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Extracting respiratory data from pulse oximeter plethysmogram traces in newborn infants
Abstract
To investigate whether valid respiratory data can be extracted from the pulse oximeter plethysmographic (pleth) trace in healthy newborn infants, pleth data were collected from the foot, and respiratory airflow was simultaneously measured using a facemask. The pleth waveform was analysed using fast Fourier transform (FFT), low-pass filtering (LPF), and by plotting the peak-to-peak amplitude variation (PtP). Using FFT in 14 term infants, the median (range) respiratory rate from the pleth signal was 43 (30-65) breaths/min, and from the flow signal it was 44 (30-67) breaths/min (median difference 0.01 breaths/min, p>0.05). Both LPF and PtP analysis yielded waveforms with a frequency similar to the respiratory rate. Respiratory information, including respiratory rate and a respiratory-like waveform, can reliably be extracted from the pleth trace of a standard pulse oximeter in newborn infants. Such analysis may be clinically useful for non-invasive assessment of respiratory problems in infants and young children.
... Respiration modulates the pulsatile pleth trace, resulting in baseline variation as well as pleth amplitude changes analogous to pulsus paradoxus. 9 We have previously shown that a respiratory waveform extracted from the pleth by an appropriate low-pass filtering algorithm gives a reliable measure of RR in healthy newborns, 10 preterm infants with ...
... 12 We have also shown that RR can be derived from analysis of pleth amplitude variations analogous to pulsus paradoxus. 10 When respiratory status deteriorates, RR tends to increase before SpO 2 decreases. 13 14 Thus continuous RR measurement could enable both earlier intervention and assessment of response to treatment. ...
Objective
There is a lack of objective measures to assess children with acute wheezing episodes. Increased respiratory rate (RR) and pulsus paradoxus (PP) are recognised markers, but poorly recorded in practice. We examined whether they can be reliably assessed from a pulse oximeter plethysmogram (‘pleth’) trace and predict clinical outcome.
Patients and methods
We studied 44 children aged 1–7 years attending hospital with acute wheeze, following initial ‘burst’ bronchodilator therapy (BT), and used custom software to measure RR and assess PP from oximeter pleth traces. Traces were examined for quality, and the accuracy of the RR measurement was validated against simultaneous respiratory inductive plethysmography (RIP). RR and PP at 1 hour after BT were compared with clinical outcomes.
Results
RR from pleth and RIP showed excellent agreement, with a mean difference (RIP minus pleth) of −0.5 breaths per minute (limits of agreement −3.4 to +2.3). 52% of 1 min epochs contained 10 s or more of pleth artefact. At 1 hour after BT, children who subsequently required intravenous bronchodilators had significantly higher RR (median (IQR) 63 (62–66) vs 43 (37–51) breaths per minute) than those who did not, but their heart rate and oxygen saturation were similar. Children with RR ≥55 per minute spent longer in hospital: median (IQR) 30 (22–45) vs 10 (7–21) hours. All children who subsequently required hospital admission had PP-analogous pleth waveforms 1 hour after BT.
Conclusion
RR can be reliably measured and PP detected from the pulse oximeter pleth trace in children with acute wheeze and both markers predict clinical outcome.
Trial registration number
UKCRN15742.
... Wertheim et al. measured the saturation pulse oxygen (SpO 2 ) and conducted frequency analysis to compare its association with the RR. It was discovered the frequency spectrum of the SpO 2 amplitude was associated with the RR (Wertheim et al. 2009). PPG sensors measure SpO 2 changes in blood vessels. ...
... The amplitude of the SpO 2 is correlated significantly with the RR (Wertheim et al. 2009). To measure the RR, the upper and lower envelope lines were extracted through spline interpolation based on the peak of the PPG signal. ...
The importance of monitoring vital signs is increasing with the increase in the number of elderly people and deaths from chronic diseases worldwide. Various studies have been conducted for vital sign monitoring, and it has been confirmed that the transmit time, gradient, and amplitude of pulse signals are highly correlated with blood pressure (BP) and respiration rate (RR). In this study, a single photoplethysmography (PPG) sensor-based wearable device is designed for the continuous monitoring of BP, RR, and heart rate (HR). The device is designed as an earphone type for fixedness and signal stability; it transmits data via an Arduino-based Bluetooth module for wireless use and supplies power via batteries. Because of the similar frequency range between pulse signals and walking signals, denoising is difficult to perform via frequency analysis, where the noise of the PPG signal is isolated via denoising long short-term memory (LSTM) auto encoder. The gradient element, HR, and envelope are extracted as features from the denoised PPG signal, and BP regression models and RR measurement algorithms are designed based on these features. Finally, the reference vital signs and signals measured by the device are compared to verify the accuracy of the device. Results show that the average errors for diastolic blood pressure (DBP), systolic blood pressure (SBP) and RR are 3.93%, 6.38%, and 8.95%, respectively.
