Effect of interventions including provision of personalised cancer risk information on accuracy of risk perception and psychological responses: A systematic review and meta-analysis

OBJECTIVE

To synthesize the literature on the effect of provision of personalised cancer risk information to individuals at population level risk on accuracy of risk perception and psychological responses.

METHODS

A systematic review and random effects meta-analysis of articles published from 01/01/2000 to 01/07/2017.

RESULTS

We included 23 studies. Immediately after provision of risk information 87% of individuals were able to recall the absolute risk estimate. Less than half believed that to be their risk, with up to 71% believing their risk to be higher than the estimate. Provision of risk information increased accuracy of perceived absolute risk immediately after risk information compared with no information (pooled RR 4.16 (95%CI 1.28-13.49), 3 studies). There was no significant effect on comparative risk accuracy (pooled RR 1.39 (0.72-2.69), 2 studies) and either no change or a reduction in cancer worry, anxiety and fear.

CONCLUSION

These findings highlight the complex cognitive processes involved in the conceptualisation of risk.

PRACTICE IMPLICATIONS

Individuals who appear to understand and are able to recall risk information most likely do not believe it reflects their own risk.

Colorectal cancer screening with faecal immunochemical testing, sigmoidoscopy or colonoscopy: a clinical practice guideline

CLINICAL QUESTION

Recent 15-year updates of sigmoidoscopy screening trials provide new evidence on the effectiveness of colorectal cancer screening. Prompted by the new evidence, we asked: "Does colorectal cancer screening make an important difference to health outcomes in individuals initiating screening at age 50 to 79? And which screening option is best?"

CURRENT PRACTICE

Numerous guidelines recommend screening, but vary on recommended test, age and screening frequency. This guideline looks at the evidence and makes recommendations on screening for four screening options: faecal immunochemical test (FIT) every year, FIT every two years, a single sigmoidoscopy, or a single colonoscopy.

RECOMMENDATIONS

These recommendations apply to adults aged 50-79 years with no prior screening, no symptoms of colorectal cancer, and a life expectancy of at least 15 years. For individuals with an estimated 15-year colorectal cancer risk below 3%, we suggest no screening (weak recommendation). For individuals with an estimated 15-year risk above 3%, we suggest screening with one of the four screening options: FIT every year, FIT every two years, a single sigmoidoscopy, or a single colonoscopy (weak recommendation). With our guidance we publish the linked research, a graphic of the absolute harms and benefits, a clear description of how we reached our value judgments, and linked decision aids.

HOW THIS GUIDELINE WAS CREATED

A guideline panel including patients, clinicians, content experts and methodologists produced these recommendations using GRADE and in adherence with standards for trustworthy guidelines. A linked systematic review of colorectal cancer screening trials and microsimulation modelling were performed to inform the panel of 15-year screening benefits and harms. The panel also reviewed each screening option's practical issues and burdens. Based on their own experience, the panel estimated the magnitude of benefit typical members of the population would value to opt for screening and used the benefit thresholds to inform their recommendations.

THE EVIDENCE

Overall there was substantial uncertainty (low certainty evidence) regarding the 15-year benefits, burdens and harms of screening. Best estimates suggested that all four screening options resulted in similar colorectal cancer mortality reductions. FIT every two years may have little or no effect on cancer incidence over 15 years, while FIT every year, sigmoidoscopy, and colonoscopy may reduce cancer incidence, although for FIT the incidence reduction is small compared with sigmoidoscopy and colonoscopy. Screening related serious gastrointestinal and cardiovascular adverse events are rare. The magnitude of the benefits is dependent on the individual risk, while harms and burdens are less strongly associated with cancer risk.

UNDERSTANDING THE RECOMMENDATION

Based on benefits, harms, and burdens of screening, the panel inferred that most informed individuals with a 15-year risk of colorectal cancer of 3% or higher are likely to choose screening, and most individuals with a risk of below 3% are likely to decline screening. Given varying values and preferences, optimal care will require shared decision making.

Risk Prediction Models for Colorectal Cancer Incorporating Common Genetic Variants: A Systematic Review

Colorectal cancer screening reduces colorectal cancer incidence and mortality. Risk models based on phenotypic variables have relatively good discrimination in external validation and may improve efficiency of screening. Models incorporating genetic variables may perform better. In this review, we updated our previous review by searching Medline and EMBASE from the end date of that review (January 2014) to February 2019 to identify models incorporating at least one SNP and applicable to asymptomatic individuals in the general population. We identified 23 new models, giving a total of 29. Of those in which the SNP selection was on the basis of published genome-wide association studies, in external or split-sample validation the AUROC was 0.56 to 0.57 for models that included SNPs alone, 0.61 to 0.63 for SNPs in combination with other risk factors, and 0.56 to 0.70 when age was included. Calibration was only reported for four. The addition of SNPs to other risk factors increases discrimination by 0.01 to 0.06. Public health modeling studies suggest that, if determined by risk models, the range of starting ages for screening would be several years greater than using family history alone. Further validation and calibration studies are needed alongside modeling studies to assess the population-level impact of introducing genetic risk-based screening programs.

Effect of communicating phenotypic and genetic risk of coronary heart disease alongside web-based lifestyle advice: the INFORM Randomised Controlled Trial

Objective

To determine whether provision of web-based lifestyle advice and coronary heart disease risk information either based on phenotypic characteristics or phenotypic plus genetic characteristics affects changes in objectively measured health behaviours.

Methods

A parallel-group, open randomised trial including 956 male and female blood donors with no history of cardiovascular disease (mean [SD] age=56.7 [8.8] years) randomised to four study groups: control group (no information provided); web-based lifestyle advice only (lifestyle group); lifestyle advice plus information on estimated 10-year coronary heart disease risk based on phenotypic characteristics (phenotypic risk estimate) (phenotypic group) and lifestyle advice plus information on estimated 10-year coronary heart disease risk based on phenotypic (phenotypic risk estimate) and genetic characteristics (genetic risk estimate) (genetic group). The primary outcome was change in physical activity from baseline to 12 weeks assessed by wrist-worn accelerometer.

Results

928 (97.1%) participants completed the trial. There was no evidence of intervention effects on physical activity (difference in adjusted mean change from baseline): lifestyle group vs control group 0.09 milligravity (mg) (95% CI −1.15 to 1.33); genetic group vs phenotypic group −0.33 mg (95% CI −1.55 to 0.90); phenotypic group and genetic group vs control group −0.52 mg (95% CI −1.59 to 0.55) and vs lifestyle group −0.61 mg (95% CI −1.67 to 0.46). There was no evidence of intervention effects on secondary biological, emotional and health-related behavioural outcomes except self-reported fruit and vegetable intake.

Conclusions

Provision of risk information, whether based on phenotypic or genotypic characteristics, alongside web-based lifestyle advice did not importantly affect objectively measured levels of physical activity, other health-related behaviours, biological risk factors or emotional well-being.

Trial registration number

ISRCTN17721237; Pre-results.

Development and Validation of Lifestyle-Based Models to Predict Incidence of the Most Common Potentially Preventable Cancers

BACKGROUND

Most risk models for cancer are either specific to individual cancers or include complex or predominantly non-modifiable risk factors.

METHODS

We developed lifestyle-based models for the five cancers for which the most cases are potentially preventable through lifestyle change in the UK (lung, colorectal, bladder, kidney, and esophageal for men and breast, lung, colorectal, endometrial, and kidney for women). We selected lifestyle risk factors from the European Code against Cancer and obtained estimates of relative risks from meta-analyses of observational studies. We used mean values for risk factors from nationally representative samples and mean 10-year estimated absolute risks from routinely available sources. We then assessed the performance of the models in 23,768 participants in the EPIC-Norfolk cohort who had no history of the five selected cancers at baseline.

