Chemical control of respiratory frequency and tidal volume during sleep in preterm infants.

During a given sleep state, respiration changes from periodic to regular and vice-versa. Because such spontaneous changes occur without changes in electro-encephalogram (EEG), electro-oculogram (EOG), electro-cardiogram (ECG) or body movements, we hypothesized that they are induced by chemical stimuli such as CO2. To test this hypothesis we examined 12 preterm infants in whom spontaneous changes in respiratory pattern were allowed to occur within the same sleep state, and infants in whom such changes were induced by inhalation of 0.3% to 1.2% CO2. Using a nosepiece and a screen flowmeter we measured the respiratory pattern, VE, f, VT, TI, TE, Ttot, VT/TI, TI/Ttot and PACO2. In REM sleep, spontaneous changes from periodic to regular were associated with increase in VE from 0.466 (mean) to 0.530 L/min (P less than 0.5) and CO2 induced changes accompanied by an increase in VE from 0.416 to 0.571 L/min (P less than 0.05). Similarly in N-REM sleep, VE increased from 0.385 to 0.445 L/min (P less than 0.05) during CO2 induced changes, and from 0.420 to 0.454 L/min (P less than 0.05) during CO2 induced changes, and from 0.420 to 0.454 L/min (P less than 0.05) during CO2 induced changes. Increased VE produced both spontaneously or by CO2 administration was associated with decreased VT, decreased Ttot, decreased VT/TI and slight increase in PACO2. We suggest that changes in respiratory pattern occurring within the same sleep state are chemically mediated.