... The novel approach presented uses pulse oximetry and low pass filters to extract RR from the pleth trace. Multiple studies have proven that this is feasible method with clear potential for aiding clinical practice; for example, the approach has potential to be used in the home for monitoring neonates and children with chronic respiratory disease, as well as in overnight studies in children with suspected obstructive sleep apnoea and monitoring for early warning of respiratory infection in children with cystic fibrosis [15,19,69]. ...
Background
Reducing the global new-born mortality is a paramount challenge for humanity. There are approximately 786,323 live births in the UK each year according to the office for National Statistics; around 10% of these newborn infants require assistance during this transition after birth. Each year around, globally around 2.5 million newborns die within their first month. The main causes are complications due to prematurity and during delivery. To act in a timely manner and prevent further damage, health professionals should rely on accurate monitoring of the main vital signs heart rate and respiratory rate.
Aims
To present a clinical perspective on innovative, non-invasive methods to monitor heart rate and respiratory rate in babies highlighting their advantages and limitations in comparison with well-established methods.
Methods
Using the data collected in our recently published systematic review we highlight the barriers and facilitators for the novel sensor devices in obtaining reliable heart rate measurements. Details about difficulties related to the application of sensors and interfaces, time to display, and user feedback are explored. We also provide a unique overview of using a non-invasive respiratory rate monitoring method by extracting RR from the pulse oximetry trace of newborn babies.
Results
Novel sensors to monitor heart rate offer the advantages of minimally obtrusive technologies but have limitations due to movement artefact, bad sensor coupling, intermittent measurement, and poor-quality recordings compared to gold standard well established methods. Respiratory rate can be derived accurately from pleth recordings in infants.
Conclusion
Some limitations have been identified in current methods to monitor heart rate and respiratory rate in newborn babies. Novel minimally invasive sensors have advantages that may help clinical practice. Further research studies are needed to assess whether they are sufficiently accurate, practical, and reliable to be suitable for clinical use.
... Modified PVI (mPVI) assessments were calculated from the same 'raw' plethysmographic recording that was used for PTT. The plethysmographic trace was low-pass filtered in order to extract the respiratory cycle data required to calculate mPVI [11]. ...
Echocardiography was combined with pulse oximetry plethysmography to investigate postnatal cardiovascular adaptation in late preterm and term infants. Median (IQR) pleth variability decreased over three days and similar, day2 15%(12–18%) preterm versus 16%(15–18%) term infants. Median (IQR) pulse transit time heart rate normalised was lower in term babies, day2 0.55(0.51–0.63) versus 0.64(0.62–0.68).
... There are many devices for monitoring respiratory rate; they can be classified into contact and noncontact monitoring systems. Contact respiratory monitoring instruments have to directly contact the body of the wearer to detect the respiratory sound [4], the humidity and temperature of airflow from exhalation and inhalation [5], chest and abdominal movement [6], transcutaneous CO 2 [7], oximetry probe (SpO 2 ) [8], etc. As opposed to contact monitoring methods, noncontact monitoring methods do not reduce patient comfort. ...
Respiratory parameters, such as respiratory rate (RR), inhalation time (tin), exhalation time (tex), and their ratio (IER=tin/tex), are of great importance to indicate clinical differences between healthy people and those with respiratory diseases. Herein, we report a respiration monitoring triboelectric nanogenerator (RM-TENG) with nanofibrous membranes, which can be used as a smart, changeable, self-powered mask filter with high filtration efficiency for monitoring multiple respiratory indices (e.g., RR, tin, tex, IER). We created a mathematical model to quantitatively analyze the effects of gap distance between two triboelectric layers on the contact area by recording the nanofibers layer's deformation profile with digital image correlation (DIC) tests. The RM-TENG is more sensitive to smaller gap distances between 1 mm - 5 mm because the high specific area of nanofibers can provide a more effective contact area. An RM-TENG built with optimized structure parameters can accurately and consistently detect the above-mentioned respiratory indices with excellent sensing stability for 40 hours. The monitored RR and IER have 100% and 93.53% agreement with the real-time RR and IER set on the ventilator, respectively. Furthermore, it has a filtration efficiency of 99 wt% for particle sizes between 0.3 µm and 5 µm. This study introduces a mask filter fabricated with a simple structure with both filtering and sensing capability, which has excellent potential for self-powered health diagnostics.
... In fact, it has been suggested that RSA may serve to gauge the developmental maturity in neonatal intensive care patients [51]. The evidence for the use of RSA in the continuous monitoring of RR in neonates is scarce [16,52]. Monasterio et al. [37] included both pulse rate and heart rate variability as features in a classifier for apnoea-related desaturations in preterm infants, nevertheless the reliability of these two signals was not assessed against a respiration standard. ...
