C-reactive protein correlates with tissue oxygen availability in patients with stable COPD

Simonetta Baldi¹, Gian Domenico Pinna¹, Piera Mombaruzzo¹, Milena Biglieri¹, Angelo De Martini¹, Paolo Palange²

¹Department of Pneumology and Biomedical Engineering, Scientific Institute of Montescano, Salvatore Maugeri Foundation IRCCS, Pavia, Italy; ²Respiratory Pathophysiology Unit, Clinical Medicine Department, “La Sapienza” University, Rome, Italy

Background: Arterial oxygen tension, oxygen delivery to tissue, and systemic inflammation are recognized as pivotal factors in the progression of chronic obstructive pulmonary disease (COPD). However, interconnections between systemic inflammation and tissue oxygen availability are scantly investigated. Tissue oxygen availability depends on arterial PaO₂, oxygen concentration, hemoglobin oxygen affinity (P₅₀), and hemoglobin oxygen binding capacity (ceHb). As the integrated changes of those indices are summarized by oxygen extraction tension (PaO_2x), the objective of this study was to explore the association between C-reactive protein (CRP) blood levels and either PaO_2x or each of its determinants, in stable COPD.

Materials and methods: Blood CRP and oxygen status of arterial blood were measured at rest while breathing room air in 44 moderate to severe stable COPD patients. PaO_2x was calculated along the shape of oxygen binding curve as the oxygen tension resulting from removal of 2.3 mmol of oxygen per liter of blood. Multiple linear regression analysis was performed with PaO₂, ceHb, and P₅₀ as independent variables, and CRP as the dependent variable, adjusting for age and sex. The analysis was repeated using PaO_2x as a sole independent variable.

Results: Multiple linear regression analysis indicated that ceHb, PaO₂, and P₅₀, were significant and independent predictors of CRP (R² = 0.52, p < 0.0001). PaO_2x alone was an even stronger predictor of CRP (R² = 0.62, p < 0.0001).

Conclusions: These findings indicate that physiological determinants of tissue oxygen availability are independently associated with CRP blood levels. Thus, improvement of tissue oxygen availability is a central therapeutic option to modulate the severity of systemic inflammatory processes in patients with COPD.

Keywords: COPD, C-reactive protein, oxygen extractivity, systemic inflammation