Background: Our laboratory has shown that induced "oscillations" in blood pressure and blood flow at 10 second intervals (~0.1 Hz) protects cerebral tissue oxygenation during central hypovolemia. While greater arterial stiffness has been associated with higher pulse pressure and blood flow pulsatility, the effect of arterial stiffness on the amplitude of these induced hemodynamic oscillations has not been examined. We hypothesize that greater arterial stiffness will result in less dampening of oscillatory blood flow, and transmission of induced oscillations at a greater amplitude. Furthermore, the impact of sex and associated hormones (testosterone, estrogen, progesterone) on arterial stiffness in young healthy human adults is contentious, with some studies suggesting that women have lower arterial stiffness, while other studies suggesting there is no difference between men and women. In this study, we explore the relationships between sex, arterial stiffness, and the amplitude of induced 0.1 Hz hemodynamic oscillations within the peripheral vasculature. Hypotheses: 1) no differences will be observed between males and females for both brachial artery (BA) stiffness and the magnitude of induced 0.1 Hz oscillations in BA velocity (BAv), and, subsequently; 2) the relationship between BA arterial stiffness and amplitude of 0.1 Hz BAv oscillations will be similar between males and females. Methods: Fourteen young and healthy human subjects (7M, 7F) completed one experimental protocol. Resting arterial pressure (via finger photoplethysmography) and BA diameter and velocity (via duplex ultrasound) were measured for 10-min. Resting arterial stiffness was examined in the BA with measurement of the beta stiffness index (calculated as the natural log of the ratio of systolic and diastolic arterial pressure divided by the ratio of systolic and diastolic BA diameters). Partial ischemia of the forearm was then induced with a pneumatic cuff on the upper arm to decrease BAv by ~70-80% from baseline. Oscillations in arterial pressure and BAv were induced by inflating and deflating bilateral thigh cuffs every 5-s (0.1 Hz) throughout the forearm ischemia period. 0.1 Hz power of BAv was quantified using Fast Fourier transformation during the oscillatory period. Resting BA stiffness and the amplitude of 0.1 Hz BAv oscillations were compared between males and females with two-tailed t-tests. Correlations between BA stiffness and BAv 0.1 Hz power were assessed using Pearson correlations for both males and females. Results: Both BA stiffness (males: 32.1±14.2 au vs. females: 36.2±23.0 au; P=0.69), and BAv 0.1 Hz power (males: 36.5±70.6 (cm/s)2 vs. females: 13.1±19.7 (cm/s)2; P=0.42) were not different between males and females. However, correlations between BA beta stiffness and BAv 0.1 Hz power were relatively strong for both sexes (males: R=0.76, P=0.05; females: R=0.77, P=0.04), although the slope of this relationship was much higher in males compared with females (3.8 vs. 0.7). Conclusions: These results demonstrate that there are no sex differences in BA stiffness or the amplitude of 0.1 Hz oscillations in BAv in young and healthy participants, but the relationship between BA stiffness and the amplitude of oscillations may be more sensitive in males compared with females.
