Respiratory Flow Measurements Research Articles

The interaction between neuromuscular forces, aerodynamic forces, and anatomical motion in the upper airway predicts the severity of pediatric OSA.

Upper airway neuromuscular response to air pressure during inhalation is an important factor in assessing pediatric subjects with obstructive sleep apnea (OSA). The neuromuscular response's strength, timing, and duration all contribute to the potential for airway collapses and the severity of OSA. This study quantifies these factors at the soft palate, tongue, and epiglottis to assess the relationship between neuromuscular control and OSA severity in 20 pediatric subjects with and without trisomy 21, under dexmedetomidine-induced sedation. The interaction between neuromuscular force and airflow pressure force was assessed based on power transferred between the airway wall and airflow calculated from airway wall motion (from cine magnetic resonance images) and air pressure acting on the airway wall (from computational fluid dynamics simulations). Airway wall motion could be asynchronous with pressure forces due to neuromuscular activation, or synchronous with pressure forces, indicating a passive response to airflow. The obstructive apnea-hypopnea index (oAHI) quantified OSA severity. During inhalation, the normalized work done through asynchronous dilation of the airway at the soft palate, tongue, and epiglottis correlated significantly with oAHI (Spearman's ρ = 0.54, 0.50, 0.64; P = 0.03, 0.03, 0.003). Synchronous collapse at the epiglottis correlated significantly with oAHI (ρ = 0.52; P = 0.02). Temporal order of synchronous and asynchronous epiglottis motion during inhalation predicted the severity of OSA (moderate vs. severe) with 100% sensitivity and 70% specificity. Subjects with severe OSA and/or trisomy 21 have insufficient neuromuscular activation during inhalation, leading to collapse and increased neuromuscular activation. Airflow-driven airway wall motion during late inhalation likely is the main determinant of OSA severity.NEW & NOTEWORTHY This is the first study that combines cine MRI and computational fluid dynamics with in vivo synchronous respiratory flow measurement to quantify the interaction between airway neuromuscular forces, aerodynamic forces, and airway anatomy noninvasively in pediatric patients with obstructive sleep apnea (OSA). The results indicate power transfer predicts OSA severity.

A Fast Calibration Method for Pneumotachograph with a 3L Syringe.

The pneumotachograph (PNT), a commonly used flowmeter in pulmonary function diagnostic equipment, is the required frequency calibration to maintain high accuracy. Aiming to simplify calibration steps, we developed a fast calibration system with a commercially available 3L syringe to provide a real output flow waveform. The acquisition of the real output flow waveform is based on the reliable measurement of in-cylinder pressure and the real-time detection of plunger speed. To improve the calibration accuracy, the tapping position for measuring in-cylinder pressure was optimized by CFD dynamic-mesh updating technique. The plunger speed was obtained by tracking the handle of the plunger with a smart terminal. Then, the real output flow was corrected using a compensation model equation. The calibration system was verified by the pulmonary waveform generator that the accuracy satisfied the requirements for respiratory flow measurement according to ATS standardization. The experimental results suggest that the developed method promises the fast calibration of PNT.

A Portable Self‐Powered Turbine Spirometer for Rehabilitation Monitoring on COVID‐19

AbstractCoronavirus disease 2019 (COVID‐19) patients may experience persistent impairment of the lungs after recovery and discharge, which can cause a decline in pulmonary function. Therefore, regular pulmonary function tests are essential for COVID‐19 recovered patients, and portable, home‐based pulmonary function test devices are of great significance during the pandemic. Herein, a portable self‐powered turbine spirometer (PSTS) is designed for respiratory flow measurement and assessment of pulmonary function with high accuracy, humidity resistance, good durability, and low cost. The respiratory airflow can directly drive PSTS to produce a sinusoidal signal with a signal‐to‐noise of 40.64 dB. By utilizing the long short‐term memory (LSTM) model, the flow is successfully predicted, and the “lag‐before‐start” and “spin‐after‐stop” defects of the turbine spirometer are eliminated effectively. For pulmonary function tests, the flow‐volume loop curve can be obtained from PSTS, and pulmonary function parameters such as inspiratory capacity (IC), forced vital capacity (FVC) and forced expiratory volume in the first 1 s (FEV1) can be calculated. The accuracy of IC is over 95%, and others can reach over 97%. A portable smart pulmonary function assessment system is further developed and used to test the pulmonary function of COVID‐19 patients one month after symptom onset, demonstrating potential for assessing rehabilitation trends and long‐term follow‐up of COVID‐19 recovered patients.

