Circadian and Ultradian Rhythmicities in Very Premature Neonates Maintained in Incubators

Six very premature babies (born at 26-28 weeks gestational age) have been studied in hospital for 11-17 weeks, while in intensive care and in an incubator. Apart from suffering occasionally from the neonatal disorders of haemolytic jaundice and 'respiratory distress of the newborn', the babies were healthy and developed normally. Initially, the babies were continuously fed intravenously, and the lighting in the ward was on continuously. Routine care was given round the clock. When their medical condition permitted it, the babies were moved in their incubator to an adjacent ward, where they took frequent (2-4 hourly) small meals by mouth, the lighting was dimmed at night, and routine care tended to be given more in the daytime. Hourly recordings of insulated skin temperature were taken throughout the study, and it is the detection of rhythmicity in these measurements that has been the subject of the present study. The methods used were Phase-weighted Stacks, Phasor Walkout and Power Spectral Analysis. These methods have previously been used mainly in geophysical studies, and their value is that they can detect weak signals in noisy data and do not assume a particular waveform of any signal. Circadian rhythmicity was found in all babies for much of the time that were in the constant environment provided by the incubator. Ultradian rhythms were sometimes present also, but they were shorter-lived, and showed a wide range of changing periods, generally in excess of 8 h. When the babies were being treated for jaundice or respiratory distress, there was a tendency for the circadian rhythms to become weaker and for a broader spectrum of ultradian periods to appear. Placing babies in the 12 h : 12 h light : dark environment provided by the ward, and instituting feeding by mouth, had, in most cases, only modest effects upon either circadian or ultradian rhythms. Thus, circadian rhythms continued (but generally with a period not exactly equal to 24 h), and ultradian rhythms, when present, often did not show periods that could be related easily to feeding or care-giving. These results are discussed in terms of evidence for endogenous and exogenous origins of the observed rhythms, and of theories that have postulated the relationship between circadian and ultradian rhythms. It is concluded that the results from the present analyses are difficult to reconcile with the view that circadian rhythms develop from interactions between ultradian oscillators. We suggest that they indicate a matu-ration of the circadian system as a consequence of increasing associations between the circadian elements that are present in the suprachiasmatic nuclei and in other oscillators of the circadian system. The new analytical methods used here also indicate that the results obtained from time-frequency analysis depend to some extent upon the method used.     

Twenty-four-hour and Ultradian Rhythmicities in Healthy Full-Term Neonates: Exogenous and Endogenous Influences

Eleven healthy, full-term babies were studied on the second day after birth and again 4 weeks later. The babies lived on a 24-h light/dark cycle (light from 0700D1900) and were bottle-fed every 4 h. Systolic blood pressure, heart rate, skin (abdomen) and rectal temperatures were measured at 10-min intervals for 24 h on each occasion of study. The behavioural state of the baby was measured at the same time, and this information was used to purify the raw data (i.e., to separate it into the endogenous, clock-driven and exogenous, lifestyle-driven components). Raw and purified data were assessed for 24-h and ultradian (12-, 8-, 6-, 4-, 3-, 2-h) periodicities by cosinor analysis. We confirm the development of 24-h rhythmicity in skin and rectal temperatures between day 2 and week 4; at the same time, ultradian rhythms (4-h) developed in all variables. For heart rate and systolic blood pressure the development of a 4-h ultradian rhythm was in phase with the behavioural changes produced by feeding; by contrast, for the temperatures, these weak exogenous components were accompanied by a stronger 4-h component, that was out of phase with feeding. Masking effects due to sleep and activity changed in size between day 2 and week 4. Also, those positive masks produced by waking activities were more marked in the light, whereas the negative masks produced by sleep were more marked in the dark. Some implications of these results for the development of rhythmicity in infants, particularly whether due to lifestyle or the development of internal processes, are discussed.     

