Increase In Mean Flow Velocity Research Articles

Assessment of cerebral oxygenation oscillations in subjects with hypertension

PurposeThe objective of this study was to assess the spontaneous oscillations in subjects with hypertension based on the wavelet transform of cerebral oxygenation signal measured with near-infrared spectroscopy (NIRS). MethodsContinuous recordings of NIRS and arterial blood pressure (ABP) signals were obtained from simultaneous measurements in 20 healthy subjects (age: 70.8±5.2years) and 22 subjects with hypertension (age: 72.5±6.8years). ResultsUsing spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.4–2Hz; II, 0.15–0.4Hz; III, 0.06–0.15Hz; IV, 0.02–0.06Hz and V, 0.005–0.02Hz). The amplitudes of Δ[Hb] and Δ[HbO2] in intervals I, II and III were significantly higher in hypertensive patients, who have increased mean flow velocity in middle cerebral artery (MCA), compared to that in the healthy subjects (p<0.01). The amplitudes of the ABP in frequency intervals III and V were significantly higher in hypertensive patients than in the healthy subjects (p<0.01). ConclusionsThe present findings revealed that hypertension and increased mean flow velocity in MCA have significant effect on the cerebral oscillations. The higher cerebral oscillations might be related to the intracerebral atherosclerosis in response to systemic hypertension. In addition, the higher spontaneous oscillations in intervals III and V in ABP indicate a metabolic regulation and myogenic response to hypertension.

Nonlinear fluid-induced vibration and instability of an embedded piezoelectric polymeric microtube using nonlocal elasticity theory

Nonlinear vibration and instability of a smart piezoelectric microtube made of poly-vinylidene fluoride embedded in an elastic medium is investigated. The tube conveys an isentropic, incompressible fluid flowing in a fully developed irrotational manner. This smart microtube is modeled as a thin shell based on the nonlinear Donnell's shell theory. Effects of mean flow velocity, fluid viscosity, elastic medium modulus, temperature change, imposed electric potential, small scale and aspect ratio on the vibration behavior of the microtube are analyzed. The results indicated that increasing mean flow velocity considerably changes the nonlinearity effects on instability of embedded piezoelectric polymeric microtube so that small scale and temperature change effects become negligible. It has also been found that stability of the system is strongly dependent on the imposed electric potential. The system studied in this article can be used as sensors and actuators in sensitive applications.

Comparison of passive leg raising and hyperemia on macrovascular and microvascular responses

Passive leg raising is a simple diagnostic maneuver that has been proposed as a measure of arterial vasodilator reserve and possibly endothelial function. While passive leg raising has previously been shown to lower blood pressure, increase flow velocity and cause brachial artery dilation, its effects on microvascular flow has not been well studied. Also, passive leg raising has been directly compared previously to upper arm but never to lower arm occlusion of blood flow induced hyperemia responses. We compared changes in macrovascular indices measured by brachial artery ultrasound and microvascular perfusion measured by Laser Doppler Flowmetry induced by passive leg raising to those provoked by upper arm and lower arm induced hyperemia in healthy subjects. Upper arm induced hyperemia increased mean flow velocity by 398%, induced brachial artery dilatation by 16.3%, and increased microvascular perfusion by 246% (p<.05 for all). Lower arm induced hyperemia increased flow velocity by 227%, induced brachial artery dilatation by 10.8%, and increased microvascular perfusion by 281%. Passive leg raising increased flow velocity by 29% and brachial artery dilatation by 5.6% (p<.05 for all), but did not change microvascular perfusion (−5%, p=ns). In conclusion, passive leg raising increases flow velocity orders of magnitude less than does upper arm or lower arm induced hyperemia. Passive leg raising-induced brachial artery dilatation is less robust than either of these hyperemic techniques. Finally, although upper arm and lower arm hyperemia elicits macrovascular and microvascular responses, passive leg raising elicits only macrovascular responses.

