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Biomedical subjects

P A Oberg

Publications and source records attributed to P A Oberg.

At least 19 recordsLinked to original sources
PubMed1996

Single-fibre laser Doppler flowmetry and electromyography for evaluating microcirculation in forearm muscle during static and continuous handgrip contractions.

A technique is described for intramuscular measurement of muscle blood flow in the forearm, by using a 0.5-mm thin optical single-fibre for laser Doppler flowmetry (LDF) inserted percutaneously. Continuous recordings were performed of the brachioradial muscle during an 11-min series of alternating 1-min periods of increased static contraction and rest determined by an electronic handgrip forcemeter and surface electromyography (EMG) of the muscle. Stepwise increased handgrip contractions were performed at 10%, 20%, 30%, 40% and 50% maximal voluntary contraction (MVC). This was followed by a similar series of continuous contractions. Finally, an endurance test was performed with a handgrip force of 50% MVC maintained for as long as possible. A group of ten healthy men of different ages was studied. Signal processing was done on line by computer. Successive increases in rootmean square (rms)-EMG and a fall in the mean power frequency (MPF) of the EMG spectrum occurred during the series of static contractions, which evoked perceived local fatigue in the forearm. Muscle blood flow recorded simultaneously showed no change from resting level during contractions at 10%, 20% and 30% MVC, while at 40% and 50% MVC mean increases of 150% and 200% were recorded. Blood flows measured during the rest periods showed large variability with no significant changes. This was also found after continuous contractions of the same intensities. The endurance time was 1.2-3.5 min (mean 2.4 min). Muscle blood flow showed mean increases of 214%, 256% and 229% of resting level each minute of the maintained contraction. Nevertheless, EMG signs of local fatigue developed, such as a rise in rms-EMG and a fall in MPF, and the subject experienced local fatigue. To conclude, this technique of percutaneous, continuous LDF recorded, at high sensitivity, the microcirculation at different fluxes and EMG-defined muscle activity.

Adult↗
PubMed1996

Optical aspects of a fibre-optic sensor for respiratory rate monitoring.

A new sensor for respiratory rate monitoring is described. The sensor uses an optical fibre that detects the evaporated humidity from the mouth and/or nose at each exhalation. The condensed humidity substantially alters the coupling of light from the optical fibre to the surrounding medium, which can be monitored by a photo-detector. The sensing principle is evaluated using ray-tracing simulation and scattering measurements.

Computer Simulation↗
PubMed1996

Laser Doppler flowmetry: characteristics of a modified single-fibre technique.

The single-fibre percutaneous laser Doppler technique has been used in previous studies of intramuscular blood flow. This method facilitates studies of blood flow in deep tissue volumes and minimises the tissue trauma. The technique has been further developed with the aim of improving the signal quality. This has been accomplished by modifying the geometry of the fibre tip. By melting the fibre core material, lenses of different shapes are formed. Flat, spherical and 'pear'-type tips have been manufactured and are evaluated theoretically and experimentally. The paraxial theory cannot accurately predict the position of zones of highest irradiance. Therefore, a ray-tracing program has been developed in the C language, by means of which some of the optical properties of the modified fibre tips can be simulated. Iso-irradiance graphs and beam profiles are calculated for the three different fibre tips. Measured and calculated irradiance curves are used for evaluation of the properties of the ray-tracing model. The three types of fibre tips are also evaluated and compared in flow models. The sphere and pear-type probes show a higher flow sensitivity than the flat-end type. These improvements in flow sensitivity are interpreted as being related to the larger, strongly irradiated tissue volumes in front of the fibres. Intramuscular measurements with the pear-type probe show high sensitivities to induced blood flow changes.

Evaluation Studies as Topic↗
PubMed1996

A new single-fibre laser Doppler flowmeter based on digital signal processing.

