scholarly journals The effect of an acute increase in central blood volume on the response of cerebral blood flow to acute hypotension

2015 ◽  
Vol 119 (5) ◽  
pp. 527-533 ◽  
Author(s):  
Shigehiko Ogoh ◽  
Ai Hirasawa ◽  
Jun Sugawara ◽  
Hidehiro Nakahara ◽  
Shinya Ueda ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Blood Volume ◽  
Cerebral Autoregulation ◽  
Central Blood Volume ◽  
Acute Change ◽  
Acute Hypotension ◽  
Acute Increase ◽  
Cuff Occlusion ◽  
Dynamic Cerebral Autoregulation

The purpose of the present study was to examine whether the response of cerebral blood flow to an acute change in perfusion pressure is modified by an acute increase in central blood volume. Nine young, healthy subjects voluntarily participated in this study. To measure dynamic cerebral autoregulation during normocapnic and hypercapnic (5%) conditions, the change in middle cerebral artery mean blood flow velocity was analyzed during acute hypotension caused by two methods: 1) thigh-cuff occlusion release (without change in central blood volume); and 2) during the recovery phase immediately following release of lower body negative pressure (LBNP; −50 mmHg) that initiated an acute increase in central blood volume. In the thigh-cuff occlusion release protocol, as expected, hypercapnia decreased the rate of regulation, as an index of dynamic cerebral autoregulation (0.236 ± 0.018 and 0.167 ± 0.025 s−1, P = 0.024). Compared with the cuff-occlusion release, the acute increase in central blood volume (relative to the LBNP condition) with LBNP release attenuated dynamic cerebral autoregulation ( P = 0.009). Therefore, the hypercapnia-induced attenuation of dynamic cerebral autoregulation was not observed in the LBNP release protocol ( P = 0.574). These findings suggest that an acute change in systemic blood distribution modifies dynamic cerebral autoregulation during acute hypotension.

The Effect Of An Acute Increase In Central Blood Volume On Dynamic Cerebral Autoregulation

2015 ◽  
Vol 47 ◽  
pp. 156
Author(s):  
Shigehiko Ogoh ◽  
Ai Hirasawa ◽  
Jun Sugawara ◽  
Hidehiro Nakahara ◽  
Shinya Ueda ◽  
...  
Keyword(s):  
Blood Volume ◽  
Cerebral Autoregulation ◽  
Central Blood Volume ◽  
Acute Increase ◽  
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.

Relationship of cerebral blood flow to cardiac output, mean arterial pressure, blood volume, and alpha and beta blockade in cats

1980 ◽  
Vol 52 (6) ◽  
pp. 745-754 ◽  
Author(s):  
Dudley H. Davis ◽  
Thoralf M. Sundt
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Cerebral Blood Flow ◽  
Blood Volume ◽  
Cerebral Autoregulation ◽  
Major Change ◽  
Beta Blockade ◽  
Content Type ◽  
Therapeutic Implications ◽  
Arterial Blood

✓ The relationship among cerebral blood flow (CBF), blood volume, cardiac output (CO), and mean arterial blood pressure (MABP) at varying levels of arterial CO2 tensions (PaCO2) were studied in 70 normal cats. The CBF was measured from the clearance curve of xenon−133 and CO with a thermal dilution catheter placed in the pulmonary artery. The CBF, CO, and MABP values varied appropriately with changes in PaCO2, confirming the reliability of the preparations and the presence of normal autoregulatory responses. Moderate hypovolemia that did not change MABP did, nevertheless, significantly decrease CO and CBF. In an effort to determine if this decrease in CO and CBF were coupled responses, the effects of beta stimulation, hypervolemia, and alpha and beta blockade were investigated. Propranolol, in a dosage insufficient to change MABP, decreased both CO and CBF. This agent abolished the CO response to elevations in PaCO2 but not the CBF response, making it unlikely that this CBF reduction resulted from impaired cerebral autoregulation. Isoproterenol, which, in contrast to propranolol, does not cross the normal blood-brain barrier, alone or in combination with phenoxybenzamine, produced a 38% and 72% increase in CO, respectively, without a change in CBF. Alpha blockade (no major change in CO) and beta blockade (major decrease in CO) did not significantly effect cerebral autoregulation to changes in MABP from angiotensin. The ability of the brain to resist increases in MABP and CO and maintain normal CBF is explained by normal cerebral autoregulation. However, its vulnerability to modest decreases in blood volume, which cannot be attributed to variations in perfusion pressure, is unexplained but obviously has important therapeutic implications. This may be related to reduction in CO, changes in autonomic activity, or a decrease in the size of the perfused capillary bed.

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