Impact analysis of river morphology and roughness variability on hydropeaking based on numerical modelling

AbstractHydropeaking due to operations of storage hydropower plants was highlighted as one of the main stresses on aquatic ecology by the European Water Framework Directive. Nevertheless, hydropower must be seen as a high‐value resource in the renewable energy sector. However, very few studies deal with the physical processes behind the artificial unsteady flows, as the variability of local river morphology and roughness in general. Thus, the aim of the present study is to address these issues on the basis of one‐dimensional hydrodynamic numerical modelling. In total, four Austrian rivers have been investigated, which were further divided into 13 sub‐reaches according to their bed slope. From single and multiple linear regression models, it was possible to relate potential retentions of peak flow for peak duration of &lt;2 h and for bed slopes &lt;0.005 to the spatial extent of wetted width between base and peak flows, independent of the selected ramping rate (discharge relationship between base and peak flows). Moreover, the ramping velocity (rate of decreasing water level between peak and base flows) correlated positively with an increase in depth variance during peak flow, which was related further to an increase in mean flow velocities and a higher specific discharge over the 13 selected reaches. Nevertheless, within sensitivity testing, it could be proven that increases in channel roughness cause an increase in peak flow retention and a decrease of the ramping velocities for the decreasing limb. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Electro-thermo-mechanical nonlinear nonlocal vibration and instability of embedded micro-tube reinforced by BNNT, conveying fluid

Nonlinear vibration and stability of a smart composite micro-tube made of Poly-vinylidene fluoride (PVDF) reinforced by Boron-Nitride nanotubes (BNNTs) embedded in an elastic medium under electro-thermal loadings is investigated. The BNNTs are considered to be long straight fibers and the composite used in this study is in the category of piezoelectric fiber reinforced composites (PEFRC). The micro-tube is conveying a fully developed isentropic, incompressible and irrotational fluid flow. The smart micro-tube is modeled as a thin shell based on the nonlinear Donnell's shell theory. Effects of mean flow velocity, fluid viscosity, elastic medium modulus, temperature change, imposed electric potential, small scale, aspect ratio, volume percent and orientation angle of the BNNTs on the vibration behavior of the micro-tube are taken into account. The results indicate that increasing mean flow velocity considerably increases the nonlinearity effects so that small scale and temperature change effects become negligible. It has also been found that stability of the system is strongly dependent on the imposed electric potential and the volume percent of BNNTs reinforcement. The system studied in this article can be used as sensor and actuator in the sensitive applications.

Moderate correlation between breath‐holding and CO2 inhalation/hyperventilation methods for transcranial doppler evaluation of cerebral vasoreactivity

Both CO(2) inhalation followed by hyperventilation and breath-holding have been utilized to measure cerebral vasomotor reactivity (VMR) but their correlation has been poorly studied and understood. A retrospective study was conducted in 143 subjects (62.6 ± 15.8 years old, 64% men) with transcranial Doppler ultrasonography measurement of mean flow velocity (MFV) at baseline, after 30 seconds of breath-holding, and after CO(2) inhalation followed by hyperventilation, in the left and right middle cerebral artery. Breath-holding index (BHI) was calculated as the percentage of MFV increase from baseline per second of apnea. CO(2) inhalation/hyperventilation index (CO(2) /HV) was calculated as the percentage of MFV difference between CO(2) inhalation and hyperventilation. There were 75 carotid arteries with >70% stenosis or occlusion, and 18 middle cerebral arteries with >50% stenosis or occlusion. The mean BHI was 0.93 ± 0.7 and 0.89 ± 0.6, whereas the mean CO(2) /HV was 61 ± 26% and 60 ± 26%, respectively, on the right and left sides. The correlation between BHI and CO(2) /HV was moderate on the right (r = 0.33; p < 0.01) and left sides (r = 0.38; p < 0.01). Multivariate linear regression analysis indicated that age (p = 0.01) and history of stroke (p = 0.007) were associated independently with an impaired VMR on the right as measured by CO(2) /HV. No predictors for impaired VMR by CO(2) /HV on the left and by BHI on either side were found. CO(2) /HV and BHI are only moderately correlated. Further studies are necessary to determine which method more accurately predicts clinical morbidity. © 2012 Wiley Periodicals, Inc. J Clin Ultrasound 2012; Published online in Wiley Online Library.

