Model-based stability assessment of ventilatory control in overweight adolescents with obstructive sleep apnea during NREM sleep.

Obstructive sleep apnea (OSA) involves the interplay of several different factors such as an unfavorable upper airway anatomy, deficiencies in pharyngeal muscle responsiveness, a low arousal threshold, and ventilatory control instability. Although the stability of ventilatory control has been extensively studied in adults, little is known about its characteristics in the pediatric population. In this study, we developed a novel experimental setup that allowed us to perturb the respiratory system during natural non-rapid eye movement (NREM) sleep conditions by manipulating the inspiratory pressure, provided by a bilevel pressure ventilator, to induce sighs after upper airway stabilization. Furthermore, we present a modeling framework that utilizes the noninvasively measured ventilatory responses to the induced sighs and spontaneous breathing data to obtain representations of the processes involved in the chemical regulation of respiration and extract their stability characteristics. After validation with simulated data, the modeling technique was applied to data collected experimentally from 11 OSA and 15 non-OSA overweight adolescents. Statistical analysis of the model-derived stability parameters revealed a significantly higher plant gain and lower controller gain in the OSA group (P = 0.046 and P = 0.007, respectively); however, no differences were found in loop gain (LG) and circulatory time delay between the groups. OSA severity and LG, within the 0.03-0.04-Hz frequency band, were significantly negatively associated (r = -0.434, P = 0.026). Contrary to what has been found in adults, our results suggest that in overweight adolescents, OSA is unlikely to be initiated through ventilatory instability resulting from elevated chemical loop gain.

Autonomic and metabolic effects of OSA in childhood obesity.

This study investigates the effects of exposure to intermittent hypoxia on cardiovascular autonomic control and metabolic function in obese children with obstructive sleep apnea (OSA). Each subject underwent: (1) a polysomnography; (2) morning fasting blood samples and a subsequent FSIVGTT; (3) noninvasive measurement of respiration, arterial blood pressure, and heart rate during supine and standing postures. Assessment of adiposity was performed using a DEXA scan. From these measurements, we deduced the pertinent sleep parameters, Bergman minimal model parameters and the parameters characterizing a minimal model of cardiovascular variability. Results suggest that intermittent hypoxia in OSA contributes independently to insulin resistance and autonomic dysfunction in overweight children.

Time-varying closed-loop modeling of autonomic control in pediatric obstructive sleep apnea syndrome during cold face stimulation.

Adults with obstructive sleep apnea syndrome (OSAS) are known to have impaired autonomic function but the corresponding effects in children appear to be more subtle. Model-based analysis of the cardiovascular response to cold face test (CFT) was used to quantify daytime autonomic dysfunction. The increase in transfer gain between respiration and RRI was not different between controls and OSAS. However, the transfer gain between "surrogate cardiac output" (pulse pressure+R-R interval) and systolic blood pressure (SBP) and the transfer gain between cardiac output and SBP both increased significantly in controls but not in OSAS during CFT. These findings suggest that the parasympathetic function remains relatively normal in pediatric OSAS, but cardiovascular sympathetic reactivity is impaired.

Cardio-respiratory Uncoupling in Congenital Central Hypoventilation Syndrome.

Congenital Central Hypoventilation Syndrome (CCHS) is a rare disorder with failure of automatic control of breathing, defined by lack of an appropriate ventilatory response to hypercarbia and hypoxia. However, more detailed evaluation of cardiorespiratory coupling has not been previously performed in those with CCHS. We postulate that those with CCHS have disjointed cardiorespiratory responses to ventilatory challenges due to their alterations in sympathetic modulation. Therefore, we performed ventilatory rebreathing challenges with hypercarbia and hypoxia on 5 subjects with CCHS (age 21.2 ± 5.3 years; 3 females) and 7 controls (age 20.0 ± 4.0 years; 4 females). We measured breath-to-breath respiratory parameters (airflow, PETco2, Sao2), ECG, and continuous non-invasive blood pressure. As previously shown, when compared to controls CCHS subjects lacked ventilatory responses to isocapnic hypoxia (p=0.004) and hyperoxic hypercarbia (p=0.002). During hypercapnia, both control and CCHS subjects had similar rates of decrease in R-R intervals (RRI; slope -1.3 ± 2.5 vs. -1.4 ± 1.1, n.s.) and increase in beat-to-beat averaged blood pressure (MBP; slope 1.2 ± 0.3 vs. 0.4 ± 0.1, n.s.) as PETco2increased. During hypoxia, both control and CCHS groups had similar rates of decrease in RRI (slope 14.2 ± 3.0 vs. 7.5 ± 3.9, n.s.) and increase in MBP (slope -1.11 ± 1.12 vs. -0.9 ± 0.8, n.s.) as Sao2decreased. We conclude that despite having a markedly diminished ventilatory response to hypercarbia and hypoxia, subjects with CCHS have normal cardiovascular responses to these challenges. We speculate that this indicates that chemoreceptors are functional.