A new laser Doppler flowmeter, based on a personal computer with a digital signal processor for detecting the blood perfusion in skeletal muscle, was designed and evaluated. An infrared laser diode (750 nm) fed a single optical fibre, 400 microns in diameter, which was introduced into the muscle. A PC equipped with a digital processing unit was used for emulation of the laser Doppler algorithm and for presentation of the measurement results. The Doppler signal power spectral density and corresponding flow values were visualized on the computer screen continuously in real-time, and could also be saved on the hard disk for off-line analyses. The graphic-user interface supported by Labwindows software made the system easy to use. It is possible to alter in the software the signal processing and the ways in which the signals and results are presented. The new system was evaluated by using a flow model as well as a mechanical model. The model studies showed linear relationships between particle velocity and flow in the range of 0-5 mm s-1. The system was also tested in measurements of the blood flow in the brachioradial muscle, and was found to have advantages over our previously used systems.

Algorithms↗
PubMed1995

Effects of psychophysiological stress on trapezius muscles blood flow and electromyography during static load.

Mental stress was induced by the Stroop colour word task (CW task) and the effects on the microcirculation and electromyography (EMG) in the upper portion of the trapezius muscle were studied during a series of fatiguing, standardized static contractions. A lowered blood flow of the skin recorded continuously by laser-Doppler flowmetry (LDF) was used as a stress indicator in addition to an elevated heart rate. Muscle blood flow was recorded continuously by LDF using a single optical fibre placed inside the muscle, and related to surface EMG. A group of 20 healthy women of different ages was examined. Recordings were made during a 50-min period in the following sequence: a 10-min series of alternating 1-min periods of rest and stepwise increased contraction induced by keeping the arms straight and elevated at 30, 60, 90 and 135 degrees with a 1-kg load carried in each hand; a 10-min recovery period without load; a repeated contraction series with simultaneous performance of the CW task; a second 10-min recovery period, and a second contraction series without CW task. Signal processing was done on line by computer. The LDF and root mean square (rms)-EMG values were calculated, as well as the EMG mean power frequency (MPF) for fatigue. The CW-task added to the contraction series caused an increase in the heart rate accompanied by a decrease in the blood flow to the skin and a 30% increase in the blood flow in the exercising muscle. Both returned to normal during the subsequent recovery period and showed normal levels during the final contraction series without CW. The rms-EMG showed a 20% increase that persisted during the final contraction series performed without CW. There was no influence on MPF. This CW has previously been shown to evoke an increased secretion of adrenaline from the adrenal medullae to the blood. The increased blood flow in the exercising muscle would therefore appear to have been caused by beta-adrenoceptor vasodilatation, and the fall in the blood flow in the skin by alpha-adrenoceptor vasoconstriction. The findings may have implications for work situations characterized by repetitive static loads to the shoulder muscles and psychological stress.

Adult↗
PubMed1995

Microcirculation in the upper trapezius muscle during sustained shoulder load in healthy women--an endurance study using percutaneous laser-Doppler flowmetry and surface electromyography.

Microcirculation in the upper portion of the trapezius muscle was measured percutaneously in a group of 16 healthy women of different ages by continuous laser-Doppler flowmetry (LDF) in relation to electromyography (EMG) during an endurance test. During the measurements the subject kept her arms straight and elevated at 45 degrees in the scapular plane and held a 1-kg load in each hand as long as possible. This was followed by rest with the arms hanging and carrying no load. The 10-min recording period comprised 1-min initial rest followed by the endurance test and then recovery. Signal processing was done by computer on line. The LDF and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) were performed. The amount of load produced was on average 2,267 (SD 939) N.m.s, i.e. shoulder torque x time expressed as Newton meter seconds, and the endurance time was 4.3 (SD 1.20) min. The rms-EMG as well as the LDF increased significantly during endurance, both when related to endurance time and to amount of load. The MPF showed no significant changes. The mean total increase in muscle blood flow was 175% of that recorded in the initial rest period. The average increase per each 10 s of contraction was 2.9%. Maximum was reached during the 1st min of recovery followed by a fall to the base level that was reached within 77 s on average. The amount of load produced and the blood flow increase was smaller than that found in a separate study of men, indicating a lower functional capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Measurement by laser-Doppler flowmetry of microcirculation in lower leg muscle at different blood fluxes in relation to electromyographically determined contraction and accumulated fatigue.