The brain at work

Our understanding of the cerebral blood flow (CBF) response to exercise has evolved dramatically over some 20 years in parallel with the advent of new methods to measure brain perfusion in humans. Previously, the Kety–Schmidt method was the only method available for evaluation of CBF in humans. The outflow from the brain through the internal jugular vein was taken to represent CBF and no change was found during exercise, probably because the spinal veins become more important when humans are upright as is the case for most exercise studies (Ide & Secher, 2000). As a consequence, it was often considered that exercise was the exception for which cerebral ‘activation’ (and maybe thinking?) was not required. Yet, with the introduction of methods that evaluate brain tissue flow (133Xenon-clearance) or inflow to the brain through the common or, ideally the internal carotic artery, an ∼20% increase in CBF during mild- to moderate-intensity dynamic exercise was observed. The CBF then levels out or maybe decreases when exercise becomes intense, with the decrease in the arterial carbon dioxide tension accompanying the exponential increase in ventilation. Thus CBF, and indeed cerebral oxygenation responses during incremental exercise, were hypothesised to follow an inverted U-shaped curve. The vast majority of human studies have applied a transcranial Doppler (TCD) approach to evaluate changes in CBF during exercise. Although this approach has the advantage that it can be used during high-intensity dynamic exercise of a large muscle mass, when using the TCD technique one must assume that the diameter of the isonated artery does not change. This assumption has become universally accepted although TCD was introduced by R. Aaslid (1984) to detect vasospasm after neurosurgical procedures. In support of the supposition that the diameter of the isonated artery at the base of the brain (often the middle cerebral artery (MCA)) remains constant during exercise, an inverted U-shape response to incremental exercise is detected with the TCD, and the magnitude of the increase in mean flow velocity is similar to that determined by other estimates of CBF (∼20%). In contrast, the diameter of the MCA increases in response to hypoxia (Wilson et al. 2011) and constricts in response to the administration of the α1-adrenergic receptor agonist phenylephrine (Ogoh et al. 2011), indicating that there is a need for new ambulatory methods for the evaluation of CBF. In a recent issue of The Journal of Physiology, Vogiatzis et al. (2011) introduced a new method using near-infrared spectroscopy to detect CBF (in the frontal lobe) during progressive exercise after bolus injection of idocyanine green, with and without hypoxia, in trained cyclists. It is comforting that the inverted U-shape CBF response to incremental exercise is confirmed by this initiative, and that the validity of the method is supported by an increase in CBF during hypoxia. Yet, as mentioned by the authors, the determined CBF is unreasonably low (23 ml min−1 100 g−1) compared to a normal value of ∼50 ml min−1 100 g−1 and the increase with CBF during exercise is twice as large as normally found. Near-infrared light has to pass through the skin and the scalp to reach the frontal lobe and the authors consider that the low skin (and scalp) blood flow could influence the result. Accordingly, it would be of value if this method for determination of CBF were repeated during exercise after skin blood flow is eliminated, e.g. by cooling the skin or after the administration of phenylephrine (Ogoh et al. 2011). The TCD technique has been invaluable for the development in understanding the brain at work both under normoxic and hypoxic conditions; however, it is problematic that the TCD evaluation of CBF is expressed as a velocity. Such a limitation may be surmounted by using near-infrared spectroscopy to determine CBF during exercise (Vogiatzis et al. 2011), although the extent of the influence of skin blood flow must be established. Similarly, flow in basal cerebral arteries may be evaluated by duplex ultrasound (Wilson et al. 2011) as it is established for peripheral arteries. Accordingly, we now have two additional methods available to take the evaluation of CBF during hypoxic exercise to new heights and the study by Vogiatzis et al. (2011) provides support to the notion that exercise in hypoxia is limited by cerebral oxygen supply and brain oxygenation.

The effect of propranolol on cerebrovascular reactivity to visual stimulation in migraine

Background Propranolol is effective for migraine prophylaxis. However, its exact mechanism is not known. We postulated that the protective effect is due to the lowering of cerebrovascular reactivity (CVR). To verify this, we applied photic stimuli to migraineurs and analyzed the results. Methods We checked the mean flow velocity (MFV) of the posterior cerebral artery by transcranial Doppler in 22 migraineurs during a headache-free period and in 14 normal controls. During the photic stimulation, MFV was remeasured and the CVR was estimated in both groups. Migraineurs received prophylactic propranolol for 2 months, and they were then reevaluated for the above-mentioned parameters and assessed for a headache index (HI). Results There were no baseline differences in MFV between migraineurs and controls before treatment. Both groups showed a similar degree of increase in MFV with the photic stimulation, thus CVR was not significantly different between them. After the treatment period, CVR decreased significantly in migraineurs compared to baseline (p < 0.01), although MFV remained unchanged. The prophylactic effect of propranolol treatment on symptomatic migraine was demonstrated on the HI, which significantly improved (p < 0.05). Conclusions Considering that CVR was decreased but the baseline MFV was not changed in the posterior cerebral artery prior to the visual stimulation in migraineurs after propranolol treatment, we assume that the protective effect of propranolol was not due to the direct effect on the cerebral vessels but due to the modulation of the CVR to sensory stimulation through its action on central centers associated with autonomic vascular tone.

