The distance-saturation product predicts mortality in idiopathic pulmonary fibrosis.
BACKGROUND
The 6-min walk test (6MWT) has prognostic value in various pulmonary disorders including idiopathic pulmonary fibrosis (IPF). We determined the individual prognostic accuracy of distance walked and oxygen saturation during the 6MWT in patients with IPF. We defined a new composite index, the distance-saturation product (DSP), which is the product of distance walked and lowest oxygen saturation during the 6-min walk test. We compared the performance of the DSP to the individual 6MWT parameters in predicting mortality.


METHODS
We evaluated pulmonary function tests, 6-min walk parameters and the DSP between survivors and non-survivors. The ability of each measure to discriminate outcomes was determined by receiver operator curves.


RESULTS
81 patients (48 survivors, 33 non-survivors) were included. Pulmonary function tests were similar and did not correlate with survival. Desaturation was greater (89.4% versus 83.7%, P<0.001) and distance walked was lower (406.9 versus 181.3m, P = 0.005) in non-survivors. The DSP was significantly lower among non-survivors (364.8 versus 153.5m%, P < 0.001) and predicted mortality more accurately than either individual 6MWT component (P = 0.035 versus desaturation, P=0.040 versus distance). A DSP <200 m% was associated with a seven-fold greater risk of 12-month mortality and an 18.0% shorter median survival compared with a DSP > 200 m% (P < 0.001).


CONCLUSIONS
Each component of the 6-min walk independently predicted mortality in IPF with greater accuracy than spirometry. However, a composite of both parameters, the DSP, provides slightly greater accuracy and represents a novel measure for assessing survival in patients with IPF.
Lettieri
Christopher J
CJ
Pulmonary & Critical Care Medicine, Walter Reed Army Medical Center, 6900 Georgia Ave., NW, Washington, DC 20307, USA. christopher.lettieri@us.army.mil
Nathan
Steven D
SD
Browning
Robert F
RF
Barnett
Scott D
SD
Ahmad
Shahzad
S
Shorr
Andrew F
AF
D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D011237:Predictive Value of Tests; D011379:Prognosis; D011446:Prospective Studies; D011658:Pulmonary Fibrosis / Q000097:blood / Q000401:mortality*; D012129:Respiratory Function Tests / Q000379:methods; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016138:Walking / Q000502:physiology*
D010100:Oxygen