PubMed Health⌕ Search

Biomedical subjects

A Weydahl

Publications and source records attributed to A Weydahl.

11 recordsLinked to original sources
PubMed2001

Geomagnetic disturbance associated with decrease in heart rate variability in a subarctic area.

BACKGROUND: Physical environmental variables, such as the natural variation in the geomagnetic field in and around the earth, influence biological processes and human health. The effect of geomagnetic disturbances on heart rate variability (HRV) in healthy students in a subarctic area is studied herein. SUBJECTS AND METHODS: Seven-day records by Holter ECG were obtained from eight clinically healthy subjects in Alta, Norway (70 N). Frequency- and time-domain measures of HRV were compared between 24-hour spans of high geomagnetic disturbance versus quiet conditions. RESULTS: A 5.9% increase in the 24-hour average of HR (P = 0.020) and a 25.2% decrease in HRV (P = 0.002) were documented on days of high geomagnetic disturbance. The decrease in spectral power was found primarily at frequencies lower than 0.04 Hz and was not statistically significant around 3.6 sec. CONCLUSIONS: The physiological mechanism involved may be other than the parasympathetic, usually identified with spectral power centered around 3.6 sec, a spectral region wherein no statistically significant differences were found.

Adult↗
PubMed2001

Geomagnetic activity influences the melatonin secretion at latitude 70 degrees N.

Factors other than light may affect variations in melatonin, including disturbances in the geomagnetic field. Such a possibility was tested in Alta, Norway, located at latitude 70 degrees N, where the aurora borealis is a result of large changes in the horizontal component (H) of the geomagnetic field. Geomagnetic disturbances are felt more strongly closer to the pole than at lower latitudes. Also noteworthy in Alta is the fact that the sun does not rise above the horizon for several weeks during the winter. To examine whether changes in geomagnetic activity influence the secretion of melatonin, saliva was collected from 25 healthy subjects in Alta several times during the day-night and at different times of the year. Single cosinor analyses yielded individual estimates of.the circadian amplitude and MESOR of melatonin. A 3-hour mean value for the local geomagnetic activity index, K, was used for approximately the same 24-hour span. A circadian rhythm was found to characterize both melatonin and K, the peak in K (23:24) preceding that of melatonin (06:08). During the span of investigation, a circannual variation also characterized both variables. Correlation analyses suggest that changes in geomagnetic activity had to be of a certain magnitude to affect the circadian amplitude of melatonin. If large enough (> 80 nT/3 h), changes in geomagnetic activity also significantly decreased salivary melatonin concentration.

Adolescent↗
PubMed2001

Alternating light-darkness-influenced human electrocardiographic magnetoreception in association with geomagnetic pulsations.

