Mechanisms of hypertension in patients with chronic obstructive pulmonary disease and acute respiratory failure

PURPOSE: To investigate the effects of hypoxemia, hypercapnia, and cardiovascular hormones (norepinephrine, endothelin-1, and atrial natriuretic factor) on blood pressure during acute respiratory failure. PATIENTS AND METHODS: Patients with chronic obstructive pulmonary disease and acute respiratory failure were divided into four groups of 10 patients each: hypoxemia-normocapnia, hypoxemia-hypercapnia, hypoxemia-hypocapnia, and normoxemia-hypercapnia. Plasma norepinephrine levels were determined by high-performance liquid chromatography with electrochemical detection. Plasma endothelin-1 and atrial natriuretic factor levels were radioimmunoassayed after chromatographic preextraction.RESULTS: Systolic blood pressure and cardiovascular hormone levels were greater in patients with hypercapnia (whether or not they also had hypoxemia) than in those with normocapnia and hypoxemia. For example, in patients with hypercapnia and normoxemia, the mean (+/- SD) systolic blood pressure was 183+/-31 mm Hg and the mean norepinephrine level was 494+/-107 pg/mL, as compared with 150+/- 6 mm Hg and 243+/-58 pg/mL in those with normocapnia and hypoxemia (both P<0.05). Similar results were seen for endothelin-1 and atrial natriuretic factor levels, and for the comparisons of hypoxemic patients who were hypercapnic with those who were normocapnic. CONCLUSIONS: These results suggest that blood carbon dioxide levels, rather than oxygen levels, are responsible for hypertension during acute respiratory failure, perhaps as a result of enhanced sympatho-adrenergic activity.