Ultradian and circadian compartmentalization of respiratory and metabolic exchanges in small laboratory vertebrates

Carbon dioxide emission (VCO2) taken as an index of respiratory and metabolic exchanges, was continuously recorded during 4-30 consecutive days in 100 quail, 87 chicks, 347 rats, 665 mice and 70 guinea-pigs which were under controlled environmental parameters. Harmonic analysis, fast Fourier transform, chi-square periodograms, peak and trough intervals were computed with VCO2 values obtained with CO2 concentrations sampled every 20 min on the CO2 recordings. In LD 12:12 alternation, circadian rhythms were observed in all quail, chicks, rats and mice, but only in 80% of the guinea-pigs. Ultradian VCO2 rhythms, with periods which show statistically significant interspecies differences, were assessed. For each of the 5 species these computed periods, which were the same in LL and DD, were: 1.17 h for quail and chickens, 1.25 h for rats, 1.50 h for mice and 1.0 h for guinea-pigs. In LD 12:12 these periods were different during L and D in quail, chicks, rats and mice, but not in guinea-pigs. The amplitudes of these ultradian variations were, according to the species, 10-20% of their mean VCO2 levels. These ultradian rhythms persist in the absence (or masking) of circadian rhythms, e.g. in LD 12:12 in 20% of guinea-pigs and in LL in 87% of Japanese quail and in 23% of Sprague-Dawley rats. Moreover, these ultradian rhythms persist during starvation, locomotor activity restraint and ageing. These ultradian VCO2 cycles which are related to rest-activity variations appear to be basic physiological rhythms with a genetic origin.     

Analysis of the biorhythm frequency of bordered enterocytes during normal and inverted feeding regimens

The study was performed during the period close to equinox in 236 male mice C57 Bl strain, sacrificed at equal intervals during 5 days. In paraffin sections, 5--6 mcm thick, stained after Dominici-Kedrovsky, with additional application of PAS-reaction and alcian blue, the cell height and width in the small intestine border enterocyte zone were determined. Calculation of autocorrelative function with the following determination of spectral density, infradian, circadian and ultradian biorhythmical components were estimated, as well as their changes under the influence of feeding regime inversion. At evening feeding, the greatest width of the brush border coinsides the beginning and the end of the digestion period. The width of the dark apical zone, where mitochondria are concentrated, synchronously changes at the end of digestion with the brush border, and then- with the cell basal zone. At morning feeding, by the degree of circadian phase change, the most liable are the indices reflecting organoid status, which are closely involved in absorbtion processes. Ultradian rhythm produces, on the background of circadian changes, additional raisis and abatements. Spectral composition, under inadequate feeding, is demonstrated to become more complex, mainly at the expense of ultradian rhythms, that speaks of their importance for the processes of adaptive rhythmical rearrangement.     

Effect of geomagnetic activity on the rhythm of resistance of rats to hypoxia

The resistance of male Wistar rats to acute hypoxia was estimated from the lifetime at an "altitude" of 11.5 km above sea level from 13 to 21 p.m. and in different seasons of a year. Identical types of rhythms (circaseptan, circasemiseptan, infradian, circadian, and ultradian) of geomagnetic activity and lifetime were revealed. It was found that the periods of basal rhythms either coincide or are multiple. It was shown that the rhythms of geomagnetic activity (including nonbasal rhythms) affect lifetime rhythms (especially ultradian rhythms). As the periods of the rhythms decrease, the number of rhythms for both parameters increase (ultradian rhythms are most numerous), and relative differences in the values of periods (they are minimal for ultradian rhythms) and the amplitudes of rhythms decrease.     

UVA‐induced reset of hydroxyl radical ultradian rhythm improves temporal lipid production in Chlorella vulgaris

We report for the first time that the endogenous, pseudo‐steady‐state, specific intracellular levels of the hydroxyl radical (si‐OH) oscillate in an ultradian fashion (model system: the microalga, Chlorella vulgaris), and also characterize the various rhythm parameters. The ultradian rhythm in the endogenous levels of the si‐OH occurred with an approximately 6 h period in the daily cycle of light and darkness. Further, we expected that the rhythm reset to a shorter period could rapidly switch the cellular redox states that could favor lipid accumulation. We reset the endogenous rhythm through entrainment with UVA radiation, and generated two new ultradian rhythms with periods of approximately 2.97 h and 3.8 h in the light phase and dark phase, respectively. The reset increased the window of maximum lipid accumulation from 6 h to 12 h concomitant with the onset of the ultradian rhythms. Further, the saturated fatty acid content increased approximately to 80% of total lipid content, corresponding to the peak maxima of the hydroxyl radical levels in the reset rhythm. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:673–680, 2014     

