Biomedical subjects

D H Liang

Publications and source records attributed to D H Liang.

11 recordsLinked to original sources

PubMed1999

The nerve-electrode interface of the cochlear implant: current spread.

One of the fundamental facets of the cochlear implant that must be understood to predict accurately the effect of an electrical stimulus on the auditory nerve is the nerve-electrode interface. One aspect of this interface is the degree to which current delivered by an electrode spreads to neurons distant from it. This paper reports a direct mapping of this current spread using recordings from single units from the cat auditory nerve. Large variations were seen in the degree to which the different units are selective in responding to electrodes at different positions within the scala tympani. Three types of units could be identified based on the selectiveness of their response to the different electrodes in a linear array. The first type of unit exhibited a gradual increase in threshold as the stimulating site was moved from more apical to more basal locations within the scala tympani. The second type of unit exhibited a sharp local minimum, with rapid increases in threshold in excess of 6 dB/mm in the vicinity of the minimum. At electrode sites distant from the local minima the rate of change of the threshold approached that of the first type of units. The final type of unit also demonstrated a gradual change in threshold with changing electrode position, however, two local minima, one apical and one basal, could be identified. These three types are hypothesized to correspond to units which originate apical to the electrode array, along the electrode array and basal to the electrode array.

Acoustic Stimulation↗

PubMed1998

Paradoxical embolism of a shotgun pellet.

Paradoxical embolism of a projectile from the venous to arterial system is a rare occurrence, which can cause diagnostic confusion. We present a case of venous embolism of a shotgun pellet from the left upper extremity to the noncoronary sinus of the aortic valve across a secundum-type atrial septal defect. Prevention of distal embolism of the pellet was presumably a result of its containment by flow vortices created within the sinuses of Valsalva.

Adult↗

PubMed1998

New real-time interactive cardiac magnetic resonance imaging system complements echocardiography.

OBJECTIVES: We conducted an initial clinical trial of a newly developed cardiac magnetic resonance imaging (CMRI) system. We evaluated left ventricular (LV) function in 85 patients to compare the clinical utility of the CMRI system with echocardiography, the current noninvasive gold standard. BACKGROUND: Conventional CMRI systems require cardiac-gating and respiratory compensation to synthesize a single image from data acquired over multiple cardiac cycles. In contrast, the new CMRI system allows continuous real-time dynamic acquisition and display of any scan plane at 16 images/s without the need for cardiac gating or breath-holding. METHODS: A conventional 1.5T Signa MRI Scanner (GE, Milwaukee, Wisconsin) was modified by the addition of an interactive workstation and a bus adapter. The new CMRI system underwent clinical trial by testing its ability to evaluate global and regional LV function. The first group (A) consisted of 31 patients with acceptable echocardiography image quality. The second group (B) consisted of 31 patients with suboptimal echocardiography image quality. The third group (C) consisted of 29 patients with severe lung disease or congenital cardiac malformation who frequently have suboptimal echo study. Two independent observers scored wall motion and image quality using the standard 16-segment model and rank-order analysis. RESULTS: CMRI evaluation was complete in less than 15 min. In group A, no significant difference was found between ECHO and CMRI studies (p = NS). In group B, adequate visualization of wall segments was obtained 38% of the time using ECHO and 97% of the time using CMRI (p < 0.0001). When grouped into coronary segments, adequate visualization of at least one segment occurred in 18 of 30 patients (60%) with ECHO and in all 30 patients (100%) with CMRI (p < 0.0001). In group C, adequate visualization of the wall segments was obtained in 58% (CI 0.53-0.62) of the time using echocardiography and 99.7% (CI 0.99-1.0) of the time using CMRI (p < 0.0001). CONCLUSIONS: The new CMRI system provides clinically reliable evaluation of LV function and complements suboptimal echocardiography. In comparison with the conventional CMRI, the new CMRI system significantly reduces scan time, patient discomfort and associated cost.