RESULTS

In men, the combined risk model showed good discrimination [AUC, 0.71; 95% confidence interval (CI), 0.69-0.73] and calibration. Discrimination was lower in women (AUC, 0.59; 95% CI, 0.57-0.61), but calibration was good. In both sexes, the individual models for lung cancer had the highest AUCs (0.83; 95% CI, 0.80-0.85 for men and 0.82; 95% CI, 0.76-0.87 for women). The lowest AUCs were for breast cancer in women and kidney cancer in men.

CONCLUSIONS

The discrimination and calibration of the models are both reasonable, with the discrimination for individual cancers comparable or better than many other published risk models.

IMPACT

These models could be used to demonstrate the potential impact of lifestyle change on risk of cancer to promote behavior change.

The associations between the response efficacy and objective and subjective change in physical activity and diet in the Information and Risk Modification trial

OBJECTIVES

Many health promotion campaigns and interventions focussing on improving health-related behaviours have been based on targeting response efficacy. This is based on the assumption that response efficacy is an important modifiable determinant of behaviour change. This study aimed to quantify the association between response efficacy and objective and subjective measures of physical activity and diet.

STUDY DESIGN

Prospective cohort analysis of data from a randomised controlled trial.

METHODS

A total of 953 participants were assessed for response efficacy at baseline and 12 weeks following randomisation to interventions to increase physical activity and improve diet. Subjective measures were collected via a self-report questionnaire that included two questions used to derive the Cambridge Index of physical activity and questions about daily or weekly fruit and vegetable, whole grain, meat and fish intake, based on the dietary guidelines to lower cardiovascular risk. Objective measures were quantified using accelerometers and plasma carotenoids.

RESULTS

The mean change in response efficacy for physical activity was +0.5 (standard deviation [SD] 2.0) and for diet was +0.5 (SD 2.1).There were no clinically or statistically significant associations between baseline or change in response efficacy and objective and subjective measures of physical activity or objective measures of diet. There was a small statistically significant association between baseline response efficacy and change in self-reported wholegrain consumption, but this is unlikely to be clinically significant.

CONCLUSIONS

Response efficacy is not a fundamental determinant of diet and physical activity and should not be the main focus of interventions targeting these behaviours.

Delivery and impact of the NHS Health Check in the first 8 years: a systematic review

BACKGROUND

Since 2009, all eligible persons in England have been entitled to an NHS Health Check. Uncertainty remains about who attends, and the health-related impacts.

AIM

To review quantitative evidence on coverage (the proportion of eligible individuals who attend), uptake (proportion of invitees who attend), and impact of NHS Health Checks.

DESIGN AND SETTING

A systematic review and quantitative data synthesis. Included were studies or data reporting coverage or uptake and studies reporting any health-related impact that used an appropriate comparison group or before- and-after study design.

METHOD

Eleven databases and additional internet sources were searched to November 2016.

RESULTS

Twenty-six observational studies and one additional dataset were included. Since 2013, 45.6% of eligible individuals have received a health check. Coverage is higher among older people, those with a family history of coronary heart disease, those living in the most deprived areas, and some ethnic minority groups. Just under half (48.2%) of those invited have taken up the invitation. Data on uptake and impact (especially regarding health-related behaviours) are limited. Uptake is higher in older people and females, but lower in those living in the most deprived areas. Attendance is associated with small increases in disease detection, decreases in modelled cardiovascular disease risk, and increased statin and antihypertensive prescribing.

CONCLUSION

Published attendance, uptake, and prescribing rates are all lower than originally anticipated, and data on impact are limited, with very few studies reporting the effect of attendance on health-related behaviours. High-quality studies comparing matched attendees and non-attendees and health economic analyses are required.

A randomised controlled trial of the effect of providing online risk information and lifestyle advice for the most common preventable cancers: study protocol

BACKGROUND

Cancer is a leading cause of mortality and morbidity worldwide. Prevention is recognised by many, including the World Health Organization, to offer the most cost-effective long-term strategy for the control of cancer. One approach that focuses on individuals is the provision of personalised risk information. However, whether such information motivates behaviour change and whether the effect is different with varying formats of risk presentation is unclear. We aim to assess the short-term effect of providing information about personalised risk of cancer in three different formats alongside lifestyle advice on health-related behaviours, risk perception and risk conviction.

METHODS

In a parallel group, randomised controlled trial 1000 participants will be recruited through the online platform Prolific. Participants will be allocated to either a control group receiving cancer-specific lifestyle advice alone or one of three intervention groups receiving the same lifestyle advice alongside their estimated 10-year risk of developing one of the five most common preventable cancers, calculated from self-reported modifiable behavioural risk factors, in one of three different formats (bar chart, pictograph or qualitative scale). The primary outcome is change from baseline in computed risk relative to an individual with a recommended lifestyle at three months. Secondary outcomes include: perceived risk of cancer; anxiety; cancer-related worry; intention to change behaviour; and awareness of cancer risk factors.

DISCUSSION

This study will provide evidence on the short-term effect of providing online information about personalised risk of cancer alongside lifestyle advice on risk perception and health-related behaviours and inform the development of interventions.

TRIAL REGISTRATION

ISRCTN17450583. Registered 30 January 2018.

Expert Elicitation of Multinomial Probabilities for Decision-Analytic Modeling: An Application to Rates of Disease Progression in Undiagnosed and Untreated Melanoma

BACKGROUND

Expert elicitation is required to inform decision making when relevant "better quality" data either do not exist or cannot be collected. An example of this is to inform decisions as to whether to screen for melanoma. A key input is the counterfactual, in this case the natural history of melanoma in patients who are undiagnosed and hence untreated.

OBJECTIVES

To elicit expert opinion on the probability of disease progression in patients with melanoma that is undetected and hence untreated.

METHODS

A bespoke webinar-based expert elicitation protocol was administered to 14 participants in the United Kingdom, Australia, and New Zealand, comprising 12 multinomial questions on the probability of progression from one disease stage to another in the absence of treatment. A modified Connor-Mosimann distribution was fitted to individual responses to each question. Individual responses were pooled using a Monte-Carlo simulation approach. Participants were asked to provide feedback on the process.

RESULTS

A pooled modified Connor-Mosimann distribution was successfully derived from participants' responses. Feedback from participants was generally positive, with 86% willing to take part in such an exercise again. Nevertheless, only 57% of participants felt that this was a valid approach to determine the risk of disease progression. Qualitative feedback reflected some understanding of the need to rely on expert elicitation in the absence of "hard" data.

CONCLUSIONS

We successfully elicited and pooled the beliefs of experts in melanoma regarding the probability of disease progression in a format suitable for inclusion in a decision-analytic model.

A Modeling Study of the Cost-Effectiveness of a Risk-Stratified Surveillance Program for Melanoma in the United Kingdom

BACKGROUND

Population-wide screening for melanoma is unlikely to be cost-effective. Nevertheless, targeted surveillance of high-risk individuals may be.

OBJECTIVES

To estimate the cost-effectiveness of various surveillance strategies in the UK population, stratified by risk using a simple self-assessment tool scoring between 0 and 67.

METHODS

A decision model comparing alternative surveillance policies from the perspective of the UK National Health Service over 30 years was developed. The strategy with the highest expected net benefit for each risk score was identified, resulting in a compound risk-stratified policy describing the most cost-effective population-wide strategy. The overall expected cost and quality-adjusted life-years (QALYs), the incremental cost-effectiveness ratio, and associated uncertainty were reported.

RESULTS

The most cost-effective strategy is for those with a Williams score of 15 to 21 (relative risk [RR] of 0.79-1.60 vs. a mean score of 17 in the United Kingdom) to be offered a one-off full-body skin examination, and for those with a score of 22 or more (RR 1.79+) to be enrolled into a quinquennial monitoring program, rising to annual recall for those with a risk score greater than 43 (RR 20.95+). Expected incremental cost would be £164 million per annum (~0.1% of the National Health Service budget), gaining 15,947 additional QALYs and yielding an incremental cost-effectiveness ratio of £10,199/QALY gained (51.3% probability <£30,000).