Knowledge of the pathological instabilities in the breathing pattern can provide valuable insights into the cardiorespiratory status of the critically-ill infant as well as their maturation level. This paper is concerned with the measurement of respiratory rate (RR) in premature infants. We compare the rates estimated from (a) the chest impedance pneumogram, (b) the ECG-derived respiratory rhythms, and (c) the PPG-derived respiratory rhythms against those measured in the reference standard of breath detection provided by attending clinical staff during 165 manual breath counts. We demonstrate that accurate RR estimates can be produced from all sources for RR in the 40 - 80 bpm (breaths per min) range. We also conclude that the use of indirect methods based on the ECG or the PPG poses a fundamental challenge in this population due to their poor behaviour at fast breathing rates (upwards of 80 bpm).
... Al-Khalidi et al. 2 describe the main approaches and categorize them into contact and noncontact methods. In the contact-based category, some methods include the measurement of respiratory sound, 4,5 airflow, 6 chest and abdominal movement, 7-14 transcutaneousCO 2 , 2 oxygensaturation, [15][16][17] ECG derivation, 18 and capacitance. 3 Noncontact based approaches include optical-based 19,20 andthermalimaging. ...
Heart rate and through-body blood perfusion are vital measurements in all stages of patient care, be it predictive, in the clinical setting, or outpatient monitoring. Irregular, underachieving, or overperforming heart rate is the main precursor of most cardiovascular diseases that have severe long-term complications. In addition to heart rate, the shape of the pulse waveforms can indicate the heart's valve health and electrophysiology health. The goal of the study was to design a noninvasive device for continuously measuring a patient's heart rate with clinical-grade accuracy along with the ability to indicate pulse waveforms for the patient and physician. An accurate, easy-to-use heart-rate measuring device prototype was developed that did not require the sensor to have direct skin contact to obtain measurements. The statistical analysis of the data gathered by the prototype compared to the data collected from the industry standard device indicated significant correlation. The two-sample T-test for the data recorded from the prototype and the data collected from the industry commercially available pulse oximeter showed a P-value of 0.521, which indicates that there was no significant difference between the prototype and the commercially available pulse oximeter when measuring heart rate.
... While inspired by existing work, our segmentation algorithm is specially tuned to isolate the (start, stop) duration of each individual breath. In contrast, the majority of the respiration monitoring works focus only on breathing rate estimation [14,7,71]e.g., reliably isolating the peak of each breath. In addition, segmentation in speech recognition is threshold based and is used to separate speech vs. non-speech frames [32,38] -such approaches do not directly work in our case as the thresholds need to be different for different frames, over the full breathing gesture signal. ...
We propose BreathPrint, a new behavioural biometric signature based on audio features derived from an individual's commonplace breathing gestures. Specifically, BreathPrint uses the audio signatures associated with the three individual gestures: sniff, normal, and deep breathing, which are sufficiently different across individuals. Using these three breathing gestures, we develop the processing pipeline that identifies users via the microphone sensor on smartphones and wearable devices. In BreathPrint, a user performs breathing gestures while holding the device very close to their nose. Using off-the-shelf hardware, we experimentally evaluate the BreathPrint prototype with 10 users, observed over seven days. We show that users can be authenticated reliably with an accuracy of over 94% for all the three breathing gestures in intra-sessions and deep breathing gesture provides the best overall balance between true positives (successful authentication) and false positives (resiliency to directed impersonation and replay attacks). Moreover, we show that this breathing sound based biometric is also robust to some typical changes in both physiological and environmental context, and that it can be applied on multiple smartphone platforms. Early results suggest that breathing based biometrics show promise as either to be used as a secondary authentication modality in a multimodal biometric authentication system or as a user disambiguation technique for some daily lifestyle scenarios.
... A number of studies have demonstrated the feasibility of extracting respiration rate from plethysmograms. For example, in a study involving 14 infants, the frequency spectra of their plethysmograms indicated respiration rate related peaks (Wertheim et al., 2009). ...
Problem statement: An important indicator of an individualâs health is respiration rate. It is the average number of times air is inhaled and exhaled per minute. Existing respiration monitoring methods require an instrument to be attached to the patientâs body during the recording. This is a discomfort to the patient and the instrument can be dislodged from its position. Approach: In this study a novel noncontact, thermal imaging based respiration rate measurement method is developed and evaluated. Facial thermal videos of 16 children (age: Median = 6.5 years, minimum = 6 months, maximum = 17 years) were processed in the study. The recordings were carried out while the children rested comfortably on a bed. The childrenâs respiration rates were also simultaneously measured using a number of conventional contact based methods. Results: This allowed comparisons with the thermal imaging method to be carried out. The image capture rate was 50 frames per second and the duration of a thermal video recording was 2 min per child. The thermal images were filtered and segmented to identify the nasal region. An algorithm was developed to automatically track the identified nasal area. This region was partitioned into eight equal concentric segments. The pixel values within each segment were averaged to produce a single thermal feature for that segment of the image. A respiration signal was obtained by plotting each segment��s feature against time. Conclusion: Respiration rate values were automatically calculated by determining the number of oscillations in the respiration signals per minute. A close correlation (coefficient = 0.994) was observed between the respiration rates measured using the thermal imaging method and those obtained using the most effective conventional contact based respiration method.
