Cerebral hemodynamic alterations in patients with Covid-19

Background/aim

Coronavirus 2019 disease (Covid-19) was first seen in December 2019 and afterwards it became pandemic. Several systemic involvements have been reported in Covid-19 patients. In this study, it was aimed to investigate the cerebrovascular hemodynamics in patients with Covid-19.

Materials and methods

The sample of this study included 20 patients hospitalized in our clinic diagnosed with Covid-19 via PCR modality and 20 healthy volunteers of similar age and sex. Bilateral middle cerebral arteries were investigated with transcranial Doppler ultrasonography. Basal cerebral blood flow velocities and vasomotor reactivity rates were determined and statistically compared.

Results

When patient and control groups were compared, the mean blood flow velocity was found to be higher in Covid-19 patients than in the healthy volunteers and it was statistically significant (P = 0.00). The mean vasomotor reactivity rates values were found to be lower in the Covid-19 group than the healthy group and was also statistically significant (P = 0.00).

Conclusion

An increase in basal cerebral blood velocity and a decrease in vasomotor reactivity rates in patients with Covid-19 can be considered as an indicator of dysfunction of cerebral hemodynamics in the central nervous system and this can be evaluated as a result of endothelial dysfunction.

Evaluation of Sympathetic Vasomotor Fibres in Carpal Tunnel Syndrome Using Continuous Wave Doppler Ultrasonography

Sympathetic vasomotor fibres carried by the median nerve and ulnar nerve innervate their respective sensory territories. The sympathetic vasomotor fibres of the median nerve were evaluated in patients with carpal tunnel syndrome and in healthy volunteers using continuous wave Doppler ultrasonography. The pulsatility index of the radialis indicis artery and the radial palmar digital artery of the little finger were measured at baseline and after stimulation. The maximal increase in the pulsatility index of each artery was measured. This was significantly lower for the radialis indicis artery in the CTS group than in the healthy controls. However, there was no significant difference in the maximal increase in pulsatility index of the radial palmar digital artery of the little finger between both groups. Sympathetic vasomotor fibres of the median nerve are affected in carpal tunnel syndrome. Continuous wave Doppler ultrasonography is easy to use and should be investigated further as a possible diagnostic tool for the confirmation of carpal tunnel syndrome.

Detecting gas-induced vasomotor changes via blood oxygenation level-dependent contrast in healthy breast parenchyma and breast carcinoma

PURPOSE

To evaluate blood oxygenation level-dependent (BOLD) contrast changes in healthy breast parenchyma and breast carcinoma during administration of vasoactive gas stimuli.

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) was performed at 3T in 19 healthy premenopausal female volunteers using a single-shot fast spin echo sequence to acquire dynamic T2 -weighted images. 2% (n = 9) and 5% (n = 10) carbogen gas mixtures were interleaved with either medical air or oxygen in 2-minute blocks, for four complete cycles. A 12-minute medical air breathing period was used to determine background physiological modulation. Pixel-wise correlation analysis was applied to evaluate response to the stimuli in breast parenchyma and these results were compared to the all-air control. The relative BOLD effect size was compared between two groups of volunteers scanned in different phases of the menstrual cycle. The optimal stimulus design was evaluated in five breast cancer patients.

RESULTS

Of the four stimulus combinations tested, oxygen vs. 5% carbogen produced a response that was significantly stronger (P < 0.05) than air-only breathing in volunteers. Subjects imaged during the follicular phase of their cycle when estrogen levels typically peak exhibited a significantly smaller BOLD response (P = 0.01). Results in malignant tissue were variable, with three out of five lesions exhibiting a diminished response to the gas stimulus.

CONCLUSION

Oxygen vs. 5% carbogen is the most robust stimulus for inducing BOLD contrast, consistent with the opposing vasomotor effects of these two gases. Measurements may be confounded by background physiological fluctuations and menstrual cycle changes. J. Magn. Reson. Imaging 2016;44:335-345.

Functional TCD: regulation of cerebral hemodynamics--cerebral autoregulation, vasomotor reactivity, and neurovascular coupling

Three main mechanisms influence cerebral hemodynamics, with the aim of adapting the cerebral blood flow to the metabolic demand of the brain. Cerebral autoregulation ensures stable perfusion of the brain, independent of the systemic blood pressure. Vasomotor reactivity reflects the hemodynamic responses to modifications of the arterial pCO2/pH of the brain tissue. Neurovascular coupling adapts the perfusion to increased metabolic demand as a consequence of enhanced brain activity to permit reasonable functioning of cells. Different methods using transcranial Doppler sonography have been developed to characterize these mechanisms in healthy subjects and under pathologic conditions. The most established applications in clinical settings are described, and the results of specific research studies are briefly reported.

Differential recovery in cardiac and vasomotor sympathetic functional markers in a patient with acute autonomic sensory and motor neuropathy

Acute autonomic sensory and motor neuropathy (AASMN) is characterized by prominent dysautonomia with somatic sensory and motor impartment. Prominent dysautonomia is observed during the early phase of AASMN. We herein describe a case of AASMN that involved prolonged autonomic failure and disturbance of sensation despite a rapid recovery from motor weakness. The early and delayed heart-to-mediastinum ratios on (123)I-meta-iodobenzylguanidine myocardial scintigraphy were decreased and improved within seven months. However, orthostatic hypotension was prolonged. These results suggest a differential improvement in the cardiac and vasomotor sympathetic functions.

