Showing papers in "Physiological Measurement in 1993"
TL;DR: The results of this study indicate that a neural network can be trained to distinguish between PPG pulses from normal and diseased lower limb arteries.
Abstract: An artificial neural network (ANN) was trained to classify photoelectric plethysmographic (PPG) pulse waveforms for the diagnosis of lower limb peripheral vascular disease (PVD). PPG pulses from the lower limbs, and pre- and post-exercise Doppler ultrasound ankle to brachial systolic blood pressure ratio measurements were obtained from patients referred to a vascular investigation laboratory. A single PPG pulse from the big toe of each leg was processed and normalized, and used as input data to the ANN. The ANN outputs represented the diagnostic classifications (normal, significant PVD and major PVD) and the ANN was trained with the ankle to brachial pressure indices (ABPI). The back-propagation learning algorithm was used to train the ANN for 500 epochs with a PPG training set of pulses from 100 legs. The results of this study indicate that a neural network can be trained to distinguish between PPG pulses from normal and diseased lower limb arteries.
72 citations
TL;DR: Changes in posture and body movement were recognizable from the changes in the temperature profile, and well visualized using a three-dimensional display of the successive temperature profiles in the bed.
Abstract: For the assessment of body movements during sleep, a system for monitoring the temperature in bed was developed. The system consists of 16 temperature sensors and a data logger with a memory card. Fifteen of the temperature sensors were arranged in line 6 cm apart on a flat cable. The temperatures at these 15 points in the bed, and the room temperature measured by the additional sensor, were stored on the memory card at predetermined intervals. The data were transferred into a microcomputer and analysed. Changes in posture and body movement were recognizable from the changes in the temperature profile, and well visualized using a three-dimensional display of the successive temperature profiles in the bed. The time of body movement was estimated from the derivative of the temperature profile. Comparison between this estimation and the video recording showed good agreement. The linear arrangement of the sensors provides a high-resolution temperature profile during sleep.
72 citations
TL;DR: In a simulation experiment a life-size skull model was filled with NaCl solutions of different concentrations in each half, so as to model the impedances of a normal and an oedematous hemisphere and the impedance differences could be clearly detected by a coil system of 25 mm diameter.
Abstract: Using a primary coil that induces eddy currents in a volume conductor, and a pair of secondary coils configured to form a differential transformer, it is possible to measure the conductivity of a volume conductor by the magnetic fields of the induced eddy currents. This method is especially favourable for measuring impedance of the brain, as the low conductance of the surrounding skull interferes only very slightly with the measuring process. In a simulation experiment a life-size skull model was filled with NaCl solutions of different concentrations in each half, so as to model the impedances of a normal and an oedematous hemisphere. The impedance differences could be clearly detected by a coil system of 25 mm diameter.
70 citations
TL;DR: The cell membrane capacitance (Cm) was independent of temperature in the range 25-40 degrees C and was significantly higher for blood with ethylenediaminetetraacetic acid (EDTA) as anticoagulant than that forBlood with sodium citrate and acid citrate dextrose (ACD).
Abstract: A method was developed for simultaneously measuring plasma resistance, cell interior resistance and cell membrane capacitance of blood. A three-element circuit model for simulating the impedance of blood was evaluated by comparing measured and calculated impedance frequency curves and was found feasible. The values of the three elements of the model could be determined by measuring the impedance amplitudes at three different frequencies. The cell membrane capacitance (Cm) was independent of temperature in the range 25-40 degrees C and was significantly higher for blood with ethylenediaminetetraacetic acid (EDTA) as anticoagulant than that for blood with sodium citrate and acid citrate dextrose (ACD). The Cm value of blood from patients with high erythrocyte sedimentation rate (ESR) was found to be significantly higher than that of blood from patients with low ESR. This suggests that the membrane capacitance might be a potential parameter for clinical applications.
58 citations
TL;DR: Observed differences for Rp and C(m) among samples with various anticoagulants indicate that the type of antICOagulant influences the electrical properties of the red cells and the plasma.
