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Biomedical subjects

J L Semmlow

Publications and source records attributed to J L Semmlow.

At least 19 recordsLinked to original sources
PubMed1992

Noninvasive acoustical detection of coronary artery disease using the adaptive line enhancer method.

Previous studies have indicated that heart sounds may contain information which is useful in the detection of occluded coronary arteries. Specifically, previous work based on analysing heart sounds recorded during the diastolic portion of the cardiac cycle, when blood flow through the coronary arteries is maximum, has shown that additional frequency components are present in patients with coronary artery disease. To further explore the application of advanced signal processing techniques to the noninvasive detection of coronary artery disease, a new signal-processing approach is presented using adaptive line enhancing (ALE) and spectral estimation of diastolic heart sounds taken from recordings made at the patient's bedside. This approach comprises two cascaded processes. In the first the ALE method is used to enhance the diastolic heart sounds and eliminate background noise. In the second process, either autoregressive (AR) or autoregressive moving average (ARMA) spectral methods are used to estimate the model parameters. Model parameters (the power spectral density (PSD) functions and the poles of the AR or ARMA method) were used to diagnose patients as diseased or normal. Results showed that normal and abnormal recordings were correctly identified in 39 of 43 cases using the new method. These results also confirm that high-frequency energy above 400 Hz is associated with coronary stenosis.

Coronary Disease↗
PubMed1992

Application of adaptive filters to noninvasive acoustical detection of coronary occlusions before and after angioplasty.

Previous studies have indicated that coronary stenoses produce sounds due to the turbulent blood flow in these vessels [1]-[10]. Measurement of these signals forms the basis of our noninvasive approach to the detection of coronary artery disease. It is during diastole that coronary blood flow is maximum and the sounds associated with turbulent blood flow through partially occluded coronary arteries would be loudest [1]-[10]. Isolated diastolic heart sounds taken from recordings made at the patient's bedside were modeled using the autoregressive (AR) and autoregressive moving average (ARMA) methods [4], [7] after adaptive line enhancement (ALE). Decisions were made in a blind fashion without prior knowledge of whether a given recording was made before or after angioplasty. Resulting model frequency spectra showed greater high-frequency components (between 400 and 800 Hz) in preangioplasty patients, and a consistent shift in amplitude of the second pole pairs of the AR and ARMA methods with surgery. Blind assessment, based on frequency spectra and poles, correctly classified the diastolic recordings in 18 of 20 cases. These results provide strong evidence supporting our hypothesis that coronary stenoses produce detectable sounds during diastole [1]-[10].

Angioplasty, Balloon, Coronary↗
PubMed1991

Application of the ARMA method to acoustic detection of coronary artery disease.

To further explore the application of advanced signal processing techniques to the noninvasive detection of coronary artery disease, 30 patients (10 angioplasty and 20 normal or abnormal) were tested using autoregressive moving average (ARMA) modelling of the diastolic heart sound data. It is during diastole that coronary blood flow is maximum and sounds associated with turbulent blood flow through partially occluded coronary arteries would be loudest. Model parameters (the power spectral density (PSD) functions and the poles of the ARMA method) were used to separate the normal patients from the abnormal patients in the normal/abnormal study, or to decide whether the recordings were made before or after angioplasty in the angioplasty study. The decisions were made 'blind', without knowledge of the actual disease states of the patients for the normal/abnormal study and without prior knowledge of whether a given recording was made before or after angioplasty for the angioplasty study. Results from the angioplasty and the normal/abnormal studies showed that pre- and post-angioplasty records were correctly distinguished in 8 out of 10 cases, and normal and abnormal records were correctly distinguished in 17 of 20 cases. These results also confirmed that high frequency energy above 400 Hz is probably associated with coronary stenosis.

Aged↗
PubMed1991

Vergence control of central and peripheral disparities.

The results of previous studies using either small or large target configurations suggest that open-loop (OL) vergence response dynamics may depend on the peripheral extent of the target. To investigate systemically the effect of peripheral target extent on dynamic vergence control, OL vergence responses to central, peripheral, and central-plus-peripheral targets were recorded. Open-loop disparity stimuli included steps, ramps, and sinusoids. It was found that the OL step and ramp responses to the central target were more rapid and exhibited significantly more step and multiple-step movements than those for either the peripheral or the central-plus-peripheral targets. During OL ramp stimulation, the maximum disparity for which tracking could be maintained was largest for the peripheral target. Sinusoidal responses showed the greatest gain for the central target. For all three types of stimuli, responses to the central-plus-peripheral target showed characteristics that were somewhat between those for the central and the peripheral targets. These results resolve some previously conflicting findings about open-loop vergence dynamics and suggest that large peripheral disparity stimulation initiates slow fusion of a visual scene, whereas small central disparity stimulation produces more rapid movements for precise binocular tracking of targets moving in depth.