Effects of intermittent theta burst stimulation on cerebral blood flow and cerebral vasomotor reactivity

OBJECTIVES

To determine whether intermittent theta burst stimulation influences cerebral hemodynamics, we investigated changes induced by intermittent theta burst stimulation on the middle cerebral artery cerebral blood flow velocity and vasomotor reactivity to carbon dioxide (CO(2)) in healthy participants. The middle cerebral artery flow velocity and vasomotor reactivity were monitored by continuous transcranial Doppler sonography. Changes in cortical excitability were tested by transcranial magnetic stimulation.

METHODS

In 11 healthy participants, before and immediately after delivering intermittent theta burst stimulation, we tested cortical excitability measured by the resting motor threshold and motor evoked potential amplitude over the stimulated hemisphere and vasomotor reactivity to CO(2) bilaterally. The blood flow velocity was monitored in both middle cerebral arteries throughout the experimental session. In a separate session, we tested the effects of sham stimulation under the same experimental conditions.

RESULTS

Whereas the resting motor threshold remained unchanged before and after stimulation, motor evoked potential amplitudes increased significantly (P = .04). During and after stimulation, middle cerebral artery blood flow velocities also remained bilaterally unchanged, whereas vasomotor reactivity to CO(2) increased bilaterally (P = .04). The sham stimulation left all variables unchanged.

CONCLUSIONS

The expected intermittent theta burst stimulation-induced changes in cortical excitability were not accompanied by changes in cerebral blood flow velocities; however, the bilateral increased vasomotor reactivity suggests that intermittent theta burst stimulation influences the cerebral microcirculation, possibly involving subcortical structures. These findings provide useful information on hemodynamic phenomena accompanying intermittent theta burst stimulation, which should be considered in research aimed at developing this noninvasive, low-intensity stimulation technique for safe therapeutic applications.

Vasomotor reactivity as a predictor for syncope in patients with orthostatism

OBJECTIVES

Syncope in patients with orthostatic hypotension (OH) may be the result of impaired cerebral autoregulation. Cerebral autoregulation status can be determined by assessing cerebral vasomotor reactivity (VMR). We assessed and compared VMR in patients with OH with and without syncope.

MATERIAL AND METHODS

Twenty-nine patients with OH underwent transcranial Doppler (TCD) and the Diamox test (1 g acetazolamide IV) for assessing VMR during elaboration of their OH syndrome. The percent difference between cerebral blood flow velocities (BFV) in the middle cerebral (MCA) and vertebral (VA) arteries before and after acetazolamide was defined as VMR%. We considered increases of BFV of ≥ 40% as being indicative of good VMR and classified our study patients as having good or impaired VMRs accordingly.

RESULTS

Mean VMR% values of the MCA and VA in patients with OH with syncope (n = 12) were significantly lower as compared with patients with OH without syncope (n = 17): 25.2 ± 20.5% and 42.5 ± 18.6%; 20.9 ± 15.5% and 40.8 ± 28.5%, respectively (P < 0.05).

CONCLUSIONS

Among patients with OH, we found an association between the presence of syncope and impaired VMR. Assessment of VMR among patients with OH may predict those who are at higher risk to faint and fall and to support more aggressive intervention.

Ultrasound assessment of brachial endothelial vasomotor function in addition to carotid plaque echolucency for predicting cardiovascular events in patients with coronary artery disease

BACKGROUND

Single assessment of either flow-mediated vasodilatation of the brachial artery (FMD) or carotid plaque echolucency provides prognostic information for both cerebrovascular and coronary events.

OBJECTIVES

This study tested the hypothesis that combined assessment using carotid plaque echolucency and FMD may have an additive effect when predicting cardiovascular events in patients with coronary artery disease (CAD).

METHODS

Ultrasound assessment of carotid plaque echolucency with integrated backscatter (IBS) analysis (calibrated IBS=intima-media IBS value-adventitia IBS) and FMD was performed in 547 consecutive patients with CAD. All the study patients were followed up prospectively for a period of ≤ 60 months until the occurrence of one of the following cardiovascular events: cardiac death, non-fatal myocardial infarction, unstable angina requiring coronary revascularization, or ischemic stroke.

RESULTS

During a mean follow-up period of 52 ± 10 months, 69 cardiovascular events occurred. A multivariate Cox proportional hazard model after 1000 bootstrapped resampling demonstrated that calibrated IBS and FMD were significant, independent predictors of future cardiovascular events after adjustment for known risk factors (calibrated IBS, HR 0.88, 95% CI 0.83-0.93; FMD, HR 0.76, 95% CI 0.68-0.85). The c-statistics, net reclassification improvement (NRI), and integrated discrimination improvement (IDI) analyses showed that the combination of calibrated IBS and FMD values had a greater incremental effect on the predictive value of known risk factors for cardiovascular events.

CONCLUSIONS

Combined assessment of brachial endothelial function and carotid plaque echolucency is an independent predictor of cardiovascular events and improves risk prediction when added to known risks.

Pulsed wave Doppler ultrasonography for the assessment of peripheral vasomotor response in an elderly population

PURPOSE

To assess sympathetic vasomotor activity and its changes with age, using pulsed wave Doppler ultrasound.