Geomagnetic variations of partly interplanetary origin, with cyclic signatures in human affairs and pathology include the incidence of various diseases, regarding which this study of healthy subjects attempted to determine an underlying mechanism by worldwide archival and physiological monitoring, notably of heart rate variability (HRV). In the past half-century, the possible health and other hazards of natural, solar variability-driven temporal variations in the earth's magnetic field have become a controversial subject in view of the inconsistent results. Some well-documented claims of associations between geomagnetic storms and myocardial infarction or stroke have been rejected by a study based on more comprehensive data analyzed by rigorous methods - covering, however, only part of a solar cycle in only part of a hemisphere. It seems possible that inter-solar cycle and geographic variability, if not geographic differences, may account for discrepancies. Herein, we examine the start of a planetary study on any influence of geomagnetic disturbances that are most pronounced in the auroral oval, on human HRV. The magnetic field variations exhibit complex spectra and include the frequency band between 0.001-10 Hz, which is regarded as ultra-low frequency by physicists. Since the 'ultra-low-frequency' range, like other endpoints used in cardiology, refers to much higher frequencies than the about-yearly changes that are here shown to play a role in environmental-organismic interactions revealed by HRV, the current designations used in cardiology are all placed in quotation marks to indicate the need for possible revision. Whether or not this suggestion has an immediate response, we have pointed to a need for the development of instrumentation and software that renders the assessment of circadian, infradian and even infra-annual (truly low frequency) modulations routinely feasible. HRV was examined on the basis of nearly continuous 7-day records by ECG between December 10, 1998, and November 2, 2000, on 19 clinically healthy subjects, 21 to 54 years of age, in Alta, Norway. A geomagnetic record was obtained from the Auroral Observatory of the University of Tromsø. First, frequency-domain measures of HRV were compared for each person in 24-hour spans of high geomagnetic disturbance versus quiet conditions. Second, cross-spectra between geomagnetic activity and HRV measures were quantified via the squared coherence spectrum using 7-day time series. A 7.5% increase in the 24-hour average of heart rate, HR (P = 0.00020) and a decrease in HRV were documented on days of high geomagnetic disturbance. The decrease in HRV was validated statistically for the 'total frequency', 'TF' endpoint (18.6% decrease, P= 0.00009). The decrease in spectral power was found primarily in the 'circaminutan frequency', 'VLF' (21.9% decrease, P< 0.000001) in conjunction with the 'minutes-to-hours' component, ultra-low-frequency, 'ULF' (15.5% decrease, P= 0.00865) and circadecasecundan 'low frequency', 'LF' (14.2% decrease, P = 0.00187) regions of the spectrum. Power-law scaling of the power spectra did not show any statistically significant difference. It is noteworthy that most of the decrease in HRV, except for the circaminutan (VLF) component, was observed only in the season in which sunshine alternated with darkness (D/L), a finding suggesting a mechanism influenced by the alternation of light and darkness. The hypothesis of a light-dark-influenced magnetoreception was also supported by cross-spectral analysis. Group-averaged coherence at frequencies coincident with the geomagnetic Pc 6 pulsations (with periods ranging from 10 minutes to 5 hours) differed with a statistical significance (P < 0.000001) among the three natural lighting conditions, the association being weaker during UL or D/D than during D/L. By contrast, no statistically significant differences were found in terms of the circadian and circasemidian frequencies in relation to the alternation of sunshine with darkness or rather circannual rhythm stage. In conclusion, evidence is provided herein that an alteration of HRV is most apparent in the circaminutan ('VLF') region, which is clinically important, because a reduction in its power is a predictor of morbidity and mortality from cardiovascular disease. The circadecasecundan ('LF') component of HRV also decreased in association with geomagnetic disturbance, which may reflect an episodic alteration of arterial pressure related to changes in geomagnetic activity. Lastly, our study suggests the existence of a light-dark-influenced magnetoreception mechanism in humans involving mainly the Pc 6 band of the magnetic field.

Adult↗
PubMed2001

Can nutrition influence circadian rhythm and heart rate variability?

Recent studies indicate that there is an interaction between biorhythms, the biological clock and triggers, which may be important in the pathogenesis of altered heart rate variability (HRV) and blood pressure variability (BPV). Circadian rhythms are under the influence of, and physiological variables are mediated by the activation of the adrenals, sympathetic/parasympathetic, hypothalamic and pituitary activity. Emotional stress, physical exertion, sleep deprivation and large fatty meals are major triggers of myocardial ischemia, angina, infarction, sudden cardiac death (SCD) and stroke. These events have been reported to exhibit a circadian variation with increased frequency in the second quarter of the day, which has also been observed in our studies on Indians. Recent studies indicate that altered HRV and BPV are also important in the pathogenesis and progression of heart failure, atheroma and thrombosis. Mediation via beta-blockers, oestrogens, n-3 fatty acids, vitamin E and coenzyme Q10 and fasting appears to have a beneficial influence whereas progestins, nifedipine, stress and exercise may have an adverse effect on HRV and BPV. We have reported that plasma levels of vitamin E and C are lower in the second quarter of the day than at other times, indicating their role in the pathogenesis of variability and cardiac events. Prospective studies also indicate that HRV and BPV are important and independent risk factors for cardiovascular events. However, no study has yet been conducted in patients with abnormal HRV and BPV in a randomized, placebo-controlled intervention trial to find out whether improvement in variability can cause a significant reduction in cardiovascular events. There is a need to study the role of n-3 fatty acids, coenzyme Q10, the effect of regular physical training, medication and ACE inhibitors in patients with abnormal HRV and BPV to demonstrate that improving variability can modulate cardiovascular events.

Animals↗
PubMed1995

Time-dependent glycemic response to exercise in winter and spring in the subarctic.

Twenty healthy athletes exercised for 30 min at four different times (beginning at 1130 and 1630) in December (darkness period) and in April (18 h of daylight). Four hours after intake of a standardized meal, a 30-min bike exercise with an intensity of 60% maximal O2 uptake was performed. Blood samples (fingertip) were drawn at 1, 5, 10, and 30 min into exercise and 5, 10, and 30 min after termination of exercise for determination of blood glucose. Glucose values were normalized by reexpressing each as a percentage of the starting value. The total area under the glucose-time curves as well as the area below the starting value was calculated. Areas were tested for the effect of sex, time of day, and season by analysis of variance. For the group as a whole during exercise, a significant effect was found by analysis of variance for sex, time of exercise, and season. During recovery, significant differences were found for sex and time of exercise but not for season. The minimal integrated glucose response to exercise occurred in females, who also showed the most rapid return to baseline values during the recovery period. Exercise in the morning produced the smallest glucose response for both sexes and faster recovery compared with exercise in the afternoon. This was also the case overall for exercise in December compared with April. This finding implies that the glycemic response may be influenced by season and timing of exercise, which may be of importance for athletes involved in vigorous training and patients with diabetes mellitus.

