Circadian rhythmicity in cardiac stress reactivity:
using the VU-AMS in a constant routine protocol

A.P.J. van Eekelen1 and J.H. Houtveen2

1Department of Psychonomics, University of Amsterdam, Amsterdam, The Netherlands
2Utrecht University, Utrecht, The Netherlands

 

Buijs et al. [1] have provided anatomical and functional evidence that the biological clock has direct regulatory control over the activity of the hypothalamic-pituitary-adrenocortical (HPA) axis. Because a substantial functional relationship between HPA and sympathoadrenal responses has been established, it seems logical to suggest that the biological clock may also influence autonomic (i.e. sympathetic and parasympathetic) reactivity to stress. The present study, therefore, aims to investigate the circadian rhythmicity of autonomic reactivity to stress in healthy subjects.

To examine this, a constant routine protocol was used (see also [2]). This procedure aims to control for the masking effects of sleep, posture and physical activity changes by requiring subjects to remain awake in a semi-recumbent position for a period of >24 hours. The environment in which the subjects resided during this routine was closed off from the external world, and lighting, temperature and food intake conditions were kept constant. For 19 subjects (group 1), the experiment started at 09:00 hours, whereas for 15 more subjects (group 2), it started twelve hours later, at 21:00 hours. This prevented the circadian phase being confounded by time, possibly associated with accumulating stress and/or sleepiness over the course of the experiment.

The stressor task battery - composed of four cognitive computer tasks and a cold pressor test - started at 11:00 (or 23:00) hours, and was repeated every three hours throughout the experiment. The duration of this task battery was approximately 45 minutes. Sympathetic and parasympathetic cardiac reactivities to the tasks were estimated by continuously monitoring the pre-ejection period (PEP) and respiratory sinus arithmia (RSA) using the VU-AMS device. This device was attached to the subject throughout the experiment.

Data analyses were then performed. Only time frames corresponding with the tasks were analysed. These data were analysed in segments representing 32 seconds, using the PTFAP software V2.10 [3]. This software was used for artefact pre-processing, and for computing mean heart periods and high-frequency heart period power values to estimate RSA (i.e. 0.125-0.5 Hz, using discrete Wavelet transformations). The B-points were determined manually for each ensemble-averaged ICG segment (i.e. 30 s) to obtain PEP values. Finally, repeated measures ANOVAs were used to explore the effects of time of day and time-on task on autonomic stress reactivity.

References

  1. Buijs, R.M.; Wortel, J.; Heerikhuize, J.J.; Feenstra, M.G.P.; TerHorst G.J.; Romijn H.J.; Kalsbeek, A. (1999). Anatomical and functional demonstration of a multisynpatic suprachiasmatic nucleus adrenal (cortex) pathway. Eur J Neurosci, 11, 1535-1544.
  2. Czeisler, C.A.; Klerman, E.B. (1999). Circadian and sleep-dependent regulation of hormone release in humans. Recent Prog Horm Res, 54, 97-130.
  3. Houtveen, J.H.; Molenaar, P.C.M. (2001). Comparison between the Fourier and Wavelet methods of spectral analysis applied to stationary and non-stationary heart period data. Psychophysiology, 38, 729-735.

Paper presented at Measuring Behavior 2002 , 4th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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