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Functional Transcranial Doppler Ultrasound for Monitoring Cerebral Blood Flow
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Daily rhythm of cerebral blood flow velocity

Deirdre A Conroy1, Arthur J Spielman, Rebecca Q Scott

  • 1Department of Psychology, The Graduate School and University Center of the City University of New York, New York, USA. deirdre.conroy@att.net.

Journal of Circadian Rhythms
|March 12, 2005
PubMed

Insights

Cerebral blood flow velocity (CBFV) shows a 24-hour circadian rhythm, independent of sleep. This rhythm, linked to core body temperature, may explain lower morning CBFV and increased risk of cerebrovascular events.

Area of Science:

  • Neuroscience
  • Chronobiology
  • Cardiovascular Physiology

Background:

  • Cerebral blood flow velocity (CBFV) exhibits diurnal variations, being lower in the morning.
  • Two hypotheses explain these changes: sleep-related processes or an endogenous circadian rhythm.
  • Understanding these fluctuations is crucial for explaining morning-related health events.

Purpose of the Study:

  • To investigate the time-of-day changes in CBFV over 30 hours of sustained wakefulness.
  • To determine if CBFV fluctuations are associated with an endogenous circadian rhythm.
  • To explore the relationship between CBFV rhythms and core body temperature (CBT).

Main Methods:

  • Eleven subjects participated in a modified constant routine protocol.
  • Transcranial Doppler (TCD) ultrasonography continuously monitored middle cerebral artery CBFV.
  • Core body temperature (CBT), end-tidal carbon dioxide (EtCO2), blood pressure, heart rate, and salivary dim light melatonin onset (DLMO) were recorded.

Main Results:

  • Both CBT and CBFV displayed significant 24-hour rhythms under constant conditions (R2 = 0.62 and R2 = 0.68).
  • A 6-hour (90-degree) phase difference was observed between CBT (peak at 6:05 am) and CBFV (peak at 12:02 pm) rhythms.
  • CBFV rhythm closely tracked CBT rhythm (r = 0.77), indicating a strong correlation.

Conclusions:

  • Time-of-day variations in CBFV are regulated by a circadian oscillator, independent of sleep.
  • The 90-degree phase difference between CBT and CBFV rhythms may explain lower morning CBFV.
  • This phase difference coincides with periods of cognitive decline and increased cardiovascular/cerebrovascular events, warranting further mechanistic study.

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