74- 75:Daily rhythm of cerebral blood flow velocity 76- -- 114- sleep-associated processes or 2) time of day changes in CBFV are due to 115: an endogenous circadian rhythm independent of sleep. The aim of this 116- study was to examine CBFV over 30 hours of sustained wakefulness to -- 131- A non-linear multiple regression, cosine fit analysis revealed that 132: both the CBT and CBFV rhythm fit a 24 hour rhythm (R^2 = 0.62 and R^2 = 133- 0.68, respectively). Circadian phase position of CBT occurred at 6:05 -- 135- difference between these two rhythms (t = 4.9, df = 10, p < 0.01). Once 136: aligned, the rhythm of CBFV closely tracked the rhythm of CBT as 137- demonstrated by the substantial correlation between these two measures -- 142- In conclusion, time of day variations in CBFV have an approximately 24 143: hour rhythm under constant conditions, suggesting regulation by a 144- circadian oscillator. The 90 degree-phase angle difference between the -- 453- clock time for the CBT nadir and CBFV nadir (Synergy software, 454: Kaleidagraph Version 3.6). Third, the minimum of the circadian rhythm 455- of CBT and salivary DLMO were also used as markers of the endogenous -- 478- A 24 hour non-linear multiple regression, cosine fit analysis revealed 479: that the overall mean CBT rhythm (n = 11) fit a 24 hour cosine rhythm 480- (R^2 = 0.62, p < 0.01), Figure [100]1. The mean CBT across all subjects -- 482- non-linear multiple regression, cosine analysis fit a 24 hour cosine 483: rhythm (R^2 = 0.67, p < 0.01), Figure [102]2. The mean CBFV across 484- subjects was 40.6 cm/sec (+/- 0.54 cm/sec). Salivary DLMO occurred 7.7 -- 489- 490:CBFV rhythm is 90 degrees out of phase with the CBT rhythm 491- -- 500- difference between the phase of CBT and CBFV. However, this subject's 501: CBT rhythm was highly unusual, with the nadir occurring at 11:35 am on 502- Day 2. Nevertheless, we felt the most appropriate way to present the -- 554- particularly the 3-4.5 hour phase difference in neurobehavioral 555: functioning relative to the CBT rhythm that has been previously 556- demonstrated in constant routine protocols [[111]25]. -- 624- between Et [CO2 ]and CBT is similar to that found by Spengler et al. 625: [[129]40], who showed a consistent but small amplitude circadian rhythm 626- in mean end-tidal Et[CO2 ]on a CR protocol. Et[CO2 ]showed a trend -- 653- pressure, the phase of CBFV reaches its lowest values during the hours 654: before 12 pm. This further suggests that the endogenous rhythm of CBFV 655- may be associated with the risk of CVAs in the late morning hours even -- 660- Overall, the results demonstrate that CBFV, in the absence of sleep, 661: exhibits properties of a circadian rhythm, as it rises and falls across 662- a 24 hour period. The 6 hour (90 degree) phase angle difference in the 663: CBFV rhythm with respect to the CBT rhythm may help explain previous 664- findings of lower CBFV values in the morning. The phase difference -- 787- 14. Yan H, Shan Y, Huang W, Bai Y, Zhang Q: Effect of body position 788: changes and circadian rhythm on cerebral blood flow velocity. 789- Space Med Eng (Beijing) 1997, 10(6):421-4. [174]OpenURL -- 897- [228]Publisher Full Text [229]OpenURL 898: 40. Spengler C, Czeisler C, Shea S: An endogenous circadian rhythm of 899- respiratory control in humans.