Adolescent↗

PubMed1998

Native tissue harmonic imaging improves endocardial border definition and visualization of cardiac structures.

BACKGROUND: The purpose of this study was to examine the impact of native tissue harmonic imaging on endocardial border definition, wall motion scoring, and visualization of intracardiac structures. METHODS AND RESULTS: For wall motion analysis, 60 consecutive patients underwent standard transthoracic echocardiograms in both harmonic and fundamental modes. Three experienced echocardiographers reviewed each echocardiogram. Endocardial border definition for each wall segment was graded from 1 to 4 (1 = excellent endocardial definition). Wall motion was scored by using a standard 16-segment model and 1 to 5 scale. For visualization of cardiac structures, 50 consecutive patients were studied. Two experienced interpreters reviewed each echocardiogram for both normal and abnormal structures by using the following scoring scale: (1) harmonic is much better than fundamental, (2) harmonic is slightly better than fundamental, (3) harmonic and fundamental are equivalent, (4) fundamental is slightly better than harmonic, and (5) fundamental is much better than harmonic. Visualization of 64% (95% confidence interval [CI] 0.61 to 0.66) of all segments improved in harmonic mode, with 26% (95% CI 0.24 to 0.29) improving from poor/not seen to good/excellent. Of 444 segments deemed poor/not seen, visualization of 312 (70%) (95% CI 0.66 to 0.75) improved to good/excellent with harmonic mode. Of these 312 segments, 55% comprised the lateral and anterior walls on apical views. Interobserver agreement on endocardial border definition was 82% to 86%. Scoring of wall motion was altered in 171 of 1075 (16%) of segments by harmonic mode. This was significantly greater than the interobserver disagreement, which was only 10% (p<0.002). Mitral valve chordae and papillary muscles were visualized slightly/much better with harmonic mode in 40 of 50 echocardiograms. Left atrial boundaries were seen slightly/much better in harmonic mode in 29 of 50 studies. Abnormal structures were seen slightly/much better in harmonic mode in 12 of 14 cases. CONCLUSIONS: Native tissue harmonic imaging has significant impact on endocardial border definition and wall motion scoring and improves the visualization of both normal and abnormal cardiac structures.

Cardiomyopathies↗

PubMed1997

Role of compensatory enlargement and shrinkage in transplant coronary artery disease. Serial intravascular ultrasound study.

BACKGROUND: Compensatory enlargement of the vessel wall has been described in the early stages of native atherosclerosis. Whether compensatory enlargement plays a role in transplant coronary artery disease is not known. The objective of this study was to determine, by use of serial intravascular ultrasound (IVUS), whether compensatory dilation occurs in transplant coronary artery disease over time. METHODS AND RESULTS: Seventy-five heart transplant recipients with 151 matched coronary segments were selected for the presence of intimal disease progression as detected by serial IVUS examinations 1 to 3 years apart. Intimal disease progression was defined as a > 10% increase in intimal area (IA). IVUS catheter location in follow-up studies was verified angiographically in relation to branch vessels. Luminal area (LA) and total vessel area (TA) were measured at each site. Intimal area (IA = TA-LA) was calculated. Changes in IA (delta IA) and TA (delta TA) between baseline and follow-up IVUS were compared: delta IA, 2.9 +/- 0.2 mm2: delta TA, 2.7 +/- 0.4 mm2. A remodeling index (RI) was defined as RI = delta TA/delta IA. Three subgroups could be distinguished: over compensation (RI > I), partial compensation (RI 0 to 1), and no compensation or shrinkage (RI < or = 0). Seventy-four segments (49%) showed overcompensation, 44 (29%) showed partial compensation, and 33 (22%) showed no compensation or shrinkage. CONCLUSIONS: In this study, serial IVUS shows that early after cardiac transplantation, a large proportion of the coronary segments with progression of intimal thickening have compensatory dilation of the vessel wall. However, a substantial number of coronary segments (22%) show no compensatory dilation or shrinkage. The progressive luminal narrowing in transplant patients may be due in part to vessel shrinkage or the lack of compensatory dilation over time.

