Extremes of cerebral blood flow during hypercapnic squat‐stand maneuvers

Abstract

Squat‐stand maneuvers (SSMs) are a popular method of inducing blood pressure (BP) oscillations to reliably assess dynamic cerebral autoregulation (dCA), but their effects on the cerebral circulation remain controversial. We designed a protocol whereby participants would perform SSMs under hypercapnic conditions. Alarmingly high values of cerebral blood flow velocity (CBFV) were recorded, leading to early study termination after the recruitment of a single participant. One healthy subject underwent recordings at rest (5 min sitting, 5 min standing) and during two SSMs (fixed and random frequency). Two sets of recordings were collected; one while breathing room air, one while breathing 5% CO 2 . Continuous recordings of bilateral CBFV (transcranial Doppler), heart rate (ECG), BP (Finometer), and end‐tidal CO 2 (capnography) were collected. Peak values of systolic CBFV were significantly higher during hypercapnia ( p < 0.01), and maximal values exceeded 200 cm.s −1 . Estimates of dCA (ARI) during hypercapnia were impaired relative to poikilocapnia ( p = 0.03). The phase was significantly reduced under hypercapnic conditions ( p = 0.03). Here we report extremely high values of CBFV in response to repeated SSMs during induced hypercapnia, in an otherwise healthy subject. Our findings suggest that protocols performing hypercapnic SSMs are potentially dangerous. We, therefore, urge caution if other research groups plan to undertake similar protocols.

Novel application of a force sensor during sit‐to‐stands to measure dynamic cerebral autoregulation onset

“…Previously published sit-to-stand methodology measuring the TD before the onset of the dCA response does not report the true moment of AO from the chair and therefore does not measure the exact start of the stimulus that drops peripheral blood pressure. While force sensors have been used in the kinetic characterization of a sit-to-stand (Galli et al, 2008) and tilt sensors have been used during dCA repeated squat-stands (Barnes et al, 1985(Barnes et al, , 2017(Barnes et al, , 2018(Barnes et al, , 2021Batterham et al, 2020;Klein et al, 2020;Panerai et al, 2021), we are the first to apply a force sensor during a hemodynamic recording to improve the accuracy of the TD before the onset of the dCA response. While the force sensor does not assess the duration or acceleration of the sit-to-stand, the purpose of the force sensor was to detect the exact moment of AO to precisely time the start of the physiological response and the TD before the onset of dCA.…”

“…Prior studies have implemented a tilt sensor to objectively measure the angle of the squatting motion during dCA repeated squat-stand maneuvers (Barnes et al, 1985(Barnes et al, , 2017(Barnes et al, , 2018(Barnes et al, , 2021Batterham et al, 2020;Panerai et al, 2021) and one study examined the differing transition time between young and older adults during a stand-to-sit with a goniometer (Klein et al, 2020). However, it was unclear if the transition time detected by the goniometer was measured simultaneously with the physiologic response to improve the accuracy of the TD before the onset of the dCA response (Klein et al, 2020).…”

Force sensor reduced measurement error compared with verbal command during sit‐to‐stand assessment of cerebral autoregulation

“…We acknowledge that the present study did not implement an accelerometer to normalize the dCA response to the speed of the sit-to-stand as others have previously done (Barnes et al, 2018(Barnes et al, , 2021Batterham et al, 2020;Panerai et al, 2021). Our ongoing work is currently implementing both the force sensor and an accelerometer to identify the precise moment of AO and the speed of stance during the dCA measure.…”

Force Sensor Reduces Measurement Error during Sit-to-Stand Assessment of Cerebral Autoregulation

“…While prior studies have implemented an accelerometer to normalize the dCA response to the speed of the sit-to-stand, the accelerometer was not temporally aligned with the physiological dCA response and the moment of stance was not determined. [8][9][10][11][12][13] Implementation of a force sensor will address this limitation by measuring the exact time of stance (AO) during the dCA measure. Therefore, implementing both the force sensor and accelerometer may improve the accuracy of sit-to-stand dCA measures by accounting for both the timing and speed of the sit-tostand.…”

“…While previous studies have shown the ability to implement an accelerometer to detect the angle and speed of the sit-to-stand, [8][9][10][11][12][13][14] we are the first to implement a custom force sensor to improve the temporal accuracy of the TD response. 15 Our methodology uses a force sensor to simultaneously measures the sit-to-stand reaction time with the physiological dCA response.…”