Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O2 (P(tc)O2) > or = 20% (PD(20)P(tc)O2) in young children. Rint was calculated using the linear back-extrapolation method (Rint(L)) and the end-interrupter method (Rint(EI)). Twenty-two children (mean age, 5.2 +/- 1.1 years; range, 3.4 - 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. P(tc)O2, Rint(L), and Rint(EI) were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation. P(tc)O2 decreased significantly during M challenge, from 85 +/- 6 mmHg (B) to 62 +/- 9 mmHg (P < 0.05), and increased after BD inhalation, to 82 +/- 8 mmHg. Rint(L) and Rint(EI) increased significantly during M challenge, from 0.94 +/- 0.2 KPa/L/s and 1.11 +/- 0.19 KPa/L/s (B) to 1.27 +/- 0.35 KPa/L/s and 1.47 +/- 0.37 KPa/L/s, respectively (P < 0.05), and decreased after BD inhalation to 0.80 +/- 0.17 KPa/L/s and 0.95 +/- 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD(20)P(tc)O2 at a dose of M ranging from 50-400 microg. At the PD(20)P(tc)O2, significant changes in Rint(L) and Rint(EI) (sensitivity index (SI) > or = 2) were found in 79% and 63% of children, respectively. We conclude that: 1) M challenge using P(tc)O2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge.

Patterns of events occurring at the end of apneas have rarely been reported in infants. No previous studies have compared these patterns to those of spontaneous events during sleep. We examined 163 isolated apneas in 17 infants (47 +/- 4 wk postconceptional age) who underwent polysomnography for suspected upper airway problems. Mean apnea duration was 6.5+/-1.5 s (range, 5 to 11.5 s), 78% of apneas occurred in active sleep, and 67% of apneas were obstructive. We recorded the occurrence of body movement or augmented breath and analyzed changes in EEG frequency > or = 1 s, heart rate, and oxygen saturation value at the end of apneas and of a control ventilatory period defined as a period of breathing equal in duration to the apnea and preceding the apnea by 1 min. We found that 7.9% of apneas and 11.6% of control periods were followed by an augmented breath and that 14.1% of apneas and 0.5% of control periods were followed by a body movement. The percentages of motor events or no event differed significantly after the apneas (p = 0.008) compared with the control periods. A significant increase in EEG frequency was observed at the end of the apneas compared with the control periods (p < 0.04). EEG frequency increased after 61% of the apneas. Neither heart rate nor oxygen saturation value changed after the control periods. Heart rate decreased significantly after the apneas not followed by a motor event (p = 0.02) but not after the apneas followed by a body movement. We conclude that 1) at termination of isolated apneas in infants, a motor event was rare, whereas an EEG frequency increase was common; 2) event patterns at apnea termination differed from those at control period termination.

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