Influence of nocturnal and daytime sleep on initial orthostatic hypotension

• Published in: European journal of applied physiology Vol. 115; no. 2; pp. 269 - 276
• Main Authors: Lewis, N. C. S., Jones, H., Ainslie, P. N., Thompson, A., Marrin, K., Atkinson, G.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-02-2015; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Blood Pressure; Body Temperature; Cerebrovascular Circulation; Exercise; Fainting; Heart Rate; Human Physiology; Humans; Hypotension, Orthostatic - physiopathology; Laboratories; Male; Melatonin; Melatonin - metabolism; Occupational Medicine/Industrial Medicine; Original Article; Orthostatic hypotension; Photoperiod; Physical fitness; Physiology; Sleep; Sports Medicine; Veins & arteries; Velocity; United Kingdom > UK; Postural change; Cerebral blood flow; Blood pressure
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-014-3010-y

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.