PubMed Health⌕ Search

Biomedical subjects

P Johnston

Publications and source records attributed to P Johnston.

At least 19 recordsLinked to original sources
PubMed2003

Butter as an indicator of regional persistent organic pollutant contamination: further development of the approach using polychlorinated dioxins and furans (PCDD/Fs), and dioxin-like polychlorinated biphenyls (PCBs).

The potential for use of butter as a widely available, relatively uniform lipid-rich matrix for the determination of spatial distributions of persistent organic pollutants has already been demonstrated. The present study determines the contributions to toxicity equivalence (TEQ) from polychlorinated dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) using butter samples from 24 countries world wide. Concentrations of PCDD/Fs and dioxin-like PCBs ranged from 0.07 to 5.69 pg SigmaWHO-TEQ g(-1) lipid. For most samples, PCDD/F TEQ fell within ranges reported for European dairy products over the last decade (0.3-2 pg x g(-1) lipid I-TEQ), though a single sample from Spain was a notable exception. Other than this sample, the highest values were recorded for samples from the Netherlands and Italy, with those from India, China and Tunisia also being relatively high. The contribution from non-ortho-PCBs was particularly significant in samples from Germany, Austria, Italy, the Czech Republic, Tunisia, India and Argentina. Although overall TEQs were generally highest in European and Mediterranean butters, elevated levels were also apparent in industrializing regions of Asia (India, China) and Latin America (Argentina). More detailed regional studies would be necessary to identify likely dioxin and PCB sources in each case. Nevertheless, this study supports the utility of butter as a monitoring matrix that may be especially applicable in regions for which monitoring programmes are currently lacking.

Animals↗
PubMed2002

Adjuvant treatment of colorectal cancer (current expert opinion derived from the Third International Conference: Perspectives in Colorectal Cancer, Dublin, 2001).

This article summarises the progress that has been made in the adjuvant treatment of colorectal cancer over the last decade. In view of the consequent improvements in recurrence rates and in overall survival, the development of effective adjuvant treatments for colorectal cancer is considered as one of the most important to be made in clinical oncology over the last decade. Treatment recommendations based on evidence-based data and on expert opinions are summarised in this manuscript. However, a consensus cannot be reached on all aspects of treatment because of data that is currently emerging that will influence clinical practice and because of the many ongoing clinical trials. Those involved in the treatment of colorectal cancer should therefore be encouraged to continue to provide optimal patient care and to participate in well designed clinical trials in order to increase the evidence upon which they can base their clinical judgements and in order to make further progress.

Antineoplastic Agents↗
PubMed2002

A comparison of magnetic resonance imaging and neurophysiological studies in the assessment of cervical radiculopathy.

Neurophysiological studies (NPS) are often used by both neurosurgeons and neurologists to supplement neuroimaging findings in the diagnosis of cervical radiculopathy and in operative decision-making. The aim of this study was to assess whether nerve conduction and electromyographic studies added significant information to that obtained from high resolution MRI to warrant routine use. Over the 10-year period (1991-2001), we identified 48 patients who underwent both preoperative NPS and MRI for cervical radiculopathy. Sensitivity of MRI and NPS for diagnosing cervical radiculopathy was 93 and 42%, respectively. Whilst the positive predictive values for MRI and NPS were similar (91% versus 86%), the former had a higher negative predictive value (25% versus 7%). In only one case was the decision to operate based on NPS despite a negative MRI. We therefore suggest that in patients with clinical and MRI evidence of cervical radiculopathy, NPS has limited additional diagnostic value.

Adult↗
PubMed2001

Enzyme-catalyzed therapeutic agent (ECTA) design: activation of the antitumor ECTA compound NB1011 by thymidylate synthase.

The in vivo administration of enzyme-inhibiting drugs for cancer and infectious disease often results in overexpression of the targeted enzyme. We have developed an enzyme-catalyzed therapeutic agent (ECTA) approach in which an enzyme overexpressed within the resistant cells is recruited as an intracellular catalyst for converting a relatively non-toxic substrate to a toxic product. We have investigated the potential of the ECTA approach to circumvent the thymidylate synthase (TS) overexpression-based resistance of tumor cells to conventional fluoropyrimidine [i.e. 5-fluorouracil (5-FU)] cancer chemotherapy. (E)-5-(2-Bromovinyl)-2'-deoxy-5'-uridyl phenyl L-methoxyalaninylphosphoramidate (NB1011) is a pronucleotide analogue of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdU), an antiviral agent known to be a substrate for TS when in the 5'-monophosphorylated form. NB1011 was synthesized and found to be at least 10-fold more cytotoxic to 5-FU-resistant, TS-overexpressing colorectal tumor cells than to normal cells. This finding demonstrates that the ECTA approach to the design of novel chemotherapeutics results in compounds that are selectively cytotoxic to tumor cell lines that overexpress the target enzyme, TS, and therefore may be useful in the treatment of fluoropyrimidine-resistant cancer.