CFD study on mean flow engine for wind power exploitation

Acoustic oscillation can be induced in a closed branch tube by a mean gas flow in a trunk tube passing the opening of the branch tube. Based on this principle, novel aerodynamically driven generator and thermoacoustic refrigerator can be manufactured. Large-eddy simulation (LES) of turbulence was applied to simulate aerodynamically driven acoustic oscillation in a mean flow engine (MFE) with a cross-junction configuration. It is shown that a standing-wave acoustic field is established inside the closed branch tube at certain mean flow velocities. Different acoustic and hydrodynamic modes occur with the increase of mean flow velocity. Furthermore, Strouhal number has strong effects on acoustic and hydrodynamic modes of the MFE. Under present computational conditions, critical acoustic pressure amplitudes in the first and fifth acoustic modes occur when St = 0.39 and St = 0.94 respectively. It would be beneficial to design MFEs operating in the third acoustic mode to obtain strong acoustic oscillation.

Metabolic syndrome and cerebral vasomotor reactivity

Metabolic syndrome has been proposed as a risk factor for stroke and transient ischaemic attack. One pathophysiological mechanism could be impairment of endothelial function. Thus, we hypothesized that cerebral vasomotor reactivity would be decreased in patients with metabolic syndrome, compared to patients without metabolic syndrome. In this retrospective analysis, 83 consecutive patients (aged 59.19 ± 15.98; 33 women) underwent Doppler examination for carotid artery disease including bi-hemispherical vasomotor reactivity assessment using transcranial Doppler monitoring. Vasomotor reactivity data were analyzed from the hemisphere with no or low-grade carotid stenosis (<40%). Cerebral vasomotor reactivity was calculated as percent increase in mean flow velocity per mmHg pCO(2) during 2 min of 5% CO(2) inhalation delivered by anesthesia mask (normal if ≥ 2%/mmHg). Univariate and multivariable linear regression models were used to determine factors, including metabolic syndrome, that were independently associated with pathologic vasomotor reactivity. After adjusting for the presence of contralateral carotid stenosis and ipsilateral stroke in the multivariable model, metabolic syndrome was independently associated with lower vasomotor reactivity values (2.27 ± 1.24% vs. 2.68 ± 1.37; ß = -0.258, P = 0.033). In this model, there was no association of cerebral vasomotor reactivity with age, gender, race, cardiac disease, current statin therapy, or small vessel disease. Our findings suggest that impaired cerebral vasomotor reactivity may be a mediator of stroke in patients with metabolic syndrome, a syndrome affecting a significant and growing proportion of the population. A prospective longitudinal study is warranted to study the cerebral haemodynamic effect of metabolic syndrome.

Channel Morphology Response to Selective Wood Removals in a Sand‐Laden Wisconsin Trout Stream

AbstractLarge sand bed loads in trout stream headwaters can limit salmonid spawning habitat and reproductive success. This phenomenon has been observed in many northern Wisconsin watersheds, where historic logging practices are the likely source of the sediment loading. Presently, sediment transport is limited by abundant woody debris, causing channels to aggrade and bury gravels. We evaluated the impacts of a wood debris and beaver dam removal remediation strategy on fine sediment transport and exposure of the underlying gravel and cobble substrates in a second‐order Lake Superior tributary. A 300‐m treatment reach received selective wood removals and was compared with both an upstream 300‐m reference reach receiving no alteration and a downstream reach to monitor the effects of transferred fine sediment. Physical channel measurements were taken before the wood removal process, with repeat sampling at 10 and 12 months posttreatment. The wood removal treatment resulted in a significant 25% narrowing of mean stream widths, a 32% increase in mean flow velocities, a 58% reduction in the sand bed load, and a 400% increase in the available coarse substrate across the channel. Grain size distributions coarsened noticeably from pre‐ to posttreatment. Water depth and temperature were not altered by the treatment, and the reference station physical measures were relatively unchanged over the 12‐month study period. Immediately after the wood removal there was an observable pulse of sediment traveling through the downstream reach that increased the sand bed load, increased stream widths, and filled pools. However, these impacts diminished with time, and near‐preremoval conditions had returned after 12 months. The wood removal treatment caused a significant reduction in sand content and enhanced the availability of salmonid spawning substrates.

