An impedance pneumography signal quality index: Design, assessment and application to respiratory rate monitoring.

Impedance pneumography (ImP) is widely used for respiratory rate (RR) monitoring. However, ImP-derived RRs can be imprecise. The aim of this study was to develop a signal quality index (SQI) for the ImP signal, and couple it with a RR algorithm, to improve RR monitoring. An SQI was designed which identifies candidate breaths and assesses signal quality using: the variation in detected breath durations, how well peaks and troughs are defined, and the similarity of breath morphologies. The SQI categorises 32 s signal segments as either high or low quality. Its performance was evaluated using two critical care datasets. RRs were estimated from high-quality segments using a RR algorithm, and compared with reference RRs derived from manual annotations. The SQI had a sensitivity of 77.7 %, and specificity of 82.3 %. RRs estimated from segments classified as high quality were accurate and precise, with mean absolute errors of 0.21 and 0.40 breaths per minute (bpm) on the two datasets. Clinical monitor RRs were significantly less precise. The SQI classified 34.9 % of real-world data as high quality. In conclusion, the proposed SQI accurately identifies high-quality segments, and RRs estimated from those segments are precise enough for clinical decision making. This SQI may improve RR monitoring in critical care. Further work should assess it with wearable sensor data.This work was supported by a UK Engineering and Physical Sciences Research Council (EPSRC) Impact Acceleration Award awarded to PHC; the EPSRC [EP/H019944/1]; the Wellcome EPSRC Centre for Medical Engineering at King’s College London [WT 203148/Z/16/Z]; the Oxford and King’s College London Centres of Excellence in Medical Engineering funded by the Wellcome Trust and EPSRC under grants [WT88877/Z/09/Z] and [WT088641/Z/09/Z]; the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy’s & St Thomas’ NHS Foundation Trust and King’s College London; the NIHR Oxford Biomedical Research Centre Programme; a Royal Academy of Engineering Research Fellowship (RAEng) awarded to DAC; and EPSRC grants EP/P009824/1 and EP/N020774/1 to DAC

Development and clinical application of impedance pneumography technique

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

Liikkuva potilas: moniparametrisen hengitystaajuusmittauksen käyttökelpoisuus

Respiratory rate is one of the vital signs used to measure the body’s general physical health. Abnormal respiratory rate or a change in breathing frequency may indicate deterioration in the condition of a patient. Thus, respiratory rate measurement would benefit the mobile patients on general hospital wards where no continuous monitoring exists. This environment requests wireless and reliable respiratory monitoring that would be robust against motion artefacts that impede the reliability of common respiratory rate measurements currently available. Electrocardiography (ECG) and photoplethysmography (PPG) are common measurements in intensive care but also in sub-acute care setting. Respiration modulates the ECG and PPG waveforms in several ways that can be exploited to derive respiratory rate from these physiological signals. In ECG, the effect of breathing is seen as both amplitude and frequency modulation, whereas in PPG also baseline modulation is present. This thesis investigated the feasibility of ECG and pulse oximetry derived respiratory rate measurements during different activities and motion states. The performances of these derived methods were evaluated together with impedance pneumography and respiratory inductive plethysmography against capnography reference using statistical analysis. A major part of this thesis consisted of the data collection, signal processing and algorithm development required to create these derived methods. According to the results acquired, the use of ECG-derived respiration (EDR) methods based on QRS-amplitude as part of a multi-parameter respiratory rate algorithm would be feasible. However, all evaluated pulse oximetry derived respiration (PDR) methods were found to be unfit for use due to high susceptibility to motion artefacts. The development of a multi-parameter respiratory rate algorithm continues.Hengitystaajuus luetaan yhdeksi kehon yleisestä terveydestä kertovaksi vitaaliparametriksi. Epänormaali hengitystaajuus tai hengitystaajuuden muutos voi olla merkki potilaan kunnon huononemisesta ja siksi hengitystaajuuden seurannasta olisi hyötyä myös sairaaloiden vuodeosastoilla, missä potilaat liikkuvat ilman jatkuvaa valvontaa. Tällaisessa ympäristössä hengityksen seurannan tulisi toimia langattomasti ja luotettavasti. Monet yleisesti käytetyt hengitystaajuusmittaukset kärsivät kuitenkin liikkeen aiheuttamista häiriöistä, jotka heikentävät menetelmien luotettavuutta. Elektrokardiografia (EKG) ja fotopletysmografia (PPG) ovat yleisiä mittauksia myös tehohoidon ulkopuolella. Hengitys vaikuttaa näiden fysiologisten signaalien muotoon usealla tavalla, joita voidaan hyödyntää hengitystiedon johtamiseen näistä parametreistä. Sydänsähkökäyrän QRS-kompeksien amplitudi ja sykevälivaihtelu ovat yhteydessä hengitykseen samoin kuin fotopletysmografisen pulssiaallon perusviiva, amplitudi sekä pulssivälivaihtelu. Tässä diplomityössä tutkittiin EKG:stä ja PPG:stä johdettujen hengitystaajuusmittausten käyttökelpoisuutta erilaisissa liiketilanteissa. Näiden johdettujen menetelmien suorituskykyä verrattiin tilastollisen analyysin keinoin impedanssipneumografian ja hengitysinduktiivisen pletysmografian kanssa kapnografialla mitattuja vertailuarvoja vastaan. Työ koostui suurelta osin myös näiden menetelmien luomiseen vaaditusta aineiston keräämisestä, signaalinkäsittelystä sekä algoritmikehityksestä. Saatujen tulosten perusteella EKG:stä johdetut amplitudipohjaiset menetelmät olisivat hyödyllisiä moniparametrisessa hengitystaajuusmittauksessa käytettynä. Sen sijaan kaikki kehitetyt PPG:stä johdetut hengitystaajuusmenetelmät todettiin käyttökelvottomiksi liikkeen aiheuttamien häiriöiden vuoksi. Moniparametrisen hengitystaajuusmittauksen kehitystyö jatkuu

