Influence of nocturnal and daytime sleep on initial orthostatic hypotension.

N.C.S Lewis, H. Jones, P.N. Ainslie, A. Thompson, Kelly Marrin, G. Atkinson

Research output: Contribution to journalArticle

Abstract

Purpose The incidence of vasovagal syncope is more common in the morning. Previous researchers have reported negligible diurnal variation in the physiological responses associated with initial orthostatic hypotension (IOH). Nevertheless, physical activity and sleep prior to morning and afternoon test times have not been controlled and may influence the findings. We designed a semi-constant routine protocol to examine diurnal variation in cardiorespiratory and cerebrovascular responses to active standing. Methods At 06:00 and 16:00 hours, nine males (27 ± 9 years) completed an upright-stand protocol. Altimetry-measured sleep durations were 3.3 ± 0.4 and 3.2 ± 0.6 h immediately prior to the morning and afternoon test times. Continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv), mean arterial blood pressure (MAP), heart rate (HR), and end-tidal carbon dioxide were obtained. Intestinal body temperature and salivary melatonin concentrations were also measured. Results Compared with the afternoon, resting HR and body temperature were 4 ± 2 beats min−1 and 0.45 ± 0.2 °C lower, respectively, whereas melatonin concentration was 28.7 ± 3.2 pg ml−1 higher in the morning (P ≤ 0.02). Although all individuals experienced IOH at both times of the day, the initial decline in MAP during standing was 13 ± 4 mmHg greater in the afternoon (P = 0.01). Nevertheless, the decline in MCAv was comparable at both times of day (mean difference: 2 ± 3 cm s−1; P = 0.5). Conclusion These findings indicate that a bout of sleep in the afternoon in healthy young individuals results in greater IOH that is compensated for by effective cerebral blood flow regulation.
Original languageEnglish
Pages (from-to)269-276
Number of pages8
JournalEuropean Journal of Applied Physiology
Volume115
Issue number2
Early online date4 Oct 2014
DOIs
Publication statusPublished - 1 Feb 2015

Keywords

  • Blood pressure
  • Cerebral blood flow
  • Postural change

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