Freire - PFT Flashcards
What is the difference between the airway on the left and those on the right -> how will this affect the flow-volume curves?
- Fixed upper airway obstruction on the right -> hamburger shaped flow-volume curve
What are 6 important PFT’s?
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Spirometry: for obstruction vs. restriction (pre- and post-)
1. Max voluntary ventilation (max vol that can be exhaled per min by pt breathing as rapidly and deeply as possible, aka max breathing capacity) - Lung volumes: usually done in a hx; may not have this in a dr.’s office
- DLCO: for interstitial/restrictive diseases
- ABG’s: arterial blood-gas -> acute disease in ICU
- Methacholine challenge: bronchial reactivity
- Stress test (CPEx): evaluation of EKG, BP, and gases to evaluate O2 consumption, CO2 production
How do flow-volume graphs vary by lung disease type?
- Both obstruction and restriction will reduce vital capacity (so this will NOT tell you if you have obstructive or restrictive disease)
- Obstructive: DEC FEV-1/FVC ratio, NOT restrictive -> other way to tell difference is by the FLOW VELOCITIES
- Restrictive: pts tend to have hyper-flows due to the higher elastic recoil (effort-independent portion of the curve) -> at given point of volume, they will have high velocity flows
What are 2 important things to evaluate when looking at a Spirometry output?
- Duration >6 seconds = adequate collection of volume
- Analyze the effort of the ventilation (no coughs or lags)
1. Volume and time
What is the difference between the normal forced expiration curve and that in restrictive disease (image)?
What does spirometry measure?
- Measures vital capacity (forced or slow)
1. Important to assess the “quality of the effort”
2. Spirometry w/o a graphic tracing has little value (vol-time tracing
3. If expiration 6 seconds or more, likelihood is you have a full collection of air -> must evaluate the quality of the test
When is the TLC reduced? What about the VC?
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TLC is reduced in:
1. Diseases of the thorax
2. Inspiratory muscle weakness
3. Pleural diseases
4. Loss of functioning alveoli -
VC is reduced in:
1. Chest pain (don’t inhale to the max)
2. Fatigue
3. Poor effort - THIS IS WHAT WE NEED TO KNOW -> remember these factors that can influence vol distribution and measurement
What is going on here?
- Plethysmograph (body box)
- Measures the total body gas (not just in the lungs)
- When you shut the valve in the mouthpiece, you can measure the pressure difference between the box and outside -> can measure the FRC (which is not measurable via spirometry
What are the clinical application and indications for diffusion PFT’s (i.e., DLCO)?
- Differentiate between asthma & COPD (chronic bronchitis and emphysema)
- Differentiate between interstitial and chest wall disease
- Suspected pulmonary vascular disease (P-HTN)
- Dyspnea with chest x-ray infiltrates
What happens to the flow-volume curve with a fixed UA obstruction?
Hamburger bun loop
What things can affect the DL?
- DL is affected by the VA (alveolar ventilation)
1. DL is reduced 0-25% by 50% reduction in TLC - Change in DLCO 7% per gram of Hb
- DL is determined from alveolar volume (VA), initial, and final alveolar CO concentration, and breath-holding time
What is the mechanism of dyspnea in pts w/COPD?
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Dynamic hyperinflation: increased FRC and residual vol, so new level of hyperinflation -> this is the reason why functioning stops when you do physical activity
1. Reducing the RV is how we help COPD’ers - Airflow obstruction associated with COPD can lead to air trapping and hyperinflation that worsen during exercise (due to INC RR -> dynamic hyperinflation at end of graph)
1. Exercise uses inspiratory capacity (IC), but COPD pts have limited IC (which DEC w/physical activity) -> start stacking air onto previous breath until you reach TLC, and you have to stop
2. IC appears to correlate more strongly to dyspnea than measures of airflow such as FEV1. - Hyperinflation and air trapping develop over many years
- Static hyperinflation refers to findings of COPD at rest
What is the lung diffusing capacity? How is it measured?
- Rate at which gas enters the blood
1. Divided by the driving pressure of the gas (partial pressure difference between alveoli and pulmonary capillaries) ml/min/dL - CO is used to measure DL because:
1. It has a high affinity for Hb (210x O2) and
2. Is found in low concentration in blood prior to testing (assumed 0)
What 4 values are determined by PFT’s?
- Volume: usually integrated with flow and time in the eval of PFT’s
- Flow
- Time
- Pressure: usually done in ICU
- NOTE: these are the dimensions that modify lung health
How is spirometry done?
- Pt usually in a sitting position
- Mouthpiece and nose clips to prevent air leakage
- After quiet tidal breathing, pt makes a maximal inspiratory effort (from FRC) to TLC (total lung capacity), then maximal expiratory effort until “all the air is out” (RV)
- 3 acceptable efforts ensure reproducibility
- Good coaching is KEY!!
- NOTE: expiratory effort should be continued at least for 6 seconds (preferably for 10 sec)
What happens to DLCO in pulmonary vascular disease?
Isolated reduction in DLCO
What is dynamic hyperinflation?
