Effects of short-term mechanical hyperventilation on cerebral blood flow and dynamic cerebral autoregulation in critically ill patients with sepsis

2016 ◽  
Vol 76 (3) ◽  
pp. 226-233 ◽  
Author(s):  
Ronan M. G. Berg ◽  
Ronni R. Plovsing
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Critically Ill ◽  
Critically Ill Patients ◽  
Cerebral Autoregulation ◽  
Short Term ◽  
Dynamic Cerebral Autoregulation

scholarly journals Utilization of the repeated squat-stand model for studying the directional behavior of the cerebral pressure-flow relationship

2020 ◽  
Author(s):  
Lawrence Labrecque ◽  
Jonathan Smirl ◽  
Patrice Brassard
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Mean Arterial Pressure ◽  
Cerebral Autoregulation ◽  
Healthy Subjects ◽  
Blood Velocity ◽  
Pressure Flow ◽  
Flow Changes ◽  
Relative Change ◽  
Dynamic Cerebral Autoregulation

Hysteresis in the cerebral pressure-flow relationship describes the superior ability of the cerebrovasculature to buffer cerebral blood flow changes when mean arterial pressure (MAP) acutely increases compared to when it decreases. This phenomenon can be evaluated by comparing the relative change in middle cerebral artery mean blood velocity (MCAv) per relative change in MAP (%ΔMCAv/%ΔMAP) during either acute increases or decreases in MAP induced by repeated squat-stands (RSS). However, no real baseline can be employed for this particular protocol as there is no true stable reference point. Herein, we characterized the %ΔMCAv/%ΔMAP metric using the greatest MAP oscillations induced by RSS without using an independent baseline value. We also examined whether %ΔMCAv/%ΔMAP during each RSS transition were comparable between each other over the 5-min period. %ΔMCAv/%ΔMAP was calculated using the minimum to maximum MCAv and MAP for each RSS performed at 0.05 Hz and 0.10 Hz. We compared averaged %ΔMCAv/%ΔMAP during MAP increases and decreases in 74 healthy subjects [9 women; 32 ± 13 years]. %ΔMCAv/%ΔMAP was lower for MAP increases than MAP decreases (0.05 Hz: 1.25 ± 0.22 vs. 1.35 ± 0.27 %/%, p<0.0001; 0.10Hz: 1.31 ± 0.24 vs. 1.60 ± 0.50 %/%, p<0.0001). For both frequency and MAP direction, time during RSS had no effect on %ΔMCAv/%ΔMAP. This novel analytical method supports the use of the RSS model to evaluate the directional behavior of the pressure-flow relationship. These results contribute to the importance of considering the direction of MAP changes when evaluating dynamic cerebral autoregulation.

scholarly journals Impaired dynamic cerebral autoregulation in trained breath-hold divers

2019 ◽  
Vol 126 (6) ◽  
pp. 1694-1700 ◽  
Author(s):  
M. Erin Moir ◽  
Stephen A. Klassen ◽  
Baraa K. Al-Khazraji ◽  
Emilie Woehrle ◽  
Sydney O. Smith ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Autoregulation ◽  
Cerebral Blood Flow Velocity ◽  
Carbon Dioxide Partial Pressure ◽  
Breath Hold ◽  
Dynamic Cerebral Autoregulation

Breath-hold divers (BHD) experience repeated bouts of severe hypoxia and hypercapnia with large increases in blood pressure. However, the impact of long-term breath-hold diving on cerebrovascular control remains poorly understood. The ability of cerebral blood vessels to respond rapidly to changes in blood pressure represents the property of dynamic autoregulation. The current investigation tested the hypothesis that breath-hold diving impairs dynamic autoregulation to a transient hypotensive stimulus. Seventeen BHD (3 women, 11 ± 9 yr of diving) and 15 healthy controls (2 women) completed two or three repeated sit-to-stand trials during spontaneous breathing and poikilocapnic conditions. Heart rate (HR), finger arterial blood pressure (BP), and cerebral blood flow velocity (BFV) from the right middle cerebral artery were measured continuously with three-lead electrocardiography, finger photoplethysmography, and transcranial Doppler ultrasonography, respectively. End-tidal carbon dioxide partial pressure was measured with a gas analyzer. Offline, an index of cerebrovascular resistance (CVRi) was calculated as the quotient of mean BP and BFV. The rate of the drop in CVRi relative to the change in BP provided the rate of regulation [RoR; (∆CVRi/∆T)/∆BP]. The BHD demonstrated slower RoR than controls ( P ≤ 0.001, d = 1.4). Underlying the reduced RoR in BHD was a longer time to reach nadir CVRi compared with controls ( P = 0.004, d = 1.1). In concert with the longer CVRi response, the time to reach peak BFV following standing was longer in BHD than controls ( P = 0.01, d = 0.9). The data suggest impaired dynamic autoregulatory mechanisms to hypotension in BHD. NEW & NOTEWORTHY Impairments in dynamic cerebral autoregulation to hypotension are associated with breath-hold diving. Although weakened autoregulation was observed acutely in this group during apneic stress, we are the first to report on chronic adaptations in cerebral autoregulation. Impaired vasomotor responses underlie the reduced rate of regulation, wherein breath-hold divers demonstrate a prolonged dilatory response to transient hypotension. The slower cerebral vasodilation produces a longer perturbation in cerebral blood flow velocity, increasing the risk of cerebral ischemia.

