Relative impact of respiratory muscle activity on tidal flow and end expiratory volume in healthy neonates

Diaphragmatic electromyography in infants: an overview of possible clinical applications

Preterm infants often experience breathing instability and a hampered lung function. Therefore, these infants receive cardiorespiratory monitoring and respiratory support. However, the current respiratory monitoring technique may be unreliable for especially obstructive apnea detection and classification and it does not provide insight in breathing effort. The latter makes the selection of the adequate mode and level of respiratory support difficult. Electromyography of the diaphragm (dEMG) has the potential of monitoring heart rate (HR) and respiratory rate (RR), and it provides additional information on breathing effort. This review summarizes the available evidence on the clinical potential of dEMG to provide cardiorespiratory monitoring, to synchronize patient-ventilator interaction, and to optimize the mode and level of respiratory support in the individual newborn infant. We also try to identify gaps in knowledge and future developments needed to ensure widespread implementation in clinical practice. IMPACT: Preterm infants require cardiorespiratory monitoring and respiratory support due to breathing instability and a hampered lung function. The current respiratory monitoring technique may provide unreliable measurements and does not provide insight in breathing effort, which makes the selection of the optimal respiratory support settings difficult. Measuring diaphragm activity could improve cardiorespiratory monitoring by providing insight in breathing effort and could potentially have an important role in individualizing respiratory support in newborn infants.

Diaphragm electrical activity during weaning of nasal high-flow therapy in preterm infants

OBJECTIVE

To determine whether electrical activity of the diaphragm (Edi) changes with weaning nasal high-flow (HF) therapy in preterm infants according to a standardised protocol.

DESIGN

Prospective observational cohort study.

SETTING

Neonatal intensive care unit.

PATIENTS

Preterm infants born at <32 weeks gestation, receiving nasal HF as part of routine clinical care.

INTERVENTIONS

Infants recruited to the study had their HF weaned according to set clinical criteria. Edi was measured using a modified gastric feeding tube serially from baseline (pre-wean) to 24-hours post-wean.

MAIN OUTCOME MEASURES

Change in Edi from baseline was measured at four time points up to 24 hours after weaning. Minimum Edi during expiration, maximum Edi during inspiration and amplitude of the Edi signal (Edi_delta) were measured. Clinical parameters (heart rate, respiratory rate and fraction of inspired oxygen) were also recorded.

RESULTS

Forty preterm infants were recruited at a mean corrected gestational age of 31.6 (±2.7) weeks. Data from 156 weaning steps were analysed, 91% of which were successful. Edi did not change significantly from baseline during flow reduction steps, but a significant increase in diaphragm activity was observed when discontinuing HF (median increase in Edi_delta immediately post-discontinuation 1.7 µV (95% CI: 0.6 to 3.0)) and at 24 hours 1.9 µV (95% CI: 0.7 to 3.8)). No significant difference in diaphragm activity was observed between successful and unsuccessful weaning steps.

CONCLUSIONS

A protocolised approach to weaning has a high probability of success. Edi does not change with reducing HF rate, but significantly increases with discontinuation of HF from 2 L/min.

Respiratory muscle function in the newborn: a narrative review

Our aim was to summarise the current evidence and methods used to assess respiratory muscle function in the newborn, focusing on current and future potential clinical applications. The respiratory muscles undertake the work of breathing and consist mainly of the diaphragm, which in the newborn is prone to dysfunction due to lower muscle mass, flattened shape and decreased content of fatigue-resistant muscle fibres. Premature infants are prone to diaphragmatic dysfunction due to limited reserves and limited capacity to generate force and avoid fatigue. Methods to assess the respiratory muscles in the newborn include electromyography, maximal respiratory pressures, assessment for thoraco-abdominal asynchrony and composite indices, such as the pressure-time product and the tension time index. Recently, there has been significant interest and a growing body of research in assessing respiratory muscle function using bedside ultrasonography. Neurally adjusted ventilator assist is a novel ventilation mode, where the level of the respiratory support is determined by the diaphragmatic electrical activity. Prolonged mechanical ventilation, hypercapnia and hypoxia, congenital anomalies and systemic or respiratory infection can negatively impact respiratory muscle function in the newborn, while caffeine and synchronised or volume-targeted ventilation have a positive effect on respiratory muscle function compared to conventional, non-triggered or pressure-limited ventilation, respectively. IMPACT: Respiratory muscle function is impaired in prematurely born neonates and infants with congenital anomalies, such as congenital diaphragmatic hernia. Respiratory muscle function is negatively affected by prolonged ventilation and infection and positively affected by caffeine and synchronised compared to non-synchronised ventilation modes. Point-of-care diaphragmatic ultrasound and neurally adjusted ventilator assist are recent diagnostic and therapeutic technological developments with significant clinical applicability.