... A number of studies have demonstrated the feasibility of extracting respiration rate from plethysmograms. For example, in a study involving 14 infants, the frequency spectra of their plethysmograms indicated respiration rate related peaks (Wertheim et al., 2009). ...
Problem statement: An important indicator of an individuals health is respiration rate. It is the average number of times air is inhaled and exhaled per minute. Existing respiration monitoring methods require an instrument to be attached to the patients body during the recording. This is a discomfort to the patient and the instrument can be dislodged from its position. Approach: In this study a novel noncontact, thermal imaging based respiration rate measurement method is developed and evaluated. Facial thermal videos of 16 children (age: Median = 6.5 years, minimum = 6 months, maximum = 17 years) were processed in the study. The recordings were carried out while the children rested comfortably on a bed. The childrens respiration rates were also simultaneously measured using a number of conventional contact based methods. Results: This allowed comparisons with the thermal imaging method to be carried out. The image capture rate was 50 frames per second and the duration of a thermal video recording was 2 min per child. The thermal images were filtered and segmented to identify the nasal region. An algorithm was developed to automatically track the identified nasal area. This region was partitioned into eight equal concentric segments. The pixel values within each segment were averaged to produce a single thermal feature for that segment of the image. A respiration signal was obtained by plotting each segments feature against time. Conclusion: Respiration rate values were automatically calculated by determining the number of oscillations in the respiration signals per minute. A close correlation (coefficient = 0.994) was observed between the respiration rates measured using the thermal imaging method and those obtained using the most effective conventional contact based respiration method.
... To date, the detection of HR and BR by PPG has mostly been applied to adult patients, with many different algorithms having been proposed [71e74]. Although they have not been tested on preterm infants, they have been used for newborn term infants [71,75,76] and term infants in the NICU [69,71], with very high correlations of r ¼ 0.99 between the reference ECG and PPG, as well as between a reference BR and PPG. The possible problems with this method for preterm and/or term infants concern uncontrolled movements leading to artefacts [69] and the complicated realization of a breathing protocol to calibrate the analysis. ...
Sleep is important for the development of preterm infants. During sleep, neural connections are formed and the development of brain regions is triggered. In general, various rudimentary sleep states can be identified in the preterm infant, namely active sleep (AS), quiet sleep (QS) and intermediate sleep (IS). As the infant develops, sleep states change in length and organization, with these changes as important indicators of brain development. As a result, several methods have been deployed to distinguish between the different preterm infant sleep states, among which polysomnography (PSG) is the most frequently used. However, this method is limited by the use of adhesive electrodes or patches that are attached to the body by numerous cables that can disturb sleep. Given the importance of sleep, this review explores more unobtrusive methods that can identify sleep states without disturbing the infant. To this end, after a brief introduction to preterm sleep states, an analysis of the physiological characteristics associated with the different sleep states is provided and various methods of measuring these physiological characteristics are explored. Finally, the advantages and disadvantages of each of these methods are evaluated and recommendations for neonatal sleep monitoring proposed.
... Recent evidence indicates that the measurement of RR from the pulse oximeter signal, or photoplethysmogram (PPG), may be possible. Numerous groups have previously demonstrated that evaluating the respiratory-related fluctuations from the PPG signal is both a biologically plausible and technically attainable approach to obtaining RR using a variety of methods including: inspection of the respiratory oscillations in the filtered PPG [15,25,27,[31][32][33]; frequency spectra-based approaches [28,35]; frequency-based smart fusion approaches using multiple modulations [18]; independent component analysis [36]; short-time Fourier transform analysis [34]; neural networks [26]; variable frequency complex demodulation methods [13,21]; autoregressive models [23,24,29]; pulse width variability [17]; and approaches based on the continuous wavelet transform by our own group [2, 10-12, 22, 30]. This cumulative body of evidence strongly suggests the possibility of deriving RR from a single combined sensing system that leverages standard pulse oximetry. ...
