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Biomedical subjects

P Hamilton

Publications and source records attributed to P Hamilton.

At least 19 recordsLinked to original sources
PubMed2005

Modern and historical fluxes of halogenated organic contaminants to a lake in the Canadian arctic, as determined from annually laminated sediment cores.

Two annually laminated cores collected from Lake DV09 on Devon Island in May 1999 were dated using 210Pb and 137Cs, and analyzed for a variety of halogenated organic contaminants (HOCs), including polychlorinated biphenyls (PCBs), organochlorine pesticides, short-chain polychlorinated n-alkanes (sPCAs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polybrominated diphenyl ethers (PBDEs). Dry weight HOC concentrations in Lake DV09 sediments were generally similar to other remote Arctic lakes. Maximum HOC fluxes often agreed well with production maxima, although many compound groups exhibited maxima at or near the sediment surface, much later than peak production. The lower than expected HOC concentrations in older sediment slices may be due to anaerobic degradation and possibly to dilution resulting from a temporary increase in sedimentation rate observed between the mid-1960s and 1970s. Indeed, temporal trends were more readily apparent for those compound classes when anaerobic metabolites were also analyzed, such as for DDT and toxaphene. However, it is postulated here for the first time that the maximum or increasing HOC surface fluxes observed for many of the major compound classes in DV09 sediments may be influenced by climate variation and the resulting increase in algal primary productivity which could drive an increasing rate of HOC scavenging from the water column. Both the fraction (F(TC)) and enantiomer fraction (EF) of trans-chlordane (TC) decreased significantly between 1957 and 1997, suggesting that recent inputs to the lake are from weathered chlordane sources. PCDD/Fs showed a change in sources from pentachlorophenol (PeCP) in the 1950s and 1960s to combustion sources into the 1990s. Improvements in combustion technology may be responsible for the reducing the proportion of TCDF relative to OCDD in the most recent slice.

Arctic Regions↗
PubMed2003

Long- and short-time analysis of heartbeat sequences: correlation with mortality risk in congestive heart failure patients.

We analyze RR heartbeat sequences with a dynamic model that satisfactorily reproduces both the long- and the short-time statistical properties of heart beating. These properties are expressed quantitatively by means of two significant parameters, the scaling delta concerning the asymptotic effects of long-range correlation, and the quantity 1-pi establishing the amount of uncorrelated fluctuations. We find a correlation between the position in the phase space (delta, pi) of patients with congestive heart failure and their mortality risk.

Biophysics↗
PubMed2002

Memory beyond memory in heart beating, a sign of a healthy physiological condition.

We describe two types of memory and illustrate each using artificial and actual heartbeat data sets. The first type of memory, yielding anomalous diffusion, implies the inverse power-law nature of the waiting time distribution and the second the correlation among distinct times, and consequently also the occurrence of many pseudoevents, namely, not genuinely random events. Using the method of diffusion entropy analysis, we establish the scaling that would be determined by the real events alone. We prove that the heart beating of healthy patients reveals the existence of many more pseudoevents than in the patients with congestive heart failure.

Computer Simulation↗
PubMed2002

Early vascular abnormalities and de novo nitrate tolerance in diabetes mellitus.