METHODS

We recruited 20 young adults (24-37 years old) and 20 older individuals (60-81 years old). Pulsed wave Doppler ultrasound was applied over the right radial artery to measure blood flow at rest and after a voluntary inspiratory cough eliciting sympathetic activation. The maximal (Vmax), minimal (Vmin), time-averaged (TAMaxV) blood flow velocity, and the pulsatility index (PI) were calculated and compared between groups.

RESULTS

At rest, PI was similar in both groups but Vmax and TAMaxV were higher in the older group (p < 0.05). Vmax, Vmin, and TAMaxV decreased, and PI increased after inspiratory cough in both groups (p ≤ 0.001), but this increase was lower in the older group (p < 0.001). TAMaxV after coughing was higher in the older group (p < 0.05). Heart rate did not differ significantly within or between groups.

CONCLUSIONS

The older group exhibited reduced vasomotor reactivity of the radial artery after sympathetic stimulus. Peripheral vasomotor response should be interpreted with caution in elderly populations.

Role of vascular bed compliance in vasomotor control in human skeletal muscle

The current view of neurogenic vasomotor control in skeletal muscle is based largely on changes in vascular bed resistance. The purpose of this study was to determine to what extent vascular bed compliance may also play a role in this regulation. For this purpose, pressure waveforms (Millar and Finometer) and flow waveforms (Doppler ultrasound) were measured simultaneously in the brachial artery of seven healthy individuals during physiological manoeuvres which were expected to produce non-neurogenic changes in resistance (wrist-cuff occlusion; n = 5) or compliance (arm elevation; n = 6) of the forearm vascular bed. Vascular resistance (R) was calculated from the average flow and pressure values. A lumped Windkessel model was used to obtain vascular bed compliance (C) from these concurrently measured waveforms. Compared with baseline (3.81 +/- 1.59 ml min(-1) mmHg(-1)), wrist occlusion increased R (65 +/- 75%; P < 0.05) with minimal change in C (-15 +/- 16%; n.s.). Compared with the arm in neutral position (0.0075 +/- 0.003 ml mmHg(-1)), elevation of the arm above heart level produced a 86 +/- 41% increase in C (P < 0.05) with little change in R (-5 +/- 11%). In addition, neurogenic changes were assessed during lower body negative pressure (LBNP) and a cold pressor test (CPT; n = 7). Lower body negative pressure induced a 29 +/- 24% increase in R and a 26 +/- 12% decrease in C (both P < 0.05). The CPT induced no consistent change in R but a 22 +/- 7% reduction in C (P < 0.05). It was concluded that vascular bed compliance is an independent variable which should be considered along with vascular bed resistance in the mechanics of vasomotor regulation in skeletal muscle.

Regional cerebral blood flow and cerebrovascular reactivity during chronic stage of stroke-like episodes in MELAS -- implication of neurovascular cellular mechanism

BACKGROUND

Ischemic vascular hypothesis as a causative role in the pathogenesis of stroke-like episodes in MELAS remains to be debated.

METHODS

This study consisted of two parts. Part 1 is a clinicoradiological study during acute stage of 18 consecutive stroke-like episodes in six patients with MELAS. Part 2 is a SPECT study to assess the regional cerebrovascular reactivity (rCVR) to acetazolamide during chronic stage in five patients with MELAS.

RESULTS

Headache and epileptic seizure were the most common presenting symptoms. Unique features of acute stroke-like lesions included progressive spread of cortical lesions with vasogenic edema, focal periodic epileptiform discharges, focal hyperperfusion, and cortical laminar necrosis during subacute stage. During chronic stage, SPECT showed hypoperfusion in non-affected occipital cortex in three patients as well as in previously affected regions in four. The rCVR was preserved in three patients, focally impaired in one, and extensively impaired in one, but relatively preserved in the occipital cortex in all patients.

CONCLUSIONS

Stroke-like episodes could be non-ischemic neurovascular events initiated by neuronal hyperexcitability. Once neuronal hyperexcitability develops in a focal brain region, epileptic activities depolarize adjacent neurons, leading to a propagation of epileptic activities into the surrounding cortex, and resulting in energy imbalance. The mechanisms for neuronal hyperexcitability remain to be elucidated.

Evaluation of vasomotor reactivity by transcranial Doppler sonography in patients with acute stroke who have symptomatic intracranial and extracranial stenosis

OBJECTIVE

In patients with large artery disease, determining the cerebral hemodynamic state and following its alterations may be a good marker for predicting long-term outcome. The aim of our study was to compare the changes in vasomotor reactivity (VMR) of patients with symptomatic intracranial and extracranial artery stenosis. We also examined whether VMR after stroke influences the long-term prognosis for these patients.

METHODS

Forty-one patients were included in the study. To determine the cerebral hemodynamic state, transcranial Doppler ultrasound examinations and acetazolamide tests were performed after acute stroke and repeated after 6 months. We compared the VMR on admission and at 6 months, together with changes in VMR, of the patients with symptomatic intracranial and extracranial artery stenosis. By calculating the Barthel index at 6 months, we examined whether VMR had an effect on an improvement in their quality of life.