Validation of a new wearable device for type 3 sleep test without flowmeter.

BackgroundVentilation monitoring during sleep is performed by sleep test instrumentation that is uncomfortable for the patients due to the presence of the flowmeter. The objective of this study was to evaluate if an innovative type 3 wearable system, the X10X and X10Y, is able to correctly detect events of apnea and hypopnea and to classify the severity of sleep apnea without the use of a flowmeter.Methods40 patients with sleep disordered breathing were analyzed by continuous and simultaneous recording of X10X and X10Y and another certified type 3 system, SOMNOtouch, used for comparison. Evaluation was performed in terms of quality of respiratory signals (scores from 1, lowest, to 5, highest), duration and classification of apneas, as well as identification and duration of hypopneas.Results580 periods were evaluated. Mean quality assigned score was 3.37±1.42 and 3.25±1.35 for X10X and X10Y and SOMNOtouch, respectively. The agreement between the two systems was evaluated with grades 4 and 5 in 383 out of 580 cases. A high correlation (r2 = 0.921; p<0.001) was found between the AHI indexes obtained from the two systems. X10X and X10Y devices were able to correctly classify 72.3% of the obstructive apneas, 81% of the central apneas, 61.3% of the hypopneas, and 64.6% of the mixed apneas when compared to SOMNOtouch device.ConclusionThe X10X and X10Y devices are able to provide a correct grading of sleep respiratory disorders without the need of a nasal cannula for respiratory flow measurement and can be considered as a type 3 sleep test device for screening tests.

Documenting Spatial Variation of SCG Signals for Optimal Sensor Placement

Introduction Seismocardiography (SCG) (low frequency cardiovascular vibrations acquired on the chest wall) has potential for early noninvasive detection of heart failure (HF) deterioration. However, inaccurate sensor placement may significantly limit the method's utility. Objective To document SCG waveform spatial variability to aid in sensor placement and quantification of sensor position shifts on the signal reproducibility. Methods SCG signals were recorded in 15 healthy subjects using 36 accelerometers placed on the anterior chest wall along with simultaneous ECG and respiratory flow measurements (Figure 1). SCG waveforms were segmented using ECG beats. SCG feature points were identified according to previous studies and chest surface acceleration maps created. Results Figure 2 suggests that SCG may be loudest and positive (i.e., anterior or outward) acceleration at the left lower sternal border (LLSB) during the aortic opening and closure periods. A negative (i.e. posterior or inward) acceleration was observed around the LLSB location during the isovolumic contraction time period. The SCG intra-group variability with change in sensor position is shown in Table 1.Table 1: SCG intra-group variability with sensor position change Conclusions Optimal sensor location was found around the LLSB between 3rd to 5th ICS. Use of this location may help increase robustness of SCG signal interpretation and its utility for HF monitoring. Further, change in sensor locations of 3 cm around 4thICS at LLSB (the target sensor location) resulted in only a ∼7 % change in waveform variability and ∼9 % change in PEP, which if true, would better facilitate ambulatory use and sensor placement by patients.

Greenness Availability and Respiratory Health in a Population of Urbanised Children in North-Western Italy.

Paediatric Asthma contributes in paediatric global burden of diseases, as the most common chronic disease in children. Children are exposed to many environmental risk-factors, able to determine or worsen respiratory diseases, and contributing to asthma and asthma-like symptoms increases, especially in metropolitan areas. In urban settings, surrounding vegetation (greenness) may provide important benefits to health, including the promotion of physical activity and the mitigation of air and noise pollution. The aim of this study was to investigate the association between greenness and respiratory health. A total of 187 children (10–13 yrs old) were recruited in Turin, the north-western part of Italy. The prevalence of asthma and asthma-like symptoms was calculated from self-reported data collected by SIDRIA questionnaire. Spirometry test was performed to obtain respiratory flow measurements. Greenness was measured at individual level through the Normalised Difference Vegetation Index (NDVI) estimations from remote-sensing images. Higher exposure (3rd tertile vs. 1st tertile) to NDVI was associated to significantly lower ORs for asthma [0.13 CI 95% 0.02–0.7, p = 0.019], bronchitis [0.14 CI 95% 0.05–0.45, p = 0.001], and current wheezing [0.25 CI 95% 0.09–0.70, p = 0.008]. A significative positive association was found between greenness and FEF25–75, since children exposed to the 2nd tertile of NDVI reported a significantly decreased FEF25–75 compared to those in the 3rd tertile [B: −2.40; C.I.95%: −0.48–0.01; p = 0.049]. This cross-sectional study provided additional data on still inconsistent literature referring to respiratory health in children and green spaces, attesting a positive effect of greenness in a specific area of Italy. Further research is still needed.