Abstract: The relationship between the electrical impedance parameters and the haematocrit of normal human blood has been determined at 37 degrees C in the haematocrit range of 20-60% for four types of anticoagulant: ACD, EDTA, sodium heparin and buffered sodium citrate. For plasma resistance Rp and interior resistance Ri, the measured data could be fitted by both the exponential expression and the Maxwell-Fricke expressions, Rp=a/(1-h)+b and Ri=a/h+b, where a and b are constants and h is the haematocrit expressed as a decimal. The membrane capacitance Cm was found to be directly proportional to the haematocrit and could be normalized to 100% haematocrit by the Fricke formula, C100=Cm/(1- rho p/Rp), where rho p is the resistivity of plasma. Observed differences for Rp and C, among samples with various anticoagulants indicate that the type of anticoagulant influences the electrical properties of the red cells and the plasma.
57 citations
TL;DR: Validation of the reflectometer with an airway model gave accuracies and reproducibilities in the range 5-10%, and the effect of breathing pattern on airway areas is demonstrated.
Abstract: A practical implementation of acoustic reflectometry for determining airway areas in routine clinical use is described Advances over previous systems include portability, free breathing during measurements, no need to equilibrate with helium/oxygen, and real-time display of airway areas Validation of the reflectometer with an airway model gave accuracies and reproducibilities (coefficient of variation (CV)) in the range 5-10% With human volunteers, the within-run CV was typically 10%, and the day-to-day CV was 20% The effect of breathing pattern on airway areas is demonstrated In ten normal volunteers, acoustic and magnetic resonance imaging (MRI) methods of assessing pharyngeal and glottal areas were compared The results (mean+or-SD) for the oropharynx were 10+or-03 cm2 acoustically and 09+or-05 cm2 by MRI (p=077) The corresponding figures for glottal areas were 13+or-03 cm2 and 11+or-04 cm2 (p=009)
55 citations
TL;DR: It is demonstrated that the static mechanical properties and geometry of vascular specimens can be quantified in vitro with the new high-resolution CT scanner and can be compared subsequently with histological analysis to provide further insight into the understanding of atherogenesis.
Abstract: Vascular diseases are frequently associated with changes in the mechanical properties of the arterial wall. Existing techniques for studying arterial geometry and mechanical properties in vitro are often destructive, since they involve sectioning of the specimen into strips, or provide average measurements of the mechanical properties over the volume of intact specimens. We developed a high-resolution computed tomography (CT) scanner for in vitro studies of arterial geometry and static elastic properties. The x-ray image intensifier based system can acquire single transverse images, or a volume image, with 2 mm-1 resolution. Images were obtained through an intact abdominal aortic aneurysm at five pressures. The incremental circumferential Young's modulus E(inc) was calculated from the internal and external circumferences, and at physiological pressures E(inc) of the aneurysm was found to be 275 times greater than that of the normal aorta proximal to it. A volume image of the specimen provided landmarks that allowed histological sections to be obtained at locations coincident with those where the elasticity was measured. The histological analysis revealed a sixfold decrease in elastin content in the aneurysm, compared to the normal aorta. We have demonstrated that the static mechanical properties and geometry of vascular specimens can be quantified in vitro with the new high-resolution CT scanner and can be compared subsequently with histological analysis to provide further insight into the understanding of atherogenesis.
50 citations
TL;DR: The LDI enables rapid non-invasive detailed analysis of blood flow patterns in skin and correlates well with other methods for measuring skin perfusion, and may lead to further understanding of the local mechanisms for regulation of oxygen supply to tissue.
