title: The Interaction Between Heart Systole and Cerebral Circulation During Lower Body Negative Pressure Test.
abstract: The time constant (τ[s]) estimates how fast the arterial part of the cerebrovascular bed fills with blood volume during the cardiac cycle, whereas a product of τ and heart rate (HR) (τ*HR[%]) assesses how this period of arterial filling is related to an entire heart cycle. In this study we aimed to investigate cerebral hemodynamics using τ and τ*HR during a progressive lower body negative pressure (LBNP) test.Transcranial Doppler cerebral blood flow velocity (CBFV), Finapres arterial blood pressure (ABP), and HR, along with end-tidal CO2, were simultaneously recorded in 38 healthy volunteers during an LBNP test. The τ was estimated using mathematical transformation of ABP and CBFV pulse waveforms. After a gradual shortening of τ from baseline (0.20 ± 0.06 s) to maximal LBNP before the onset of presyncope (0.15 ± 0.05 s), we observed a significant increase in τ at presyncope (0.24 ± 0.15 s; p = 0.0001). In the course of LBNP, the τ*HR did not significantly change from baseline (25.6 ± 5.7 % vs 26.6 ± 8.9 %, p = n.s.) except for presyncope, when it increased to 40.4 ± 21.1 % (p < 0.000001). Because the time needed to fill the arterial part of the cerebrovascular bed with blood is prolonged during presyncope, an increased part of the heart cycle seems to be spent on the cerebral blood supply.
authors.affiliation: Department of Biomedical Engineering, Wroclaw University of Technology, Plac Grunwaldzki 13 (D1), Wroclaw, 50-377, Poland. magdalena.kasprowicz@pwr.wroc.pl.
authors.forename: Kasprowicz
authors.initials: K
authors.lastname: Magdalena
authors.affiliation: Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.affiliation: Department of Neurology, Alfried-Krupp-Krankenhaus, Essen, Germany.
authors.forename: Rolf R
authors.initials: RR
authors.lastname: Diehl
authors.affiliation: Department of Neurology, University Hospital Aachen, Aachen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Haubrich
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D013575:Syncope / Q000503:physiopathology*; D013599:Systole / Q000502:physiology*; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult
keywords: Cerebral arterial time constant; Cerebrovascular hemodynamics; Lower body negative pressure test