Evaluation of Correlation between Surface Diaphragm Electromyography and Airflow Using Fixed Sample Entropy in Healthy Subjects

In clinic, the acquisition of airflow with nasal prongs, masks, thermistor to monitor respiratory function is more uncomfortable and inconvenience than surface diaphragm electromyography (EMGdi) using electrode pads. The EMGdi with strong electrocardiograph (ECG) interference affect the extraction of its characteristic information. In this work, surface EMGdi and airflow signals of 20 subjects were collected under 5 incremental inspiratory threshold loading protocols from quiet breathing to maximum forced breathing. First, we filtered out the ECG interference in EMGdi based on the combination of stationary wavelet transform and the positioning of ECG to obtain pure EMGdi (EMGdip). Second, the Spearman's rank correlation coefficients between EMGdi and EMGdip quantified by time series fixed sample entropy (fSampEn), root mean square (RMS), and envelope were compared to verify the robustness of the fSampEn to ECG. A comparative analysis of correlation between fSampEn of EMGdi and inspiratory airflow and the correlation between envelope of EMGdip (EMGdie) and inspiratory airflow found that there was no significant difference between the two, indicating the feasibility of using fSampEn to predict airflow. Moreover, fSampEn of EMGdi was used as characteristic parameter to build a quantitative relationship with the airflow by polynomial regression analysis. Mean coefficient of determination of all subjects in any breathing state is greater than 0.88. Finally, nonlinear programming method was used to solve a universal fitting coefficient between fSampEn of EMGdi and airflow for each subject to further evaluate the possibility of using surface EMGdi to monitor and control respiratory activity.

Respiratory Oscillometry in Newborn Infants: Conventional and Intra-Breath Approaches

BACKGROUND

Oscillometry has been employed widely as a non-invasive and standardized measurement of respiratory function in children and adults; however, limited information is available on infants.

AIMS

To establish the within-session variability of respiratory impedance (Zrs), to characterize the degree and profile of intra-breath changes in Zrs and to assess their impact on conventional oscillometry in newborns.

METHODS

109 healthy newborns were enrolled in the study conducted in the first 5 postpartum days during natural sleep. A custom-made wave-tube oscillometry setup was used, with an 8-48 Hz pseudorandom and a 16 Hz sinusoidal signal used for spectral and intra-breath oscillometry, respectively. A resistance-compliance-inertance (R-C-L) model was fitted to average Zrs spectra obtained from successive 30-s recordings. Intra-breath measures, such as resistance (Rrs) and reactance (Xrs) at the end-expiratory, end-inspiratory and maximum-flow points were estimated from three 90-s recordings. All natural and artifact-free breaths were included in the analysis.

RESULTS

Within-session changes in the mean R, C and L values, respectively, were large (mean coefficients of variation: 10.3, 20.3, and 26.6%); the fluctuations of the intra-breath measures were of similar degree (20-24%). Intra-breath analysis also revealed large swings in Rrs and Xrs within the breathing cycle: the peak-to-peak changes amounted to 93% (range: 32-218%) and 41% (9-212%), respectively, of the zero-flow Zrs magnitude.

DISCUSSION

Intra-breath tracking of Zrs provides new insight into the determinants of the dynamics of respiratory system, and highlights the biasing effects of mechanical non-linearities on the average Zrs data obtained from the conventional spectral oscillometry.

Transcutaneous monitoring of diaphragm activity as a measure of work of breathing in preterm infants

OBJECTIVE

Monitoring work of breathing (WOB) is important to assess the pulmonary condition and adjust respiratory support in preterm infants. Conventional WOB measurement (esophageal pressure, tidal volume) is invasive and we hypothesized that monitoring diaphragm activity could be a noninvasive alternative to estimate WOB. The objective was to determine the correlation between conventional WOB measures and diaphragm activity, in preterm infants.

METHODS

WOB and diaphragm activity, measured with transcutaneous electromyography (dEMG), were simultaneously recorded at different nasal continuous positive airway pressure (nCPAP) levels. During a 30-s recording at each nCPAP level, dEMG parameters, inspiratory WOB (WOB_i ), and pressure time product (PTP_in ) were calculated per breath. The correlation coefficient between WOB- and dEMG-measures was calculated using single breaths and after aggregating all breaths into deciles of incremental WOB_i .

