Measuring Ventilatory Activity with Structured Light Plethysmography (SLP) Reduces Instrumental Observer Effect and Preserves Tidal Breathing Variability in Healthy and COPD

Measurement of thoraco-abdominal synchrony using respiratory inductance plethysmography: technical aspects and a proposal to overcome its limitations

BACKGROUND

Thoraco-abdominal asynchrony (TAA) is usually assessed by respiratory inductance plethysmography. The main parameter used for its assessment is the calculation of the phase angle based on Lissajous plots. However, there are some mathematical limitations to its use.

RESEARCH DESIGN AND METHODS

Sequences of five breaths were selected from a) normal subjects, b) COPD patients, both at rest and during exercise, and c) patients with obstructive apnea syndrome. Automated analysis was performed calculating phase angle, loop rotation (clockwise or counterclockwise), global phase delay and loop area. TAA severity was estimated quantitatively and in subgroups.

RESULTS

2290 cycles were analyzed (55% clockwise rotation). Phase angle ranged from -86.90 to + 88.4 degrees, while global phase delay ranged from -179.75 to + 178.54. Despite a good correlation with global phase delay (p < 0.01, ANOVA test), phase angle and loop area were not able to correctly classify breaths with severe deviation and paradoxical movements (p=ns, Bonferroni post hoc test).

CONCLUSIONS

Global phase delay covers the whole spectrum of TAA situations in a single value. It may be a relevant parameter for diagnosis and follow-up of clinical conditions leading to TAA.

CLINICAL TRIAL REGISTRATION

The trial from which the traces were obtained was registered at ClinicalTrials.gov ;(identifier: NCT04597606).

The use of time-of-flight camera to assess respiratory rates and thoracoabdominal depths in patients with chronic respiratory disease

INTRODUCTION

Over the last 5 years, the analysis of respiratory patterns presents a growing usage in clinical and research purposes, but there is still currently a lack of easy-to-use and affordable devices to perform such kind of evaluation.

OBJECTIVES

The aim of this study is to validate a new specifically developed method, based on Kinect sensor, to assess respiratory patterns against spirometry under various conditions.

METHODS

One hundred and one participants took parts in one of the three validations studies. Twenty-five chronic respiratory disease patients (14 with chronic obstructive pulmonary disease (COPD) [65 ± 10 years old, FEV₁  = 37 (15% predicted value), VC = 62 (20% predicted value)], and 11 with lung fibrosis (LF) [64 ± 14 years old, FEV₁  = 55 (19% predicted value), VC = 62 (20% predicted value)]) and 76 healthy controls (HC) were recruited. The correlations between the signal of the Kinect (depth and respiratory rate) and the spirometer (tidal volume and respiratory rate) were computed in part 1. We then included 66 HC to test the ability of the system to detect modifications of respiratory patterns induced by various conditions known to modify respiratory pattern (cognitive load, inspiratory load and combination) in parts 2 and 3.

RESULTS

There is a strong correlation between the depth recorded by the Kinect and the tidal volume recorded by the spirometer: r = 0.973 for COPD patients, r = 0.989 for LF patients and r = 0.984 for HC. The Kinect is able to detect changes in breathing patterns induced by different respiratory disturbance conditions, gender and oral task.

CONCLUSIONS

Measurements performed with the Kinect sensors are highly correlated with the spirometer in HC and patients with COPD and LF. Kinect is also able to assess respiratory patterns under various loads and disturbances. This method is affordable, easy to use, fully automated and could be used in the current clinical context. Respiratory patterns are important to assess in daily clinics. However, there is currently no affordable and easy-to-use tool to evaluate these parameters in clinics. We validated a new system to assess respiratory patterns using the Kinect sensor in patients with chronic respiratory diseases.