Adolescent↗
PubMed1994

Evening melatonin in January after changes in hours of habitual exercise during fall among youths living in the subarctic.

Secretion of the hormone melatonin shows a circadian rhythm and is inhibited by light. Light therapy with phase shifting of the melatonin rhythm has been used as treatment of sleeping problems and seasonal affective disorders (SAD). Exercise has also been shown to suppress the melatonin secretion. In order to investigate the effect of increased level of habitual physical activity upon melatonin secretion in areas with extreme short days and high level of midwinter insomnia, 18 high school students participated in this study. Their habitual physical activity throughout two consecutive falls were recorded. The following January, blood samples were taken for melatonin analyses from 1530h to 2300h. After the fall with highest habitual activity level, the plasma melatonin showed significantly decreased values at all sampling times compared to values after lowest level of activity. The relative increase in melatonin level at 2300h, however, tended to be of a greater magnitude after the fall with highest activity compared to the fall with lowest activity (p = .094). A change in habitual level of activity should be thought of as a possible help for treating midwinter insomnia and SAD.

Adolescent↗
PubMed1991

Sex differences in the effect of exercise upon sleep.

A survey in a high school in the city of Tromsø in the spring of 1988 was designed to examine the characteristics of sleep and factors promoting and disturbing sleep. Out of 621 students 465 (74.9%) responded to 11 questions about last night's sleep and what the individual perceived as usual sleep (10 questions). On this information two sleep-quality scores, a special score for last night's sleep and a general score for what is perceived as usual sleep, were computed. The sleep-quality score was the sum of answers identical to a preset "right" answer indicating good sleep-quality. Multiple regression analyses separately by sex showed that different variables influence sleep-quality of boys and girls. Activity and intensity of exercise were taken into the regression model for the special sleep-score for boys but not for girls. For girls psychological factors seemed of greater importance to sleep-quality than exercise.

Adult↗
PubMed1991

Sleep-quality among girls with different involvement in competitive sports during fall in the Arctic Circle.

Eight high-school girls participating in competitive sports and six non-participating girls living north of the polar circle recorded their sleep once a week during the Fall, including the period when the sun does not rise above the horizon. Sleep-quality scores were computed as the sum of answers identical to a present "right" answer indicating good sleep-quality. Significant differences on sleep-quality between the two groups were found, but a significant influence of amount of daylight or exercise could not be confirmed. When sleep-quality was ranked during three periods through the Fall, the girls participating in competitive sports showed a trend of increasing sleep-quality and the nonparticipants a decreasing one. An explanation based on influence of exercise thresholds upon sleep-quality is presented.

Adaptation, Psychological↗
PubMed1987

Daily spot-checking versus chronobiologic monitoring of human differential surface (rib versus breast) temperature.

A healthy, physically active woman, 35 years of age, living in Minneapolis, automatically monitored her skin surface temperature (ST) 3 inches above each nipple and on a rib below each breast for almost 3 months. In this paper a portion of that period is analyzed, namely, from October 24, 1984 (day 1 of menstruation) to November 16, 1984 (day 1 of next menstruation). On both sides, the differences between the skin surface temperature over the rib and over the breast (rib-breast DST) were calculated for each hour. The DST starts with a negative value on day 1, then becomes less negative up to around day 6, when the DST becomes positive. The means of DST during certain hours show extremely variable patterns. Even by using DST along with changes in activity and environmental temperature, circadian rhythms must be assessed. Around the clock monitoring is more reliable than a daily 1-hr mean check at a fixed time of the day. On the left side, DST mesors have a first macroscopic peak around days 8-10, another on day 14, and still others later in the cycle. On the right side, DST mesors follow a similar pattern, changing from negative to positive values. Peaking at day 10 is not as marked on the right side as on the left. The peak on day 14 is clear for both sides. With around the clock monitoring and the computation of the mesor of the differences between the temperatures at the two sites, an increase around the "estimated" ovulation time may be expected if care is also taken to account for the effects of periods of exercise and/or environmental changes.

Adult↗