Pharyngeal distensibility during expiration is an independent predictor of the severity of obstructive sleep apnoea.

Pharyngeal distensibility and collapsibility reflect the passive properties of tissue in the airway, are an indicator of the ease with which an airway can be deformed and are related to the severity of obstructive sleep apnoea (OSA). During normal tidal respiration, the collapsibility of the pharynx during expiration is passive without confounding by neuromuscular activation that occurs during inspiration. We evaluated the distensibility and collapsibility of the upper airway in subjects with OSA during wakefulness using sophisticated dynamic computed tomography (CT) imaging. We hypothesized that the dynamic changes of the upper airway during expiration would be related to the severity of OSA. Twenty-three patients with OSA and eight normal subjects underwent simultaneous measurement of respiratory flow and airway calibre using ultrafast CT. The change in pharyngeal cross-sectional area divided by the change in concomitant flow (as distensibility or collapsibility) was measured and compared across different severities of OSA. The slope of this relationship between delta area and delta flow during expiration was significantly higher in severe OSA when compared with normal controls and mild-moderate OSA. Differences in airway distensibility or collapsibility between severity groups were significant in expiration but not in inspiration. Distensibility or collapsibility contributed most to the apnoea-hypopnoea index in regression modelling. Age, gender, and body mass index (BMI) were not significant independent predictors. Our study demonstrates that airway distensibility during the expiratory phase of awake respiration is correlated with the severity of OSA.

Design and Experiments for a Kind of Capacitive Type Sensor Measuring Air Flow and Pressure Differential

A kind of capacitive type air flow sensor is designed and fabricated for respiratory flow measurement. Major sensitive elements of the sensor are two parallel placed capacitance plates which are perpendicularly fixed on the sidewall of the air channel. The flow and pressure differential of air can be calculated by measuring the change of the micro capacitance, which is initiated by air pressure. The Bernoulli equation and the continuous equation of the fluid are used for theoretical analysis. The mechanical analysis and FEM (finite element method) is used to make the optimum design for the sensor. Then, the micro capacitance measuring circuit using the so called peak detection method is fabricated and corresponding A/D convert digital circuit are also made. Experimental result indicates the capacitance measuring circuit has little error. The accuracy, sensitivity, and resolution of the circuit reach 0.2% FS, 1.4089 V/pF, 0.003 pF respectively, which indicates this kind of system is feasible in practical applications.

The Effect of Aerosol Saline on Laboratory-Induced Dyspnea.

In the 'placebo arm' of a recent study, we found that aerosol saline (sham treatment) produced substantial relief of laboratory-induced dyspnea (Breathing discomfort-BD) in nearly half the subjects. The sham intervention included a physiological change, and instructions to subjects could have produced expectation of dyspnea relief. In the present study, we attempted to discover whether the response to sham aerosol was driven by behavioral or physiological aspects of the intervention. Dyspnea (air hunger) was evoked by constraining tidal volume during graded hypercapnia. We measured [Formula: see text] versus BD relationship before and after aerosol saline. To minimize subjects' expectations of dyspnea relief, participants were clearly instructed that we would only deliver saline aerosol. In Protocol 1, we delivered aerosol saline with a ventilator (mimicking our prior study); in Protocol 2, we delivered aerosol without a ventilator. Administration of aerosol saline had little effect on BD in this group of subjects with one exception: one subject experienced appreciable reduction in BD in Protocol 1. This treatment effect was less in Protocol 2. The two most likely explanations are (a) that procedures surrounding ventilator administration of aerosol produced a psychological placebo treatment effect even though the subject knew a drug was not given; (b) there were behavioral changes in breathing undetected by our measurements of respiratory flow and volume that altered the subjects comfort. When the expectation of treatment effect is minimized, a significant reduction in dyspnea in response to saline placebo is uncommon but not impossible.