Fundamental relationships between arterial baroreflex sensitivity and dynamic cerebral autoregulation in humans

2010 ◽  
Vol 108 (5) ◽  
pp. 1162-1168 ◽  
Author(s):  
Yu-Chieh Tzeng ◽  
Samuel J. E. Lucas ◽  
Greg Atkinson ◽  
Chris K. Willie ◽  
Philip N. Ainslie
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Transfer Function ◽  
Blood Flow Velocity ◽  
Cerebral Autoregulation ◽  
Baroreflex Sensitivity ◽  
Cerebral Blood Flow Velocity ◽  
Arterial Baroreflex ◽  
Dynamic Cerebral Autoregulation

The functional relationship between dynamic cerebral autoregulation (CA) and arterial baroreflex sensitivity (BRS) in humans is unknown. Given that adequate cerebral perfusion during normal physiological challenges requires the integrated control of CA and the arterial baroreflex, we hypothesized that between-individual variability in dynamic CA would be related to BRS in humans. We measured R-R interval, blood pressure, and cerebral blood flow velocity (transcranial Doppler) in 19 volunteers. BRS was estimated with the modified Oxford method (nitroprusside-phenylephrine injections) and spontaneous low-frequency (0.04–0.15) α-index. Dynamic CA was quantified using the rate of regulation (RoR) and autoregulatory index (ARI) derived from the thigh-cuff release technique and transfer function analysis of spontaneous oscillations in blood pressure and mean cerebral blood flow velocity. Results show that RoR and ARI were inversely related to nitroprusside BRS [ R = −0.72, confidence interval (CI) −0.89 to −0.40, P = 0.0005 vs. RoR; R = −0.69, CI −0.88 to −0.35, P = 0.001 vs. ARI], phenylephrine BRS ( R = −0.66, CI −0.86 to −0.29, P = 0.0002 vs. RoR; R = −0.71, CI −0.89 to −0.38, P = 0.0001 vs. ARI), and α-index ( R = −0.70, CI −0.89 to −0.40, P = 0.0008 vs. RoR; R = −0.62, CI −0.84 to −0.24, P = 0.005 vs. ARI). Transfer function gain was positively related to nitroprusside BRS ( R = 0.62, CI 0.24–0.84, P = 0.0042), phenylephrine BRS ( R = 0.52, CI 0.10–0.79, P = 0.021), and α-index ( R = 0.69, CI 0.35–0.88, P = 0.001). These findings indicate that individuals with an attenuated dynamic CA have greater BRS (and vice versa), suggesting the presence of possible compensatory interactions between blood pressure and mechanisms of cerebral blood flow control in humans. Such compensatory adjustments may account for the divergent changes in dynamic CA and BRS seen, for example, in chronic hypotension and spontaneous hypertension.

Cerebral blood flow and dynamic cerebral autoregulation during ethanol intoxication and hypercapnia

2003 ◽  
Vol 10 (2) ◽  
pp. 195-198 ◽  
Author(s):  
Martin Blaha ◽  
Rune Aaslid ◽  
Colleen M Douville ◽  
Reinaldo Correra ◽  
David W Newell
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebral Autoregulation ◽  
Ethanol Intoxication ◽  
Dynamic Cerebral Autoregulation

scholarly journals Cerebral blood flow regulation and cognitive function in women with posttraumatic stress disorder

2018 ◽  
Vol 125 (5) ◽  
pp. 1627-1635 ◽  
Author(s):  
Shigehiko Ogoh ◽  
Jeung-Ki Yoo ◽  
Mark B. Badrov ◽  
Rosemary S. Parker ◽  
Elizabeth H. Anderson ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cognitive Function ◽  
Transfer Function ◽  
Cognitive Dysfunction ◽  
Cerebral Autoregulation ◽  
Stress Disorder ◽  
Flow Regulation ◽  
Head Up Tilt ◽  
Dynamic Cerebral Autoregulation

Posttraumatic stress disorder (PTSD) is associated with structural and functional alterations in a number of interacting brain regions, but the physiological mechanism for the high risk of cerebrovascular disease or impairment in brain function remains unknown. Women are more likely to develop PTSD after a trauma than men. We hypothesized that cerebral blood flow (CBF) regulation is impaired in women with PTSD, and it is associated with impairment in cognitive function. To test our hypothesis, we examined dynamic cerebral autoregulation (CA) and cognitive function by using a transfer function analysis between arterial pressure and middle cerebral artery blood velocity and the Stroop Color and Word test (SCWT), respectively. We did not observe any different responses in these hemodynamic variables between women with PTSD ( n = 15) and healthy counterparts (all women; n = 8). Cognitive function was impaired in women with PTSD; specifically, reaction time for the neutral task of SCWT was longer in women with PTSD compared with healthy counterparts ( P = 0.011), but this cognitive dysfunction was not affected by orthostatic stress. On the other hand, transfer function phase, gain, and coherence were not different between groups in either the supine or head-up tilt (60°) position, or even during the cognitive challenge, indicating that dynamic CA was well maintained in women with PTSD. In addition, there was no relationship between cognitive function and dynamic CA. These findings suggest that PTSD-related cognitive dysfunction may not be due to compromised CBF regulation. NEW & NOTEWORTHY Cognitive function was impaired; however, dynamic cerebral autoregulation (CA) as an index of cerebral blood flow regulation was not impaired during supine and 60° head-up tilt in women with PTSD compared with healthy females. In addition, there was no relationship between cognitive function and dynamic CA. These findings suggest that the mechanism of PTSD-related cognitive dysfunction may not be due to CBF regulation.

scholarly journals 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

2018 ◽  
Vol 40 (1) ◽  
pp. 135-149 ◽  
Author(s):  
Jan Willem J Elting ◽  
Jeanette Tas ◽  
Marcel JH Aries ◽  
Marek Czosnyka ◽  
Natasha M Maurits
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Transit Time ◽  
Phase Difference ◽  
Cerebral Autoregulation ◽  
Cerebral Blood Flow Velocity ◽  
Intraclass Correlation ◽  
Arterial Blood ◽  
Dynamic Cerebral Autoregulation

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.

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