Accuracy and reliability of the optoelectronic plethysmography and the heart rate systems for measuring breathing rates compared with the spirometer

Measuring breathing rates without a mouthpiece is of interest in clinical settings. Electrocardiogram devices and, more recently, optoelectronic plethysmography (OEP) methods can estimate breathing rates with only a few electrodes or motion-capture markers placed on the patient. This study estimated and compared the accuracy and reliability of three non-invasive devices: an OEP system with 12 markers, an electrocardiogram device and the conventional spirometer. Using the three devices simultaneously, we recorded 72 six-minute epochs on supine subjects. Our results show that the OEP system has a very low limit of agreement and a bias lower than 0.4% compared with the spirometer, indicating that these devices can be used interchangeably. We observed comparable results for electrocardiogram devices. The OEP system facilitates breathing rate measurements and offers a more complete chest-lung volume analysis that can be easily associated with heart rate analysis without any synchronisation process, for useful features for clinical applications and intensive care.

Tidal spirometric curves obtained from a nasal cannula

Spirometry is a gold standard to assess lung function, and to identify respiratory impairments seen in obstructive lung diseases. The method is used for periodic monitoring, but it only provides snapshot information, and it requires forceful exhalation which is associated with limited reliability and repeatability. Several studies indicate that tidal flow-volume curves measured by pneumotachography or plethysmography can also be used to assess lung function. These methods avoid the forced manoeuvre, but are complex to set up or sensitive to movement. In the present work we address the long-standing problem of the unavailability of an easy-to-use and accurate method for monitoring tidal breathing frequently or even continuously. We show that pressure recordings from a nasal cannula can be accurately converted into scaled flow-volume curves by means of an algorithm that continuously calibrates itself. The method has been validated by feeding realistic healthy and unhealthy breathing patterns to anatomically correct 3D-printed upper airways of an infant and an adult, and by comparing the imposed flow-volume curves to the pressure-derived flow-volume curves. The observed very high level of accuracy opens the route towards remotely monitoring patients with chronic lung diseases.

Tidal Breathing Parameters Measured by Structured Light Plethysmography in Newborns: Is It Feasible in Neonatal Intensive Care Unit?

OBJECTIVE

Structured light plethysmography (SLP) is a novel and noncontact respiratory assessment technique. It provides tidal breathing measurement in patients difficult to cooperate. In this study, we aimed to determine data for tidal breathing parameters measured by SLP in newborns.

STUDY DESIGN

Infants between 2 and 5 days of life without having any respiratory symptoms were eligible for this observational study. In total, 5 minutes of tidal breathing was recorded using SLP (Thora-3Di, PneumaCare Ltd, Cambridge, U.K.) in each infant. Various tidal breathing parameters including timing indices, flow-based parameters, and regional parameters were obtained from SLP data.

RESULTS

A total of 57 infants underwent measurements in the study. Evaluable recordings from 42 term and 11 late preterm infants were analyzed. Median gestational age and birthweight of the infants were 38 (37-39) weeks and 3,195 (2,790-3,585) g, respectively. In terms of flow-based parameters, "tidal inspiratory flow at 50% of inspiratory volume divided by tidal expiratory flow at 50% of expiratory volume" was 1.29 (1.13-1.53). Relative contribution of the thorax to each breath in percentage was measured as 38.67 (28.21-43.60). Median values of left-right hemithoracic asynchrony and thoraco-abdominal asynchrony were 6.92 (5.35-9.04) and 17.96 (12.98-36.44) degrees in the study population, respectively. There were no differences in tidal breathing parameters except "hemithoracic asynchrony" between term and late preterm infants. Hemithoracic asynchrony was significantly lower in term neonates than late preterms.

CONCLUSION

SLP was found to be feasible to obtain measures of tidal breathing parameters in newborns and it could be performed successfully even in the first days of life.

Non-Invasive Respiratory Assessment in Duchenne Muscular Dystrophy: From Clinical Research to Outcome Measures

Ventilatory failure, due to the progressive wasting of respiratory muscles, is the main cause of death in patients with Duchenne muscular dystrophy (DMD). Reliable measures of lung function and respiratory muscle action are important to monitor disease progression, to identify early signs of ventilatory insufficiency and to plan individual respiratory management. Moreover, the current development of novel gene-modifying and pharmacological therapies highlighted the urgent need of respiratory outcomes to quantify the effects of these therapies. Pulmonary function tests represent the standard of care for lung function evaluation in DMD, but provide a global evaluation of respiratory involvement, which results from the interaction between different respiratory muscles. Currently, research studies have focused on finding novel outcome measures able to describe the behavior of individual respiratory muscles. This review overviews the measures currently identified in clinical research to follow the progressive respiratory decline in patients with DMD, from a global assessment to an individual structure–function muscle characterization. We aim to discuss their strengths and limitations, in relation to their current development and suitability as outcome measures for use in a clinical setting and as in upcoming drug trials in DMD.