RESULTS

Fifteen preterm infants were included (median gestational age, 28 weeks). Single-breath analysis showed a poor median correlation of 0.27 (interquartile range [IQR], 0.03 to 0.33) and 0.08 (IQR, -0.03 to 0.28), respectively, for WOB_i and PTP_in with peak diaphragmatic activity (dEMG_peak ). A modest median correlation coefficient of 0.65 (IQR, 0.13 to 0.79) and 0.43 (IQR, -0.33 to 0.69) was found for, respectively, WOB_i and PTP_in with dEMG_peak in the aggregated analysis.

CONCLUSION

Diaphragm activity showed a modest correlation with WOB_i and PTP_in in an aggregated analysis. This finding warrants further studies in infants with more significant lung disease.

Relationship between thoracoabdominal mobility and hours of life in infants: A cross-sectional study

Assessing the relationship between thoracoabdominal mobility (TAM) in newborns (NBs) is relevant for a greater understanding of pulmonary kinematics. This study aimed to assess the association between TAM, hours of life and respiratory rate (RR) in term NBs. Healthy NBs were included in the sample. They were filmed for 2 min, with markers in the lateral region of the trunk, delimiting the thoracic and abdominal areas. TAM and RR were assessed using a MATLAB® routine. For kinematic analysis, an algorithm created graphs presenting thoracoabdominal mobility. A total of 26 NBs were evaluated. TAM was the only variable that exhibited a statistically significant intergroup difference, showing that the fewer the hours of life, the greater the mobility. Simple linear regression analysis showed that RR can explain 31% of the variation in abdominal mobility (p = 0.002). Thus, the fewer the hours of life, the greater the TAM of NBs, with a predominance of abdominal compartment mobility.

Assessing paediatric exercise-induced bronchoconstriction using electromyography

BACKGROUND

Asthma is one of the most common chronic diseases in childhood, occurring in up to 10% of all children. Exercise-induced bronchoconstriction (EIB) is indicative of uncontrolled asthma and can be assessed using an exercise challenge test (ECT). However, this test requires children to undergo demanding repetitive forced breathing manoeuvres. We aimed to study the electrical activity of the diaphragm using surface electromyography (EMG) as an alternative measure to assess EIB.

METHODS

Forty-two children suspected of EIB performed an ECT wearing a portable EMG amplifier. EIB was defined as a fall in FEV 1 of more than 13%. Children performed spirometry before exercise, and at 1, 3 and 6 min after exercise until the nadir FEV1 was attained and after the use of a bronchodilator. EMG measurements were obtained between spirometry measurements.

RESULTS

Twenty out of 42 children were diagnosed with EIB. EMG peak amplitudes measured at the diaphragm increased significantly more in children with EIB; 4.85 μV (1.82-7.84), compared to children without EIB; 0.20 μV (-0.10-0.54), (p<0.001) at the lowest FEV 1 post-exercise. Furthermore, the increase in EMG peak amplitude could accurately distinguish between EIB and non-EIB using a cut-off of 1.15 μV (sensitivity 95%, specificity 91%).

CONCLUSION

EMG measurements of the diaphragm are strongly related to the FEV1 and can accurately identify EIB. EMG measurements are a less invasive, effort-independent measure to assess EIB and could be an alternative when spirometry is not feasible.

Nasal high flow in preterm infants: A dose-finding study

OBJECTIVE

To investigate the relationship between applied flows of nasal high flow (NHF) and physiological outcomes and work of breathing (WOB), to identify an optimal delivery flow which results in reduced WOB in preterm infants.

DESIGN

A prospective observational clinical study with randomly applied NHF rates.

PATIENTS AND SETTING

Preterm infants within 72 hours of commencement of NHF respiratory support.

INTERVENTIONS

Infants were initially placed on 8 L/min of NHF and flows of 2, 4, and 6 L/min were then applied in random order.

MEASUREMENTS AND RESULTS

WOB was measured using transcutaneous electromyography and respiratory inductance plethysmography. Physiological variables were also recorded. Measurements taken 10 minutes after each flow change were compared with 8 L/min. Sixteen infants with a median gestational age of 28 (range 24-31) weeks and postnatal age of 14 (2-55) days were included in the study. The median flow rate before the study was 6 (4-8) L/min and a fraction of inspired oxygen (FiO₂ ) was 0.21 (0.21-0.26). Changes in flow resulted in changes in activity in the front diaphragm (P = .027) and intercostals (P = .034). The electrical activity of the front diaphragm at 8 L/min was significantly lower than that at 2 L/min (P = .016). Respiratory rate was lowest at 6 L/min (P = .002) and SpO₂ /FiO₂ was highest at 8 L/min (P < .04).

