Measurement of obstructive airway disease in children during sleep

Abstract

Many important developmental milestones occur during childhood, and approximately half of childhood is spent asleep. Any chronic disturbance of physiology during this time can negatively affect normal development and life-long potential. Sleep-disordered breathing (SDB) and asthma are common disorders of airway function, and are well established causes of sleep disruption. There is now strong evidence to support a bidirectional relationship between these disorders, but it remains difficult to measure objective indices of asthma without disturbing the child’s sleep.

Previous investigations have been limited by conventional measurement techniques, or methods that were individually-designed for a specific disease. None simultaneously measured sleep and asthma, or did so continuously. This research evaluated a new method for measuring complex respiratory patterns overnight by continuously recording breath sounds and movement, without attaching anything to the child or interfering with their sleep. The investigational device is called “Sonomat”.

The results from this work are presented in six chapters. First, a local clinical population was audited to compare the prevalence of SDB before and after surgical treatment intervention. Persistent SDB, especially snoring, was very common. Despite being the dominant symptom used clinically to differentiate normal from abnormal breathing in sleep, snoring has rarely been measured or reported in studies.

Second, a group of children with a background diagnosis of asthma – who also presented with symptoms of SDB – were studied overnight using conventional polysomnography (PSG) and the Sonomat device. Their clinical results and demographic characteristics are presented together in a single chapter. Subsequent chapters in this thesis are based mainly on this cohort of patients.

Third, the levels of agreement between the two methods (i.e., PSG and Sonomat) were examined. The Sonomat provided a better quantitative measure of snoring, and otherwise demonstrated good or very good agreement with PSG findings. In addition to respiratory measures, the Sonomat recorded body movement profiles that enabled an assessment of the presence and extent of sleep disruption.

Fourth, Sonomat studies were recorded during active asthma in awake children. Pathological lung sounds, such as wheeze, were validated by physician auscultation. All overnight studies were examined for evidence of such sounds. These signs are not usually quantified because conventional methods of sleep measurement are unable to detect them. Coughing and scratching were also identified in the recordings.

Fifth, a sample of children underwent multiple all-night studies to evaluate the utility of the Sonomat when used at home. Importantly, this provided preliminary data on the night-to-night variability of snoring and asthma signs. Finally, associations between objective sleep measures and two validated questionnaires were examined. As the risk for a sleep disorder increased, asthma-related quality-of-life decreased.

Taken together, the work presented herein reveals new and unexpected insights into the relationship between upper- and lower-airway dysfunction, and their influence on sleep, both in hospital and at home.