ORIGINAL ARTICLES

POLYCYTHÆMIA AND IRON DEFICIENCY IN PULMONARY "EMPHYSEMA"

The aim of this study was to assess the erythropoietic response to hypoxaemia in patients with diffuse idiopathic pulmonary fibrosis (DIPF), and to speculate on the underlying mechanisms.

Patients on an established chronic respiratory failure due to DIPF or chronic obstructive pulmonary disease (COPD) were studied. The erythropoietic response to hypoxaemia in both conditions was assessed. We studied 18 patients with DIPF and 29 patients with COPD in respiratory failure in a stable stage, free from acute infection and congestive heart failure. Blood gases, erythrocytic parameters, as well the serum levels of iron, ferritin and erythropoietin were determined.

All the DIPF patients studied, apart from two, had normal or subnormal haematocrit values. The patients with COPD had an inconsistant response to hypoxaemia; 12 had normal or subnormal haematocrit values and the remaining 17 were erythraemic. The mean value of erythropoietin (EPO) in both DIPF and COPD patients was significantly higher than normal.

In conclusion, patients with DIPF exhibit a lack of erythropoietic response to hypoxaemia, despite the augmented erythropoietin levels. This may reflect a defective bone marrow erythropoietic response in DIPF patients. It is suggested that the pathophysiology of DIPF underlies this mechanism.

PURPOSE: An association between activation of the renin-angiotensin system and enhanced erythropoiesis has been observed in patients with several diseases, including congestive heart failure and hypertension. Our goal was to examine whether the renin-angiotensin system is associated with secondary erythrocytosis in patients with chronic obstructive pulmonary disease (COPD).

SUBJECTS AND METHODS: Plasma renin activity, plasma aldosterone concentration, serum erythropoietin level, and serum angiotensin converting enzyme (ACE) activity were measured in 12 patients with COPD and secondary erythrocytosis [mean (±SD) hematocrit of 53% ± 3%] and in 12 matched controls with COPD who did not have erythrocytosis (hematocrit 45% ± 5%). All patients had chronic hypoxemia (PaO₂ <60 mm Hg).

RESULTS: Both plasma renin and aldosterone levels were threefold greater in patients with secondary erythrocytosis compared to controls. No difference in erythropoietin levels was observed between patients with or without secondary erythrocytosis. Renin levels (r = 0.45; P = 0.02) but not erythropoietin levels (r = 0.15; P = 0.47) were correlated with hematocrit in the entire sample. Renin levels and PaO₂ were the only variables independently and significantly associated with hematocrit values in a multiple linear regression model.

CONCLUSION: Activation of the renin-angiotensin system is associated with the development of secondary erythrocytosis in chronically hypoxemic patients with COPD. The exact mechanism is not yet fully understood, but angiotensin II may be responsible for inappropriately sustained erythropoietin secretion or direct stimulation of erythroid progenitors.