Independence between Rhythms of Temperature and Progesterone in Mares

We investigated the ultradian and diurnal body temperature and plasma progesterone concentration rhythms and the temporal relationship between them in mares during the midluteal phase. Data were obtained from 6 mares at 3-h intervals for 3 consecutive days. Cosinor analysis showed that body temperature acrophases occurred in the evening, whereas the progesterone acrophases occurred in the early morning (3 mares) and at night (3 mares). The spectral analysis of the temperature data showed periods of 24 hr for all mares and of 8 hr for 1 mare. In contrast, the periods observed for plasma progesterone concentration were quite divergent (24 and 12 hr). The small variation in the rhythmic parameters of body temperature suggests that its oscillator system is stable. No phase relationship was detected between the rhythmometric parameters of body temperature and plasma progesterone concentration, suggesting that the physiological mechanisms of control of the 24 hr and ultradian rhythm of the two variables are not coupled during the midluteal phase.     

Independence between Rhythms of Temperature and Progesterone in Mares

We investigated the ultradian and diurnal body temperature and plasma progesterone concentration rhythms and the temporal relationship between them in mares during the midluteal phase. Data were obtained from 6 mares at 3-h intervals for 3 consecutive days. Cosinor analysis showed that body temperature acrophases occurred in the evening, whereas the progesterone acrophases occurred in the early morning (3 mares) and at night (3 mares). The spectral analysis of the temperature data showed periods of 24 hr for all mares and of 8 hr for 1 mare. In contrast, the periods observed for plasma progesterone concentration were quite divergent (24 and 12 hr). The small variation in the rhythmic parameters of body temperature suggests that its oscillator system is stable. No phase relationship was detected between the rhythmometric parameters of body temperature and plasma progesterone concentration, suggesting that the physiological mechanisms of control of the 24 hr and ultradian rhythm of the two variables are not coupled during the midluteal phase.     

Ultradian, circahoral and circadian structures in endothermic vertebrates and humans

1. For more than 30 years many studies have been carried out concerning rhythms with periods approaching 24 hr (circadian rhythms). 2. The latter have been demonstrated as resulting from environmental 24 hr synchronizers (zeitgebers), but they usually persist in the absence of a 24 hr synchronization, which proves their endogenous nature. 3. Biological rhythms with periods less than 20 hr (ultradian rhythms) and particularly those approaching 1 hr (circahoral rhythms) have been determined: for motility, rest-activity, sleep phases, endocrine secretions and other physiological functions. 4. These ultradian and circahoral rhythms have been found in rodents, birds, monkeys and humans. 5. Existing at all stages of ontogeny, they have been proved to be endogenous and species and strain specific. 6. As these ultradian rhythms can be influenced by environmental factors and sometimes by circadian rhythms they are not truly periodic, so therefore cannot be computed by the usual processes of mathematical time analysis.     

Circadian organization of a subarctic rodent, the northern red-backed vole (Clethrionomys rutilus)

Arctic and subarctic environments are exposed to extreme light: dark (LD) regimes, including periods of constant light (LL) and constant dark (DD) and large daily changes in day length, but very little is known about circadian rhythms of mammals at high latitudes. The authors investigated the circadian rhythms of a subarctic population of northern red-backed voles (Clethrionomys rutilus). Both wild-caught and third-generation laboratory-bred animals showed predominantly nocturnal patterns of wheel running when exposed to a 16:8 LD cycle. In LL and DD conditions, animals displayed large phenotypic variation in circadian rhythms. Compared to wheel-running rhythms under a 16:8 LD cycle, the robustness of circadian activity rhythms decreased among all animals tested in LL and DD (i.e., decreased chi-squared periodogram waveform amplitude). A large segment of the population became noncircadian (60% in DD, 72% in LL) within 8 weeks of exposure to constant lighting conditions, of which the majority became ultradian, with a few individuals becoming arrhythmic, indicating highly labile circadian organization. Wild-caught and laboratory-bred animals that remained circadian in wheel running displayed free-running periods between 23.3 and 24.8 h. A phase-response curve to light pulses in DD showed significant phase delays at circadian times 12 and 15, indicating the capacity to entrain to rapidly changing day lengths at high latitudes. Whether this phenotypic variation in circadian organization, with circadian, ultradian, and arrhythmic wheel-running activity patterns in constant lighting conditions, is a novel adaptation to life in the arctic remains to be elucidated.     

