CONTENTS
- Rapid reference: Approach to PFT interpretation 🚀
- About pulmonary function tests (PFTs)
- Obstruction
- Restriction
- Nonspecific ventilatory limitation
- DLCO
- Bronchial responsiveness:
- Neuromuscular weakness & inspiratory pressures
- Changes in PFTs over time
- Questions & discussion
abbreviations used in the pulmonary section: 7
- ABPA: Allergic bronchopulmonary aspergillosis 📖
- AE-ILD: Acute exacerbation of ILD 📖
- AEP: Acute eosinophilic pneumonia 📖
- AFB: Acid fast bacilli
- AIP: Acute interstitial pneumonia (Hamman-Rich syndrome) 📖
- ANA: Antinuclear antibody 📖
- ANCA: Antineutrophil cytoplasmic antibodies 📖
- ARDS: Acute respiratory distress syndrome 📖
- ASS: Antisynthetase syndrome 📖
- BAL: Bronchoalveolar lavage 📖
- BiPAP: Bilevel positive airway pressure 📖
- CEP: Chronic eosinophilic pneumonia 📖
- CF: Cystic fibrosis 📖
- COP: Cryptogenic organizing pneumonia 📖
- CPAP: Continuous positive airway pressure 📖
- CPFE: Combined pulmonary fibrosis and emphysema 📖
- CTD-ILD: Connective tissue disease associated interstitial lung disease 📖
- CTEPH: Chronic thromboembolic pulmonary hypertension 📖
- DAD: Diffuse alveolar damage 📖
- DAH: Diffuse alveolar hemorrhage 📖
- DIP: Desquamative interstitial pneumonia 📖
- DLCO: Diffusing capacity for carbon monoxide 📖
- DRESS: Drug reaction with eosinophilia and systemic symptoms 📖
- EGPA: Eosinophilic granulomatosis with polyangiitis 📖
- FEV1: Forced expiratory volume in 1 second 📖
- FVC: Forced vital capacity 📖
- GGO: Ground glass opacity 📖
- GLILD: Granulomatous and lymphocytic interstitial lung disease 📖
- HFNC: High flow nasal cannula 📖
- HP: Hypersensitivity pneumonitis 📖
- IPAF: Interstitial pneumonia with autoimmune features 📖
- IPF: Idiopathic pulmonary fibrosis 📖
- IVIG: Intravenous immunoglobulin 📖
- LAM: Lymphangioleiomyomatosis 📖
- LIP: Lymphocytic interstitial pneumonia 📖
- MAC: Mycobacterium avium complex 📖
- MCTD: Mixed connective tissue disease 📖
- NIV: Noninvasive ventilation (including CPAP or BiPAP) 📖
- NSIP: Nonspecific interstitial pneumonia 📖
- NTM: Non-tuberculous mycobacteria 📖
- OHS: Obesity hypoventilation syndrome 📖
- OP: Organizing pneumonia 📖
- OSA: Obstructive sleep apnea 📖
- PAP: Pulmonary alveolar proteinosis 📖
- PE: Pulmonary embolism 📖
- PFT: Pulmonary function test 📖
- PLCH: Pulmonary Langerhans cell histiocytosis 📖
- PPFE: Pleuroparenchymal fibroelastosis 📖
- PPF: Progressive pulmonary fibrosis 📖
- PVOD/PCH Pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis 📖
- RB-ILD: Respiratory bronchiolitis-associated interstitial lung disease 📖
- RP-ILD: Rapidly progressive interstitial lung disease 📖
- TNF: Tumor necrosis factor
- UIP: Usual interstitial pneumonia 📖
additional abbreviations used in this chapter:
- ERV: Expiratory reserve volume.
- FRC: Functional reserve capacity.
- TLC: Total lung capacity.
- RV: Residual volume.
usual approach: starting with spirometry
before starting: inspect flow-volume loops
- Are loops consistent and of high quality?
- Is there any evidence of large airway obstruction?
interpretative algorithm starting with spirometry:
- FEV1/FVC is normal/high ➡️
- FVC is normal ➡️
- FEV1 is low ➡️ Nonspecific ventilatory limitation.
- FEV1 is normal ➡️
- DLCO is normal ➡️ Completely normal.
