Do high participation rates improve effects of population-based general health checks?

The aim is to investigate if the effect of a health check differs between areas with different participation rates. The Inter99 population-based randomized lifestyle intervention study covered 73 areas within the suburbs of Copenhagen, Denmark. Adults aged 30-60years were randomly drawn from a population and were randomized to intervention group (n=11,483) or control group (n=47,122). Participation rates in the health check varied considerably between areas (mean 52%; range 35-85%). In separate survival analyses, area participation rate was included both as a continuous exposure variable and as a categorical variable (tertiles; low: 35-49%, meddle: 50-54%, high: 55-84%). All persons in the intervention and control group were followed in registers for 10-year total mortality and combined events (ischemic heart disease, stroke, or both). In adjusted models (including sociodemographic variables, ethnicity, number of children and comorbidity), among men, there was no difference in risk of death between areas with varying participation rates. Surprisingly, among women living in high-participation areas a significantly higher risk of all-cause mortality (HR: 1.32 [1.03-1.69]) was found in the intervention group (ref=controls). For both men and women, in no areas there was any difference between intervention and control group in incident IHD/stroke. Higher participation rates in population based health checks is probably unlikely to improve the effects of these, and may in worst case be harmful in subgroups of the population. Further well-designed studies within non-participation research should have high priority and are required to establish link between health checks and risk of death in subgroups of the population.

Acute effects of caffeine ingestion on signal-averaged electrocardiograms.

BACKGROUND: Although moderate caffeine ingestion has not been shown to be arrhythmogenic, caffeine toxicity can cause severe cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. Atrial fibrillation and ventricular tachycardia have been associated with prolongation of P-wave and QRS complex durations on signal-averaged electrocardiograms. This study investigated acute effects of caffeine ingestion on signal-averaged P-wave and QRS complexes. METHODS AND RESULTS: Signal-averaged electrocardiograms were obtained from 12 normal subjects (6 men, 6 women; ages 21 to 26 years) before and after ingestion of caffeine (5 mg/kg body weight) or placebo in a randomized, double-blind, crossover fashion. Electrocardiograms for signal averaging were recorded from electrodes left in a constant location. After bandpass filtering (30 to 300 Hz) and amplification, signals were sampled over 7.2 minutes at 2000 Hz. Signal-averaged P-wave and QRS complex durations did not significantly change after placebo ingestion. After caffeine ingestion QRS duration prolonged in 9 of 11 subjects at 90 minutes (mean +/- SEM = 0.8+/-0.3 ms, P< .02) and in 8 of 9 after 3 hours (1.1+/-0.2 ms, P< .001). No significant change in P-wave duration or heart rate was found after caffeine ingestion at any test interval. Average caffeine level in saliva 90 minutes after ingestion was 6.6+/-1.6 (SD) microg/dL. CONCLUSIONS: Although probably not arrhythmogenic in normal subjects, moderate caffeine ingestion does produce a small but statistically significant prolongation of signal-averaged QRS complexes. Further prolongation caused by excessive caffeine intake may be a factor in the genesis of arrhythmias associated with caffeine toxicity.

Hemodynamic effects of acute caffeine ingestion in young adults.

This study investigated hemodynamic effects of acute caffeine ingestion in young adults 21 to 26 years of age. Data showed an increase in heart rate corrected velocity of circumferential fiber shortening at an indexed afterload up to 4.5 hours following caffeine consumption.