RESULTS

We observed a significantly higher initial VMR of the ipsilateral hemisphere in patients with intracranial stenosis (22.4 +/- 9.1 versus 13.4 +/- 12.8; P = .013). At 6 months, the VMR obtained from the ipsilateral hemisphere was better in patients with extracranial stenosis than in the patients with intracranial stenosis (P = .01). The ipsilateral VMR measured on admission showed a positive correlation with the Barthel index at 6 months (P = .007; r = 0.434).

CONCLUSIONS

Our study showed that VMR in patients with acute stroke who have extracranial and intracranial artery stenosis measured by using a transcranial Doppler examination may have value in predicting long-term outcome.

Smoking cessation normalizes coronary endothelial vasomotor response assessed with 15O-water and PET in healthy young smokers

Cigarette smoking is one of the risk factors of cardiovascular diseases and is related to abnormal peripheral and coronary vascular vasomotion. Coronary vascular endothelial dysfunction is caused by chronic smoking in smokers without epicardial coronary artery stenosis. The coronary endothelial vasomotion abnormality is restored by interventions such as l-arginine or vitamin C infusion. However, to our knowledge, the effect of smoking cessation on coronary vasomotor response has not been elucidated. Therefore, the aim of this study was to assess the effect of smoking cessation on coronary vasomotor response by quantitative myocardial blood flow (MBF) measurement using (15)O-water and PET.

METHODS

Fifteen young smokers (Brinkman index > 100; mean age +/- SD, 26 +/- 4 y) with no evidence of heart disease or cardiovascular risk factors, except for smoking, and age-matched nonsmokers (n = 12) were enrolled in this study. MBF was measured at rest, during the cold pressor test (CPT), before and at 1 and 6 mo after smoking cessation. In addition, MBF measurement during adenosine triphosphate (ATP) infusion was performed before and at 6 mo after smoking cessation. In nonsmokers, MBF was measured at rest, during ATP infusion, and during the CPT.

RESULTS

MBF at rest and during ATP infusion did not differ between smokers and nonsmokers (0.73 +/- 0.12 vs. 0.80 +/- 0.15 mL/g/min and 3.15 +/- 1.43 vs. 3.69 +/- 0.76 mL/g/min, respectively; P = not significant). In contrast, MBF during the CPT in smokers was lower than that in nonsmokers (0.90 +/- 0.19 vs. 1.12 +/- 0.28 mL/g/min; P < 0.05). There was no significant difference in MBF either at rest or during ATP infusion between before and after smoking cessation, but MBF during the CPT increased at 1 mo in comparison with before cessation of smoking (0.90 +/- 0.19 vs. 1.02 +/- 0.22 mL/g/min; P < 0.01). An improvement of MBF response to the CPT was preserved at 6 mo after smoking cessation.

CONCLUSION

Coronary vasomotor abnormality assessed by MBF response to the CPT was improved at 1 mo after smoking cessation. These findings indicate that coronary endothelial dysfunction may be reversible within 1 mo after smoking cessation in healthy young smokers.

PET-measured heterogeneity in longitudinal myocardial blood flow in response to sympathetic and pharmacologic stress as a non-invasive probe of epicardial vasomotor dysfunction

PURPOSE

We investigated whether a myocardial perfusion gradient during pharmacologically induced hyperemia also occurred during sympathetic stimulation with cold pressor testing (CPT), which commonly induces a paradoxical coronary vasoconstriction in individuals with coronary risk factors.

METHODS

Myocardial blood flow (MBF) was measured in absolute units (ml/g/min) with 13N-ammonia and PET at rest, during CPT, and during pharmacologic vasodilation in 59 participants with coronary risk factors ("at risk") and in 43 healthy individuals (controls). MBF was assessed globally as mean MBF, and in the mid and mid-distal myocardium of the left ventricle (LV). A decrease in MBF from mid to mid-distal LV myocardium was defined as MBF difference indicative of a perfusion gradient.

RESULTS

The change in mean MBF to CPT (DeltaMBF) in the at-risk group was significantly reduced compared with controls (0.05+/-0.19 vs 0.31+/-0.20 ml/g/min, p<0.0001), whereas mean MBF during pharmacologic vasodilation in the at-risk group tended to be lower than in controls (1.72+/-0.71 vs 2.00+/-0.64 ml/g/min, p=NS). Absolute MBFs during CPT and pharmacologic vasodilation were significantly lower in the mid-distal than in the mid LV myocardium, resulting in a significant MBF difference in the at-risk group (0.15+/-0.06 and 0.27+/-0.12 ml/g/min, p<0.0001) that was not observed in controls (0.007+/-0.05 and 0.014+/-0.10 ml/g/min, p=NS). In the at-risk group there was a significant correlation between the difference of mid to mid-distal MBF during CPT and that during pharmacologic vasodilation (r=0.43, p<0.004), suggesting functional alterations of epicardial vessels as the predominant cause for the observed MBF difference.

CONCLUSION

The relative decrease in MBF from the mid to the mid-distal left-ventricular myocardium suggests an intracoronary pressure decline during CPT and pharmacologic vasodilation, which is likely to reflect an impairment of flow-mediated epicardial vasomotor function.