Circadian and Ultradian Rhythms in Blood Glucose and Plasma Insulin of Healthy Adults

The circadian and ultradian variations of blood glucose and plasma insulin have been characterized individually and as a group phenomenon in five healthy young adults studied while adhering as closely as possible to their usual routine of sleep, activity, meal content and timing. Three complementary methods were used to analyze the data: displaying raw data as a function of time; cosinor method according to Nelson and Halberg; and time series analyses as proposed by De Prins and Malbecq. The subjects were studied in the laboratory and their life routine were controlled, but very close to that of their habitual routine. They had mainly ultradian rhythms of blood glucose (mainly about 6 hr) and circadian rhythms of immunoreactive insulin (I.R.I.). Blood glucose ultradian rhythms seem to be mainly but not exclusively mealtime dependent, while I.R.I, circadian rhythms appear to be primarily endogenous in origin. Therefore, the role played by insulin in the control of blood glucose levels seems to be programmed on a circadian basis rather than by a time independent feedback phenomenon as postulated by the conventional homeostatic hypothesis. The advantage of this chronophysiologic approach is to consider circadian rhythms of both I.R.I. and insulin effectiveness as an adaptive phenomenon able to maintain blood sugar changes in the ultradian domain of rhythms.     

Comparative Analysis of Ultradian and Circadian Behavioural Rhythms for Diagnosis of Biorhythmic State of Animals

A chronobiological procedure has been developed for evaluation of living conditions, behaviour and internal state of free-ranging animals. It is based on continuous recordings of activity and feeding with subsequent comparison of levels, daily patterns as well as daily and ultradian rhythms. Telemetric observations were carried out on alpaca, sheep, Przewalski horse, roe deer, red deer and mouflon under various conditions. The time patterns of the different species were analysed macroscopically and by autocorrelation function and power spectral analysis. A stable ultradian structure of behaviour was obvious especially for ruminants. A more unstable, adaptive time pattern was found in Przewalski horses. Activity as a multi-purpose behaviour was generally more variable than feeding which in most cases was of clearly rhythmic and harmonic structure. Degrees of Functional Couplings (DFCs) were used for comparison of rhythmic structure. DFCs express the percentage of the circadian component and harmonic ultradian components in relation to all rhythmic components of a spectrum. They were found to be high in well adapted, healthy and undisturbed individuals but were lowered during periods of adaptation, sickness or social interactions.     

Circadian and Ultradian Rhythms in Heart Rate and Motor Activity of Smokers, Abstinent Smokers, and Nonsmokers

In a field study, heart rate and motor activity were assessed continuously in 12 male smokers during 2 smoking and 2 abstinence days and in 12 male nonsmokers during 4 days. A circadian analysis revealed earlier activity acrophases in smokers than nonsmokers and earlier heart rate acrophases in abstinent than smoking smokers. Furthermore, heart rate acrophases of smoking smokers significantly anticipated activity acrophases;, whereas in abstinent smokers and nonsmokers the two parameters oscillated in phase. With the use, in smoking smokers, of the individual average smoking interval as a hypothetical ultradian period length, significant periodicities were found for heart rates in 16 and for activity in 15 of 24 observation days. These rhythms were nicotine independent and based on heart rate and activity increases prior to lighting up the cigarettes. Individual frequency spectra for the 16 h after getting up and the 7 h after going to bed did not reveal single dominant frequencies but rather complex frequency distributions. Power spectra of the daytime data revealed no group differences for activity and no heart rate differences between smoking smokers and nonsmokers. In abstinent smokers, however, a significant reduction of heart rate frequencies slower than 1 cycle/135 min and a significant increase of heart rate frequencies faster than 1 cycle/20 min were observed as compared with all other groups. This effect persisted over the 2 abstinence days, suggesting an activity-independent change in the frequency distribution of heart rates after quitting smoking.     

Circadian and Ultradian Rhythms in Heart Rate and Motor Activity of Smokers,Abstinent Smokers,and Nonsmokers

In a field study, heart rate and motor activity were assessed continuously in 12 male smokers during 2 smoking and 2 abstinence days and in 12 male nonsmokers during 4 days. A circadian analysis revealed earlier activity acrophases in smokers than nonsmokers and earlier heart rate acrophases in abstinent than smoking smokers. Furthermore, heart rate acrophases of smoking smokers significantly anticipated activity acrophases;, whereas in abstinent smokers and nonsmokers the two parameters oscillated in phase. With the use, in smoking smokers, of the individual average smoking interval as a hypothetical ultradian period length, significant periodicities were found for heart rates in 16 and for activity in 15 of 24 observation days. These rhythms were nicotine independent and based on heart rate and activity increases prior to lighting up the cigarettes. Individual frequency spectra for the 16 h after getting up and the 7 h after going to bed did not reveal single dominant frequencies but rather complex frequency distributions. Power spectra of the daytime data revealed no group differences for activity and no heart rate differences between smoking smokers and nonsmokers. In abstinent smokers, however, a significant reduction of heart rate frequencies slower than 1 cycle/135 min and a significant increase of heart rate frequencies faster than 1 cycle/20 min were observed as compared with all other groups. This effect persisted over the 2 abstinence days, suggesting an activity-independent change in the frequency distribution of heart rates after quitting smoking.     