Impaired visual evoked flow velocity response in cerebral amyloid angiopathy

Animal models of cerebral amyloid angiopathy (CAA) exhibit abnormal vascular reactivity. We determined whether vascular reactivity, measured by transcranial Doppler ultrasound (TCD), is reduced in humans with CAA. Cases were recruited from an established prospective study of CAA. Healthy controls were recruited from a study of normal aging. Evoked mean flow velocity increase in the posterior cerebral artery (PCA) was measured while subjects viewed a flashing alternating checkerboard stimulus. In a separate but partially overlapping cohort we measured the mean flow velocity increase in the middle cerebral artery (MCA) while subjects inhaled carbon dioxide. The visual evoked mean flow velocity increase was 8.0 +/- 6.1% in CAA (n = 11) compared to 17.4 +/- 5.7% in controls (n = 9, p = 0.002). The PCA pulsatility index, a marker of distal vascular resistance, was higher in CAA (CAA 1.35 +/- 0.35, control 1.04 +/- 0.14, p = 0.03). Among CAA subjects, lower visual evoked mean flow velocity increase was associated with a higher number of hemorrhages seen on MRI (r = -0.87, p = 0.0005) and higher MRI white matter hyperintensity volume (r = -0.67, p = 0.02). The MCA response to carbon dioxide did not differ between CAA and control in 20 subjects (9 CAA, 11 control, p = 0.54). Cerebral amyloid angiopathy (CAA) was associated with decreased vascular reactivity in response to visual stimulation, possibly reflecting the occipital predilection of the disease. The association of posterior cerebral artery (PCA) evoked flow velocity response with elevated PCA pulsatility index and MRI markers of small vessel disease suggests that abnormal PCA evoked flow velocity in CAA is caused by pathology of the distal resistance vessels.

The Relationship between Velocity and Cerebral Resistance during Vasomotor Reactivity Testing: Should We Report a Different Measurement?

Introduction and Objective Changes in arterial resistance are an important aspect in the regulation of cerebral blood flow. Vasomotor reactivity testing with transcranial Doppler (TCD) is used commonly to report findings in terms of mean flow velocity changes. Yet, the pertinent clinical question is about resistance changes. How effectively do the cerebral resistance vessels dilate and constrict, or what is their vasomotor capacity? In this study, we examine the relationship between cerebral flow velocity and resistance and propose a new measurement for vasomotor reactivity studies. Methods We recruited 35 healthy subjects and measured TCD mean flow velocities in the middle cerebral artery during vasoreactivity testing using 6% CO2 inhalation (hypercapnia) to produce cerebral vasodilatation, and controlled hyperventilation (hypocapnia) to produce vasoconstriction. Brachial blood pressure was also recorded. Mean Resistance (mean blood pressure/mean flow velocity) was calculated at baseline, hypercapnia, and hypocapnia. We compared the % change from baseline in both mean flow velocity (cm/s) and Mean Resistance (mmHg s/cm), in relation to gender and age. Results For the group overall, hypercapnia produced a 39.3 ± 19.9% increase in mean flow velocity; however, this resulted in only a 21.9 ± 9.9% decrease in Mean Resistance. Whereas during hypocapnia, a 32.4 ± 9.3% decrease in velocity produced a much larger increase in Mean Resistance (48.9 ± 22.2%). Young women had the greatest capacity to vasodilate, showing a 26.1 ± 9.2% decrease in Mean Resistance (46.0 ± 14.6% increase in velocity). However, young men showed the largest change during vasoconstriction; a 59.5 ± 31.6% increase in Mean Resistance (35.3 ± 9.5% decrease in velocity). Conclusions Large velocity increases during hypercapnia do not represent large changes in resistance. Whereas small velocity decreases during hypocapnia actually represent much larger changes in resistance, the calculation of Mean Resistance is a more clinically relevant measurement to report than velocity alone, and should be incorporated into TCD studies in the future.