CONCLUSION

In preterm infants, changes in WOB resulting from randomly applied levels of NHF can be demonstrated by measuring the electrical activity of the diaphragm and intercostal muscles with transcutaneous electromyography. In combination with physiological measurements, the similarities in electrical activity between 4, 6, and 8 L/min suggest that these three flows may be equally as effective.

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.

Tidal breathing flow profiles during sleep in wheezing children measured by impedance pneumography

For the first time, impedance pneumography (IP) enables a continuous analysis of the tidal breathing flow volume (TBFV), overnight. We studied how corticosteroid inhalation treatments, sleep stage, and time from sleep onset modify the nocturnal TBFV profiles of children. Seventy children, 1-5 years old and with recurrent wheezing, underwent three, full-night TBFVs recordings at home, using IP. The first recorded one week before ending a 3-months inhaled corticosteroids treatment, and remaining two, 2 and 4 weeks after treatment. TBFV profiles were grouped by hour from sleep onset and estimated sleep stage. Compared with on-medication, the off-medication profiles showed lower volume at exhalation peak flow, earlier interruption of expiration, and less convex middle expiration. The differences in the first two features were significant during non-rapid eye movement (NREM), and the differences in the third were more prominent during REM after 4 h of sleep. These combinations of TBFV features, sleep phase, and sleep time potentially indicate airflow limitation in young children.

Processing transcutaneous electromyography measurements of respiratory muscles, a review of analysis techniques

Transcutaneous electromyography (tc-EMG) has been used to measure the electrical activity of respiratory muscles during inspiration in various studies. Processing the raw tc-EMG signal of these inspiratory muscles has shown to be difficult as baseline noise, cardiac interference, cross-talk and motion artefacts can influence the signal quality. In this review we will discuss the most important sources of signal noise in tc-EMG of respiratory muscles and the various techniques described to suppress or reduce this signal noise. Furthermore, we will elaborate on the options available to develop or improve an algorithm that can be used to guide the approach for analysis of tc-EMG signals of inspiratory muscles in future research.

Tidal breathing flow volume profiles during sleep in wheezing infants measured by impedance pneumography

Overnight analysis of tidal breathing flow volume (TBFV) loops, recorded by impedance pneumography (IP), has been successfully applied in the home monitoring of children with wheezing disorders. However, little is known on how sleep physiology modifies the relationship between TBFV profiles and wheeze. We studied such interactions in wheezing infants. Forty-three infants recruited because of recurrent lower airway symptoms were divided into three groups based on their risk of asthma: high (HR), intermediate (IR), or low (LR). Sedated patients underwent infant lung function testing including assessment of airway responsiveness to methacholine at the hospital and a full-night recording of TBFV profiles at home with IP during natural sleep. Overnight TBFV indexes were estimated from periods of higher and lower respiration variability, presumably belonging to active [rapid eye movement (REM)] and quiet [non-REM (NREM)] sleep, respectively. From 35 valid recordings, absolute time indexes showed intrasubject sleep phase differences. Peak flow relative to time and volume was lower in HR compared with LR only during REM, suggesting altered expiratory control. Indexes estimating the concavity/convexity of flow decrease during exhalation suggested limited flow during passive exhale in HR compared with IR and LR, similarly during NREM and REM. Moreover, during REM convexity was negatively correlated with maximal flow at functional residual capacity and methacholine responsiveness. We conclude that TBFV profiles determined from overnight IP recordings vary because of sleep phase and asthma risk. Physiological changes during REM, most likely decrease in respiratory muscle tone, accentuate the changes in TBFV profiles caused by airway obstruction. NEW & NOTEWORTHY Impedance pneumography was used to investigate overnight tidal breathing flow volume (TBFV) indexes and their interactions with sleep phase [rapid eye movement (REM) vs. non-REM] at home in wheezing infants. The study shows that TBFV indexes vary significantly because of sleep phase and asthma risk of the infant and that during REM the changes in TBFV indexes caused by airway obstruction are accentuated and better associated with lung function of the infant.