CONCLUSIONS

The risk-stratified policy would be expensive to implement but cost-effective compared with typical UK thresholds (£20,000-£30,000/QALY gained), although decision uncertainty is high. Phased implementation enrolling only higher risk individuals would be substantially less expensive, but with consequent foregone health gain.

External validation of risk prediction models for incident colorectal cancer using UK Biobank

BACKGROUND

This study aimed to compare and externally validate risk scores developed to predict incident colorectal cancer (CRC) that include variables routinely available or easily obtainable via self-completed questionnaire.

METHODS

External validation of fourteen risk models from a previous systematic review in 373 112 men and women within the UK Biobank cohort with 5-year follow-up, no prior history of CRC and data for incidence of CRC through linkage to national cancer registries.

RESULTS

There were 1719 (0.46%) cases of incident CRC. The performance of the risk models varied substantially. In men, the QCancer10 model and models by Tao, Driver and Ma all had an area under the receiver operating characteristic curve (AUC) between 0.67 and 0.70. Discrimination was lower in women: the QCancer10, Wells, Tao, Guesmi and Ma models were the best performing with AUCs between 0.63 and 0.66. Assessment of calibration was possible for six models in men and women. All would require country-specific recalibration if estimates of absolute risks were to be given to individuals.

CONCLUSIONS

Several risk models based on easily obtainable data have relatively good discrimination in a UK population. Modelling studies are now required to estimate the potential health benefits and cost-effectiveness of implementing stratified risk-based CRC screening.

Effect of interventions incorporating personalised cancer risk information on intentions and behaviour: a systematic review and meta-analysis of randomised controlled trials

OBJECTIVE

To provide a comprehensive review of the impact on intention to change health-related behaviours and health-related behaviours themselves, including screening uptake, of interventions incorporating information about cancer risk targeted at the general adult population.

DESIGN

A systematic review and random-effects meta-analysis.

DATA SOURCES

An electronic search of MEDLINE, EMBASE, CINAHL and PsycINFO from 1 January 2000 to 1 July 2017.

INCLUSION CRITERIA

Randomised controlled trials of interventions including provision of a personal estimate of future cancer risk based on two or more non-genetic variables to adults recruited from the general population that include at least one behavioural outcome.

RESULTS

We included 19 studies reporting 12 outcomes. There was significant heterogeneity in interventions and outcomes between studies. There is evidence that interventions incorporating personalised cancer risk information do not affect intention to attend or attendance at screening (relative risk 1.00 (0.97-1.03)). There is limited evidence that they increase smoking abstinence, sun protection, adult skin self-examination and breast examination, and decrease intention to tan. However, they do not increase smoking cessation, parental child skin examination or intention to protect skin. No studies assessed changes in diet, alcohol consumption or physical activity.

CONCLUSIONS

Interventions incorporating personalised cancer risk information do not affect uptake of screening, but there is limited evidence of effect on some health-related behaviours. Further research, ideally including objective measures of behaviour, is needed before cancer risk information is incorporated into routine practice for health promotion in the general population.

Risk accuracy of type 2 diabetes in middle aged adults: Associations with sociodemographic, clinical, psychological and behavioural factors

OBJECTIVE

To identify the proportion of individuals with an accurate perception of their risk of type 2 diabetes (T2D) prior to, immediately after and eight weeks after receiving a personalised risk estimate. Additionally, we aimed to explore what factors are associated with underestimation and overestimation immediately post-intervention.

METHODS

Cohort study based on the data collected in the Diabetes Risk Communication Trial. We included 379 participants (mean age 48.9 (SD 7.4) years; 55.1% women) who received a genotypic or phenotypic risk estimate for T2D.

RESULTS

While only 1.3% of participants perceived their risk accurately at baseline, this increased to 24.7% immediately after receiving a risk estimate and then dropped to 7.3% at eight weeks. Those who overestimated their risk at baseline continued to overestimate it, whereas those who underestimated their risk at baseline improved their risk accuracy. We did not identify any other characteristics associated with underestimation or overestimation immediately after receiving a risk estimate.

CONCLUSION

Understanding a received risk estimate is challenging for most participants with many continuing to have inaccurate risk perception after receiving the estimate.

PRACTICE IMPLICATIONS

Individuals who overestimate or underestimate their T2D risk before receiving risk information might require different approaches for altering their risk perception.

Responses to provision of personalised cancer risk information: a qualitative interview study with members of the public

BACKGROUND

It is estimated that nearly 600,000 cancer cases in the UK could have been avoided in the past five years if people had healthier lifestyles. A number of theories of behaviour change suggest that before people will change health behaviours, they must accept that a risk applies to them. This study aimed to explore the views of the public on receiving personalised cancer risk information and the potential for that information to motivate behaviour change.

METHODS

We conducted 27 interviews with members of the public (mean age 49 ± 23 years). Each participant completed a questionnaire to allow calculation of their risk of developing the most common cancers (10 for women, 8 for men). During the interviews we presented their risk using a web-based tool developed for the study and discussions covered their views on receiving that information. Each interview was audio-recorded and then analysed using thematic analysis.

RESULTS

Participants generally viewed the concept of personalised cancer risk positively. The first reaction of almost all when presented with their 10-year risk of an individual cancer without any further context was that it was low and not concerning. Views on what constituted a high risk ranged widely, from 0.5 to 60%. All felt seeing the impact of changes in lifestyle was helpful. For some this led to intentions to change behaviour, but reductions in risk were not always motivating as the risks were considered low and differences small.

CONCLUSIONS

Provision of personalised cancer risk was well received and may be a useful addition to other cancer prevention initiatives. Further work is needed in particular to develop ways to present cancer risk that reflect the general perception of what constitutes a risk high enough to motivate behaviour change and help patients contextualise a less well known health risk by providing a frame of reference.

Views of commissioners, managers and healthcare professionals on the NHS Health Check programme: a systematic review

OBJECTIVE

To synthesise data concerning the views of commissioners, managers and healthcare professionals towards the National Health Service (NHS) Health Check programme in general and the challenges faced when implementing it in practice.

DESIGN

A systematic review of surveys and interview studies with a descriptive analysis of quantitative data and thematic synthesis of qualitative data.

DATA SOURCES

An electronic literature search of MEDLINE, Embase, Health Management Information Consortium, Cumulative Index of Nursing and Allied Health Literature, Global Health, PsycInfo, Web of Science, OpenGrey, the Cochrane Library, NHS Evidence, Google Scholar, Google, ClinicalTrials.gov and the International Standard Randomised Controlled Trial Number registry from 1 January 1996 to 9 November 2016 with no language restriction and manual screening of reference lists of all included papers.

INCLUSION CRITERIA

Primary research reporting views of commissioners, managers or healthcare professionals on the NHS Health Check programme and its implementation in practice.

RESULTS

Of 18 524 citations, 15 articles met the inclusion criteria. There was evidence from both quantitative and qualitative studies that some commissioners and general practice (GP) healthcare professionals were enthusiastic about the programme, whereas others raised concerns around inequality of uptake, the evidence base and cost-effectiveness. In contrast, those working in pharmacies were all positive about programme benefits, citing opportunities for their business and staff. The main challenges to implementation were: difficulties with information technology and computer software, resistance to the programme from some GPs, the impact on workload and staffing, funding and training needs. Inadequate privacy was also a challenge in pharmacy and community settings, along with difficulty recruiting people eligible for Health Checks and poor public access to some venues.

CONCLUSIONS

The success of the NHS Health Check Programme relies on engagement by those responsible for its commissioning, management and delivery. Recognising and addressing the challenges identified in this review, in particular the concerns of GPs, are important for the future of the programme.

