Development and clinical application of impedance pneumography technique

Assessment of the lung function is essential in the diagnosis and management of respiratory disease such as asthma. However, conventional spirometry requires difficult manoeuvres from the subject and is thus unsuitable for young children and infants. This renders the diagnosis of childhood asthma often qualitative, time-consuming and clinically challenging. However, information relating to the lung function can be derived from restful tidal breathing (TB) as well. Traditionally TB has been recorded in short intervals in laboratory conditions with obtrusive instrumentation using a face mask or a mouth piece. The principal aim of this thesis was to develop a noninvasive and convenient, yet highly accurate method for recording TB over extended time periods for clinical purposes, especially in young children. The measurement methodology developed within this thesis is based on impedance pneumography (IP), where breathing is recorded through the respiratory variations of the electrical impedance of the thorax. This is established by placing four skin electrodes on the upper body and connecting them to a recording device. The main focus was in ensuring the accuracy of the IP-derived tidal flow recording as compared to direct measurement from the mouth. This was established by attenuating the distortive cardiac oscillations (CGO) of the impedance signal and by optimising the locations of the skin electrodes. The complete method was then validated in healthy adults during respiratory loading (n=17) and in preschool children with wheezing disorder (n=20). The CGO attenuation was realised through an ensemble averaging based signal processing algorithm. The algorithm takes into account the respiratory modulation of the CGO waveform thus enabling efficient CGO attenuation while preserving the respiratory component of the signal unchanged. The newly proposed electrode configuration provides consistently more linear impedance to lung volume ratio than those previously established in the literature. The complete method integrating these developments provided highly accurate TB flow signal during normal and altered respiratory mechanics (loading) in adults and during induced bronchoconstriction in young children. It may be concluded that in this thesis significant improvements were realised with the IP technique. These improvements were experimentally validated in two studies and the integrated system was found to consistently provide an accurate respiratory flow signal. The method may have clinical implications for the diagnosis of respiratory diseases especially in non-cooperative subjects, such as young children

Observational study of inhaled corticosteroid treatment for improved expiratory variability index in steroid-naive asthmatic children

Non peer reviewe

Sources of variability in expiratory flow profiles during sleep in healthy young children

Standard lung function tests are not feasible in young children, but recent studies show that the variability of expiratory tidal breathing flow-volume (TBFV) curves during sleep is a potential indirect marker of lower airway obstruction. However, the neurophysiological sources of the TBFV variability in normal subjects has not been established. We investigated sleep stages and body position changes as potential sources for the TBFV curve variability. Simultaneous impedance pneumography (IP), polysomnography (PSG) and video recordings were done in 20 children aged 1.4-6.9 years without significant respiratory disorders during sleep. The early part of expiratory TBFV curves are less variable between cycles of REM than NREM sleep. However, within individual sleep cycles, TBFV curves during N3 are the least variable. The differences in TBFV curve shapes between sleep stages are the main source of overnight variability in TBFV curves and the changes in body position have a lesser impact.Peer reviewe

Expiratory variability index is associated with asthma risk, wheeze and lung function in infants with recurrent respiratory symptoms

Non peer reviewe

Nocturnal Heart Rate Variability Spectrum Characterization in Preschool Children with Asthmatic Symptoms

Asthma is a chronic lung disease that usually develops during chilhood. Despite that symptoms can almost be controlled with medication, early diagnosis is desirable in order to reduce permanent airway obstruction risk. It has been suggested that abnormal parasympathetic nervous system (PSNS) activity might be closely related with the pathogenesis of asthma, and that this PSNS activity could be reflected in cardiac vagal control. In this work, an index to measure the spectral regularity of the high frequency (HF) component of heart rate variability (HRV) spectrum, named peakness (P), is proposed. Three different implementations of P, based on electrocardiogram (ECG) recordings, impedance pneumography (IP) recordings and a combination of both, were employed in the characterization of a group of pre-school children classified attending to their risk of developing asthma. Peakier componentswere observed in the HF band of those children classified as high-risk (p < 0.005), who also presented reduced sympathvoagal balance. Results suggest that high-risk of developing asthma might be related with a lack of adaptability of PSNS

Noninvasive cardiorespiratory signals analysis for asthma evolution monitoring in preschool children

Despite its increasing prevalence, diagnosis of asthma in children remains problematic due to their difficulties in producing repeatable spirometric maneuvers. Moreover, low adherence to inhaled corticosteroids (ICS) treatment could result in permanent airway remodeling. The growing interest in a noninvasive and objective way for monitoring asthma, together with the apparent role of autonomic nervous system (ANS) in its pathogenesis, have attracted interest towards heart rate variability (HRV) and cardiorespiratory coupling (CRC) analyses. In this work, HRV and CRC were analyzed in 70 children who were prescribed ICS treatment due to obstructive bronchitis. They underwent three different electrocardiogram and respiratory signals recordings, during and after treatment period. After treatment completion, they were followed up during 6 months and classified attending to their current asthma status. Vagal activity, as measured from HRV, and CRC, were reduced after treatment in those children at lower risk of asthma, whereas it kept unchanged in those with a worse prognosis. Results suggest that HRV analysis could be useful for the continuous monitoring of ANS anomalies present in asthma, thus contributing to evaluate the evolution of the disease, which is especially challenging in young children

Heart Rate Variability Analysis in Risk of Asthma Stratification

Early diagnosis of asthma is crucial to avoid long-term effects such as permanent airway obstruction. Pathogenesis of asthma has been related with autonomic nervous system (ANS) dysfunction, concretely with abnormal parasympathetic activity. As heart rate variability (HRV) analysis does reflect ANS activity, it has been employed here in risk of asthma stratification

Development and clinical application of impedance pneumography technique

Assessment of the lung function is essential in the diagnosis and management of respiratory disease such as asthma. However, conventional spirometry requires difficult manoeuvres from the subject and is thus unsuitable for young children and infants. This renders the diagnosis of childhood asthma often qualitative, time-consuming and clinically challenging. However, information relating to the lung function can be derived from restful tidal breathing (TB) as well. Traditionally TB has been recorded in short intervals in laboratory conditions with obtrusive instrumentation using a face mask or a mouth piece. The principal aim of this thesis was to develop a noninvasive and convenient, yet highly accurate method for recording TB over extended time periods for clinical purposes, especially in young children. The measurement methodology developed within this thesis is based on impedance pneumography (IP), where breathing is recorded through the respiratory variations of the electrical impedance of the thorax. This is established by placing four skin electrodes on the upper body and connecting them to a recording device. The main focus was in ensuring the accuracy of the IP-derived tidal flow recording as compared to direct measurement from the mouth. This was established by attenuating the distortive cardiac oscillations (CGO) of the impedance signal and by optimising the locations of the skin electrodes. The complete method was then validated in healthy adults during respiratory loading (n=17) and in preschool children with wheezing disorder (n=20). The CGO attenuation was realised through an ensemble averaging based signal processing algorithm. The algorithm takes into account the respiratory modulation of the CGO waveform thus enabling efficient CGO attenuation while preserving the respiratory component of the signal unchanged. The newly proposed electrode configuration provides consistently more linear impedance to lung volume ratio than those previously established in the literature. The complete method integrating these developments provided highly accurate TB flow signal during normal and altered respiratory mechanics (loading) in adults and during induced bronchoconstriction in young children. It may be concluded that in this thesis significant improvements were realised with the IP technique. These improvements were experimentally validated in two studies and the integrated system was found to consistently provide an accurate respiratory flow signal. The method may have clinical implications for the diagnosis of respiratory diseases especially in non-cooperative subjects, such as young children