Noninvasive assessment of cardiovascular autonomic control in pediatric obstructive sleep apnea syndrome.

Studies suggest that Obstructive Sleep Apnea Syndrome (OSAS) is causally related to abnormal cardiovascular autonomic control in adults, but this has not been established in pediatric OSAS. The goal of this study was to quantify autonomic system dysfunction, as manifested by cardiovascular response abnormalities, in children with OSAS. During wakefulness, we continuously measured the ECG, arterial blood pressure and airflow in each subject. These measurements were made during the following conditions: spontaneous breathingin the supine posture (baseline), spontaneous breathing in the standing posture (orthostatic stress); tracking of the subject's own prior spontaneous breathing pattern while supine (mental stress), and during a cold face challenge. Using spectral analysis and modeling techniques, we sought to computationally delineate the physiological mechanisms that mediate these abnormalities. Our preliminary results suggest that the autonomic effects of pediatric OSAS differ from those in adult in that parasympathetic activity remains relatively normal despite the elevated peripheral sympathetic drive.

Noninvasive assessment of cardiovascular autonomic control in pediatric obstructive sleep apnea syndrome.

Studies suggest that obstructive sleep apnea syndrome (OSAS) is causally related to abnormal cardiovascular autonomic control in adults, but this has not been established in pediatric OSAS. The goal of this study was to quantify autonomic system dysfunction, as manifested by cardiovascular response abnormalities, in children with OSAS. During wakefulness, we continuously measured the ECG, arterial blood pressure and airflow in each subject. These measurements were made during the following conditions: spontaneous breathing in the supine posture (baseline), spontaneous breathing in the standing posture (orthostatic stress); tracking of the subject's own prior spontaneous breathing pattern while supine (mental stress), and during a cold face challenge. Using spectral analysis and modeling techniques, we sought to computationally delineate the physiological mechanisms that mediate these abnormalities. Our preliminary results suggest that the autonomic effects of pediatric OSAS differ from those in adult in that parasympathetic activity remains relatively normal despite the elevated peripheral sympathetic drive.

Home ventilator low-pressure alarms fail to detect accidental decannulation with pediatric tracheostomy tubes.

BACKGROUND: Positive-pressure ventilators are equipped with low-inspiratory-pressure alarms to protect patients from hypoventilation. Small uncuffed tracheostomy tubes have a high resistance, and may not trigger these alarms during decannulation. STUDY OBJECTIVE: To determine whether ventilator low-inspiratory-pressure alarms are effective in detecting tracheostomy decannulation. DESIGN: We connected tracheostomy tubes of varying inner diameters (3.0 to 6.0 mm) to a home ventilator and simulated decannulation using low (tidal volume [VT], 600 mL; peak inspiratory pressure [PIP], 25 cm H(2)O), medium (VT, 800 mL; PIP, 30 cm H(2)O), and high (VT, 1,000 mL; PIP, 35 cm H(2)O) ventilator settings. RESULTS: When the ventilator low-inspiratory-pressure alarm was set at 4 cm H(2)O below the desired PIP, it failed to alarm for simulated decannulation of tracheostomy tubes < 4.5 mm on low and medium settings, and < 4.0 mm on high settings. When the ventilator low-inspiratory-pressure alarm was set at 10 cm H(2)O below the desired PIP, it failed to alarm with tracheostomy tubes < 6.0 mm. CONCLUSION: We conclude that ventilator low-inspiratory-pressure alarms fail to alarm during simulated decannulation with small tracheostomy tubes commonly used in children. We speculate that low-inspiratory-pressure alarms set at 4 cm H(2)O below the desired PIP will detect more decannulation than when set at 10 cm H(2)O below the desired PIP.

Latex allergy in children on home mechanical ventilation.

