Mia Folke

Critical review of non-invasive respiratory monitoring in medical care

Respiratory failure can be difficult to predict. It can develop into a life-threatening condition in just a few minutes, or it can build up more slowly. Thus continuous monitoring of respiratory activity should be mandatory in clinical, high-risk situations, and appropriate monitoring equipment could be life-saving. The review considers non-invasive methods and devices claimed to provide information about respiratory rate or depth, or gas exchange. Methods are categorised into those responding to movement, volume and tissue composition detection; air flow; and blood gas concentration. The merits and limitations of the methods and devices are analysed, considering information content and their ability to minimise the rate of false alarms and false non-alarms. It is concluded that the field of non-invasive respiratory monitoring is still in an exploratory phase, with numerous reports on specific device solutions but less work on evaluation and adaptation to clinical requirements. Convincing evidence of the clinical usefulness of respiratory monitors is still lacking. Devices responding only to respiratory rate, and lacking information about actual gas exchange, will have limited clinical value. Furthermore, enhancement in specificity and sensitivity to avoid false alarms and non-alarms will be necessary to meet clinical requirements. Miniature CO2 sensors are identified as one route towards substantial improvement.

Case-Based Reasoning Systems in the Health Sciences: A Survey of Recent Trends and Developments

The health sciences are, nowadays, one of the major application areas for case-based reasoning (CBR). The paper presents a survey of recent medical CBR systems based on a literature review and an e-mail questionnaire sent to the corresponding authors of the papers where these systems are presented. Some clear trends have been identified, such as multipurpose systems: more than half of the current medical CBR systems address more than one task. Research on CBR in the area is growing, but most of the systems are still prototypes and not available in the market as commercial products. However, many of the projects/systems are intended to be commercialized.

Comparative Provocation Test of Respiratory Monitoring Methods

Objective.The aim of this study was to compare clinicallyrelevant performance of: 1) a prototype respiratory sensor based oncapnometry with two alternative signal receptor fixations, 2) afiberoptic humidity sensor and 3) human visual observation. Comparativeprovocation tests were performed on volunteers at the Post-AnesthesiaCare Unit at Västerås Central Hospital. Methods.Theexperimental tests involved 10 healthy, voluntary test subjects,instructed to intersperse normal breathing with protocol provocations ofbreath holding, limb and head movements, and nasal oxygen supplement.The signal outputs from the three respiratory monitoring methods wererecorded on a personal computer. The signal analysis included visualcategorising of the signals and counting breath events. Recognising thatnone of the methods could act as reference, events were classified as“unanimous,” “majority” or“minority” events depending on how many of the three methodsthat detected a breath. Results.The average total recording timewas 37 minutes per subject. The respiratory rates varied from 6.5 to 19breaths per minute, with a mean value of 11.4 breaths/minute. The breathhold duration ranged from 18 to 50 seconds. Discrepancies between thethree methods were found in more than 20% of the marked events.The most frequent majority events were due to events not recorded by theobserver who, on the other hand, contributed the least to minorityevents. The provocations made by the subjects during the measurement didnot increase the rates of majority and minority events, compared toperiods of no provocation. The fiberoptic device exhibited a largercount of minority events but a smaller contribution to majority eventsthan the capnometry prototype. Conclusions.The capnometry andfiberoptic sensors exhibit differences in responses that may beunderstood from basic principles. The importance of the physicalapplication of the sensor to the patient was clearly observed. Theoptimum design remains to be found.

A new capnograph based on an electro acoustic sensor

End tidal carbon dioxide measurements with an electro acoustic capnograph prototype have been demonstrated. The aim of this study was to verify that it is possible to obtain an adequate capnogram using the prototype and to investigate the influence of ambient temperature and humidity variations. By simultaneous measurements with a reference capnograph, on subjects performing exercise, hypo- and hyperventilation, PETCO2 readings from the reference were compared with the output signal from the prototype. The capnogram from the prototype correlated well with the reference in terms of breath time. The first parts of the expiration and inspiration phases were steeper for the reference than the prototype. The output signal from the prototype correlated well with the reference PETCO2 readings with a correlation coefficient of 0.93 at varied temperature and relative humidity.

