Interactions Between Carotid Arterial Stiffness, Amplitude of Cerebral Blood Flow Oscillations, and Cerebral Tissue Oxygenation During Simulated Hemorrhage in Humans


Introduction: Inducing 0.1 Hz (10-s cycle) oscillations in cerebral blood flow attenuates the reduction in cerebral tissue oxygenation during simulated hemorrhage in humans. It is unknown, however, how stiffness of the cerebral feed arteries influences the magnitude of cerebral blood flow oscillations, and/or the protection of cerebral tissue oxygenation. When 0.1 Hz oscillations are induced during simulated hemorrhage, we hypothesize that: 1) arterial stiffness of the internal carotid artery (ICA) will increase from rest; 2) the amplitude of 0.1 Hz oscillations in cerebral blood flow will be higher in individuals with stiffer arteries, and; 3) the reduction in cerebral tissue oxygenation will be smaller with higher amplitude of cerebral blood flow oscillations.

Methods: 8 healthy human participants (age: 30.1±7.6 y) underwent a 10-min hypovolemic oscillatory lower body negative pressure (OLBNP) protocol, where chamber pressure oscillated every 5-s between -30 mmHg and -90 mmHg (i.e., 0.1 Hz). ICA beta stiffness index was calculated from measurements of ICA diameter (via ultrasound imaging), and arterial pressure (via finger photoplethysmography). Middle cerebral artery velocity (MCAv) was measured using transcranial doppler ultrasound, and cerebral tissue oxygenation (ScO2) was measured with near infrared spectroscopy. Fast Fourier transformation was used to quantify oscillations in mean MCAv at ~0.1 Hz.

Results: While Mean MCAv 0.1 Hz oscillations increased from baseline to OLBNP (N=8, 34.0±33.9 (cm/s)2vs. 104.7±58.1(cm/s)2, p=0.01), ICA beta stiffness did not increase (N=5, 6.1±0.7 au vs. 8.2±2.7 au, p=0.21). There was no relationship between baseline ICA beta stiffness and the percent change in mean MCAv 0.1 Hz oscillations (N=5; r=0.44, p=0.46). ScO2 decreased from baseline to OLBNP (N=8, 66.5±2.9 % vs. 64.8±2.9%,p=0.03), but there was also no relationship between the percent change in mean MCAv 0.1 Hz oscillations and the decrease in ScO2(r=0.28, p=0.50).

Conclusions: Based on these data, 0.1 Hz OLBNP does not affect ICA stiffness, and there is no relationship between ICA stiffness, amplitude of induced 0.1 Hz cerebral blood flow oscillations, and the reduction in cerebral tissue oxygenation during simulated hemorrhage. However, as this analysis was performed retrospectively, and arterial stiffness was not initially an outcome measure, there was limited data available for analysis. This limitation will be addressed in a project currently in progress in our laboratory.


Research Appreciation Day Award Winner - School of Biomedical Sciences, 2024 Department of Physiology & Anatomy (Integrative Physiology) Award - 1st Place