Laser-based absorption spectroscopy as a technique for rapid in-line analysis of respired gas concentrations of O2 and CO2

The use of sidestream analyzers for respired gas analysis is almost universal. However, they are not ideal for measurements of respiratory gas exchange because the analyses are both temporally dissociated from measurements of respiratory flow and also not generally conducted under the same physical conditions. This study explores the possibility of constructing an all optical, fast response, in-line breath analyzer for oxygen and carbon dioxide. Using direct absorption spectroscopy with a diode laser operating at a wavelength near 2 μm, measurements of expired carbon dioxide concentrations were obtained with an absolute limit of detection of 0.04% at a time resolution of 10 ms. Simultaneously, cavity enhanced absorption spectroscopy at a wavelength near 760 nm was employed to obtain measurements of expired oxygen concentrations with an absolute limit of detection of 0.26% at a time resolution of 10 ms. We conclude that laser-based absorption spectroscopy is a promising technology for in-line analysis of respired carbon dioxide and oxygen concentrations.

Cross-Correlation-Based Optical Flowmeter

In this paper, an optical flowmeter based on the cross-correlation technique is proposed. Two parallel laser beams are made to cross a transparent pipe wherein a turbulent air flows. The laser beams are detected by two position-sensitive detectors (PSDs) whose output signals are processed by software. The cross-correlation function between the signals is calculated, which yields the time delay between them. The flow velocity is then obtained by the ratio of the distance between the laser beams to the time delay. The flowmeter is applicable for measuring human respiratory flow in a noninvasive way. An experimental prototype is built, and results are provided. A detailed description of the experimental setup and of measurement procedures are presented and discussed. Results have been very promising and have shown the potential of the system developed here in performing human respiratory flow measurements, particularly those suitable for neonates.

DETECTING CARDIORESPIRATORY COORDINATION BY RESPIRATORY PATTERN ANALYSIS OF HEART PERIOD DYNAMICS — THE MUSICAL RHYTHM APPROACH

The purpose of this study was to demonstrate that cardiorespiratory coordination can be unveiled by analyzing solely the heart period data from electrocardiogram (ECG). The analysis was done (1) on the basis of symbolic musical pattern analysis to detect intermittent cardiorespiratory phase coordination and (2) on the quantitative evaluation of respiratory sinus arrhythmia (RSA) to examine long-term frequency coordination between heartbeat and respiration. The methods were applied to 196 ECGs of 98 healthy subjects. The results showed that at night (1) intermittent phase coordination occurred reproducibly in individual subjects, and (2) long-term frequency ratios statistically approached 4:1 over all subjects to within an accuracy of 0.02, although individual values ranged from 2.5–6.0 with a high intraindividual reproducibility (r=0.94, day A versus day B). Moreover, intermittent phase coordination ratios and long-term frequency ratios corresponded to each other with a remarkably high correlation (r=0.95). In the light of clinical applications, the coordination analysis presented here has an enormous advantage over those techniques depending on respiratory flow measurements, because the pattern technique requires only ECG recordings, and it is thus applicable over a longer period of time under daily life conditions.

Respiratory flow measurements and anesthetic drugs: some in vitro observations

Study Objective: To illustrate the influence of anesthetic gases on respiratory flow measurements and to correct this influence. Design: In vitro evaluation. Setting: Laboratory. Measurements and Main Results: An in vitro method using a 120-L Tissot water-seal spirometer was used along with a Bicore CP-100, designed for use in intensive care units, and a Datex Ultima, designed for use in the operating room. The flow transducer of one of the instruments being tested was placed in the gas inlet of the Tissot so that simultaneous measurements could be made. Timed flows (2 to 60 L/min) of various gases (O 2 and air) and gas mixtures (halothane-O 2, isoflurane-O 2, N 2O-O 2, and N 2O-O 2-isoflurane) were used and the measurements made by the Tissot and the test instrument compared. The Datex Ultima, which includes software corrections for anesthetics, was able to accurately measure gas flows (2 to 60 L/min) of air, 100% oxygen, and anesthetic gas mixtures to within ±10% of measurements made by the Tissot. The Bicore CP-100, intended for use with mechanically ventilated patients, accurately measured air and 100% oxygen flow rate to within ±8% of the measurements made by the Tissot, but there were large errors (up to 40%) when anesthetics were used. Conclusions: This study illustrates the effects of anesthetic gases on measurements of ventilatory flow and the need to ascertain whether corrections are needed to improve the accuracy of flow transducers.