Adult↗

PubMed1997

Forward-looking catheters.

Current intravascular ultrasound catheters provide a cross-sectional view of the blood vessel that limits their ability to visualize severely stenosed or occluded vessels. Forward-looking ultrasound catheters can overcome these limitations. Development of a practical forward-looking ultrasound catheter requires solutions to address the need for improved lateral resolution and depth of penetration presented by the forward-looking format. Methods are also needed to generate the forward-looking scan within the space constraints of a catheter. New developments using mechanical scanning methods suggest that a practical device appears achievable. Two-dimensional, as well as three-dimensional imaging, may be possible. Early efforts towards a phased array scanner have also begun.

Animals↗

PubMed1996

Are heart-lung transplant recipients protected from developing transplant coronary artery disease? A case-matched intracoronary ultrasound study.

BACKGROUND: Accelerated coronary artery disease is a major cause of mortality in heart transplant recipients; however, it does not appear to play a major role in the clinical outcome of heart-lung transplant recipients. The purpose of this study was to determine whether the incidence and severity of transplant coronary artery disease as detected by intracoronary ultrasound in heart-lung transplant recipients are less than those encountered in heart transplant recipients. METHODS AND RESULTS: We studied the left anterior descending coronary artery with the use of intracoronary ultrasound imaging in 22 heart-lung transplant recipients at the time of their routine annual coronary angiogram. Twenty-two heart transplant recipients were case matched for number of years after transplant at ultrasound study, recipient age, donor age, and diagnosis of nonischemic cardiomyopathy. Mean intimal area, intimal index, Stanford class, and incidence of at least moderate disease (Stanford class > or = 3) were measured and calculated in each group and then compared between the two groups. Mean intimal area (1.6 +/- 2.5 versus 3.8 +/- 2.8 mm2), mean intimal index (0.07 +/- 0.10 versus 0.22 +/- 0.14), mean Stanford class (1.7 +/- 1.0 versus 2.7 +/- 1.2), and incidence of Stanford class > or = 3 (14% versus 45%) were significantly lower in the heart-lung transplant recipient group. CONCLUSIONS: The incidence and severity of transplant coronary artery disease are much less in patients receiving heart-lung transplants than in those receiving heart transplants alone.

Adult↗

PubMed1996

Prediction of angiographic disease by intracoronary ultrasonographic findings in heart transplant recipients.

BACKGROUND: Intracoronary ultrasonography has proven to be a more sensitive test than angiography for the detection of intimal thickening in transplant recipients. However, the prognostic significance of the intimal thickening detected by intracoronary ultrasonography has not been proven. METHOD: During a 1-year period, 70 transplant recipients without angiographically apparent coronary artery disease underwent intracoronary ultrasonography examination. For each intracoronary ultrasonography study an intimal index, defined as the ratio of the plaque area to the area within the media, was measured for the most diseased segment imaged. The subsequent annual follow-up angiograms of these 70 patients were reviewed for the development of visually apparent coronary artery disease. The time since transplantation for the 70 patients without angiographically apparent coronary artery disease ranged from 1 to 15 years, with a mean of 4.2 years an median of 3.9 years. Mean duration of angiographic follow-up was 2.0 years (range 1 to 3 years). RESULTS: Angiographically apparent coronary artery disease developed on follow-up angiograms in 13 of the 70 patients, with a mean time to development of 1.5 years. Four of 46 patients (9%) with an intimal index < 0.3 subsequently had angiographically apparent coronary artery disease, whereas of 25 patients (36%) with an intimal index > or = 0.3 subsequently had angiographically apparent coronary artery disease. Odds ratio for future angiographically apparent coronary artery disease between patients with an intimal index > or = and intimal index < 0.3 was 5.9 (p < 0.01 by Fisher's Exact test). In a subgroup of 22 patients more than 5 years after transplantation at the time of intracoronary ultrasonography, 12 had an intimal index < 0.3 and 10 had an intimal index > or = 0.3. In this subgroup none of the 12 patients with an intimal index < 0.3 had angiographically apparent coronary artery disease and only 1 of the 10 with an intimal index > or = 0.3 had angiographically apparent coronary artery disease (difference not significant). CONCLUSIONS: The presence of moderate to severe intimal thickening by intracoronary ultrasonography is predictive of the future development of angiographically apparent coronary artery disease among patients more than 1 year and less than 5 years after transplantation. This same degree of intimal thickening may not carry the same prognostic significance among patients greater than 5 years after transplantation without the development of angiographically apparent coronary artery disease.