The impact of carotid stenting on the hemodynamic parameters and cerebrovascular reactivity of the ipsilateral middle cerebral artery

The study was conducted to determine the effect of carotid angioplasty and stenting (CAS) on the hemodynamic parameters and cerebrovascular reactivity (CVR) of the ipsilateral middle cerebral artery (MCA) and examine the relation between preprocedural exhausted CVR and perioperative neurologic events. The study included 29 patients with severe extracranial carotid stenosis undergoing CAS. Transcranial Doppler imaging was performed before the procedure, 2 days, and 2 to 4 months postoperatively. Peak systolic velocity, end-diastolic velocity, mean flow velocity, and pulsatility index of the ipsilateral MCA were recorded at rest. CVR was assessed with the breath holding test: the increase of mean flow velocity and the breath holding index were calculated. Peak systolic and mean flow velocities increased significantly in both postoperative studies compared to the preoperative values, end-diastolic velocity was significantly elevated only in the first study, and pulsatility index did not change significantly. When stimulated by breath holding, preoperative mean flow velocity did not increase significantly compared with the resting values; however, it did increase significantly during breath holding in both studies after CAS. The breath holding index improved significantly from -0.35 (-0.71 to 0.55) to 0.38 (0.12 to 0.61) at 2 days (P = .049) and 0.44 (0.31 to 0.92) at 2 to 4 months (P = .020). Exhausted CVR of the MCA preoperatively was associated with increased risk of neurological complications during or after the procedure (P = .006). CAS may improve the hemodynamic parameters and the vasomotor reactivity in the ipsilateral MCA. Exhausted CVR is associated with an increased risk of periprocedural neurologic complications.

Abnormal Pressure Passive Dilatation of Cerebral Arterioles in the Elderly With Isolated Systolic Hypertension

The aim of this study was to investigate the cerebrovascular adaptability to 2 sequential pressor stimuli in elderly patients with isolated systolic hypertension. Ten healthy elderly normotensive subjects (68 to 82 years), 10 elderly subjects with isolated systolic hypertension (63 to 82 years), and 10 young normotensive subjects (24 to 40 years) took part in the study. A pressor reaction, using sequential cold pressor and handgrip stimulation, was induced. The cerebrovascular response to the pressor stimulation was measured by transcranial Doppler determination of the mean flow velocity in the middle cerebral arteries. In all of the subjects, blood pressure increased during handgrip (+12 mm Hg, P<0.001 in the young; +18 mm Hg, P<0.01 in the elderly normotensive subjects; +19 mm Hg, P<0.001 in the hypertensive patients versus baseline). In the hypertensive subjects, the pressure increase persisted well into the recovery period. The pressure increase caused a significant increase in mean flow velocity in the middle cerebral arteries only in the elderly subjects. Cold pressor test increased blood pressure in all of the subjects during stimulation and the first 2 minutes of the recovery period (at whole-curve ANOVA: F=22.03, P<0.001 in the young participants; F=18.3, P<0.001 in the normotensive elderly; and F=13.04, P<0.001 in the hypertensive elderly). Mean flow velocity in the middle cerebral arteries significantly increased only in the hypertensive subjects. In the elderly hypertensive patients, the cerebrovascular reaction to adrenergic stimuli was more impaired than in the elderly normotensive subjects. This event can amplify the pressure insult on cerebral hemodynamics and increase the predisposition to cerebral damage, such as vascular cognitive impairment or stroke.

Cerebral blood flow velocity changes during meaningful and meaningless gestures – a functional transcranial Doppler study

The aim of the study was to use functional transcranial Doppler to investigate the possibility of revealing different activation patterns during healthy subjects' performance of meaningful and meaningless actions. Mean flow velocity (MFV) changes were recorded in middle cerebral arteries (MCAs) of 26 normal subjects during a rest phase and during performance of meaningful and meaningless actions. The meaningful task consisted of pouring sugar into a cup with a teaspoon. The meaningless action was an arm movement similar to that necessary for pouring sugar in a cup but without any tool and thus without a goal. Performing actions with or without meaning was associated with different patterns of MFV changes, as documented by the triple interaction condition x performing arm x side of recording [F(1, 25)=10.977; P=0.003]. During the meaningful action, MFV in MCAs increased significantly more than during the meaningless action. During the meaningless action, the MFV increase was significantly higher in the contralateral than in the ipsilateral MCA to the arm performing the task and the meaningful action determined a bilateral MFV increase only when the task was performed with the left arm. When the same task was performed with the right arm, the MFV increase was significantly higher in the contralateral than in the ipsilateral MCA. These findings suggest that the content of an action can influence MFV changes and further confirm the usefulness of transcranial Doppler in neuropsychological investigation.

