Functional implications of impaired dynamic cerebral autoregulation in young healthy women; a comparative investigation

Abstract

Women exhibit higher prevalence of orthostatic hypotension with presyncopal symptoms compared to men. These symptoms could be influenced by an attenuated ability of the cerebrovasculature to respond to rapid changes in blood pressure (BP) [dynamic cerebral autoregulation (dCA)]. However, the influence of sex on dCA remains equivocal. We compared dCA in 11 women (25 ± 2 y) and 11 age-matched men (24 ± 1 y) using a multimodal approach including a sit-to-stand maneuver and forced oscillations (5 min of squat-stand performed at 0.05 and 0.10 Hz). The prevalence of initial orthostatic hypotension (IOH; decrease in systolic ≥ 40 mmHg and/or diastolic BP ≥ 20 mmHg) during the first 15 sec of sit-to-stand was determined as a functional outcome. In women, the decrease in mean middle cerebral artery blood velocity (MCAvmean) following the sit-to-stand was greater (−20 ± 8 vs. -11 ± 7 cm sec-1; p=0.018) and the onset of the regulatory change (time lapse between the beginning of the sit-to-stand and the increase in the conductance index (MCAvmean/mean arterial pressure(MAP)) was delayed (p=0.007). Transfer function analysis gain during 0.05 Hz squat-stand was ∼48% higher in women (6.4 ± 1.3 vs. 3.8 ± 2.3 sec; p=0.017). The prevalence of IOH was comparable between groups (4/9 vs. 5/9, p=0.637). These results indicate the cerebrovasculature of healthy women has an attenuated ability to react to large and rapid changes in BP in the face of preserved orthostasis, which could be related to a higher cerebrovascular reserve to face a rapid transient hypotension.NEWS & NOTEWORTHYThe novel findings of this study are that healthy women have impaired dynamic cerebral autoregulation, although the prevalence of orthostatic intolerance was similar in women and men. These results indicate the cerebrovasculature of healthy women has an attenuated ability to react to large and rapid changes in blood pressure in the face of preserved orthostasis, which could be related to a higher cerebrovascular reserve to face a rapid transient hypotension.

Novel Application of a Force Sensor during Sit-to-Stands to Measure Dynamic Cerebral Autoregulation Onset

“…We hypothesized that measuring AO precisely with a force sensor would identify previously unobserved variability in standing dynamics compared to estimating AO from a verbal command or other methods. (6,8,10,13) We have shown that while healthy young adults may demonstrate a faster transition reaction speed during a sit-to-stand dCA recording,(4, 8) older adults and individuals post-stroke may differ in their AO response. We have shown that the TD before the onset of dCA, which typically occurs within 10 seconds, (6,8,10,14) could potentially be skewed in some individuals by more than 2.5 seconds, which would directly affect dCA metrics.…”

“…Based on previously published methodology, the TD before the onset of the dCA regulatory response was measured as seconds between performing the sit-to-stand and a continuous increase in CVC without transient reduction (CVC = MCAv/MAP). (6,10) Rather than estimating AO in the recording as 60 seconds, our force sensor marks the exact AO time. We calculated the difference in the TD response when using the force sensor compared to estimating AO at 60 seconds, or when the participant was asked to stand.…”

“…(9) To counteract the drop in blood pressure, dCA responds by increasing the conductance of MCAv to the cerebrovascular system before MAP increases in the peripheral vascular system. (6) While previous studies in healthy young and older adults have performed the sit-to-stand technique to measure the dCA response, (6,8,(10)(11)(12)(13)(14)(15) the exact methods of characterizing dCA have varied between studies. While some report having the individual stand quickly (within 0-3 seconds) and mark the initiation of standing as when the verbal command was given, (6,(10)(11)(12) others report having the individual place their feet on a stool in front of them (legs at 90 degrees) and mark the initiation of standing from when their feet touch the floor.…”

“…(6) While previous studies in healthy young and older adults have performed the sit-to-stand technique to measure the dCA response, (6,8,(10)(11)(12)(13)(14)(15) the exact methods of characterizing dCA have varied between studies. While some report having the individual stand quickly (within 0-3 seconds) and mark the initiation of standing as when the verbal command was given, (6,(10)(11)(12) others report having the individual place their feet on a stool in front of them (legs at 90 degrees) and mark the initiation of standing from when their feet touch the floor. (8,(13)(14)(15) However, the moment of standing from a seated position is not objectively marked.…”

“…(16) To address this gap in the literature, we developed a force sensor to determine the kinetic moment of arise-and-off (AO). ( 16) Compared to estimating AO from a verbal command similar to previous work, (6,(10)(11)(12) we hypothesized that measuring the exact moment of AO, measured with a force sensor, would alter the calculation of the TD before the onset of the dCA response. We conducted the procedure twice separated by 15 minutes (T1= first sit to stand and T2 = second sit to stand).…”