Single-fibre percutaneous laser-Doppler flowmetry (LDF) of the tibialis anterior muscle was performed continuously for measurement of the microcirculation during different blood fluxes, as well as in relation to different muscle activities and fatigue determined electromyographically (EMG). The laser-Doppler power spectrum density function was studied in a frequency range of 0-8.2 Hz as representing the blood flow most selectively. Reduced blood flow from tourniquet inflation caused a decrease in signal power density, compared to that of intact blood flow at rest. During postocclusion reactive hyperaemia an increased signal power was recorded. This reached its maximum within 4.4 (SD 1.88) s after deflation of the tourniquet. The different fluxes were recorded at high sensitivity and disturbances were small. Periods of 1-min static dorsi-flexion of the foot at 10, 20, 30, 40, and 50% MVC (maximal voluntary contraction) with 1-min rest between were associated with a significant increase in LDF, the recordings obtained during the rest periods showing a tendency towards an increase. A decrease in the EMG mean power frequency (MPF) indicated accumulated fatigue. The LDF for the rest periods that followed upon continuous contractions up to the same MVC levels showed a tendency towards an increase but variability was large. With further development, these techniques may be useful in the evaluation of insufficiency of the peripheral circulation.

Adult↗
PubMed1995

The time-variable photoplethysmographic signal; dependence of the heart synchronous signal on wavelength and sample volume.

The photoplethysmorgraphic signal (PPG) from forearm skin and the ECG were recorded simultaneously from healthy subjects. The optical signal was derived with a fibre-optic probe which consisted of 61 fibre pairs. The peak-to-peak averaged a.c.-signal was calculated. The dependency of this signal and the signal-to-noise ratio (SNR) on the light wavelength and on sample volume was studied. The light intensities used at 560 nm were 0.015 and 0.029 mWmm-2 and at 940 nm we used 0.029, 1.37 and 2.77 mWmm-2. A theoretical model for calculation of the sample volumes was also developed. The amplitude and SNR of the a.c.-signal at 560 nm is larger than at 940 nm at the same intensity (0.029 mWmm-2). At 940 nm using 1.37 and 2.77 mWmm-2 the a.c.-signal increased with the number of fibre pairs (volume) while the SNR was little affected. At 560 nm it is suggested that the major contribution to the a.c.-signal is pulsations in the ascending arterioles and at 940 nm from pulsations in the larger vessels deeper in the tissue volume under study.

Adult↗
PubMed1994

Presentation and evaluation of a new optical sensor for respiratory rate monitoring.

A new optical sensor for respiratory rate monitoring was simultaneously compared with an acoustic sensor and a transthoracic impedance plethysmograph during normoventilation in the respiratory rate range of 9-17 breaths per minute. The response characteristics of the optical sensor were then measured during simulation of central apnoea and tachypnoea. Visual observation was chosen as the reference method for monitoring the respiratory rate. The measurements were performed in ten healthy volunteers and the respiratory signals recorded on an analogue tape and strip-chart recorder and analysed off-line. The response characteristics of the fibre optic sensor corresponded well with those of the acoustic sensor and impedance plethysmograph. All three methods responded rapidly to an apnoeic event.

Adult↗
PubMed1994

Design and evaluation of a fibre-optic sensor for limb blood flow measurements.

A fibre-optic microbending sensor for clinical use in venous occlusion plethysmography (VOP) has been developed. The sensor utilizes the microbending principle to detect the volume expansion of a limb following venous occlusion. This principle is based on the loss of energy in an optical fibre that undergoes mechanical perturbations. A comparative study of 10 healthy subjects has been made between the new fibre-optic sensor and a mercury strain-gauge sensor. Each subject's limb blood flow was recorded 10 times. The two sensor types were positioned closely together on the same limb. The result of the study shows a high correlation (r = 0.949) verifying that the fibre-optic sensor's performance makes it a suitable alternative to the mercury strain-gauge sensor.

Adult↗
PubMed1993

Continuous percutaneous measurement by laser-Doppler flowmetry of skeletal muscle microcirculation at varying levels of contraction force determined electromyographically.

