Stato dell'arte sui dispositivi medici indossabili per il monitoraggio dei parametri vitali

I dispositivi indossabili (DI) per il monitoraggio dei parametri vitali sono utilizzati in ospedali, telemedicina e studi clinici per la rilevazione continua di tali parametri. Questi dispositivi sono indossabili, portatili, economicamente accessibili, dotati di hardware avanzato e algoritmi per l'analisi di dati. Essi facilitano l'identificazione e il monitoraggio di "biomarkers digitali". Una ricerca avanzata su PubMed, degli articoli pubblicati dal 2019 al 2023 a complemento di un precedente lavoro di revisione della letteratura, ha evidenziato un aumento esponenziale degli articoli scientifici riguardanti l'uso dei DI, dimostrando la loro efficacia nel supportare il lavoro medico e potenzialmente ridurre i costi della sanità

A Textile Sleeve for Monitoring Oxygen Saturation Using Multichannel Optical Fibre Photoplethysmography

Textile-based systems are an attractive prospect for wearable technology as they can provide monitoring of key physiological parameters in a comfortable and unobtrusive form. A novel system based on multichannel optical fibre sensor probes integrated into a textile sleeve is described. The system measures the photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), which is then used to calculate oxygen saturation (SpO2). In order to achieve reliable measurement without adjusting the position of the garment, four plastic optical fibre (POF) probes are utilised to increase the likelihood that a high-quality PPG is obtained due to at least one of the probes being positioned over a blood vessel. Each probe transmits and receives light into the skin to measure the PPG and SpO2. All POFs are integrated in a stretchable textile sleeve with a circumference of 15 cm to keep the sensor in contact with the subject's wrist and to minimise motion artefacts. Tests on healthy volunteers show that the multichannel PPG sensor faithfully provides an SpO2 reading in at least one of the four sensor channels in all cases with no need for adjusting the position of the sleeve. This could not be achieved using a single sensor alone. The multichannel sensor is used to monitor the SpO2 of 10 participants with an average wrist circumference of 16.0 ± 0.6 cm. Comparing the developed sensor's SpO2 readings to a reference commercial oximeter (reflectance Masimo Radical-7) illustrates that the mean difference between the two sensors' readings is -0.03%, the upper limit of agreement (LOA) is 0.52% and the lower LOA is -0.58%. This multichannel sensor has the potential to achieve reliable, unobtrusive and comfortable textile-based monitoring of both heart rate and SpO2 during everyday life

Happisaturaation mittaaminen puettavilla laitteilla

Veren happisaturaatio on tärkeä fysiologinen parametri, joka kuvaa veressä olevan hapen määrää ja antaa tärkeää tietoa kudosten hapensaannista. Happisaturaatio voidaan määrittää fotopletysmografiamittauksen (engl. photoplethysmography, PPG) avulla. Usein happisaturaatio mitataan sormenpäähään kiinnitettävällä pulssioksimetrilla, joka rajoittaa käyttäjän normaaleja toimintoja. Käyttäjää häiritsemättömät puettavat laitteet, kuten älykellot ja -sormukset, tarjoavat uusia mahdollisuuksia happisaturaation mittaamiseen. Tämän työn tavoitteena on esitellä puettavilla laitteilla toteutettavien happisaturaatiomittauksien mahdollisia anturiratkaisuja, mittauksiin liittyviä haasteita ja tulevaisuudennäkymiä. Happisaturaatiota mittaavissa puettavissa laitteissa voidaan hyödyntää erilaisia anturiratkaisuja. Erilaisilla anturiratkaisuilla pyritään mittaamaan mahdollisimman hyvälaatuista PPG-signaalia sovelluskohteeseen parhaiten soveltuvalla tavalla. PPG-mittauksessa voidaan vaikuttaa esimerkiksi mittauspaikan valintaan tai PPG-anturissa käytettäviin ratkaisuihin, kuten valonlähteen ja valoanturin sijoitteluun toisiinsa nähden. Tällä hetkellä happisaturaatiota on mahdollista mitata vain harvoilla puettavilla laitteilla, sillä mittauksiin liittyy useita ratkaisemattomia haasteita. PPG-signaaliin aiheutuu esimerkiksi helposti liikeartefaktaa eli mittausanturin liikkumisesta aiheutuvaa kohinaa. Lisäksi anturin mittauspaikkaan kohdistaman voiman tulee olla sopiva, jotta mitattava signaali olisi hyvälaatuista. Yksilöiden väliset erot esimerkiksi ihonvärissä tai painoindeksissä aiheuttavat myös vaihtelevuutta mittaustuloksiin. Jos nämä haasteet onnistutaan ratkaisemaan, tulevaisuudessa puettavilla laitteilla toteutettavaa happisaturaatiomittausta voitaisiin käyttää useissa sovelluskohteissa. Puettavilla laitteilla toteutettava happisaturaatiomittaus mahdollistaa ajasta ja paikasta riippumattoman jatkuva-aikaisen monitoroinnin. Ajasta ja paikasta riippumattoman monitoroinnin ansiosta joitakin kliinisessä ympäristössä aikaa vieviä tutkimuksia, kuten unen seurantaa, voitaisiin tulevaisuudessa toteuttaa mahdollisesti myös kotioloissa. Erityisesti keuhkosairauksia sairastavat potilaat voisivat hyötyä jatkuva-aikaisesta happisaturaation mittaamisesta kotioloissa, sillä keuhkosairauksia sairastavilla potilailla happisaturaatiolukemat voivat olla sairauden vuoksi normaalia matalampia

