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Biomedical subjects

F Halberg

Publications and source records attributed to F Halberg.

At least 523 records · Page 29Linked to original sources
PubMedDate not supplied

Circadian susceptibility rhythm of the rat to alloxan.

The susceptibility of rats to alloxan undergoes a circadin rhythm. The toxicity rhythm, presumably involving injury to liver, kidney and other sites, pancreatic beta-cells in particular, is demonstrated in pooled data from 370 mature inbred Fischer or Minnesota Sprague-Dawley rats of both sexes kept in light from 06(00) to 18(00) alternating with darkness, some with free access to Purina laboratory chow with tap water at all times and some other rats subjected to one of three starvation schedules: 1) a 28-h fast before an intravenous alloxan injection; 2) a 28-h fast, except for a 4-h ad libitum feeding before injection; 3) a 28-h fast, except for a 4-h pre-injection tube-feeding of Nutrament (Mead and Johnson, Evansville, Indiana), 1.5 ml/100 g body weight. Survival time data on an additional 200 inbred Fischer rats reveal, next, that susceptibility to alloxan increases as the starvation span is lengthened from 24 to 84 h. The shortening in survival time indicative of this susceptibility increase is nonlinear; a circadian rhythmic change in susceptibility to alloxan is seen as a statistically significant wave-form indicative of the basic (persisting) rhythm, of applied interest as well to students of experimental diabetes.

Alloxan↗
PubMedDate not supplied

Circadian and circatrigintan rhythms in pulse, oral temperature and blood pressure of a clinically healthy Japanese woman.

The circadian and circatrigintan (menstrual) system of a healthy Japanese woman has been quantified by single cosinor analyses. The results obtained at only 2 frequencies are discussed against the background of prior chronobiologic information. The paper documents different acrophase relations of rhythms with different frequencies in the same variables and includes a sketch of the position of the single cosinor method as a tool in a methodologic armamentarium of broader interest in anthropology, medicine and more generally in biology.

Adult↗
PubMedDate not supplied

Time-dependent effects of ASA administration on blood pressure in healthy subjects.

Several studies aimed at testing the effects of low-dose acetylsalicylic acid treatment (ASA, aspirin) in the prevention of preeclampsia conclude that beneficial effects of such treatment outweigh adverse ones. Since recent results suggest that desired effects upon lipoperoxides and beta-adrenergic receptors are dependent on the circadian timing of ASA administration, we aim to study if ASA therapy can be optimized by timing according to the rest-activity cycle. Accordingly, before conducting clinical trials on pregnant women, we have examined in clinically healthy subjects the possibility that effects of ASA upon blood pressure could indeed be time-dependent. We studied 55 healthy subjects (35 men and 20 women), 19-24 years of age (mean +/- SD: 20.9 +/- 1.8). Subjects were living on their usual diurnal waking (approximately 08:00 to approximately 24:00), nocturnal resting routine during sampling, following every-day life conditions without any restriction. The systolic, mean arterial and diastolic blood pressures and heart rates of each subject were automatically monitored every 30 min. for 48 hrs with an ABPM-630 Colin (Komaki, Japan) device before and after a one-week course of aspirin (500 mg/day). Subjects were randomly assigned to one of three groups, according to the circadian timing of administration of the daily dose of ASA: within two hours of awakening (R x 1), seven to nine hours after awakening (R x 2), or within two hours before bedtime (R x 3). The second blood pressure profile was obtained during the sixth and seventh days of treatment (to avoid differences in activity dependent on the day of the week). Results indicate a statistically significant blood pressure reduction (negative mean area between the blood pressure profiles obtained before and after aspirin administration) only when ASA was given seven to nine hours after awakening (R x 2; P = .012, .003, and .006 for systolic, mean arterial and diastolic blood pressure, respectively). These results were corroborated by a non-parametric (sign) test, also indicating the significant reduction in systolic and diastolic BP for R x 2 (P = .003 and .010, respectively). Non-invasive BP monitoring combined with the proper analysis of the time series thus obtained could then provide a cost-effective approach for testing the circadian optimization of long-term ASA administration for both cardiovascular disease prophylaxis and prevention of preeclampsia.

Adult↗
PubMedDate not supplied

Heart rate and blood pressure chronomes during and after pregnancy.

