Increase In Blood Flow Velocity Research Articles

The Effects of Acarbose Treatment on Intimal Hyperplasia in a Rat Carotid Endarterectomy Model of Diet-Induced Insulin Resistance

Increased carotid restenosis due to revascularization therapy is associated with insulin resistance. We hypothesize that glucose control using acarbose may attenuate intimal hyperplasia in rat carotid endarterectomy model of diet-induced insulin resistance. Rats were fed low-fat complex carbohydrate (control) or high-fat sucrose (insulin resistance) for 4 months. Three days preoperatively, some high-fat-sucrose rats were on acarbose, remainder of the rats received placebo. Rat carotids were assessed with duplex pre-and postoperatively. Acarbose and placebo continued for 2 weeks. Glucose, insulin, blood flow velocities and intimal hyperplasia were determined. High-fat sucrose plus acarbose attenuated intimal hyperplasia. Post-drug high-fat sucrose glucose decreased. Blood flow velocities postoperatively elevated above baseline. High-fat sucrose increased blood flow velocities postoperatively, which was attenuated with acarbose. Glucose control by acarbose in rat carotid endarterectomy model of diet-induced insulin resistance resulted in attenuation of intimal hyperplasia.

Long-Term Effect of Microsurgical Inguinal Varicocelectomy on Testicular Blood Flow

We aimed to investigate the long-term effect of microsurgical inguinal varicocelectomy on testicular blood flow using color Doppler sonography (CDS) in this observational study. A total of 30 patients clinically diagnosed with left varicocele who underwent a microsurgical inguinal varicocelectomy were examined 3 times with CDS for testicular blood flow parameters, first before, then 3 months after, and finally 6 months after the operation. CDS values of testicular blood flow (peak systolic velocity, end diastolic velocity, resistive index, and pulsatility index) were measured from testicular, capsular, and intratesticular arteries. We also evaluated preoperative and postoperative semen parameters. The mean values of blood flow velocities in the left testicular artery (peak systolic and end diastolic) increased and resistance indices (resistive and pulsatility) in the left capsular and intratesticular arteries decreased significantly after surgery (P < .05). No significant difference was detected between the preoperative and postoperative blood flow parameters in the right testicular, capsular, or intratesticular arteries (P < .05). In the semen analysis run 3 months after the operations, statistically significant increases were found in sperm concentration (P < .001), morphology percentage (P < .001), and total motile sperm concentration (P = .009). The increase in blood flow velocity in the testicular artery and the decrease in resistive and pulsatility indices in the capsular and intratesticular branches of the artery may be strong indicators of an increase in testicular arterial blood flow into the testicular tissue. Our data show that a significant improvement occurs in testicular blood supply and sperm parameters after microsurgical inguinal varicocelectomy.

Central Command And Vertebral Blood Flow During Static Arm Exercise In Humans

Previous our study reported that central modulation of the cardiovascular system via descending signals from higher brain centers (central command) contribute to middle cerebral artery blood flow regulation during static exercise. PURPOSE: In this study, we examined the influence of central command on static exercise-induced increase in vertebral artery blood flow (QVA). METHODS: Ten young women performed static elbow flexion for two minutes at 30% of maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity while QVA and cardiorespiratory responses were recorded. RESULTS: The rating of perceived exertion for the exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean ± SD; 4.9±1.2 for CONT vs. 3.7±1.4 for EX+VIB; P < 0.05). The increases in mean arterial pressure, heart rate, and cardiac output during EX+VIB were also lower than those developed during CONT, while the end-tidal CO2 tension was unchanged in both conditions. The increase in the QVA during EX+VIB was lower than that during CONT (42±10 vs. 24±13%; P < 0.01). CONCLUSIONS: These results demonstrate an increase in vertebral artery blood flow during static exercise and that a central command-mediated decrease in vertebral blood flow during exercise is linked to changes in regional cerebral activity and metabolism. Sato K, Sadamoto T, Ueda-Sasahara C, Shibuya K, Shimizu-Okuyama S, Osada T, Kamo M, Saito M & Kagaya A (2009). Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women. Exp Physiol. (in press)