Diurnal rhythm of the total antioxidant activity of saliva of children with chronic viral hepatitis

The diurinal rhythms of a total antioxidant activity of a saliva were investigated depending on activity of the inflammatory process in a liver of children with chronic virus hepatitis HBV and HCV. The circadian rhythms were found desynchronized, which was showed in lowering of the mesor value, oscillations amplitude, and a rhythm inversion and transformation, as an additional biorhythmological criterion of the presence of the chronic hepatitis of a viral etiology. A tendency of a circadian rhythm to remain with a daily acrophasis but with a law level of amplitude oscillations and a mesor was to be observed after the treatment of children with inactive HBV. By an active HBV a circadian rhythm with it's inversion has been renewed. It was determined the remaining of an ultradian rhythm with increasing level of amplitude oscillations after the treatment of inactive HCV. The law amplitude oscillations and a insignificant increasing of a meror level were characteristic for the circadian rhythm of total AOA of the children with active HBV. It was proved the possibility of usage of the biorhythmological parameters of diurinal rhythms of total AOA as a criteria of efficiency of the conducted therapy for the given group with disease children.     

Ultradian rhythms in renal excretion in dogs

Urine flow, urinary osmolality, concentrations of sodium and potassium were measured every 10 min for 24 hours in 6 female dogs, whose sleep-wake stages were monitored electrographically. Experiments were conducted under hydration and progressive dehydration conditions. Visual examination and spectral analysis revealed significant diurnal ultradian rhythms of about 200 min/cycle in urine flow, which were out of phase with similar rhythms in osmolality in different hydratory conditions. Diurnal rhythms with similar characteristics were found in urinary potassium only in the hydration condition. Sodium excretions did not show consistent rhythmic patterns. No consistent rhythms were found in nocturnal urine parameters in different hydratory conditions. The variations in renal activities were related to the dogs' diurnal ultradian sleep-wake cycle, urine volume increased and osmolality decreased during diurnal waking episodes, and conversely volume decreased and osmolality increased during the diurnal sleep episodes.     

Direct cell-cell communication: a new approach derived from recent data on the nature and self-organisation of ultradian (circahoralian) intracellular rhythms

Recent data concerning ultradian (circahoralian) intracellular rhythms are used to assess the biochemical mechanisms of direct cell-cell communication. New results and theoretical considerations suggest a fractal nature of ultradian rhythms and their self-organisation. The fundamental and innate nature of these rhythms relates to their self-similarity at different levels of cell and tissue organisation. They can be detected in cell-free systems as well as in cells and organs in vivo. Such rhythms are a means of finding an optimal state of cell function rather than achieving a state of absolute stability. As a consequence, oscillations, being irregular and numerous by the set of periods, are resilient to functional overload and injury. Recent data on the maintenance of their fractal structure and, especially on the selection of optimal periods are discussed. The positive role of chaotic dynamics is stressed.The ultradian rhythm of protein synthesis in hepatocytes in vitro was used as a marker of direct cell-cell communication. The system demonstrates cell cooperation and synchronisation throughout the cell population, and suggests that the ultradian rhythms are self-organised. These observations also led to the detection of mechanisms of direct cell-cell communication in which extracellular factors have an essential role. Experimental evidence indicated the involvement of gangliosides and/or catecholamines in this large-scale synchronisation of protein synthesis. The response of all, or a major part, of the cell population is important; after the initial trigger effect, a periodic pattern is retained for some time. The influence of Ca2+-dependent protein kinases on protein phosphorylation can be a final step in the phase modulation of rhythms during cell-cell synchronisation.The intercellular medium plays an important role in self-synchronisation of ultradian rhythms between individual cells. Low cooperative activity of hepatocytes of old rats resulted from altered composition of the intercellular medium rather than direct effects of animal and cellular ageing. Similarly, in the whole body, changes in levels of gangliosides and catecholamines in the blood serum, a natural intercellular medium, can be critical events in age-dependent changes of the serum and accordingly cell-cell synchronisation. Hepatocytes of old rats exhibit some of the properties of young cells following an increase in blood serum ganglioside level, as well as, in in vitro conditions, after the addition of gangliosides to the culture medium.Together with data on ultradian functional and metabolic rhythms, all the material reviewed here allows us to propose a mechanism of direct cell-cell cooperation via the medium in which the cells exist, that supplements the nervous and hormonal central regulation of organ functions. Ultradian intracellular rhythms may thus provide a finer framework within which the integrated dynamics of respiration, heart rate, brain activity, and even behavioural patterns, are brought to an optimal functional pattern. Innate and direct cell-cell cooperation may have been employed as a means of intercellular regulation during the course of metazoan evolution, that preceded nervous regulation and is presently retained in mammals.     

