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Objective To estimate whether migraine in mid-life is associated with mortality from cardiovascular disease, other causes, and all causes.Design Population based cohort study.Setting Reykjavik, Iceland.Participants 18 725 men and women, born 1907-35 and living in Reykjavik and adjacent communities.Main outcome measures Mortality from cardiovascular disease, non-cardiovascular disease, and all causes. Questionnaires and clinical measures were obtained in mid-life (mean age 53, range 33-81) in the Reykjavik Study (1967-91). Headache was classified as migraine without aura, migraine with aura, or non-migraine headache. Median follow-up was 25.9 years (0.1-40.2 years), with 470 990 person years and 10 358 deaths: 4323 from cardiovascular disease and 6035 from other causes. We used Cox regression to estimate risk of death in those with migraine compared with others, after adjusting for baseline risk factors.Results People with migraine with aura were at increased risk of all cause mortality (adjusted (for sex and multivariables) hazard ratio 1.21, 95% confidence interval 1.12 to 1.30) and mortality from cardiovascular disease (1.27, 1.13 to 1.43) compared with people with no headache, while those with migraine without aura and non-migraine headache were not. Further examination of mortality from cardiovascular disease shows that people with migraine with aura were at increased risk of mortality from coronary heart disease (1.28, 1.11 to 1.49) and stroke (1.40, 1.10 to 1.78). Women with migraine with aura were also at increased risk of mortality from non-cardiovascular disease (1.19, 1.06 to 1.35).Conclusions Migraine with aura is an independent risk factor for cardiovascular and all cause mortality in men and women. The risk of mortality from coronary heart disease and stroke mortality is modestly increased in people with migraine, particularly those with aura.
We review the effects of herbivory and other environmental factors on pollen performance in plants. We conclude that natural levels of variation in herbivory and other environmental factors during pollen development are often sufficient to cause significant differences in pollen performance, and that the differences in pollen performance are likely to be caused by differences in the provisioning of pollen grains. From an evolutionary perspective, we discuss how pollen and ovule provisioning may be negatively genetically correlated and how this would maintain genetic variation for pollen performance within populations. Furthermore, the highly plastic nature of pollen performance provides the potential for genotypes to respond differently to environmental variation (genotype–environment interactions), which would also promote the maintenance of genetic variation in pollen performance.
Several studies have explored a possible association between migraine and hypertension, with contradictory results. Because of this uncertainty the relation between blood pressure (BP) and migraine was studied in 10,366 men and 11,171 women in a population-based longitudinal study. A modified version of the 1988 International Headache Society criteria was used for diagnosis of migraine. Logistic regression analysis was used. The crude 1-year prevalence of migraine was 5.2% among men and 14.1% among women. No significant association was found between hypertension and migraine. For a one standard deviation (SD) increase in diastolic BP the probability of having migraine increased 14% (P = 0.11) for men and 30% (P < 0.0001) for women. For a 1-SD increase in systolic BP the probability of having migraine decreased 19% (P = 0.007) for men and 25% (P < 0.0001) for women. It was also found that for a 1-SD increase in pulse pressure the probability of having migraine decreased 13% (P = 0.005) for men and 14% (P < 0.0001) for women. In a population-based study of men and women it was found that subjects with migraine had lower pulse pressure, lower systolic BP and higher diastolic BP compared with controls.
SUMMIARY1. The relationship between active force and stimulation frequency (0-25--5/sec) was studied at 36-37o C in isolated papillary muscles of the rabbit.2. The muscle's force producing capability at a given frequency was determined as the isometric twitch response to a test stimulus that was applied at various times after a priming period. The optimum contractile response was obtained at an interval of 0-8 sec between the test pulse and the last stimulus of the priming period.3. The optimum contractile response exceeded the steady-state twitch amplitude at all stimulation frequencies higher than 1/sec. While the steady-state twitch response declined at frequencies higher than 4/sec, the optimum contractile response was steadily increased as the stimulation frequency was raised.4. The optimum contractile response was also determined after priming the muscle with a sinusoidal a.c. pulse (field strength, 10 V (r.m.s.)/cm; frequency, 20 c/s; duration, 2-5 sec). The optimum contractile response obtained after a.c. stimulation was 2-2 times greater than the maximal steady-state response. Its absolute value was 67-3 + 6-1 mN/mm2 (mean + sxE. of mean, n = 6).5. The twitch potentiation produced by priming the muscle at a given frequency decayed exponentially in two phases after optimum contractile response had been attained. The time constants of the two phases, determined after a.c. stimulation, were 2-6 ± 0-8 (n = 4) and 92-0 + 13-3 sec (n = 7), respectively.6. The optimum contractile response determined at various stimulation frequencies was linearly related to the fraction of time during which the cell membrane was depolarized (beyond -40 mV) by the action potentials.
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