Animals↗
PubMed2001

In vitro and in vivo comparison of three different intravascular ultrasound catheter designs.

Intravascular ultrasound (IVUS) is an invasive imaging modality, which provides detailed two-dimensional images of blood vessels. There are currently two different types of IVUS catheters available, namely, the phased-array and the mechanical designs. The operating ultrasound frequency of these catheters ranges from 20 to 40 MHz. This study sought to evaluate the image quality, accuracy of diameter and pullback length measurements, and catheter handling characteristics of three different IVUS catheters currently available for clinical use using both in vitro phantom models and in patients undergoing percutaneous coronary intervention (PCI). In gelatin phantom models, image quality assessed on a semiquantitative scale was significantly different between the three IVUS catheters (P = 0.01) with the 40-MHz catheter providing the best images. Accuracy of lumen diameter measurements, when compared to optical microscopy, were similar between the three IVUS catheter designs (all R(2) = 0.99). There were no significant differences in accuracy of pullback length measurements in vitro between the three designs. However, there were differences in the performance of the three IVUS catheters when used for preinterventional imaging in patients undergoing PCI. Both mechanical IVUS catheters were associated with lower procedural, fluoroscopy, and lesion crossing times compared to the phased-array catheter (all P < 0.05). There were no significant differences between the catheters during postinterventional IVUS imaging. There were also small but potentially important differences with regards to clinical events and complications associated with the use of the different IVUS catheters during the PCI procedures, reflecting differences in catheter design.

Aged↗
PubMed2001

Incineration and human health. State of knowledge of the impacts of waste incinerators on human health.

After pollutants from an incineration facility disperse into the air, some people close to the facility may be exposed directly through inhalation or indirectly through consumption of food or water contaminated by deposition of the pollutants from air to soil, vegetation, and water. For metals and other pollutants that are very persistent in the environment, the potential effects may extend well beyond the area close to the incinerator. Persistent pollutants can be carried long distances from their emission sources, go through various chemical and physical transformations, and pass numerous times through soil, water, or food.

Environmental Health↗
PubMed2001

Anaerobic codigestion of hog and poultry waste.

Anaerobic batch tests were performed using hog and poultry wastes in various proportions. Treatments that received both wastes produced higher yields of biogas, up to 200 +/- 30 mL/g volatile solids (VS) destroyed, and methane, up to 130 +/- 20 mL/g VS destroyed, compared to either waste alone.

Anaerobiosis↗
PubMed2001

Effects of ethanol and naltrexone in a model of traumatic brain injury with hemorrhagic shock.

BACKGROUND: Ethanol predisposes to traumatic injury and causes respiratory depression and cardiovascular compromise in models of traumatic brain injury (TBI) and hemorrhagic shock (HS). Endogenous opioids may play a role in ethanol intoxication and TBI. We studied the effects of ethanol and the opiate antagonist agent naltrexone (NTX) in a TBI/HS model. METHODS: Fifty-six pigs (20 kg) were anesthetized with isoflurane, intubated, instrumented, and subjected to fluid percussion TBI with concurrent 30 ml/kg hemorrhage over 30 min. Seven groups were studied: Control, EtOH, NTX, INJ, INJ/EtOH, INJ/NTX, and INJ/EtOH/NTX. Ethanol (2 g/kg IV) was given preinjury, followed by infusion of 0.4 g/kg/hr. NTX 0.3 mg/kg intravenous was given 5 min postinjury. Parameters monitored for 120 min postinjury included minute ventilation (VE), blood pressure (MAP), cerebral perfusion pressure (CPP), cerebral venous lactate (Lac), arterial and cerebral venous blood gases, and brain tissue PtiO2. RESULTS: Ethanol levels at injury were 220 mg/dL. Ethanol-treated animals had depression of hypercapnic ventilatory response, which was reversed by administration of naltrexone. MAP and CPP were significantly lower in injured animals, but were not significantly improved by NTX. Cerebral venous pH was lower and lactate was higher in ethanol-treated animals. CONCLUSION: In this TBI/HS model, NTX reverses ethanol-induced depression of hypercapnic ventilatory response but does not improve MAP, CPP, or metabolic acidosis. This suggests that the respiratory effects of ethanol in TBI, but not the hemodynamic effects, may be mediated by opiate receptor activation.

