Al. Patel et al., Inspired CO2 and O-2 in sleeping infants rebreathing from bedding: relevance for sudden infant death syndrome, J APP PHYSL, 91(6), 2001, pp. 2537-2545
Some infants sleep facedown for long periods with no ill effects, whereas o
thers become hypoxemic. Rebreathing of expired air has been determined by C
O2 measurement; however, O-2 levels under such conditions have not been det
ermined. To evaluate this and other factors influencing inspired gas concen
trations, we studied 21 healthy infants during natural sleep while facedown
on soft bedding. We measured gas exchange with the environment and bedding
, ventilatory response to rebreathing, and concentrations of inspired CO2 a
nd O-2. Two important factors influencing inspired gas concentrations were
1) a variable seal between bedding and infants' faces and 2) gas gradients
in the bedding beneath the infants, with O-2-poor and CO2-rich air nearest
to the face, fresher air distal to the face, and larger tidal volumes being
associated with fresher inspired air. Minute ventilation increased signifi
cantly while rebreathing because of an increase in tidal volume, not freque
ncy. The measured drop in inspired O-2 was significantly greater than the a
ccompanying rise in inspired CO2. This appears to be due to effects of the
respiratory exchange ratio and differential tissue solubilities Of CO2 and
O-2 during unsteady conditions.