The following question is based on the shown pulmonary function tests (PFTs). Assume in each case that the test result is adequate and reproducible.
Key:
FVC |
L |
Forced Vital Capacity |
FEV1 |
L |
Forced Expiratory volume in 1 second |
FEV1/FVC |
% |
Ratio of the above |
RV |
L |
Residual volume at end expiration |
TLC |
L |
Total Lung Capacity |
DLCO corr |
ml/min/mmHg |
Diffusing capacity for carbon monoxide, corrected for Hb |
A 46-year-old female has presented with several months of progressive shortness of breath and lethargy compromising her previously active lifestyle. She is markedly hypoxic, with a resting SpO2 of 88% in air. She has had PFTs performed recently as an outpatient
Predicted |
Actual |
% Predicted |
Post Bronchodilator |
% Change |
|
FVC (L) |
3.56 |
3.35 |
94 |
2.77 |
-6 |
FEV1 (L) |
2.88 |
2.70 |
93 |
2.31 |
-4 |
FEV1/FVC (%) |
81 |
82 |
83 |
||
RV (L) |
1.90 |
2.03 |
107 |
||
TLC (L) |
5.22 |
5.11 |
98 |
||
DLCO corr (ml/min/mmHg) |
23.25 |
7.96 |
34 |
Normal lung function, markedly impaired diffusion of gases
Problem is not in the lungs but with the blood flow i.e. pulmonary vascular disease/pulmonary hypertension
Any 2 of:
idiopathic or familial PAH
cardiac disease - L sided
connective tissue disease /SLE
drug induced
chronic thromboembolic disease (2 marks)
Formal pulmonary function tests have also been asked about in Question 21.2 from the first paper of 2014 and the identical Question 9.1 from the first paper of 2011.
To approach this systematically:
An isolated defect in the diffusing capacity for carbon monoxide could be anaemia, but the "corr" in the SAQ refers to the correction of the DLCO for the patient's haemoglobin value, which excludes this as a differential. Other possible causes (according to UpToDate) include:
Pellegrino, Riccardo, et al. "Interpretative strategies for lung function tests."European Respiratory Journal 26.5 (2005): 948-968.
The American Thoracic Society has a page which features an excellent bibliography of the articles which support their interpretation standards.