Ventilatory drive and the apnea-hypopnea index in six-to-twelve year old children

Peripheral hypercapnic chemosensitivity at rest and progressive exercise intensities in males and females

Peripheral hypercapnic chemosensitivity (PHC) is the ventilatory response to hypercapnia and is enhanced with acute whole body exercise. However, little is known about the mechanism(s) responsible for the exercise-related increase in PHC and if progressive exercise leads to further augmentation. We hypothesized that unloaded cycle exercise (0 W) would increase PHC but progressively increasing the intensity would not further augment the response. Twenty healthy subjects completed two testing days. Day 1 was a maximal exercise test on a cycle ergometer to determine peak power output (Wmax). Day 2 consisted of six 12-min stages: 1) rest on chair, 2) rest on bike, 3) 0 W unloaded cycling, 4) 25% Wmax, 5) 50% Wmax, and 6) ∼70% Wmax with ∼10 min of rest between each exercise stage. In each stage, PHC was assessed via two breaths of 10% CO2 (∼21% O2) repeated five times with ∼45 s between each to ensure end-tidal CO2 ([Formula: see text]) and ventilation returned to baseline. Prestimulus [Formula: see text] was not different between rest and unloaded cycling (P = 0.478). There was a significant increase in PHC between seated rest and 25% Wmax (0.71 ± 0.37 vs. 1.03 ± 0.52 L·mmHg-1·min-1, respectively, P = 0.0006) and between seated rest and unloaded cycling (0.71 ± 0.37 vs. 1.04 ± 0.4 L·mmHg-1·min-1, respectively, P = 0.0017). There was no effect of exercise intensity on PHC (1.03 ± 0.52 vs. 0.95 ± 0.58 vs. 1.01 ± 0.65 L·mmHg-1·min-1 for 25, 50, and 70% Wmax, P = 0.44). The increased PHC response from seated rest to unloaded and 25% Wmax, but no effect of exercise intensity suggests a possible feedforward/feedback mechanism causing increased PHC sensitivity through the act of cycling.NEW & NOTEWORTHY Unloaded exercise significantly increased the peripheral hypercapnic ventilatory response (HCVR) compared with rest. However, increases in exercise intensity did not further augment peripheral HCVR. Males had a greater peripheral HCVR compared with females, but there was no interaction between sex and intensity. The lack of sex interactions suggests the mechanism augmenting the peripheral HCVR with exercise is independent of sex. The increase in peripheral HCVR with exercise is likely due to central command.

Peripheral hypercapnic chemosensitivity in trained and untrained females and males during exercise

Hypercapnic chemosensitivity is the response to the increased partial pressure of carbon dioxide and results from central and peripheral chemosensor stimulation. The hypercapnic chemosensitivity of the peripheral chemoreceptors is potentially impacted by acute exercise, aerobic fitness, and sex. We sought to determine the peripheral chemoresponse to transient hypercapnia at rest and during exercise in males and females of various fitness. We hypothesized that 1) higher fitness participants would have lower hypercapnic chemosensitivity compared with those with lower fitness and 2) males would have a higher chemoresponse than females. Forty healthy participants (20 females) participated in one test day involving transient hypercapnic chemosensitivity testing and a maximal exercise test. Chemosensitivity testing involved two breaths of 10% CO₂ repeated five times (45 s to 1 min between repeats) at rest and the first two stages of a maximal exercise test. There was no significant difference between higher and lower aerobic fitness groups, (mean difference 0.23 ± 0.22 rest; -0.07 ± 0.04 stage 1; 0.11 ± 0.17 stage 2 L/mmHg·min) during each stage (P = 0.472). However, we saw a significant increase in the hypercapnic response during stage 1 (0.98 ± 0.4 L/mmHg·min) compared with rest (0.79 ± 0.5 L/mmHg·min; P = 0.01). Finally, at 80 W, males had a higher chemoresponse compared with females, which persisted following body surface area correction (0.56 ± 0.2 vs. 0.42 ± 0.2 L/mmHg·min·m², for females and males respectively (P = 0.038). Our findings suggest that sex, unlike aerobic fitness, influences peripheral hypercapnic chemosensitivity and that context (i.e., rest vs. exercise) is an important consideration.NEW & NOTEWORTHY The hypercapnic chemoresponse to transient CO₂ showed an increase during acute physical activity; however, this response did not persist with further increases in intensity and was not different between participants of different aerobic fitness. Males and females show a differing response to CO₂ during exercise when compared with an iso-V̇co₂. Our results suggest that adaptations that lead to increased aerobic fitness do not impact the hypercapnic ventilatory response but there is an effect of sex.

Very Severe Obstructive Sleep Apnea in Children: Outcomes of Adenotonsillectomy and Risk Factors for Persistence

Objectives

(1) To describe the clinical, demographic and polysomnographic (PSG) characteristics of children with very severe obstructive sleep apnea (OSA) without significant comorbidities; (2) to assess the outcomes following tonsillectomy and adenoidectomy (T&A); and (3) to determine predictors of persistence of OSA after T&A.