Examining the Effects of Cardiovascular Effort on Blood Flow Velocity: A Duplex Doppler Ultrasonography Study

Ultrasonography (US) is frequently used to investigate anatomical structures in a non‐invasive manner. Duplex US combines conventional US imaging of blood vessels with Doppler US analysis of blood flowing through them, providing an opportunity to acquire data on flow velocities in real‐time. This study compares the blood flow velocity in a resting individual with the velocity measured after cardiovascular activity. Velocity (cm/s) was measured through the abdominal aorta. A mixed‐sex sample of young, healthy volunteers (n=20) from the SUNY Downstate College of Medicine focused on physical activity on the lower limbs for four minutes, after which the post‐effort velocity was obtained. Results showed a mean increase in blood flow velocity of 61.5%, with a maximum increase of 166.5% and minimum positive increase of 21.6%. Standard deviation of the increase in blood flow velocity was 56.4%. An unexpected result was found in two cases, in which the post‐effort flow velocity showed a small decrease instead of the expected increase. These findings suggest that an increase in physical effort in the lower limbs requires a greater supply of blood; thus, the observed flow velocity increases. Duplex US allows for the capture and analysis of data in real‐time in various healthcare settings, without requiring invasive or expensive, radiation‐intense procedures such as MRI.Grant Funding Source: AAA

Indication for cholinergically mediated cerebral vasodilatation during static exercise in humans

Cholinergically mediated vasodilatation is reported in humans, but its importance for cerebral perfusion during exercise is unknown. The increase in middle cerebral artery blood flow velocity (MCA Vmean) during static handgrip exercise was evaluated by blockade of acetylcholine receptors as well as with beta‐adrenergic blockade, in nine males in separate, randomized and counterbalanced trials over two minutes. Mean arterial pressure (MAP) increased during both 25 % and 40 % maximal voluntary contraction (MVC) handgrip (P &lt; 0.01) with no effect of treatment. Resting cardiac output was reduced by ~20% with beta‐adrenergic blockade (P &lt; 0.05) and increased by ~40% with vagal‐blockade (P &lt; 0.05). Compared to control, exercise‐induced increases in cardiac output were attenuated with beta‐adrenergic blockade (P &lt; 0.01) and abolished with cholinergic blockade. MCA Vmean increased ~16% during control exercise (independent of intensity; P &lt; 0.01). During 25% MVC handgrip, both cholinergic and beta‐adrenergic blockade abolished the exercise‐induced increase in MCA Vmean (~3 % and ~7 %, respectively), whereas at 40 % MVC only cholinergic blockade abolished the increase. These findings suggest that the increase in cerebral perfusion during exercise is dependent upon cardiac output, but that a cholinergically mediated vasodilatatory mechanism may also be important.

Cerebrovascular Carbon Dioxide Reactivity and Delayed Cerebral Ischemia After Subarachnoid Hemorrhage

To determine the predictors of impaired cerebrovascular reactivity (CVR) and the value of CVR in predicting delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH). Prospective observational study. We evaluated CVR during the following intervals: period 1, SAH days 0 to 3; period 2, SAH days 4 to 7; and period 3, SAH days 8 to 10. Normal CVR was defined as an increase in mean blood flow velocity of at least 2% per 1-mm Hg increase in PCO(2). Neurointensive care unit of the Columbia Presbyterian Medical Center. Thirty-four consecutive patients with acute SAH who underwent measurement of changes in the middle cerebral artery mean blood flow velocity after carbon dioxide challenge. Occurrence of DCI. Delayed cerebral ischemia occurred in 10 patients (29%). Impaired CVR was more frequent in patients with a poor clinical grade on admission and at the time of examination. During period 1, there was only a trend toward lower CVR in patients who later developed DCI (1.1% vs 1.9% per 1-mm Hg increase in PCO(2); P = .07). However, those who developed DCI had progressively lower CVR during periods 2 (0.7%/mm Hg vs 2.1%/mm Hg; P < .001) and 3 (0.6%/mm Hg vs 2.4%/mm Hg; P < .001). Independent predictors of DCI included a decrease in CVR between periods 1 and 2 (P = .03) and a poor Hunt-Hess score (P = .04). Impaired CVR at any point had a sensitivity for subsequent DCI of 91% and a specificity of 49%. Impaired CVR in response to carbon dioxide challenge is frequent after SAH, particularly in patients with a poor clinical grade. Progressive loss of normal CVR identifies patients at high risk for DCI, and persistently normal reactivity implies a low risk.