Atherosclerosis in Women With Endometriosis

Patients with chronic inflammatory states (i.e. rheumatoid arthritis, systemic lupus erythematosus, Crohn’s disease) may show acceleration of atherosclerosis. Oxidative stress, which is known to be associated with atherosclerosis, has recently been proved to play a role in the development and progression of endometriosis. In addition, activated macrophages, production of inflammatory cytokines, and mildly oxidized LDL play similar roles in both atherosclerosis and endometriosis. The purpose of the current study is to determine whether women with endometriosis have greater subclinical atherosclerosis than the general population. Cross sectional study. This study included 66 women with endometriosis and 66 age-matched controls (± 3 years). All subjects were ≥ 35 years old and were regularly menstruating. Exclusion criteria were diabetes, hypertension, hypercholesterolemia, renal or metabolic diseases. Control group subjects had no detectable endometriotic lesions at surgical examination and had not previously undergone surgical treatment for endometriosis; they underwent surgery for uterine myomas (n = 33), ovarian cysts (n = 21), and pelvic pain (n = 12). Before laparoscopy, all patients underwent carotid scanning. Intima-media thickness (IMT) was measured on the far wall of the distal portion of the common carotid artery on each side 1cm proximal to the bulb. The arterial wall distensibility coefficient (DC) was calculated by dividing the relative stroke change in the diameter of the arterial wall through the pulse pressure, defined as systolic blood pressure minus diastolic blood pressure. Transcranial Doppler was used to evaluate cerebrovascular reactivity to hypercapnia, the breath-holding index (BHI) was obtained by dividing the percent increase in mean flow velocity occurring during breath-holding by the time (seconds) in which the subjects held their breath after a normal inspiration. Before surgery after at least 10 hours of fasting and not smoking blood samples were taken to determine the levels of LDL, HDL, cholesterol, triglycerides, fibrinogen, C-reactive protein, homocysteine, fasting glycemia, antithrombin III, plasminogen, protein C, protein S, and activated protein C resistance. Univariate comparisons of cases and controls were conducted by Mann-Whitney U test for continuous data and χ2 test for categorical data. No significant difference was detected in mean (± SD) age between study and control group (41.0 ± 3.7 and 40.8 ± 4.4 years; p = 0.287); body mass index and smoking status were similar in the two groups. All the biochemical parameters evaluated had similar levels in women with and without endometriosis. IMT was similar in women with endometriosis and in controls both on left (mean ± SEM, 0.444 ± 0.021 and 0.484 ± 0.020 mm, respectively; p = 0.330) and right (0.456 ± 0.025 and 0.473 ± 0.015 mm, respectively; p = 0.648) carotid artery. Similarly, no significant difference was observed in the DC between women with endometriosis and controls both on left (mean ± SEM, 4.738 ± 2.111 and 4.374 ± 2.246 × 10-3 /mmHg; respectively; p = 0.539) and right (4.939 ± 0.287 and 5.132 ± 0.241 × 10-3 /mmHg, respectively; p = 0.178) carotid artery. No significant difference was observed in the BHI between women with and without endometriosis. Our observations indicate that patients with endometriosis do not have more subclinical atherosclerosis than the general population.

Modeling the effects of tidal loading on mid‐ocean ridge hydrothermal systems

Tidal signals are observed in numerous time‐series measurements obtained from mid‐ocean ridge hydrothermal systems. In some instances these tidal signals are clearly the result of ocean currents, but in other instances it appears that the signals may originate in the subseafloor formation. In order to explore the effect of ocean tidal loading on mid‐ocean ridge hydrothermal systems, we apply a one‐dimensional analytical model of tidal loading on a poroelastic half‐space and develop a two‐dimensional numerical model of tidal loading on a poroelastic convection cell. The one‐dimensional models show that for a reasonable range of fluid, elastic, and hydrological properties, the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers. The two‐dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid‐ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust. These continuum models predict that outflow temperature perturbations will be very small (&lt;10−4°C), but in real systems where the continuum hypothesis does not always apply, the perturbations may be on the order of ∼0.1°C. The models predict relatively large perturbations to fluid velocity at the seafloor. For high‐temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases. Flow reversals at the seafloor are predicted in some regions of net low‐temperature outflow and net inflow during the tidal cycle. In the subseafloor, tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust. Tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor.