Ultradian,Circadian and Circannual Rhythms of Blood Glucose and Injected Insulins Documented in Six Self-Controlled Adult Diabetics

The aim of the study was to document during one to two years individual rhythmic patterns in blood glucose and injected insulin in self-controlled insulin dependent (C-peptide negative) diabetics with home blood glucose monitoring. Two females and four males with diurnal activity from 0700 to 2300 self-determined their blood glucose three to six times a day over a period of 12–27 months. Circadian and ultradian rhythms were analysed for each subject on a monthly basis to document annual rhythms. Blood glucose (BG) estimated circadian acrophases were located between 2200 and 0300 for all patients and months with few exceptions. A correlation was found between circadian mesors and amplitudes of BG in four subjects. Annual changes in BG were validated for each subject with large interindividual differences in peak times. The individual mean of injected insulin (II) varied from 40 to 80 iU with annual changes validated for each subject. A group pattern was observed with a peak time either in the autumn (four patients) or in the summer (two patients). A circadian rhythm of II was detected in almost all monthly means and for all patients. Locations of computed peak time ? of II exhibited a great stability for a given individual but large interindividual differences. Thus the rather constant ? location of BG for all subjects contrasted with interindividual differences in ? locations of II. These results suggest that rhythmic changes in BG and II should be recognized when forming a realistic strategy for timing and dosing time(s) of insulin.     

Ultradian, Circadian and Circannual Rhythms of Blood Glucose and Injected Insulins Documented in Six Self-Controlled Adult Diabetics

The aim of the study was to document during one to two years individual rhythmic patterns in blood glucose and injected insulin in self-controlled insulin dependent (C-peptide negative) diabetics with home blood glucose monitoring. Two females and four males with diurnal activity from 0700 to 2300 self-determined their blood glucose three to six times a day over a period of 12-27 months. Circadian and ultradian rhythms were analysed for each subject on a monthly basis to document annual rhythms. Blood glucose (BG) estimated circadian acrophases were located between 2200 and 0300 for all patients and months with few exceptions. A correlation was found between circadian mesors and amplitudes of BG in four subjects. Annual changes in BG were validated for each subject with large interindividual differences in peak times. The individual mean of injected insulin (II) varied from 40 to 80 iU with annual changes validated for each subject. A group pattern was observed with a peak time either in the autumn (four patients) or in the summer (two patients). A circadian rhythm of II was detected in almost all monthly means and for all patients. Locations of computed peak time φ of II exhibited a great stability for a given individual but large interindividual differences. Thus the rather constant φ location of BG for all subjects contrasted with interindividual differences in φ locations of II. These results suggest that rhythmic changes in BG and II should be recognized when forming a realistic strategy for timing and dosing time(s) of insulin.     

Circadian and Ultradian Periodicities of Grooming Behavior in Family Groups of Common Marmosets (Callithrix jacchus) in Captivity

Three families' groups of common marmosets were observed to describe the characteristics of their grooming rhythmicity, as the duration of the episodes of self- and social grooming made and received by the animals, in captivity under natural environmental conditions. Data were collected by focal animal sampling, at 20 min hourly intervals during 16 non-consecutive days, from January to March in 1994 (sunrise: 05:24 h ± 2 min; sunset: 17:34 h ± 1 min). Time series were obtained for each individual and for each family through hourly duration of grooming. Family time serie was obtained through the mean of its individuals time series. Spectral analysis revealed statistically significant circadian rhythms for all families and individuals. Ultradian components were detected in 50% of the families and in 46.7% of the animals. Acrophases of self- and social grooming calculated by Single Cosinor took place between 9:21 h and 10:39 h, for the families. For individuals self- and social grooming made and received, acrophases occurred from 8:35 h to 12:43 h. The confidence limits of acrophases did not show differences between the families and the individuals within the families, irrespective of their sex, age and reproductive condition, suggesting that this behavior has a stronger temporal marking. Grooming has circadian and ultradian components of rhythmicity in captive families' groups of common marmosets, under natural environmental conditions. Since only some animals showed the ultradian component, it may be consequence of social or environmental masking, or yet phenotypic plasticity of temporal genotype. Further studies are needed to test these possibilities.     