Reference equations for tidal breathing parameters using structured light plethysmography

Tidal breathing measurements can be used to identify changes in respiratory status. Structured light plethysmography (SLP) is a non-contact tidal breathing measurement technique. Lack of reference equations for SLP parameters makes clinical decision-making difficult. We have developed a set of growth-adjusted reference equations for seven clinically pertinent parameters of respiratory rate (f_R), inspiratory time (t_I), expiratory time (t_E), duty cycle (t_I/total breath time), phase (thoraco-abdominal asynchrony (TAA)), relative thoracic contribution (RTC) and tidal inspiratory/expiratory flow at 50% volume (IE50).

Reference equations were developed based on a cohort of 198 seated healthy subjects (age 2–75 years, height 82–194 cm, 108 males). We adopted the same methodological approach as the Global Lung Function Initiative (GLI) report on spirometric reference equations. 5 min of tidal breathing was recorded per subject. Parameters were summarised with their medians. The supplementary material provided is an integral part of this work and a reference range calculator is provided therein.

We found predicted f_R to decrease with age and height rapidly in the first 20 years and slowly thereafter. Expected t_I, t_E and RTC followed the opposite trend. RTC was 6.7% higher in females. Duty cycle increased with age, peaked at 13 years and decreased thereafter. TAA was high and variable in early life and declined rapidly with age. Predicted IE50 was constant, as it did not correlate with growth.

These reference ranges for seven key measures ensure that clinicians and researchers can identify tidal breathing patterns in disease and better understand and interpret SLP and tidal breathing data.

A set of reference equations for seven key tidal breathing parameters measured using structured light plethysmography (SLP) to help clinicians better understand and interpret SLP data and the value of tidal breathing patternshttps://bit.ly/2Og2H3h

Noncontact Respiratory Monitoring Using Depth Sensing Cameras: A Review of Current Literature

There is considerable interest in the noncontact monitoring of patients as it allows for reduced restriction of patients, the avoidance of single-use consumables and less patient-clinician contact and hence the reduction of the spread of disease. A technology that has come to the fore for noncontact respiratory monitoring is that based on depth sensing camera systems. This has great potential for the monitoring of a range of respiratory information including the provision of a respiratory waveform, the calculation of respiratory rate and tidal volume (and hence minute volume). Respiratory patterns and apneas can also be observed in the signal. Here we review the ability of this method to provide accurate and clinically useful respiratory information.

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.

Characteristics of respiratory measures in young adults scanned at rest, including systematic changes and "missed" deep breaths

Breathing rate and depth influence the concentration of carbon dioxide in the blood, altering cerebral blood flow and thus functional magnetic resonance imaging (fMRI) signals. Such respiratory fluctuations can have substantial influence in studies of fMRI signal covariance in subjects at rest, the so-called "resting state functional connectivity" technique. If respiration is monitored during fMRI scanning, it is typically done using a belt about the subject's abdomen to record abdominal circumference. Several measures have been derived from these belt records, including the windowed envelope of the waveform (ENV), the windowed variance in the waveform (respiration variation, RV), and a measure of the amplitude of each breath divided by the cycle time of the breath (respiration volume per time, RVT). Any attempt to gauge respiratory contributions to fMRI signals requires a respiratory measure, but little is known about how these measures compare to each other, or how they perform beyond the small studies in which they were initially proposed. Here, we examine the properties of these measures in hundreds of healthy young adults scanned for an hour each at rest, a subset of the Human Connectome Project chosen for having high-quality physiological records. We find: 1) ENV, RV, and RVT are all correlated, and ENV and RV are more highly correlated to each other than to RVT; 2) respiratory events like deep breaths exhibit characteristic heart rate elevations, fMRI signal changes, head motions, and image quality abnormalities time-locked to large deflections in the belt traces; 3) all measures can "miss" deep breaths; 4) RVT "misses" deep breaths more than ENV or RV; 5) all respiratory measures change systematically over the course of a 14.4-min scan. We discuss the implications of these findings for the literature and ways to move forward in modeling respiratory influences on fMRI scans.

