Middle cerebral artery flow velocity and pulse pressure during dynamic exercise in humans

Exercise challenges cerebral autoregulation (CA) by a large increase in pulse pressure (PP) that may make systolic pressure exceed what is normally considered the upper range of CA. This study examined the relationship between systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) and systolic ( Vs), diastolic ( Vd). and mean ( Vm) middle cerebral artery (MCA) blood flow velocity during mild, moderate, and heavy cycling exercise. Dynamic CA and steady-state changes in MCA V in relation to changes in arterial pressure were evaluated using transfer function analysis. PP increased by 37% and 57% during moderate and heavy exercise, respectively ( P < 0.05), and the pulsatility of MCA V increased markedly. Thus exercise increased MCA Vm and Vs ( P < 0.05) but tended to decrease MCA Vd ( P = 0.06). However, the normalized low-frequency transfer function gain between MAP and MCA Vm and between SBP and MCA Vs remained unchanged from rest to exercise, whereas that between DBP and MCA Vd increased from rest to heavy exercise ( P < 0.05). These findings suggest that during exercise, CA is challenged by a rapid decrease rather than by a rapid increase in blood pressure. However, dynamic CA remains able to modulate blood flow around the exercise-induced increase in MCA Vm, even during high-intensity exercise.

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Direct Cerebral Vasodilatory Effects of Sevoflurane and Isoflurane

Anesthesiology ◽

10.1097/00000542-199909000-00019 ◽

1999 ◽

Vol 91 (3) ◽

pp. 677-677 ◽

Cited By ~ 236

Author(s):

Basil F. Matta ◽

Karen J. Heath ◽

Kate Tipping ◽

Andrew C. Summors

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Cerebral Blood Flow ◽

Mean Arterial Pressure ◽

Arterial Pressure ◽

Middle Cerebral Artery ◽

Flow Velocity ◽

Cerebral Artery ◽

Blood Flow Velocity ◽

End Tidal

Background The effect of volatile anesthetics on cerebral blood flow depends on the balance between the indirect vasoconstrictive action secondary to flow-metabolism coupling and the agent's intrinsic vasodilatory action. This study compared the direct cerebral vasodilatory actions of 0.5 and 1.5 minimum alveolar concentration (MAC) sevoflurane and isoflurane during an propofol-induced isoelectric electroencephalogram. Methods Twenty patients aged 20-62 yr with American Society of Anesthesiologists physical status I or II requiring general anesthesia for routine spinal surgery were recruited. In addition to routine monitoring, a transcranial Doppler ultrasound was used to measure blood flow velocity in the middle cerebral artery, and an electroencephalograph to measure brain electrical activity. Anesthesia was induced with propofol 2.5 mg/kg, fentanyl 2 micro/g/kg, and atracurium 0.5 mg/kg, and a propofol infusion was used to achieve electroencephalographic isoelectricity. End-tidal carbon dioxide, blood pressure, and temperature were maintained constant throughout the study period. Cerebral blood flow velocity, mean blood pressure, and heart rate were recorded after 20 min of isoelectric encephalogram. Patients were then assigned to receive either age-adjusted 0.5 MAC (0.8-1%) or 1.5 MAC (2.4-3%) end-tidal sevoflurane; or age-adjusted 0.5 MAC (0.5-0.7%) or 1.5 MAC (1.5-2%) end-tidal isoflurane. After 15 min of unchanged end-tidal concentration, the variables were measured again. The concentration of the inhalational agent was increased or decreased as appropriate, and all measurements were repeated again. All measurements were performed before the start of surgery. An infusion of 0.01% phenylephrine was used as necessary to maintain mean arterial pressure at baseline levels. Results Although both agents increased blood flow velocity in the middle cerebral artery at 0.5 and 1.5 MAC, this increase was significantly less during sevoflurane anesthesia (4+/-3 and 17+/-3% at 0.5 and 1.5 MAC sevoflurane; 19+/-3 and 72+/-9% at 0.5 and 1.5 MAC isoflurane [mean +/- SD]; P<0.05). All patients required phenylephrine (100-300 microg) to maintain mean arterial pressure within 20% of baseline during 1.5 MAC anesthesia. Conclusions In common with other volatile anesthetic agents, sevoflurane has an intrinsic dose-dependent cerebral vasodilatory effect. However, this effect is less than that of isoflurane.

