Effect of exercise on three-equation D[sub L]CO in sarcoidosis and idiopathic pulmonary fibrosis

Impairment in CO pulmonary diffusing capacity (D[sub L]CO) may be a factor limiting exercise in interstitial lung disease (ILD). We used the three-equation D[sub L]CO (D[sub L]CO[sub 3EQ]) method to measure single breath D[sub L]CO during exercise to determine whether limited ability of D[sub L]CO to increase during exercise is related to exercise induced hypoxemia in two different ILD, idiopathic pulmonary fibrosis (IPF), and sarcoidosis. The D[sub L]CO[sub 3EQ] technique involves continuous monitoring of exhaled CO and an inert tracer gas and accounts for CO uptake during the inhalation, breath holding, and exhalation phases of a breathing maneuver. This technique determines D[sub L]CO without requiring breath holding, allowing its use in patients with ILD during exercise. In 15 patients with ILD (8 sarcoidosis and 7 IPF) and 7 normal, healthy subjects, we determined D[sub L]CO[sub 3EQ] at rest and during 2 levels of steady state exercise, 35% and 70% of the previously determined maximal power output. From rest to the 70% level of exercise, D[sub L]CO[sub 3EQ] (units in mL⋅min⁻¹⋅mmHg⁻¹ and in % predicted D[sub L]CO[sub SB] at rest) increased from 34.6+SE 2.7 (118%) to 48.7+SE 4.0 (164%) in control subjects, from 23.0 +SE 2.8 (86%) to 33.8 +SE 3.8 (126%) in sarcoidosis, and from 15.9 +SE 0.7 (67%) to 20.5 +SE 0.8 (87%) in the IPF patients. The % increase in D[sub L]CO[sub 3EQ] for a given increase in VO₂ expressed as % of maximal predicted, was smaller in the IPF group when compared to both the sarcoidosis (p<0.0001) and the control groups (p