helium. The concentration of helium is then measured after expiration. The volume of air which is ventilated is then calculated according to the degree of dilution of the helium.
Nitrogen washout
A method for calculating serial/anatomical dead space in the conducting airways up to and including the terminal bronchioles (usually 150mL).
Nitrogen washout process
The subject takes a breath of pure oxygen and then exhales through a valve which measures nitrogen levels. At first, pure oxygen is exhaled, representing the dead space volume as the air exhaled never reached the alveoli and underwent gaseous exchange.
Then, a mixture of dead space air and alveolar air is expired, meaning the detected concentration of nitrogen increases as nitrogen rich air from the dead space reaches the valve. After a few breaths, the lungs are washed out of pure oxygen, meaning that purely alveolar air is expired, with the nitrogen levels reflecting that of alveolar air. The levels of nitrogen measured over time can be used to calculate the anatomical dead space volume of the lungs.
Capacities
composed of 2 or more lung volumes. These are fixed as they do not change with the pattern of breathing.
Type 1 respiratory failure
• involves low oxygen, and normal or low carbon dioxide levels. (hypoxaemia (PaO2 <8 kPa / 60mmHg) with normocapnia (PaCO2 <6.0 kPa / 45mmHg))
• It usually occurs due to ventilation/perfusion (V/Q) mismatch –the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lung tissue
• As a result of the ventilation/perfusion mismatch, PaO2 falls, and PaCO2 rises. The rise in PaCO2 rapidly triggers an increase in a patient’s overall alveolar ventilation, which corrects the PaCO2 but not the PaO2 due to the different shapes of the CO2 and O2 dissociation curves.
Type 1 respiratory failure causes
• Occurs because of damage to lung tissue eg including pulmonary oedema, pneumonia, acute respiratory distress syndrome, and chronic pulmonary fibrosing alveoloitis.
• Causes : Reduced ventilation and normal perfusion (e.g. pneumonia, pulmonary oedema, bronchoconstriction) OR Reduced perfusion with normal ventilation (e.g. pulmonary embolism)
Type 2 respiratory failure causes
Hypoventilation can occur for several reasons, including:
Increased resistance as a result of airway obstruction (e.g. COPD)
Reduced compliance of the lung tissue/chest wall (e.g. pneumonia, rib fractures, obesity)
Reduced strength of the respiratory muscles (e.g. Guillain-Barré, motor neurone disease)
Reduced respiratory drive (e.g. opioids and other sedatives)
Type 2 respiratory failure
involveshypoxaemia (PaO2 is <8 kPa / 60mmHg) with hypercapnia (PaCO2 >6.0 kPa / 45mmHg).
• It occurs as a result of alveolar hypoventilation, which prevents patients from being able to adequately oxygenate and eliminate CO2 from their blood.
• This leads to PaO2 falling(due to lack of oxygenation) and PaCO2 rising(due to lack of ventilation and elimination of CO2).
Normal residual volume in a healthy man
1200 ml
eNO (exhaled nitric oxide)
Simple measure of nitric oxide in exhaled breath
Measure in ppb
Generally increased in asthma
Not ‘diagnostic’
A reflection of eosinophilic airway inflammation
Normal eNO
<25 ppb
High eNO
> 50 ppb
What is transfer estimate
Ability to transfer O2 by passive diffusion from alveoli to capillaries
FRC value
2.4L
RV value
1.2L
ERV value
1.2L
Tidal volume value
0.5L
IRV value
3L
VC value
4.7L
TLC value
5.9L
IC value
3.5L
Flow-volume graph
Flow is greatest at start of expiration then decreases linearly as lungs are emptied
Measured in L/min with spirometer
Obstructive Flow-volume graph
Scalloped
Shifts left and kink
Decreased VC
Increased RV and TLC
Restrictive Flow-volume graph
Shifts right
Decreased VC, RV , TLC
What would be the expected V/Q ratio in the lung at the level of the 1st rib in a healthy patient
Greater than normal V/Q ratio- ventilation is greater than perfusion due to effect of gravity
Which part of the lung has the lowest V/Q ratio
Base of lung
What best describes the gradient of the graph of lung volume against trans-lung pressure
Lung compliance
Valsalva manoeuvre
Breathing method which involves moderately forceful exhalation against a closed airway (I.e. closed mouth and pinching the nose)
Breathlessness has a wide variety of causes and it is useful to measure lung volumes to investigate the cause of the disease. Which of the following statements describes the functional residual capacity?
The volume of gas in the lungs at the end of a normal exhalation
