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Pattern of Variables Describing Desaturator COPD Patients, as Revealed by Cluster Analysis^*

^* From the "A. Galateo" Lung Disease Hospital (Drs. Toraldo and Lorenzo), Third Division ASL/LE/1, San Cesario di Lecce, Lecce, Italy; the Laboratory of Human Anatomy (Drs. Nicolardi and De Nuccio), Department of Biological and Environmental Sciences and Technologies, University of Lecce, Lecce, Italy; and Pulmonary Unit (Dr. Ambrosino), Cardio-Thoracic Department. University Hospital, Pisa, Italy.

Correspondence to: Domenico Maurizio Toraldo, MD, Via A.C. Casetti 73100 Lecce, Italy; e-mail: d.torald{at}tin.it

Study objectives: The aims of this study were to define, by cluster analysis, a pattern of clinical variables that differentiate desaturator (D) from nondesaturator (ND) patients affected by COPD, and to identify daytime variables that are predictive of nocturnal desaturation.

Patients: Fifty-one random, consecutive COPD outpatients (20 women; mean [± SD] age, 69.6 ± 4.0 years) with mild daytime hypoxemia (PaO₂, 60 to 70 mm Hg) were enrolled into the study. Obstructive sleep apnea syndrome patients were excluded.

Measurements and results: Lung volumes, arterial blood gas levels, and mean pulmonary artery pressure (MPAP) were measured, and nocturnal desaturation was evaluated with nighttime polygraphy. With least squares simple linear regression, the percentage of total recording time was highly correlated with a total nocturnal recording time of arterial oxygen saturation of < 90 mm Hg (T₉₀) and MPAP (R = 0.84; R² = 71.20%); T₉₀ was also highly correlated with daytime PaCO₂ (R = 0.70; R² = 48.96%). Multiple regression showed that T₉₀ was highly correlated with both MPAP and PaCO₂ (R² = 97.75%). Hierarchical cluster analysis conducted with these three variables showed that D and ND patients differed in both nocturnal and daytime variables. The mean T₉₀ was 30 ± 3.5% in 19.2% and 8%, respectively, of the D and ND groups. Moreover, two D subgroups differing in MPAP and two ND subgroups differing in PaCO₂ were identified.

Conclusions: D patients may be identified by a pattern of T₉₀, MPAP, and PaCO₂ values, rather than by T₉₀ alone, with the latter two variables being predictors of nocturnal desaturation severity.

Key Words: arterial oxygen saturation • cluster analysis • COPD • hypoxemia • pulmonary hypertension • sleep-related hypoxemia

This article has been cited by other articles:

				S. Kostianev, B. Marinov, D. Iluchev, D. Toraldo, G. Nicolardi, F. De Nuccio, and N. Ambrosino Is the more (intricate) the better? Chest, October 1, 2006; 130(4): 1275 - 1276. [Full Text] [PDF]