Respiratory rate is recognized as a clinically important parameter for monitoring respiratory status on the general care floor (GCF). Currently, intermittent manual assessment of respiratory rate is the standard of care on the GCF. This technique has several clinically-relevant shortcomings, including the following: (1) it is not a continuous measurement, (2) it is prone to observer error, and (3) it is inefficient for the clinical staff. We report here on an algorithm designed to meet clinical needs by providing respiratory rate through a standard pulse oximeter. Finger photoplethysmograms were collected from a cohort of 63 GCF patients monitored during free breathing over a 25-min period. These were processed using a novel in-house algorithm based on continuous wavelet-transform technology within an infrastructure incorporating confidence-based averaging and logical decision-making processes. The computed oximeter respiratory rates (RRoxi) were compared to an end-tidal CO2 reference rate (RRETCO2). RRETCO2 ranged from a lowest recorded value of 4.7 breaths per minute (brpm) to a highest value of 32.0 brpm. The mean respiratory rate was 16.3 brpm with standard deviation of 4.7 brpm. Excellent agreement was found between RRoxi and RRETCO2, with a mean difference of -0.48 brpm and standard deviation of 1.77 brpm. These data demonstrate that our novel respiratory rate algorithm is a potentially viable method of monitoring respiratory rate in GCF patients. This technology provides the means to facilitate continuous monitoring of respiratory rate, coupled with arterial oxygen saturation and pulse rate, using a single non-invasive sensor in low acuity settings.
... Respiration waveform was observed in the plots of the wavelet transforms. In another study involving 14 infants, of median age 2 days, the feasibility of extracting respiratory information from the plethsmogram traces was also demonstrated (22). The magnitude frequency spectra of the plethsmogram traces showed peaks associated with respiration rate. ...
Respiration rate is an important indicator of a person's health, and thus it is monitored when performing clinical evaluations. There are different approaches for respiration monitoring, but generally they can be classed as contact or noncontact. For contact methods, the sensing device (or part of the instrument containing it) is attached to the subject's body. For noncontact approaches the monitoring is performed by an instrument that does not make any contact with the subject. In this article a review of respiration monitoring approaches (both contact and noncontact) is provided. Concerns related to the patient's recording comfort, recording hygiene, and the accuracy of respiration rate monitoring have resulted in the development of a number of noncontact respiration monitoring approaches. A description of thermal imaging based and vision based noncontact respiration monitoring approaches we are currently developing is provided. Pediatr. Pulmonol. 2011; 46:523–529. © 2011 Wiley-Liss, Inc.
... Indeed, numerous groups have previously demonstrated that respiratory-related fluctuations in the PPG signal are both physiologically plausible and their measurement, technically attainable. Technical solutions to their measurement include: inspection of the respiratory oscillations in the filtered PPG [7,9,[16][17][18][19]; frequency spectra-based approaches [10,21] independent component analysis [22] Short-Time Fourier Analysis (STFT) [20]; neural networks [8]; variable frequency complex demodulation methods (VFCDM) [2,4]; autoregressive models [5,6,11]; and approaches based on the continuous wavelet transform (CWT) by our own group [3,[12][13][14][15]. These studies have ranged in cohort size from 4 to 36 subjects and have comprised a wide range of subject types including healthy adult volunteers, patients undergoing abdominal procedures, chest clinic patients, children, and neonates. ...
The presence of respiratory information within the pulse oximeter signal (PPG) is a well-documented phenomenon. However, extracting this information for the purpose of continuously monitoring respiratory rate requires: (1) the recognition of the multi-faceted manifestations of respiratory modulation components within the PPG and the complex interactions among them; (2) the implementation of appropriate advanced signal processing techniques to take full advantage of this information; and (3) the post-processing infrastructure to deliver a clinically useful reported respiratory rate to the end user. A holistic algorithmic approach to the problem is therefore required. We have developed the RR(OXI) algorithm based on this principle and its performance on healthy subject trial data is described herein.
Finger PPGs were collected from a cohort of 139 healthy adult volunteers monitored during free breathing over an 8-min period. These were subsequently processed using a novel in-house algorithm based on continuous wavelet transform technology within an infrastructure incorporating weighted averaging and logical decision making processes. The computed oximeter respiratory rates (RR(oxi)) were then compared to an end-tidal CO2 reference rate RR(ETCO2).
RR(ETCO2) ranged from a lowest recorded value of 2.97 breaths per min (br/min) to a highest value of 28.02 br/min. The mean rate was 14.49 br/min with standard deviation of 4.36 br/min. Excellent agreement was found between RR(oxi) and RR(ETCO2), with a mean difference of -0.23 br/min and standard deviation of 1.14 br/min. The two measures are tightly spread around the line of agreement with a strong correlation observable between them (R2 = 0.93).
These data indicate that RR(oxi) represents a viable technology for the measurement of respiratory rate of healthy individuals.
