INFLUENCE OF SLEEP ON PULMONARY CAPILLARY VOLUME IN NORMAL AND ASTHMATIC SUBJECTS

To determine the effect of sleep upon intrapulmonary blood volume (as reflected by measurements of pulmonary capillary volume (Vc), 5 normal subjects and 15 asthmatic patients were monitored overnight in our sl eep laboratory. Ve was determined before and after sleep from four mea surements of DL(CO) using a single-breath technique, with subjects ins piring different oxygen concentrations for each measurement. Spirometr y was performed in the supine posture before presleep Ve measurements and immediately upon awakening before postsleep Ve measurements. As de fined by a greater than or equal to 15% overnight reduction in FEV(1), 10 asthmatic subjects demonstrated nocturnal worsening. FEV(1) decrea sed from 61.2 +/- 15.1 to 40.9 +/- 16.2% of predicted (p = 0.0001) in the 10 asthmatic patients with nocturnal worsening. Asthmatic patients with nocturnal worsening also demonstrated a 15.7 +/- 16.6% increase in VC from presleep to awakening (p = 0.02). Normal subjects and asthm atic patients without nocturnal worsening exhibited no significant ove rnight change in FEV(1) or Vc. We conclude that in asthmatic patients with nocturnal worsening sleep is likely associated with an increase i n intrapulmonary blood volume.