OBJECTIVE: The haemodynamic consequence of altered mechanical wall properties in diabetes can impair the compliance characteristics or pulsatile function of arteries before changes in calibre or peripheral resistance become evident. We studied the sensitivity of pulsatile and steady-state haemodynamic variables in identifying vascular abnormalities and assessing arterial responsiveness to glyceryl trinitrate (GTN) in patients with diabetes, free from clinical complications of the disease. METHODS: Radial artery pressure waveforms were recorded in 22 patients with diabetes and 22 age- and sex-matched control subjects, using a calibrated tonometer device. A computer-based assessment of the diastolic pressure decay was used to quantify changes in arterial waveform morphology in terms of pulsatile (arterial compliance) and steady-state (peripheral resistance) haemodynamics. Pressure pulse waveforms were recorded before and 3, 6 and 9 min after the administration of 300 micro g of GTN. RESULTS: Of the pulsatile and steady-state impedance parameters, only small artery compliance was significantly different in patients, 4.7 ml/mmHg (95% CI 3.8-5.8), compared with control subjects 7.1 ml/mmHg (95% CI 5.4-8.7); (p < 0.05). In response to GTN small artery compliance increased, and systemic vascular resistance decreased significantly in control subjects; (p < 0.05) but remained unchanged in patients with diabetes. CONCLUSIONS: Arterial waveform analysis proved more sensitive in detecting early vascular abnormalities and tracking the haemodynamic effects of GTN in patients with diabetes than changes in total peripheral resistance. The diminished responsiveness of the arterial vasculature to organic nitrates may have therapeutic implications for the treatment of cardiovascular disease in diabetes mellitus.

Adult↗
PubMed2002

Preventing glycaemic excursions in diabetic patients requiring percutaneous endoscopic gastrostomy (PEG) feeding after a stroke.

AIMS AND METHODS: Enteral feeding for diabetic patients with a stroke is often associated with hyperglycaemia and/or hypoglycaemia, which can adversely influence neurological recovery. We have developed a structured enteral feeding programme aimed at establishing 'normal' feeding patterns and avoiding marked glycaemic excursions. RESULTS: Of 332 consecutive patients admitted to an acute stroke unit, 20 of 41 diabetic patients required PEG feeding. Over the initial 24-48 h, patients had 22- h feeds with continuous intravenous infusion of soluble insulin. Thereafter, they were established on three feeds per day. Soluble insulin was given prior to each feed with isophane insulin at 2200 h. Average duration of feed was 13 +/- 8 days with an achieved glucose level of 8.7 +/- 2.5 (mean +/- SD) mmol/l associated with 0.8 episodes of biochemical hypoglycaemia (< 3 mmol/l) each week. CONCLUSIONS: A structured enteral feeding programme for PEG-fed diabetic patients can improve the quality of care with avoidance of marked glycaemic excursions.

Aged↗
PubMed2002

Effect of folate supplementation on mucosal cell proliferation in high risk patients for colon cancer.

AIMS: Intracellular folate deficiency has been implicated in colonic carcinogenesis in epidemiological studies and animal and human cancer models. Our aim was to determine the effect of folate supplementation on patients with recurrent adenomatous polyps using rectal mucosal cell proliferation as a biomarker. PATIENTS AND METHODS: Eleven patients with recurrent adenomatous polyps of the colon were randomised into a treatment group (n=6) receiving a dietary supplement of 2 mg folic acid per day for three months and a control group (n=5) receiving a placebo. Rectal biopsies where taken at 10 cm from the anal verge prior to supplementation and repeated at four, 12, and 18 weeks from the start of the supplementation. Each biopsy was immediately incubated in culture medium enriched with bromodeoxyuridine (BrdU). The S phase cells which incorporated BrdU into their DNA were identified following immunohistochemical staining. Twenty five orientated crypts were identified for each time point and the number and position of BrdU positive and BrdU negative cells were counted. BrdU labelling indices (LIs) were calculated for the entire crypt and for each of five equal compartments running consequently from the base to the luminal surface. RESULTS: The LI of the treatment group (9.1 (6.7, 12.3)) and the control group (9.3 (7.8, 10.3)) were comparable at the start. Over the duration of the supplementation period, LI in the control group did not alter significantly (9.3 (7.8, 10.3) v 9.6 (8.9, 10.4)). However, LI of the folate treated group was lowered after 12 weeks of supplementation (9.1 (6.7, 12.3) v 7.4 (5.3, 9.6)). Analysis of the LI for compartments within the crypt showed that the most significant drop in number of proliferating cells was in the upper most regions of the crypt. CONCLUSION: These data indicate that (a) folate supplementation decreases colonic mucosal cell proliferation in a high risk group for colon cancer and (b) the most significant reduction takes place at the luminal aspect of the crypt.