A reduction in inspiratroy capacity during exercise (common in COPD -> dyspnea)
What are the indications for PFT’s?
- Dyspnea, cough (symptoms)
- Pre-operative evaluation: elective thoracic surgery, esp. in the mediastinum
- Occupational exposure
- Disability
- Severity (“lung age”): accelerated rate of LOF in smokers (it’s important to educate your patients about this)
1. Rate of progression of the disease is important - Rx response
- Other
How is the quality of this graph?
- Good -> duration at least 6 seconds, no lag time at the beginning, no interruptions
How do you determine the severity of a DLCO abnormality? What might cause this value to be high?
- High >140 % predicted (EX: bleeding into the lung)
- Normal 81-140%
- Borderline low 76-80%
- Mild decrease 61-75%
- Moderate decrease 41-60%
- Severe decrease < 40%
Is peak flow effort dependent?
Yes
What are the techniques for measuring DLCO?
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Single Breath: simple, standardized and less affected by uneven distribution of ventilation
1. Relatively insensitive to COHB back pressure, e.g., CO back pressure in smokers reduces DLCO
2. Requires inhaled VC of > 1 L and 10 secs of breath holding -> this is difficult for pts w/restrictive disease (major limitation in interpretation of these tests) - Steady State
- Rebreathing method
- DL is determined from alveolar volume (VA), initial, and final alveolar CO concentration, and breath-holding time
What does this image show in the red circle?
- Effort-dependent portion at the beginning and effort-independent portion at the end (cannot be faked -> red circle)
- No scooping in this image
What would a fixed obstruction flow-volume loop look like?
Hamburger shape
What would the flow-volume loop look like in a variable upper airway obstruction? What are some examples?
- Variable extra-thoracic obstruction seen in inhalation
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Examples: vocal cord paralysis, tracheal stenosis, goiter
1. You may hear inspiratory stridor
What things do you look for on a spirometry output like this?
- Inhalation is usually more susceptible to how motivated the patient is
- First thing you do is look at the graph and evaluate the effort -> CRITERIA IS 6 seconds of exhalation and no interruptions in the effort (i.e., hiccups, cough)
- First part of exhalation effort dependent, but the latter portion, you cannot fake -> effort-independent portion of the flow-volume loop
What tests can you use to measure the TLC?
- Body plethysmograph (gold standard): can calculate the FRC and RV (can’t measure these with spirometry) -> this could be on the exam
- Nitrogen washout
- Helium dilution: inhale a known amount, then equilibrium and measurement of volume (see attached image)
- Chest radiography
What is the MVV maneuver?
- Maximum voluntary ventilation: breathe in and out as deeply and as fast as you can for 12 seconds
- Max respiration: liters per minute
1. Deep breath in and out, >TV
2. As hard (max) and as fast (RR) as possible - 10-12 seconds; ideal test image attached
- 40x FEV-1 is normal: internal consistency -> check FEV-1 x 40 (if <80% of this value, then the value is likely suboptimal)
- Uninterrupted (cough/effort)
What does this image show?
- Scooping of a bad COPD’er
When might a DLCO test be useful?
To evaluate restrictive lung disease
What do the emphysema compliace curve, forced expiration, and spirogram look like? How do these compare to normal?
- More compliant -> more air trapping
- FEV-1/FVC <70%
- Concomitant restriction defect is seen in < 10% of COPD patients
How does smoking cessation affect the decline of lung function in COPD?
- Can increase time to symptoms, disability, and death by quitting sooner (see graph)
- Important reason to do evaluation studies sequentially
What do the normal compliance curve, forced expiration, and spirogram look like (image)?
What do the asthma compliace curve, forced expiration, and spirogram look like? How do these compare to normal?
- Compliance not changed, but you do have air trapping, so FEV-1/FVC is <80% (showing some obstruction)
What do these two graphs show?
Spirometry showing significant bronchodilator response
What are the lung volumes that we need to know (graph)? What does spirometry measure?
- If name has the word capacity, it is the sum of 2 or more volumes
- Spirometry measures the vital capacity = tidal volume + inspiratory reserve + expiratory reserve
- KNOW THIS GRAPH
What do the fibrosis compliace curve, forced expiration, and spirogram look like? How do these compare to normal?
- Decreased compliance
- Hyper-flows: flow velocities higher for e/instantaneous volume due to INC elastic recoil
- Increased elastic recoil
- Decreased residual volumes
- A normal SVC (slow vital capacity) excludes a significant restrictive disorder -> normal vital capacity probably does not have restrictive lung disease
How are compliance, elastance, TLC, and RV affected by emphysema, asthma, and fibrosis?
- See graph for TLC and RV associated w/these conditions
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Compliance is the change in volume that the lung has with a given change in pressure (inverse of elastance)
1. Emphysema: destruction of lung parenchyma and reduced elastic recoil (INC compliance)
2. Increased volume requires significant amount of change in pressure for fibrosed (restrictive disease) lungs with increased elastic recoil (decreased compliance)
3. Asthma compliance curve: similar to normal