- DLCO is low ➡️ Suggests pulmonary vascular disease, early interstitial lung disease, early emphysema, or some combination of these processes (e.g., combined pulmonary fibrosis and emphysema).
- FVC is low ➡️
- TLC is normal ➡️ Nonspecific ventilatory limitation.
- TLC is low ➡️ Restriction.
- FVC is normal ➡️
- FEV1/FVC is low ➡️
- FEV1 is normal ➡️
- FVC is normal ➡️ Mild obstruction or normal variant (look for soft signs of obstruction).
- FVC is low ➡️
- TLC is normal/high ➡️ Obstruction
- TLC is low ➡️ Mixed obstruction & restriction
- FEV1 is low ➡️
- FVC is normal ➡️ Obstruction
- FVC is low ➡️
- TLC is normal/high ➡️ Obstruction
- TLC is low ➡️ Mixed obstruction & restriction.
- FEV1 is normal ➡️
approach to interpretation of lung volumes (& sorting out types of restriction)
obstruction
- FRC (functional residual capacity) and FRC/TLC ratio are elevated.
- Residual volume (RV) and RV/TLC are elevated (although note that this may also occur with neuromuscular weakness or poor effort).
- Inspiratory capacity (IC) is reduced.
simple restriction (i.e., intraparenchymal restriction)
- Key finding: all volumes are reduced, with normal ratios between the volumes.
- Other features suggestive of simple restriction:
- Reduced DLCO suggests intraparenchymal restriction. Alternatively, DLCO is often preserved in patients with extraparenchymal restriction. However, DLCO may be reduced in extraparenchymal restriction, if there is atelectasis or markedly reduced lung volumes. (Murray 2022)
- Increase in FEV1/FVC and convex flow-volume curve suggest intraparenchymal restriction. (Murray 2022)
mixed disorder (restriction + obstruction)
- Key defining features of a mixed disorder:
- (1) Obstruction (e.g., based on reduced FEV1/FVC).
- (2) Restriction, based on reduced TLC (total lung capacity).
neuromuscular weakness & related conditions
- Key finding:
- ~Normal FRC (functional residual capacity), since FRC is determined solely by the balance of lung recoil versus chest wall compliance.
- Both the inspiratory capacity and expiratory reserve capacity are reduced (weakness reduces the ability to either inhale or exhale).
- Residual volume and RV/TLC are increased (due to inability to fully exhale).
- Other findings that support this diagnosis:
- Normal DLCO would be expected (unless there is concomitant atelectasis).
- Related:
- Suboptimal effort: may have essentially the same pattern of abnormalities.
- Chest wall restriction: This is often similar to neuromuscular weakness, but the FRC (functional residual capacity) may be low. Exact findings may vary depending on the precise etiology of the restriction.
obesity
- Lung volumes for most obese people fall within the range of normal values until BMI is above ~40 kg/m2. (ATS/ERS 2022)
- Obesity tends to cause the following sequence of changes in lung volumes: (Murray 2022)
- 1st: Reduction in the ERV (expiratory reserve volume).
- 2nd: Reduction in the FRC (functional reserve capacity).
- 3rd: Reduction in TLC (total lung capacity). Many patients with obesity may have a relatively reduced TLC that nonetheless falls within the range of normal values. (figure below from DerangedPhysiology)
- DLCO can be elevated (possibly related to increased blood flow), normal, or may be reduced (due to basal atelectasis).
- Pulmonary:
- Severe asthma.
- Respiratory distress.
- Pneumothorax.
- Hemoptysis.
- MI or stroke within 3 months.
- Uncontrolled hypertension.
- Aneurysm (thoracic, abdominal, or cerebral).
- Recent surgery:
- Eye or ear surgery.
- Thoracic or abdominal surgery
- Neurosurgery.
- Potentially communicable disease (e.g., tuberculosis, COVID).
- Inability to follow instructions.
- Pain (e.g., chest, abdominal, or facial pain).
spirometry
- Spirometry refers to measurements of volumes and flow of air during forced inhalation and exhalation. This generates the following data:
- FEV1: Volume of gas exhaled in the first second of a forced exhalation.