Variability of Tidal Breathing Parameters in Preterm Infants and Associations with Respiratory Morbidity during Infancy: A Cohort Study

OBJECTIVE

To test whether low variability of tidal volume (V_T) and capnographic indices are predictive of subsequent respiratory morbidity in preterm infants.

STUDY DESIGN

In a birth cohort of 133 preterm infants, lung function was performed at 44 weeks postmenstrual age. Associations between the coefficient of variation (CV) of V_T (CV_VT) and of expired CO₂ volume per breath (CV_VE,CO2) with rehospitalization, wheeze, and inhalation therapy during infancy were assessed using logistic regression. Area under the curve (AUC) analysis was used to assess whether outcome prediction using bronchopulmonary dysplasia (BPD) classification was enhanced by CV_VT or CV_VE,CO2.

RESULTS

For each IQR decrease in CV_VT (range, 4%-35%) and CV_VE,_CO2 (range, 5%-40%), the OR for rehospitalization increased by 2.25 (95% CI, 1.21-4.20) and 2.31 (95% CI, 1.20-4.45), respectively. The predictive value of BPD for rehospitalization was improved when CV_VT or CV_VE,CO2 was added to the model, with the AUC increasing from 0.56 to 0.66 in both models. No association was found for the other outcomes.

CONCLUSIONS

Compared with BPD classification alone, including near-term variability of tidal breathing parameters improves the prediction of rehospitalization in infancy. These findings may inform parent counseling and monitoring strategies in preterm infants.

Transcutaneous electromyographic respiratory muscle recordings to quantify patient-ventilator interaction in mechanically ventilated children

Background

To explore the feasibility of transcutaneous electromyographic respiratory muscle recordings to automatically quantify the synchronicity of patient–ventilator interaction in the pediatric intensive care unit.

Methods

Prospective observational study in a tertiary paediatric intensive care unit in an university hospital. Spontaneous breathing mechanically ventilated children < 18 years of age were eligible for inclusion. Patients underwent a 5-min continuous recording of ventilator pressure waveforms and transcutaneous electromyographic signal of the diaphragm. To evaluate patient–ventilator interaction, the obtained neural inspiration and ventilator pressurization timings were used to calculate trigger and cycle-off errors of each breath. Calculated errors were displayed in the dEMG-phase scale.

Results

Data of 23 patients were used for analysis. Based on the dEMG-phase scale, the median rates of synchronous, dyssynchronous and asynchronous breaths as classified by the automated analysis were 12.2% (1.9–33.8), 47.5% (36.3–63.1), and 28.9% (6.6–49.0).

Conclusions

The dEMG-phase scale quantifying patient–ventilator breath synchronicity was demonstrated to be feasible and a reliable scale for mechanically ventilated children, reflected by high intra-class correlation coefficients. As this non-invasive tool is not restricted to a type of ventilator, it could easily be clinical implemented in the ventilated pediatric population. However; correlation studies between the EMG signal measured by surface EMG and esophageal catheters have to be performed.

Diaphragmatic activity during weaning from respiratory support in preterm infants

OBJECTIVE

To determine if weaning from nasal continuous positive airway pressure (nCPAP) to lesser supportive low flow nasal cannula (LFNC) results in a change in electrical activity of the diaphragm in preterm infants.

DESIGN

Prospective observational study.

SETTING

Neonatal intensive care unit.

PATIENTS

Stable preterm infants weaned from nCPAP to LFNC (1 L/min).

MAIN OUTCOME MEASURES

Change in diaphragmatic activity, expressed as amplitude, peak and tonic activity, measured by transcutaneous electromyography (dEMG) from 30 min before (baseline) until 180 min after weaning. Subgroup analysis was performed based on success or failure of the weaning attempt.

RESULTS

Fifty-nine preterm infants (gestational age: 29.0±2.4 weeks, birth weight: 1210±443 g) accounting for 74 weaning attempts were included. A significant increase in dEMG amplitude (median, IQR: 21.3%, 3.6-41.4), peak (22.1%, 8.7-40.5) and tonic activity (14.3%, -1.9-38.1) was seen directly after weaning. This effect slowly decreased over time. Infants failing the weaning attempt tended to have a higher diaphragmatic activity than those successfully weaned.

CONCLUSIONS

Weaning from nCPAP to LFNC leads to an increase in diaphragmatic activity measured by dEMG and is most prominent in preterm infants failing the weaning attempt. dEMG monitoring might be a useful parameter to guide weaning from respiratory support in preterm infants.