... Two presentations explored alternative ways of making respiratory measurements in quiet unsedated infants. FOSTER et al. [85] used electrical impedance tomography to question current teaching that the dependent lung in side-lying infants is poorly ventilated, while OLDEN et al. [86] showed that useful respiratory data (allowing accurate estimation of respiratory rate) could be extracted from the raw signal of a pulse oximeter. ...
The aim of this report is to describe the highlights of the European Respiratory Society annual congress in Berlin, Germany. The best abstracts in asthma and allergy, cystic fibrosis, respiratory infection, paediatric and neonatal intensive care, paediatric investigative techniques (in particular respiratory physiology and bronchoscopy) and respiratory epidemiology are presented and set in the context of the current literature.
PurposeRespiration during sleep is one of the indicators of an individual’s health. However, many respiratory measurement devices need to be worn by the patient and can affect sleep. We introduce here a novel, easy-to-use, respiratory rate-monitoring sensor made of stretchable piezoelectric material that can be used conveniently at home as well as in a clinical setting.Methods
We enrolled 6 members of a family as volunteers ranging in age from 9 months to 69 years. The sensor was used to continuously record respiratory rate data for all individuals during sleep.ResultsThe sensor could detect known breathing patterns such as stable, unstable, or deep breathing as well as apnea during sleep. We observed significant differences in the respiratory rates and respiratory stability between subjects during sleep.Conclusion
The piezoelectric sensor was effective in people in all age groups, paving a way for future use as a convenient and reliable mode of respiratory assessment for adults as well as neonates at home and in a clinical setting.
Respiratory rate (RR) is an important vital sign used in the assessment of acutely ill patients. It is also used as to predict serious deterioration in a patient's clinical condition. Convenient electronic devices exist for measurement of pulse, blood pressure, oxygen saturation and temperature. Although devices which measure RR exist, none has entered everyday clinical practice.
We developed a contactless portable respiratory rate monitor (CPRM) and evaluated the agreement in respiratory rate measurements between existing methods and our new device. The CPRM uses thermal anemometry to measure breath signals during inspiration and expiration.
RR data were collected from 52 healthy adult volunteers using respiratory inductance plethysmography (RIP) bands (established contact method), visual counting of chest movements (established non-contact method) and the CPRM (new method), simultaneously. Two differently shaped funnel attachments were evaluated for each volunteer.
Data showed good agreement between measurements from the CPRM and the gold standard RIP, with intra-class correlation coefficient (ICC): 0.836, mean difference 0.46 and 95% limits of agreement of -5.90 to 6.83. When separate air inlet funnels of the CPRM were analysed, stronger agreement was seen with an elliptical air inlet; ICC 0.908, mean difference 0.37 with 95% limits of agreement -4.35 to 5.08.
A contactless device for accurately and quickly measuring respiratory rate will be an important triage tool in the clinical assessment of patients. More testing is needed to explore the reasons for outlying measurements and to evaluate in the clinical setting.
Pneumonia is the leading infectious cause of death in children worldwide, with most deaths occurring in developing countries. Measuring respiratory rate is critical to the World Health Organization's guidelines for diagnosing childhood pneumonia in low-resource settings, yet it is difficult to accurately measure. We conducted a systematic review to landscape existing respiratory rate measurement technologies. We searched Pubmed, Embase, and Compendex for studies published through September 2017 assessing the accuracy of respiratory rate measurement technologies in children. We identified 16 studies, with two describing manual devices and 14 describing automated devices. While both studies describing manual devices took place in low-resource settings, all studies describing automated devices were conducted in well-resourced settings. Direct comparison between studies was complicated by small sample size, absence of a consistent reference standard and variations in comparison methodology. There is an urgent need for affordable and appropriate innovations that can reliably measure a child's respiratory rate in low-resource settings. Accelerating development or scale-up of these technologies could have the potential to advance childhood pneumonia diagnosis worldwide.
Breathing rate (BR) is a key physiological parameter used in a range of clinical settings. Despite its diagnostic and prognostic value, it is still widely measured by counting breaths manually. A plethora of algorithms have been proposed to estimate BR from the electrocardiogram (ECG) and pulse oximetry (photoplethysmogram, PPG) signals. These BR algorithms provide opportunity for automated, electronic and unobtrusive measurement of BR in both healthcare and fitness monitoring. This paper presents a review of the literature on BR estimation from the ECG and PPG. Firstly, the structure of BR algorithms and the mathematical techniques used at each stage are described. Secondly, the experimental methodologies which have been used to assess the performance of BR algorithms are reviewed, and a methodological framework for the assessment of BR algorithms is presented. Thirdly, we outline the most pressing directions for future research, including the steps required to use BR algorithms in wearable sensors, remote video monitoring, and clinical practice.
Purpose of review:
To discuss the physiological significance and clinical value of dynamic preload variables in spontaneously breathing patients.