Optical Fibre-Based Pulse Oximetry Sensor with Contact Force Detection

A novel optical sensor probe combining monitoring of blood oxygen saturation (SpO2) with contact pressure is presented. This is beneficial as contact pressure is known to affect SpO2 measurement. The sensor consists of three plastic optical fibres (POF) used to deliver and collect light for pulse oximetry, and a fibre Bragg grating (FBG) sensor to measure contact pressure. All optical fibres are housed in a biocompatible epoxy patch which serves two purposes: (i) to reduce motion artefacts in the photoplethysmogram (PPG), and (ii) to transduce transverse loading into an axial strain in the FBG. Test results show that using a combination of pressure measuring FBG with a reference FBG, reliable results are possible with low hysteresis which are relatively immune to the effects of temperature. The sensor is used to measure the SpO2 of ten volunteers under different contact pressures with perfusion and skewness indices applied to assess the quality of the PPG. The study revealed that the contact force ranging from 5 to 15 kPa provides errors of <2%. The combined probe has the potential to improve the reliability of reflectance oximeters. In particular, in wearable technology, the probe should find use in optimising the fitting of garments incorporating this technology

Endotracheal tube placement with fibre optic sensing

Unrecognised oesophageal intubation is often described as a ‘Never Event’; an entirely preventable and extremely serious incident. However, there is still prevalence, with severe consequences for the patient. The current gold standards of visually confirming passage through the vocal cords, observing chest movement, and end-tidal capnography all have limitations. There is an opportunity for an alternative method to determine the correct endotracheal tube placement in the trachea. One such solution is described here, through the development of a compact fibre optic sensor integrated into a standard endotracheal tube. The sensor contains no electrical components inside the invasive portion of the device, and it is magnetic resonance imaging safe. The spectral characteristics of the trachea and oesophagus are observed using a fibre optic probe, with the presence of oxyhaemoglobin being used to distinguish the tissues. A novel epoxy sensor is then designed using plastic optical fibres. A rounded top with a square base sensor shape had the least impact on the overall performance of the ETT. Furthermore, by forming the sensor with two illumination fibres, pulse oximetry can be performed. A fibre separation distance between 1.27 and 2.54 mm is optimal. However, a Monte Carlo simulation demonstrates a viable separation of 0.5 to 3 mm. ThereforeHowever, by reducing this to 0.88 mm, a more compact sensor can be produced whilst still retaining a classification rate (average correct identification of trachea and oesophagus) of >89.2% in ex-vivo models. Two methods for emitting light perpendicularly to the fibre axis are explored, demonstrating that bending the fibres caused an optical power loss of 29.0%, whereas cleaving the fibres at 45° produced an 81.9% loss. The position of the sensor on the endotracheal tube is investigated, finding that integration behind the cuff is preferable. However, placement outside the main lumen of the ETT is also a viable option. Computational methods to process spectral measurements are developed. Data for these methods was provided by two experiments on two different sensor types, providing a high tissue classification rate for both the trachea and oesophagus. The first experiment consisted of 9 ex-vivo porcine samples, producing a correct tissue identification of up to 100.0%. The second consisted of 10 sensors on 1 ex-vivo porcine sample, yielding a maximum correct tissue identification of 89.2% when a support vector machine classifier was used. Application of the sensor in an animal study, which consisted of 3 porcine subjects, generated a maximum correct tissue identification of 98.31.6% using principal component analysis and aa support vector machine. The data were recorded over a combined time of 348 minutes, obtained during varying cuff pressures, endotracheal tube orientations, and movement. Finally, suggested future developments to the sensor design and computational methods demonstrate a potential route to improving tissue identification rates. Changes to the experimental protocol are described to verify classification rates. Concepts for exchanging the spectrometer for photodiodes and optical filters to reduce the cost of the opto-electronic units display potential. The technology has applications in wider healthcare, with examples of integration within naso-/oro- gastric tubes and other invasive medical devices given

