Platelet size in patients with chronic airflow obstruction with and without hypoxaemia.

Platelet size, expressed as mean platelet volume, was estimated in 35 patients with chronic airflow obstruction and a wide range of arterial oxygen tension (PaO2) values. In these patients there was a negative correlation between MPV and PaO2 (r = -0.70). Mean platelet volume was greater (9.41 (0.86) fl) in 20 patients with an arterial PaO2 of 8 kPa (60 mm Hg) or less than in 18 normal subjects (8.21 (0.63) fl; p less than 0.001). After 24 hours of supplemental oxygen treatment there was a small fall in mean platelet volume, from 9.47 (1.06) to 8.96 (0.8) fl (p less than 0.05) in 12 hypoxaemic patients (PaO2 breathing air less than or equal to 8 kPa) but no change in nine non-hypoxaemic patients. Larger platelets are considered to be haemostatically more active, leading to abnormal platelet function, which may contribute to the development of pulmonary vascular damage in chronic hypoxaemia. Supplemental oxygen may partially reverse these changes by modifying platelet size and activity.