Validity of the Pneumonitor for RR intervals acquisition for short-term heart rate variability analysis extended with respiratory data in pediatric cardiac patients

BACKGROUND: Breathing pattern alterations change the variability and the spectral content of the RR intervals (RRi) from electrocardiogram (ECG). However, actually there is no solution on how to record and control participant’s breathing without influencing its natural rate and depth in heart rate variability (HRV) studies. AIM: The aim of the study was to assess the validity of the Pneumonitor for acquisition of short-term (5 min) RRi in comparison to the reference ECG method for analysis of heart rate (HR) and HRV parameters in the group of pediatric patients with cardiac disease. METHODS: Nineteen patients of both sexes participated in the study. ECG and Pneumonitor were used to record RRi from 5 min static rest conditions, the latter also to measure the relative tidal volume and respiratory rate. The validation comprised the Student’s t-test, Bland-Altman analysis, Intraclass Correlation Coefficient and Lin’s concordance correlation. The possible impact of the respiratory activity on the agreement between ECG and Pneumonitor was also assessed. RESULTS: Acceptable agreement for number of RRi, mean RR, HR and HRV measures calculated based on RRi acquired using ECG and Pneumonitor was presented. There was no association between breathing pattern and RRi agreement between devices. CONCLUSIONS: Pneumonitor might be considered appropriate for cardiorespiratory studies in the group of pediatric cardiac patients in rest condition

Breathing Rate Estimation From the Electrocardiogram and Photoplethysmogram: A Review.

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. First, the structure of BR algorithms and the mathematical techniques used at each stage are described. Second, the experimental methodologies that have been used to assess the performance of BR algorithms are reviewed, and a methodological framework for the assessment of BR algorithms is presented. Third, 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

