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

Case-control study of heart rate variability and sleep apnea in childhood sickle cell disease

Obstructive sleep apnea (OSA) is common in sickle cell disease (SCD) despite the absence of overweight, suggesting a specific pathophysiology. We previously showed that otherwise healthy children with increased pharyngeal compliance, a main endotype of OSA, exhibited decreased sympathetic modulation. Our objective was to assess whether modifications of heart rate variability (HRV) and compliance are associated in SCD. Cases (children with SCD, African or Caribbean ethnicity) and controls (otherwise healthy children, same ethnicity), aged 4-18 years, were selected from our database of children referred for OSA and matched for sex, age, and obstructive apnea-hypopnoea index (OAHI) score. The children underwent polysomnography and acoustic pharyngometry (to compute compliance). HRV analyses were performed from 5 min ECG recordings in wakeful, NREM, and REM sleep states and from the whole night. Twenty-one pairs were analysed (median age 10.5 years, 24 girls). Children with SCD had lower BMI z-scores and more tonsil hypertrophy than control children. Children with SCD and OSA (OAHI ≥2/hour) were characterised by lower compliance than children with SCD without OSA. An inverse relationship between compliance and SD2 (HRV from whole night, inversely related to sympathetic modulation) was evidenced (negative relationship in SCD: R = -0.63, p = 0.002 vs. positive relationship in controls R = 0.59, p = 0.006). In conclusion, while the decrease in sympathetic modulation in control children may contribute to increasing pharyngeal compliance, its decrease seems protective in children with sickle cell disease, which underlines the specificity of OSAS pathophysiology in SCD that could be due to sickle cell disease related smooth muscle dystonia.

Altered Cortical Information Interaction During Respiratory Events in Children with Obstructive Sleep Apnea-Hypopnea Syndrome

Obstructive sleep apnea-hypopnea syndrome (OSAHS) significantly impairs children's growth and cognition. This study aims to elucidate the pathophysiological mechanisms underlying OSAHS in children, with a particular focus on the alterations in cortical information interaction during respiratory events. We analyzed sleep electroencephalography before, during, and after events, utilizing Symbolic Transfer Entropy (STE) for brain network construction and information flow assessment. The results showed a significant increase in STE after events in specific frequency bands during N2 and rapid eye movement (REM) stages, along with increased STE during N3 stage events. Moreover, a noteworthy rise in the information flow imbalance within and between hemispheres was found after events, displaying unique patterns in central sleep apnea and hypopnea. Importantly, some of these alterations were correlated with symptom severity. These findings highlight significant changes in brain region coordination and communication during respiratory events, offering novel insights into OSAHS pathophysiology in children.

A decrease in plant gain, namely CO2 stores, characterizes dysfunctional breathing whatever its subtype in children

Background: Whether dysfunctional breathing (DB) subtype classification is useful remains undetermined. The hyperventilation provocation test (HVPT) is used to diagnose DB. This test begins with a 3-min phase of hyperventilation during which fractional end-tidal CO₂ (FETCO₂) decreases that could be an assessment of plant gain, which relies on CO₂ stores. Our aim was to assess 1) whether the children suffering from different subtypes of DB exhibit decreased plant gain and 2) the relationships between HVPT characteristics and plant gain. Methods: We retrospectively selected 48 children (median age 13.5 years, 36 females, 12 males) who exhibited during a cardiopulmonary exercise test either alveolar hyperventilation (transcutaneous PCO₂ < 30 mmHg, n = 6) or inappropriate hyperventilation (increased VE'/V'CO₂ slope) without hypocapnia (n = 18) or dyspnea without hyperventilation (n = 18) compared to children exhibiting physiological breathlessness (dyspnea for sports only, n = 6). These children underwent tidal-breathing recording (ventilation and FETCO₂ allowing the calculation of plant gain) and a HVPT. Results: The plant gain was significantly higher in the physiological group as compared to the dyspnea without hyperventilation group, p = 0.024 and hyperventilation without hypocapnia group, p = 0.008 (trend for the hyperventilation with hypocapnia group, p = 0.078). The slope of linear decrease in FETCO₂ during hyperventilation was significantly more negative in physiological breathlessness group as compared to hyperventilation without hypocapnia group (p = 0.005) and dyspnea without hyperventilation group (p = 0.049). Conclusion: The children with DB, regardless of their subtype, deplete their CO₂ stores (decreased plant gain), which may be due to intermittent alveolar hyperventilation, suggesting the futility of our subtype classification.

Clinical Characteristics Combined with Craniofacial Photographic Analysis in Children with Obstructive Sleep Apnea

Purpose

Distinguishing obstructive sleep apnea (OSA) in a high-risk population remains challenging. This study aimed to investigate clinical features to identify children with OSA combined with craniofacial photographic analysis.

Methods

One hundred and forty-five children (30 controls, 62 with primary snoring, and 53 with OSA) were included. Differences in general demographic characteristics and surface facial morphology among the groups were compared. Risk factors and prediction models for determining the presence of OSA (obstructive sleep apnea-hypopnea index>1) were developed using logistic regression analysis.