A bench evaluation of fraction of oxygen in air delivery and tidal volume accuracy in home care ventilators available for hospital use

BACKGROUND

Turbine-powered ventilators are not only designed for long-term ventilation at home but also for hospital use. It is important to verify their capabilities in delivering fraction of oxygen in air (F_IO₂) and tidal volume (V_T).

METHODS

We assessed the F_IO₂ accuracy and the V_T delivery in four home care ventilators (HCV) on the bench. The four HCV were Astral 150, Elisée 150, Monnal T50 and Trilogy 200 HCV, which were connected to a lung model (ASL 5000). For assessing F_IO₂ accuracy, lung model was set to mimic an obstructive lung and HCV were set in volume controlled mode (VC). They supplied with air, 3 or 15 L/min oxygen and F_IO₂ was measured by using a ventilator tester (Citrex H4^TM). For the V_T accuracy, the lung model was set in a way to mimic three adult configurations (normal, obstructive, or restrictive respiratory disorder) and one pediatric configuration. Each HCV was set in VC. Two V_T (300 and 500 mL) in adult lung configuration and one 50 mL V_T in pediatric lung configuration, at two positive end expiratory pressures 5 and 10 cmH₂O, were tested. V_T accuracy was measured as volume error (the relative difference between set and measured V_T). Statistical analysis was performed by suing one-factor ANOVA with a Bonferroni correction for multiple tests.

RESULTS

For Astral 150, Elisée 150, Monnal T50 and Trilogy 200, F_IO₂ averaged 99.2%, 93.7%, 86.3%, and 62.1%, respectively, at 15 L/min oxygen supplementation rate (P<0.001). Volume error was 0.5%±0%, -38%±0%, -9%±0%, -29%±0% and -36%±0% for pediatric lung condition (P<0.001). In adult lung configurations, Monnal T50 systematically over delivered V_T and Trilogy 150 was sensitive to lung configuration when V_T was set to 300 mL at either positive end-expiratory pressure (PEEP).

CONCLUSIONS

HCV are different in terms of F_IO₂ efficiency and V_T delivery.

Physiology masterclass: Extremes of age: newborn and infancy

The first breath after birth is the most difficult in life. What happens before, during and after it?

The first breath after birth is the most difficult in life. What happens before, during and after it?http://ow.ly/YBOU6

Transcutaneous electromyography of the diaphragm: A cardio-respiratory monitor for preterm infants

INTRODUCTION

Chest impedance (CI) is the current standard for cardio-respiratory monitoring in preterm infants but fails to provide direct and quantitative information on diaphragmatic activity. Transcutaneous electromyography (dEMG) is able to measure diaphragmatic activity, but its feasibility and repeatability to monitor respiratory rate (RR) and heart rate (HR) in preterm infants needs to be established.

METHODS

RR and HR were measured simultaneously by dEMG and CI for 1-hour on day 1, 3, and 7 of life in 31 preterm infants (gestational age 29.6 ± 1.8 weeks; birth weight 1380 ± 350 g) on non-invasive respiratory support. Six fixed 1-minute time intervals were selected from each 1-hour recording and both RR and HR were calculated using all intervals or only those with stable dEMG and CI recordings.

RESULTS

dEMG was well tolerated and signal quality was good. Both RR and HR measured by dEMG and CI were significantly correlated (RR: r = 0.85, HR: r = 0.98) and showed good agreement by the Bland-Altman plot (mean difference (limits of agreement): RR: -2.3 (-17.3 to 12.7) breaths/min and HR: -0.3 (-5.3 to 4.7) beats/min. When analyzing only stable recordings, the correlation (r = 0.92) and agreement (-1.8 (-12.3 to 8.7) breaths/min) for RR improved. Subgroup analyses for postnatal age, gestational age, and mode of support showed similar results suggesting good repeatability of dEMG.

CONCLUSION

This study shows that monitoring RR and HR with transcutaneous dEMG is feasible and repeatable in preterm infants.

The Effect of Caffeine on Diaphragmatic Activity and Tidal Volume in Preterm Infants

OBJECTIVE

To determine the effect of caffeine on diaphragmatic activity, tidal volume (Vt), and end-expiratory lung volume (EELV) in preterm infants.