THE OCCURRENCE AND FUNCTIONS OF ULTRADIAN RHYTHMS

Ultradian oscillations with periods between 5 min and 4 h have been described in cell-free extracts, single-celled eukaryotes, cultured cells and embryos. Whereas some of these potentially oscillatory systems (e.g. glycolysis) may only exhibit this type of behaviour rarely if at all in vivo , other ultradian oscillators in lower eukaryotes are rhythms and probably have timekeeping functions. Rhythms with ultradian periods of 10 min to 20 h in oxygen consumption and carbon dioxide production have also been studied in endotherm animals: these rhythms may be modified by variations of environmental parameters and by circadian and infradian synchronizers. Interspecies and interstrain differences strongly suggest that these rhythms are endogenous and have a genetic origin. We suggest that the temporal organization of biochemical and physiological processes facilitates optimization of thermodynamic maintenance of the organism within the random fluctuations of its physicochemical environment and contributes to genetic selection.     

Ultradian activity rhythms in large groups of newly hatched chicks (Gallus gallus domesticus)

A clutch of young chicks housed with a mother hen exhibit ultradian (within day) rhythms of activity corresponding to the brooding cycle of the hen. In the present study clear evidence was found of ultradian activity rhythms in newly hatched domestic chicks housed in groups larger than natural clutch size without a mother hen or any other obvious external time-keeper. No consistent synchrony was found between groups housed in different pens within the same room. The ultradian rhythms disappeared with time and little evidence of group rhythmicity remained by the third night. This disappearance over time suggests that the presence of a mother hen may be pivotal for the long-term maintenance of these rhythms. The ultradian rhythm of the chicks may also play an important role in the initiation of brooding cycles during the behavioural transition of the mother hen from incubation to brooding. Computer simulations of individual activity rhythms were found to reproduce the observations made on a group basis. This was achievable even when individual chick rhythms were modelled as independent of each other, thus no assumptions of social facilitation are necessary to obtain ultradian activity rhythms on a group level.     

An Experimental Analysis and Comparison of Three Rhythms of Movements in Bean (Phaseolus Vulgaris L.)

Three types of rhythmic movements of Phaseolus vulgaris L. (pole beans) were examined collectively and their characteristics compared. Although the ultradian rhythms of shoot circumnutation and leaf movement, as well as the circadian rhythm of leaf movement, occurred simultaneously, each rhythm could be expressed independently of the other two. Shoot circumnutation and ultradian leaf movements displayed the same period (80 min at 25°C and Q₁₀⋍2), while the period of the circadian leaf movements was not temperature dependent (Q₁₀⋍1). Interaction into the plant between two ultradian rhythms (shoot circumnutation and ultradian leaf movement) with the same period and coexistence in the pulvinus of an ultradian with a circadian rhythm are discussed.     