Abstract: Laser Doppler imaging is a new development in the field of laser Doppler flowmetry The authors were recently loaned the Lisca laser Doppler perfusion imager (LDI) manufactured by Lisca Development, Linkoping, Sweden for assessment against other methods for assessment of skin perfusion In order to evaluate the device, it was applied to imaging flux changes induced in human skin during the tuberculin reaction Flux values were compared directly with those from conventional lightguide laser Doppler flowmetry, and parameters measured using two other methods for assessment of tissue perfusion, dynamic thermographic imaging and tissue spectrophotometry The results showed very good correlations between the various methods In addition, the LDI showed that very large differences in flux values (up to 5 V) could be found within distances of only 2 mm during the tuberculin reaction and that focal centres of low flux values surrounded by higher values ('craters') could be found not only at the centre, but elsewhere in the lesion The LDI enables rapid non-invasive detailed analysis of blood flow patterns in skin and correlates well with other methods for measuring skin perfusion Its use to examine heterogeneity of microvascular blood flow patterns may lead to further understanding of the local mechanisms for regulation of oxygen supply to tissue
49 citations
TL;DR: This paper describes the construction of a scanning laser ophthalmoscope interfaced to a computer, which has a number of significant advantages for digital retinal imaging, and permits imaging at various wavelengths with no consequent degradation in image quality.
Abstract: The authors describe the construction of a scanning laser ophthalmoscope interfaced to a computer, which has a number of significant advantages for digital retinal imaging. First, it has better uniformity of illumination than the fundus camera and operates at much lower light levels. Secondly, it permits imaging at various wavelengths with no consequent degradation in image quality; in particular, the value of imaging at infrared wavelengths to give greater tissue penetration is demonstrated. Finally, by introducing the capability for confocal imaging, tomographic images can be taken, improving the perceptibility of features situated deep in the retina. Typical images are shown to demonstrate the potential of this instrument.
47 citations
TL;DR: Several problems observed in the analysis of the present MEG and EEG data suggest that the simultaneous measurement and analysis of multichannel EEG and MEG data will substantially increase spatio-temporal resolution.
Abstract: Median nerve somatosensory evoked potentials (SEP) and magnetic fields (SEF) were recorded in two subjects with multichannel devices. Single-moving- and multiple-stationary-dipole models were compared with the brain electric source analysis program of Scherg. Subcortical sources, reflecting the afferent neural volley when entering the brainstem and leaving the thalamus, were found only in the SEP. The analysis of SEF and SEP revealed a minimum of four overlapping source activities in the region of the contralateral post- and precentral cortical projection areas. Two sources in the depth of the central sulcus could not be resolved unambiguously. The third, more superficial source, which probably reflects activation of area 1, was better defined in the source analysis of the SEP, because dipole orientation was close to radial. The fourth source was more posterior. Several problems observed in the analysis of the present MEG and EEG data suggest that the simultaneous measurement and analysis of multichannel EEG and MEG data will substantially increase spatio-temporal resolution.
44 citations
TL;DR: A method is described that accounts for multichannel brain field data (EEG) epochs by a single oscillating dipole source in terms of phase angles, and produces a potential distribution for each frequency point ('FFT dipole approximation').
Abstract: A method is described that accounts for multichannel brain field data (EEG) epochs, after transformation into the frequency domain, by a single oscillating dipole source in terms of phase angles. The method produces a potential distribution for each frequency point ('FFT dipole approximation'). These maps can be subjected to conventional equivalent dipole source fittings in terms of amplitudes. We studied the equivalent source locations for the different temporal EEG frequency bands (delta/theta/alpha) in 12 normal subjects during the collection of reports of spontaneous thoughts. Some of the thought reports were classed into two modes, 'visual imagery' and 'abstract', and the associated equivalent source locations during the 2 s immediately prior to these reports were computed. Different equivalent source locations were found for the different spectral components of the EEG, implying that different neural generator populations generate the different frequencies. Further, the different types of spontaneous thought, i.e. different modes of cortical functioning, were found to be associated with the activity of different neuronal generator sources that operated at the same frequency at different source locations.
TL;DR: Differences may be explained by the results from a series of measurements on a whole-body resistance simulator in which it appears that for skin contact resistance > 200 omega the Holtain device is unable to sustain a constant current and therefore records a lower impedance than the true value.