STUDY DESIGN

Using transcutaneous electromyography of the diaphragm (dEMG), we measured diaphragmatic activity from 30 minutes before (baseline) to 3 hours after administration of an intravenous caffeine-base loading dose in 30 spontaneously breathing preterm infants (mean gestational age, 29.1 ± 1.3 weeks), most of whom were on noninvasive respiratory support. Diaphragmatic activity was expressed as the percentage change in dEMG amplitude, area under the curve, respiratory rate, and inspiratory and expiratory times. Using respiratory inductive plethysmography, we measured changes in Vt and EELV from baseline. These outcome variables were calculated at 8 fixed time points after caffeine administration (5, 15, 30, 60, 90, 120, 150, and 180 minutes) and compared with baseline.

RESULTS

Caffeine administration resulted in rapid (within 5 minutes) increases in dEMG amplitude (median, 43%; IQR, 24%-63%; P < .001) and area under the curve (median, 28%; IQR, 14%-48%; P < .001). Vt also increased by a median of 30% (IQR, 7%-48%), and this change was significantly correlated with the change in dEMG amplitude (r = 0.67; P < .001). These effects were relatively stable until 120 minutes after caffeine administration. Caffeine did not consistently impact EELV, respiratory rate, or inspiratory and expiratory times.

CONCLUSION

Caffeine treatment results in a rapid and sustained increase in diaphragmatic activity and Vt in preterm infants.

The effects of prone and supine positions on the regional distribution of ventilation in infants and children using electrical impedance tomography

Background

Positioning of ill children is often used to optimise ventilation–perfusion matching, thereby improving oxygenation.

Objectives

To determine the effects of supine and prone positions, and different head positions, on the distribution of ventilation in healthy, spontaneously breathing infants and children between the ages of 6 months and 9 years.

Methods

Electrical impedance tomography measurements were recorded from participants in supine and prone positions. Head positions included the head turned to the left and right in supine and prone positions, and in the midline in the supine position. Distribution of ventilation was described using end-expiratory–end-inspiratory relative impedance change.

Results

A total of 56 participants (boys = 31 [55%]; girls = 25 [45%]) were studied. The dorsal lung was significantly better ventilated than the ventral lung (P < 0.001) in both body positions. The majority of participants (83%) had greater ventilation in the dorsal lung in both positions, whilst five participants (10%) demonstrated consistently better ventilation in the non-dependent lung in both positions. Head position had no effect on the distribution of ventilation.

Conclusions

This study demonstrates that the distribution of ventilation in healthy, spontaneously breathing infants and children in supine and prone positions is not as straightforward as previously thought, with no clear reversal of the adult pattern evident.

Challenging a paradigm: positional changes in ventilation distribution are highly variable in healthy infants and children

RATIONALE

Current understanding is that infants and children preferentially ventilate non-dependent lungs, a reversal of that of adults, based on studies using krypton-81m ventilation scanning. Participants in these studies had lung disease and were either sedated or ventilated. There is little understanding of the distribution of ventilation in spontaneous breathing healthy infants and children.

OBJECTIVES

This study aimed to determine the effects of side lying on the distribution of ventilation in healthy, spontaneously breathing infants and children between the ages of 6 months and 9 years.

METHODS AND MEASUREMENTS

Measurements were taken using electrical impedance tomography (EIT) in supine, left and right side lying. Distribution of ventilation was described using end-expiratory to end-inspiratory relative impedance change.

RESULTS

Fifty-six (31, 55% male) participants were studied. Nineteen (35%) participants consistently showed greater ventilation in the non-dependent lung, eight (15%) consistently showed greater ventilation in the dependent lung and 28 (51%) showed a varied pattern between left and right side lying. Overall, left side lying resulted in significantly better mean ventilation of the right (non-dependent) lung (P < 0.01). Distribution of ventilation in right side lying was relatively equal between left and right lungs.

CONCLUSIONS

This study demonstrates that the distribution of ventilation in spontaneously breathing infants and children is not as straightforward as previously described. The distribution of ventilation was variably affected by body position with no clear reversal of the adult pattern evident.

Electrical activity of the diaphragm (Edi) values and Edi catheter placement in non-ventilated preterm neonates

OBJECTIVE

The electrical activity of the diaphragm (Edi) reflects neural respiratory drive. Edi peak correlates with inspiratory drive and Edi minimum (Edi min) correlates with the tonic activity of the diaphragm. Edi data in non-ventilated preterm neonates have not been determined.The primary aim of this study was to determine Edi values in non-ventilated preterm neonates throughout postnatal maturation and with various types of noninvasive respiratory support. The secondary aim was to evaluate the success or complications of placement of the Edi catheter in premature neonates.

