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Thoracic insufficiency syndrome (TIS) is a collection of chest and spine malformations that results in progressively restrictive pulmonary mechanics and an inability of the thorax to adequately support lung growth. Many children with TIS are too young to perform standard pulmonary function tests, yet need functional assessments of their restrictive thoracic disease. We report on the sleep architecture and frequency of sleep-related breathing abnormalities in 11 children with TIS who underwent overnight polysomnography from retrospective chart review. Ten of 11 (92%) had sleep disordered breathing as defined by currently accepted criteria of apnea-hypopnea index (AHI) >2 events/hr. The median AHI was 4.3 events/hr, with obstructive hypopneas (median 3.7 events/hr) accounting for 75% of abnormalities. Respiratory events occurred most frequently during REM sleep (median REM-AHI 17.3 events/hr), and were associated with oxyhemoglobin desaturation, and rarely carbon dioxide retention. Sleep disordered breathing with hypoxemia appears to be a common but under recognized problem among children with TIS. Polysomnogram may have a role as a non-invasive screening tool used in conjunction with other functional respiratory assessments in children with TIS, and warrants further study in a prospective manner.

The effects of vagal nerve stimulation on sleep-related breathing have not been well-described in children. Vagal nerve stimulation was reported to cause decreases in airflow during sleep, although most studies reported this condition to be clinically insignificant. We present a retrospective case series of nine children who underwent polysomnography after vagal nerve-stimulator placement. All children, except for one, had sleep-disordered breathing after stimulator implantation. We describe in further detail a child who manifested severe, obstructive sleep apnea postimplantation, with apneas occurring regularly and consistently with stimulator activity, resulting in an elevated apnea-hypopnea index of 37 per hour. Polysomnography was repeated with the stimulator turned off, and revealed complete resolution of the stimulator-related sleep apnea. With the vagal nerve stimulator back on, continuous positive airway pressure treatment was effective in normalizing the apnea-hypopnea index. This study demonstrates that severe and clinically significant disturbances in sleep-related breathing may occur with vagal nerve stimulators. Obstructive apneas of this severity, related to vagal nerve stimulators, were not previously described in pediatric patients. This effect on sleep-related breathing warrants further investigation and care in managing pediatric patients.

The detection of inspiratory resistive (R) loads was studied in nonasthmatic children (NA), asthmatic children (A), and children with a history of life-threatening asthma (LTA). It was hypothesized that the LTA children would have a reduced ability to detect added mechanical loads as measured by the Weber fraction, which assesses the resistive load detection threshold (ΔR50/R0). Subjects were separated from the investigator, were seated in a soundproofed room, and breathed through a nonrebreathing valve with the inspiratory port connected to the loading manifold. The subject's inspiratory baseline resistance (Raw) was measured by the interrupter method. Ten magnitudes of R loads and no-load were presented randomly 10 times each for a single inspiration. The loads were presented in three trials. Subjects pressed a button if they detected the presence of a load. The ΔR50 was determined from the % detection-ΔR curve. R0 was the sum of the subject's Raw and the minimal resistance of the apparatus. The ΔR50/R0 for children with life- threatening asthma was significantly greater than for asthmatic and nonasthmatic children. The increased ΔR50/R0 suggests that children with LTA are at risk of life-threatening asthma attacks, in part because it requires a greater change in resistance above their baseline resistance before they sense an increased mechanical load such as presented to them by bronchoconstriction during an asthmatic attack. Pediatr Pulmonol. 2001; 32:44–48. © 2001 Wiley-Liss, Inc.

The perception of inspiratory resistive (R) loads was studied in nonasthmatic children and in children with a history of life-threatening asthma. It was hypothesized that the children with life-threatening asthma would have a reduced sensitivity to added mechanical loads as measured by magnitude estimation of resistive loads (ME). The subjects were screened from the experimenter and seated in a sound-isolated room in a lounge chair facing an oscilloscope, and they respired through a nonbreathing valve with the inspiratory port connected to the loading manifold. The oscilloscope displayed the inspiratory V, and each subject was required to inspire to the same peak V for each breath. The subject's inspiratory background R was measured by the interrupter method. Five magnitudes of R loads and no-load were presented randomly 10 times each for a single inspiration after the illumination of a light cue. The subjects were initially given a training trial breathing to the V target. The loads were presented in two trials. The load was estimated using the modified Borg scale. The slope of the log-log relationship between R load magnitude and the ME is a measure of the sensitivity of the subject to R loads. The slope for children with life-threatening asthma was significantly less than that for asthmatic and nonasthmatic children. There were no significant differences in the slope related to race, sex or age in the nonasthmatic children or in the asthmatic children. The reduced sensitivity to increased R loads suggests that these children are at risk of a life-threatening asthmatic attack in part because of an underestimation or delay in the perception of the increased mechanical load that occurs during an asthmatic attack.