- FVC: Volume of gas exhaled during the entire forced exhalation.
- Flow-volume curves: Graph of airflow as a function of volume during inhalation and exhalation.
- Volume-time curve: Graph of the volume exhaled over time.
- Spirometry is the simplest pulmonary function test. For example, it may be obtained in the office of some primary care physicians.
- Spirometry alone may be sufficient to track progression of patients with known obstructive lung disease (e.g., asthma or COPD), or as a screening test.
body plethysmography (“body box”)
- Body plethysmography involves the patient sitting in a sealed box. By measuring pressures in the box and in the airway while the patient breathes, the lung volumes can be calculated.
- Body plethysmography is required to calculate absolute lung volumes (e.g., the total lung capacity). This is required to confirm a diagnosis of restrictive physiology.
gas transfer (diffusion of carbon monoxide; DLCO)
- Assessment of lung function involves measurement of how much carbon monoxide can be transported across the patient's lungs during a single breath (DLCO).
- DLCO may be useful for the diagnosis of pulmonary vascular abnormalities, or subtle interstitial abnormalities that don't affect the total volume of gas moving into and out of the lungs.
- Further discussion of DLCO below: ⚡️
bronchoprovocation and bronchodilator responsiveness
- Airflow through the lungs may be affected by bronchodilators, or by bronchial irritants (methacholine). Evaluating these changes may be helpful for the diagnosis and management of obstructive lung diseases (especially asthma).
- More on bronchoprovocation below: ⚡️
- More on bronchodilator responsiveness below: ⚡️
defining characteristics of a purely obstructive pattern
- (1) Reduced FEV1/FVC is the key parameter. Controversy exists regarding whether to use a fixed cutoff (<0.7) or age-appropriate normative values.
- FEV1/FVC normally falls with age, so using a fixed cutoff may underdiagnose obstruction in younger patients and overdiagnose obstruction in older patients.
- For COPD, a fixed cutoff (FEV1/FVC <0.7) may provide better prediction of COPD-related hospitalization and mortality (perhaps because it indirectly factors age into the equation). Additionally, all clinical trials of COPD have been based on this cutoff.
- (2) Decreased FEV1.
- (3) FVC may be normal or decreased (decreased FVC may occur due to severe gas trapping).
soft signs of obstruction
- Patients with subtle obstruction may have normal values of FEV1/FVC. In this case, additional evidence of obstruction may be helpful to suggest the diagnosis:
- Scooping of the flow-volume curve, especially towards the end of expiration (this usually indicates obstruction, but it can be normal in older patients).
- Persistent expiratory flow for >6 seconds on a volume-time curve (normally, expiration is complete within <6 seconds). (Fishman 2023)
- FEF 25-75 (maximum mid-expiratory flow)
- FEF 25-75 is the flow rate between 25-75% of the FVC.
- FEF 25-75 may be more sensitive for obstruction than FEV1/FVC, but less specific.
- ATS/ERS 2022 guidelines state that FEF 25-75% is highly variable, poorly reproducible, and not specific for small airway disease.
- FEV3/FVC: Obstruction may become more notable towards end-expiration, so FEV3/FVC may be more sensitive than FEV1/FVC for mild obstruction.
- Slow vital capacity (SVC) is greater than forced vital capacity (FVC). Patients with obstructive lung disease may experience dynamic compression of their airways during a rapid, forced exhalation maneuver involved in measuring FVC. If SVC (slow vital capacity) is >100 ml larger than the FVC (forced vital capacity), this supports the presence of dynamic airway collapse during forced exhalation. (ATS/ERS 2022)
- Changes in lung volumes reflective of gas trapping: discussed above. ⚡️
- Positive response to bronchodilator. An improvement in FEV1, FVC, or both supports the presence of obstructive physiology. ⚡️
- Lungs are hyperinflated radiographically: 📖
causes of obstruction
- Upper airway obstruction (discussed further in the section below 👇).
- Bronchiectasis (including cystic fibrosis).
- Small airways disease:
- Asthma.
- COPD (including emphysema and chronic bronchitis).
- Acute bronchitis.
- Bronchiolitis of various etiologies (especially bronchiolitis obliterans).
- Some interstitial lung diseases:
- LAM (lymphangioleiomyomatosis).