STUDY OBJECTIVE: Determining the incidence of latex allergy in children receiving home mechanical ventilation. BACKGROUND: The prevalence of latex allergy in the general population ranges from 0.1 to 1.0%. However, in patients with spina bifida and other chronic medical conditions associated with repeated exposure to latex, the prevalence may be as high as 60%. Children receiving home mechanical ventilation are frequently exposed to latex products. Therefore, we hypothesized that these children would be at increased risk for latex allergy. DESIGN: Fifty-seven children receiving home mechanical ventilation (31 boys, 26 girls; mean [+/- SD] age, 7.8+/-6.6 years; range, 0.3 to 23.2 years) were enrolled. A radioallergosorbent test (RAST) for latex was administered and serum IgE levels were obtained in all patients. RESULTS: Seventeen patients (29.8%) were found to have a positive RAST for latex. Patients with latex allergy had required mechanical ventilation for an average of 6.1+/-4.1 years vs. 5.5+/-5.4 years (p = 0.69; not significant) in those without latex allergy. Eleven of 17 patients (64.7%) had elevated serum IgE levels in the group with latex allergy vs only 14 of 40 patients (35.0%) in the group with a negative latex RAST (p = 0.04; odds ratio, 3.4). CONCLUSION: We conclude that there is a high incidence of latex allergy in children requiring home mechanical ventilation. We speculate that screening all children receiving home mechanical ventilation may lead to the identification of patients with previously undiagnosed latex allergy and the prevention of untoward reactions from exposure to latex.

Should children with suspected obstructive sleep apnea syndrome and normal nap sleep studies have overnight sleep studies?

STUDY OBJECTIVES: Overnight polysomnography (ONP) is the "gold standard" for the diagnosis of sleep-disordered breathing, but it is expensive and time-consuming. Thus, daytime nap studies have been used as screening tests. If the findings of a nap study are normal or mildly abnormal, should ONP be performed? Do specific abnormalities in nap studies predict abnormal findings in ONP? To answer these questions, we conducted this study. DESIGN: Retrospective chart review. SETTING: Children's hospital. PARTICIPANTS: One hundred forty-three children with suspected obstructive sleep apnea syndrome secondary to isolated adenotonsillar hypertrophy, who had normal or mildly abnormal nap studies, and underwent ONP. MEASUREMENTS AND RESULTS: We compared daytime nap and overnight polysomnograms in 143 children (52 girls; mean [+/- SD] age, 5.6 +/- 3.1 years). Total sleep time was 1 h in daytime nap, and 5.1 +/- 1.3 h in ONP. The interval between the two studies was 5.9 +/- 4.8 months. The findings of 59% of the nap studies were mildly abnormal, while 66% of overnight studies were abnormal. No individual nap study parameter (including short obstructive apneas, hypopneas, hypoxemia, hypoventilation, snoring, paradoxical breathing, gasping, retractions) had good sensitivity at predicting abnormal overnight polysomnograms, but most had good specificity and positive predictive value. CONCLUSIONS: We conclude that individual nap study parameters are not very sensitive in predicting abnormal ONP findings. However, when nap study parameters are abnormal, the chance of obstructive sleep apnea syndrome is high.

Comparison of apnea identified by respiratory inductance plethysmography with that detected by end-tidal CO(2) or thermistor. The CHIME Study Group.

As part of the Collaborative Home Infant Monitoring Evaluation (CHIME) we compared apnea identified by a customized home monitor using respiratory inductance plethysmography (RIP) with simultaneously recorded polysomnography-acquired nasal end-tidal CO(2) (PET(CO(2))) and nasal/oral thermistor in 422 infants during overnight laboratory recordings to determine concordance between techniques, sources of disagreement, and capacity of RIP to detect obstructed breaths within an apnea. Among 233 episodes of apnea identified by at least one method as >/= 16 s, 120 were observed by the CHIME monitor, 219 by PET(CO(2)), and 163 by thermistor. The positive predictive value of the CHIME-identified apnea was 89.2% (95% CI 83, 95) and 73% (95% CI 65, 81) for PET(CO(2)) and thermistor, respectively. However, the sensitivity of the CHIME monitor in identifying events detected by the other methods was only approximately 50%. Among 87 apnea events identified by all three techniques, no two methods showed high agreement in measurement of apnea duration: RIP and PET(CO(2)) (ICC = 0.54), RIP and thermistor (ICC = 0.13), PET(CO(2)) and nasal thermistor (ICC = 0.41). Among the 179 breaths identified by RIP as obstructed, 79.9% were judged to be obstructed on the PET(CO(2)) and 80.4% were judged to be obstructed on the thermistor channel. Among 238 breaths identified on PET(CO(2)) as obstructed, 54.2% were determined to be obstructed by RIP. Among 204 breaths identified on thermistor as obstructed, 55. 4% were determined to be obstructed by RIP. Reasons for discrepancies in apnea detection among channels included body movement, partial airway obstruction, and obstructed breaths. Despite these limitations the CHIME monitor provides an opportunity to record physiological data previously unavailable in the home.