Enhancement and suppression of ultradian and circadian rhythms across the female hamster reproductive cycle

The impact of ovarian hormones on hamster ultradian rhythms (URs) is unknown. We concurrently monitored URs and circadian rhythms (CRs) of home cage locomotor activity during the estrous cycle, pregnancy, and lactation of Syrian hamsters. URs with a mean period of 4-5 h were evident during the dark phase in more than 90% of females on days 1 and 2 of the estrous cycle but were significantly less prevalent on cycle days 3 and 4. The period of the UR did not vary as a function of estrous cycle stage, but at all stages, the UR period was longer in the dark than the light phase. The UR acrophase occurred significantly earlier on cycle day 4 than on days 1 and 2, and UR robustness and amplitude were reduced on days 3 and 4. Robustness, mesor, and amplitude of CRs were greater during cycle days 3 and 4; timing of the CR acrophase was delayed on day 4 relative to all other cycle days. Effects of the estrous cycle on URs were evident only during the dark phase. The proportion of hamsters displaying dark phase URs increased significantly during early and late gestation and decreased during lactation. Pregnancy significantly increased UR complexity, robustness, and amplitude. The emergence of URs over gestation was paralleled by decrements in the robustness and amplitude of CRs, which also were absent in a significant proportion of dams during lactation but re-emerged at weaning of litters. The changing endocrine profile of the estrous cycle, hormonal dynamics of pregnancy and lactation, and nursing demands placed on dams are each associated with alterations in the expression of ultradian and circadian locomotor rhythms. Diminution of CRs and augmentation of URs may afford greater behavioral flexibility during life stages when interactions with mates and offspring are less predictable.     

Diurnal rhythms of free estradiol and cortisol during the normal menstrual cycle in women with major depression

To investigate whether depression is accompanied by changes in diurnal rhythms of free estradiol and cortisol in different phases of the menstrual cycle, we measured these two hormone levels in saliva samples collected every 2 h for 24 h from 15 healthy normally cycling women and 12 age-matched normally cycling women suffering from major depression taking antidepressants. The assessments were repeated four times over one menstrual cycle: during menstruation and in the late follicular/peri-ovulating, early to mid-luteal and late luteal phases, respectively. Quantification with a nonlinear periodic regression model revealed distinct diurnal rhythms in free estradiol and free cortisol in all subjects. For the diurnal cortisol rhythm, significant differences were found in the peak-width and ultradian amplitude among different menstrual phases, both in controls and depressed patients, while no significant differences were found between the two groups. The diurnal estradiol rhythm, on the other hand, was quite consistent among different menstrual phases within both groups, while the depressed patients had overall larger amplitudes than controls, which is negatively correlated with disease duration. Significant positive correlations between the two hormone rhythms were found for 24-h mean level (mesor), peak, and trough in late luteal phase, and for ultradian harmonics in early to mid-luteal phase in controls, but only for ultradian harmonics in late follicular/peri-ovulating phase and for acrophase in the menstruation phase in depressed patients. A sub-analysis was also performed in patients who received Fluoxetine (n = 7). The findings implicate a close correlation between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, both of which may be involved in depression.     

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.     

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.     

Circadian and ultradian rhythms in heart rate variability.

AIM: Heart rate variability (HRV) patterns reflect the changing effect of sympathetic and parasympathetic modulation of the autonomic nervous system. While overall and circadian heart rate (HR) and HRV are well characterized by traditional measures, there is currently no method to measure ultradian cycles of HR and HRV. MATERIALS AND METHODS: HR/HRV for each 2-min interval was calculated using normal-to-normal interbeat intervals from overnight polysomnographic ECGs in 113 subjects, aged 58+/-10 years (65 male, 48 female). HR, SDNN2, high-frequency power (HF) and the LF (low-frequency power)/HF ratio were plotted. A curve-fitting algorithm, developed in MatLab, identified cyclic patterns of HR/HRV and extracted parameters to characterize them. Results were compared for older vs. younger patients, males vs. females, with vs. without severe sleep apnea, and for the upper and lower half of sleep efficiency. RESULTS: Ultradian patterns for different HR/HRV indices had variable correspondences with each other and none could be considered surrogates. Differences were seen for all comparison groups, but no one marker was consistently different across comparisons. CONCLUSION: Each HR/HRV parameter has its own rhythm, and the correspondence between these rhythms varies greatly across subjects. Quantification of ultradian patterns of HRV is feasible and could provide new insights into autonomic physiology.     

Temporal organization of the thyroid gland in A/He mice (morphometric investigation)

Biological rhythms of structural elements of the thyroid gland of A/He mice were studied by morphometric methods followed by spectral amplitude and phase analysis on the Minsk-32 computer. The morphological data show that the activity of the organ is maximal at night. The biorhythms have a complex frequency spectrum, including intradian, circadian, and ultradian components.