STUDY DESIGN

This was a prospective observational study of non-ventilated neonates <33 weeks gestation. Data were collected weekly using an Edi catheter placed in neonates on highflow nasal cannula (HFNC), nasal cannula (NC) or room air (RA). Clinical stability was determined by measuring heart rate (HR), respiratory rate (RR) and oxygen saturation (Sats). Success and adverse events of Edi catheter placement was monitored. Statistics were obtained by analysis of variance, P<0.05 was considered significant.

RESULT

Seventeen neonates were enrolled at 26 to 33 weeks postmenstrual age and studied from 1 to 10 weeks in duration. Overall Edi peak was 10.8±3.7 mcV (range 3.7 to 18.7) and Edi min was 2.8±1.1 mcV (range 0.8 to 7.6). There was no difference in Edi peak and min over postmenstrual ages within or between neonates, and no difference between those neonates on HFNC, NC or RA. HR, RR and Sats were not different over postmenstrual age or between any groups. The Edi catheter was placed successfully in 100% of these neonates. There were no adverse events noted.

CONCLUSION

In clinically stable neonates, the inspiratory drive (Edi peak) and tonic activity (Edi min) do not change with postnatal maturation or with the level of noninvasive respiratory support. The Edi catheter can be placed successfully in these premature neonates. These Edi data have the potential to guide ventilatory management of premature neonates.

Respiratory muscle activity related to flow and lung volume in preterm infants compared with term infants

Infants with chronic lung disease (CLD) have a capacity to maintain functional lung volume despite alterations to their lung mechanics. We hypothesize that they achieve this by altering breathing patterns and dynamic elevation of lung volume, leading to differences in the relationship between respiratory muscle activity, flow and lung volume. Lung function and transcutaneous electromyography of the respiratory muscles (rEMG) were measured in 20 infants with CLD and in 39 healthy age-matched controls during quiet sleep. We compared coefficient of variations (CVs) of rEMG and the temporal relationship of rEMG variables, to flow and lung volume [functional residual capacity (FRC)] between these groups. The time between the start of inspiratory muscle activity and the resulting flow (tria)--in relation to respiratory cycle time--was significantly longer in infants with CLD. Although FRC had similar associations with tria and postinspiratory activity (corrected for respiratory cycle time), the CV of the diaphragmatic rEMG was lower in CLD infants (22.6 versus 31.0%, p = 0.030). The temporal relationship of rEMG to flow and FRC and the loss of adaptive variability provide additional information on coping mechanisms in infants with CLD. This technique could be used for noninvasive bedside monitoring of CLD.

Lung volume, breathing pattern and ventilation inhomogeneity in preterm and term infants

Background

Morphological changes in preterm infants with bronchopulmonary dysplasia (BPD) have functional consequences on lung volume, ventilation inhomogeneity and respiratory mechanics. Although some studies have shown lower lung volumes and increased ventilation inhomogeneity in BPD infants, conflicting results exist possibly due to differences in sedation and measurement techniques.

Methodology/Principal Findings

We studied 127 infants with BPD, 58 preterm infants without BPD and 239 healthy term-born infants, at a matched post-conceptional age of 44 weeks during quiet natural sleep according to ATS/ERS standards. Lung function parameters measured were functional residual capacity (FRC) and ventilation inhomogeneity by multiple breath washout as well as tidal breathing parameters. Preterm infants with BPD had only marginally lower FRC (21.4 mL/kg) than preterm infants without BPD (23.4 mL/kg) and term-born infants (22.6 mL/kg), though there was no trend with disease severity. They also showed higher respiratory rates and lower ratios of time to peak expiratory flow and expiratory time (t_PTEF/t_E) than healthy preterm and term controls. These changes were related to disease severity. No differences were found for ventilation inhomogeneity.

Conclusions

Our results suggest that preterm infants with BPD have a high capacity to maintain functional lung volume during natural sleep. The alterations in breathing pattern with disease severity may reflect presence of adaptive mechanisms to cope with the disease process.

Development of an apnea detector for neonates using diaphragmatic surface electromyography

Respiratory diseases are among the most important and serious conditions that can affect the newborn baby. A cessation of breathing, longer than 15 seconds, or accompanied by hypoxia or bradycardia, is called apnea of prematurity (AOP) and has been found in more than 50% of premature infants. An apnea detector used in infant monitoring has been designed and constructed and is intended to be applied in a clinical environment. Diaphragmatic surface EMG has been used as the technique for detecting apnea episodes due to a direct relation with the respiratory drive. Both obstructive and central apnea can be determined as well as heart rate. Good performance and feasibility have been shown by the prototype.