Abnormal Vasomotor Function of the Epicardial Coronary Arteries in Children Five to Eight Years After Arterial Switch Operation

OBJECTIVES

This study sought to test the vasoreactivity of the translocated coronary arteries after arterial switch operation (ASO) using quantitative angiographic analysis and intracoronary Doppler flow wire velocimetry.

BACKGROUND

Late coronary artery events occur in 3% to 8% of patients after the ASO. Previous studies of coronary flow reserve have yielded disparate results.

METHODS

Nineteen children previously underwent ASO (13 boys, age 5.4 +/- 3.2 years, weight 22.3 +/- 10.6 kg), and six control patients were enrolled in the study. Each patient underwent quantitative angiographic assessment of the epicardial coronary arteries before and after administration of nitroglycerin and coronary blood flow volume assessment before and after administration of adenosine and acetylcholine. The results were compared between groups.

RESULTS

Epicardial coronary artery dilation in response to intracoronary nitroglycerin was significantly less in the ASO group than in the control group (left anterior descending [LAD], 5.0 +/- 0.05% vs. 18.0 +/- 4.5%, p = 0.0009; right coronary artery [RCA], 4.0 +/- 0.07% vs. 32.7 +/- 12.7%, p = 0.006). Moreover, the coronary blood flow volume reserve was reduced in ASO patients compared with control patients after intracoronary infusion of acetylcholine (2.3 +/- 0.9 vs. 4.9 +/- 1.7, p = 0.0003) or adenosine (2.7 +/- 1.5 vs. 5 +/- 0.5, p = 0.002).

CONCLUSIONS

Epicardial coronary arteries fail to dilate normally in children after ASO, and the calculated coronary flow volume reserve is consequently reduced.

Increase in capillary perfusion following low-intensity ultrasound and microbubbles during postischemic reperfusion

OBJECTIVES

We postulated that the increase in shear stress caused by microbubbles in the presence of low-intensity ultrasound increases vasodilation in ischemia/reperfusion.

DESIGN

Prospective, randomized, and blinded experimental study.

SETTING

Research laboratory.

SUBJECTS

Forty hamsters were subjected to ischemia/reperfusion and observed by intravital microscopy.

INTERVENTIONS

Ultrasound (2.5 MHz, 1.3 mechanical index, 2.0 peak pressure) was applied to the hamster cheek pouch in ischemia/reperfusion with and without microbubbles (Levovist or Sono Vue) at baseline (15 mins) and at the beginning (15 mins) of reperfusion after ischemia (30 mins).

MEASUREMENTS AND MAIN RESULTS

Arterial diameter (A2-A3, 38.5 +/- 5.3 microm; A4,15.0 +/- 7.0 microm), red blood cell velocity, wall shear stress, permeability, perfused capillary length, and adherent leukocytes in venules were evaluated. Lipid peroxides were also determined in the systemic blood. Ultrasound and microbubbles in reperfusion significantly increased the diameter (A2-A3 Sono Vue, 33%; Levovist, 53% vs. ischemia/reperfusion, p < .05; A4, Sono Vue, 93%; Levovist, 104% vs. ischemia/reperfusion, p < .05), red blood cell velocity, flow, and shear stress in both A4 and A2-A3 arterioles. Shear stress was significantly higher with Levovist (A2-A3, 105%; A4, 185%) and Sono Vue (A2, 108%; A4, 140% vs. ischemia/reperfusion, p < .05) than ultrasound alone in arterioles. With ischemia/reperfusion, perfused capillary length was reduced significantly, whereas it increased with Levovist and Sono Vue (43%, 41% vs. ischemia/reperfusion p < .05). Lipid peroxides increased early during reperfusion and remained at increased levels throughout reperfusion. Lipid peroxides were unchanged after ultrasound alone or ultrasound with Sono Vue or Levovist during ischemia/reperfusion. With ultrasound there was a significant increase in vascular permeability vs. ischemia/reperfusion. Treatment with Sono Vue (-36%) and Levovist (-57%) decreased permeability vs. ischemia/reperfusion in reperfusion (p < .001). Ischemia/reperfusion had significantly increased leukocyte adhesion. Ultrasound alone (-39%) or with Sono Vue (-64%) and Levovist (-57%) caused smaller increases in leukocyte adhesion than ischemia/reperfusion (p < .05).

CONCLUSIONS

Ultrasound and microbubbles equilibrate microvascular shear stress, thus avoiding the failure of capillary perfusion in postischemic reperfusion.

Effects of smoking on nitric oxide synthesis in epicardial normal and atheromatous coronary arteries

The effects of an intracoronary infusion of N(G)-monomethyl-L-arginine (LNMMA) followed by intracoronary administration of nitroglycerin in non-stenotic proximal and distal coronary segments were studied in 11 patients with coronary artery disease and in 19 subjects with "normal arteriograms". In normal subjects, LNMMA induced significant constriction (p<0.01) of proximal and distal vessels in non-smokers and smokers. In normal non-smokers, the reduction in coronary luminal diameter of proximal segments was significantly greater compared to normal smokers (p<0.05). In patients with coronary artery disease, LNMMA induced significant constriction of proximal and distal vessels in smokers, and only distal constriction in non-smokers (p<0.01). The reduction in coronary luminal diameter of the distal segments in normal smokers, and in both groups in patients with coronary artery disease was significantly greater compared with proximal segments (p<0.05). Therefore, the difference in vasomotor response to LNMMA in relation to smoking is localised to the proximal coronary segments.