Results

The BMI (z-score), tonsil hypertrophy, and lower face width (adjusted age, gender, and BMI z-score) were showed significantly different in children with OSA compared with primary snoring and controls (adjusted p<0.05). The screening model based on clinical features and photography measurements correctly classified 79.3% of the children with 64.2% sensitivity and 89.1% specificity. The area under the curve of the model was 81.0 (95% CI, 73.5-98.4%).

Conclusion

A screening model based on clinical features and photography measurements would be helpful in clinical decision-making for children with highly suspected OSA if polysomnography remains inaccessible in resource-stretched healthcare systems.

Oropharyngeal obstruction and respiratory system compliance are linked to ventilatory control parameters in pediatric obstructive sleep apnea syndrome

Instable ventilatory control is an endotypic trait of obstructive sleep apnea syndrome (OSAS). This study aimed to evaluate the relationships between the anatomical compromise of the upper (oro- and naso-pharynx) and lower airways and ventilatory control (measured by chemical loop gain) in otherwise healthy children suffering from moderate to severe OSAS (apnea hypopnea index ≥ 5/hour). The children underwent ear, nose and throat examination, measurement of impedance of the respiratory system that allowed characterizing peripheral lung mechanics using the extended Resistance-Inertance-Compliance model. Physiologically constrained analytical model based on tidal breathing analysis allowed for the computation of steady-state plant gain, steady-state controller gain (CG0) and steady-state loop gain (LG0). Medium-frequency components of the feedback control system were then deduced. Fifty children (median age 11.2 years) were enrolled. Oropharyngeal obstruction was associated with decreased CG0 (0.6 [0.2; 1.0] vs 1.5 [0.5; 6.6] L.s^- 1.mmHg^- 1, p = 0.038) and LG0 (0.4 [0.2; 1.1] vs 1.2 [0.4; 9.3], p = 0.027), while nasal obstruction did not modify ventilatory control parameters. In a multivariate analysis Medium-Frequency PG was negatively related to minute ventilation and respiratory system compliance. Both upper (tonsil hypertrophy) and lower (compliance of respiratory system) airways are linked to ventilatory control in children with moderate to severe OSAS.

Cross-sectional case-control study of the relationships between pharyngeal compliance and heart rate variability indices in childhood obstructive sleep apnoea

A combination of noradrenergic and antimuscarinic agents reduces the apnea-hypopnea index (AHI) in adult patients with obstructive sleep apnoea (OSA) via reduced upper airway collapsibility, suggesting that a shift in the sympathovagal balance improves OSA. The objectives of our present case-control study were to assess heart rate variability (HRV) indices in the stages of sleep in children with and without OSA to evaluate OSA-induced sleep HRV modifications and to assess whether increased collapsibility measured during wakefulness is associated with reduced sympathetic activity during non-rapid eye movement (NREM) sleep. Three groups of 15 children were matched by sex, age, z-score of body mass index and ethnicity: non-OSA (obstructive AHI [OAHI] <2 events/hr), mild (OAHI ≥2 to <5 events/hr) or moderate-severe (OAHI ≥5 events/hr) OSA. Pharyngeal compliance was measured during wakefulness using acoustic pharyngometry. HRV indices (time and frequency domain variables) were calculated on 5-min electrocardiography recordings from polysomnography during wakefulness, NREM and REM sleep in periods free of any event. As compared to children without OSA, those with OSA (n = 30) were characterised by increased compliance and no physiological parasympathetic tone increase in REM sleep. Children with increased pharyngeal compliance (n = 21) had a higher OAHI due to higher AHI in NREM sleep, whereas their sympathetic tone was lower than that of those with normal compliance (n = 24). In conclusion, children with increased pharyngeal compliance exhibit decreased sympathetic tone associated with increased AHI in NREM sleep. Therapeutics directed at sympathovagal balance modifications should be tested in childhood OSA.

Children with down syndrome and sleep disordered breathing display impairments in ventilatory control

OBJECTIVES

To investigate the role of ventilatory control instability (i.e. loop gain) in children with Down syndrome and sleep disordered breathing.

METHODS

Children (3-19 years) with Down syndrome and sleep disordered breathing (n = 14) were compared with typically developing children (n = 14) matched for age, sex and sleep disordered breathing severity. All children underwent overnight polysomnography. Spontaneous sighs were identified and a 180s analysis window (60s pre-sigh to 120s post-sigh) containing flow measurements and oxygen saturation were created. Loop gain, a measure of the sensitivity of the negative feedback loop that controls ventilation, was estimated by fitting a mathematical model of ventilatory control to the post-sigh ventilatory pattern. Results; Loop gain was significantly higher in children with Down syndrome compared to matched typically developing children (median loop gain [interquartile range]: 0.36 [0.33, 0.55] vs 0.32 [0.24, 0.38]; P = 0.0395). While children with Down syndrome also had significantly lower average oxygen saturation associated within each analysis window compared to typically developing children (mean ± standard deviation: 96.9 ± 1.3% vs 98.0 ± 1.0%; P = 0.0155), loop gain was not related to polysomnographic measures of hypoxia.

CONCLUSIONS

Higher loop gain in children with Down syndrome and sleep disordered breathing indicates that these children have more unstable ventilatory control, compared to age, sex and sleep disordered breathing severity matched typically developing children. This may be due to an inherent impairment in ventilatory control in children with Down syndrome contributing to their increased risk of sleep disordered breathing which may inform alternative treatment options for this population.