Lateralization of cerebral blood flow in juvenile absence seizures

Cerebrovascular blood flow in absence seizures and flow patterns during the ictal period have not been thoroughly investigated. We aimed to evaluate cerebral blood flow changes in typical juvenile absence seizures during the ictal and postictal phases. Seizures were recorded in three patients (mean age: 21 +/- 1 years) with multiple daily typical absence seizures. Simultaneous video electroencephalography and bilateral middle cerebral artery transcranial Doppler ultrasonography recordings were conducted during seizures. Basal, ictal, and postictal blood flow velocities were recorded bilaterally, and offline analyses were performed in relation with generalized spike and wave discharges. Total of 43 seizures were recorded. Ictal increase and postictal decrease of cerebral blood flow velocities were significant for both sides (P < 0.001). The interhemispheric asymmetry in the ictal velocity increase was significant (P < 0.05). The interhemispheric asymmetry in the postictal velocity decrease was not significant (P > 0.05). The blood flow velocity increase after seizure onset indicates a vascular coupling mechanism. A sudden and then a gradual decrease in blood flow velocity, which lasted even after the seizure ceased, might suggest a preventive mechanism to avoid excessive seizure duration or even an absence status epilepticus. Significant asymmetries in increase and a symmetrical decrease may support the cortical focus theory.

Electrical Foot Stimulation: A Potential New Method of Deep Venous Thrombosis Prophylaxis

The purpose of this study was to compare venous blood flow velocity of intermittent pneumatic compression to electrical stimulation of the foot. A prospective randomized controlled study of 40 healthy volunteers was conducted. Subjects were seated for 4 hours during which they received electrical stimulation of the sole of the foot or intermittent pneumatic compression of the foot... Short-term electrical foot stimulation is at least as effective as foot intermittent pneumatic compression in increasing popliteal and femoral blood flow velocity. [corrected] Popliteal and femoral venous blood flow velocities were measured via Doppler ultrasonography. Blood flow velocity in the nonstimulated or noncompressed lower extremity served as a simultaneous control. For both the femoral and popliteal veins, the electrical foot stimulation group exhibited a greater increase in blood flow velocity than the intermittent pneumatic compression group. Electrical foot stimulation was noninferior relative to standard intermittent pneumatic compression. Specifically, this result of a greater increase in blood flow velocity is achieved at time = 120 minutes for the femoral vein (t = 2.70; p = .005) and time = 120 (t = 2.75; p = .004) and 240 (t = 2.27; p = .014) minutes for the popliteal vein. Short-term electrical foot stimulation is at least as effective as knee-high intermittent pneumatic compression in increasing popliteal and femoral blood flow velocity. Electrical foot stimulation has the potential to be an effective method of deep venous thrombosis prophylaxis.

Kidney-Pancreas Transplantation Does Not Improve Retinal Arterial Flow Velocities in Type 1 Diabetic Uremic Patients

Kidney-Pancreas Transplantation Does Not Improve Retinal Arterial Flow Velocities in Type 1 Diabetic Uremic Patients

Role of color Doppler indices in predicting disease-free survival of breast cancer patients during neoadjuvant chemotherapy

