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Biomedical subjects

B Hök

Publications and source records attributed to B Hök.

At least 19 recordsLinked to original sources
PubMed2003

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.

Breath Tests↗
PubMed1999

[To use the stethoscope correctly is not easy. The intricate art of auscultation should receive more attention in medical education].

Although the stethoscope is used daily by almost every physician, the full potential of the art of stethoscopy is seldom tapped. It has been replaced by newer and more costly techniques. In the article it is argued that more time in medical education should be allocated to stethoscopy, so that it can be used in selecting patients who will benefit most from examination with modern diagnostic tools. The medical technological background of stethoscopy is also reviewed, as are the reasons why it is difficult to give sound advice on the choice of stethoscope.

Acoustics↗
PubMed1995

Respiratory monitoring during postoperative analgesia.

Respiratory monitoring, using a novel flow sensor based on an acoustic principle, has been investigated in 30 patients during postoperative analgesia. Each patient was subjected to monitoring and human observation for 8 hr. The study was performed by independent observers at three clinics. Significant correlation was noted between respiratory rate (RR) determined by the sensor and the observers. Recordings of respiratory duration index (RDI), breathing time intervals (BTIs) indicated high sensitivity of the instrument to respiratory depression and perturbations in the breathing rhythm. More than 800 apnea alarms were noted, using an alarm setting of 30 sec; 61% of the categorized alarms were noted by the observers as true apneas. From the recordings it was shown that the number of alarms can be reduced by a factor of four if the alarm setting is changed to 45 sec. We conclude that the suggested technique, with slight modifications, provides adequate respiratory monitoring of patients during postoperative analgesia.

Acoustics↗
PubMed1995

Bio-acoustic signals from stenotic tube flow: state of the art and perspectives for future methodological development.

To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.

Acoustics↗
PubMed1995

A bioacoustic method for timing of respiration at cardiac investigations.

At cardiac investigations Doppler echocardiography is an established technique for the recording of intracardial and intravascular flow velocities. Transvalvular and venous flows are, however, markedly influenced by respiration. Since the start of inspiration is the important time of reference, accurate recording of the respiratory phase is important when analysing these flow velocities. A bioacoustic technique was therefore adopted to meet this demand and was tested in 10 normal subjects. Oesophageal balloon technique was used as a reference, and the bioacoustic technique was compared with a respiratory inductive plethysmograph. The average delay for the acoustic sensor signal compared to the oesophageal pressure changes was 205 +/- 46 (SD) ms, ranging from 160 to 320 ms for normal breathing, and is comparable to that of the respiratory inductive plethysmograph (210 +/- 90 ms). The bioacoustic technique is easier to apply than the respiratory inductive plethysmograph. The sensitivity to disturbances can be further reduced by signal processing and the method has clinical potential for the future.

Adult↗
PubMed1993

A new respiratory rate monitor: development and initial clinical experience.

The need for continuous, noninvasive, and reliable respiratory rate monitoring during recovery from general anesthesia has long been recognized. Alternative principles can be grouped into those detecting the respiratory effort, and those detecting the actual result, i.e. the respiratory gas flow. The second category is of greatest interest for patient monitoring. In this paper, we report the development and initial clinical experience with a new acoustic air-flow sensor. By differential, multipoint detection of the air-flow in the mouth and nose region, the sensor can easily discriminate against different kinds of interference, including motion artefacts. The sensor is nonexpensive, rugged, simple to apply and inherently safe. An instrument with continuous display of respiratory rate, and an audiovisual apnea alarm has been designed and built. The complete system has been tested on patients during recovery after general anesthesia. In 16 patients, the respiratory rate displayed by the instrument has been correlated against that visually observed. A good correlation was obtained. Minor discrepancies can be explained from the fact that visual observation corresponds to the respiratory effort, whereas the sensor detects the actual air flow. In 12 patients, 24 hour simultaneous recordings were made of respiratory rate with the new sensor, with simultaneous recording of the oxygen saturation and the heart rate with a pulse oximeter. It was found that the new sensor reliably recorded respiratory depression and apnea. Such events may in some patients be as frequent as one incident per hour. One case of 'Ondine's curse' provided clear evidence that pulse oximetry has a low sensitivity to respiratory disorders.

Adult↗
PubMed1993

Experimental evaluation of two new sensors for respiratory rate monitoring.

Visual observation was chosen as the reference method for measuring the respiratory rate in ten healthy volunteers. The new fibre-optic and acoustic sensors were simultaneously compared with capnography and transthoracic impedance plethysmography during normoventilation in the respiratory rate range of 6-24 breaths per minute and at a fixed respiratory rate of 13 breaths per minute. In addition a simulation of central apnoea was performed. All the measurements were recorded on an analogue tape recorder and a strip-chart recorder and analysed off line. The analyses of the recordings were performed by a person who was unable to see the monitoring systems. There was no discrepancy in the results of these methods. Each of the methods responded rapidly to an apnoeic event. The new fibre-optic and acoustic sensors correlate well with more traditional methods such as capnography and transthoracic impedance plethysmography for respiratory rate monitoring.

Acoustics↗
PubMed1992

Remote auscultatory patient monitoring during magnetic resonance imaging.

