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Biomedical subjects

P C Li

Publications and source records attributed to P C Li.

15 recordsLinked to original sources
PubMed1995

Profile of opportunistic infections among HIV-1 infected people in Hong Kong.

BACKGROUND: To determine the spectrum of opportunistic infections in patients with human immunodeficiency virus (HIV-1) infection in Hong Kong. METHODS: A retrospective study of 214 HIV-1-infected patients, seen between December 1984 and December 1993 in a specialist clinic for HIV/AIDS: RESULTS: A majority (94%) of the patients in the cohort were male; 84% had acquired HIV via sexual contacts. Two-thirds were ethnic Chinese. Ninety-two (43%) had developed AIDS, and 54(25%) had presented with other non AIDS-defining opportunistic infections during the study period. The primary AIDS defining illnesses of 80 patients were infections: Pneumocystis carinii pneumonia (50%), extrapulmonary tuberculosis (10%) and cytomegalovirus (CMV) disease (8%). Opportunistic infections among Chinese and non-Chinese were similar in spectrum, though higher frequencies of infection with CMV, Mycobacterium avium intracellulare and tuberculosis were seen among Chinese, whereas the opposite was true for Pneumocystis carinii pneumonia, toxoplasmosis and cryptosporidiosis. Disseminated Penicillium marneffei infection was another significant disease for HIV-positive patients. Common non AIDS-defining opportunistic infections included herpes zoster, oral candidiasis, herpes simplex infection and genital/anal wart. The median CD4 count at HIV diagnosis for AIDS patients was much lower than non-AIDS patients (147 vs 546/ul). Survival of deceased AIDS patients was poor, with a median of only five months. Survival has however, apparently, improved over the recent years. CONCLUSIONS: In Hong Kong, Pneumocystis carinii pneumonia remained the most common primary AIDS event, while Penicillium marneffei was emerging as another significant cause of major infection. Herpes zoster and oral candidiasis were the two most frequently encountered minor opportunistic infections.

AIDS-Related Opportunistic Infections↗
PubMed1994

Management of tetanus: a review of 18 cases.

Eighteen patients with generalized tetanus seen during an 8-year period in three regional hospitals in Hong Kong are reviewed. Eighty-nine per cent of the patients were intravenous heroin addicts who developed a severe type of generalized tetanus with autonomic dysfunction. Pain or stiffness of the neck or back was the commonest presenting symptom, followed by trismus and dysphagia. Most of the patients developed muscle spasms within 24 h of the onset of presenting symptoms. Early ventilatory support and tracheostomy, together with intensive nursing care, were the mainstay of the treatment. Pulmonary and gastrointestinal complications were common during the course of illness and treatment of autonomic dysfunction was often unsatisfactory. The case fatality rate was 25% among the heroin addicts, but full recovery was the usual outcome for those who survived. The simultaneous administration of intrathecal tetanus immunoglobulin tends to reduce mortality.

Adult↗
PubMed1994

Improved detectability with blocked element compensation.

The inability of diagnostic ultrasound to detect low contrast lesions deep inside the body has limited its success in cancer diagnosis. To enhance low contrast detectability, two-dimensional, very large arrays (VLA's) providing greatly improved spatial resolution have been proposed. Due to discontinuous acoustic windows into the body, however, a significant fraction of such an array might be blocked resulting in degraded detectability in clinical situations. To compensate for this degradation, an object dependent method utilizing multiple receive beams has been proposed and shown to effectively reduce undesired beamforming artifacts. To further explore the method's capabilities, simulations have been done quantifying improvements in contrast resolution. Using the contrast-to-noise ratio (CNR) as a performance measure, results show that low contrast detectability is determined by sidelobe energy in the point spread function if the total aperture size is not reduced. Moreover, contrast resolution can be restored using the object dependent method if the number of blocked elements is not very significant. If the number of blocked elements is large, however, the method breaks down and performance improvements are minimal.

Image Enhancement↗
PubMed1994

Efficient two-dimensional blocked element compensation.

Very large, two-dimensional, anisotropic arrays have been proposed to improve ultrasound image quality. Due to noncontiguous acoustic windows into the body, however, a significant portion of such an aperture may be blocked. Blocked elements result in high sidelobes in the point spread function, degrading image quality. To compensate for this, an object dependent method using multiple receive beams has been recently proposed. This method is effective in removing undesired sidelobes. However, previous results were for one-dimensional arrays where only lateral beams were used for estimation. With two-dimensional arrays, the distribution of blocked elements can change beam characteristics, both laterally and elevationally. In other words, receive beams must be formed in both directions for better performance. Although straightforward in principle, extension of the algorithm from one dimension to two increases computational complexity dramatically. Furthermore, the restricted elevational steering capability of anisotropic arrays also limits performance. In this paper, several computationally efficient algorithms for two-dimensional blocked element compensation are proposed and evaluated. It is shown that undesired sidelobes can be effectively removed using only a limited number of receive beams. Image quality can therefore be restored in the presence of blocked elements without significantly increasing hardware complexity.

Ultrasonography↗
PubMed1994

Elevational spatial compounding.

Spatial compounding has long been explored to reduce coherent speckle noise in medical ultrasound. By laterally translating a one-dimensional array, partially correlated measurements made at different look directions can be obtained and incoherently averaged. The lateral resolution, however, is limited by the sub-array length used for each independent measurement. To reduce speckle contrast without compromising lateral resolution, a new spatial compounding technique using two-dimensional, anisotropic arrays is proposed. This technique obtains partially correlated measurements by steering the image plane elevationally with small inclinations. Incoherent averaging is then performed by adding image magnitudes. Therefore, contrast resolution is improved only at the price of a slightly wider elevational beam. Note that although anisotropic arrays have limited steering capability in elevation, grating lobes are not considered influential since only small inclinations are needed between measurements. Simulations have been performed to show both the change in spatial resolution and the improvement in contrast resolution. Results indicated minimal increase in the correlation length both laterally and axially. It was also shown that detectability can be significantly enhanced by increasing the number of measurements or increasing the differential inclination between measurements. This technique is therefore effective for reducing speckle noise while maintaining in-plane spatial resolution. Furthermore, it demonstrates a new application of two-dimensional anisotropic arrays in spite of their limited elevational steering capability.