- PLCH (pulmonary Langerhans cell histiocytosis).
- Sarcoidosis.
approach to sorting out the etiology of obstruction
- Normal DLCO suggests asthma or chronic bronchitis.
- Reduced DLCO suggests emphysema or combined disorders (e.g., combined pulmonary fibrosis and emphysema).
severity of obstruction based on FEV1
- GOLD grading system for COPD:
- FEV1 >80% predicted = Mild (GOLD 1)
- FEV1 50-80% predicted = Moderate (GOLD 2)
- FEV1 30-50% predicted = Severe (GOLD 3)
- FEV1 <30% predicted = Very severe (GOLD 4)
- ATS/ERS 2022 grading system for FEV1 reduction:
- Mild reduction: Z-score -1.65 to -2.5
- Moderate reduction: Z-score -2.51 to -4.0
- Severe reduction: Z-score < -4.1
- ⚠️ Large airway obstruction initially won't affect FEV1 or FVC. For example, a tracheal lumen <8 mm may cause an abnormal flow-volume loop. In contrast, FEV1 may remain >90% predicted until the trachea is <6 mm! (Murray 2022)
- Evaluation of flow-volume loops is generally the best strategy for detecting upper airway obstruction. This should ideally be done visually on every set of pulmonary function tests. Upper airway obstruction usually causes visually recognizable abnormalities.
flow volume loops for diagnosis of large airway obstruction
basics
- Variable extrathoracic obstruction will cause selective flattening of inspiratory airflow.
- Variable intrathoracic obstruction will cause selective flattening of expiratory airflow.
- A fixed lesion located anywhere will cause flattening of both inspiratory and expiratory airflow.
some features may be especially suggestive of large airways disorders
- Sudden drop in expiratory flow (left panel of figure below).
- Notching of expiratory flow (middle panel, below).
- Oscillations of expiratory flow (right panel, below).
- (Additional discussion in the section on tracheobronchomalacia: 📖)
other signs of upper airway obstruction
Empey index
- Empey index = (FEV1 in ml)/(Peak Expiratory Flow Rate in L/min).
- Upper airway obstruction often causes a disproportionate reduction in peak expiratory flow rate as compared to FEV1. 📄
- This may be more sensitive for fixed obstruction, or variable intrathoracic obstruction (since it evaluates expiratory airflow).
- A normal value of the Empey index is below ~8-10 ml/L/min.
- Values >8 ml/L/min suggest the presence of central or upper airway obstruction. (ATS/ERS 2022) These should prompt a careful review of the flow-volume loop. (Fishman 2023)
expiration/inspiratory flow comparison (FIF/FEF ratio)
- FIF = forced inspiratory flow rate (i.e., the velocity of inhaling).
- FEF = forced expiratory flow rate (i.e., the velocity of exhaling).
- FIF 50%/FEF 50%:
- This is the ratio of inspiratory flow at 50% forced vital capacity, as compared to expiratory flow rate at 50% forced vital capacity. Essentially the ratio compares the flow velocities during the middle of the breath.
- FIF50/FEF50 <1: Extrathoracic variable obstruction or possibly neuromuscular weakness (neuromuscular weakness may disproportionately affect the inspiratory flow).
- FIF50/FEF50 ~1: Fixed extrathoracic obstruction.
- FIF50/FEF50 >1: Intrathoracic obstruction. (ATS/ESR 2022)
defining a purely restrictive pattern:
- FEV1/FVC is normal or elevated.
- FVC is reduced.
- TLC (total lung capacity) must be reduced.
- Note that a definite diagnosis of restriction requires measurement of total lung capacity using body plethysmography. Only ~50% of patients who appear to have restriction on spirometry (e.g., normal FEV1/FVC with reduced FVC) actually have restriction when tested with body plethysmography. (Murray 2022)
causes of restriction
- Intraparenchymal restriction:
- Interstitial lung disease (e.g., IPF, NSIP, sarcoidosis, medication-induced).
- Alveolar filling process (e.g., pneumonia, cryptogenic organizing pneumonia).
- Atelectasis (e.g., complete obstruction of a bronchus).
- Status post lung resection.