Mini review shows that structured light plethysmography provides a non-contact method for evaluating breathing patterns in children

AIM

Structured light plethysmography (SLP) is a novel light-based method that captures chest wall movements to evaluate tidal breathing. We carried out a narrative mini review of the clinical use of SLP in paediatrics.

METHODS

PubMed and Google Scholar were searched for papers published in English up to December 2018. This identified a methodology paper published in 2010 and eight full papers, including three paediatric studies and one paediatric case report. We also included data from ten conference abstracts and one clinical case study.

RESULTS

We found data that validated the ability of SLP to differentiate airway obstruction from tidal breathing parameters and bronchodilator responsiveness for children aged two years and over. Non-contact measurement of regional chest wall movement was a unique feature. Feasibility data were scarce and more studies are needed, especially in infants. Preliminary studies suggest that SLP has the potential to be used in cases of dysfunctional breathing and neuromuscular diseases and as a follow-up tool after lung infections or surgery.

CONCLUSION

Structured light plethysmography has been validated to demonstrate lung function abnormality in paediatric asthma, but further studies are needed to demonstrate its benefits over current practice and how it can be used for other conditions.

Physiological Validation of an Airborne Ultrasound Based Surface Motion Camera for a Contactless Characterization of Breathing Pattern in Humans

Characterizing the breathing pattern in naturally breathing humans brings important information on respiratory mechanics, respiratory muscle, and breathing control. However, measuring breathing modifies breathing (observer effect) through the effects of instrumentation and awareness: measuring human breathing under true ecological conditions is currently impossible. This study tested the hypothesis that non-contact vibrometry using airborne ultrasound (SONAR) could measure breathing movements in a contactless and invisible manner. Thus, first, we evaluated the validity of SONAR measurements by testing their interchangeability with pneumotachograph (PNT) measurements obtained at the same time. We also aimed at evaluating the observer effect by comparing breathing variability obtained by SONAR versus SONAR-PNT measurements. Twenty-three healthy subjects (12 men and 11 women; mean age 33 years - range: 20-54) were studied during resting breathing while sitting on a chair. Breathing activity was described in terms of ventilatory flow measured using a PNT and, either simultaneously or sequentially, with a SONAR device measuring the velocity of the surface motion of the chest wall. SONAR was focused either anteriorly on the xiphoid process or posteriorly on the lower part of the costal margin. Discrete ventilatory temporal and volume variables and their coefficients of variability were calculated from the flow signal (PNT) and the velocity signal (SONAR) and tested for interchangeability (Passing-Bablok regression). Tidal volume (VT) and displacement were linearly related. Breathing frequency (BF), total cycle time (TT), inspiratory time (TI), and expiratory time (TE) met interchangeability criteria. Their coefficients of variation were not statistically significantly different with PNT and SONAR-only. This was true for both the anterior and the posterior SONAR measurements. Non-contact vibrometry using airborne ultrasound is a valid tool for measuring resting breathing pattern.

ERS statement on respiratory muscle testing at rest and during exercise

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

A case of unexplained dyspnoea: when lung function testing matters!

“Lung function corner” articles in Breathe present the results of a lung function test and the authors then debate the interpretation, including potential controversies and background from the literature. As section editors of this newly created section of Breathe, we felt it was important to write the first article, which highlights the usefulness of lung function testing in guiding clinical diagnosis especially in difficult cases such the one we discuss here.

Diverse methods are available for assessment of the respiratory muscles; the technique used should be tailored to the question posed.http://ow.ly/ChbX30m91bt