med 610 clinical respiratory diseases & critcare med

Pulmonary Function Testing

Case 11 Answer

A 36 year-old woman presents with a several month history of worsening dyspnea on exertion and exercise limitation. She is a life-long non-smoker and has no history of asthma or other known pulmonary diseases. She has had to stop going out with her weekly running group because she can no longer keep up with her friends.

Her pulmonary function testing is as follows:

  Pre-Bronchodilator (BD)
Test Actual Predicted % Predicted
FVC (L) 0.88 3.34 26
FEV1 (L) 0.87 2.87 30
FEV1/FVC (%) 99 86  
RV (L) 1.61 1.40 115
TLC (L) 1.61 4.73 53
RV/TLC (%) 65 29  
DLCO* corr 20 26.6 75
*DLCO is measured in ml/min/mmHg

A flow-volume loop is not available for this case.

Case 11 Interpretation

This patient has reduced FEV1 and FVC with a preserved FEV1/FVC ratio, a finding that is suggestive, but not diagnostic of a restrictive process. The presence of a reduced TLC confirms the presence of a restrictive defect. Based on the fact that her TLC is 53% of predicted, this would be labeled as a “moderate” restrictive defect. The patient has an essentially normal DLCO. Although the value is technically less than 80% of predicted, due to the inherent variability in this test, values in this range are considered normal. This suggests that her alveolar-capillary interface for gas exchange for normal and further suggests that her restrictive process is due to a process extrinsic to the pulmonary parenchyma.

This patient was sent for further pulmonary function testing. She had a 17% drop in her FVC from the sitting to supine position. Her maximum inspiratory pressures (– 35 cm H20), maximum expiratory pressure (- 50 cm H20) and peak cough flow (180 L/min) were all markedly reduced relative to normal values, findings that are indicative of muscle weakness. Upon further evaluation by a neurologist, the patient was found to have Limb Girdle Muscular Dystrophy.

 

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