A system for patient monitoring during magnetic resonance imaging (MRI) is described. The system is based on remote auscultation of heart sounds and respiratory sounds using specially developed pickup heads that are positioned on the precordium or at the nostrils and connected to microphones via polymer tubing. The microphones operate in a differential mode outside the strong magnetic field to reduce various sources of interference from the MRI equipment. After amplification, the signal is transmitted as infrared light to a small, battery-operated receiver and a headphone set. Thus, the patient can be simultaneously auscultated both inside and outside the shielded MRI room by infrared transmission through a metal mesh window. Bench tests of the system show that common mode acoustic noise is suppressed by approximately 30 dB in the frequency region of interest (100-1,000 Hz), and that polymer tubing having a diameter of approximately 2 mm can be used for efficient sound transmission. Recordings in situ show satisfactory detection of both heart sounds and respiratory sounds, although the signal is somewhat masked by noise during imaging. A clinical test incorporating 17 sedated or anesthetized patients was also performed. In all but four cases, the quality of the breath and heart sounds was regarded as acceptable or better.

Acoustics↗
PubMed1992

The IOP-IOL. A probe into the eye.

The intraocular lens (IOL) implant can be looked upon as a probe into the space of the eye. Adapting that view, it is logical to furnish the IOL-probe with biomedical sensors that would explore its environment. A sensor is presented for continuous monitoring of intraocular pressure (IOP), incorporated in the haptics of an IOL. The sensor consists of a capacitative spiral circuit, needing no energy, correlating its resonance frequency to the actual IOP. This resonance frequency is remotely and non-invasively detected by an external device located in a spectacle frame.

Biosensing Techniques↗
PubMed1978

Aspects of present and future possibilities for intraluminal pressure recordings in the urogenital tract.

In this brief survey some aspects of present and future possibilities for intraluminal pressure recordings in the urogenital tract are considered. It is emphasized that present water-filled catheter-manometer systems are afflicted with several biotechnical disadvantages. Although the micro-transducers and centre-hole catheters seem to be superior to conventional pressure recording systems, they ought to be further improved. Feed-back pressure transducers, electronic compensation, and micro-manometers could be realistic alternatives for pressure recordings in the urogential tract in the future. Some results from pressure recordings obtained with different measuring systems are presented and discussed.

Catheterization↗
PubMedDate not supplied

Anesthesia and monitoring during whole body radiation in children.

During whole body radiation therapy of children, treatment may be done in places not equipped with acceptable scavenging systems for anesthetic gases and where clinical observation of the patient may be impossible. In order to solve this problem, the authors have used a total intravenous (IV) anesthetic technique using midazolam, pancuronium, and fentanyl. With midazolam as the only hypnotic agent, the problem with scavenging is solved, and a computer simulation of the plasma concentration of midazolam is presented. A modified stethoscope for monitoring during radiation also has been developed. This anesthetic technique and the stethoscope have been used in seven children. The total IV anesthesia proved to be a useful method for children during whole body radiation. The modified stethoscope functioned very well and was a useful complement to the monitoring equipment.

Anesthesia, Intravenous↗
PubMedDate not supplied

Postanesthesia monitoring revisited: frequency of true and false alarms from different monitoring devices.

STUDY OBJECTIVES: To determine the frequency of true and false alarms and to determine the frequency of alarm failures for various parameters when using a postanesthesia monitoring system. DESIGN: Open prospective study. SETTING: Postanesthesia care unit at a university hospital. PATIENTS: 123 ASA physical status I-IV patients who underwent general or spinal-epidural anesthesia for general, urologic, orthopedic, ophthalmologic, otolaryngologic, or plastic surgery. MEASUREMENTS AND MAIN RESULTS: Monitoring included ECG, oxygen saturation, and respiratory rate (RR) by either transthoracic impedance or nasal-oral air-flow detection. We undertook careful, continuous observation of patients and monitors, recording of true and false alarms; the latter were defined as those coinciding with a clearly observed, unrelated cause. During a mean observation period of 101 minutes per patient, the average frequency of pulse oximetry alarms was once every 8 minutes, with 77% of the alarms being false, caused by sensor displacement, motion artifacts, poor perfusion, or a combination of these factors. Apnea alarms occurred on average once every 37 minutes, with the "false" fraction being 28% and 27% for impedance and flow detection, respectively. The impedance sensor failed to detect apnea on at least 6 occasions; the flow sensor failed on 1 occasion. The coincidence of pulse oximetry and apnea alarms was small, and ECG exhibited a low alarm rate but a high fraction of false alarms. Patients receiving opioids and neuromuscular relaxants had a higher frequency of "true" apneas than patients not receiving these drugs. No clear correlation was found in regard to age distribution, type of surgery, duration of anesthesia, oxygen administration, or ASA physical status between the patient groups that exhibited many apneas or many pulse oximeter alarms and the whole study population. CONCLUSIONS: The high frequency of apnea strongly motivates the use of continuous RR monitoring, preferably by flow-sensing techniques, since both central and obstructive apneas are then detected. Further study and development is necessary before pulse oximetry can be unconditionally recommended for postanesthesia monitoring.

Adolescent↗