Cell Division↗
PubMed2001

Predicting performance on the Royal College of Physicians and Surgeons of Canada internal medicine written examination.

BACKGROUND: Although the written component of the Royal College of Physicians and Surgeons of Canada (RCPSC)internal medicine examination is important for obtaining licensure and certification as a specialist, no methods exist to predict a candidate's performance on the examination. METHOD: We obtained data from 5 Canadian universities from 1988 to 1998 in order to compare raw scores from the American Internal Medicine In-Training Examination (AIMI-TE) with raw scores and outcomes (pass or fail) of the written component of the RCPSC internal medicine examination. RESULTS: Mean scores on the AIMI-TE correlated well with scores on the RCPSC internal medicine written examination for all postgraduate years (r = 0.62, r = 0.55 and r = 0.65 for postgraduate years 1, 2 and 3 respectively). Scores above the 50th percentile on the AIMI-TE w/ere predictive of a low failure rate (< 1.5%) on the RCPSC internal medicine written examination, whereas scores at or below the 10th percentile were associated with a high failure rate (about 24%). INTERPRETATION: Candidates who are eligible to take the written component of the RCPSC certification examination in internal medicine can use the AIMI-TE to predict their performance on the Canadian examination. The AIMI-TE is a useful test for residents in all levels of training, because the examination scores have a strong relation to expected performance on the Canadian examination for each year of postgraduate training.

Canada↗
PubMed2001

The use of denaturing high-pressure liquid chromatography for the detection of mutations in thiopurine methyltransferase.

The level of expression of the enzyme thiopurine methyltransferase (TPMT) is an important determinant of the metabolism of drugs used both in the treatment of acute leukaemia (6-mercaptopurine and 6-thioguanine) and as an immunosuppressant in patients with autoimmune diseases or following organ transplantation (azathioprine). Studies of enzyme activity in red blood cells have shown that TPMT expression displays genetic polymorphism with 11% of individuals having intermediate and one in 300 undetectable levels. Patients with biallelic mutations and undetectable enzyme activity suffer life-threatening myelosuppression when treated with conventional doses of these drugs. Patients with intermediate activity have an increased risk of drug-associated toxicity. In the Caucasian populations studied to date, intermediate activity is associated with mutations at two sites of the TPMT gene, G460A and A719G (designated TPMT*3A), in 80% of cases. Detection of these mutations has, to date, been based on the analysis of restriction digests of PCR products. In order to simplify this process we have investigated the ability of denaturing high pressure liquid chromatography (DHPLC) to detect the A719G mutation. DHPLC of PCR products from 15 known heterozygotes (TPMT*3A/TPMT*1) and 18 known homozygotes (TPMT*1/TPMT*1) gave a clear pattern difference between the groups and 100% concordance with the results of restriction digests. These results suggest DHPLC represents a valuable technique for accurate and rapid detection of pharmacologically important mutations in the TPMT gene.

Antineoplastic Agents↗
PubMed2001

Reducing hospital inpatient length of stay for patients with diabetes.

AIMS: To ascertain the effect of routine review by a diabetes nurse advisor on length of stay for medical and surgical inpatients with diabetes. METHODS: Inpatients with diabetes were identified prospectively from January 1997 until December 1998 (792 in 1997 and 819 in 1998). A new post of diabetes nurse advisor was introduced in January 1998 to optimize diabetes management. Length of stay was calculated retrospectively from hospital computer records. RESULTS: Median length of stay in 1997 was 11 days in medicine and 8 days in surgery. In 1998, the nurse advisor made 1936 visits to 819 patients; median length of stay fell to 8 days in medicine and 5 days in surgery (P < 0.001). Bed occupancy by patients with diabetes fell from 6.8 to 4.0%. Mean length of stay across the hospital remained unchanged. CONCLUSIONS: The introduction of a ward-based diabetes nurse advisor was associated with significant reductions in length of stay in inpatients with diabetes. Since this study was not a randomized study, other factors may have contributed to this change. However, the consistency of the reduction across specialities suggests the post itself had an important effect.

