Biomedical subjects

Raymond Leung

Publications and source records attributed to Raymond Leung.

5 recordsLinked to original sources

PubMed2005

Ciliary central microtubular orientation is of no clinical significance in bronchiectasis.

It has been suggested that patients with bronchiectasis might have increased central microtubular orientation angle (CMOA), which leads to poor coordination of ciliary beating, and consequently impairment of airway defence. We have employed transmission electron microscopy to assess CMOA of ciliated nasal mucosa in a cohort of 133 (81F, 56.8+/-16.1yr) stable bronchiectasis and 59 healthy subjects (30F, 49.3+/-22.1yr). There was no significant difference in CMOA between bronchiectasis (13.2 degree) and control subjects (13.0 degree, P=0.82). There was no significant difference in CMOA among patients according to the etiology of bronchiectasis, presence of nasal symptoms, or sputum status of Pseudomonas aeruginosa infection. Patients with more severe bronchiectasis, i.e. those with FEV(1) <60%, FVC <60%, or more than 4 bronchiectatic lung lobes, had significantly lower CMOA than their counterparts (P<0.05). There was no correlation between CMOA with age, 24h sputum volume, exacerbation frequency, FEV(1), FVC, or the number of bronchiectatic lung lobes (P>0.05). CMOA correlated with ciliary beat frequency (negative), and the percent of cilia showing ultrastructural or microtubular defects (P<0.05). Central microtubular orientation angle does not correlate with clinically important parameters, in contrary to the results reported by previously published smaller scale studies.

Adolescent↗

PubMed2005

Transform and embedded coding techniques for maximum efficiency and random accessibility in 3-D scalable compression.

This study investigates random accessibility and efficiency enhancements in highly scalable video and volumetric compression. With the advent of interactive multimedia technology, random accessibility has emerged as an increasingly important consideration in the design and optimization process. In this paper, we assess the impact that the transform, embedded coding components, and code-block configurations have on the compression efficiency and accessibility of a scalable codestream. We develop performance bounds on techniques which exploit temporal redundancy within the confines of a feed-forward compression system. We also examine their random access properties to argue the significance of motion-adaptive subband transforms. When information-theoretic measures are used to determine the potential benefits of three-dimensional (3-D) context coding, we find that most of the coding gain is attributed to code-block extension, rather than interslice context modeling itself. To gain further insight into the tradeoffs that the coding part has to offer, we run a series of simulations to determine code-block partitioning strategies which maximize reconstruction quality and space-time localization. The LIMAT framework and EBCOT coding paradigm have laid a solid foundation for further progress in the development of highly scalable 3-D compression systems.

Algorithms↗

PubMed2004

Plasma concentration of urotensin II is raised in hypertension.

OBJECTIVES: Urotensin II is the most potent vasoconstrictor known. Its role in hypertension has not been investigated. Here, we studied the plasma levels in hypertensive and normotensive human subjects. DESIGN: A cross-sectional case-control study. SETTING: Hypertension clinic and research clinic of a university teaching hospital. PARTICIPANTS: Sixty-two hypertensive outpatient subjects (52% male, aged 57 +/- 13 years) and 62 normotensive controls (45% male, aged 54 +/- 13 years) recruited from the general population. MAIN OUTCOME MEASURES: Plasma urotensin II levels measured by radioimmunoassay, systolic and diastolic blood pressure. RESULTS: Plasma urotensin II was 8.8 +/- 0.9 pmol/l in normotensive controls and 13.6 +/- 1.4 pmol/l in hypertensive subjects (P = 0.005). In multiple regression analysis, systolic blood pressure was related to plasma urotensin II (beta = 0.31, P < 0.001) and age (beta = 0.28, P = 0.001), accounting for 10 and 8%, respectively, of the variance in systolic blood pressure. There was no significant correlation with gender, renal function or diabetes. CONCLUSIONS: Plasma urotensin II was raised in hypertensive patients compared to normotensive controls, and was directly related to systolic blood pressure. Our findings raise the possibility that urotensin II may have an aetiological role in hypertension and its complications.

Aged↗

PubMed2002

Exhaled and sputum nitric oxide in bronchiectasis: correlation with clinical parameters.

STUDY OBJECTIVES: Although there has been tremendous attention on endogenous nitric oxide (NO) production in many respiratory and systemic diseases, little is known on NO production in bronchiectasis. DESIGN AND SETTING: We determined exhaled and sputum NO levels in 109 patients with stable bronchiectasis (71 women; mean +/- SD age, 58.2 +/- 14.1 years) and 78 control subjects (39 women; mean age, 56.7 +/- 12.1 years) by using an automatic chemiluminescence analyzer. MEASUREMENTS AND RESULTS: There was no significant difference in exhaled NO between patients with bronchiectasis and control subjects (p = 0.11). Bronchiectasis patients with Pseudomonas aeruginosa infection had a significantly lower exhaled, but not sputum, NO levels than their counterparts and control subjects (p = 0.04 and p = 0.009, respectively). Exhaled NO correlated with 24-h sputum volume in P aeruginosa-infected patients (r = - 0.36; p = 0.002). After adjustment for sputum volume and number of bronchiectatic lung lobes, P aeruginosa-infected patients still had lower exhaled NO levels than their counterparts (p = 0.01). There was no correlation between exhaled NO with FEV(1), FVC, and the number of bronchiectatic lung lobes (p > 0.05). Sputum NO levels were not different between patients and control subjects (p = 0.64), and had no correlation with clinical parameters. CONCLUSION: Exhaled NO appears to be reduced among bronchiectasis patients with P aeruginosa infection independent of other clinical parameters, and further studies on the potential mechanisms and pathogenetic implications of this reduction should be pursued.

Adult↗

PubMedDate not supplied

Clinical value of ciliary assessment in bronchiectasis.

Although ciliary dysfunction and numerous ultrastructural defects have been described, and these could be etiologically important in the development of bronchiectasis, their correlation with relevant clinical parameters have not been systematically evaluated. We have prospectively evaluated the prevalence and clinical significance of ciliary beat frequency and ultrastructural defects of nasal respiratory mucosa obtained from 152 stable patients with idiopathic bronchiectasis (100F, 57.7 +/- 15.2 yrs) and 127 control subjects (58F, 56.0 +/- 24.2 yrs). Bronchiectasis patients had significantly slower ciliary beat frequency (p < 0.05), and a greater percent of patients had central and peripheral microtubular defects (OR 14.4, 95% CI 5.6-36.8), namely, extra peripheral microtubules, "9 + 1", "8 + 2", and compound cilia (p < 0.05), but not microtubular disarrangement, extra matrix or ciliary tail abnormalities (p > 0.05), than controls. Bronchiectasis patients also had a greater proportion of cilia with any ultrastructural microtubular defects, compound cilia, and ciliary tails than controls (p < 0.05). Ciliary beat frequency did not correlate with clinically relevant parameters (p > 0.05). However, the percent of cilia with central, but not peripheral, microtubular defects correlated with 24 h sputum volume (r = 0.40, p = 0.001, and r = -0.04, p = 0.70, respectively) and FEV1 (r = -0.24, p = 0.01, and r = 0.00, p = 0.99 respectively). Our results strongly suggest a pathogenic role for central microtubular defects in the development of idiopathic bronchiectasis.

Adult↗