Factors Associated With Engagement With a Web-Based Lifestyle Intervention Following Provision of Coronary Heart Disease Risk: Mixed Methods Study

Background

Web-based interventions provide the opportunity to combine the tailored approach of face-to-face interventions with the scalability and cost-effectiveness of public health interventions. This potential is often limited by low engagement. A number of studies have described the characteristics of individuals who engage more in Web-based interventions but few have explored the reasons for these variations.

Objective

We aimed to explore individual-level factors associated with different degrees of engagement with a Web-based behavior change intervention following provision of coronary heart disease (CHD) risk information, and the barriers and facilitators to engagement.

Methods

This study involved the secondary analysis of data from the Information and Risk Modification Trial, a randomized controlled trial of a Web-based lifestyle intervention alone, or alongside information on estimated CHD risk. The intervention consisted of three interactive sessions, each lasting up to 60 minutes, delivered at monthly intervals. Participants were characterized as high engagers if they completed all three sessions. Thematic analysis of qualitative data from interviews with 37 participants was combined with quantitative data on usage of the Web-based intervention using a mixed-methods matrix, and data on the views of the intervention itself were analyzed across all participants.

Results

Thirteen participants were characterized as low engagers and 24 as high engagers. There was no difference in age (P=.75), gender (P=.95), or level of risk (P=.65) between the groups. Low engagement was more often associated with: (1) reporting a negative emotional reaction in response to the risk score (P=.029), (2) perceiving that the intervention did not provide any new lifestyle information (P=.011), and (3) being less likely to have reported feeling an obligation to complete the intervention as part of the study (P=.019). The mixed-methods matrix suggested that there was also an association between low engagement and less success with previous behavior change attempts, but the statistical evidence for this association was weak (P=.16). No associations were seen between engagement and barriers or facilitators to health behavior change, or comments about the design of the intervention itself. The most commonly cited barriers related to issues with access to the intervention itself: either difficulties remembering the link to the site or passwords, a perceived lack of flexibility within the website, or lack of time. Facilitators included the nonjudgmental presentation of lifestyle information, the use of simple language, and the personalized nature of the intervention.

Conclusions

This study shows that the level of engagement with a Web-based intervention following provision of CHD risk information is not influenced by the level of risk but by the individual’s response to the risk information, their past experiences of behavior change, the extent to which they consider the lifestyle information helpful, and whether they felt obliged to complete the intervention as part of a research study. A number of facilitators and barriers to Web-based interventions were also identified, which should inform future interventions.

Patient experience of NHS health checks: a systematic review and qualitative synthesis

OBJECTIVE

To review the experiences of patients attending NHS Health Checks in England.

DESIGN

A systematic review of quantitative and qualitative studies with a thematic synthesis of qualitative studies.

DATA SOURCES

An electronic literature search of Medline, Embase, Health Management Information Consortium, Cumulative Index of Nursing and Allied Health Literature, Global Health, PsycInfo, Web of Science, OpenGrey, the Cochrane Library, National Health Service (NHS) Evidence, Google Scholar, Google, Clinical Trials.gov and the ISRCTN registry to 09/11/16 with no language restriction and manual screening of reference lists of all included papers.

INCLUSION CRITERIA

Primary research reporting experiences of patients who have attended NHS Health Checks.

RESULTS

20 studies met the inclusion criteria, 9 reporting quantitative data and 15 qualitative data. There were consistently high levels of reported satisfaction in surveys, with over 80% feeling that they had benefited from an NHS Health Check. Data from qualitative studies showed that the NHS Health Check had been perceived to act as a wake-up call for many who reported having gone on to make substantial lifestyle changes which they attributed to the NHS Health Check. However, some had been left with a feeling of unmet expectations, were confused about or unable to remember their risk scores, found the lifestyle advice too simplistic and non-personalised or were confused about follow-up.

CONCLUSIONS

While participants were generally very supportive of the NHS Health Check programme and examples of behaviour change were reported, there are a number of areas where improvements could be made. These include greater clarity around the aims of the programme within the promotional material, more proactive support for lifestyle change and greater appreciation of the challenges of communicating risk and the limitations of relying on the risk score alone as a trigger for facilitating behaviour change.

Incorporating cancer risk information into general practice: a qualitative study using focus groups with health professionals

BACKGROUND

It is estimated that approximately 40% of all cases of cancer are attributable to lifestyle factors. Providing people with personalised information about their future risk of cancer may help promote behaviour change.

AIM

To explore the views of health professionals on incorporating personalised cancer risk information, based on lifestyle factors, into general practice.

DESIGN AND SETTING

Qualitative study using data from six focus groups with a total of 24 general practice health professionals from the NHS Nene Clinical Commissioning Group in England.

METHOD

The focus groups were guided by a schedule covering current provision of lifestyle advice relating to cancer and views on incorporating personalised cancer risk information. Data were audiotaped, transcribed verbatim, and then analysed using thematic analysis.

RESULTS

Providing lifestyle advice was viewed as a core activity within general practice but the influence of lifestyle on cancer risk was rarely discussed. The word 'cancer' was seen as a potentially powerful motivator for lifestyle change but the fact that it could generate health anxiety was also recognised. Most focus group participants felt that a numerical risk estimate was more likely to influence behaviour than generic advice. All felt that general practice should provide this information, but there was a clear need for additional resources for it to be offered widely.

CONCLUSION

Study participants were in support of providing personalised cancer risk information in general practice. The findings highlight a number of potential benefits and challenges that will inform the future development of interventions in general practice to promote behaviour change for cancer prevention.

The spectrum effect in tests for risk prediction, screening, and diagnosis

The spectrum effect describes the variation between settings in performance of tests used to predict, screen for, and diagnose disease. In particular, the predictive use of a test may be different when it is applied in a general population rather than in the study sample in which it was first developed. This article discusses the impact of the spectrum effect on measures of test performance, and its implications for the development, evaluation, application, and implementation of such tests.

Risk prediction models for colorectal cancer in people with symptoms: a systematic review

Background

Colorectal cancer (CRC) is the fourth leading cause of cancer-related death in Europe and the United States. Detecting the disease at an early stage improves outcomes. Risk prediction models which combine multiple risk factors and symptoms have the potential to improve timely diagnosis. The aim of this review is to systematically identify and compare the performance of models that predict the risk of primary CRC among symptomatic individuals.

Methods

We searched Medline and EMBASE to identify primary research studies reporting, validating or assessing the impact of models. For inclusion, models needed to assess a combination of risk factors that included symptoms, present data on model performance, and be applicable to the general population. Screening of studies for inclusion and data extraction were completed independently by at least two researchers.

Results

Twelve thousand eight hundred eight papers were identified from the literature search and three through citation searching. 18 papers describing 15 risk models were included. Nine were developed in primary care populations and six in secondary care. Four had good discrimination (AUROC > 0.8) in external validation studies, and sensitivity and specificity ranged from 0.25 and 0.99 to 0.99 and 0.46 depending on the cut-off chosen.

Conclusions

Models with good discrimination have been developed in both primary and secondary care populations. Most contain variables that are easily obtainable in a single consultation, but further research is needed to assess clinical utility before they are incorporated into practice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-016-0475-7) contains supplementary material, which is available to authorized users.

Offering statins to a population attending health checks with a 10-year cardiovascular disease risk between 10% and 20

BACKGROUND

In 2014 the UK National Institute for Health and Care Excellence recommended reducing the threshold for offering statin therapy to patients from a 10-year modelled risk of cardiovascular disease (CVD) of 20% to 10%.

AIM

To describe the response of patients in UK primary care with a CVD risk between 10% and 20% to an invitation to attend a consultation to discuss statins.

DESIGN AND SETTING

Review of electronic medical records at one GP practice in the East of England.

METHOD

We invited all patients who had attended an NHS Health Check at the practice, had a QRisk(®) score between 10% and 20%, and were not prescribed statins to attend designated clinics in the practice to discuss starting statins. We reviewed the medical records to identify those who had attended the clinics and those who had chosen to start a statin.