- Extraparenchymal restriction:
- Neuromuscular weakness.
- Chest wall: Kyphoscoliosis.
- Pleura: Effusion, pneumothorax, or pleural thickening.
- Abdomen: Obesity, pregnancy, abdominal compartment syndrome.
Lung volumes may be used to differentiate different types of restriction, as discussed above: ⚡️
definition of nonspecific pattern
- (a) Reduced FEV1 and/or FVC.
- (b) Normal FEV1/FVC ratio.
- (c) Normal TLC (total lung capacity).
causes of a nonspecific pattern
- Mild obstruction: Obstruction causes an elevated residual volume. This decreases the FVC, without decreasing the TLC. Furthermore, if patients are unable to fully exhale during the allotted time, this may falsely reduce the FVC. A reduction in the FVC will tend to elevate the FEV1/FVC (which may mask obstruction).
- Mild restriction, especially mild extrapulmonary restrictive processes (e.g., obesity and/or neuromuscular weakness). These processes may be associated with elevated residual volume. As the residual volume increases with worsening disease, the first abnormality to surface may be a reduction in FEV1 and/or FVC.
- Combination of a restrictive process and an obstructive process which mask one another (e.g., combined pulmonary fibrosis and emphysema).
- Poor test performance (e.g., poor effort).
- 💡 When followed over time, some patients may eventually manifest with unequivocally obstruction or unequivocal restriction. Thus, patients with nonspecific ventilatory limitation may have subtle obstructive or restrictive physiological abnormalities.
approach to sorting out the etiology of a nonspecific pattern:
- Look for soft signs of obstruction (discussed above: ⚡️).
- Look for signs of poor effort: The flow-volume curve may show early glottic closure or interruption of expiration due to poor effort. (ATS/ERS 2022)
PRISM (preserved ratio impaired spirometry)
PRISM is defined based on spirometry, with the following criteria:
- (a) FEV1 <80% reference.
- (b) FEV1/FVC ratio is normal after bronchodilation. (GOLD 2024 guidelines)
clinical significance of PRISM
- PRISM is present in ~10% of patient populations. (Gold 2024)
- Risk factors for PRISM may include:
- Smoking.
- Morbid obesity.
- Measurement of TLC (total lung capacity) may help clarify the underlying physiology.
prognosis of PRISM
- Over time, PRISM may transition to normal spirometry, restriction, or obstruction.
- Transition to obstruction occurs in ~25% of patients. Risk factors for this transition include lower baseline FEV1, older age, and current smoking. (Gold 2024)
reduced DLCO
understanding the significance of reduced DLCO
- DLCO below <50% very roughly predicts desaturation with exercise. However, much of the desaturation with exercise is often due to ventilation/perfusion mismatching (rather than abnormal diffusion), so there is no precise relationship between DLCO and oxygen saturation.
causes of reduced DLCO
- Pulmonary vascular process (this is the primary consideration for isolated & severe reduction in DLCO, since severe ILD would cause restriction).
- Pulmonary embolism.
- Pulmonary hypertension.
- Pulmonary arteriovenous malformation.
- Hepatopulmonary syndrome.
- Emphysema (this is the most common cause of isolated, mild reduction in DLCO. Reduction in DLCO may occur before an obstructive abnormality becomes apparent.)
- Interstitial lung diseases.
- Low tidal volume:
- Neuromuscular weakness.
- Localized loss of lung parenchyma (e.g., pneumonectomy, complete bronchial obstruction causing functional pneumonectomy).
- Hematologic abnormality is less likely:
- Anemia (if DLCO isn't corrected for hemoglobin).
- Carbon monoxide poisoning or heavy smoking.
dissecting DLCO into Va and Kco
- DLCO equals the product of two quantities:
- Va, the alveolar volume, which is a measurement of the volume of the breath.
- Kco, the transfer coefficient, which is a measurement of the efficacy of gas exchange.
- Evaluation of the individual components (Va and Kco) may help sort out different causes of a reduced DLCO:
some useful ratios
- FVC/DLCO ratio:
- The ratio is obtained by dividing the FVC (% predicted) by the DLCO (% predicted).
