title: Central Pulsatile Pressure and Flow Relationship in the Time and Frequency Domain to Characterise Hydraulic Input to the Brain and Cerebral Vascular Impedance.
abstract: In the time domain, pulsatile flow and pressure can be characterised as the ratio of the late systolic boost of flow or pressure to the pulse amplitude so as to estimate the hydraulic input to the brain. While vascular impedance has been widely used to represent the load presented to the heart by the systemic circulation, it has not been applied to the cerebral circulation.We set out to study the relationship between the pressure and the flow augmentation index (AIx) in the time domain and to determine cerebral vascular impedance using aortic blood pressure and cerebral blood flow waveforms in the frequency domain. Twenty-four young subjects (aged 21-39 years) were recruited; aortic pressure was derived using SphygmoCor from radial pressure. Flow waveforms were recorded from the middle cerebral artery. In three subjects, we performed the Valsalva manoeuvre to investigate their response to physiological intervention. There was a linear relationship between flow and pressure AIx, and cerebral impedance values were similar to those estimated for low resistance vascular beds. Substantial change in pressure and flow wave contour was observed during the Valsalva manoeuvre; however, the relationship in both the time and the frequency domains were unchanged. This confirms that aortic pressure and cerebral flow waveform can be used to study cerebral impedance.
authors.affiliation: Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.
authors.forename: Mi Ok
authors.initials: MO
authors.lastname: Kim
authors.affiliation: Department of Cardiology, St Vincent's Clinic, Suite 810, 438 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia. m.orourke@unsw.edu.au.|University of New South Wales/VCCRI, Sydney, NSW, Australia. m.orourke@unsw.edu.au.
authors.forename: Michael F
authors.initials: MF
authors.lastname: O'Rourke
authors.affiliation: Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.|St Vincent's Clinic, Suite 810, 438 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Audrey
authors.initials: A
authors.lastname: Adji
authors.affiliation: Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.
authors.forename: Alberto P
authors.initials: AP
authors.lastname: Avolio
mesh_terms: D000328:Adult; D062186:Arterial Pressure / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D017097:Electric Impedance; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging* / Q000502:physiology; D011673:Pulsatile Flow / Q000502:physiology*; D063177:Pulse Wave Analysis; D017585:Ultrasonography, Doppler, Transcranial; D014636:Valsalva Maneuver / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*; D055815:Young Adult
keywords: Central aortic pressure; Cerebral vascular impedance; Pressure waveform analysis