Convergence, Ocular↗
PubMed1991

Influence of peripheral degradation on the identification of eccentric targets (revised).

When the peripheral field is degraded, or 'modulated', as occurs with certain corrective lenses, identification of a peripheral image requires combined head and eye movements to place the image within a relatively clear section of the field. In such cases the time required to identify a peripheral object increases systematically. Previous experiments involving severely restricted peripheral fields (slit viewing) have indicated that the increase in identification time is primarily determined by the dynamics of the head movement. Head movement characteristics, in turn, are related to the nature of the peripheral distortion. To describe more complex peripheral distortions, a 'modulation' function is developed which provides a realistic, quantitative measure of the deficit induced by a given distortion. Modification in head movement can be traced directly to the influence of this modulation function.

Electrooculography↗
PubMed1990

Suppression of sensitivity to change in target disparity during vergence eye movements.

It has been demonstrated recently in human psychophysical experiments that sensitivity to surround displacement is suppressed during convergence eye movements. To determine whether sensitivity to changes in target disparity is also reduced, responses to test disparities that were superimposed on standard 4 degrees step disparities were investigated. The test disparities consisted of brief (20 ms) positive and negative pulses as well as steps (in the range of +/- 0.6 degrees). A two-alternative forced-choice procedure was used in which the test disparity was presented in either the first or the second portion of a trial. The results showed that suppression of both test pulse and step disparities began before the start of the convergence movement and continued during the movement. Maximum suppression was about 0.50 to 0.85 log units and occurred between 150 ms before to 50 ms after convergence onset. The differences in sensitivity curves for pulse and step stimuli suggest the presence of different central and peripheral neural factors during vergence eye movements.

Eye Movements↗
PubMed1990

Detection of coronary occlusions using autoregressive modeling of diastolic heart sounds.

Previous studies have indicated that diastolic heart sounds may contain information useful in the detection of occluded coronary arteries. In this study, recordings of diastolic heart sound segments were modeled by autoregressive (AR) methods including the adaptive recursive least-square lattice (RLSL) and the gradient lattice predictor (GAL). Application of the Akaike criterion demonstrated that between 5 and 15 AR coefficients are required to completely describe a diastolic segment. The reflection coefficients, prediction coefficients, zeros of the polynomial of the inverse filter, and the AR spectrum were determined over a number (N = 20-30) of diastolic segments. Preliminary results indicate that the averaged AR spectrum and the zeros of the inverse filter polynomial can be used to distinguish between normal patients and those with coronary artery disease.

Algorithms↗
PubMed1990

Ultrasonic two-axis rotation detector.

A two-axis rotation monitor is described which determines the relative displacement between a pair of ultrasonic detectors using the phase difference of a continuous ultrasound wave generated by a single, distant source. The monitor has been used to measure head rotations around the vertical and horizontal axes, but can easily be adopted to other body segment rotations or translations. The device produces high sensitivity recordings of wide spatial and dynamic range. Although the device is quite linear with good isolation between channels, a computer-based linearization/calibration routine is described which further increases linearity and reduces crosstalk. The device is unobtrusive, inexpensive, and has proven reliable and easy to use.

Equipment Design↗
PubMed1990

Modeling sound generation in stenosed coronary arteries.

Acoustic measurements obtained from sensitive microphones placed on the chest are being used in a procedure to noninvasively diagnose coronary artery disease. Utilizing specially developed signal processing techniques, the spectral content of isolated diastolic heart sounds has been estimated and usually shows an increase in high-frequency components in patients with occlusive coronary arteries. In order to establish a theory for the origin of these spectral features, a sound source model has been developed which combines an incremental network model of the left coronary artery tree with a transfer function model describing arterial chamber resonant characteristics. The network model predicts flow in both normal and stenosed coronary arteries. From this flow information, the arterial chamber transfer function model predicts the development of acoustic signals from the chamber resonant characteristics. The transfer function of a segment of coronary artery demonstrates two resonance frequencies. These resonance frequencies depend upon the length and diameter of the chamber segment, as well as upon the distal hydraulic impedance loading the segment. The lower resonance frequency can be excited by the usual flow fluctuations (low frequency) in the coronary artery. In cases of stenosis, the wideband spectral characteristics of the turbulence produced by the stenosis excites both the low and high resonance frequencies. In a small sample of patients, the spectra obtained from isolated diastolic acoustic signals recorded by a chest microphone agree well with those predicted by this theory.

