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 sleep laboratory. VC was determined before and after sleep from four measurements of DLCO using a single-breath technique, with subjects inspiring different oxygen concentrations for each measurement. Spirometry was performed in the supine posture before presleep VC measurements and immediately upon awakening before postsleep VC measurements. As defined by a > or = 15% overnight reduction in FEV1, 10 asthmatic subjects demonstrated nocturnal worsening. FEV1 decreased 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 asthmatic patients without nocturnal worsening exhibited no significant overnight change in FEV1 or VC. We conclude that in asthmatic patients with nocturnal worsening sleep is likely associated with an increase in intrapulmonary blood volume.