Endotracheal tube placement with fibre optic sensing

Unrecognised oesophageal intubation is often described as a ‘Never Event’; an entirely preventable and extremely serious incident. However, there is still prevalence, with severe consequences for the patient. The current gold standards of visually confirming passage through the vocal cords, observing chest movement, and end-tidal capnography all have limitations. There is an opportunity for an alternative method to determine the correct endotracheal tube placement in the trachea. One such solution is described here, through the development of a compact fibre optic sensor integrated into a standard endotracheal tube. The sensor contains no electrical components inside the invasive portion of the device, and it is magnetic resonance imaging safe. The spectral characteristics of the trachea and oesophagus are observed using a fibre optic probe, with the presence of oxyhaemoglobin being used to distinguish the tissues. A novel epoxy sensor is then designed using plastic optical fibres. A rounded top with a square base sensor shape had the least impact on the overall performance of the ETT. Furthermore, by forming the sensor with two illumination fibres, pulse oximetry can be performed. A fibre separation distance between 1.27 and 2.54 mm is optimal. However, a Monte Carlo simulation demonstrates a viable separation of 0.5 to 3 mm. ThereforeHowever, by reducing this to 0.88 mm, a more compact sensor can be produced whilst still retaining a classification rate (average correct identification of trachea and oesophagus) of >89.2% in ex-vivo models. Two methods for emitting light perpendicularly to the fibre axis are explored, demonstrating that bending the fibres caused an optical power loss of 29.0%, whereas cleaving the fibres at 45° produced an 81.9% loss. The position of the sensor on the endotracheal tube is investigated, finding that integration behind the cuff is preferable. However, placement outside the main lumen of the ETT is also a viable option. Computational methods to process spectral measurements are developed. Data for these methods was provided by two experiments on two different sensor types, providing a high tissue classification rate for both the trachea and oesophagus. The first experiment consisted of 9 ex-vivo porcine samples, producing a correct tissue identification of up to 100.0%. The second consisted of 10 sensors on 1 ex-vivo porcine sample, yielding a maximum correct tissue identification of 89.2% when a support vector machine classifier was used. Application of the sensor in an animal study, which consisted of 3 porcine subjects, generated a maximum correct tissue identification of 98.31.6% using principal component analysis and aa support vector machine. The data were recorded over a combined time of 348 minutes, obtained during varying cuff pressures, endotracheal tube orientations, and movement. Finally, suggested future developments to the sensor design and computational methods demonstrate a potential route to improving tissue identification rates. Changes to the experimental protocol are described to verify classification rates. Concepts for exchanging the spectrometer for photodiodes and optical filters to reduce the cost of the opto-electronic units display potential. The technology has applications in wider healthcare, with examples of integration within naso-/oro- gastric tubes and other invasive medical devices given