RESULTS

Of 410 patients invited, 100 (24.4%) patients attended the designated clinics and 45 (11%) chose to start a statin. Those who chose to start a statin were older and with a higher QRisk(®) than those who did not. Among those who attended, individuals who started a statin had a higher QRisk(®) than those who did not and were more likely to be current or ex-smokers.

CONCLUSIONS

The proportion choosing to start a statin was substantially lower than previously estimated. Large population-based studies with long-term follow-up are needed to assess the impact on health and workload of this change in guidance.

Impact of provision of cardiovascular disease risk estimates to healthcare professionals and patients: a systematic review

OBJECTIVE

To systematically review whether the provision of information on cardiovascular disease (CVD) risk to healthcare professionals and patients impacts their decision-making, behaviour and ultimately patient health.

DESIGN

A systematic review.

DATA SOURCES

An electronic literature search of MEDLINE and PubMed from 01/01/2004 to 01/06/2013 with no language restriction and manual screening of reference lists of systematic reviews on similar topics and all included papers.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

(1) Primary research published in a peer-reviewed journal; (2) inclusion of participants with no history of CVD; (3) intervention strategy consisted of provision of a CVD risk model estimate to either professionals or patients; and (4) the only difference between the intervention group and control group (or the only intervention in the case of before-after studies) was the provision of a CVD risk model estimate.

RESULTS

After duplicates were removed, the initial electronic search identified 9671 papers. We screened 196 papers at title and abstract level and included 17 studies. The heterogeneity of the studies limited the analysis, but together they showed that provision of risk information to patients improved the accuracy of risk perception without decreasing quality of life or increasing anxiety, but had little effect on lifestyle. Providing risk information to physicians increased prescribing of lipid-lowering and blood pressure medication, with greatest effects in those with CVD risk >20% (relative risk for change in prescribing 2.13 (1.02 to 4.63) and 2.38 (1.11 to 5.10) respectively). Overall, there was a trend towards reductions in cholesterol and blood pressure and a statistically significant reduction in modelled CVD risk (-0.39% (-0.71 to -0.07)) after, on average, 12 months.

CONCLUSIONS

There seems evidence that providing CVD risk model estimates to professionals and patients improves perceived CVD risk and medical prescribing, with little evidence of harm on psychological well-being.

Risk Prediction Models for Colorectal Cancer: A Systematic Review

Colorectal cancer is the second leading cause of cancer-related death in Europe and the United States. Survival is strongly related to stage at diagnosis and population-based screening reduces colorectal cancer incidence and mortality. Stratifying the population by risk offers the potential to improve the efficiency of screening. In this systematic review we searched Medline, EMBASE, and the Cochrane Library for primary research studies reporting or validating models to predict future risk of primary colorectal cancer for asymptomatic individuals. A total of 12,808 papers were identified from the literature search and nine through citation searching. Fifty-two risk models were included. Where reported (n = 37), half the models had acceptable-to-good discrimination (the area under the receiver operating characteristic curve, AUROC >0.7) in the derivation sample. Calibration was less commonly assessed (n = 21), but overall acceptable. In external validation studies, 10 models showed acceptable discrimination (AUROC 0.71-0.78). These include two with only three variables (age, gender, and BMI; age, gender, and family history of colorectal cancer). A small number of prediction models developed from case-control studies of genetic biomarkers also show some promise but require further external validation using population-based samples. Further research should focus on the feasibility and impact of incorporating such models into stratified screening programmes.

The pathway to diagnosis of type 1 diabetes in children: a questionnaire study

OBJECTIVE

To explore the pathway to diagnosis of type 1 diabetes (T1D) in children.

DESIGN

Questionnaire completed by parents.

PARTICIPANTS

Parents of children aged 1 month to 16 years diagnosed with T1D within the previous 3 months.

SETTING

Children and parents from 11 hospitals within the East of England.

RESULTS

88/164 (54%) invited families returned the questionnaire. Children had mean±SD age of 9.41±4.5 years. 35 (39.8%) presented with diabetic ketoacidosis at diagnosis. The most common symptoms were polydipsia (97.7%), polyuria (83.9%), tiredness (75.9%), nocturia (73.6%) and weight loss (64.4%) and all children presented with at least one of those symptoms. The time from symptom onset to diagnosis ranged from 2 to 315 days (median 25 days). Most of this was the appraisal interval from symptom onset until perceiving the need to seek medical advice. Access to healthcare was good but one in five children presenting to primary care were not diagnosed at first encounter, most commonly due to waiting for fasting blood tests or alternative diagnoses. Children diagnosed at first consultation had a shorter duration of symptoms (p=0.022) and children whose parents suspected the diagnosis were 1.3 times more likely (relative risk (RR) 1.3, 95% CI 1.02 to 1.67) to be diagnosed at first consultation.

CONCLUSIONS

Children present with the known symptoms of T1D but there is considerable scope to improve the diagnostic pathway. Future interventions targeted at parents need to address the tendency of parents to find alternative explanations for symptoms and the perceived barriers to access, in addition to symptom awareness.

Risk prediction models for melanoma: a systematic review

Melanoma incidence is increasing rapidly worldwide among white-skinned populations. Earlier diagnosis is the principal factor that can improve prognosis. Defining high-risk populations using risk prediction models may help targeted screening and early detection approaches. In this systematic review, we searched Medline, EMBASE, and the Cochrane Library for primary research studies reporting or validating models to predict risk of developing cutaneous melanoma. A total of 4,141 articles were identified from the literature search and six through citation searching. Twenty-five risk models were included. Between them, the models considered 144 possible risk factors, including 18 measures of number of nevi and 26 of sun/UV exposure. Those most frequently included in final risk models were number of nevi, presence of freckles, history of sunburn, hair color, and skin color. Despite the different factors included and different cutoff values for sensitivity and specificity, almost all models yielded sensitivities and specificities that fit along a summary ROC with area under the ROC (AUROC) of 0.755, suggesting that most models had similar discrimination. Only two models have been validated in separate populations and both also showed good discrimination with AUROC values of 0.79 (0.70-0.86) and 0.70 (0.64-0.77). Further research should focus on validating existing models rather than developing new ones.

'Looking for the needle in the haystack': a qualitative study of the pathway to diagnosis of type 1 diabetes in children

OBJECTIVE

To explore the pathway to diagnosis of type 1 diabetes (T1D) in children from the perspective of the child, family and general practitioner (GP).

DESIGN

Qualitative interview study.

PARTICIPANTS

Parents of children aged 1 month to 16 years diagnosed with new onset T1D within the previous 3 months, children over 6 years diagnosed with new onset T1D within the previous 3 months and GPs who saw those children prior to diagnosis.

SETTING

Children and parents were identified and recruited from two hospitals within the East of England.

RESULTS

The parents of 16 children (2-16 years) were interviewed. The total interval from onset of symptoms to diagnosis ranged from 6 to 127 days. The appraisal interval was the longest for almost all children and the diagnostic interval the shortest. Even with some knowledge of T1D, it took many parents several weeks of a complex cyclical and iterative decision-making process and often a physical trigger, such as weight loss, to decide to consult a healthcare professional. By that stage, many had already made or suspected the diagnosis of T1D themselves. Five GPs were interviewed. They felt that the main challenges to diagnosing T1D in children were the rarity of the condition coupled with how well most of the children appeared, and the difficulty in obtaining urine or blood samples from children.

CONCLUSIONS

This study highlights the difficulties for parents and GPs in recognising the early symptoms of T1D. It suggests that future interventions should be targeted at parents in the appraisal interval and include the importance of timely presentation to a healthcare professional and the differences between types 1 and 2 diabetes. Primary care physicians should also take parental concerns seriously and do urine dipstick tests during the consultation for children with symptoms of T1D.