The aim of our study was to evaluate whether blood flow in locally advanced and inflammatory breast cancer before and after neoadjuvant chemotherapy using color Doppler ultrasonography can be used to monitor the response to therapy and identify possible correlations between survival and various Doppler indices. Fifty patients with breast cancer underwent Doppler evaluation of the tumor with determination of Doppler indices such as pulsatility index (PI), resistive index (RI), and peak systolic velocity (PSV). RI and PI decreased in 27 (54%) and 20 (40%) patients, respectively, and increased in 23 (46%) and 30 (60%) patients, respectively. Thirty (60%) patients showed a decrease in PSV and 20 (40%) patients an increase. Patients with an intratumoral blood flow velocity increase after chemotherapy had a greater likelihood of local recurrence and metastasis compared with patients in whom flow velocity decreased after chemotherapy. The study also confirmed a greater correlation between Doppler PSV and clinical assessment. Tumor flow velocity measured by Doppler ultrasound can be used as an independent marker of disease-free survival in patients with breast cancer.

Assessment of cerebrovascular reactivity during major depression and after remission of disease

Background:There are a growing number of studies suggesting that depression may increase the risk of stroke. Impaired autoregulation of vascular tone may contribute to a higher risk of developing cerebrovascular diseases. Cerebrovascular reactivity (CVR) reflects the compensatory dilatory capacity of cerebral arterioles to a dilatory stimulus and is an important mechanism that ensures constant cerebral blood flow. There is a hypothesis that CVR is reduced in major depression, which would explain the association between depression and stroke.Objectives:The aim of this study was to investigate the effect of depression on CVR in cerebral vessels by comparing CVR during the depression phase with that during remission.Material and Methods:Using the apnea test, we assessed CVR in 16 patients with unipolar depression during disease and after remission of disease by calculating the increase in cerebral blood flow velocity after breath-holding (the apnea test). Blood flow velocities were measured by transcranial Doppler ultrasound (TCD).Results:CVR was significantly reduced in the depression phase in comparison to that in the remission phase. However, this change was not seen in all the patients.Conclusion:CVR was reduced in most of the depressed patients. The decreased CVR, as indicated by the changes in peak systolic velocity (PSV) and mean flow velocity (MFV) of the middle cerebral artery, in depressed patients was more marked on the right side, which could point to a vascular basis for some kinds of depression. We recommend that other studies, with larger samples, be done; future studies should assess whether the changes in the CVR varies with the severity and type of depression.

Cardiovascular effects of dipyrone and propofol on hemodynamic function in rabbits

To evaluate the short-term cardiovascular effects of IV administration of dipyrone (metamizole) as an intraoperative analgesic during total IV anesthesia with propofol. 6 healthy female New Zealand White rabbits. Anesthesia was induced with propofol (4.0 to 8.0 mg/kg, IV) and maintained with the same drug (1.2 to 1.3 mg/kg/min, IV). After induction, 3 doses of dipyrone (65 mg/kg each) were administered IV at 25-minute intervals. Before and for 10 minutes after each dipyrone injection, the following vascular and hemodynamic variables were recorded at the left common carotid artery every minute after the first injection: vessel diameter; peak systolic, minimum diastolic, end-diastolic, and mean blood flow velocities; mean volumetric flow; resistance and pulsatility indices; mean arterial blood pressure (MAP); heart rate; arterial oxygen saturation (SpO(2)); and end-tidal partial pressure of CO(2) (PETCO(2)). Echocardiography was performed after the second injection. The same variables were measured at the abdominal aorta (AA) after the third injection. Dipyrone injections caused a significant, transient decrease in the resistance index at the AA. Also detected were a minor decrease in pulsatility index at the left common carotid artery and a minor increase in end-diastolic blood flow velocity at the AA. The MAP, heart rate, SpO(2), and PETCO(2) did not significantly change after injections. A comparison of HR and MAP after the first and third bolus injections revealed only minor changes. Dipyrone used with propofol anesthesia in rabbits appeared not to significantly impair cardiovascular and hemodynamic function.

Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women

We examined the role of central command in static exercise-induced increase in middle cerebral artery mean blood flow velocity (V(MCA)). Eleven young female subjects performed static elbow flexion for 2 min at 30% maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity. The rating of perceived exertion in exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean +/- s.d.; 4.8 +/- 1.1 for CONT versus 3.5 +/- 1.0 for EX+VIB; P < 0.05). The increases in mean arterial pressure (36 +/- 8 versus 22 +/- 7%; P < 0.05), heart rate (36 +/- 16 versus 21 +/- 7%; P < 0.05) and cardiac output (56 +/- 26 versus 39 +/- 14%; P < 0.05) during EX+VIB were also lower than those during CONT. Similarly, the increase in the V(MCA) during EX+VIB was lower than that during CONT (29 +/- 5 versus 17 +/- 14%; P < 0.05). These results suggest that the influence of central command contributes to cerebral blood flow regulation during static exercise and the decrease in V(MCA) is likely to be caused by attenuated brain activation in the central command network and/or by the reduction in cardiac output.

Total Blood Volume Is Maintained in Nonhydropic Fetuses with Severe Hemolytic Anemia

Objective: Fetal alloimmune anemia is associated with increased blood flow velocities and cardiomegaly. In severe cases, hydrops can develop. We investigated whether the decrease of red blood cell volume is associated with a reduction or expansion of plasma volume. Methods: In 86 alloimmunized fetuses that received a first intrauterine transfusion, we calculated fetal total blood volumes (i.e. fetoplacental blood volumes) using a dilutional principle of fetal hemoglobin with adult hemoglobin. The relation between total blood volume and estimated fetal weight, severity of anemia and hydrops was analyzed. Results: Gestational age ranged from 17 to 35 weeks. Mean hemoglobin deficit was 6.8 standard deviations (range 2.1–11.7) below the normal mean. Fetal total blood volume was significantly related to estimated fetal weight (p < 0.001). Mean total blood volume in nonhydropic fetuses was 123 ml/kg (n = 74) and in hydropic fetuses 144 ml/kg (n = 12). There was a significant relation between total blood volume per kg body weight and hydrops (p = 0.035); however, there was no relation with severity of anemia (p = 0.94). Conclusion: In the human nonhydropic fetus with severe hemolytic anemia, total blood volume is maintained: the decrease in red blood cell volume is thus compensated by an increase in plasma volume. In hydropic fetuses, however, total blood volume seems to be increased. This is in accordance with the hypothesis that congestive heart failure plays a role in the pathophysiology of hydrops in anemic fetuses.

Cerebrovascular reactivity over time-course – From major depressive episode to remission

Introduction Depression is a prospective risk factor for stroke. Little is known, however, about the pathophysiologic links leading to this association. Cerebrovascular reactivity (CVR) reflects the compensatory dilatory capacity of cerebral arterioles to a dilatory stimulus and is an important mechanism to provide constant cerebral blood flow. In the absence of major arterial stenosis, an impaired CVR has been associated with a higher risk of stroke. We hypothesized that CVR might be continuously reduced in patients with major depression even after successful remission thus contributing to the association between depression and stroke. Materials and methods We investigated CVR in a group of patients ( N = 29) in the acute episode of depressive illness and after 21 months under euthymic condition. A healthy control group ( N = 33) was investigated at comparable time intervals. All patients and controls were otherwise healthy. CVR was investigated by calculating the increase in cerebral blood flow velocity after stimulation with acetazolamide. Blood flow velocities were measured by transcranial doppler ultrasound. Results A group of acutely depressed patients presented a significantly reduced CVR compared to controls. On follow-up 21 months later after treatment and remission, CVR in the patient group had significantly improved, whereas CVR in the control group remained unchanged. Confounding factors had no significant influence. Discussion CVR is impaired during major depression. Since CVR seems to improve after treatment of depression, the contribution to an increased stroke risk among depressive patients may be true for a subgroup only and needs to be further investigated.