- FVC/DLCO ratio significantly higher than ~1.3-1.6 suggests the presence of pulmonary hypertension (or perhaps another pulmonary vascular disorder). (27888395, ERJ 50:PA861; 36196716, 26936321)
- Va/TLC ratio:
- This is the ratio of the Va (alveolar volume) divided by the total lung capacity.
- The normal ratio of Va/TLC is roughly 0.85 to 0.9
- Va/TLC ratio which is substantially lower than 0.85 suggests significant gas maldistribution in the lungs. (ATS/ERS 2022)
causes of increased DLCO
- Obesity (thought to reflect increased pulmonary blood volume).
- Alveolar hemorrhage (DLCO increase by >30% is highly suggestive).
- Congestion of the pulmonary vasculature:
- Early heart failure.
- Systemic-to-pulmonary shunting (i.e., left-to-right shunt).
- Asthma.
- Polycythemia (only if the DLCO isn't corrected based on hemoglobin).
criteria for positive response
- A positive bronchodilator response is defined as an improvement of either FEV1 or FVC by >10% of the normal predicted value. (ATS/ERS 2022)
- ⚠️ Note that this isn't a relative increase of 10% compared to the patient's baseline value. It is an increase of greater than 10% of the normal predicted value.
- Flow-volume loops should look similar when comparing before and after bronchodilator administration (otherwise, variable effort may be causing artefactual changes).
clinical significance
- COPD:
- (1) COPD diagnosis: Failure of bronchodilation to improve the FEV1/FVC above 0.7 is part of the definition of COPD (i.e., irreversible airflow obstruction).
- (2) COPD management: In the context of known COPD, bronchodilator responsiveness shouldn't affect clinical management.
- This is discussed further in the COPD chapter: 📖
- Asthma:
- The presence of bronchodilator responsiveness may support a clinical diagnosis of asthma.
- Very high levels of responsiveness (e.g., FEV1 >50% improved) suggests very unstable airways with an increased risk of poor asthma control and mortality.
utility
- Its primary use is to exclude asthma if PC20 is >16 mg/ml. However, patients with asthma can have a negative methacholine challenge if they are currently asymptomatic (e.g., in the context of exercise-induced asthma, early occupational asthma, or recent steroid therapy). (Murray 2022)
- Bronchoprovocation is generally more useful among patients with a normal baseline spirometry.
contraindications
- FEV1 below 60% (<60% is a relative contraindication; <50% is an absolute contraindication). (Fishman 2023) If baseline FEV1 is reduced, bronchodilator responsiveness is usually more appropriate.
- Recent upper respiratory tract infection.
- Recent administration of bronchodilator.
- Ingestion of coffee within 6 hours of the test.
- Cold-air breathing, hyperventilation, or exercise within six hours of testing. (Fishman 2023)
- Other contraindications to pulmonary function tests in general. ⚡️
interpretation
- The primary endpoint is the concentration that causes a 20% reduction in the FEV1 (PC20):
- PC20 >16 mg/ml: normal.
- PC20 4-16 mg/ml: borderline airway hyperresponsiveness.
- PC20 1-4 mg/ml: mild airway hyperresponsiveness.
- PC20 0.25-1 mg/ml: moderate airway hyperresponsiveness.
- PC20 <0.25 mg/ml: marked airway hyperresponsiveness.
- Recently updated guidelines recommend reporting the cumulative provocative dose of methacholine delivered (PD20) that causes a 20% fall in FEV1 to ensure reproducibility across hospitals. (28461290) This is interpreted as follows:
- PD20 >2 uM (>400 ug): normal.
- PD20 0.5-2 uM (100-400 ug): borderline airway hyperresponsiveness.
- PD20 0.13-0.5 uM (25-100 ug): mild airway hyperresponsiveness.
- PD20 0.03-0.13 uM (6-25 ug): moderate airway hyperresponsiveness.
- PD20 <0.03 uM (<6 ug): marked airway hyperresponsiveness.
- Symptoms should also be recorded, since these may assist in judging a borderline test result.
- Methacholine may rarely induce a flare of vocal cord dysfunction, which could be discernible based on audible stridor and variable cuts in the inspiratory flow-volume loop.
causes of increased airway hyperresponsiveness
- Asthma (only 70% specific for asthma).