The middle cerebral artery flow velocities during head-up tilt testing in diabetic patients with autonomic nervous system dysfunction

BACKGROUND

The goal of this study was to examine the effects of diabetes mellitus on the trend of mean arterial velocity (v(m)) in both middle cerebral arteries during head-up tilt (HUT).

METHODS

The study was performed in 20 patients, 9 females and 11 males (mean age 51 +/- 12 years) with an average 17-year history of insulin-dependent diabetes mellitus type I or II and a dysfunction of the autonomic nervous system confirmed by cardiocirculatory tests [Valsalva maneuver, deep breathing test, handgrip test, orthostatic test and spectral analysis of heart rate (HR) variability], and 19 age-matched healthy volunteers, 9 females and 10 males (mean age 48 +/- 6.8 years). v(m) was measured by a transcranial Doppler monitoring system during a 5-min baseline period, followed by a 5-min HUT in the upright position (90 degrees ). Mean arterial blood pressure (MAP), HR and end-tidal CO(2) (Et-CO(2)) were monitored concomitantly.

RESULTS

In healthy volunteers, v(m) decreased stepwise during the first minute of HUT, reaching a minimum during the last 2 min of the test (v(m): basal 63.0 +/- 11.7 cm/s, 1st min 57.6 +/- 12.2 cm/s, 2nd min 55.9 +/- 12.6 cm/s, 3rd min 53.4 +/- 12.6 cm/s, 4th min 52.1 +/- 12.7 cm/s, 5th min 51.3 +/- 13.5 cm/s). In the supine position, v(m) recovered and reached the resting v(m) values. It declined gradually during HUT and less steeply in diabetic (v(m): basal 54.4 +/- 10.1 cm/s, 1st min 51.96 +/- 9.3 cm/s, 2nd min 50.7 +/- 11.6 cm/s, 3rd min 50.5 +/- 11.4 cm/s, 4th min 49.5 +/- 10.7 cm/s, 5th min 48.8 +/- 11.5 cm/s) than in healthy subjects. v(m) differed significantly (p = 0.00) between rest and HUT in both groups. The differences in MAP, HR and Et-CO(2) during rest and HUT between the groups were not statistically significant (p DeltaMAP = 0.36, p DeltaHR = 0.86, p DeltaEt-CO(2) = 0.97). The results of the analysis of variance of v(m) for repeated measurements between the two groups of subjects were highly significant (p = 0.00). The model of linear regression analysis was significant (p = 0.007). Diabetes was significant in the model (p = 0.00), while DeltaMAP, DeltaHR and DeltaEt-CO(2) were not.

CONCLUSIONS

These findings may indicate that vasomotor responses during HUT testing are decreased in diabetic patients.

Effects of intravenous nesiritide on human coronary vasomotor regulation and myocardial oxygen uptake

BACKGROUND

Nesiritide, recombinant human B-type natriuretic peptide, has been shown to be efficacious in the treatment of decompensated heart failure. The effects of intravenous nesiritide on the human coronary vasculature have not been studied.

METHODS AND RESULTS

Ten patients underwent right and left heart catheterization. Baseline coronary blood flow was determined using quantitative coronary angiography (QCA) and an intracoronary Doppler-tipped guidewire. Myocardial oxygen uptake was measured using a coronary sinus catheter. Patients then received an intravenous infusion of nesiritide (2 microg/kg bolus followed by 0.01 microg/kg per min infusion) for 30 minutes. Right atrial pressure decreased 52% (P=0.012), pulmonary artery mean pressure decreased 19% (P=0.03), pulmonary capillary wedge pressure decreased 46% (P=0.002), and mean arterial pressure decreased 11% (P=0.007). QCA demonstrated a 15% increase in coronary artery diameter from a baseline of 2.6+/-0.8 to 3.0+/-0.8 mm at 30 minutes (P=0.007). The coronary velocity measure of average peak velocity increased 14% from 20.8+/-6.4 at baseline to 23.8+/-7.2 cm/s at 5 minutes (P=0.015) and then returned to baseline for the remainder of the infusion. Coronary blood flow increased 35% (P=0.007), whereas coronary resistance decreased 23% at 15 and 30 minutes (P=0.036). Myocardial oxygen uptake decreased 8% during the nesiritide infusion (P=0.043).

CONCLUSIONS

Nesiritide exerts coronary vasodilator effects on both the coronary conductance and resistance arteries. Despite a decrease in coronary perfusion pressure, coronary artery blood flow is increased, coronary resistance is decreased, and myocardial oxygen uptake is decreased.

Refractory vasomotor angina in subclinical hyperthyroidism demonstrating focal and segmental coronary vasoconstriction

We describe a case of refractory vasomotor angina in the setting of unrecognized subclinical hyperthyroidism. Despite aggressive medical therapy, frequent rest angina recurred until diagnosis and treatment of Grave s Disease, which presented asymptomatically. Both spontaneous focal vasospasm and inducible segmental coronary vasoconstriction were demonstrated during invasive provocative testing. Subclinical hyperthyroidism should be considered in the differential diagnosis when treating refractory vasomotor angina, especially in women over 50 years old, a population at particular risk for undiagnosed thyroid disease.

