Exertional hypoxemia is more severe in ﬁbrotic interstitial lung
disease than in COPD
P. DU PLESSIS,
Department of Medicine, University of British Columbia, Vancouver, BC;
Centre for Heart Lung Innovation, University of
British Columbia, Vancouver, BC;
Department of Physical Therapy, University of British Columbia, Vancouver, BC;
Department of Medicine, University of Calgary, Calgary, AB, Canada
Background and objective: Despite its clinical and
prognostic signiﬁcance, few studies have evaluated the
severity of exertional oxygen desaturation in ﬁbrotic
interstitial lung disease (ILD). Our objectives were to
identify clinical and physiological variables that predict
the extent of exertional oxygen desaturation in ﬁbrotic
ILD and to quantify the severity of desaturation com-
pared to chronic obstructive pulmonary disease (COPD).
Methods: This retrospective study compared the results
of 6-min walk test (6MWT) performed while breathing
room air in ﬁbrotic ILD patients and COPD patients eligi-
ble for pulmonary rehabilitation. Outcomes included the
oxygen saturation (SpO
) nadir and the change in SpO
from rest during a 6MWT. Predictor variables were identi-
ﬁed on unadjusted analysis, followed by multivariate anal-
ysis to identify independent predictors of desaturation.
Results: The study included 134 patients with ﬁbrotic
ILD and 274 patients with COPD. The ILD and COPD
cohorts had similar age, sex, frequency of major comor-
bidities, walk distance, baseline SpO
and baseline Borg
dyspnoea scores. DL
was the strongest predictor of
desaturation in both cohorts. Compared to patients with
COPD, ILD patients had signiﬁcantly lower SpO
values (88.1 Æ 6.4 vs 91.0 Æ 4.6) and greater decrease
from baseline (7.4 Æ 5.2 vs 4.5 Æ 3.7) after
adjusting for demographic features and pulmonary
physiology (P < 0.0005), with greater between-group
differences at lower DL
Conclusion: Patients with ﬁbrotic ILD have greater oxy-
gen desaturation during 6MWT compared to patients
with COPD when adjusting for demographic features
and pulmonary physiology. These ﬁndings suggest the
need for disease-speciﬁc studies to evaluate the poten-
tial utility of ambulatory oxygen in ﬁbrotic ILD.
chronic obstructive pulmonary disease, exercise,
hypoxemia, idiopathic pulmonary ﬁbrosis, oxygen.
6MWD, 6-min walk distance; 6MWT, 6-min
walk test; DL
, diffusion capacity of the lung for carbon
, forced expiratory volume in 1 s; FVC, forced
vital capacity; ILD, interstitial lung disease; PFT, pulmonary
function test; RV, residual volume; SpO
, oxygen saturation;
TLC, total lung capacity.
Interstitial lung disease (ILD) is a diverse group of enti-
ties that cause damage to the lung parenchyma
through varying degrees of inﬂammation and ﬁbrosis.
Fibrotic ILDs result in restrictive ventilatory physiology
and impaired gas exchange, frequently leading to exer-
tional hypoxemia and functional limitation. The clinical
and prognostic importance of exertional hypoxemia is
well established, with multiple studies demonstrating a
strong correlation of exertional desaturation with dys-
pnoea and mortality.
Despite its importance, few
studies have evaluated the severity, predictors and
management of exertional oxygen desaturation in
Chronic obstructive pulmonary disease (COPD) is a
common condition typically caused by cigarette smok-
ing that results in a chronic inﬂammatory response
involving the airways and lung parenchyma.
characterized by persistent and progressive airﬂow lim-
itation as well as impaired gas exchange that leads to
dyspnoea and functional limitation. Despite similar fea-
tures of dyspnoea and functional limitation in both ILD
and COPD, the extent of exertional hypoxemia is often
profound in patients with advanced ILD and may be
more severe than in COPD. The objectives of this study
were to: (i) identify clinical and physiological variables
SUMMARY AT A GLANCE
Few studies have evaluated the severity of exertional
hypoxemia in ﬁbrotic interstitial lung disease (ILD).
We demonstrate that exertional hypoxemia is more
common and severe in ﬁbrotic ILD compared to
COPD. More ILD-speciﬁc studies are needed to
evaluate the potential utility of ambulatory oxygen
in ﬁbrotic ILD.
Correspondence: Christopher J. Ryerson, Department of
Medicine, St. Paul’s Hospital, 1081 Burrard Street, Ward 8B,
Vancouver, BC V6Z 1Y6, Canada. Email: email@example.com
Received 24 April 2017; invited to revise 21 June, 22 August
and 18 October 2017; revised 21 July, 20 September and
31 October 2017; accepted 31 October 2017.
(Associate Editor: Melissa Benton; Senior Editor: Fanny Ko).
© 2017 Asian Paciﬁc Society of Respirology Respirology (2018) 23, 392–398