Synchronization in the human cardiorespiratory system.

We investigate synchronization between cardiovascular and respiratory systems in healthy humans under free-running conditions. For this aim we analyze nonstationary irregular bivariate data, namely, electrocardiograms and measurements of respiratory flow. We briefly discuss a statistical approach to synchronization in noisy and chaotic systems and illustrate it with numerical examples; effects of phase and frequency locking are considered. Next, we present and discuss methods suitable for the detection of hidden synchronous epochs from such data. The analysis of the experimental records reveals synchronous regimes of different orders n:m and transitions between them; the physiological significance of this finding is discussed.

A Plethysmographic Method for Assessment of Lung Function in Mechanically Ventilated Very Low Birth Weight Infants

We have developed and tested a plethysmographic method for assessment of lung function in mechanically ventilated very low birth weight infants during intensive care. Information about the mechanics of the respiratory system is obtained from the respiratory flow as measured by volume displacement plethysmography and from airway pressure measured in the artificial airway. Data on lung volumes, ventilation, and distribution of ventilation is obtained simultaneously by combining the respiratory flow measurements with nitrogen concentration analyses of the respiratory gas. No significant differences were found when the estimations of mechanical parameters and FRC were compared with reference methods and when determinations of the same parameters were repeated in the same subjects. The plethysmograph was shown to be safe and convenient to use, even in studies lasting several hours.

ICU monitoring of ventilation distribution.

The oxygen washin method has been shown to be a practical way to measure functional residual capacity (FRC) in the intensive care unit. The ventilator oxygen concentration is increased and measurements of respiratory flow and oxygen concentration at the mouth are made with the patient monitoring system. No additional personnel, bedside equipment or ventilator attachments are required. A feasibility study was performed to determine if this method could be used to estimate a continuous distribution of ventilation with respect to ventilation to volume ratio VA/V. Due to gas mixing in the ventilator, the inspired oxygen fraction does not increase instantaneously to its new value. An equation was derived which models the lung as 50 discrete compartments and accounts for the transient change in mean inspired oxygen fraction. A digital computer simulation demonstrated good distribution recovery for one and two mode ventilation distributions. Continuous distributions were computed for four post cardiac surgery patients at four levels of positive end expiratory pressure (PEEP). In these patients a linear increase in the amount of ventilation in the normal VA/V range occurred with increasing PEEP, i.e., slow and fast spaces tended to move centrally toward a more normal VA/V range. At zero PEEP 26% of the ventilation occurred in the normal range and this increased to 49% at 15 PEEP. Dead space fraction was poorly estimated and spurious modes occurred in the high VA/V range.

Dual Gated Nuclear Cardiac Images

A data acquisition system has been developed to collect camera events simultaneously with continually digitized electrocardiograph signals and respiratory flow measurements. Software processing of the list mode data creates more precisely gated cardiac frames. Additionally, motion blur due to heart movement during breathing is reduced by selecting events within a specific respiratory phase. Thallium myocardium images of a healthy volunteer show increased definition. This technique of combined cardiac and respiratory gating has the potential of improving the detectability of small lesions, and the characterization of cardiac wall motion.

Measurement of respiratory flow by inductance pneumography.

Measurement of respiratory flow by inductance pneumography.

A Planar Fluidic Flowmeter Applicable to Respiratory Flows

Tests are described on a bidirectional fluidic flowmeter for respiratory measurements using the principle first described by Tanney. Good dynamic response and acceptable linearity is achieved over most of the very wide flow range conditions encountered in respiratory flow measurements. A flow range of 380 litres/minute with a signal-to-noise ratio of 150 and a transient rate flow change of 14,500 litres/minute/second were measured for the best flowmeter configuration.

A mathematical model for the ultrasonic measurement of respiratory flow.

A mathematical model is developed for the measurement of respiratory air flow, based on the phase shift of ultrasonic pulse trains. A correction is made for the velocity of found as a function of gas composition, moisture, temperature and pressure. Error estimates and calibration procedures as they relate to clinical application are discussed.