Ultrasonics↗
PubMed1993

Real-time arrhythmia identification from automated analysis of intraatrial and intraventricular electrograms.

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two-Channel Rate-Morphology (2CRM) was introduced. It is a real-time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle-by-cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two-channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter-fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single-cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).

Algorithms↗
PubMed1993

Clinical profile of Chinese patients with systemic lupus erythematosus.

In the 9-year period between 1982 and 1991, 137 patients attending a medical clinic of Queen Elizabeth Hospital, Hong Kong, were diagnosed as having systemic lupus erythematosus according to the American Rheumatism Association's criteria for classification. The female-to-male ratio was 16 to 1. Commonly the onset age was between 20 and 40. Malar rash (70%), arthritis (70.8%) and nephropathy (69.3%) were the most common manifestations. Anti-nuclear factor was invariably positive, whereas anti-extractable nuclear antigen antibodies were positive in varying degrees--Sm 12.7%, nRNP 28.8%, Ro 60.2%, La 8.4%. There were 22 deaths during the follow-up period, two-thirds from active diseases. Gastro-intestinal bleeding and opportunistic infection were common complications.

Adolescent↗
PubMed1993

Enhanced phagocyte chemiluminescence in asymptomatic HIV infection.

Seventeen asymptomatic HIV infected patients were studied for their phagocyte function in vitro, in comparison with that of eight normal healthy persons. Chemiluminescence was measured using whole blood by means of a microtitreplate luminometer. Light indices, cumulative light indices and rapidity of responses were recorded. The patients had a lower phagocyte count (13.17 +/- 0.85 x 10(9)/l) but a more rapid and intense chemiluminescence response. The latter was demonstrated by a higher peak light index and cumulative response. The observed enhanced phagocyte activity may reflect an early failure of T cell regulatory functions, or a compensatory mechanism in response to the underlying immunodeficiency.

Adult↗
PubMed1992

Synthetic aperture imaging using a Lagrange based filtering technique.

Synthetic aperture imaging using a catheter based, circular phased array providing high resolution, dynamic focusing has been explored. Due to the high input impedance and low signal-to-noise ratio (SNR) of a classic single element synthetic aperture system, multi-element synthetic aperture processing has been proposed with SNR improvement of about 8 dB for a 33 element aperture. Reconstruction in this case uses an optimal filtering approach based on minimizing the mean square error between filter output and desired beam pattern. This approach, however, does not directly control both mainlobe beamwidth and sidelobe levels. To overcome this problem, a Lagrange based filter design technique has been developed that not only satisfies the minimum energy criterion, but also constrains sidelobe levels under a certain threshold. The new technique provides better spatial and contrast resolution. Both the mathematical formulation and simulation results are presented.

Algorithms↗
PubMed1991

Effects of increased heart rate and sympathetic tone on intraventricular electrogram morphology.

Electrogram pattern recognition by way of morphologic analysis has been proposed as a technique that may improve discrimination of ventricular tachycardia from sinus rhythm by antitachycardia devices. The potential impact that increases in heart rate and sympathetic tone could have on such techniques, however, has not been previously determined. A comparative study was undertaken to quantify possible changes in ventricular electrogram morphology using correlation waveform, area of difference, and amplitude analyses in 6 patients during atrial overdrive pacing at cycle lengths of 600 and 400 ms (group A), in 13 patients during infusions of physiologic doses of epinephrine (group B), and in 20 patients undergoing infusions of isoproterenol (group C). Four patients were in both groups A and B. A bipolar intraventricular template of cardiac depolarization during sinus rhythm at rest was compared with depolarization during subsequent passages of sinus rhythm at rest and subsequently increased heart rate. In 36 of 39 patients, waveform configuration as assessed by correlation waveform analysis remained relatively stable during atrial overdrive pacing, epinephrine infusion, and isoproterenol infusion when compared with sinus rhythm at rest. The correlation value did not fall below 0.950 in any patient. Area of difference values for the same 36 patients changed by an average of 6 and 37% during atrial overdrive pacing at cycle lengths of 600 and 400 ms intervals, respectively, by 3% during epinephrine infusion, and by 17% during isoproterenol infusion. In these same patients, there was an average change in electrogram amplitude of -1% during atrial overdrive pacing at 600 ms, 26% during pacing at 400 ms, -1% during epinephrine infusion, and 12% during isoproterenol infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[Relation between malondialdehyde generation by platelets and plasma thromboxane B2 and diagnostic classification by syndrome differentiation of traditional Chinese medicine in stroke during acute stage].

The malondialdehyde generation by platelets and TXB2 in poor platelet plasma were examined in 36 patients with stroke during acute stage. By CT examination 19 cases were diagnosed hemorrhagic, 17 cases ischemic; while by syndrome differentiation of TCM 16 cases belonged to Zhongzangfu(middle internal organs), 20 cases Zhongjingluo (middle channels). Results showed that the malondialdehyde generation by platelets was reduced, TXB2 in poor platelet plasma increased in patients, compared with those in the healthy controls. This finding was common in stroke during acute stage and was not related to diagnostic classes by either CT examination or syndrome differentiation of TCM. This study indicates that maintenance of normal platelet function may have significant implication in the prevention and treatment of cerebrovascular disease.

Adult↗