Recent findings:
Dynamic preload variables reflect the response of the cardiac output to a modification of preload and can therefore be used to assess fluid responsiveness. Continuous dynamic parameters that are calculated from the variations in the arterial and plethysmographic waveforms following a mechanical breath have been shown to predict fluid responsiveness much better than static preload parameters. These parameters are displayed on many patient monitors though their use is limited to mechanically ventilated patients. However, spontaneous breathing may also induce significant hemodynamic changes because of the repetitive negative swings in the pleural pressure. By better understanding the physiological basis of these changes, the same 'dynamic parameters' can be used to gain unique physiological insights during spontaneous breathing. These include the ability to identify and/or monitor respiratory rate, respiratory effort (e.g., patient-ventilator asynchrony), fluid responsiveness (to some degree), pulsus paradoxus (e.g. asthma, cardiac tamponade), and, importantly, upper airway obstruction.
Summary:
Although originally intended to be used only during mechanical ventilation, 'dynamic parameters' may offer valuable clinical information in spontaneously breathing patients.
Respiratory rate (RR) is a valuable early marker of illness in vulnerable infants, but current monitoring methods are unsuitable for sustained home use. We have demonstrated accurate measurement of RR from brief recordings of pulse oximeter plethysmogram (pleth) trace in full-term neonates in hospital. This study assessed the feasibility of this method in preterm infants during overnight recordings in the home. We collected simultaneous overnight SpO2, pleth and respiratory inductive plethysmography (RIP) on 24 preterm infants in the home. RR from pleth analysis was compared with RR from RIP bands; pleth quality was assessed by the presence of visible artefact. Median (range) RR from RIP and pleth were not significantly different at 42 (25–65) and 42 (25–64) breaths/min. Median (range) % of epochs rejected due to artefact was 20 (8–75) for pleth and 10 (3–53) for RIP. Our results suggest that home RR monitoring by pulse oximeter pleth signal is accurate and feasible.
Non-invasive monitoring of breathing is a holy grail in paediatric respiratory, neonatal and sleep medicine. Respiratory rate is a key marker for the surveillance of sick infants and children (1-3), while repeated infant apnoeic episodes are associated with an increased risk of apparent life-threatening events (4). In clinical pulse oximetry, the photoplethysmographic (pleth) signal is assessed mainly to infer the validity of measured arterial oxygen saturation. This article is protected by copyright. All rights reserved.
The aim of this study was to investigate whether respiratory information can be derived from pulse oximetry plethysmogram (pleth) recordings in acutely wheezy preschool children. A digital pulse oximeter was connected via 'Bluetooth' to a notebook computer in order to acquire pleth data. Low pass filtering and frequency analysis were used to derive respiratory rate from the pleth trace; the ratio of heart rate to respiratory rate (HR/RR) was also calculated. Recordings were obtained during acute wheezy episodes in 18 children of median age 31 months and follow-up recordings from 16 of the children were obtained when they were wheeze-free. For the acutely wheezy children, frequency analysis of the pleth waveform was within 10 breaths/min of clinical assessment in 25 of 29 recordings in 15 children. For the follow-up measurements, frequency analysis of the pleth waveform showed similarly good agreement in recordings on 15 of the 16 children. Respiratory rate was higher (p < 0.001), and HR/RR ratio was lower (p = 0.03) during acute wheeze than at follow-up. This study suggests that respiratory rate can be derived from pleth traces in wheezy preschool children.
Pulse oximetry is based on the technique of photoplethysmography (PPG) wherein light transmitted through tissues is modulated by the pulse. In addition to variations in light modulation by the cardiac cycle, the PPG signal contains a respiratory modulation and variations associated with changing tissue blood volume of other origins. Cardiovascular, respiratory, and neural fluctuations in the PPG signal are of different frequencies and can all be characterized according to their sinusoidal components. PPG was described in 1937 to measure blood volume changes. The technique is today increasingly used, in part because of developments in semiconductor technology during recent decades that have resulted in considerable advances in PPG probe design. Artificial neural networks help to detect complex nonlinear relationships and are extensively used in electronic signal analysis, including PPG. Patient and/or probe-tissue movement artifacts are sources of signal interference. Physiologic variations such as vasoconstriction, a deep gasp, or yawn also affect the signal. Monitoring respiratory rates from PPG are often based on respiratory-induced intensity variations (RIIVs) contained in the baseline of the PPG signal. Qualitative RIIV signals may be used for monitoring purposes regardless of age, gender, anesthesia, and mode of ventilation. Detection of breaths in adult volunteers had a maximal error of 8%, and in infants the rates of overdetected and missed breaths using PPG were 1.5% and 2.7%, respectively. During central apnea, the rhythmic RIIV signals caused by variations in intrathoracic pressure disappear. PPG has been evaluated for detecting airway obstruction with a sensitivity of 75% and a specificity of 85%. The RIIV and the pulse synchronous PPG waveform are sensitive for detecting hypovolemia. The respiratory synchronous variation of the PPG pulse amplitude is an accurate predictor of fluid responsiveness. Pleth variability index is a continuous measure of the respiratory modulation of the pulse oximeter waveform and has been shown to predict fluid responsiveness in mechanically ventilated patients including infants. The pleth variability index value depends on the size of the tidal volume and on positive end-expiratory pressure. In conclusion, the respiration modulation of the PPG signal can be used to monitor respiratory rate. It is probable that improvements in neural network technology will increase sensitivity and specificity for detecting both central and obstructive apnea. The size of the PPG respiration variation can predict fluid responsiveness in mechanically ventilated patients.
