No abstract

Noninvasive studies of ventilation and ventilatory pattern were performed serially in 15 normal infants in the first 4 mo of life during REM and quiet sleep with the barometric method. We measured tidal volume (VT), total respiratory cycle time (Ttot), inspiratory time (Ti), expiratory time (TE), mean inspiratory flow (VT/TI), and respiratory "duty cycle" (TI/Ttot). Vt, Ttot, TI, TE, VT/TI, and VT/Ttot but not TI/Ttot increased with age. In all age groups, Ttot, TI, and TE but not VT/TI were greater in quiet than in REM sleep. In the first 2 mo of life, VT was greater in quiet than in REM sleep; in the older infants, VT/Ttot was smaller in quiet than in REM sleep. TI/Ttot was not dependent on sleep state. Thus, because VT/Ttot = VT/TI X TI/Ttot, the increase in VT/Ttot with age results from an increase in mean inspiratory flow rather than from changes in respiratory "duty cycle". Further, the "on-switching" as well as the "off-switching" of inspiratory activity depends on sleep state.

SummaryThe time spent in REM, quiet, and indeterminate sleep was computed in 13 aborted SIDS infants and compared to that spent in the same sleep states .in 19 normal infants. Aborted sudden infant death syndrome (SIDS) infants were studied within a week of their aborted SIDS episode and subsequently at monthly intervals through the age of 4 months. Normal infants were studied at 1,2,3, and 4 months of age. Sleep staging was performed by two independent observers using electroencephalogram, electrooculogram, electromyogram and behavioral criteria. Although there was an increase in the percentage of time spent in quiet sleep with age in both normal and aborted SIDS infants, the significantly greater regression coefficients in normal infants (6.3 versus 2.9; P < 0.01) indicate that there are differences in the two groups and suggest a maturational abnormality or delay in sleep state distribution in aborted SIDS infants. SpeculationThe results of this study suggest that the differences in sleep state distribution between aborted sudden infant death syndrome and normal infants share a common pathophysiologic alteration with the ventilatory and cardiac abnormalities reported by us elsewhere, perhaps involving the catecholaminergic system. Previous studies from this laboratory have demonstrated that infants with aborted sudden infant death syndrome (SIDS) have increased heart rate and decreased heart rate variability (7), smaller QT index (3), and a greater COz-induced increase in minute ventilation (4) than do normal infants during both REM and quiet sleep. We have hypothesized that these findings are most consistent with an increase in the level of sympathoadrenal activity. Because the activity of the autonomic nervous system fluctuates during each sleep state, especially during REM sleep (2), we asked whether these ventilatory and cardiac differences depend on differences in the time spent in each sleep state. We, therefore, compared the time spent in REM, quiet, and indeterminate sleep in 13 aborted SIDS infants and in 19 age-matched normal infants during serial observations at monthly intervals in the first 4 months of life. MATERIALS AND METHODS STUDY POPULATIONWe defined an aborted SIDS infant as one who has experienced at least one episode of unexplained apnea and unresponsiveness with cyanosis or pallor requiring mouth to mouth resuscitation or vigorous physical stimulation for revival. The mean age of the infants at the time of the first aborted SIDS episode was 2 months, with a range of 1 to 4 months. Nine of the 13 infants were observed to be asleep shortly before their apneic episode; the level of 1 Of consciousness was unknown in the remaining four. Detailed clinical and laboratory assessment failed to reveal an explanation for the aborted SIDS episode. The laboratory evaluation included blood counts, serum glucose, calcium, magnesium, sodium, potassium and chloride, acid-base and blood gas analysis, chest x-ray, conventional 12-lead electrocardiogram, an electroencephalogram (EEG), and a roentgenographi...

The effect of CO2 on the ventilatory pattern of 18 normal infants was studied during sleep at monthly intervals through the age of 4 mo. Using the barometric method, we measured tidal volume (VT), respiratory cycle time (Ttot), inspiratory time (TI), and expiratory time (TE). Two percent CO2 produced no change in TI and a significant increase in VT and mean inspiratory flow (VT/TI). There was no consistent change in TE or Ttot in either sleep state at any age. The percent increase from base line in instantaneous minute ventilation (VT/Ttot) during REM sleep was similar to that during quiet sleep. We conclude that with inhalation of 2% CO2 in the first 4 mo of life 1) the increase in VT/Ttot results solely from an increase in VT and the percent increase in VT/Ttot is the same in both sleep states and 2) the reflex termination of inspiration by inflation does not play an important role in eupnea during sleep because the increase in VT is not associated with a decrease in TI.

T o assess ventilatory control during sleep in infants at risk for the sudden infant death syndrome (SIDS), we made serial measurements of resting tidal volume (Vt), respiratory cycle time (Ttot), and the ventilatory changes resulting from inhalation of 2% Con in aborted S l D S infants in rapid eye movement and quiet sleep and compared them to a group of normal infants during the first 4 months of life. Ventilation was measured by the barometric method, and sleep was staged using electroencephalogram, electrooculogram, and electromyogram and behavioral criteria.Although resting instantaneous minute ventilation (Vt/Ttot) was virtually the same in both groups of infants, Vt tended to be smaller (by up to 50% in the first 2 months) and Ttot tended to be shorter in aborted S l D S than in normal infants in both rapid eye movement and quiet sleep. The increase in the mean Vt/Ttot with 2% COz is greater by about 5 to 20% in aborted SIDS than in normal infants at 3 and 4 months of age in both sleep states. These findings, together with our previous findings that aborted S l D S infants have an increase in heart rate and a shortening of the QT interval, provide indirect evidence that infants a t high risk for S l D S may have increased sympathoadrenal activity.