Variation between countries in the frequency of diabetic ketoacidosis at first presentation of type 1 diabetes in children: a systematic review

AIMS/HYPOTHESIS

Type 1 diabetes is the most frequent endocrine disease in children, with 65,000 children diagnosed worldwide every year. Up to 80% of these children present with diabetic ketoacidosis (DKA), which is associated with both short-term risks and long-term consequences. This study aimed to characterise the worldwide variation in presentation of type 1 diabetes to inform future interventions to reduce this excess morbidity and mortality.

METHODS

This was a systematic review of studies indexed on PubMed, EMBASE, Web of Science, Scopus or CINAHL before March 2011 that included unselected groups of children presenting with new-onset type 1 diabetes, reported the proportion presenting with DKA and used a definition of DKA based on measurement of pH or bicarbonate.

RESULTS

Sixty-five studies of cohorts comprising over 29,000 children in 31 countries were included. The frequency of DKA at diagnosis ranged from 12.8% to 80%, with highest frequencies in the United Arab Emirates, Saudi Arabia and Romania, and the lowest in Sweden, the Slovak Republic and Canada. Multivariable modelling showed the frequency of DKA was inversely associated with gross domestic product, latitude and background incidence of type 1 diabetes.

CONCLUSIONS/INTERPRETATION

This is the first description of the variation in frequency of DKA at presentation of type 1 diabetes in children across countries. It demonstrates large variations that may, at least in part, be explained by different levels of disease awareness and healthcare provision and suggests ways to decrease the excess morbidity and mortality associated with DKA at diagnosis.

Factors associated with the presence of diabetic ketoacidosis at diagnosis of diabetes in children and young adults: a systematic review

OBJECTIVE

To identify the factors associated with diabetic ketoacidosis at diagnosis of type 1 diabetes in children and young adults.

DESIGN

Systematic review.

DATA SOURCES

PubMed, EMBASE, Web of Science, Scopus, and Cinahl and article reference lists.

STUDY SELECTION

Cohort studies including unselected groups of children and young adults presenting with new onset type 1 diabetes that distinguished between those who presented in diabetic ketoacidosis and those who did not and included a measurement of either pH or bicarbonate in the definition of diabetic ketoacidosis. There were no restrictions on language of publication.

RESULTS

46 studies involving more than 24,000 children in 31 countries were included. Together they compared 23 different factors. Factors associated with increased risk were younger age (for <2 years old v older, odds ratio 3.41 (95% confidence interval 2.54 to 4.59), for <5 years v older, odds ratio 1.59 (1.38 to 1.84)), diagnostic error (odds ratio 3.35 (2.35 to 4.79)), ethnic minority, lack of health insurance in the US (odds ratio 3.20 (2.03 to 5.04)), lower body mass index, preceding infection (odds ratio 3.14 (0.94 to 10.47)), and delayed treatment (odds ratio 1.74 (1.10 to 2.77)). Protective factors were having a first degree relative with type 1 diabetes at the time of diagnosis (odds ratio 0.33 (0.08 to 1.26)), higher parental education (odds ratios 0.4 (0.20 to 0.79) and 0.64 (0.43 to 0.94) in two studies), and higher background incidence of type 1 diabetes (correlation coefficient -0.715). The mean duration of symptoms was similar between children presenting with or without diabetic ketoacidosis (16.5 days (standard error 6.2) and 17.1 days (6.0) respectively), and up to 38.8% (285/735) of children who presented with diabetic ketoacidosis had been seen at least once by a doctor before diagnosis.

CONCLUSIONS

Multiple factors affect the risk of developing diabetic ketoacidosis at the onset of type 1 diabetes in children and young adults, and there is potential time, scope, and opportunity to intervene between symptom onset and development of diabetic ketoacidosis for both parents and clinicians.

Risk stratification for sudden cardiac death

Recent advances in pharmacological and device-based therapies have provided a range of management options for patients at risk of sudden cardiac death (SCD). Since all such interventions come with their attendant risks, however, stratification procedures aimed at identifying those who stand to benefit overall have gained a new degree of importance. This review assesses the value of risk stratification measures currently available in clinical practice, as well as of others that may soon enter the market. Parameters that may be obtained only by performing invasive cardiac catheterisation procedures are considered separately from those that may be derived using more readily available non-invasive techniques. It is concluded that effective stratification is likely to require the use of composite parameters and that invasive procedures might only be justified in specific sub-groups of patients.

Control of cell volume in skeletal muscle

Regulation of cell volume is a fundamental property of all animal cells and is of particular importance in skeletal muscle where exercise is associated with a wide range of cellular changes that would be expected to influence cell volume. These complex electrical, metabolic and osmotic changes, however, make rigorous study of the consequences of individual factors on muscle volume difficult despite their likely importance during exercise. Recent charge-difference modelling of cell volume distinguishes three major aspects to processes underlying cell volume control: (i) determination by intracellular impermeant solute; (ii) maintenance by metabolically dependent processes directly balancing passive solute and water fluxes that would otherwise cause cell swelling under the influence of intracellular membrane-impermeant solutes; and (iii) volume regulation often involving reversible short-term transmembrane solute transport processes correcting cell volumes towards their normal baselines in response to imposed discrete perturbations. This review covers, in turn, the main predictions from such quantitative analysis and the experimental consequences of comparable alterations in extracellular pH, lactate concentration, membrane potential and extracellular tonicity. The effects of such alterations in the extracellular environment in resting amphibian muscles are then used to reproduce the intracellular changes that occur in each case in exercising muscle. The relative contributions of these various factors to the control of cell volume in resting and exercising skeletal muscle are thus described.

Membrane potentials in Rana temporaria muscle fibres in strongly hypertonic solutions

Conventional microelectrode methods were used to measure variations in resting membrane potentials, E(m), of intact amphibian skeletal muscle fibres over a wide range of increased extracellular tonicities produced by inclusion of varying extracellular concentrations of sucrose. Moderate increases in extracellular tonicity to up to 2.6x normal (2.6tau) under Cl(-) free conditions produced negative shifts in E(m) that followed expectations for the K(+) Nernst equation (E(K)) applied to a perfect osmometer containing a conserved intracellular K(+) content despite any accompanying cell volume change. In contrast, E(m) remained stable in fibres studied in otherwise similar Cl(-) containing solutions, consistent with E(m) stabilization despite negative shifts in E(K) through inward cation-Cl(-) co-transport activity. Short exposures to higher tonicities (>3tau) similarly produced negative shifts in E(m) in Cl(-) free but not Cl(-) containing solutions. However, prolonged exposures to solutions of >3tau caused gradual net positive changes in E (m) in both Cl(-) containing and Cl(-) free solutions suggesting that these changes were independent of cation-Cl(-) transport. Indeed, there was no evidence of cation-Cl(-) co-transport activity in strongly hypertonic solutions despite its predicted energetic favourability, suggesting its possible regulation by E (m) in muscle. Additional findings implicated a failure to maintain greatly increased transmembrane [K(+)] gradients in these E(m) changes. Thus: (1) halving or doubling [K(+)](e) produced negative or positive shifts in E(m), respectively in isotonic or moderately hypertonic (<2.7tau), but not strongly hypertonic (>3tau) solutions; (2) subsequent restoration of isotonic extracellular conditions produced further positive changes in E(m) consistent with a dilution of the depleted [K(+)](i) by fibres regaining their original resting volumes; (3) quantitative modelling similarly predicted a gradual net efflux of K(+) as the balance between active and passive [K(+)] fluxes altered due to increased transmembrane [K(+)] gradients in hypertonic and low [K(+)](e) solutions. However, the observed positive changes in E(m) in the most strongly hypertonic solutions eventually exceeded these predictions suggesting additional limitations on Na(+)/K(+)-ATPase activity in strongly hypertonic solutions.

