ICL 2.3: Lung Volumes & Pulmonary Function Tests Flashcards
what are the reference values for spirometry?
in the USA, ethnically appropriate NHANES III reference equations published in 1999 for those ages 8 – 80 years of age are recommended
it’s based on height, sex, and ethnicity
what are the reference values for lung volumes and diffusing capacity?
no specific set of reference equations is recommended (or mandated), however a list of potentially suitable reference equations is available
what factors effect the lung function testing that you need to be aware of?
- vital capacity decreases with age which is normal because lung elasticity decreases
- residual volume increases with age
- males have larger lung function than females
- tall individuals have larger volumes and higher flows; increased weight doesn’t mean that you’ll have higher lung flow
- lung function values plateau at 20-30 years of age –> lung capacity decreases 30 mLs/year after that
- african americans have lower spirometry
what happens to lung capacity with age?
vital capacity decreases
when the lung volume decreases, the residual volume increases because there’s loss of function
what are all the different tests that are done during a pulmonary function test?
- spirometry
- flow Volume Loop
- bronchodilator response
- lung volumes
- diffusion capacity (DLCO)
- bronchoprovocation testing
- maximum respiratory pressures
- simple and complex cardiopulmonary exercise testing
what is spirometry?
you blow into a machine and it will measure your flow vs. volume
the spirometer can measure up to 8 L with a flow between 0 and 14 L/sec
so the spirometer will give you a graph that is expired time vs. volume
then from this first graph, you can make a volume vs. flow loop (L/sec)
what is the FVC?
FVC = forced vital capacity
the whole volume that you can breath out after a deep inspiration
FEV1 is what you blow out in the first second but FVC is another 4/5 seconds and you get a little more air out
what is a flow volume and time volume graph for a spirometer?
go watch….
flow volume is a loop
time volume is a curved line that plateaus
what is a positive bronchodilator response?
if someone is having bronchospasm, give them a B2 agonists to dilate their bronchioles
if their FEV1 or the FVC increases by 12% or 200 mLs then this is considered a positive bronchodilator response
this means the airway improved and the patient has a reversible illness
what is your total lung capacity?
it’s your vital capacity + residual volume
your vital capacity is the volume when you take a really deep breath and blow all the way out
what is the expiratory reserve volume?
ESV is the amount you can expire extra after you have normally inspired and expired
it’s the maximal volume of air that can be exhaled from the end-expiratory position
what is the functional residual capacity?
FRC = ERV + RV
the amount of air that stays in your lung after you expire normally
it’s the volume in the lungs at the end-expiratory position
slide 10
what is inspiratory reserve volume?
the amount of air you can inspire after normal inspiration
it’s the maximal volume that can be inhaled from the end-inspiratory level
slide 10
what is the inspiratory capacity?
the amount of air you can inspire after a normal expiration
IC = tidal volume + IRV
what is tidal volume?
Tidal volume: that volume of air moved into or out of the lungs during quiet breathing
TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation
what is residual volume?
the volume of air remaining in the lungs after a maximal exhalation
what is total lung capacity?
the volume in the lungs at maximal inflation, the sum of VC and RV
what is the maximal voluntary ventilation?
the volume of air expired in a specified period during repetitive maximal effort
what is the limitation of spirometry?
you can’t measure the residual volume or diffusion capacity
what are the techniques that can be used to measure lung volume?
- body plethysmography
2. gas dilution
what is body plethysmopgrahy?
it’s a measurement of intrathoracic gas volume (thoracic gas volume [TGV]) at the time of airflow occlusion (typically FRC), the compressible gas within the thorax
you ask the patient to sit in a booth and you close the box which is attached to filters and pressure gauges
then you ask the patient to breath in and out and you measure the pressure and volume of the air in the box when the person breaths in vs. out
since the box is a closed space, P1V1=P2V2 and you measure the change in the volume of the whole chest wall and the air surrounding the patient in the box and you can find the residual volume because of this!
what are gas dilution techniques?
measures gas volume that communicates via the airways, using a mass balance approach
mass balance equation uses the initial volume and tracer gas concentration, and the final tracer concentration to calculate the volume in the patient’s lungs at the moment the tracer gas breathing began –> assume the tracer gas is largely insoluble, inert, and well mixed in the lung
we use it to measure residual volume – you breath in an inert gas that doesn’t distribute well in the lungs and then you measure the amount of gas that leaves you after expire; whatever didn’t come out is the residual volume
how does COPD effect results from body plethysmography vs. gas dilution?
in patients with obstructive lung disease and gas-trapping, functional residual capacity (FRC) determined by plethysmopgrahy may be higher than measured by gas dilution
how is diffusing capacity measured?
