Quantitative 15 steps exercise oximetry as a marker of disease severity inpatients with chronic obstructive pulmonary disease

Background: Hypoxemia is a common complication of chronic obstructive pulmo nary disease and a major factor in patients' prognosis and quality of life. The response to exercise has been evaluated by various means but no standa rdization has been accepted. Objectives: To suggest a simple outpatient technique for evaluating the res ponse of arterial oxygen saturation to exercise for use as a marker of dise ase severity. Patients and methods: Ninety-six patients with various degrees of COPD1 wer e divided into three groups: mild (forced expiratory volume in 1 sec >65%), moderate (FEV12 between 50 and 65%), and severe (FEV1 <50%). Using continu ous oximeter recording we measured oxygen saturation during 15 steps of cli mbing, and quantified oxygen desaturation by measuring the "desaturation ar ea," defined as the area under the curve of oxygen saturation from the begi nning of exercise through the lowest desaturarion point and until after rec overy to the baseline level of oxygen percent saturation. Desaturation was correlated to spirometry, lung gas volumes, blood gas analysis, and 6 min w alking distance. Results: A good correlation was found between severity of COPD and baseline SaO(2),(3) lowest SaO(2), recovery time, and desaturation area. A negative correlation was found between desaturation area and FEV, (r=-0.65), FEV1/f orced vital capacity (r=-0.58), residual volume to total lung capacity (r=0 .52), and diffusing lung capacity for carbon monoxide (r=-0.52). In stepwis e multiple regression analysis only FEV, correlated significantly to desatu ration area. A good correlation was noted between 6 min walking distance an d desaturation area with the 15 steps technique (r=0.56). Conclusions: In patients with severe COPD, arterial hypoxemia during exerci se can be assessed by simple 15 steps oximetry. This method can serve both as a marker for disease severity and to determine the need for oxygen suple mentation.