Study objectives: To determine predictors of oxygen
desaturation during submaximal exercise in patients with various lung
Design and setting: This retrospective case
series used pulmonary function laboratory results from all patients
referred to a major tertiary-care center.
measurements: All patients ≥ 35 years old who underwent
spirometry, diffusing capacity of the lung for carbon monoxide
(Dlco), lung volumes, and pulse oximetry during 3-min
submaximal step-test exercise during 1996 were included (4,545 men and
3,472 women). Logistic regression models, correcting for gender, age,
and weight, determined the odds ratios (ORs) for oxygen desaturation of≥
4% during exercise for each category of lung function abnormality
(compared to those with entirely normal lung function).
Results: Approximately 74% of the patients had airways
obstruction, while only 5.6% had restriction of lung volumes. One
third of those with obstruction had a low Dlco, compared to
56% with restriction, while 2.7% had a low Dlco without
obstruction or restriction. The risk of oxygen desaturation during
submaximal exercise was very high (OR, 34) in patients with restriction
and low Dlco (as in interstitial lung disease) and in
patients with obstruction and low Dlco (as in COPD; OR,
18), intermediate (OR, 9) in patients with only a low Dlco,
and lowest in those with a normal Dlco (OR, 4 if
restricted; OR, 2 if obstructed). A cut point of Dlco< 62% predicted resulted in 75% sensitivity and specificity for
exercise desaturation. No untoward cardiac events occurred in any
patients during or following the submaximal exercise tests.
Conclusions: The risk of oxygen desaturation during
submaximal exercise is very high in patients with a low
Dlco. Submaximal exercise tests are safe, even in elderly
patients with heart and lung diseases.