Animals↗
PubMed2000

Timing of the Last Glacial Maximum from observed sea-level minima

During the Last Glacial Maximum, ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today. But few direct estimates exist of the volume of the ice sheets, or the timing and rates of change during their advance and retreat. Here we analyse four distinct sediment facies in the shallow, tectonically stable Bonaparte Gulf, Australia--each of which is characteristic of a distinct range in sea level--to estimate the maximum volume of land-based ice during the last glaciation and the timing of the initial melting phase. We use faunal assemblages and preservation status of the sediments to distinguish open marine, shallow marine, marginal marine and brackish conditions, and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio-hydro-isostatic modelling. Our results indicate that from at least 22,000 to 19,000 (calendar) years before present, land-based ice volume was at its maximum, exceeding today's grounded ice sheets by 52.5 x 10(6) km. A rapid decrease in ice volume by about 10% within a few hundred years terminated the Last Glacial Maximum at 19,000 +/- 250 years.

Journal Article↗
PubMed2000

Nurses' perceptions of the reliability of an automated medication dispensing system.

Automated medication dispensing systems (AMDS) technology is increasingly being implemented in health care facilities to reduce the risk of medication errors. However, the case study evidence of their effectiveness has so far been mixed. It has been suggested that the attitudes of nursing staff toward AMDS can be an important factor in influencing whether or not the technology will be successfully implemented. Nurses' attitudes toward AMDS were examined at Riverview Health Centre, a long-term care facility where the Meditrol automated dispensing system had been installed the previous year. It was found that nurses were generally distrustful of AMDS and skeptical that it had reduced medication errors. A number of technological, organizational, and social factors has been put forward to explain this distrust. In addition, the efforts of hospital administrators to raise nurses' confidence in the system's reliability were also delineated.

Adult↗
PubMed2000

Making EMRs really work: the Southeast Health Center experience.

While electronic medical records (EMRs) have long held the promise of improved efficiency and quality, they have not yet made significant inroads into ambulatory care. One reason may be attempted EMR implementation in "old paradigm" clinic models. Southeast Health Center (SEHC) in Indianapolis, Indiana, began by reengineering its clinic procedures; only then did staff look for a computerized record. Because the new clinic model meshed nicely with the design of a relatively new EMR, a joint project was undertaken to test this EMR in SEHC's unique environment. This article details the reengineering, EMR implementation, project dynamics, results, and lessons learned.

Decision Making, Organizational↗
PubMed1999

Food but not a chemically defined diet interferes with maintenance of intragastric pH at a predefined level using continuous pH-stat-adjusted intravenous infusion of ranitidine in healthy volunteers.

Eight healthy volunteers were used to determine the influence of a normal diet (food) versus an isocaloric chemically defined diet (CDD) on the dose of ranitidine infused continuously over 12 hr, required to maintain the intragastric pH > or = 5 or above. The dose of ranitidine used was adjusted by the pH-stat instrument, Gastrojet, and a target pH of 5.0 was selected. The average ranitidine dose was 43.5 mg for food, 28.3 mg for CDD, and 25.7 mg for fasting. Despite the higher dose of ranitidine used with food, the control of pH was lower than the desired and preset value of pH > or = 5: the average mean pH was 3.99 for food, 5.11 for CDD, and 5.75 for fasting. The percentage of time of pH > or = 5 was 32.0% for food, 73.7% for CDD, and 80.1% for fasting. Thus, when persons are fed a normal diet there is a need for higher doses of ranitidine to maintain the gastric pH > or = 5.0. Even with frequent monitoring of intragastric pH with the Gastrojet, there is much greater variability in pH control with food than with CDD or fasting, and the preset and desired pH level was not achieved. This difficulty in achieving desired end points of pH control when switching from a fasting to a fed state needs to be considered when intravenous ranitidine is used to obtain strict control of intragastric pH.

Adult↗
PubMed1999

The effect of ketamine on 0.25% and 0.125% bupivacaine for caudal epidural blockade in children.

Forty boys aged from one to five years undergoing orchidopexy were randomly allocated to receive one of two solutions for caudal epidural injection. Group A received 1 ml.kg-1 of 0.125% bupivacaine with ketamine 0.5 mg.kg-1 and Group B received 1 ml.kg-1 of bupivacaine 0.25% with ketamine 0.5 mg.kg-1. Postoperative pain was assessed by means of a modified Objective Pain Score and analgesia was administered if this score exceeded four. The median duration of caudal analgesia was 8 h in Group A compared with 9.5 h in Group B (P<0.05). The time taken to recover the ability to walk was a median of two h in Group A and three h in Group B (P<0.05). There were no differences between the groups in the incidence of urinary retention or postoperative sedation.

Acetaminophen↗
PubMed1998

On the trail of Leonardo.

A night course taken almost 25 years ago sparked an interest in Leonardo da Vinci that has become a passion for a London, Ont., neurosurgeon. Dr. Rolando Del Maestro now boasts one of the largest collections of da Vinci artifacts in North America.

Anatomy, Artistic↗