The tidal flow volume (TFV) loop ratios of (1) time to peak flow (tPTEF) to total expiratory time (tE) [tPTEF/tE] and (2) volume to peak flow (VPTEF) to expired volume (VE) [VPTEF/VE] are reported to decrease with age in early life, and to decrease in subjects with obstructive airways disease (OAD). However, the mechanisms behind these changes are not well known. Thus, we reanalyzed data from 24 healthy neonates (mean birthweight: 3.49 kg ± 0.42 kg (SD)), 26 presently asymptomatic asthmatic children (age: 33 ± 21 months), and 26 controls (age: 34 ± 19 months) to elucidate what is responsible for the changes in these ratios in health and disease. Lung function was measured by TFV loops (SensorMedics 2600) at 1 hour of life and on the following day in the neonates, and before and after inhaled nebulized salbutamol (0.05 mg/kg) in the asthmatics and their controls.
The observed decreases in mean tPTEF/tE and VPTEF/VE from 1 hour to 1 day of life (neonates) were entirely due to increased tE and VE, respectively secondary to a decrease in respiratory rate (P = 0.03). In asthmatics (young children), the decreased baseline tPTEF/tE and VPTEF/VE were due to lower tPTEF and VPTEF, with no significant differences in tEe and VE in asthmatics and controls. The improved ratios in asthmatic children following inhalation of a bronchodilator were mainly due to increased tPTEF and VPTEF. Our observations point out the importance of evaluating both tPTEF and either tPTEF/tE or VPTEF/VE when attempting to differentiate between changes in ratios that are related to age versus changes that reflect underlying obstructive airways disease. Pediatr. Pulmonol. 1997; 24:391–396.
Two important parameters that are generally under continual observation during clinical monitoring are heart rate (HR) variability and breathing interval (BI) of patients. Current HR monitoring during night-long childhood respiratory sleep studies is well tolerated but BI monitoring requires instrumentation, like nasal cannula, that can be less accommodating for children. In this study, BI was extracted from the photoplethysmographic (PPG) signals using a two-stage signal processing technique termed zero-phase digital filtering. Eight children (7 male) aged 8.6 +/- 2.6 years were recruited to perform two breathing activities: during tidal and with customized externally applied inspiratory resistive loading (IRL). The accuracy of BI derived from the PPG signals was compared with that estimated by a calibrated air pressure transducer in children. Statistical analysis revealed that mean BI attained from the PPG signals were significantly related during tidal breathing (r(2) = 0.76; range 0.61-0.83; p < 0.05) and with the IRL (r(2) = 0.79; range 0.68-0.85; p < 0.05) in the absence of motion artefacts. Preliminary findings herein suggest that besides having the capability to monitor HR and arterial blood oxygen saturation measurements, the PPG signals can be used to derive BI for children. This can be an attractive alternative for children who are more disturbed by intrusive techniques in prolonged clinical monitoring.
We have developed an automated algorithm to allow the measurement of respiratory rate directly from the photoplethysmogram (pulse oximeter waveform).
To test the algorithm's ability to determine respiratory rate in children.
A convenience sample of patients attending a paediatric Accident and Emergency Department was monitored using a purpose-built pulse oximeter and the photoplethysmogram (PPG) recorded. Respiration was also recorded by an observer activating a push-button switch in synchronization with the child's breathing. The switch marker signals were processed to derive a manual respiratory rate that was compared with the wavelet-based oximeter respiratory rate derived from the PPG signal.
Photoplethysmograms were obtained from 18 children aged 18 mo to 12 y, breathing spontaneously at rates of 17 to 27 breaths per minute. There was close correspondence between the wavelet-based oximeter respiration rate and the manual respiratory rate, with the difference between them being less than one breath per minute in all children.
Our automated algorithm allows the accurate determination of respiratory rate from photoplethysmograms of a heterogeneous group of children. We believe that our automated wavelet-based signal-processing techniques could soon be easily incorporated into current pulse oximetry technology.