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H van Woerden

Publications and source records attributed to H van Woerden.

6 recordsLinked to original sources
PubMed2005

Analysis of renal service provision in south and mid Wales.

OBJECTIVES: This paper estimates point prevalence of renal replacement therapy (RRT) utilization within population strata defined by geography and deprivation in south and mid Wales. It investigates spatial accessibility of main and satellite renal units by comparing population and patient numbers within bands of travel time. STUDY DESIGN: Prevalence study based on patient registers. METHODS: From a list of patient and renal unit locations, geocoded at the level of unit postcodes, and electoral division-level denominator population data, we calculated RRT point prevalence for the 16 unitary authorities in the study area, fifths of small area deprivation, and three bands of travel time from the nearest main renal unit and any (main or satellite) unit. RESULTS: Overall point prevalence was 633 per million population (pmp) and this varied from 256 to 780 pmp across unitary authorities. RRT prevalence was lower in more deprived areas. Sixty-nine percent of the population and 73% of patients lived within 30 min of a main renal unit. Eighty-four percent of the population and 88% of patients lived within 30 min of a main or satellite renal unit. CONCLUSIONS: The provision of satellite renal units has significantly improved spatial accessibility of RRT services. However, a substantial proportion of the population remains geographically distant from renal units. This has important implications for planning of future provision of RRT, given the inverse relationship between RRT acceptance and travel time, and the impact on quality of life of patients who travel frequently to renal units.

Geography↗
PubMed2004

Dust mites living in human lungs--the cause of asthma?

Asthma does not have a clear cause and may represent a cluster of diseases. We propose that asthma in house dust mite sensitive patients may be caused by recurrent inhalation of live dust mites which are able to live for some time in the bronchioles of the lung. To provide themselves with a food source, the mites may purposefully excrete proteolytic enzymes, including Der p1, which increase epithelial shedding by freeing cells from the basement membrane. The mites then feed on the shed respiratory epithelial cells. Consequent loss of an intact respiratory epithelium exposes underlying tissues to dust mite protein and other allergens triggering sensitisation to these proteins. Later, repeated infestation provokes an allergic response which manifests itself as asthma attacks. The evidence for this hypothesis was tested against the Bradford-Hill criteria for causation; consistency, strength, temporal association and dose response. Potential areas for further research were also identified. The association between asthmatic symptoms and pulmonary acariasis was consistent across a number of studies. Determining the strength of the association and any dose response requires more work which is dependent on the development of better tests for the detection of mites in sputum. There was tentative evidence of a temporal association in the published studies identified. Biological plausibility and experimental evidence was available for pulmonary acariasis in primates and arsenic treatment was effective in humans. Better tests for mites in sputum are needed, as is work to assess more modern anti-acaricidal drugs in dust mite sensitive asthmatics.

Allergens↗
PubMed1999

Accretion of low-metallicity gas by the Milky Way.

Models of the chemical evolution of the Milky Way suggest that the observed abundances of elements heavier than helium ('metals') require a continuous infall of gas with metallicity (metal abundance) about 0.1 times the solar value. An infall rate integrated over the entire disk of the Milky Way of approximately 1 solar mass per year can solve the 'G-dwarf problem'--the observational fact that the metallicities of most long-lived stars near the Sun lie in a relatively narrow range. This infall dilutes the enrichment arising from the production of heavy elements in stars, and thereby prevents the metallicity of the interstellar medium from increasing steadily with time. However, in other spiral galaxies, the low-metallicity gas needed to provide this infall has been observed only in associated dwarf galaxies and in the extreme outer disk of the Milky Way. In the distant Universe, low-metallicity hydrogen clouds (known as 'damped Ly alpha absorbers') are sometimes seen near galaxies. Here we report a metallicity of 0.09 times solar for a massive cloud that is falling into the disk of the Milky Way. The mass flow associated with this cloud represents an infall per unit area of about the theoretically expected rate, and approximately 0.1-0.2 times the amount required for the whole Galaxy.

Astronomical Phenomena↗
PubMed1983

Radionuclide bone scintigraphy in patients with histiocytosis X.

The term histiocytosis X (HX) refers to a spectrum of disorders varying from unifocal eosinophilic granuloma (UEG), multifocal eosinophilic granuloma (MEG), to the Abt-Letterer-Siwe syndrome. In a series of 16 patients with different types of HX and skeletal lesions, whole body bone scintigraphy was performed at the time of diagnosis and during follow up. Results were compared with radiographic findings. In patients with MEG with or without extra-skeletal dissemination bone scintigraphy revealed cold spots or hot spots, but half of the lesions were not visualised scintigraphically, resulting in false negative scans. In UEG the lesions were visualised as areas of increased uptake or as a cold spot with increased uptake at its borders. No false negative scans were encountered. The reliability of skeletal scintigraphy in patients with HX seems to depend on the type of the disorder: in UEG bone scintigraphy is a safe procedure. In MEG false negative bone scans have to be expected, and radiography is superior.

Adult↗
PubMed1981

Experiences with recurring ventricular catheter obstructions.

Seven cases are presented of recurrent ventricular catheter obstruction, an infrequent but serious problem in the management of hydrocephalus. Plugging of the catheter was caused by detritus rather than by choroid plexus. A retrospective analysis of 214 shunt revisions indicated that obstruction both by detritus and by choroid plexus were incidental phenomena in the great majority of the cases - the former type occurring mainly within the first month, the latter between 3 and 6 months after operation. It is suggested that the ultimate cause of recurrent catheter obstruction by detritus may be destruction or ablation of the ependymal lining of the ventricles (e.g. by an inflammatory process), which easily provides debris to the catheter. In 4 of the cases insertion of the catheter into the opposite ventricle prevented further recurrence, when reinsertion into the same ventricle had been ineffective. In one case, with scarcely dilated ventricles, external decompression was helpful. In patients with compartmentalisation of the ventricles (substantiated in one of our patients) one might consider removal of the septa via craniotomy before the insertion of the catheter.

Cerebrospinal Fluid Shunts↗