Whereas conventional time-unspecified single measurements of blood pressure and heart rate may mislead, influenced as they are, among other factors, by the individual's emotional state, position, diet and external stimuli generally, the chronobiologic evaluation of predictable variability in these physiologic variables assesses early cardiovascular disease risk in pregnancy by (a) the use of fully ambulatory devices and (b) the proper processing of the time series thus obtained. We have used this approach to quantify changes in 24-h synchronized circadian characteristics of cardiovascular variables in two consecutive pregnancies of a clinically healthy woman. The results were then compared with those obtained from data sampled after the second pregnancy. Blood pressure and heart rate were automatically monitored, at 1-h intervals, each time for at least 48 consecutive hours, and for a total of 76 days of monitoring in each pregnancy. Circadian parameters of those circulatory variables were computed for each 48-h profile of measurements by the least-squares fit of a 24-h cosine curve. Regression analysis of parameters thus obtained revealed patterns of variation of circadian rhythm-adjusted means and amplitudes with gestational age. In both pregnancies, the predictable variability of the circadian rhythm-adjusted mean of blood pressure can be approximated by a second-order polynomial model on gestational age: a steady linear decrease in systolic, mean arterial and diastolic blood pressures up to the 22nd week of pregnancy is followed by an increase up to the day of delivery. This pattern of variation is not found for data similarly sampled during non-pregnancy on the same woman. This longitudinal study confirms and extends to ambulatory everyday life conditions the predictable pregnancy-associated variability in blood pressure and heart rate and also allows the establishment of prediction and confidence limits for cardiovascular parameters in a healthy pregnancy.

Animals↗
PubMedDate not supplied

Ultradian-infradian variation of cardiac creatine phosphokinase (CPK) activity in male Holtzman rats.

Reference standards were sought for use in the search of any indications of myocardial damage by an alteration of the time structure, or chronome, of creatine phosphokinase (CPK) "MB" isoenzyme activity in the heart of the male Holtzman rat. 144 rats were kept on 6 lighting regimens staggered by 4 hours, 24 rats per chamber. On 8 consecutive days, hearts from 3 animals from each chamber were harvested and weighed. The left ventricle was dissected, homogenized in a buffer solution at 4 degrees C and stored frozen at -20 degrees C until analysis. A supernatant aliquot of each sample was analyzed by a discontinuous gradient elution from DEAE-Shephadex A-50 columns. The CPK isoenzymes were quantified by the Rosalki method. Results of the CPK assay from each time point were analyzed by linear and nonlinear least-squares rhythmometry. Among other components, a 168h or circaseptan rhythm characterized CPK activity in the heart of Holtzman rats. This component and other ultradian and circadian aspects of the time structure of rhythms and trends, the chronome of a given variable, may serve, by any eventual alteration of their dynamic characteristics, as gauges of potential cardiac damage prior to the occurrence of an increase in the overall mean of the enzymatic activity.

Activity Cycles↗
PubMedDate not supplied

Broad scope of a newly developed actometer in chronobiology, particularly chronocardiology.

The scope and the details of a newly developed actometer were introduced. We are able to select a desired threshold of gravity(g)-forces between 0.01g and 0.50g and to simultaneously monitor 3 kinds of activity along with an averaged g-force every minute. As a routine study, we monitored at settings of 0.01g, 0.05g and 0.20g and averaged on one channel. Part of the time, physical activity was monitored together with ambulatorily monitored blood pressure (BP) and the ECG, or at least heart rate (HR). Physical activity showed a circasemiseptan and circaseptan periodicity as well as the circadian component, especially in subjects with an irregular sleep-wakefulness life style. On the average, physical activity was greater on a working day than on a holiday. Everyday physical activity reflects in part the ability to exercise, and it is expected that this actometer can contribute or provide an objective individualized quality-of-life index. The effect of physical activity on circadian profiles of BP, HR and HR variability is also examined. We observed that BP started to increase several hours before getting up. This fact likely shows that there is an endogenous circadian rhythm in BP, independently of the sleep-wakefulness cycle. Lastly, we investigated the relationship between physical activity and HR in patients permanently paced; we confirmed that the DDDR pacing mode was more physiological than the VVI or VVIR mode. This newly developed actometer will bring about further progress in chronobiology.

Adult↗
PubMedDate not supplied

Cross-spectral coherence between geomagnetic disturbance and human cardiovascular variables at non-societal frequencies.

A 35-year-old cardiologist monitored himself with an automatic ABPM-630 (Colin Electronics) monitor, mostly at 15-minute intervals around-the-clock for three years with a few interruptions. In this subject with a family history of high blood pressure and stroke, a cross-spectral analysis revealed a statistically significant coherence at 27.7 days between systolic and diastolic blood pressure and heart rate vs. the geomagnetic disturbance index, Kp. A lesser peak in coherence was found for systolic blood pressure with Kp at a trial period of 4.16 days (P = 0.046). These results suggest that changes in geomagnetism may influence the human circulation, at least in the presence of familial cardiovascular disease risk, and they may do so at frequencies that have no precise human-made cyclic worldwide match.

Adult↗
PubMedDate not supplied

Agostino Carandente.

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Chronobiology Phenomena↗