Cross-sectional study of loop gain abnormalities in childhood obstructive sleep apnea syndrome.

STUDY OBJECTIVES: We aimed to assess ventilatory control in typically developing children with and without obstructive sleep apnea (OSA). METHODS: Otherwise healthy children referred for suspicion of OSA were recruited. In addition to polysomnography, we analyzed loop, controller and plant gains (ie, LG, CG, and PG), which reflect the stability of control, chemoreceptor sensitivity and the pulmonary control of blood gases in response to changes in ventilation, respectively, from tidal breathing recordings during wakefulness. Two bivariate (ventilation, end-tidal CO2: one unconstrained and one constrained) and one trivariate (plus end-tidal oxygen) unconstrained model were used to assess model consistency and oxygen chemosensitivity. RESULTS: In sum, 54 children (median age 11.6 years) were included. Children with OSA (n = 19, [obstructive apnea-hypopnea index] OAHI ≥2.h-1) had a higher plant gain compared with those without OSA (n = 35), and it was positively correlated with apnea hypopnea index (AHI) (r2 = 0.10, p < 0.020). The two models showed consistent results. The bivariate constrained model showed that children with OAHI ≥5.h-1 showed an increased steady-state plant gain compared with children with OAHI <5.h-1. The trivariate model did not show evidence of any abnormality of oxygen chemosensitivity. CONCLUSION: Plant gain may contribute to OSA pathophysiology in children, and therapies directed at its reduction should be tested.

The utility of acoustic pharyngometry and rhinometry in pediatric obstructive sleep apnea syndrome.

OBJECTIVE: Our objective was to evaluate the usefulness of acoustic pharyngometry and rhinometry in assessing obstructive sleep apnea (OSA) syndrome in children. PATIENTS/METHODS: Patients who were hospitalized for polysomnography underwent acoustic pharyngometry and rhinometry in sitting and supine positions to measure anatomical (pharyngeal and nasopharyngeal) volumes and collapsibility characteristics (reduction of pharyngeal volume, estimated pharyngeal compliance, and reduction of nasopharyngeal volume). RESULTS: In this study, we prospectively enrolled 103 children (median age, 10.4 years; 47 girls). Measures obtained from rhinometry correlated with height and were further height-normalized whereas measures obtained from pharyngometry did not correlate with height. Sleep apnea was ruled out in 51 subjects, while 52 children fulfilled OSA criteria (35 with obstructive apnea-hypopnea index ≥ 2 and < 5.h-1 [mild] and 17 with an index ≥ 5). The three groups differed on the z-score of BMI, the reduction of pharyngeal volume when supine, the estimated pharyngeal compliance and the supine normalized nasopharyngeal volume. These four factors linearly correlated with the apnea index even though children without OSA and mild OSA were found to be similar overall. A multivariate analysis with apnea index as the dependent variable and BMI z-score, neck circumference, mean pharyngeal area in supine position, estimated pharyngeal compliance and normalized nasopharyngeal volume as independent variables, showed that only BMI z-score and estimated compliance remained independent predictors of obstructive apnea (r2 value = 0.25, p < 0.0001). CONCLUSION: An increase in pharyngeal compliance is an independent risk factor of OSA syndrome in children; it can be measured using acoustic pharyngometry while awake.

24-hour BP in children with congenital central hypoventilation syndrome.

OBJECTIVE: To study circadian BP patterns in patients with congenital central hypoventilation syndrome (CCHS). DESIGN: Case-control study. SETTING: Teaching hospital in Paris, France. PATIENTS: Eleven patients with CCHS (median age, 13 years; range, 6 to 18 years) and 11 sex- and height-matched control subjects. INTERVENTION: None. METHODS: Each subject underwent 24-h ambulatory BP monitoring. Oxygen saturation and end-tidal PCO(2) were monitored noninvasively. Polysomnography was performed to determine sleep times. All patients with CCHS received mechanical ventilation during sleep. Mean values for systolic BP (SBP) and diastolic BP (DBP) during wakefulness and sleep were analyzed. Nocturnal BP "dipping" was defined as the difference in mean SBP (and/or DBP) between wakefulness and sleep, divided by individual waking mean values. BP "dippers" were defined as subjects showing at least 10% nocturnal dipping. RESULTS: Patients with CCHS had BPs in the low normal range of normative data. As compared to control subjects, patients with CCHS had lower BP during wakefulness (p = 0.003 and p = 0.016 for SBP and DBP, respectively), and higher BP during sleep (p = 0.016 and p = 0.002). Nocturnal BP dipping was abnormally reduced in patients with CCHS (p = 0.000). Ten of the 11 patients with CCHS were BP nondippers, compared to none of the control subjects. CONCLUSION: The abnormal circadian BP pattern observed in children and adolescents with CCHS may be related to autonomic nervous dysfunction. Lifelong cardiovascular follow-up is recommended for patients with CCHS.

Sleep desaturation: comparison of two oximeters.

Oxygen saturation is measured by pulse oximetry during sleep studies. Body movements and peripheral vasoconstriction related to respiratory events may interfere with measurements by conventional oximeters. Our objective was to compare the detection rate of sleep desaturations by two oximeters, one of which used new motion-resistant technology. We studied 34 children (median age, 13 years; range, 3-18) with suspected sleep-disordered breathing. During polysomnography, oxygen saturation was measured by two oximeters set on fast mode: the motion-resistant Radical oximeter (2-sec averaging), and the conventional Nellcor N-200 oximeter (2-3-sec averaging). Respiratory events were identified based on airflow signal. The numbers of respiratory event-related desaturations > or =3% or > or =5% detected by each oximeter were determined. Valid desaturations were defined using the Nellcor plethysmographic waveform and the Radical signal-quality data. Hypoxemic respiratory events were those with associated valid desaturation. In total, 1,278 respiratory events were identified and pooled. Basal oxygen saturation measured just before event onset was not different between oximeters (Radical: 98%; range, 84-100; Nellcor: 97%; range, 86-100; P = ns). However, the Radical detected a greater number of valid desaturations than did the Nellcor for any level of desaturation (respectively, N = 651 and 476 desaturations > or =3%, P < 0.001; and N = 232 and 146 desaturations > or =5%, P = 0.01). Consequently, for each patient, the number of hypoxemic respiratory events per hour of sleep was greater using the Radical than using the Nellcor (P = 0.002, and P = 0.021, for desaturation > or =3% and > or =5%, respectively). In conclusion, standardized oximeter settings are required to achieve more accurate assessments of hypoxemia in children with sleep-disordered breathing.