Mechanisms of Single and Multiple Borderzone Infarct: Transcranial Doppler Ultrasound/Magnetic Resonance Imaging Correlates

Background and Purpose: Hemodynamic patterns after borderzone (BZ) infarction are variable and dynamic. However, stroke mechanisms in different types of BZ infarctions have not been systematically studied by magnetic resonance angiography (MRA) and transcranial Doppler ultrasonography (TCD). Methods: Forty-nine patients who experienced a stroke limited to the territory of either the superficial or internal borderzone proved on MRI included in our registry, corresponding to 4% of 1,200 patients with ischemic stroke, were studied. All these patients underwent MRA, extracranial Doppler ultrasonography, TCD and other investigations from the standard protocol of our registry. Twenty of them (41%) had a posterior BZ infarct, 14 (29%) an anterior BZ infarct, 10 (20%) a subcortical BZ infarct and 5 (10%) bilateral BZ infarcts. Results: Unilateral internal carotid artery (ICA) tight stenosis or occlusion ipsilateral to the lesion was present in 14 patients (70%) with a posterior BZ infarct, in 72% of those with an anterior BZ infarct, in 80% of those with a subcortical BZ infarct and in 80% of those with bilateral BZ infarcts. TCD showed cross-filling of the middle cerebral artery via the anterior communicating artery in 5 patients (25%) with a posterior BZ infarct and 10% had an increased mean flow velocity (MFV) in the ipsilateral P1 posterior cerebral artery (PCA). In patients with an anterior BZ infarct, 3 (23%) had an MFV increase in the contralateral A1 anterior cerebral artery (ACA), and 2 (15%) had a higher MFV in the ipsilateral PCA. An elevated velocity at midline depths with reversed A1 ACA flow direction was seen in 2 patients (20%) with a subcortical infarct, and 1 patient (10%) had an MFV increase in the ipsilateral P1 PCA. Left ventricular systolic dysfunction (ejection fraction <40%) was present in 50% of patients with a posterior BZ infarct, in 36% of those with an anterior BZ infarct, in 20% of those with a subcortical BZ infarct and bilateral BZ infarcts each. Conclusion: The association of severe ICA stenosis or occlusion with cardiopathies and left ventricular dysfunction may play a critical role in those with BZ infarcts having inadequate collateral supply, while a cardioembolism or acute ICA dissection may also cause BZ infarction due to the rapidity of the occlusive process and the inability of the cerebral vasculature to recruit collateral pathways quickly enough.

Basilar and middle cerebral artery reactivity in patients with migraine.

Migraine has been reported as a possible risk factor for ischemic stroke. The mechanisms underlying this association are unknown. To evaluate cerebrovascular reactivity to hypercapnia in the anterior and posterior circulation of patients with migraine, as reduced cerebrovascular reactivity is associated with a predisposition to stroke in various clinical conditions. Using transcranial Doppler ultrasonography, changes in flow velocity during apnea were measured in both middle cerebral arteries and in the basilar artery of 15 control subjects and 30 patients with migraine (15 with aura and 15 without aura) during an attack-free period. Cerebrovascular reactivity was evaluated using the breath-holding index, which is calculated by dividing the percent increase in mean flow velocity recorded during a breath-holding episode by its duration (in seconds) after a normal inspiration. Vascular reactivity in the middle cerebral arteries was similar in patients and controls and significantly lower in the basilar artery of patients with migraine with aura compared with the other 2 groups (P <.0001). These findings show that in patients with migraine with aura, there is an impairment in the adaptive cerebral hemodynamic mechanisms in the posterior circulation. This fact could have pathogenetic implications since the association between migraine and stroke frequently regards patients with migraine with aura, and cerebral infarcts occur more commonly in the vertebrobasilar district.