Abstract: Four commercial whole-body impedance measuring systems (Holtain, RJL, Bodystat and EZcomp) were compared on two separate occasions for a group of normal subjects. The first set of readings in 21 subjects demonstrated a significant difference of approximately 6% between the Holtain measurement and the higher reading from the Bodystat or RJL systems. The differences between the RJL and Bodystat readings were much less (mean difference 0.6%). Similar differences between the Holtain and EZcomp or Bodystat measurements were demonstrated on a second occasion for a group of 11 subjects. Given that these devices operate by supplying a constant current, the differences may be explained by the results from a series of measurements on a whole-body resistance simulator in which it appears that for skin contact resistance > 200 Omega the Holtain device is unable to sustain a constant current and therefore records a lower impedance than the true value.
TL;DR: The new fibre-optic and acoustic sensors correlate well with more traditional methods such as capnography and transthoracic impedance plethysmography for respiratory rate monitoring and responded rapidly to an apnoeic event.
Abstract: 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.
TL;DR: The model developed can be useful for interpreting clinical findings and as a framework for research into cerebral autoregulation.
Abstract: The instantaneous relationship between arterial blood pressure (BP) and cerebral blood flow velocity (CBFV), measured with Doppler ultrasound in the anterior cerebral artery, is represented by a vascular waterfall model comprising vascular resistance, compliance, and critical closing pressure. One min recordings obtained from 61 low birth weight newborns were fitted to the model using a least-squares procedure with correction for the time delay between the BP and CBFV signals. A sensitivity analysis was performed to study the effects of low-pass filtering (LPF), cutoff frequency, and noise on the estimated parameters of the model. Results indicate excellent fitting of the model (F-test, p < 0.0001) when the BP and CBFV signals are LPF at 7.5 Hz. Reconstructed CBFV waveforms using the BP signal and the model parameters have a mean correlation coefficient of 0.94 with the measured flow velocity tracing (N = 232 epochs). The model developed can be useful for interpreting clinical findings and as a framework for research into cerebral autoregulation.
TL;DR: By correcting the effect of ultrasonic pulse length, it has been shown that the accuracy of the blood vessel diameter measurement can be increased significantly over a range of conditions.
Abstract: Blood vessel diameter measurement is crucial to volume flow measurement in medical ultrasound. The accuracy of the measurement is examined in this study. Experiments were made on three kinds of tube using four transducers on three commercial duplex ultrasound scanners. The accuracy of the inner diameter measurement is affected by ultrasonic pulse length. By correcting this effect, it has been shown that the accuracy of the measurement can be increased significantly over a range of conditions.
TL;DR: Four numerical methods that could be used for solving the EEG and MEG problem are reviewed and the relative merits of the methods and the various options for using them to solve the epilepsy problem are evaluated.
Abstract: In view of the complexity of the conductivity and the geometry of the human head, a numerical method would appear to be necessary for the adequate calculation of the electric potential and the magnetic induction generated by electric sources within the brain. Four numerical methods that could be used for solving this problem are the finite-difference method, the finite-element method, the boundary-element method, and the finite-volume method. These methods could be used to calculate the electric potential and the magnetic induction directly. Alternatively, they could be applied to the electric potential or the electric field and the magnetic induction could then be determined by numerical integration of the Biot-Savart law. In this paper the four numerical methods are briefly reviewed. Thereafter the relative merits of the methods and the various options for using them to solve the EEG and MEG problem are evaluated.
TL;DR: Experimental results suggest that dentists typically apply a force to metal crowns of about 60 N for a few seconds, followed by the application of a steady force of about 20 to 30 N when lower forces are applied to porcelain crowns.
