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 39-year-old female has presented in ED with severe, acute on chronic shortness of breath, now affecting her at rest. She has a 15-pack year history of smoking. She has had PFTs performed recently as an outpatient. Her chest X-ray shows marked bi-basal hyper-lucency.

Predicted

Actual

% Predicted

Post Bronchodilator

% Change

FVC (L)

3.15

1.50

48

0.83

-10

FEV1 (L)

2.65

0.52

20

0.53

+2

FEV1/FVC (%)

83

54

14

RV (L)

1.49

3.13

210

TLC (L)

4.44

4.74

107

DLCO corr

(ml/min/mmHg)

24.85

6.70

27

  1. What pattern of abnormality is shown?
  1. Suggest two likely diagnoses.                                                                   (20% marks)

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College answer

Severe, non-reversible obstructive lung disease     
Smoking related lung disease  
Alpha 1 antitrypsin deficiency                          (2 marks) 

Discussion

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:

  • FVC is the forced vital capacity, and here it is significantly decreased, which ordinarily simply means that the spirometry effort was poor, but the college assure us that each test was "adequate and reproduceable" so the patient must truly have reduced FVC.
  • FEV1 is the forced expired volume over 1 second, and is a measure of maximal air flow. A decreased FEV1 which fails to improve with bronchodilators demonstrates a irreversible obstructive pattern.
  • FEV1/FVC ratio is a measure of airway resistance which incorporates both the abovementioned metrics.
  • RV is the residual volume. A high RV suggests end-expiratory gas trapping or bullous dead space. This patient's RV is significantly increased, but the college do not make any specific comment on this.
  • TLC is the total lung capacity. In this case, the TLC is 107% of normal. On the basis of this, one might say that there is hyperinflation of the lungs. The college do not mention this.
  • DLCO is the diffusing capacity for carbon monoxide, a measure of the efficiency of the lung as a gas exchange surface. In this case, the DLCO is 27% of predicted, demonstrating a significant diffusion defect (which is probably not a measurement error, given the normal TLC). The "corr" in the SAQ refers to the correction of the DLCO for the patient's haemoglobin value, which we are not supplied with.

In summary, this patient has hyperinflated lungs with a severe irreversible obstructive pattern. The history we are given (smoker, but too young to have such severe bibasal bullous emphysema) suggests something might be congenitally broken in her lungs. As such, the college offer α-1 antitrypsin deficiency as one of the differentials. A list of (vaguely) plausible differentials might include:

References

References

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.