Laser-Doppler flowmetry (LDF) and electromyography (EMG) were used simultaneously for measuring skeletal muscle blood perfusion in relation to static load and fatigue. Percutaneous single-fibre LDF and bipolar surface EMG of the trapezius muscle were performed continuously during a 10-min series of alternating periods of static contractions and rest, each of 1-min duration. The muscle was exposed to static load expressed as shoulder torque, by keeping the arms straight and elevated at 30, 60, 90 and 135 degrees. On-line computer processing of the LDF and EMG signals made possible the interpretation of the relationship between the perfusion and the activity of the muscle. The LDF and root mean square (rms)-EMG were normalized by using the average value of the serial examinations of each individual as a reference value. Spectrum analyses of EMG showed the lowest variability for median frequency (MDF) in the frequency range 10-1000 Hz and mean power frequency (MPF) at 2-1000 Hz. The LDF power spectrum density during low (muscle rest) and high (high-force muscle contraction) perfusion indicated that disturbances were small when measurements were performed during sustained static contraction with as little movement as possible. Vasomotion, i.e. rhythmic variations in the blood flow, were present and showed a frequency of 5-6 cycles.min-1. Application of a tourniquet to the upper arm caused an arrest of the microcirculation in the distally situated brachioradial muscle which was followed by a postischaemic hyperaemia upon removal of the torniquet.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women--a study using percutaneous laser-Doppler flowmetry and surface electromyography.

Microcirculation in the upper portion of the trapezius muscle was measured percutaneously by continuous laser-Doppler flowmetry (LDF) during two 10-min series of alternating 1-min periods of static contraction and rest determined electromyographically (EMG). Stepwise increased contraction was induced by keeping the arms straight and elevated at 30, 60, 90 and 135 degrees, which was repeated with a 1-kg load carried in each hand. Thereafter, fatigue and recovery were recorded while the subject kept her arms straight and elevated at 45 degrees carrying the 1-kg hand load as long as possible, followed by rest with arms hanging and no load. A group of 16 healthy women of different ages was studied. Signal processing was done on line using a 386 SX computer. The LDF- and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) and median spectrum frequency were performed. The rms-EMG increased significantly with an increase in the calculated shoulder torque (r = 0.75). Accumulated local fatigue was indicated by a decrease in MPF with increased shoulder angle and added load (r = -0.54). Blood flow increased with increased shoulder angle (r = 0.82, with hand load r = 0.62) and with increased shoulder torque (r = 0.72), and also showed a significant increase with increased EMG activity (r = 0.74). The LDF showed a negative correlation to MPF (r = -0.67), with increased values when MPF was lowered. During the endurance test, a moderate increase of LDF occurred which reached its maximum during the 1st min of recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Accuracy of pulse oximetry at various haematocrits and during haemolysis in an in vitro model.

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60-100 per cent. At a haematocrit level of 41-44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10-11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.

Hematocrit↗
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↗
PubMed1993

Venous occlusion plethysmography using a fiber-optic sensor.

This paper presents the results of comparative testing of a fiber-optic sensor used as an alternative to the mercury strain-gauge in a clinically well-established technique for limb blood flow assessment, venous occlusion plethysmography. In this research the measurement of volume changes following venous occlusion has been performed with a variety of methods including the commonly used mercury strain-gauge. Temperature drift and long-term instability are problems associated with the mercury strain-gauge. In addition, environmental protection authorities are prohibiting the marketing of mercury sensors, beginning in 1993. Evaluation and optimization of the fiber optic microbending sensor is described in detail. Comparison with the mercury strain-gauge sensor is made for in lower limb blood flow measurements.

Equipment Design↗
PubMed1992

Impedance plethysmography for blood flow measurements in human limbs. Part 2. Influence of limb cross-sectional area.

The cross-sectional area of a limb varies along the extremity. This is of great importance when impedance plethysmography is used for limb blood flow studies. The actual measurement site, as well as the interelectrode distance, must be carefully selected to avoid underestimation of the blood flow value. The distance between the potential electrodes should be less than 10 cm for an adult subject.

Adult↗