Coronary Circulation↗
PubMed1990

Noninvasive detection of coronary stenoses before and after angioplasty using eigenvector methods.

Previous studies done by our group suggest that partially occluded coronary arteries may generate sounds due to turbulent blood flow. To support these previous findings the frequency spectra of diastolic heart sounds are compared before and after angioplastic surgery. Since the low-level sounds associated with partially occluded coronary arteries are contaminated with considerable background noise, traditional FFT analysis may not produce accurate frequency spectra. Indeed, in a previous study using the same data, no significant differences were found in the diastolic heart sounds before and after angioplastic surgery. In this study, three eigenvector methods (Pisarenko, MUSIC, and Minimum-Norm) have been selected to generate the frequency spectra because of their higher resolution, particularly in the presence of noise. Although the Pisarenko method produced spurious zeros and could not be used, the other two methods produced spectra showing, in most cases, a marked decrease in high-frequency spectral components following angioplasty.

Algorithms↗
PubMed1990

Identification of peripheral visual images in a laterally restricted gaze field.

When the peripheral visual field is restricted or distorted, as occurs with certain spectacle lenses, the identification of objects in the periphery requires a coordinated head and eye movement. Initial experiments on the identification of peripheral images under such restrictions show that the degradation in performance is defined by a consistent additional delay in the time required to identify the image correctly. An analysis of the motor movements shows that performance is solely determined by movements of the head; eye movements are sufficiently precise and fast so they do not limit performance. A quantitative model of the identification task was developed and model simulations confirmed the experimental findings that head movement variables, specifically response latency and movement duration, uniquely determine identification performance. Hence, improved performance under these conditions must come from modifications in head-movement control either through training or adaptive processes.

Adult↗
PubMed1989

Suppression of sensitivity to surround displacement during vergence eye movements.

Suppression was investigated psychophysically in three human observers by measuring their loss of sensitivity to brief (20 ms) simultaneous vertical displacement (up to 0.5 degrees) of horizontal lines during 4 degrees convergence eye movements. A two-alternative forced choice procedure was used in which the stimulus was presented either in the first or second portion of a trial. The amplitude of the displacement pulse, the time of the pulse relative to convergence onset, and the portion of a trial in which the stimulus was presented were randomized. The results showed that suppression began about 200 ms before, and continued until 350 ms after, convergence onset with maximum loss occurring at 25 to 125 ms after convergence onset. The maximum sensitivity loss was about 0.25 to 0.30 log units. Since peripheral factors were minimized by the use of a brief stimulus presentation and an eccentrically placed surround, the suppression found was primarily attributed to central neural mechanisms. Finally, the suppression of sensitivity to pulse displacement during the initial phase of the vergence movement is consistent with a recently developed dual-mode model of the vergence system, in which the initial transient portion of a step response is preprogrammed whereas the final sustained portion is maintained by continuous feedback control.

Choice Behavior↗
PubMed1989

Mechanisms of short-term saccadic adaptation.

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.

Adolescent↗
PubMed1989

Comparison of five methods of assessment of intestinal viability.

A strain gauge device called the electronic contractility meter (ECM) was designed to measure quantitatively intestinal ischemic damage by delivering electrical stimuli to the intestine. Threshold stimulus level (TSL) was the minimum stimulus in milliamps necessary to produce a smooth muscle contractile response. TSL scale ranged from zero to 100 milliamps. Resection and anastomosis in ischemic intestinal segments was carried out in 30 dogs to compare TSL, intestinal color, peristalsis, Doppler ultrasound and resection margin histology with survival. There were five fatal anastomotic leaks, all resulting from intestinal necrosis. Doppler pulse in the marginal artery (MA) was absent at four of the five anastomoses that leaked versus eight of the 25 that healed (p less than or equal to 0.01). Mean TSL at the resection site was 38 +/- 7 milliamps in surviving dogs versus 51 +/- 4 milliamps in nonsurvivors (p less than or equal to 0.001). Mean TSL of normal intestine was 22 +/- 2 milliamps. Both TSL and Doppler ultrasound also correlated with resection margin histology (p less than or equal to 0.02 and p less than or equal to 0.005, respectively). Presence of peristalsis did not correlate with histologic grade or survival rate. Intestinal color correlated with resection margin histology (p less than or equal to 0.001) but not survival. The ECM and Doppler ultrasound were both superior to gross visual assessment in predicting intestinal survival. The ECM quantitatively measures tissue damage, a potential advantage over Doppler ultrasound, which provides only an estimate of local arterial blood flow.

