Magnus Harrison

Bio: Magnus Harrison is an academic researcher from Manchester Royal Infirmary. The author has contributed to research in topics: Emergency department & Gastric volvulus. The author has an hindex of 5, co-authored 22 publications receiving 554 citations.

An introduction to power and sample size estimation

Abstract: Previous evidence suggests different cortical areas naturally oscillate at distinct frequencies, reflecting tuning properties of each region. The concurrent use of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) has been used to perturb cortical regions, resulting in an observed post-stimulation response that is maximal at the natural frequency of that region. However, little is known about the spatial extent of TMS-induced activation differences in cortical regions when comparing resting state (passive) versus active task performance. Here, we employed TMS-EEG to directly perturb three cortical areas in the right hemisphere while measuring the resultant changes in maximal evoked frequency in healthy human subjects during a resting state (N=12) and during an active sensorimotor task (N=12). Our results revealed that the brain engages a higher dominant frequency mode when actively engaged in a task, such that the frequency evoked during a task is consistently higher across cortical regions, regardless of the region stimulated. These findings suggest that a distinct characteristic of active performance versus resting state is a higher state of natural cortical frequencies.

Simple nomograms to calculate sample size in diagnostic studies

Abstract: Objectives: To produce an easily understood and accessible tool for use by researchers in diagnostic studies. Diagnostic studies should have sample size calculations performed, but in practice, they are performed infrequently. This may be due to a reluctance on the part of researchers to use mathematical formulae. Methods: Using a spreadsheet, we derived nomograms for calculating the number of patients required to determine the precision of a test's sensitivity or specificity. Results: The nomograms could be easily used to determine the sensitivity and specificity of a test. Conclusions: In addition to being easy to use, the nomogram allows deduction of a missing parameter (number of patients, confidence intervals, prevalence, or sensitivity/specificity) if the other three are known. The nomogram can also be used retrospectively by the reader of published research as a rough estimating tool for sample size calculations.

The diagnosis and management of transient global amnesia in the emergency department.

Abstract: Transient Global Amnesia (TGA) is a benign and temporary loss of anterograde memory with the preservation of remote memories and immediate recall. TGA was first described in 1956 and since then epilepsy, transient ischaemic attacks (TIA), migraine and now intracranial venous stasis have been implicated in its aetiology. Precipitants of TGA include physical exertion and valsalva-like manoeuvres. In order to diagnose TGA the criteria created by Hodge and Warlow in 1990 can be used. This requires the episode of memory loss to be witnessed and involve anterograde amnesia. The patient must not have any evidence of neurological signs or deficits, features of epilepsy, active epilepsy or recent head injury. Finally the episode must have resolved within 24 h. In this case study the patient's symptoms are mistakenly attributed to a TIA. There is no increased risk of TIA or CVA in patients who have had TGA and there are no increased levels of mortality amongst these patients. In this article we aim to help doctors working in the emergency department to diagnose and manage TGA.

Analgesia and assessment of abdominal pain

Abstract: Report by Kevin Mackway-Jones, Consultant Search checked by Magnus Harrison Research Fellow A 12 year old girl presents to the emergency department with “tummy ache”. The history and examination are suggestive of appendicitis. You call the surgical team but they are unable to …

Endotracheal intubation in γ-hydroxybutyric acid intoxication and overdose

Abstract: A short cut review was carried out to establish whether intubation is always required in patients presenting with a decreased conscious level after γ-hydroxybutyrate ingestion. Altogether 95 papers were found using the reported search, of which two presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated.

How to calculate sample size in animal studies

Abstract: Calculation of sample size is one of the important component of design of any research including animal studies. If a researcher select less number of animals it may lead to missing of any significant difference even if it exist in population and if more number of animals selected then it may lead to unnecessary wastage of resources and may lead to ethical issues. In this article, on the basis of review of literature done by us we suggested few methods of sample size calculations for animal studies.

Identifying individuals with physcian diagnosed COPD in health administrative databases.

Abstract: Chronic Obstructive Pulmonary Disease (COPD) is a common chronic respiratory disease responsible for significant morbidity and mortality. Population-based health administrative databases provide a powerful and unbiased way of studying COPD in the population, however, their ability to accurately identify patients with this disease must first be confirmed. The objective was to validate population-based health administrative definitions of COPD. Previously abstracted medical records of adults over the age of 35 randomly selected from primary care practices in Ontario, Canada were reviewed by an expert panel to establish if an individual did or did not have a diagnosis of COPD. These reference designations were then linked to each individual's respective health administrative database record and compared with predefine health administrative data definitions of COPD. Concepts of diagnostic test evaluation were used to calculate and compare their test characteristics. The most sensitive health administrative definition of COPD was 1 or more ambulatory claims and/or 1 or more hospitalizations for COPD that yielded a sensitivity of 85.0% (95% confidence interval 77.0 to 91.0) and a specificity of 78.4% (95% confidence interval 73.6 to 82.7). As number of ambulatory claims in the definition increased, sensitivity decreased and specificity increased. Individuals with COPD can be accurately identified in health administrative data, and therefore it may be used to create an unbiased population cohort for surveillance and research. This offers a powerful means of generating evidence to inform strategies that optimize the prevention and management of COPD.

Non-invasive early detection of cancer four years before conventional diagnosis using a blood test.

Abstract: Early detection has the potential to reduce cancer mortality, but an effective screening test must demonstrate asymptomatic cancer detection years before conventional diagnosis in a longitudinal study. In the Taizhou Longitudinal Study (TZL), 123,115 healthy subjects provided plasma samples for long-term storage and were then monitored for cancer occurrence. Here we report the preliminary results of PanSeer, a noninvasive blood test based on circulating tumor DNA methylation, on TZL plasma samples from 605 asymptomatic individuals, 191 of whom were later diagnosed with stomach, esophageal, colorectal, lung or liver cancer within four years of blood draw. We also assay plasma samples from an additional 223 cancer patients, plus 200 primary tumor and normal tissues. We show that PanSeer detects five common types of cancer in 88% (95% CI: 80–93%) of post-diagnosis patients with a specificity of 96% (95% CI: 93–98%), We also demonstrate that PanSeer detects cancer in 95% (95% CI: 89–98%) of asymptomatic individuals who were later diagnosed, though future longitudinal studies are required to confirm this result. These results demonstrate that cancer can be non-invasively detected up to four years before current standard of care. Patients whose disease is diagnosed in its early stages have better outcomes. In this study, the authors develop a non invasive blood test based on circulating tumor DNA methylation that can potentially detect cancer occurrence even in asymptomatic patients.