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Time dynamics of cerebral blood flow during LBNP (1183.11)
Author(s) -
Kasprowicz Magdalena,
Czosnyka Marek,
Diehl rolf,
Haubrich christina
Publication year - 2014
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.28.1_supplement.1183.11
Subject(s) - presyncope , medicine , blood pressure , cardiology , heart rate , cerebral blood flow , hemodynamics , pulse pressure , stroke volume , blood flow , anesthesia
Background: The time constant (τ) estimates how fast the arterial part of cerebral vascular bed is filled with blood volume during the cardiac systole. We have demonstrated previously that τ provides new insights into time dynamics in different cardiovascular diseases and during CO2 challenge in normal subjects. In this study we aimed to investigate time dynamics of cerebral blood flow using τ during progressive lower body negative pressure (LBNP) test. Material and Methods:Simultaneous recordings of TCD cerebral blood flow velocity (CBFV) in MCA, Finapres arterial blood pressure (ABP) and heart rate (HR) along with end‐tidal CO2 (EtCO2) were performed in 38 healthy volunteers (26 ± 4 years) during LBNP test. τ and τ*HR [beat] were estimated during lower body negative pressure ‐ using mathematical transformation of ABP and CBFV pulse waveforms. The analysis of variance (ANOVA) with Bonferroni post‐hoc test were used to compare the differences in hemodynamic variables between the stages of LBNP test. The level of significance was set as 0.05. Key Results / Statistics: From baseline to maximal LBNP before the onset of presyncope the gradual shortening of τ by 74±6% (mean ±95%CI) of baseline was observed with no further decrease in τ at presyncope (76±8%) ‐ see figure 1. The τ*HR did not change significantly in the course of LBNP up to the presyncope when it increased by 119±11% of baseline (p<0.0013). At presyncope reduction in ABP was by 90±5% of baseline, in CBFV by 77±3% of baseline, and in EtCO2 by 81±5% of baseline whereas HR increased by 162±9% of baseline. Conclusion: The time constant Tau sheds light onto a new aspect of the pathophysiology of presyncope. Although the heart systole contributes an increasing part to the cerebral circulation the failure of cerebral circulation cannot be prevented. Tau*HR indicates a significant downslow of the cerebral circulation during LBNP just before the occurrence of presyncopal complaints.