Anastomosis, Surgical↗
PubMed1987

Myoelectric assessment of bowel viability.

A device capable of quantitative measurement of intestinal ischemic damage has been designed. The device is called the electrical contractility meter and employs a clip-on strain gauge transducer that delivers a precisely controlled electrical stimulus to the bowel. Threshold stimulus level (TSL) is the stimulus current in milliamperes (mA) that is necessary to produce a clearly defined smooth-muscle contraction. In 30 dogs, TSL was used to establish viability boundaries in 40 cm ischemic bowel segments. Bowel viability was assessed with the use of TSL in comparison with gross features (color, peristalsis) and blood flow measured by means of Doppler ultrasound at 2 cm intervals in the ischemic small-bowel segments. The TSL scale ranges to 100 mA and varied from a low of 22 +/- 2 mA in normal bowel outside the ischemic segment to 97 +/- 4 mA in grossly gangrenous bowel. There was a consistent correlation between rising TSL and worsening bowel color, disappearance of visible peristalsis, and progressive disappearance of audible Doppler signals. Resection and anastomosis were performed in three groups of 10 dogs at TSL measurements of 30 mA, 40 mA, and 50 mA, respectively. Dogs were killed and anastomoses were inspected on the tenth postoperative day. There were no leaks at TSL = 30 mA, one leak at TSL = 40 mA, and four leaks at TSL = 50 mA. The number of leaks at TSL = 50 mA was significantly greater than at TSL = 30 mA (p less than 0.04, Fisher's exact test). These results show that the quantitative myoelectric parameters established by this device provide a reliable in vivo assessment of bowel viability. The electrical contractility meter is easy to use and may have clinical applicability.

Animals↗
PubMed1986

Static vergence and accommodation: population norms and orthoptics effects.

The steady-state characteristics of the accommodation and vergence systems can be described by a model with six major oculomotor parameters. These include the system biases (tonic vergence and accommodation) and forward-loop gains (vergence and accommodative gains), as well as the interactive system gains (AC/A and CA/C ratios). We investigated these parameters in two populations: (1) 22 visually-normal asymptomatic individuals, and (2) 21 visually-abnormal symptomatic individuals before and after conventional orthoptic therapy. Two parameters related to system gain differentiated between the symptomatic and asymptomatic individuals: the slope of the fixation disparity curve with accommodation open-looped and the slope of the accommodative response/stimulus curve. Following orthoptic therapy, 4 static model parameters and 1 dynamic clinical parameter showed changes toward the normal mean; this included tonic accommodation, slope of the fixation disparity curve with accommodation closed-loop (2.5D), slope of the accommodative response/stimulus curve, the CA/C ratio, and the +/- 2D monocular accommodative flipper rate.

Accommodation, Ocular↗
PubMed1986

Quantitative myoelectric determination of bowel viability.

A new device designed to quantitatively measure viability in ischemic bowel was studied in 20 dogs. This strain gauge device is clipped on the serosal surface and can rapidly deliver an electrical stimulus. The threshold stimulus level (TSL) was the stimulus necessary to produce a clearly defined smooth muscle contraction. TSL was compared with blood flow measured by Doppler ultrasound at 2-cm intervals in 30-cm ischemic segments as a determinant of bowel viability. Doppler readings were taken from the bowel wall (BW), peripheral arteriolar branches of the marginal artery (PA), and marginal artery (MA), itself, at each 2-cm interval. Bowel color and peristalsis were correlated with Doppler and TSL data. TSL scale ranged from 0 to 100 mA and varied from 21 +/- 2 mA in normal bowel to 98 +/- 2 mA in gangrenous bowel. At the locus of the last audible Doppler signal in the BW, PA, and MA, mean TSL readings were 27 +/- 5, 34 +/- 6, and 48 +/- 16 mA, respectively. These readings were each significantly greater than the TSL of normal bowel at P less than or equal to 0.0001 level. Portions of each ischemic segment were resected and reanastomosed. Absence of Doppler signals in the BW and PA did not preclude healing of ischemic bowel. These data suggest that TSL measurement is more sensitive than either Doppler ultrasound or gross visual evaluation in assessment of bowel viability.

Animals↗