Thoracic Quantitative Dynamic MRI to Understand Developmental Changes in Normal Ventilatory Dynamics.

BACKGROUND: A database of normative quantitative measures of regional thoracic ventilatory dynamics, which is essential to understanding better thoracic growth and function in children, does not exist. RESEARCH QUESTION: How to quantify changes in the components of ventilatory pump dynamics during childhood via thoracic quantitative dynamic MRI (QdMRI)? STUDY DESIGN AND METHODS: Volumetric parameters were derived via 51 dynamic MRI scans for left and right lungs, hemidiaphragms, and hemichest walls during tidal breathing. Volume-based symmetry and functional coefficients were defined to compare left and right sides and to compare contributions of the hemidiaphragms and hemichest walls with tidal volumes (TVs). Statistical analyses were performed to compare volume components among four age-based groups. RESULTS: Right thoracic components were significantly larger than left thoracic components, with average ratios of 1.56 (95% CI, 1.41-1.70) for lung TV, 1.81 (95% CI, 1.60-2.03) for hemidiaphragm excursion TV, and 1.34 (95% CI, 1.21-1.47) for hemichest wall excursion TV. Right and left lung volumes at end-expiration showed, respectively, a 44% and 48% increase from group 2 (8 ≤ age < 10) to group 3 (10 ≤ age < 12). These numbers from group 3 to group 4 (12 ≤ age ≤ 14) were 24% and 28%, respectively. Right and left hemichest wall TVs exhibited, respectively, 48% and 45% increases from group 3 to group 4. INTERPRETATION: Normal right and left ventilatory volume components have considerable asymmetry in morphologic features and dynamics and change with age. Chest wall and diaphragm contributions vary in a likewise manner. Thoracic QdMRI can provide quantitative data to characterize the regional function and growth of the thorax as it relates to ventilation.

Upper Airway Vibration Perception in School-Aged Children with Obstructive Sleep Apnea.

STUDY OBJECTIVES: Children with the obstructive sleep apnea (OSA) have impaired upper airway two-point discrimination compared to controls. In addition, blunted vibration threshold detection (VT) in the palate has been recognized in adults with OSA, but has not been studied in children. Both findings are indicative of a defect in the afferent limb of the upper airway dilator reflex that could prevent upper airway dilation secondary to airway loading, resulting in airway collapse. We hypothesized that children with OSA have impaired palate VT compared to controls, and that this improves after OSA treatment. METHODS: Case-control study. Children with OSA and healthy non-snoring controls underwent polysomnography and palate VT measurements. Children with OSA were retested after adenotonsillectomy. RESULTS: 29 children with OSA (median [interquartile range] age = 9.5 [7.5-12.6] years, obstructive apnea-hypopnea index [OAHI] = 11.3 [5.7-19.5] events/h, BMI z = 1.8 [1.3-2.1]) and 32 controls (age = 11.2 [9.3-13.5] years, P = 0.1; OAHI = 0.5 [0.1-0.7] events/h, P < 0.001; BMI z = 1 [0.3-1.7], P = 0.004) were tested. OSA palate VT (1.0 [0.8-1.5] vibration units) was similar to that of controls (1 [0.8-1.3], P = 0.37). 20 children with OSA were retested 4.4 (3.2-7.1) months after treatment. OAHI decreased from 13.1 (5.8-19) to 0.6 (0.2-2.5) events per hour (P < 0.001) postoperatively, but palate VT did not change (before = 1 [0.7-1.5], after = 1.2 [0.8-1.4], P = 0.37). CONCLUSIONS: Children with OSA and controls have similar palate VT. Unlike in adults, palate VT does not seem to be affected by childhood OSA.

Airway Resistance in Children with Obstructive Sleep Apnea Syndrome.

STUDY OBJECTIVES: Enlarged tonsils and adenoids, the main cause of obstructive sleep apnea syndrome (OSAS) in children, results in upper airway (UA) loading. This contributes to the imbalance between structural and neuromotor factors ultimately leading to UA collapse during sleep. However, it is unknown whether this UA loading can cause elevated airway resistance (AR) during wakefulness. We hypothesized that children with OSAS have elevated AR compared to controls and that this improves after OSAS treatment. METHODS: Case control study performed at an academic hospital. Children with OSAS and nonsnoring healthy controls underwent baseline polysomnography and spirometry, and AR measurement by body plethysmography while breathing via an orofacial mask. Children with OSAS repeated the previously mentioned tests after adenotonsillectomy. RESULTS: 31 OSAS participants (mean age ± SD = 9.7 ± 3.0 y, obstructive apnea-hypopnea index (OAHI) median [range] = 14.9 [2-58.7] events/h, body mass index [BMI] z = 1.5 ± 1) and 31 controls (age = 10.5 ± 2.5 y, P = 0.24; OAHI = 0.4 [0-1.4], P < 0.001; BMI z = 0.9 ± 1, P = 0.01) were tested. OSAS AR at baseline was 3.9 [1.5-10.3] cmH2O/L/sec and controls 2.8 [1.4 - 6.2] (P = 0.027). Both groups had similar spirometry results. 20 patients with OSAS were tested 6.4 ± 6.6 mo after adenotonsillectomy. OAHI decreased from 15.2 [2.1-58.7] to 0.5 [0 - 5.1] events/h postoperatively (P < 0.001), and AR decreased from 4.3 [1.5 - 10.3] to 2.8 [1.7 - 4.7] cmH2O/L/sec (P = 0.009). CONCLUSIONS: Children with OSAS have elevated AR that decreases after treatment. This is likely because of upper airway loading secondary to adenotonsillar hypertrophy and may contribute to the increased frequency of respiratory diseases in untreated children with OSAS.

Cerebral Blood Flow Response to Hypercapnia in Children with Obstructive Sleep Apnea Syndrome.

STUDY OBJECTIVES: Children with obstructive sleep apnea syndrome (OSAS) often experience periods of hypercapnia during sleep, a potent stimulator of cerebral blood flow (CBF). Considering this hypercapnia exposure during sleep, it is possible that children with OSAS have abnormal CBF responses to hypercapnia even during wakefulness. Therefore, we hypothesized that children with OSAS have blunted CBF response to hypercapnia during wakefulness, compared to snorers and controls. METHODS: CBF changes during hypercapnic ventilatory response (HCVR) were tested in children with OSAS, snorers, and healthy controls using diffuse correlation spectroscopy (DCS). Peak CBF changes with respect to pre-hypercapnic baseline were measured for each group. The study was conducted at an academic pediatric sleep center. RESULTS: Twelve children with OSAS (aged 10.1 ± 2.5 [mean ± standard deviation] y, obstructive apnea hypopnea index [AHI] = 9.4 [5.1-15.4] [median, interquartile range] events/hour), eight snorers (11 ± 3 y, 0.5 [0-1.3] events/hour), and 10 controls (11.4 ± 2.6 y, 0.3 [0.2-0.4] events/hour) were studied. The fractional CBF change during hypercapnia, normalized to the change in end-tidal carbon dioxide, was significantly higher in controls (9 ± 1.8 %/mmHg) compared to OSAS (7.1 ± 1.5, P = 0.023) and snorers (6.7 ± 1.9, P = 0.025). CONCLUSIONS: Children with OSAS and snorers have blunted CBF response to hypercapnia during wakefulness compared to controls. Noninvasive DCS blood flow measurements of hypercapnic reactivity offer insights into physiopathology of OSAS in children, which could lead to further understanding about the central nervous system complications of OSAS.