Procedures for numerical analysis of circadian rhythms

Refinetti, Roberto; Lissen, Germaine Corné; Halberg, Franz

doi:10.1080/09291010600903692

Cited by 598 publications

(507 citation statements)

References 148 publications

(169 reference statements)

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“…Each time series was analyzed by cosinor rhythmometry (Nelson et al, 1979;Refinetti et al, 2007) to identify four rhythmic parameters: mesor (mean level), amplitude (half the range of oscillation), acrophase (time of peak), and robustness (strength of rhythmicity, herewith denoted by the lower-case Greek latter ρ). The cosinor procedure assigns 100% robustness only to time series that are perfectly sinusoidal; however, natural biological noise always reduces the robustness of circadian rhythms, keeping it below 100% (Refinetti, 2004), and the strength of rhythmicity can be estimated by the cosinor procedure even when the wave form of the rhythm is not sinusoidal (Refinetti et al, 2007).…”

Section: Resultsmentioning

confidence: 99%

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Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions

Alhaidary

Abdoun

Samara

et al. 2016

Research in Veterinary Science

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See next page for additional authorsThis is an author-produced, peer-reviewed version of this article. © 2016, Elsevier. Licensed under the Creative Commons NonCommercial-NoDerivs 4.0 license. Details regarding the use of this work can be found at: http://creativecommons.org/licenses/by-nc-nd/4.0/. Abstract Camels are well adapted to hot arid environments and can contribute significantly to the economy of developing countries in arid regions of the world. Full understanding of the physiology of camels requires understanding of the internal temporal order of the body, as reflected in daily or circadian rhythms. In the current study, we investigated the daily rhythmicity of 20 physiological variables in camels exposed to natural oscillations of ambient temperature in a desert environment and compared the daily temporal courses of the variables. We also studied the rhythm of core body temperature under experimental conditions with constant ambient temperature in the presence and absence of a light-dark cycle. The obtained results indicated that different physiological variables exhibit different degrees of daily rhythmicity and reach their daily peaks at different times of the day, starting with plasma cholesterol, which peaks 24 minutes after midnight, and ending with plasma calcium, which peaks 3 hours before midnight.Furthermore, the rhythm of core body temperature persisted in the absence of environmental rhythmicity, thus confirming its endogenous nature. The observed delay in the acrophase of core body temperature rhythm under constant conditions suggests that the circadian period is longer than 24 hours. Further studies with more refined experimental manipulation of different variables are needed to fully elucidate the causal network of circadian rhythms in dromedary camels.

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Section: Resultsmentioning

confidence: 99%

“…The analytical procedure includes a component of inferential statistics to calculate the probability of events as extreme as those obtained under the assumption of the null hypothesis (Nelson et al, 1979;Refinetti et al, 2007). Only events with p < 0.05 were considered to be statistically significant.…”

Section: Resultsmentioning

confidence: 99%

Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions

Alhaidary

Abdoun

Samara

et al. 2016

Research in Veterinary Science

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“…25 Laboratory measurements of rectal temperature from each dog produced time series consisting of 17 equally spaced data points, which were analyzed by cosinor rhythmometry. 26,27 Four rhythmic parameters were determined for each time series: mesor (mean level), amplitude (half the range of excursion), acrophase (time of peak) and robustness (strength of rhythmicity computed as the fraction of the variance explained by the cosine model). The cosinor procedure uses an F-test to evaluate whether the amplitude of a cosine wave fitted to the data are significantly 40 (Nelson et al 26 ).…”

Section: Resultsmentioning

confidence: 99%

Association between obesity and reduced body temperature in dogs

et al. 2010

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Background: Industrialized nations are currently experiencing an obesity epidemic, the causes of which are not fully known. One possible mechanism of enhanced energy efficiency that has received almost no attention is a reduction in the metabolic cost of homeothermy, which could be achieved by a modest lowering of body core temperature. We evaluated the potential of this obesity-inducing mechanism in a canine model of the metabolic syndrome. Methods: We compared the rectal temperature of lean dogs and obese dogs by (a) conducting cross-sectional measurements in 287 dogs of many breeds varying greatly in body size, (b) conducting longitudinal measurements in individual dogs over 7-10 years and (c) tracking rectal temperature of lean and obese dogs at 3-h intervals for 48 consecutive hours in the laboratory. Results: We found that larger dogs have lower rectal temperatures than smaller dogs and that, for the same body mass, obese dogs have lower rectal temperatures than lean dogs. The results were consistent in the cross-sectional, longitudinal and aroundthe-clock measurements. Conclusion: These findings document an association between obesity and reduced body temperature in dogs and support the hypothesis that obesity in this and other species of homeotherms may result from an increase in metabolic efficiency achieved by a regulated lowering of body temperature.

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“…[15][16][17] A two-component model, consisting of cosine curves with periods of 24 and 12 h (to approximate the non-sinusoidal waveform of BP and HR), was fitted by least squares, yielding estimates of the MESOR (Midline Estimating Statistic Of Rhythm) and of each component's double amplitude and acrophase. Results from each group were further summarized by population-mean cosinor.…”

Section: Resultsmentioning

confidence: 99%

Circadian blood pressure and heart rate characteristics in haemorrhagic vs ischaemic stroke in Chinese people

Jiang

Liu

et al. 2009

J Hum Hypertens

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To compare the circadian variation of blood pressure (BP) between patients with intra-cerebral haemorrhage (ICH) and with cerebral infarction (CI), around-the-clock BP measurements were obtained from 89 hypertensive patients with ICH, from 63 patients with CI and from 16 normotensive volunteers. The single and populationmean cosinor yielded individual and group estimates of the MESOR (Midline Estimating Statistic Of Rhythm, a rhythm-adjusted mean value), circadian double amplitude and acrophase (measures of extent and timing of predictable daily change). Comparison shows that without any difference in BP MESOR, the circadian amplitude of systolic (S) BP was larger in ICH than CI patients (Po0.001), and both groups differed from the healthy volunteers in BP MESOR and pulse pressure (Po0.001) and in the circadian amplitude of SBP (Po0.005). The smaller population circadian amplitude of diastolic (D) BP of the ICH group (P ¼ 0.042) is likely related to a larger scatter of individual circadian acrophases in this group as compared with that in the other two groups, an inference supported by a smaller day-night ratio of DBP for ICH vs CI patients (P ¼ 0.007). Heart rate (HR) variability, gauged by the standard deviation (SD), was decreased in both patient groups as compared with that in healthy controls, more so among ICH than CI patients (P ¼ 0.025). Thus, patients with ICH had a higher incidence of abnormal circadian characteristics of BP than patients with CI, the major differences relating to a larger circadian amplitude of SBP, a smaller HR-SD, and a larger incidence of odd circadian acrophases of DBP.

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Procedures for numerical analysis of circadian rhythms

Cited by 598 publications

References 148 publications

Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions

Daily rhythms of physiological parameters in the dromedary camel under natural and laboratory conditions

Association between obesity and reduced body temperature in dogs

Circadian blood pressure and heart rate characteristics in haemorrhagic vs ischaemic stroke in Chinese people

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