Impedance pneumography in respiration monitoring

Respiration monitoring provides health care professionals essential information about patients’ condition and can help diagnosing pulmonary diseases. The most reliable methods for assessment are obtrusive and include masks and can require performing manoeuvres that limit the usability with uncooperative patients like children or unconscious. In contrast, in hospital wards respiration rate and effort are intermittently assessed only visually during rounds at patient rooms leading to poor frequency of recording. Hence, early signs of deterioration in condition are often missed. Bioimpedance have been studied as a continuous and unobtrusive method for respiration monitoring. The technique is based on differences in electrical properties of tissues. A small current is fed through the body and voltage across is measured. Respiration and cardiac functions affect current flow and thus change the total impedance. Frequency of the applied current and geometry of the thorax cause also variation in the signal. When using bioimpedance to assess respiratory functions the method is called impedance pneumography. Despite of being an established and widely used method, there is ongoing research to improve its performance. One major challenge is its susceptibility to movement. However, signal processing algorithms advance all the time making development of wearable applications also possible. In this study, respiration is measured with bioimpedance and compared to signal from pneumotachometer. Two different electrode configurations were used to evaluate their performance in different positions, in supine, sitting and walking stationary. The study protocol included alternation between thoracic and diaphragmatic breathing at different depths. Respiration rates were determined with peak detection, advanced counting and Fast Fourier Transform (FFT) algorithms and their performances were compared. The results show that respiration rates were most accurately measured during supine position with Mason-Likar arm electrodes. No significant differences between thoracic and diaphragmatic breathing were seen whereas shallow breathing was occasionally hard to detect. The peak detection algorithm performed best having mean absolute error (MAE) of 0.47, 1.12 and 1.23 breaths per minute (bpm) for lying, sitting and walking, respectively. However, MAE values of FFT method were not comparable to other methods in most of the cases. Comparison between electrode configurations is not straightforward, as the measurements were not made simultaneously. Also, the study involved only relatively young and healthy subjects which are not the most abundant age group needing monitoring at hospitals. When considering patient monitoring applications, future studies should involve subjects with wider range of characteristics to obtain more definitive results about the performance of the impedance pneumography.Hengitystä monitoroimalla saadaan tärkeää informaatiota potilaan terveydentilasta sekä apua keuhkosairauksien diagnosointiin. Tällä hetkellä luotettavimmat menetelmät häiritsevät luonnollista hengitystä ja saattavat vaatia erityisiä hengityskuvioita, jotka eivät onnistu yhteistyökyvyttömiltä potilailta kuten lapsilta tai vakavasti sairailta. Toisaalta sairaaloiden osastoilla hengitystaajuutta ja hengityksen vaikeutta saatetaan ajoittain arvioida ainoastaan visuaalisesti tarkastuskierrosten aikana, jolloin tuloksien väli saattaa venyä pitkäksi eikä muutoksia huomata ajoissa. Bioimpedanssimenetelmä tarjoaa keinon jatkuvaan hengityksen monitorointiin häiritsemättä sitä. Tekniikka perustuu kudosten erilaiseen kykyyn vastustaa sähkövirran kulkua, ja sen avulla voidaan saada monesta kehontoiminnosta tietoa. Hengityksen analysoinnissa menetelmästä käytetään nimitystä impedanssipneumografia. Käytännössä kehoon syötetään pieniamplitudista virtaa ja mitataan jännitettä mittapisteiden välillä. Hengityksen aiheuttamat muutokset vaikuttavat sähkövirran kulkuun ja näin ollen muuttavat impedanssisignaalia. Myös syötetyn virran taajuus sekä rintakehän muoto vaikuttavat havaittuun impedanssiin. Vaikka menetelmä on jo vakiintunut ja laajalti käytössä, tutkijat pyrkivät jatkuvasti parantamaan bioimpedanssin mittaustekniikkaa. Yksi menetelmän heikkouksista on sen alttius liikkeestä aiheutuville häiriöille. Signaalinkäsittelymenetelmät kehittyvät kuitenkin jatkuvasti mahdollistaen myös tutkimuksen bioimpedanssin käytöstä puettavissa laitteissa. Tässä tutkimuksessa mitattiin hengitystä bioimpedanssin avulla ja verrattiin saatua signaalia pneumotakometrillä kerättyyn referenssiin. Mittauksissa käytettiin kahta eri elektrodien sijoittelua ja arvioitiin niiden toimivuutta eri asennoissa: selinmakuulta, istualtaan sekä paikallaan kävellessä. Mittausten aikana tutkittavat hengittivät eri syvyyksillä ja vaihtelivat pallea- ja rintahengityksen välillä. Saadusta datasta arvioitiin hengitystaajuutta peak detection, advanced counting ja Fast Fourier Transform -algoritmeilla ja vertailtiin niiden toimivuutta. Tutkimuksessa havaittiin, että luotettavin arvio hengitystaajuudesta saatiin makuuasennossa Mason-Likar käsielektrodeilta mitattaessa. Pallea- ja rintahengityksen välillä ei havaittu merkittäviä eroja, kun taas pinnallista hengitystä oli ajoittain vaikea havaita impedanssisignaalista. Peak detection -algoritmin suoriutui parhaiten käytetyistä metodeista. Tällä menetelmällä keskimääräinen absoluuttinen virhe oli 0.47 hengitystä minuutissa (bpm) makuulta, 1.12 bpm istualtaan ja 1.23 bpm kävellessä. FFT-algoritmilla ei saatu vertailukelpoisia arvoja hengitystiheydestä johtuen todennäköisesti liian suuresta ikkunan pituudesta. Elektrodipaikkojen vaikutusta on hankala arvioida suoraviivaisesti, sillä mittauksia ei tehty samanaikaisesti. Tutkimuksessa oli mukana ainoastaan suhteellisen nuoria ja hyväkuntoisia henkilöitä. Tällaisilta tutkittavilta mahdollisesti saadaan parempia tuloksia kuin ikääntyneiltä tai ylipainoisilta. Potilasmonitorisovelluksia ajatellen seuraaviin tutkimuksiin kannattaisi ottaa mukaan ominaisuuksiltaan laajempi joukko tutkittavia, jotta saataisiin kattavampi näyttö impedanssipneumografian suorituskyvyst