Gas sensor with electroacoustically coupled resonator

Abstract A new configuration for a gas sensor is demonstrated. The configuration consists of an electroacoustic element coupled to an acoustic resonator, such as Kundt’s tube, exhibiting a resonance frequency that is related to the velocity of sound, which, in turn is a function of the molecular mass of the gas within the resonator. Electrical impedance measurements were performed, whereby a resonance peak attributable to the resonator was identified. Contributing effects to the quality factor, Q, of the resonance, was analyzed. Predictable shifts of the resonance frequency were observed when adding CO2 and He to air, and when varying the resonator length. Linearity within the experimental accuracy was confirmed. The new sensor configuration offers the potential advantages of smaller size, improved dynamic response, and lower cost.

Technical issues related to the long-term monitoring of blood flow at different depths using LDF and PPG

The aim of this study was to evaluate an integrated probe using LDF and multiple PPG, for the long-term aspects of skin temperature and blood flow variations at different tissue depths, and especially to investigate whether the presence of the probe affects the temperature. Measurements of temperature and blood flow were performed over 60 min on the lower back of ten subjects, lying on a mattress. The surface temperature of the skin was also measured before and after the 60 min period, and repeated with three probe configurations with the probe switched on, turned off and in the absence of a probe. A general increase in the blood flow was found to occur during the 60 min interval at all depths reached by this probe, but with variations over time. No difference was found in temperatures recorded for the different probe configurations. According to our measurements, the presence of the probe does not affect the skin surface temperature at 60 min. Our investigation shows that skin temperature can be expected to increase and approach the body core temperature by just lying in supine position on the mattress. The increase in temperature and blood flow that is known to occur, possibly attributable to pressure-induced vasodilatation, must be taken into consideration when performing these kinds of measurements.

A Multi-disciplinary Approach in the Development of a Stroke Rehabilitation Tool

This work describes a method used in the development of a stroke rehabilitation tool. The method was based on three key elements. The first key element was iterations between the use of broad groups with different professionals/stakeholders and small hands-on working groups with users from the same profession. The second key element was movement between understanding differences between different organizations and professionals and understanding of specific needs within the different organizations. The final key element was including implementation aspects from the very start of the work.

Diagnosis and biofeedback system for stress

Today everyday life for many people contain many situations that may trigger stress, or result in an individual living on an increased stress level under long duration. High level of stress over time may cause serious health problems. It is known that respiratory rate in terms of hyperventilation (defined as low pCO2) is an important factor and can be used in the diagnosis of stress-related dysfunctions. It can also be used for biofeedback training but available measurement of respiratory rate and its metabolic consequences are not especially suitable for home and office use. The aim of this project is to develop a portable sensor system that can measure stress level during everyday situations e.g. at home or at work. The sensor explored here is a finger temperature (FT) sensor. FT reflects changes in sympathetic nervous system (SNS) and not hyperventilation, as SNS is an important marker of stress it is highly relevant. Clinical studies show that finger temperature, in general, decreases with stress however this changed pattern shows large individual variations. Consequently, diagnosis of stress from the FT measurements is difficult even for the clinical experts. Therefore, a computer-based stress diagnosis system is valuable. In this paper a case-based reasoning (CBR) stress management system is presented and evaluated. The results of the evaluation show a promising performance.

Assessment of the Optical Interference in a PPG-LDF System Used for Estimation of Tissue Blood Flow

The aim of this study is to assess the optical cross interference in a system including laser Doppler flowmetry (LDF) and photoplethysmography (PPG) with regard to the illuminating power of PPG-LEDs and distance between the light detector/s and light source/s.

Portable sensor system for rehabilitation of patients suffering from WAD

Whiplash Associated Disorders (WAD) are several remaining symptoms after an acceleration-/deceleration injury of the neck, often due to a road accident. Common symptoms are neck pain, headache, stiffness, loss of sensation, memory impairment and concentration difficulties. The whiplash-related injuries were estimated to cost Sweden more than SEK 4 billion 2005, the main part of these costs takes the form of compensation for loss of income, as a result of incapacity for work. The aim of this project has been to develop a training and rehabilitation system for patients suffering from WAD. The portable system is based on a 2-axis gyroscopic sensor with a computer interface. The sensor system is placed on the head of the patient and movements of the head are mirrored on the computer screen. The patient is supposed to follow a visible track on the screen. This enables interactive training facilities for patients, who can use the system unsupervised in their home environment.