- steady-state
- intra-breath
- rebreathing
- single breath
single breath is the most common technique
how do you measure diffusing capacity?
you do gas dilution but you give a gas that can diffuse through the epithelium really easily and therefore can go through to the pulmonary capillaries!
so you use CO for this!
after they’ve taken a super deep breath, have them hold their breath so the CO can diffuse from the alveoli to the blood – then once they expire, measure the amount of CO and you know what didn’t come out diffused across the epithelium to the capillaries!
if you have certain diseases that CO can’t diffuse through the lungs, the amount of CO expired will be higher and this means lower diffusing capacity
which conditions increase diffusing capacity?
- polycythemia
- left to right shunt
- asthma
- pulmonary hemorrhage
- Muller maneuver
- exercise
- supine position
which conditions decrease diffusing capacity?
- valsalva maneuver
- carboxy-hemoglobin
- lung resection
- COPD
- ILD
- pulmonary vascular disease like emboli, pulmonary HTN, vasculitis
- anemia
- submaximal inspiration or respiratory muscle weakness
what is respiratory muscle pressure?
this is important for people who have chest wall weakness like someone with MS or is a paraplegic or ALS
how do you know if their lung volume is decreased because of a neurological problem or because of their respiratory muscles?
you put a pressure gauge in their mouth and ask them inspire forcefully which will record negative pressures – then you ask them to expire forcefully which will give out a positive pressure
values of the maximal inspiratory or expiratory pressure decrease with age because muscles weaken with age
so the MIP measures diaphragm function while MEP tells you how good your cough/clearing secretions will be
so a normal MIP excludes inspiratory muscle weakness! BUT a low MIP does not reliably confirm inspiratory muscle weakness
if your MIP is less than 1/3 of normal, it means hypercarbic respiratory failure
what positional change signifies inspiratory muscle weakness?
a fall in the FVC from upright to the supine position correlates with significant inspiratory muscle weakness
FVC = forced vital capacity
what are airway challenges?
when you give a B2 antagonists to initiate bronchoconstriction!
cold air or methacholine or histamine or B2 blockers
this should cause a 20% drop in the FEV1
so you give a low methacholine concentration via inhalation and slowly increase the concentration and measure the FEV1 as you go – once it drops below 20%, record the dose of methacholine that did the patient dirty
this dose is called the challenge dose!
healthy people can tolerate more than 16 mg/mL – mild asthma will make you drop at 1-4 mg of methacholine
what pulmonary function test results indicate that there’s an obstruction?
if the FEV1/VC is less than the 5th percentile of the predicted value for that persons age, gender, height
above 80% is a normal value for FEV1 and as it drops, the obstruction gets worse –> moderate (50-79), severe (30-49), and very severe (<30)
so the classification of obstruction is based on the FEV1 value, not the ratio! as soon as the ratio is under 80 it’s considered obstruction
when you have obstruction, both your FEV1 and VC are decreased bu the FEV1 is decreased to a greater degree which is why the ratio changes with obstruction
which lung diseases are obstructive?
- asthma
2. COPD
which lung diseases are restrictive?
restrictive lung disease is usually interstitial lung disease
what pulmonary function test results indicate that there’s a restriction?
FEV1 and VC both go down at the SAME rate so the ratio is above 80! –> with obstructive diseases, the FEV1 drops much lower than the VC so the ratio is below 80
so look at the total lung capacity which you measure through body box and it will be low!
how will the flow volume curve look like with obstructive vs. restrictive disease processes?
go look at the slide….
slide 30
obstructive = emphysema, variable intrathoracic UAO, and variable extra thoracic UAO graph –> inspiration is totally normal but expiration is difficult
restrictive = restrictive parenchymal lung disease graph –> graph looks totally normal but it’s little
which of the following is used to follow disease severity in COPD?
A. diffusing capacity
B. degree of responsiveness to bronchodilators
C. forced vital capacity
D. forced expiratory volume in 1 second
D. forced expiratory volume in 1 second
a 22 year old female present to your office for followup of recurrent attacks of acute bronchitis. you suspect asthma. which of the following would you include in your spirometry testing to diagnose asthma?
A. diffusing capacity
B. if no obstruction present, add trial of bronchodilator
C. if no obstruction present, perform methacholine challenge
D. flow volume loop
C. if no obstruction present, perform methacholine challenge
it’s not B because some COPD patents may have a positive bronchodilator response because the treatment helps them! but the methacholine challenge is specific for asthma
you want to see when they hit 20% obstruction with methacholine challenge
a 72 year old male patient is admitted to the ICU with respiratory distress. a CXR obtained in the ED demonstrates bilateral pulmonary infiltrates and his DLCO is elevated. what is the most likely diagnosis?
A. pulmonary edema
B. hypersensitive pneumonitis
C. venous thromboembolic disease
D. alveolar hemorrhage
E. interstitial lung disease
D. alveolar hemorrhage