Vasomotor function of pig coronary arteries after chronic coronary occlusion

Placement of an ameroid constrictor in large-conduit pig coronary arteries causes progressive stenosis and distal myocardial ischemia. Blood perfusion in the ischemic region is partly dependent on vasomotor responses to neural and humoral factors distal to the occlusion site. To ascertain the degree of impairment of vascular function in pigs, the authors induced myocardial ischemia by placing an ameroid constrictor in the left circumflex coronary artery and examined vascular reactivity and histopathology distal to the constriction site. The sensitivity of the distal left circumflex coronary and nonoccluded control left anterior descending arteries to PGF(2alpha) was similar. After nitric oxide blockade using Nw-nitro-l-arginine methylester (l-NAME), the sensitivity and maximal contraction to PGF(2alpha) were significantly increased in both the left circumflex coronary (EC50: 5.86 +/- 0.74 vs. 3.28 +/- 0.84 microM; C(max): 4.63 +/- 0.28 vs. 6.25 +/- 0.30 g, P < 0.01) and left anterior descending (EC50: 6.57 +/- 0.73 vs. 2.78 +/- 0.16 microM; C(max): 5.09 +/- 0.37 vs. 6.95 +/- 0.39 g, P < 0.01) arteries. Substance P-induced relaxation (100 pM) was blocked to a larger degree in the distal left circumflex coronary artery when compared with the left anterior descending artery (76.9 +/- 4.2% vs. 56.4 +/- 3.1%, P < 0.05). Endothelium-independent relaxation to sodium nitroprusside was similar in the left circumflex coronary and left anterior descending arteries before and after nitric oxide blockade. Histopathologic examination showed no major differences between distal left circumflex coronary artery segments and left anterior descending artery controls. However, scanning electron microscopy showed endothelial hypertrophy and activation in specimens from the left circumflex coronary arteries. In summary, as a result of the major hemodynamic changes induced by a chronic constriction and eventual occlusion of a large coronary artery, distal segments underwent adaptive compensatory changes. Such compensation may be related to an increased nitric oxide production by the hypertrophic endothelium in response to alterations in coronary hemodynamics.

Effect of chelation therapy on endothelial function in patients with coronary artery disease: PATCH substudy

OBJECTIVES

The purpose of this study was to evaluate the effect of chelation therapy with ethylenediamine tetraacetic acid (EDTA) on endothelium-dependent vasomotor responses in patients with documented coronary artery disease (CAD).

BACKGROUND

Oxidative stress plays an important role in the dysfunction of endothelium and development of atherosclerosis. Modification of cardiac risk factors and employment of antioxidants have been shown to improve endothelial function. Ethylenediamine tetraacetic acid chelation therapy is considered to be a complementary therapy for patients with CAD and is proposed to have antioxidant properties.

METHODS

A total of 47 patients enrolled in the Program to Assess Alternative Treatment Strategies to Achieve Cardiac Health (PATCH) participated in this substudy and had complete data. High-resolution ultrasound was used to assess endothelium-dependent brachial artery flow-mediated vasodilation (FMD) in patients with CAD in a randomized, double-blind, and placebo-controlled fashion. Patients were randomized to chelation therapy or placebo. The primary end point was the absolute difference in FMD after the first and 33rd treatments (6 months) of study groups compared with their baselines.

RESULTS

At the baseline, the study population had mild impairment of FMD (7.2 +/- 3.4%). The first chelation treatment did not change FMD as compared with placebo (chelation 6.5 +/- 3.5% vs. placebo 7.4 +/- 2.9%; p value = 0.371). The brachial artery studies at six months did not demonstrate significant differences in FMD between study groups (placebo 7.3 +/- 3.4% vs. chelation 7.3 +/- 3.2%; p value = 0.961).

CONCLUSIONS

Our results suggest that EDTA chelation therapy in combination with vitamins and minerals does not provide additional benefits on abnormal vasomotor responses in patients with CAD optimally treated with proven therapies for atherosclerotic risk factors.

Acetazolamide vasoreactivity evaluated by transcranial harmonic perfusion imaging: relationship with transcranial Doppler sonography and dynamic CT

To establish the reliability and clinical significance of transcranial ultrasonic harmonic perfusion imaging (HPI), we evaluated HPI's relationships with transcranial Doppler (TCD) and with dynamic CT (DCT), during acetazolamide (ACZ) vasoreactivity tests.

METHODS

The subjects were 12 neurological patients. Time-averaged maximum velocity (TAVMX) in the middle (MCA) and posterior cerebral arteries was measured by TCD. Time-intensity (-density) curves of HPI (DCT) after bolus intravenous contrast injections were created in 3 regions of interest (ROI) on the axial plane involving the temporal lobe, basal ganglia, and thalamus on both sides. Assessments of vasoreactivity were based on comparisons conducted before and after ACZ administration in terms of: a) relative changes (%delta) of the TCD TAVMX, b) HPI contrast area enlargement, c) %delta of calculated cerebral blood volume and flow of the HPI and DCT.

RESULTS

1) TCD vasoreactivity decrease in the left MCA tended to correlate with lower frequency of HPI contrast area enlargement on the left side. 2) HPI and DCT vasoreactivity tended to be disturbed in the same side ROIs.