Alterations in triad ultrastructure following repetitive stimulation and intracellular changes associated with exercise in amphibian skeletal muscle

This study used Rana temporaria sartorius muscles to examine the effect of fatiguing electrical stimulation on the gap between the T-tubular and sarcoplasmic reticular membranes (T-SR distance) and the T-tubule diameter and compared this with corresponding effects on resting fibres exposed to a range of extracellular conditions that each replicate one of the major changes associated with muscular activity: membrane depolarisation, isotonic volume increase, acidification and intracellular lactate accumulation. Following each treatment, muscles were immersed in isotonic fixative solution and processed for transmission electron microscopy (TEM). Mean T-SR distances were estimated from orthogonal intercepts to provide estimates of diffusion distances between T and SR membranes and T-tubule diameter was estimated by measuring its shortest axis in the sampled J-SR complexes. Measurements from muscles fatigued by low frequency intermittent stimulation showed significant (P << 0.05) reversible increases in both T-SR distance and T-tubule diameter from 15.97 ± 0.37 nm to 20.15 ± 0.56 nm and from 15.44 ± 0.60 nm to 22.26 ± 0.84 nm (n = 40, 30) respectively. Exposure to increasing concentrations of extracellular [K⁺] in the absence of Cl⁻ to produce membrane depolarisation without accompanying cell swelling reduced T-SR distance and increased T-tubule diameter, whilst comparable increases in [K⁺]_e in the presence of Cl⁻ suggested that isotonic cell swelling has the opposite effect. Acidification alone, produced by NH₄Cl addition and withdrawal, also decreased T-SR distance and T-tubule diameter. A similar reduction in T-SR distance occurred following exposure to extracellular Na-lactate where such acidification was accompanied by elevations of intracellular lactate, but these conditions produced a significant swelling of T-tubules attributable to movement of lactate from the cell into the T-tubules. This study thus confirms previous reports of significant increases in T-SR distance and T-tubule diameter following stimulation. However, of membrane depolarisation, isotonic cell swelling, intracellular acidification and lactate accumulation, only isotonic cell swelling increases T-SR distance whilst membrane depolarisation and intracellular lactate likely contribute to the observed increases in T-tubule diameter.

Evaluation of the cost savings and clinical outcomes of switching patients from atorvastatin to simvastatin and losartan to candesartan in a Primary Care setting

This study was carried out in a Primary Care practice in the UK to assess the clinical and practical implications, cost savings and patients' perspective of switching to generic drugs. In the 70 patients switched from atorvastatin to simvastatin there was no significant change in mean total cholesterol 4 months after the switch (4.07 +/- 0.55 mmol/L prior to the switch and 4.10 +/- 0.73 mmol/L post-switch) and only one patient switched back because of side effects. One hundred and fifteen patients were switched from losartan to candesartan. Seven switched back but in those that remained on candesartan there was a small, significant (p = 0.0006), reduction in blood pressure after the switch (138.9/78.7 +/- 13.2/7.0 to 136.3/76.1 +/- 14.7/8.4 mmHg). No adverse events attributable to the switch were reported in either group and the net annualised savings for the year 2005-2006 were 12,715.58 pounds for the statin and 13,374.40 pounds for the antihypertensive switch, respectively.

Alterations in calcium homeostasis reduce membrane excitability in amphibian skeletal muscle

The effects of alterations in intracellular calcium homeostasis on surface membrane excitability were investigated in resting Rana temporaria sartorius muscle. This was prompted by initial results from a fatiguing stimulation protocol study that demonstrated a fibre subpopulation in which action potential generation in response to a standard 1.5 V electrical stimulus failed despite mean membrane potentials [E (m), -69+/-2.3 mV (n=14)] compatible with spike firing in a control set of quiescent muscle fibres. Intracellular micro-electrode recordings showed a similar reversible loss of excitability, attributable to an increased threshold, despite only small (7.1+/-1.8 mV) positive changes in E (m) after approximately 60-min exposures to nominally 0 Ca(2+) Ringer solutions in which Ca(2+) was replaced by Mg(2+). This effect was not reproduced by addition of Mg(2+) to the Ringer solution and persisted under conditions of Cl(-) deprivation. The effects of three pharmacological agents, cyclopiazonic acid (CPA), caffeine and 4-chloro-m-cresol (4-CmC), each known to deplete store Ca(2+) and increase cytosolic Ca(2+) through contrasting mechanisms without influencing E (m), were then investigated. All three agents produced a more rapid, but nevertheless still reversible, loss of membrane excitability than in 0 Ca(2+) Ringer solution alone. This reduction in membrane excitability persisted in fibres studied in solutions containing a normal [Ca(2+)] following prior depletion of store Ca(2+) using CPA- and 4-CmC-containing solutions. These novel findings suggest that sarcoplasmic reticulum Ca(2+) content profoundly influences surface membrane excitability, thereby providing a potential mechanism by which spike firing fails in well-polarised fibres during fatigue.

The influence of intracellular lactate and H+ on cell volume in amphibian skeletal muscle

The combined effects of intracellular lactate and proton accumulation on cell volume, Vc, were investigated in resting Rana temporaria striated muscle fibres. Intracellular lactate and H+ concentrations were simultaneously increased by exposing resting muscle fibres to extracellular solutions that contained 20-80 mm sodium lactate. Cellular H+ and lactate entry was confirmed using pH-sensitive electrodes and 1H-NMR, respectively, and effects on Vc were measured using confocal microscope xz-scanning. Exposure to extracellular lactate up to 80 mm produced significant changes in pH and intracellular lactate (from a pH of 7.24 +/- 0.03, n = 8, and 4.65 +/- 1.07 mm, n = 6, respectively, in control fibres, to 6.59 +/- 0.03, n = 4, and 26.41 +/- 0.92 mm, n = 3, respectively) that were comparable to those observed following fatiguing stimulation (6.30-6.70 and 18.04 +/- 1.78 mm, n = 6, respectively). Yet, the increase in intracellular osmolarity expected from such an increase in intracellular lactate did not significantly alter Vc. Simulation of these experimental results, modified from the charge difference model of Fraser & Huang, demonstrated that such experimental manoeuvres produced changes in intracellular [H+] and [lactate] comparable to those observed during muscle fatigue, and accounted for this paradoxical conservation of Vc through balancing negative osmotic effects resulting from the net cation efflux that would follow a titration of intracellular membrane-impermeant anions by the intracellular accumulation of protons. It demonstrated that with established physiological values for intracellular buffering capacity and the permeability ratio of lactic acid and anionic lactate, P(LacH): P(Lac-), this would provide a mechanism that precisely balanced any effect on cell volume resulting from lactate accumulation during exercise.

Effect of repetitive stimulation on cell volume and its relationship to membrane potential in amphibian skeletal muscle

The effect of electrical stimulation on cell volume, V (c), and its relationship to membrane potential, E (m), was investigated in Rana temporaria striated muscle. Confocal microscope xz-plane scanning and histology of plastic sections independently demonstrated significant and reversible increases in V (c) of 19.8+/-0.62% (n=3) and 27.1+/-8.62% (n=3), respectively, after a standard stimulation protocol. Microelectrode measurements demonstrated an accompanying membrane potential change, DeltaE (m), of +23.6+/-0.98 mV (n=3). The extent to which this DeltaE (m) might contribute to the observed changes in V (c) was explored in quiescent muscle exposed to variations in extracellular potassium concentration, [K(+)](e). E (m) and V (c) varied linearly with log [K(+)](e) and [K(+)](e), respectively, in the range 2.5-15 mM (R (2)=0.99 and 0.96), and these results were used to reconstruct an approximately linear relationship between V (c) and E (m) (DeltaV (c)=0.85E (m)+68.53; R (2)=0.99) and hence derive the DeltaV (c) expected from the DeltaE (m) during stimulation. This demonstrated that both the time course and magnitude of the increase and recovery of V (c) observed in active muscles could be reproduced by the corresponding [K(+)](e)-induced depolarisation in quiescent muscles, suggesting that the depolarisation associated with membrane activity makes a substantial contribution to the cell swelling during exercise. Furthermore, conditions of Cl(-) deprivation abolished the relationship between E (m) and V (c), supporting a mechanism in which the depolarisation of E (m) drives a passive redistribution of Cl(-) and hence cellular entry of Cl(-) and K(+) and an accompanying, osmotically driven, increase in V (c).