Abstract: Uncertainty exists about the forces applied by dentists during dental crown cementation. A measuring system was developed based around a commercially available miniature (3.8 mm high and 12.7 mm diameter) load cell. The load cell was mounted in a finger stall and the applied force measured. Experimental results suggest that dentists typically apply a force to metal crowns of about 60 N for a few seconds, followed by the application of a steady force of about 20 to 30 N. Lower forces are applied to porcelain crowns.
TL;DR: To combine stereotactic MEG and gamma knife radiosurgery seems to be a non-invasive alternative to the conventional neurosurgery in focal epilepsy.
Abstract: Two patients with complex partial epilepsy and tumour of the temporal lobe scheduled for gamma knife radiosurgery were evaluated pre- and postoperatively by multichannel magnetoencephalography (MEG). Centers of epileptic dipole activity found preoperatively disappeared after the focal irradiation as did the epileptic seizures. Thus, to combine stereotactic MEG and gamma knife radiosurgery seems to be a non-invasive alternative to the conventional neurosurgery in focal epilepsy.
TL;DR: A method for distinguishing two simultaneous fractal dimensions in FHR variation by measuring the irregularity in a series of foetal heart beat to beat intervals, which has potential as a sensitive indicator of impendingfoetal compromise.
Abstract: Describes a method for distinguishing two simultaneous fractal dimensions in foetal heart rate (FHR) variation. An irregular line was plotted from 2500 consecutive foetal heart beat to beat intervals derived from an ultrasound source. A window of 500 intervals was moved along the line in steps of 20 intervals. At each step the Richardson technique was used to make estimates of the length of the line within the window using 40 different ruler lengths. When the estimates were plotted against the ruler lengths on log-log axes the resulting curve exhibited two distinct linear regions, each demonstrating an inverse power relationship. From the two slopes the fractal dimensions were derived for unspecified low- and high-frequency FHR variation in the current window. The values of both fractal dimensions were plotted simultaneously with the irregular FHR line and were found to accord with perceived changes in FHR variation. This new method of observing FHR variability requires no preprocessing of the measured data, which are all taken into account. Not only does it represent a method for studying normal foetal behaviour but also has potential as a sensitive indicator of impending foetal compromise.
TL;DR: The BEI method would not be appropriate for use in assessing total body water and monitoring acute volume changes in patients with renal failure who are on strict fluid restriction.
Abstract: The measurement of total body water (TBW) by bio-electrical impedance (BEI) in a group of renal patients was evaluated against the tritium dilution method. The effect of haemodialysis and the presence of peritoneal dialysate on the impedance were also investigated. The correlation between the two methods was r = 0.9, with the standard deviation of the differences being 3.66 l (TBW typically 40 l). The BEI method overestimated the actual weight loss after haemodialysis, but underestimated the volume of peritoneal dialysate in situ. The BEI method would not be appropriate for use in assessing total body water and monitoring acute volume changes in patients with renal failure who are on strict fluid restriction.
TL;DR: A transducer which detects FBM non-invasively by monitoring maternal abdominal wall movements is presented and results from preliminary clinical trials of prototype transducers on 10 patients are discussed.
Abstract: Foetal breathing movement (FBM) in utero has come to play an important role in foetal diagnosis. FBM may be monitored using real time ultrasound imaging of the foetus in utero. Foetal breathing activities can also be detected by monitoring maternal abdominal wall movement in the frequency range of 0.5-2.5 Hz. The authors present a transducer which detects FBM noninvasively by monitoring maternal abdominal wall movements. Foetal heart sounds can also be monitored. The transducer presented uses piezoelectric film as the transducing medium. Results from preliminary clinical trials of prototype transducers on 10 patients are discussed.
TL;DR: A new technique for morphometric measurement of vertebral bodies has been described, in which a computerized image analysis system was used to digitize and measure standardized lateral radiographs of the thoracic and lumbar spine.