- Allergic rhinitis (~1/3 of patients).
- COPD, smoking.
- Recent respiratory infection (may cause airway hyperreactivity for up to six weeks in normal people). (Fishman 2023)
- Cystic fibrosis.
- Congestive heart failure.
- Sarcoidosis.
- Normal subjects (5-15%).
upright vs. supine forced vital capacity (FVC)
- Normally, the FVC decreases by <20% when supine. (CHEST 2007; 131: 1252)
- If the FVC decreases by >25% when supine, this suggests the presence of diaphragmatic weakness. However, a normal supine FVC doesn't exclude weakness. (Murray 2022)
maximum inspiratory pressure (MIP)
- This is the maximal negative inspiratory pressure, usually measured at FRC (functional residual capacity).
- It reflects strength of the diaphragm and inspiratory muscles.
- MIP measurement is highly effort-dependent.
- The lower limit of normal is very poorly defined, with relatively broad ranges and significant variability between different references.
- Lower limits of normal might be <71 cm in men or <39 cm in women. (5772056; Fishman 2023)
maximal expiratory pressure (MEP)
- This is the maximal positive pressure that can be exerted, usually measured at total lung capacity.
- It reflects the strength of the abdominal and other expiratory muscles.
- MEP measurement is highly effort-dependent.
- The lower limit of normal hasn't been well defined.
- Lower limits of normal might be <111 cm in men or <88 cm in women. (5772056; Fishman 2023)
- MEP <60 cm suggests potential difficulty coughing and clearing secretions.
FEV1
- Healthy nonsmokers over ~30-40 years of age lose ~30 mL/year in the FEV1.
- Patients with COPD who smoke may lose ~45-70 mL/year in their FEV1, but there is substantial variability. (Fishman 2023)
- Reduction of FEV1 by >10% within <2 years is a component of diagnostic criteria for BOS (bronchiolitis obliterans syndrome) status post bone marrow transplantation. 📖
criteria for progressive pulmonary fibrosis (PPF)
- Among patients with interstitial lung disease, either of the following may reveal disease progression:
- FVC decline >5% predicted within one year of follow-up.
- DLCO decline >10% predicted within one year of follow-up (corrected for hemoglobin).
- Further discussion of progressive pulmonary fibrosis here: 📖
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References
- 34949706 Stanojevic S, Kaminsky DA, Miller MR, Thompson B, Aliverti A, Barjaktarevic I, Cooper BG, Culver B, Derom E, Hall GL, Hallstrand TS, Leuppi JD, MacIntyre N, McCormack M, Rosenfeld M, Swenson ER. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J. 2022 Jul 13;60(1):2101499. doi: 10.1183/13993003.01499-2021 [PubMed]
Books:
- Shah, P. L., Herth, F. J., Lee, G., & Criner, G. J. (2018). Essentials of Clinical pulmonology. In CRC Press eBooks. https://doi.org/10.1201/9781315113807
- Shepard, JO. (2019). Thoracic Imaging The Requisites (Requisites in Radiology) (3rd ed.). Elsevier.
- Walker C & Chung JH (2019). Muller’s Imaging of the Chest: Expert Radiology Series. Elsevier.
- Palange, P., & Rohde, G. (2019). ERS Handbook of Respiratory Medicine. European Respiratory Society.
- Rosado-De-Christenson, M. L., Facr, M. L. R. M., & Martínez-Jiménez, S. (2021). Diagnostic imaging: chest. Elsevier.
- Murray & Nadel: Broaddus, V. C., Ernst, J. D., MD, King, T. E., Jr, Lazarus, S. C., Sarmiento, K. F., Schnapp, L. M., Stapleton, R. D., & Gotway, M. B. (2021). Murray & Nadel’s Textbook of Respiratory Medicine, 2-Volume set. Elsevier.
- Fishman's: Grippi, M., Antin-Ozerkis, D. E., Cruz, C. D. S., Kotloff, R., Kotton, C. N., & Pack, A. (2023). Fishman’s Pulmonary Diseases and Disorders, Sixth Edition (6th ed.). McGraw Hill / Medical.
- GOLD 2024: Global initiative for chronic Obstructive Lung Disease. [Full text]