Danshen protects liver grafts from ischemia/reperfusion injury in experimental liver transplantation in rats

Reperfusion injury remains one of the major problems in transplantation. Free radicals and disturbance of microcirculation are the supposed main contributors. Recent evidence shows that Danshen, a traditional Chinese drug used in vascular diseases, can scavenge radicals and improve microcirculation. This study investigates its effect on liver transplantation (LTx). Before organ recovery, female Sprague-Dawley rats (210-240 g) received intravenous Danshen or the same volume of Ringer solution as control. LTx was performed after 1 h of cold storage. Microperfusion, leukocyte-endothelium interaction and latex-bead phagocytosis were evaluated with in vivo microscopy. Survival, transaminases and histology were assessed. Immunohistology was used for TNF-alpha levels. anova and Fisher's exact test were employed for statistical analyses as appropriate. Survival increased from 60% in controls to 100% (P < 0.05). AST and LDH decreased from 3969 +/- 1255 U/l and 15444 +/- 5148 U/l in controls to 1236 +/- 410 U/l and 5039 +/- 1594 U/l, respectively (P < 0.05). In vivo microscopy revealed decreased leukocyte-adherence and increased blood flow velocity in sinusoidal zones after administration of Danshen (P < 0.05), while latex-bead phagocytosis was found in 60% of controls (P < 0.05). The TNF-alpha index decreased from 2.08 +/- 0.09 in controls to 1.09 +/- 0.09 (P < 0.05). This study clearly demonstrates hepatoprotective effects after experimental LTx, which can be explained via anti-oxidative effects, improved microcirculation and decreased Kupffer cell activation.

An animal model for the analysis of cochlear blood flood disturbance and hearing threshold in vivo

Impairment of cochlear blood flow (CBF) is considered to be important in inner ear pathology. However, direct measurement of CBF is difficult and has not been investigated in combination with hearing function. Six guinea pigs were used to show feasibility of an animal model for the analysis of cochlear microcirculation by intravital microscopy in combination with investigation of the hearing threshold by brainstem response audiometry (ABR). By the application of sodium nitroprusside (SNP), CBF was increased over 30 min. Reproducibility of measurements was shown by retest measurements. Mean baseline velocity of CBF was 109 +/- 19 mum/s. Vessel diameters had a mean value of 9.4 +/- 2.7 mum. Mean hearing threshold was 19 +/- 6 dB. In response to SNP, CBF velocity increased significantly to 161 +/- 26 mum/s. Mean arterial pressure decreased significantly to 36 +/- 11 mmHg. After the end of the application, CBF velocity recovered to a minimum of 123 +/- 17 microm/s. Within the retest, CBF velocity significantly increased to a maximum of 160 +/- 31 microm/s. Second recovery of CBF velocity was 125 +/- 14 mum/s. Within the second retest, CBF increased significantly to 157 +/- 25 microm/s. ABR thresholds did not change significantly. The increase in blood flow velocity occurred in spite of substantial hypotension as induced by a vasodilator. This may explain the fact that ABR threshold remained unchanged reflecting a maintained blood supply in this part of the brain. This technique can be used to evaluate effects of treatments aimed at cochlear microcirculation in inner ear pathologies.

Differential Increases in Blood Flow Velocity in the Middle Cerebral Artery after Tourniquet Deflation during Sevoflurane, Isoflurane or Propofol Anaesthesia

The purpose of this study was to examine the comparative effects of sevoflurane, isoflurane or propofol on cerebral blood flow velocity after tourniquet deflation during orthopaedic surgery. Thirty patients undergoing elective orthopaedic surgery were randomly divided into sevoflurane, isoflurane and propofol groups. Anaesthesia was maintained with sevoflurane, isoflurane or propofol infusion in 33% oxygen and 67% nitrous oxide, in whatever concentrations were necessary to keep bispectral index values between 45 and 50. Ventilatory rate or tidal volume was adjusted to target PaCO2 of 35 mmHg. A 2.0 MHz transcranial Doppler probe was attached to the patient's head at the temporal window and mean blood flow velocity in the middle cerebral artery was continuously measured. The extremity was exsanguinated with an Esmarch bandage and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, velocity in the middle cerebral artery and arterial blood gas analysis were measured every minute for 10 minutes after release of the tourniquet in all three groups. Velocity in the middle cerebral artery in the three groups increased for five minutes after tourniquet deflation. Because of the different cerebrovascular effects of the three agents, the degree of increase in flow velocity in the isoflurane group was greater than in the other two groups, the change in flow velocity in the propofol group being the lowest (at three minutes after deflation 40 +/- 7%, 32 +/- 6% and 28 +/- 10% in the isoflurane, sevoflurane and propofol groups respectively, P < 0.05).