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Spectral Analysis of Blood Pressure and Blood Flow Velocity in the Middle Cerebral Artery Using the Maximum Entropy Method (MEM)

Neurosonology ◽

10.2301/neurosonology.6.2 ◽

1993 ◽

Vol 6 (1) ◽

pp. 2-8

Author(s):

Tsutomu KAMO ◽

Kimihiro YONEYAMA ◽

Kayoko SAITO ◽

Midori IWASAKI ◽

Ryoko TAGA ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Spectral Analysis ◽

Middle Cerebral Artery ◽

Flow Velocity ◽

Maximum Entropy ◽

Cerebral Artery ◽

Blood Flow Velocity ◽

Maximum Entropy Method ◽

Entropy Method

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Disassociation of static and dynamic cerebral autoregulatory performance in healthy volunteers after lipopolysaccharide infusion and in patients with sepsis

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00242.2012 ◽

2012 ◽

Vol 303 (11) ◽

pp. R1127-R1135 ◽

Cited By ~ 30

Author(s):

Ronan M. G. Berg ◽

Ronni R. Plovsing ◽

Andreas Ronit ◽

Damian M. Bailey ◽

Niels-Henrik Holstein-Rathlou ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Middle Cerebral Artery ◽

Healthy Volunteers ◽

Flow Velocity ◽

Phase Difference ◽

Cerebral Artery ◽

Blood Flow Velocity ◽

Cerebral Autoregulation ◽

Artery Blood Flow

Sepsis is frequently complicated by brain dysfunction, which may be associated with disturbances in cerebral autoregulation, rendering the brain susceptible to hypoperfusion and hyperperfusion. The purpose of the present study was to assess static and dynamic cerebral autoregulation 1) in a human experimental model of the systemic inflammatory response during early sepsis and 2) in patients with advanced sepsis. Cerebral autoregulation was tested using transcranial Doppler ultrasound in healthy volunteers ( n = 9) before and after LPS infusion and in patients with sepsis ( n = 16). Static autoregulation was tested by norepinephrine infusion and dynamic autoregulation by transfer function analysis (TFA) of spontaneous oscillations between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07–0.20 Hz). Static autoregulatory performance after LPS infusion and in patients with sepsis was similar to values in healthy volunteers at baseline. In contrast, TFA showed decreased gain and an increased phase difference between blood pressure and middle cerebral artery blood flow velocity after LPS (both P < 0.01 vs. baseline); patients exhibited similar gain but lower phase difference values ( P < 0.01 vs. baseline and LPS), indicating a slower dynamic autoregulatory response. Our findings imply that static and dynamic cerebral autoregulatory performance may disassociate in sepsis; thus static autoregulation was maintained both after LPS and in patients with sepsis, whereas dynamic autoregulation was enhanced after LPS and impaired with a prolonged response time in patients. Hence, acute surges in blood pressure may adversely affect cerebral perfusion in patients with sepsis.

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Complexity of middle cerebral artery blood flow velocity: effects of tilt and autonomic failure

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1997.273.5.h2209 ◽

1997 ◽

Vol 273 (5) ◽

pp. H2209-H2216 ◽

Cited By ~ 6

Author(s):

A. P. Blaber ◽

R. L. Bondar ◽

F. Stein ◽

P. T. Dunphy ◽

P. Moradshahi ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Middle Cerebral Artery ◽

Flow Velocity ◽

Cerebral Artery ◽

Blood Flow Velocity ◽

Autonomic Failure ◽

Systemic Blood Pressure ◽

Arterial Blood ◽

Different Response

We examined spectral fractal characteristics of middle cerebral artery (MCA) mean blood flow velocity (MFV) and mean arterial blood pressure adjusted to the level of the brain (MAPbrain) during graded tilt (5 min supine, −10°, 10°, 30°, 60°, −10°, supine) in eight autonomic failure patients and age- and sex-matched controls. From supine to 60°, patients had a larger drop in MAPbrain (62 ± 4.7 vs. 23 ± 4.5 mmHg, P < 0.001; means ± SE) and MFV (16.4 ± 3.8 vs. 7.0 ± 2.5 cm/s, P < 0.001) than in controls. From supine to 60°, there was a trend toward a decrease in the slope of the fractal component (β) of MFV (MFV-β) in both the patients and the controls, but only the patients had a significant decrease in MFV-β (supine: patient = 2.21 ± 0.18, control = 1.99 ± 0.60; 60°: patient = 1.46 ± 0.24, control = 1.62 ± 0.19). The β value of MAPbrain(MAPbrain-β; 2.19 ± 0.05) was not significantly different between patients and controls and did not change with tilt. High and low degrees of regulatory complexity are indicated by values of β close to 1.0 and 2.0, respectively. The increase in fractal complexity of cerebral MFV in the patients with tilt suggests an increase in the degree of autoregulation in the patients. This may be related to the drop in MAPbrain. The different response of MFV-β compared with that of MAPbrain-β also indicates that MFV-β is related to the regulation of cerebral vascular resistance and not systemic blood pressure.

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