Study Design

Case series with chart review.

Setting

Tertiary-level freestanding children’s hospital.

Subjects and Methods

Seventy-four children aged 2 to 12 years who underwent T&A for very severe OSA (obstructive apnea-hypopnea index [AHI] >30) were included. Children with significant comorbidities were excluded. PSG variables were compared pre- and post-T&A using statistical tests. Factors affecting OSA resolution and persistence were studied.

Results

The mean (95% confidence interval) age was 4.3 (3.8-4.7) years with the majority black or Hispanic (64/74, 86%). The mean decrease in AHI after T&A was 49 (43-58) ( P < .001). Complete resolution of OSA, defined by an AHI <1, or an AHI <5 was seen in 32% (24/74) and 80% (59/74), respectively. Total sleep time (TST) greater than 5 minutes with end-tidal CO2 >50 mm Hg was strongly associated with persistent OSA. The decrease in AHI post-T&A was best predicted by higher preoperative oxygen saturation (SpO2) nadir and lower TST with SpO2 <90% ( R2 = 0.24, P < .001).

Conclusions

T&A is associated with a significant improvement but not resolution of very severe OSA. The severity of baseline hypercapnia and hypoxemia may best predict persistent OSA after T&A. The study supports obtaining routine post-T&A PSG in children with very severe OSA.

Pediatric obstructive sleep apnea

Obstructive sleep apnea syndrome (OSAS) is a disorder of airway obstruction with multisystem implications and associated complications. OSAS affects children from infancy to adulthood and is responsible for behavioral, cognitive, and growth impairment as well as cardiovascular and perioperative respiratory morbidity and mortality. OSAS is associated commonly with comorbid conditions, including obesity and asthma. Adenotonsillectomy is the most commonly used treatment option for OSAS in childhood, but efforts are underway to identify medical treatment options.

Ventilatory responses to hypercapnia during wakefulness and sleep in obese adolescents with and without obstructive sleep apnea syndrome

STUDY OBJECTIVES

Abnormal ventilatory drive may contribute to the pathophysiology of the childhood obstructive sleep apnea syndrome (OSAS). Concomitant with the obesity epidemic, more adolescents are developing OSAS. However, few studies have specifically evaluated the obese adolescent group. The authors hypothesized that obese adolescents with OSAS would have a blunted hypercapnic ventilatory response (HCVR) while awake and blunted ventilatory responses to carbon dioxide (CO(2)) during sleep compared with obese and lean adolescents without OSAS.

DESIGN

CVR was measured during wakefulness. During nonrapid eye movement (NREM) and rapid eye movement (REM) sleep, respiratory parameters and genioglossal electromyogram were measured during CO(2) administration in comparison with room air in obese adolescents with OSAS, obese control study participants, and lean control study participants.

SETTING

Sleep laboratory.

PARTICIPANTS

Twenty-eight obese patients with OSAS, 21 obese control study participants, and 37 lean control study participants.

RESULTS

The obese OSAS and obese control groups had a higher HCVR compared with the lean control group during wakefulness. During both sleep states, all 3 groups had a response to CO(2); however, the obese OSAS group had lower percentage changes in minute ventilation, inspiratory flow, inspiratory time, and tidal volume compared with the 2 control groups. There were no significance differences in genioglossal activity between groups.

CONCLUSIONS

HCVR during wakefulness is increased in obese adolescents. Obese adolescents with OSAS have blunted ventilatory responses to CO(2) during sleep and do not have a compensatory prolongation of inspiratory time, despite having normal CO(2) responsivity during wakefulness. Central drive may play a greater role than upper airway neuromotor tone in adapting to hypercapnia.

Childhood obesity and obstructive sleep apnea syndrome

The increasing prevalence of obesity in children seems to be associated with an increased prevalence of obstructive sleep apnea syndrome (OSAS) in children. Possible pathophysiological mechanisms contributing to this association include the following: adenotonsillar hypertrophy due to increased somatic growth, increased critical airway closing pressure, altered chest wall mechanics, and abnormalities of ventilatory control. However, the details of these mechanisms and their interactions have not been elucidated. In addition, obesity and OSAS are both associated with metabolic syndrome, which is a constellation of features such as hypertension, insulin resistance, dyslipidemia, abdominal obesity, and prothrombotic and proinflammatory states. There is some evidence that OSAS may contribute to the progression of metabolic syndrome with a potential for significant morbidity. The treatment of OSAS in obese children has not been standardized. Adenotonsillectomy is considered the primary intervention followed by continuous positive airway pressure treatment if OSAS persists. Other methods such as oral appliances, surgery, positional therapy, and weight loss may be beneficial for individual subjects. The present review discusses these issues and suggests an approach to the management of obese children with snoring and possible OSAS.