Abstract: A new technique for morphometric measurement of vertebral bodies has been described, in which a computerized image analysis system was used to digitize and measure standardized lateral radiographs of the thoracic and lumbar spine. The sources of error in the radiographic system and the image analysis system were assessed using vertebral phantoms and test images. Oblique projection in the radiographic image of a vertebra did not produce a significant error in the measured area. The radiographic magnification was approximately 35%. Optical non-uniformity was detected in the image analysis system, and was ascribed to the lens optics. The maximum intra-observer and inter-observer variations in vertebral area were 3.1% and 5.3% respectively for experienced observers. The technique is applicable to clinical studies of large populations, and has value in investigating vertebral deformity in the management of metabolic bone disease.
TL;DR: Equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions have been applied to interictal multichannel magnetoencephalographic recordings of a patient with complex partial epilepsy.
Abstract: Equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions have been applied to interictal multichannel magnetoencephalographic recordings of a patient with complex partial epilepsy (CPE). Averaged signals were used. At certain instances ECD solutions could be found with a very high cross-correlation coefficient between the measurements and the field, produced by the current dipole solution, typically in excess of 0.97. At these instances a highly localized distribution, very close to the ECD location, was obtained from the distributed source analysis. The ECD solution started to move when the distributed source solution began to develop activity at more than one centre. This clearly contrasted with the way the activity of the distributed source solutions changed, which turned out to be highly stable. Stringent selection criteria for using the different solutions therefore seem mandatory, especially in identifying pathological areas and volumes of the human brain.
TL;DR: First experiences indicate that the combination of a shielded room with a software suppression of the residual field entering the room is amply sufficient to allow biomagnetic measurements in a hospital environment.
Abstract: The authors describe a 28-channel magnetometer that operates as a 22-channel 'software gradiometer'. Gradiometer function is achieved by subtraction of weighted signals representing the noise field along three orthogonal axes as detected by six compensation channels. The instrument measures both normal and tangential field components; the user can select a total of 22 normal and/or tangential measuring sites from two arrays of 16 sites each. First experiences indicate that the combination of a shielded room with a software suppression of the residual field entering the room is amply sufficient to allow biomagnetic measurements in a hospital environment.
TL;DR: Heel pressures averaging 7.08 kPa, were a factor of 2.67 times greater than buttock pressure, and were higher than expected considering the depth the heels sunk to in both beds, and was attributed to covering sheets preventing true floatation at the heels.
Abstract: Pressures were measured under five anatomical sites prone to pressure sores for ten subjects, supine and sitting on two different air-fluidized beds. The beds were the Clinitron (trademark, SSI) and the Fluidair Plus (trademark, KCI Mediscus). Mean supine pressures were less than 4 kPa under four sites. The average supine buttock pressure was 2.65 kPa. This increased to 3.71 kPa upon sitting up, though pressures did not rise above the accepted capillary closing pressure, on either bed. Low interface pressures at these sites were due to good moulding between subject and bed. Heel pressures averaging 7.08 kPa, were a factor of 2.67 times greater than buttock pressure, and were higher than expected considering the depth the heels sunk to in both beds. This exceeded the accepted capillary closing pressure and was attributed to covering sheets preventing true floatation at the heels.
TL;DR: The modification of an existing 252Cf-based instrument and construction of a shielded, high-efficiency counting system are reported for the in vivo measurement of Al in the hand for the first time.
Abstract: The accumulation and toxicity of aluminium in patients with chronic renal failure is a well recognized hazard, and there is a need for a non-invasive technique to assess Al tissue load in these patients. The technique of in vivo neutron activation analysis, using a thermal neutron beam from a reactor, has been employed by previous workers, who measured Al in the hand with a detection limit of 0.4 mg for a dose equivalent of 20 mSv. However, the application of this technique is restricted by the very limited availability of nuclear reactors. We report the modification of an existing 252Cf-based instrument and construction of a shielded, high-efficiency counting system for the in vivo measurement of Al in the hand. Phantoms containing tissue-equivalent solutions of Ca, P, Na and Cl with various Al loadings were used for validation of the technique. The Al/Ca ratio in the hands of seven patients with renal failure was measured using a cyclic activation technique to compensate for the relatively low neutron output of the 252Cf source, and a detection limit of approximately 2.2 mg Al was achieved for a dose equivalent of 36 mSv. The results were compared with the Al content of iliac crest bone biopsy specimens measured using electrothermal atomic absorption spectrophotometry.
