Analysis of respiratory rate and the respiratory cycle in infants and children using an optical sensor

Abstract

Elevated respiratory rates have been described in several disease states, such as pneumonia, asthma and bronchiolitis. Despite this there are few studies defining the range of respiratory rates found in healthy children. Almost all of those which have been published have limitations and shortcomings in terms of methodology. The present study observed respiratory rates in healthy children and children with respiratory disease. The current research project had several aims. The primary aim of the study was to construct centile curves for respiratory rate (RR) by age. A newly developed optical respiratory sensor was used for this purpose. This sensor placed no restrictions on respiratory excursions and provided a novel approach to studying breathing patterns in children. The sensor was found to measure respiratory rate accurately and to measure inspiratory time and expiratory time in healthy subjects. Healthy children in this study were obtained from maternity wards, childcare centres and schools. Informed consent was obtained from all parents of children. Respiratory rates observed in 343 awake and 94 sleeping children were used to create the reference ranges for healthy children. Respiratory rates were significantly higher when children were awake compared to when they were asleep (p < 0.01, unpaired t test). During quiet sleep, RR (+SD) decreased from 41.4 (±4.1) bpm in newborn infants to 19.5 (±2.7) bpm in children aged 2.0 - 2.9 years. In awake children, RR measured in children ranged from 59.3 (±9.8) bpm to 16.9 (±4.5) bpm, in children aged 0 - 0.49 and 12.0 -12.99 years respectively. A secondary aim was to examine the sub-components of the respiratory cycle in both health and disease. Age did not have an effect on the fractional inspiratory time (T1/TTOT) in children older than two weeks. T1/ TTOT was 0.40 (±0.04) in sleeping children aged from two weeks to 3.5 years and 0.41 (±0.03) in awake children aged from two to twelve years. The centile charts for RR were useful in detecting disease, in particular pneumonia and asthma. All sleeping children with pneumonia in the study (6/6) had a RR higher than the 95th centile for healthy children. Seventy-eight per cent (7/9) of sleeping and 75% (9/12) of awake children with asthma who were younger than seven years of age also had respiratory rates above the 95th centile for healthy children. Respiratory rate correlated with body temperature in sleeping children with pneumonia (r = + 0.83, p<0.05), oxygen saturation levels in sleeping children with asthma (r = - 0.72, p<0.05) and peak expiratory flow rates in awake children with asthma (r = - 0.45, p<0.05). Fractional inspiratory time (T1/ TTOT) in children with asthma and bronchiolitis was not significantly different to the values observed in healthy children. Children with cystic fibrosis (CF) had a significantly increased mean T1 / TTOT value of 0.44 (±0.03) (p<0.05, unpaired t test). These measurements of respiratory timing reflect alterations primarily in the contribution of the abdominal compartment to breathing. It was concluded: 1 The centile charts for respiratory rate should be helpful as an aid to detecting abnormal respiratory rates in children, especially those with pneumonia. The data obtained in this thesis will allow abnormalities in rate to be quantified. 2 The newly developed optical sensor was an appropriate respiratory transducer, capable of measuring respiratory rate and detecting apnoea in health and disease. Further work in the analysis and practical application of the timing indices measured by the sensor in disease is needed.