Children with achondroplasia have midface hypoplasia, frontal bossing, spinal stenosis, rhizomelia, and a small foramen magnum. Central sleep apnea, with potential resultant sudden death, is thought to be related to compression of the spinal cord at the cervicomedullary junction in these patients. Screening polysomnography and/or cervical spine MRI are often performed for infants with achondroplasia. Decompressive suboccipital craniectomy has been performed in selected cases. We aim to better delineate the relationship between polysomnography, cervical spine MRI, and indications for surgical decompression in achondroplasia.We retrospectively review electronic medical records of all children with achondroplasia in our IRB-approved skeletal dysplasia registry who had received screening polysomnography and cervical spine MRI examination was performed. We explored correlations of polysomnography, MRI parameters, and need for decompressive surgery. Seventeen patients with both polysomnography and MRI of the cervical spine met inclusion criteria. The average age at time of the sleep study was 2.4 ± 3.6 years. An abnormal apnea-hypopnea index was found in all patients, with central sleep apnea found in 6/17. Five patients (29%) required foramen magnum decompression. We found no statistically significant correlation between central sleep apnea and abnormal MRI findings suggestive of foramen magnum stenosis. Screening polysomnography is an important tool but does not appear to correlate with MRI findings of foramen magnum stenosis. Cord compression, with either associated T2 cord signal abnormality or clinical findings of clonus, was most predictive of subsequent surgical decompression.

Distraction advancement has been advocated for treatment of obstructive sleep apnea associated with congenital midface hypoplasia. The purpose of this study was to relate changes in maxillary position to changes in obstructive sleep apnea measures on polysomnography in a consecutive series of patients.Among 26 syndromic pediatric patients undergoing Le Fort III distraction over a 5-year period, 15 had documented obstructive sleep apnea with an apnea hypopnea index greater than 5. Linear and angular displacement of key bone landmarks were measured using quantitative computed tomographic scan analysis before and after distraction. Differences of linear and angular movements of maxillary landmarks were tested between those patients with improvement of obstructive sleep apnea (apnea hypopnea index5) after treatment, and those with no improvement.Mean postoperative apnea hypopnea index was 9.5 (range, 2.1 to 22.7). Eight patients had a decrease in apnea hypopnea index following distraction (improved group) and three additional patients had resolution of symptoms but declined postoperation polysomnography. Four had no improvement or worsening of apnea hypopnea index (no improvement group). Comparison of changes in maxillary position between the improved group and the no improvement group revealed no significant difference in magnitude or direction of linear displacement of key landmarks. Postdistraction change in sella-nasion-point A angle was the only measure significantly (p = 0.02) greater in the improved group.Based on the authors' comparison of quantitative bone measurements and associated polysomnography changes, an angular increase in sella-nasion-point A angle on presurgical planning of maxillary movement for the treatment of sleep apnea may be more important than absolute linear changes in maxillary position alone.

Respiratory-related evoked potentials (RREPs) have been elicited by inspiratory occlusion and recorded over the somatosensory cortex. The first positive peak (P(1)) amplitude has been correlated with the magnitude of inspiratory loads. Since children with life-threatening asthma (LTA) have a decreased perceptual sensitivity of inspiratory loads, we hypothesized that a subpopulation of patients with LTA have an impaired ability to sense mechanical loads, and that these patients would have an abnormal RREP. The RREP was recorded from C(Z) -C(3) and C(Z) -C(4) in three groups: LTA asthmatic, control asthmatic, and nonasthmatic children. Two inspiratory-interruption occlusions trials and a control trial were recorded. All the evoked potentials were analyzed after the averaged control trial was subtracted from the averaged occlusion trials. The RREP P(1) peak was observed in all 14 nonasthmatic children and in 14 of 15 control asthmatic children. The RREP was absent in 6 of 11 patients with LTA. When present, there were no between-group significant differences in P(1) peak latency or amplitude. These results demonstrate that the RREP elicited by inspiratory occlusion is present bilaterally in nonasthmatic and asthmatic children. There is a subpopulation of LTA children in which inspiratory occlusion fails to elicit the P(1) peak of the RREP, suggesting an altered neural processing of inspiratory load information.