Circadian and Ultradian Time Patterns in Human Behaviour: Part 1: Activity Monitoring of Families from Prepartum to Postpartum

Time patterns of activity-rest rhythms during and after pregnancy are increasingly recognised as important factors for the well-being and health of young families. This longitudinal study examined activity-rest patterns of couples during late pregnancy and subsequently the alterations in the periodic structure of parental and neonatal time patterns during the first four months after birth. Part I concentrates on the effects of late pregnancy and birth to the mother's rest-activity patterns and those of the father and, after birth, what time pattern the infant developed. Part II attempts to clarify how activity patterns of the entire family agree or disagree with each other and investigates how the infant synchronises with the environment that includes the process of parent-infant interaction. Activity data of, so far, seven families (father, mother and child) were continuously recorded using non-invasive Actiwatch units. Recordings of parental activity started at the beginning of the 37th week of gestation, and were continued in parallel with the infants' recordings in three series of three weeks each until four months after birth: 1st to 3rd week, 7th to 9th week and 13th to 15th week of life. In a standardised diary, record was kept of household routines, parental activities, type of feeding, initiation of sleep or waking up. Activity data of seven non-pregnant women were collected and used as a control. Irregular nocturnal activity epochs occurred frequently in pregnant women and were absent in non-pregnant women. Period lengthenings and shortenings of the circadian rhythms appeared in both parents from prepartum to postpartum. Activity at night increased from prepartum to postpartum in mothers and fathers. Three infants showed a marked circadian rhythm between day 3 and 14 after birth. All seven infants showed a predominant circadian rhythm between day 8 and 19 after birth. The onset of daytime activity of mothers and their infants corresponded well to each other. Postpartum frequency spectra of parents and child always had some ultradian components in common. Time patterns of activity-rest rhythms of couples and parents are shown to be altered during and after pregnancy and we suggest that the infants' adaptation to the environment begins during the first week that includes the process of mother-infant interaction.     

Circadian and Ultradian Time Patterns in Human Behaviour: Part 1: Activity Monitoring of Families from Prepartum to Postpartum

Time patterns of activity-rest rhythms during and after pregnancy are increasingly recognised as important factors for the well-being and health of young families. This longitudinal study examined activity-rest patterns of couples during late pregnancy and subsequently the alterations in the periodic structure of parental and neonatal time patterns during the first four months after birth. Part I concentrates on the effects of late pregnancy and birth to the mother's rest-activity patterns and those of the father and, after birth, what time pattern the infant developed. Part II attempts to clarify how activity patterns of the entire family agree or disagree with each other and investigates how the infant synchronises with the environment that includes the process of parent-infant interaction. Activity data of, so far, seven families (father, mother and child) were continuously recorded using non-invasive Actiwatch units. Recordings of parental activity started at the beginning of the 37th week of gestation, and were continued in parallel with the infants' recordings in three series of three weeks each until four months after birth: 1st to 3rd week, 7th to 9th week and 13th to 15th week of life. In a standardised diary, record was kept of household routines, parental activities, type of feeding, initiation of sleep or waking up. Activity data of seven non-pregnant women were collected and used as a control. Irregular nocturnal activity epochs occurred frequently in pregnant women and were absent in non-pregnant women. Period lengthenings and shortenings of the circadian rhythms appeared in both parents from prepartum to postpartum. Activity at night increased from prepartum to postpartum in mothers and fathers. Three infants showed a marked circadian rhythm between day 3 and 14 after birth. All seven infants showed a predominant circadian rhythm between day 8 and 19 after birth. The onset of daytime activity of mothers and their infants corresponded well to each other. Postpartum frequency spectra of parents and child always had some ultradian components in common. Time patterns of activity-rest rhythms of couples and parents are shown to be altered during and after pregnancy and we suggest that the infants' adaptation to the environment begins during the first week that includes the process of mother-infant interaction.     

