Dynamic cerebral autoregulation estimates derived from near infrared spectroscopy and transcranial Doppler are similar after correction for transit time and blood flow and blood volume oscillations

Abstract

We analysed mean arterial blood pressure, cerebral blood flow velocity, oxygenated haemoglobin and deoxygenated haemoglobin signals to estimate dynamic cerebral autoregulation. We compared macrovascular (mean arterial blood pressure-cerebral blood flow velocity) and microvascular (oxygenated haemoglobin-deoxygenated haemoglobin) dynamic cerebral autoregulation estimates during three different conditions: rest, mild hypocapnia and hypercapnia. Microvascular dynamic cerebral autoregulation estimates were created by introducing the constant time lag plus constant phase shift model, which enables correction for transit time, blood flow and blood volume oscillations (TT-BF/BV correction). After TT-BF/BV correction, a significant agreement between mean arterial blood pressure-cerebral blood flow velocity and oxygenated haemoglobin-deoxygenated haemoglobin phase differences in the low frequency band was found during rest (left: intraclass correlation=0.6, median phase difference 29.5° vs. 30.7°, right: intraclass correlation=0.56, median phase difference 32.6° vs. 39.8°) and mild hypocapnia (left: intraclass correlation=0.73, median phase difference 48.6° vs. 43.3°, right: intraclass correlation=0.70, median phase difference 52.1° vs. 61.8°). During hypercapnia, the mean transit time decreased and blood volume oscillations became much more prominent, except for very low frequencies. The transit time related to blood flow oscillations was remarkably stable during all conditions. We conclude that non-invasive microvascular dynamic cerebral autoregulation estimates are similar to macrovascular dynamic cerebral autoregulation estimates, after TT-BF/BV correction is applied. These findings may increase the feasibility of non-invasive continuous autoregulation monitoring and guided therapy in clinical situations.

Inter-subject analysis of transfer function coherence in studies of dynamic cerebral autoregulation

“…Although most studies of TFA assessment of dynamic CA were performed with transcranial Doppler ultrasound, similar considerations above would also apply to other alternative methods for measuring CBF such as near infrared spectroscopy (Elting et al 2018).…”

Cerebral macro- and microcirculatory blood flow dynamics in successfully treated chronic hypertensive patients with and without white mater lesions

“…The second result of our study was that, irrespective of the exact mechanism for the cerebrovascular resistance increase, the mechanisms of the cerebrovascular system consisted of compromised dynamics of CA in the BP-CBFV system, and normal dynamics of cerebral blood flow regulation at the capillary level. If HBP patients are sufficiently treated, our overall findings indicate that the extent of the hemodynamic compromise of the resistance vessels does not exceed a point at which the capillary compensatory mechanisms become effective, such as shortening of the mean transit time by opening up of functional shortcuts due to capillary transit time homogenization 9,12,37 or of prolongation the mean transit time 15,38,39 via delaying venous outflow 15 . Our results at the www.nature.com/scientificreports www.nature.com/scientificreports/ capillary level support recent CBF studies which demonstrate that cerebral hypoperfusion is not always present in patients with HBP 29,40,41 , and that an intensive BP lowering was tolerated well by patients with severe SVD 41 .…”

Cerebral Microcirculatory Blood Flow Dynamics During Rest and a Continuous Motor Task

“…Under resting conditions, the differences in phase between BP or CBFV and [oxHb] or [deoxHb] range between 15 and 55° for BP-[oxHb], between 44 and 84° for CBFV-[oxHb], between 209 and 265° for BP-[deoxHb], and about 270° for the CBFV-[deoxHb] relationship (Reinhard et al, 2006; Cheng et al, 2012; Phillip et al, 2012; Fantini, 2014; Müller et al, 2016; Elting et al, 2018). The phase shift differences depend mostly on the mathematical approach used, data preparation, and the use of either spontaneous oscillatory CBF changes or enforced CBF changes by, for example, forced breathing (Reinhard et al, 2003, 2006; Cheng et al, 2012; Phillip et al, 2012; Müller et al, 2016; Elting et al, 2018). The reported mean transit times range between 190° (corresponding to 5.15 s at 0.1 Hz) in the investigation of Reinhard et al (2006), 205° in our present investigation (corresponding to 5.6 s), and 120° (corresponding to 3.2 s) in Elting et al (2018).…”

“…The phase shift differences depend mostly on the mathematical approach used, data preparation, and the use of either spontaneous oscillatory CBF changes or enforced CBF changes by, for example, forced breathing (Reinhard et al, 2003, 2006; Cheng et al, 2012; Phillip et al, 2012; Müller et al, 2016; Elting et al, 2018). The reported mean transit times range between 190° (corresponding to 5.15 s at 0.1 Hz) in the investigation of Reinhard et al (2006), 205° in our present investigation (corresponding to 5.6 s), and 120° (corresponding to 3.2 s) in Elting et al (2018). Although these transit time differences appear large, they are in the normal range when cerebral blood flow studies using positron emission tomography or dynamic susceptibility contrast-enhanced MRI are considered for comparisons.…”

“…Most VNC studies used short task periods (≤60 s) to investigate VNC (Chance et al, 1993; Obrig et al, 2000; Salinet et al, 2013, 2015; Caldas et al, 2018), and are, therefore, unsuitable for assessing TFA (Claassen et al, 2016). In addition to the TFA of the BP-CBFV macrocirculatory relationship, the TF analyses of the dynamics of the interaction between BP and [oxHb], as well as of [deoxHb] (microcirculatory response), have also shown that it is possible to grade CA failure (Reinhard et al, 2006; Cheng et al, 2012; Elting et al, 2018). The motivation behind and the hypothesis of our present study is that a long-lasting stimulus in a normal CA state shows a TFA response (either in the macrocirculatory or in the microcirculatory response) that can be used to grade VNC.…”