Related Experiment Video
Updated: Mar 21, 2026
Assessing Cerebral Autoregulation via Oscillatory Lower Body Negative Pressure and Projection Pursuit Regression
Published on: December 10, 2014
The Interaction Between Heart Systole and Cerebral Circulation During Lower Body Negative Pressure Test
Kasprowicz Magdalena1, Marek Czosnyka2, Rolf R Diehl3
1Department of Biomedical Engineering, Wroclaw University of Technology, Plac Grunwaldzki 13 (D1), Wroclaw, 50-377, Poland. magdalena.kasprowicz@pwr.wroc.pl.
Insights
Cerebral hemodynamics were assessed using time constant (τ) and τ*heart rate (HR) during lower body negative pressure. Findings indicate prolonged arterial filling time at presyncope, suggesting increased cerebral blood supply during this critical phase.
Area of Science:
- Cardiovascular physiology
- Cerebrovascular regulation
- Hemodynamic monitoring
Background:
- The time constant (τ) quantifies arterial cerebrovascular filling during the cardiac cycle.
- The τ*heart rate (HR) product relates arterial filling time to the overall cardiac cycle.
- Understanding cerebral hemodynamics during stress is crucial for cardiovascular health.
Purpose of the Study:
- To investigate changes in cerebral hemodynamics using τ and τ*HR during a progressive lower body negative pressure (LBNP) test.
- To assess the relationship between arterial filling time and cardiac cycle duration under simulated hypovolemia.
- To identify hemodynamic markers of presyncope.
Main Methods:
- Simultaneous recording of transcranial Doppler cerebral blood flow velocity (CBFV), Finapres arterial blood pressure (ABP), and HR in 38 healthy volunteers.
- Estimation of τ using mathematical transformation of ABP and CBFV pulse waveforms.
- Application of progressive lower body negative pressure (LBNP) to induce controlled hemodynamic stress and approach presyncope.
Main Results:
- The time constant (τ) shortened from baseline (0.20 ± 0.06 s) to maximal LBNP before presyncope (0.15 ± 0.05 s).
- A significant increase in τ was observed at presyncope (0.24 ± 0.15 s; p=0.0001).
- The τ*HR product remained unchanged during LBNP until presyncope, where it significantly increased (40.4 ± 21.1 %; p<0.000001).
Conclusions:
- Cerebrovascular arterial filling time (τ) is prolonged at the point of presyncope during LBNP.
- The increased τ*HR at presyncope suggests a greater proportion of the cardiac cycle is dedicated to cerebral blood supply.
- These findings highlight dynamic cerebrovascular adjustments during simulated hypovolemia and provide insights into presyncope mechanisms.
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.
Related Concept Videos
01:17Measurement of Blood Pressure
01:21Sites for measuring blood pressure
The Brachial Artery: Primary Site for Blood Pressure Measurement
01:28Special considerations while measuring blood pressure
Monitoring Both Arms:
Monitoring BP in both arms during the initial assessment is advisable, as the systolic value may differ by five to ten mm Hg between arms. For subsequent BP assessments, use the arm with the higher reading.
01:26Exercise Stress Test
Exercise stress testing, commonly known as a treadmill test, is a noninvasive procedure used to evaluate cardiovascular function and diagnose heart conditions.
Definition
An exercise stress test measures the heart's response to exertion using a treadmill or stationary bicycle. Chest electrodes record the heart's electrical activity through an ECG, and blood pressure is monitored regularly.
Purposes
01:23Assessment of blood pressure in brachial artery(two-step method)
01:27Assessment of the Cardiovascular System III: Palpation
Jugular Venous Pressure (JVP) Measurement
Position the patient at a thirty- to forty-five-degree angle or in a semi-fowler's position. Look for the highest point of pulsation in the internal jugular vein and measure the vertical distance to the angle of Loius or sternal angle. A normal JVP is 3-4 cm above...