Ultradian Rhythms in Desmodium

The leaves of Desmodium gyrans (L.F.) DC show circadian movements in the terminal and ultradian movements of the lateral leaflets. The movements are due to swelling and shrinking of motor cells in special organs. The anatomy of these pulvini is described for the lateral leaflets. Data from electrophysiological recordings using microelectrodes inserted into the lateral pulvini, together with treatments that affect the proton pumps and ion channels, have been used to develop a physiological model of the ultradian leaflet movement. It explains the oscillations in the motor cells as being due to a change between a pump state and depolarization. During the pump state, ions are taken up, causing water influx and swelling of the motor cells. Depolarization causes loss of ions and water efflux (the motor cells shrink). The roles of calcium and the phosphatidyl inositol signal chain are discussed on the basis of experiments using chemical agents that affect these processes. Since calcium oscillations are known to occur in organisms in both time and space, an attempt has been made to simulate the situation in Desmodium pulvini by a model of specially coupled oscillators. Effects of different other treatments of the lateral pulvini are discussed. Oscillations in the minute range seem to be more common and some might be related to turgor regulation and ion uptake comparable to the situation in Desmodium. The ultradian control of the lateral pulvini and the circadian control of the terminal pulvini are apparently based on different mechanisms.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish,Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

Ultradian Rhythm of Activity in Japanese Quail Groups under Semi-Natural Conditions during Ontogeny: Functional Aspects and Relation to Circadian Rhythm

The function of ultradian rhythms is not yet clearly elucidated. In particular, short-term rhythms are expressed during early ontogeny, especially in broods of precocial birds. We investigated the relationship between the clarity of the ultradian rhythm of the activity/rest cycle of a group of young Japanese quail (Coturnix japonica) and the level of social synchronisation and spatial cohesion between the birds within that group. The subjects were descended from two lines selected for either very pronounced rhythmic or arrhythmic circadian activity. We found a positive relationship between the clarity of the ultradian rhythm of the activity/rest cycle when birds were young and the clarity of the circadian rhythm of feeding activity when birds were older, but still immature. The temporal organisation of the behaviour of the chicks from these two lines was observed in outdoor aviaries, when they were 4, 8, 12 and 15 days old. The mean ultradian period expressed by groups of 12 chicks was variable, with a minimum of 6 minutes. The ultradian period lengthened regularly as chicks grew older, and reached approximately 40 min on day 15. The clarity of the ultradian rhythmicity of group activity was linked to the level of inter-individual social synchronisation and of spatial cohesion; the more pronounced the ultradian rhythms of a group, the greater the temporal and spatial cohesion of the chicks within the group. Moreover, these characteristics varied with the age of the chicks. Finally, chicks in the less rhythmic groups weighed less. These results stress the adaptive value of this temporal organisation strategy under natural conditions.     

Circadian and Ultradian Variations in the Plasma Level of Maturational Gonadotropin (GTH II) in the Indian Catfish, Clarias batrachus

Analysis of changes in the plasma levels of GTH II over a 24-h day/night cycle revealed statistically significant circadian or ultradian variation or both in its circulating level during the gonadally active months of the reproductive cycle. The 24-h average and amplitude of circadian or ultradian rhythm in GTH II increased with the advancement of ovarian development and maturation. In April, a single peak in GTH II level was noticed in the night at 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradian rhythm) was noticed with two characteristic peaks, one in the photophase and the other in the scotophase. In addition, in May a statistically significant circadian rhythm in plasma GTH II was validated with a peak located at 20.1 h. These rhythms seem to have physiological significance. The ultradian rhythm with two peaks during the reproductively active phase appears to provide a suitable physiological milieu for the temporally different yet synchronous population of oocytes for the secretion of steroids. Thus, the observed temporal organization in GTH II may have physiological consequences leading to accomplishment of reproductive process at appropriate time of the year.     

