Background: Experimental generation of 0.1 Hz oscillations (~10-s cycle) in arterial pressure and cerebral blood flow has been shown to increase tolerance to simulated hemorrhage and protect cerebral tissue oxygenation. The transmission of this pulsatile blood flow into the brain can be affected by multiple factors, including stiffness (or compliance) of the feed arteries, such as the carotid artery. A stiffer (or less compliant) carotid artery exhibits lower pulsatile dampening, resulting in greater amplitude of pulsatile blood flow. Further, while sex hormones, such as testosterone and estrogen, are known to modulate arterial stiffness, particularly with age, the effect of these hormones on carotid artery stiffness in young and healthy adult humans is unclear. For these reasons, we examined common carotid artery (CCA) stiffness and the magnitude of induced 0.1 Hz cerebral blood flow oscillations in young and healthy males and females. We hypothesized that CCA stiffness would be similar between young women vs. young men, and, subsequently, the amplitude of cerebral blood flow oscillations at 0.1 Hz would also be similar. Methods: Twelve healthy human subjects were tested (6 male, 6 female; 27.4 ± 4.3 y). Middle cerebral artery velocity (MCAv) was measured via transcranial Doppler ultrasound as an index of cerebral blood flow, mean arterial pressure (MAP) was measured via finger photoplethysmography, and CCA diameters were measured via ultrasound. Resting CCA stiffness was calculated with the beta stiffness index (natural log of the ratio of systolic and diastolic arterial pressure divided by the ratio of systolic and diastolic CCA diameters). Following a 10-min baseline period, intermittent thigh cuff inflations at 0.1 Hz and 230 mmHg (5-s inflation, 5-s deflation) were performed for 10-min ("oscillations"). 0.1 Hz oscillatory amplitudes of mean MCAv and MAP were quantified using Fast Fourier transformation during the 10-min of the oscillatory period. CCA beta stiffness and the magnitude of 0.1 Hz MCAv oscillations and MAP oscillations were compared between males and females via two-tailed t-tests. Results: There was no sex difference for resting CCA beta stiffness (males: 7.0 ± 1.0 au vs. females: 8.5 ± 3.6; P=0.35), the amplitude of 0.1 Hz oscillations in mean MCAv (males: 300.7 ± 272.4 (cm/s)2 vs. females: 343.4 ± 331.4 (cm/s)2; P=0.81), or the amplitude of 0.1 Hz oscillations in MAP (males: 901.7 ± 792.4 mmHg2 vs. females: 1072.7 ± 799.1 mmHg2; P=0.72) during the oscillatory condition. Conclusions: In young healthy adults, there were no sex differences in CCA stiffness, which may account for the similar magnitude of 0.1 Hz cerebral blood flow oscillations. Further studies are needed to examine these relationships in individuals with more variable arterial stiffness (e.g., older individuals).