Cerebral oxygenation decreases during exercise in humans with beta‐adrenergic blockade

Beta-blockers reduce exercise capacity by attenuated increase in cardiac output, but it remains unknown whether performance also relates to attenuated cerebral oxygenation. Acting as their own controls, eight healthy subjects performed a continuous incremental cycle test to exhaustion with or without administration of the non-selective beta-blocker propranolol. Changes in cerebral blood flow velocity were measured with transcranial Doppler ultrasound and those in cerebral oxygenation were evaluated using near-infrared spectroscopy and the calculated cerebral mitochondrial oxygen tension derived from arterial to internal jugular venous concentration differences. Arterial lactate and cardiac output increased to 15.3 +/- 4.2 mM and 20.8 +/- 1.5 L min(-1) respectively (mean +/- SD). Frontal lobe oxygenation remained unaffected but the calculated cerebral mitochondrial oxygen tension decreased by 29 +/- 7 mmHg (P < 0.05). Propranolol reduced resting heart rate (58 +/- 6 vs. 69 +/- 8 beats min(-1)) and at exercise exhaustion, cardiac output (16.6 +/- 3.6 L min(-1)) and arterial lactate (9.4 +/- 3.7 mM) were attenuated with a reduction in exercise capacity from 239 +/- 42 to 209 +/- 31 W (all P < 0.05). Propranolol also attenuated the increase in cerebral blood flow velocity and frontal lobe oxygenation (P < 0.05) whereas the cerebral mitochondrial oxygen tension decreased to a similar degree as during control exercise (delta 28 +/- 10 mmHg; P < 0.05). Propranolol attenuated the increase in cardiac output of consequence for cerebral perfusion and oxygenation. We suggest that a decrease in cerebral oxygenation limits exercise capacity.

Autoregulation in the Posterior Circulation Is Altered by the Metabolic State of the Visual Cortex

Previous studies suggest that dynamic autoregulation in the posterior cerebral artery (PCA) is less efficient compared to the middle cerebral artery (MCA). We examined the role of cerebral vasodilation caused by metabolic activation (ie, visual stimulus) on autoregulatory characteristics in the 2 vascular territories. Blood flow velocity in the PCA and MCA and mean arterial pressure were measured continuously in 45 healthy volunteers (62+/-3 years) while seated with eyes open. Additional 20 subjects (60+/-5 years) were examined with eyes closed and open. Autoregulation was assessed using transfer function gains in both the PCA and MCA territories in the low (0.03-0.07 Hz), high (0.07-0.15 Hz), and cardiac (approximately 1 Hz) frequency ranges. With eyes open, gains were significantly higher in the PCA compared to the MCA in the low (PCA: 1.41+/-0.09 vs MCA: 1.18+/-0.07; P=0.003) and high (PCA: 2.06+/-0.12 vs MCA: 1.61+/-0.08; P=0.0001) frequencies. Opening eyes increased blood flow velocity and reduced cerebrovascular resistance index in the PCA but not in MCA. This vasodilation in the PCA was associated with increased gain in the low (autoregulatory) frequency, whereas MCA gain did not change (PCA: 0.89+/-0.14 vs 1.31+/-0.17, MCA: 1.24+/-0.16 vs 1.16+/-0.11; P=0.02). Dilation of the PCA territory during visual cortex activation resulted in increased PCA transfer function gain without changing MCA gain. Thus, impaired autoregulation in the PCA reported in previous literature is likely the result of metabolic vasodilation and not an inherent difference in the autoregulatory characteristics of the posterior circulation.