Journal of Applied Physiology, Vol 70, Issue 6 2582-2586, Copyright © 1991 by American Physiological Society
Effects of CO2 rebreathing on pulmonary mechanics in premature infants
M. J. Miller, J. M. DiFiore, K. P. Strohl, W. A. Carlo and R. J. Martin
Department of Pediatrics, Rainbow Babies and Childrens Hospital, Case Western Reserve University, Cleveland, Ohio 44106.
The effects of hypercapnia produced by CO2 rebreathing on total pulmonary,
supraglottic, and lower airway (larynx and lungs) resistance were
determined in eight premature infants [gestational age at birth 32 +/- 3
(SE) wk, weight at study 1,950 +/- 150 g]. Nasal airflow was measured with
a mask pneumotachograph, and pressures in the esophagus and oropharynx were
measured with a fluid-filled or 5-Fr Millar pressure catheter. Trials of
hyperoxic (40% inspired O2 fraction) CO2 rebreathing were performed during
quiet sleep. Total pulmonary resistance decreased progressively as
end-tidal PCO2 (PETCO2) increased from 63 +/- 23 to 23 +/- 15 cmH2O.l-1.s
in inspiration and from 115 +/- 82 to 42 +/- 27 cmH2O.l-1.s in expiration
between room air (PETCO2 37 Torr) and PETCO2 of 55 Torr (P less than 0.05).
Lower airway resistance (larynx and lungs) also decreased from 52 +/- 22 to
18 +/- 14 cmH2O.l-1.s in inspiration and from 88 +/- 45 to 30 +/- 22
cmH2O.l-1.s in expiration between PETCO2 of 37 and 55 Torr, respectively (P
less than 0.05). Resistance of the supraglottic airway also decreased
during inspiration from 7.2 +/- 2.5 to 3.6 +/- 2.5 cmH2O.l-1.s and in
expiration from 7.6 +/- 3.3 to 5.3 +/- 4.7 cmH2O.l-1.s at PETCO2 of 37 and
55 Torr (P less than 0.05). The decrease in resistance that occurs within
the airway in response to inhaled CO2 may permit greater airflow at any
level of respiratory drive, thereby improving the infant's response to CO2.
