So you thought you knew all about lung function tests, right? Well, try these two scenarios.
In the first, both FEV1 and FVC are low, and the FEV1/FVC ratio is normal. You suspect restriction. You request a TLC by whole body plethysmography, and to your surprise, the TLC is normal.
In another patient, the FEV1 and FVC are again low, the FEV1/FVC ratio is normal, and the TLC is low. However, the FVC is disproportionately reduced compared with TLC when measured against what is considered normal.
The first pattern is called the "Non-specific pattern", while the second is termed "the complex restrictive pattern".
The non-specific pattern is not uncommon- in fact, it crops up in around 10% of PFTs. These subjects were originally thought to have airway obstruction, but it's now clear that obstruction is present in only 60% of such subjects. The other 40% are due to chest wall disorders such as obesity, or neuromuscular disorders, or due to poor technique.
These two categories need differentiating with further tests such as repetition of spirometry after administration of a bronchodilator. This will identify the cohort with obstruction. A chest Xray should pick up a lung mass or pleural effusion. Obesity should be self evident, while Maximal Inspiratory Pressure, Maximal Expiratory Pressure and Maximal Ventilation Volume should identify those with neuromuscular weakness.
Fully two-thirds of subjects with the "non-specific" pattern continue to display this pattern over the years. Only a minority evolve into a frankly obstructive or restrictive phenotype on PFT.
The other pattern, called "Complex Restriction" is much more unusual, and probably accounts for less than 2% of PFTs. Here, the FVC is disproportionately reduced in relation to the TLC, with a discrepancy of >10% in relation to normal values. This pattern occurs relatively frequently in young females. It is associated with atelectasis, diaphragmatic paralysis, mosaic air trapping on imaging, bronchiectasis, BMI>40 or <18.5 and neuromuscular weakness. The term "Complex Restriction" differentiates this group from "Simple Restriction", where the FEV1 and FVC are reduced as well, but the TLC is reduced by proportionately the same extent as the FVC. While subjects with simple restriction are likely to have ILD, those with complex restriction usually do not have ILD. An excellent account can be found in the latest edition of Mayo Clinic Proceedings: https://www.mayoclinicproceedings.org/article/S0025-6196(18)30282-9/pdf
In the first, both FEV1 and FVC are low, and the FEV1/FVC ratio is normal. You suspect restriction. You request a TLC by whole body plethysmography, and to your surprise, the TLC is normal.
In another patient, the FEV1 and FVC are again low, the FEV1/FVC ratio is normal, and the TLC is low. However, the FVC is disproportionately reduced compared with TLC when measured against what is considered normal.
The first pattern is called the "Non-specific pattern", while the second is termed "the complex restrictive pattern".
The non-specific pattern is not uncommon- in fact, it crops up in around 10% of PFTs. These subjects were originally thought to have airway obstruction, but it's now clear that obstruction is present in only 60% of such subjects. The other 40% are due to chest wall disorders such as obesity, or neuromuscular disorders, or due to poor technique.
These two categories need differentiating with further tests such as repetition of spirometry after administration of a bronchodilator. This will identify the cohort with obstruction. A chest Xray should pick up a lung mass or pleural effusion. Obesity should be self evident, while Maximal Inspiratory Pressure, Maximal Expiratory Pressure and Maximal Ventilation Volume should identify those with neuromuscular weakness.
Fully two-thirds of subjects with the "non-specific" pattern continue to display this pattern over the years. Only a minority evolve into a frankly obstructive or restrictive phenotype on PFT.
The other pattern, called "Complex Restriction" is much more unusual, and probably accounts for less than 2% of PFTs. Here, the FVC is disproportionately reduced in relation to the TLC, with a discrepancy of >10% in relation to normal values. This pattern occurs relatively frequently in young females. It is associated with atelectasis, diaphragmatic paralysis, mosaic air trapping on imaging, bronchiectasis, BMI>40 or <18.5 and neuromuscular weakness. The term "Complex Restriction" differentiates this group from "Simple Restriction", where the FEV1 and FVC are reduced as well, but the TLC is reduced by proportionately the same extent as the FVC. While subjects with simple restriction are likely to have ILD, those with complex restriction usually do not have ILD. An excellent account can be found in the latest edition of Mayo Clinic Proceedings: https://www.mayoclinicproceedings.org/article/S0025-6196(18)30282-9/pdf
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