Diabetes Mellitus↗
PubMed2001

The relationships between neonatal encephalopathy and cerebral palsy: a cohort study.

There is a high risk of cerebral palsy (CP) following neonatal encephalopathy (NE) with fits, often attributed to intrapartum asphyxia. The evidence for the association is inconclusive and antepartum factors offer an alternative explanation. A cohort study was carried out to assess the evidence for and against hypoxic ischaemic injury as the cause of NE-associated CP in term infants. A total of 57 159 consecutive births were enrolled. There were 150 cases with NE, of whom 92 had at least one fit and 58 had no fits. The incidence of all NE was 2.62 per 1000 births and of NE with fits was 1.61 per 1000 births. Infants with NE were followed-up to identify those with cerebral palsy. There were 13 cases of four-limb cerebral palsy and three with hemiplegia among the survivors. In 12 of the 13 cases of four-limb CP, a combination of low Apgar scores, an early onset acute evolving encephalopathy, acidosis, renal dysfunction and the absence of antepartum factors suggested an acute intrapartum event as the immediate cause of the NE. An obstetric event likely to cause acute hypoxic injury was identified in four of the 12 cases. The clinical picture was similar in the four with and the eight without a specific obstetric event. The pathway leading to NE-associated CP remains unexplained, but intrapartum events appear to play a major role in most cases.

Journal Article↗
PubMed2001

Stromal fibrosis of the breast.

OBJECTIVE: The purpose of this retrospective study was to describe the imaging features of stromal fibrosis of the breast and to determine the false-negative rate (number of cancers missed) at percutaneous biopsy. MATERIALS AND METHODS: Between January 1997 and October 1999, 1095 imaging-guided core biopsies were performed. Patients were included in our study if stromal fibrosis was the predominant histologic finding. Cores adjacent to previous excisional biopsies or from calcified lesions were excluded. RESULTS: Stromal fibrosis was diagnosed in 74 (6.8%) of 1095 imaging-guided core needle biopsies in 73 patients. The 10 mammographic lesions were variable in appearance. Most of the sonographic lesions were indeterminate, with 16 (25%) of 64 showing suspicious features. Discordant imaging resulted in three patients having a second core biopsy and nine patients having an excisional biopsy. The two false-negative findings were the result of an infiltrating lobular carcinoma and an infiltrating ductal carcinoma, the latter diagnosis delayed for 6 months. CONCLUSION: The low incidence (2.7%) of missed cancers in our series suggests that patients diagnosed at core biopsy as having stromal fibrosis can be treated conservatively with a short-term follow-up protocol. However, it would be prudent to continue to recommend either a second core biopsy or an excisional biopsy for imaging features that cannot be reliably differentiated from malignancy.

Adult↗
PubMed2000

World-wide genetic differentiation of Eubalaena: questioning the number of right whale species.

Few studies have examined systematic relationships of right whales (Eubalaena spp.) since the original species descriptions, even though they are one of the most endangered large whales. Little morphological evidence exists to support the current species designations for Eubalaena glacialis in the northern hemisphere and E. australis in the southern hemisphere. Differences in migratory behaviour or antitropical distribution between right whales in each hemisphere are considered a barrier to gene flow and maintain the current species distinctions and geographical populations. However, these distinctions between populations have remained controversial and no study has included an analysis of all right whales from the three major ocean basins. To address issues of genetic differentiation and relationships among right whales, we have compiled a database of mitochondrial DNA control region sequences from right whales representing populations in all three ocean basins that consist of: western North Atlantic E. glacialis, multiple geographically distributed populations of E. australis and the first molecular analysis of historical and recent samples of E. glacialis from the western and eastern North Pacific Ocean. Diagnostic characters, as well as phylogenetic and phylogeographic analyses, support the possibility that three distinct maternal lineages exist in right whales, with North Pacific E. glacialis being more closely related to E. australis than to North Atlantic E. glacialis. Our genetic results provide unequivocal character support for the two usually recognized species and a third distinct genetic lineage in the North Pacific under the Phylogenetic Species Concept, as well as levels of genetic diversity among right whales world-wide.