Ultradian Rhythm of Activity in Japanese Quail Groups under Semi-Natural Conditions during Ontogeny: Functional Aspects and Relation to Circadian Rhythm

The function of ultradian rhythms is not yet clearly elucidated. In particular, short-term rhythms are expressed during early ontogeny, especially in broods of precocial birds. We investigated the relationship between the clarity of the ultradian rhythm of the activity/rest cycle of a group of young Japanese quail (Coturnix japonica) and the level of social synchronisation and spatial cohesion between the birds within that group. The subjects were descended from two lines selected for either very pronounced rhythmic or arrhythmic circadian activity. We found a positive relationship between the clarity of the ultradian rhythm of the activity/rest cycle when birds were young and the clarity of the circadian rhythm of feeding activity when birds were older, but still immature. The temporal organisation of the behaviour of the chicks from these two lines was observed in outdoor aviaries, when they were 4, 8, 12 and 15 days old. The mean ultradian period expressed by groups of 12 chicks was variable, with a minimum of 6 minutes. The ultradian period lengthened regularly as chicks grew older, and reached approximately 40 min on day 15. The clarity of the ultradian rhythmicity of group activity was linked to the level of inter-individual social synchronisation and of spatial cohesion; the more pronounced the ultradian rhythms of a group, the greater the temporal and spatial cohesion of the chicks within the group. Moreover, these characteristics varied with the age of the chicks. Finally, chicks in the less rhythmic groups weighed less. These results stress the adaptive value of this temporal organisation strategy under natural conditions.     

Disruptions of Ultradian and Circadian Organization of Core Temperature in a Rat Model of African Trypanosomiasis Using Periodogram Techniques on Detrended Data

Periodogram techniques on detrended data were used to determine the incidence of Trypanosoma brucei brucei infection on the distribution of the core temperature of rats and the expression of temperature rhythms. In such an animal model, sudden episodic hypothermic bouts were described. These episodes of hypothermia are used here as temporal marks for the purpose of performing punctual comparisons on temperature organization. The experiment was conducted on 10 infected and 3 control Sprague‐Dawley rats reared under a 24 h light‐dark cycle. Core temperature was recorded continuously throughout the experiment, until the animals' death. Temperature distributions, analyzed longitudinally across the full duration of the experiment, exhibited a progressive shift from a bimodal to unimodal pattern, suggesting a weakening of the day/night core temperature differences. After hypothermic events, the robustness of the circadian rhythm substantially weakened, also affecting the ultradian components. The ultradian periods were reduced, suggesting fragmentation of temperature generation. Moreover, differences between daytime and nighttime ultradian patterns decreased during illness, confirming the weakening of the circadian component. The results of the experiments show that both core temperature distribution and temperature rhythm were disrupted during the infection. These disruptions worsened after each episode of hypothermia, suggesting an alteration of the temperature regulatory system.     

Ultradian Growth in Prochlorococcus spp

Species of the widespread marine prokaryote Prochlorococcus exhibited ultradian growth (faster than 1 division per day) both in situ and in culture, even though cell division is strictly phased to the light-dark cycle. Under optimal conditions a second DNA replication and cell division closely followed, but did not overlap with, the first division. The timing of cell cycle events was not affected by light intensity or duration, suggesting control by a light-triggered timer or circadian clock rather than by completion of a light-dependent assimilation phase. This mode of ultradian growth has not been observed previously and poses new questions about the regulation of cellular rhythms in prokaryotes. In addition, it implies that conclusions regarding the lack of nutrient limitation of Prochlorococcus in the open ocean, which were based on the appearance that cells were growing at their maximal rate, need to be reconsidered.     

Circadian Variations of Heart Rate and Premature Beats in Healthy Subjects and in Patients with Previous Myocardial Infarction

Chronobiological analysis of the circadian variations of heart rate, ventricular and atrial ectopies, was carried out on 11 patients with previous myocardial infarction matched with 11 controls. Individual circadian rhythms in heart rate were seen in all the control subjects but only in 6 patients with previous myocardial infarction. The behaviour of the individual circadian rhythms of premature beats was not significantly different between the two groups. A significant group rhythm in ectopies was not demonstrated, nevertheless a trend to higher frequency of arrhythmias during the activity span was detected. These results do not allow to postulate a circadian pattern of arrhythmias common to all the subjects examined. Therefore, the individual circadian behaviour of premature atrial and ventricular beats should be recognized for monitoring antiarrhythmic therapy. A significant group rhythm in heart rate was demonstrated for the two populations studied and linear discriminant analysis showed that the amplitude of this rhythm was significantly lower in patients than in controls. Possibly, myocardial infarction may affect the sinus node function producing a “flattened” range of heart rates during the 24 hours.