TL;DR: The magnetocardiographic investigation of patients with Wolff-Parkinson-White (WPW) syndrome, ventricular extrasystoles,ventricular tachycardia, and paced ventricular arrhythmias demonstrated that multichannel magnetOCardiography permits the non-invasive three-dimensional localization of arrh rhythmogenic tissue with high spatial accuracy.
Abstract: The magnetic fields caused by the human heart's electrical activity were simultaneously recorded with a multichannel superconducting quantum interference device (SQUID) system (Krenikon) for 1-10 min in 45 patients. 31-37 magnetic channels were recorded simultaneously with the electrocardiogram (ECG) and respiration. Comparison of a magnetic index and the Sokolow-Lyon index with echocardiographic findings in the quantification of left ventricular hypertrophy demonstrated the superiority of the magnetocardiogram (MCG) as compared with the ECG. The magnetocardiographic investigation of patients with Wolff-Parkinson-White (WPW) syndrome, ventricular extrasystoles, ventricular tachycardia, and paced ventricular arrhythmias demonstrated that multichannel magnetocardiography permits the non-invasive three-dimensional localization of arrhythmogenic tissue with high spatial accuracy.
TL;DR: Differences in average lung density between the mice, rats and dogs reported here are consistent with the relationship between lung morphology, metabolic rate and body size which obtains for a range of mammalian species.
Abstract: Lung density measurements using computed tomography have been made in mice, rats, and pure-bred beagles and mongrel dogs. Density was found to be dependent on a number of factors including the location of the area scanned, and the age and species of the animal. Lung density was found to decrease by approximately 40% from initial values in a group of rats scanned at intervals between 30 and 800 days old. Age-related density changes were not seen for the lungs of mice or dogs; however measurements were not made over a prolonged period. A gradient of increasing density from the base to apex of the lung was seen for 30 and 175-day-old rats (scanned in the prone position) while an apex to base density gradient was seen for both types of dog studied (scanned in the supine position). In none of the species studied was there a systematic difference in density of the right and left lungs. Differences in average lung density between the mice, rats and dogs reported are consistent with the relationship between lung morphology, metabolic rate and body size which obtains for a range of mammalian species.
TL;DR: The suitability of DAT recorders as a means for storing ultrasound Doppler signals has been evaluated, and the results show that they are an ideal instrument for recording directional Dopple signals, but like conventional tape recorders are not suitable for storing quadrature Dopplers.
Abstract: Digital audio tape recorders perform significantly better than conventional tape recorders in respect of their frequency response, dynamic range, signal-to-noise ratio, and wow and flutter figures. They also have advantages in terms of their tape size and playing time, and their ability to record additional information as 'sub-codes'. The suitability of DAT recorders as a means for storing ultrasound Doppler signals has been evaluated. The results show that they are an ideal instrument for recording directional Doppler signals, but like conventional tape recorders are not suitable for storing quadrature Doppler signals.
TL;DR: The measurement of the complex respiratory impedance at a high temporal resolution enables the observation of novel features in the impedance which appear to be associated with certain respiratory disorders.
Abstract: The measurement of the complex respiratory impedance at a high temporal resolution is described. The measurement of impedance is correlated with the breathing cycle using electrical transthoracic impedance. This allows the determination of the complex impedance at any fixed point in the respiratory cycle, which results in lower variability in the measured data when compared to the original device. The respiratory impedance in normal subjects fluctuates during the breathing cycle and has two maxima during a single breath, which occur at peak inspiratory and expiratory flow. In addition, the measurement of impedance at a high temporal resolution enables the observation of novel features in the impedance which appear to be associated with certain respiratory disorders.