Detubulation abolishes membrane potential stabilization in amphibian skeletal muscle

A recently reported stabilization ('splinting') of the resting membrane potential ( Em) observed in amphibian skeletal muscle fibres despite extracellular hyperosmotic challenge has been attributed to high resting ratios of membrane Cl- to K+ permeability ( P Cl/ P K) combined with elevations of their intracellular Cl- concentrations, [Cl-]i, above electrochemical equilibrium by diuretic-sensitive cation-Cl-, Na-Cl (NCC) and/or Na-K-2Cl (NKCC), co-transporter activity. The present experiments localized this co-transporter activity by investigating the effects of established detubulation procedures on Em splinting. They exposed fibres to introduction and subsequent withdrawal of 400 mM extracellular glycerol, high divalent cation concentrations, and cooling. An abolition of tubular access of extracellularly added lissamine rhodamine fluorescence, visualized by confocal microscopy, and of the action potential afterdepolarization together confirmed successful transverse (T-) tubular detachment. Fibre volumes, V , of such detubulated fibres, determined using recently introduced confocal microscope-scanning methods, retained the simple dependence upon 1/[extracellular osmolarity], without significant evidence of the regulatory volume increases described in other cell types, previously established in intact fibres. However detubulation abolished the Em splinting shown by intact fibres. Em thus varied with extracellular osmolarity in detubulated fibres studied in standard, Cl(-)-containing, Ringer solutions and conformed to simple predictions from such changes in assuming that intracellular ion content was conserved and membrane potential change DeltaEm was principally determined by the K+ Nernst potential. Furthermore, cation--Cl- co-transport block brought about by [Cl-]o or [Na+]o deprivation, or inclusion of bumetanide (10 microM) and chlorothiazide (10 microM) in the extracellular fluid gave similar results. When taken together with previous reports of significant Cl- conductances in the surface membrane, these findings suggest a model that contrastingly suggests a T-tubular location for cation--Cl- co-transporter activity or its regulation.

Slow volume transients in amphibian skeletal muscle fibres studied in hypotonic solutions

The influence of extracellular hypotonicity on the relationship between cell volume (V(c)) and resting membrane potential (E(m)) was investigated in Rana temporaria skeletal muscle. V(c) was measured by confocal microscope imaging of fibres through their transverse (xz) planes, and E(m) was determined using standard microelectrode techniques. Hypotonic solutions first elicited a rapid increase in fibre volume, DeltaV(R+) that fulfilled expectations of simple osmotic behaviour described in earlier reports. However, this was consistently followed by a slow increase in V(c) (DeltaV(S+)) to 10-15% above osmotic predictions. Longer (>1 h) exposures to hypotonic solutions permitted a subsequent slow decrease in V(c) (DeltaV(S-)), the eventual magnitude of which exceeded that of the preceding DeltaV(S+). Restoration of isotonic conditions elicited a prompt recovery in V(c) that matched simple osmotic predictions and thus left a net change in V(c). Such alterations in V(c) attributable to DeltaV(S+) then gradually reversed, while those due to DeltaV(S-) persisted. Both DeltaV(S+) and DeltaV(S-) persisted under conditions of Cl- deprivation. The depolarization of E(m) that accompanied DeltaV(R+) was consistent with dilution of intracellular [K(+)]. E(m) did not significantly alter during the subsequent DeltaV(S) transients. These empirical features of DeltaV(S+) and DeltaV(S-) were analysed using the quantitative charge-difference model of Fraser and Huang, published in 2004. This attributed the DeltaV(S+) to an electroneutral increase in the effective osmotic activity of normally membrane-impermeant intracellular anions. In contrast, the DeltaV(S-) could only be explained by an efflux of such anions and was accordingly comparable to organic anion-dependent regulatory volume decreases reported in other cell types.

The effect of intracellular acidification on the relationship between cell volume and membrane potential in amphibian skeletal muscle

The relationship between cell volume (V(c)) and membrane potential (E(m)) in Rana temporaria striated muscle fibres was investigated under different conditions of intracellular acidification. Confocal microscope xz-scanning monitored the changes in V(c), whilst conventional KCl and pH-sensitive microelectrodes measured E(m) and intracellular pH (pH(i)), respectively. Applications of Ringer solutions with added NH(4)Cl induced rapid reductions in V(c) that rapidly reversed upon their withdrawal. These could be directly attributed to the related alterations in extracellular tonicity. However: (1) a slower and persistent decrease in V(c) followed the NH(4)Cl withdrawal, leaving V(c) up to 10% below its resting value; (2) similar sustained decreases in resting V(c) were produced by the addition and subsequent withdrawal of extracellular solutions in which NaCl was isosmotically replaced with NH(4)Cl; (3) the same manoeuvres also produced a marked intracellular acidification, that depended upon the duration of the preceding exposure to NH(4)Cl, of up to 0.53 +/- 0.10 pH units; and (4) the corresponding reductions in V(c) similarly increased with this exposure time. These reductions in V(c) persisted and became more rapid with Cl(-) deprivation, thus excluding mechanisms involving either direct or indirect actions of pH(i) upon Cl(-)-dependent membrane transport. However they were abolished by the Na(+),K(+)-ATPase inhibitor ouabain. The E(m) changes that accompanied the addition and withdrawal of NH(4)(+) conformed to a Nernst equation modified to include realistic NH(4)(+) permeability terms, and thus the withdrawal of NH(4)(+) restored E(m) to close to control values despite a persistent change in V(c). Finally these E(m) changes persisted and assumed faster kinetics with Cl(-) deprivation. The relative changes in V(c), E(m) and pH(i) were compared to predictions from the recent model of Fraser and Huang published in 2004 that related steady-state values of V(c) and E(m) to the mean charge valency (z(x)) of intracellular membrane-impermeant anions, X(-)(i). By assuming accepted values of intracellular buffering capacity (beta(i)), intracellular acidification was shown to produce quantitatively predictable decreases in V(c). These findings thus provide experimental evidence that titration of the anionic z(x) by increased intracellular [H(+)] causes cellular volume decrease in the presence of normal Na(+),K(+)- ATPase activity, with Cl(-)-dependent membrane fluxes only influencing the kinetics of such changes.

Properties of the demarcation membrane system in living rat megakaryocytes

The demarcation membrane system (DMS) is the precursor of platelet cell membranes yet little is known of its properties in living megakaryocytes. Using confocal microscopy, we now demonstrate that demarcation membranes in freshly isolated rat marrow megakaryocytes are rapidly stained by styryl membrane indicators such as di-8-ANEPPS and FM 2-10, confirming that they are invaginations of the plasma membrane and readily accessible from the extracellular space. Two-photon excitation of an extracellular indicator displayed the extensive nature of the channels formed by the DMS throughout the extranuclear volume. Under whole-cell patch clamp, the DMS is electrophysiologically contiguous with the peripheral plasma membrane such that a single capacitative component can account for the biophysical properties of all surface-connected membranes in the majority of recordings. Megakaryocyte capacitances were in the range of 64-694 pF, equivalent to 500-5500 platelets (mean value 1850). Based upon calculations for a spherical geometry, the DMS results in a 4- to 14-fold (average 8.1-fold) increase in specific membrane capacitance expressed per unit spherical surface area. This indicates a level of plasma membrane invagination comparable with mammalian skeletal muscle. Whole-cell capacitance measurements and confocal imaging of membrane-impermeant fluorescent indicators therefore represent novel approaches to monitor the DMS during megakaryocytopoiesis and thrombopoiesis.