Adult↗

PubMed1995

[A study on relationship between balance of serum lipoprotein and the phlegm damp-blood stasis syndrome differentiation of coronary heart diseases].

75 patients were divided into A,B and C group. The LDL-C was 2.97 +/- 0.67, 4.05 +/- 0.38 and 5.25 +/- 0.98 mmol/L respectively (P > 0.01); but comparing group A or B with the normal group (D), it had no significant difference (P > 0.05). An abnormal coronary arteriography (CAG) was found in the group A in 62.1% and the group B in 57.6% (P > 0.05), while the group C in 84.6% (P < 0.01). There was unusual serum lipoprotein electrophoretogram (SLPG) in group A 75.9%, group B 84.8% and group C 100%, but it had no change in group D (P < 0.001). Five types of Syndrome Differentiation about the Phlegm damp and blood stasis (PDBS) could be found in the group A,B and C. The incidence (51.5%-55.2%) and abnormality of the SLPG (66.7%-92.5%) and CAG (68.8%-100%) of PDBS type were the highest among them. 82.7% CHD patient's clinical comprehensive diagnosis was in accordance with the SLPG and that of the CAG were 64.0%. As to the abnormal SLPG, the sensitivity and rate of coincidence of CAG was 91.7% and 69.3% (P < 0.05-0.01) respectively. The Syndrome Differentiation of PDBS was valuable in differentiating CHD. The SLPG is a good criterion for the study of CHD in TCM.

Adult↗

PubMed1991

A method for evaluating the selectivity of electrodes implanted for nerve simulation.

The scale of stimulating electrodes possible for use in functional electrical stimulation to restore motor and sensory function is rapidly approaching that of individual neurons. Although the electrodes may approach the dimensions of single nerve cells, it is unclear if the region of excitation elicited by each electrode will be correspondingly small. Previous techniques for evaluating this have either been tedious or have lacked the resolution necessary. This paper describes a method that uses the refractory interaction of the compound action potentials elicited by a stimulus pulse pair, along with high-resolution recording of those potentials, to achieve measurements of the selectivity of stimulation down to the scale of a few axon diameters. The feasibility of this technique is demonstrated in sciatic nerves of frogs (Rana Catesbiana) acutely implanted with a sapphire electrode array.

Action Potentials↗

PubMedDate not supplied

A forward-viewing intravascular ultrasound catheter suitable for intracoronary use.

Current intravascular ultrasound (IVUS) catheters provide a transverse cross-sectional view of the blood vessel, thus limiting their ability to visualize severely stenosed or occluded vessels. Forward-viewing IVUS devices can overcome these limitations. Previously described forward-viewing IVUS catheters are mechanically complex, making them too bulky for use in coronary arteries. A new design for small-forward viewing IVUS catheters was developed. Using this design, flexible 5-Fr (1.6 mm diameter) and 8-Fr (2.6 mm diameter) prototype catheters up to 110 cm long, suitable for intravascular work, were constructed. Imaging of cadaver arterial segments was performed using these prototype catheters. Structures such as branches and plaque and features such as calcium were well seen with these catheters. Correlation of lumen dimensions measured with the IVUS catheters and by histology (HIST) was excellent: IVUS = 1.06 x HIST - 1.45 mm, r2 = 0.98. This new technology holds promise as a tool for guiding intravascular interventions.

Aorta↗