Animals↗
PubMed2000

Bcl-2 expression in sequential biopsies of potentially malignant oral mucosal lesions assessed by immunocytochemistry.

OBJECTIVE: To examine, for the first time Bcl-2 expression in sequential (autogenous) oral mucosal biopsies taken from the same sites in a gender, risk-factor matched, Caucasoid sample, over a 21-year period. DESIGN: Retrospective immunocytochemical longitudinal study of archival serial biopsies. MATERIALS AND METHODS: Computer records were used to identify biopsy specimens derived from 12 patients. These were divided into four groups: (1) Histologically innocuous lesions which remained histologically innocuous. (2) Dysplastic lesions which remained dysplastic. (3) Histologically innocuous lesions which later progressed to squamous cell carcinoma (SCC). (4) Dysplastic lesions which later progressed to SCC. This represented 65 biopsies in total. Bcl-2 expression was studied using mouse antihuman BCL-2 oncoprotein clone 124 (Dako, Denmark). RESULTS: Generally, there was a lack of Bcl-2 immunoreactivity in the epithelium, with one exception in dysplastic epithelium from a group (3) patient. CONCLUSION: These findings suggest that in our series, Bcl-2 is not expressed early in oral premalignant lesions and appears to contradict previous reports. Possible explanations for this disparity are considered.

Adult↗
PubMed2000

Randomized double-blind controlled trial comparing the effects of ibuprofen with indomethacin on cerebral hemodynamics in preterm infants with patent ductus arteriosus.

A prospective randomized controlled trial was performed to compare the effects of ibuprofen with indomethacin on cerebral hemodynamics measured using near infrared spectroscopy in preterm infants during treatment for patent ductus arteriosus. Infants were randomly assigned to three intravenous doses of either indomethacin (0.20-0.25 mg/kg, 12 hourly) or ibuprofen (5-10 mg/kg, 24 hourly) and also received a dose of saline. The primary end points of the study were the effects of the first dose on cerebral blood flow (CBF) and cerebral blood volume. Fifteen infants received indomethacin and 18 received ibuprofen. The group mean (SD) values for CBF (mL x 100 g(-1) x min(-1)) before and after the first dose of indomethacin were 13.6 (4.1) and 8.3 (3.1), respectively, the change being significant (p<0.001). In contrast, no significant changes in CBF were observed with the first dose of ibuprofen, the respective before and after values being 13.3 (3.2) and 14.9 (4.7) mL x 100 g(-1) x min(-1). The median (interquartile range) value for change in cerebral blood volume (mL/100 g) after the first dose in the indomethacin group was -0.4 (-0.3 to -0.6) and in the ibuprofen group was 0.0 (0.1 to -0.1), the difference between the two groups being significant (p<0.001). Cerebral oxygen delivery changed significantly after the first dose in the indomethacin group but not in the ibuprofen group. Significant reductions in CBF, cerebral blood volume, and cerebral oxygen delivery also occurred after the 24-h dose of indomethacin, but there were no significant changes after the 48-h dose of saline in the indomethacin group or after the 24- and 48-h doses of ibuprofen. The patent ductus arteriosus closure rates after indomethacin and ibuprofen were 93 and 78%, respectively. We conclude that ibuprofen, unlike indomethacin, has no adverse effects on cerebral hemodynamics and appears to mediate patent ductus arteriosus closure.

Brain↗