Pathophysiology of pediatric obstructive sleep apnea

Sleep-disordered breathing is a common and serious cause of metabolic, cardiovascular, and neurocognitive morbidity in children. The spectrum of obstructive sleep-disordered breathing ranges from habitual snoring to partial or complete airway obstruction, termed obstructive sleep apnea (OSA). Breathing patterns due to airway narrowing are highly variable, including obstructive cycling, increased respiratory effort, flow limitation, tachypnea, and/or gas exchange abnormalities. As a consequence, sleep homeostasis may be disturbed. Increased upper airway resistance is an essential component of OSA, including any combination of narrowing/retropositioning of the maxilla/mandible and/or adenotonsillar hypertrophy. However, in addition to anatomic factors, the stability of the upper airway is predicated on neuromuscular activation, ventilatory control, and arousal threshold. During sleep, most children with OSA intermittently attain a stable breathing pattern, indicating successful neuromuscular activation. At sleep onset, airway muscle activity is reduced, ventilatory variability increases, and an apneic threshold slightly below eupneic levels is observed in non-REM sleep. Airway collapse is offset by pharyngeal dilator activity in response to hypercapnia and negative lumenal pressure. Ventilatory overshoot results in sudden reduction in airway muscle activation, contributing to obstruction during non-REM sleep. Arousal from sleep exacerbates ventilatory instability and, thus, obstructive cycling. Paroxysmal reductions in pharyngeal dilator activity related to central REM sleep processes likely account for the disproportionate severity of OSA observed during REM sleep. Understanding the pathophysiology of pediatric OSA may permit more precise clinical phenotyping, and therefore improve or target therapies related to anatomy, neuromuscular compensation, ventilatory control, and/or arousal threshold.

Oxidant stress and inflammation in the snoring child: confluent pathways to upper airway pathogenesis and end-organ morbidity

Snoring in children is increasingly being recognized as a highly prevalent condition, and indicates the presence of heightened upper airway resistance during sleep. In this paper, we present evidence to support the hypothesis that local inflammatory processes within the upper airway contribute to the pathophysiology of adenotonsillar hypertrophy and altered reflexes potentially leading to increased propensity for upper airway obstruction during sleep. Furthermore, the cumulative evidence supporting multiorgan morbidity for sleep-disordered breathing (SDB) is reviewed, and a unified hypothesis of a triple risk model proposing oxidative-inflammatory mechanisms as mediating the morbid consequences of SDB is presented. This hypothetical working model incorporates both dose-dependent disease severity components, as well as environmental and genetic elements of susceptibility.

Dynamic changes in glottal resistance during exposure to severe hypoxia in neonatal rats in situ

The neural control of respiratory airflow via the vocal fold is characterized by inspiratory abduction and postinspiratory (early expiratory) adduction causing decreases and increases in glottal resistance, respectively. The postinspiratory increase in glottal resistance plays a major role in braking the speed of expiratory airflow, to act against the high recoil pressure of the neonatal rat lung. In the present study, we investigated changes in upper airway patency during severe hypoxia in neonatal rats. We measured dynamic changes in subglottal pressure during normoxic and hypoxic conditions in an arterially perfused brainstem preparation in which we could control gas tensions accurately. Initially, hypoxia (5% O(2), 5% CO(2), and 90% nitrogen) produced an excitatory response in phrenic nerve activity accompanied by augmentation of both inspiratory-related glottal dilation and postinspiratory glottal constriction. Later, during the early stages of hypoxia-induced respiratory depression and initiation of gasping, we observed a massive reduction of the respiratory modulation of glottal resistance. In most preparations, this was transient and replaced by a paradoxic inspiratory-related glottal constriction. We propose that during severe hypoxia in the in situ preparation, paradoxic inspiratory glottal constriction can be observed during gasping, and this may impair ventilation despite the persistence of rhythmic contractions of the respiratory muscles. The latter is of clinical interest, because this may relate to the finding of cot death victims who died as a result of upper airway obstruction but without apparent apnea or rebreathing.

Behavior problems associated with sleep disordered breathing in school-aged children--the Tucson children's assessment of sleep apnea study

OBJECTIVE

The purpose of the current study was to examine prevalence of and relations between a commonly used measure of nighttime breathing problems, the Respiratory Disturbance Index (RDI), and a range of problem behaviors in community children.

METHODS

Participants were 403 unreferred children aged 6-12 years. Recruitment was completed through public elementary schools. Overnight unattended in-home polysomnography was used to assess sleep and breathing. The RDI was used as the indicator of respiratory events during sleep. The Child Behavior Checklist and the Conners' Parent Rating Scales-Revised were used to assess behavior.

RESULTS

Prevalence rates for Attention, Cognitive Problems, Aggression, Oppositional behavior, and Social Problems were greatest for subjects with high RDIs. Prevalence for Internalizing behaviors was not greater for those subjects with high RDIs. Hyperactivity was not strongly related to higher RDIs.

CONCLUSIONS

Behavioral problems may exist in the presence of nocturnal breathing events in unreferred children. Specific patterns of behavioral morbidity have still not been established. Some behaviors, such as hyperactivity, may show differing sensitivity and specificity in relation to the RDI.