CONCLUSIONS

Transcranial HPI achieves repeatable non-invasive bedside evaluation of cerebrovascular reserve capacity through qualitative and quantitative measurements of brain tissue perfusion, and will have clinical value in pathophysiological follow-up and therapeutic effectiveness determination of neurointensive care patients.

Carvedilol improves left ventricular function in heart failure patients with idiopathic dilated cardiomyopathy and a wide range of sympathetic nervous system function as measured by iodine 123 metaiodobenzylguanidine

BACKGROUND

Carvedilol treatment reduces the mortality rate in patients with congestive heart failure. It is not known whether carvedilol treatment is effective in heart failure patients with substantial cardiac sympathetic nerve dysfunction. The goal of this study was to determine the effect of chronic carvedilol treatment in patients with cardiac sympathetic nerve dysfunction of varying severity.

METHODS AND RESULTS

In 22 congestive heart failure patients with idiopathic cardiomyopathy, sympathetic nerve function was assessed before and after 7.2 +/- 2.7 months of carvedilol treatment with the use of iodine 123 metaiodobenzylguanidine (MIBG) imaging, radionuclide ventriculography, and transmyocardial norepinephrine sampling. Patients with relatively advanced impairment of cardiac sympathetic nerve function, as manifested by a baseline I-123 MIBG ratio lower than 1.40, had a statistically significant improvement in I-123 heart-mediastinum ratio with carvedilol treatment, from 1.26 +/- 0.12 to 1.39 +/- 0.20 (P =.004). Of 10 patients with a baseline I-123 MIBG ratio lower than 1.40, 9 had an increase in the heart-mediastinum ratio with carvedilol treatment. Left ventricular ejection fraction increased from 25.4% +/- 7.8% to 37.3% +/- 14.7% (P <.001), with no difference between patients with relatively advanced versus relatively preserved cardiac sympathetic nerve function.

CONCLUSION

Most patients with congestive heart failure show a favorable response in left ventricular function to carvedilol treatment, regardless of the baseline level of cardiac sympathetic nervous system function, as assessed by neuronal imaging with I-123 MIBG. Patients with relatively advanced impairment of baseline I-123 MIBG uptake are most likely to show evidence of improved cardiac sympathetic nervous system function in response to carvedilol therapy.

Flow-dependent vasomotor dysfunction of the popliteal artery related to common carotid artery intima-media thickness

This study was designed to assess a possible correlation between flow-mediated endothelium-dependent vasodilation in the popliteal artery and the intima-media thickness of the common carotid artery. Impaired vasodilation is one of early markers of atherosclerosis that has not been studied on the popliteal artery. An increase in intima-media thickness of the common carotid artery is also considered to be an indication of early stages of atherosclerosis. With use of ultrasound, the diameter of the popliteal artery was measured at rest and during reactive hyperemia after 5-minute arterial occlusion. Subsequently, the intima-media thickness was measured in left common carotid arteries in 27 patients with hyperlipidemia, in 10 patients with confirmed coronary artery disease, and in 20 healthy individuals. In healthy individuals, popliteal artery diameter increased by mean of 6.6 +/- 3.5% (p < 0.01) in relation to hyperemia. In patients with hyperlipidemia before therapy and in patients with coronary disease, no increase in diameter occurred (mean, 0.44% and -1.6%, respectively). The difference between healthy individuals and patients was statistically significant at p < 0.001. The popliteal artery seems to respond similarly to the brachial artery. When comparing the change in popliteal artery diameter and intima-media thickness of common carotid arteries, a strong negative correlation (r = -0.5713, p < 0.001) was observed in all subjects.

Measurement of vasomotor reserve in the transcranial Doppler-CO(2) test using an ultrasound contrast agent (Levovist)

BACKGROUND AND PURPOSE

Determination of vasomotor reserve (VMR) with the transcranial Doppler-CO(2) (TCD-CO(2)) test is used to assess the risk of impending cerebral ischemia in patients with high-grade stenosis or occlusion of the internal carotid artery. In patients with a poor temporal window, however, this examination is limited. The aim of this study therefore was to examine whether the use of an ultrasound contrast agent (USCA) influences the results of the TCD-CO(2) test.

METHODS

In the first part of the study, 6 control subjects and 20 patients were examined with the TCD-CO(2) test. The VMR was determined first without the application of a contrast agent and then with continuous infusion of an USCA (Levovist, 300 mg/mL, 1 mL/min). In the second part of the study, 2 tests without USCA were performed in each of 13 patients and 2 tests with USCA infusion were performed in each of 12 patients. Statistical analysis included differences between the VMR determined with the 2 comparative measurements (VMR), the mean (M(VMR)), and SD.

RESULTS

Based on the mean difference, the TCD-CO(2) test produced the same results with and without USCA (M(VMR) 1.8%), although the differences showed a wide distribution (2 SDs, +/-20.7%). Similar spreads were seen in repeated determinations of VMR in the same patient without USCA (2 SDs, +/-20.0%), whereas the distribution under continuous USCA infusion was considerably smaller (2 SDs, +/-8.2%).

CONCLUSIONS

The TCD-CO(2) test can be performed with continuous infusion of an USCA without influencing the results. Even with a good temporal window, the results of the TCD-CO(2) test show better reproducibility and thus better reliability if an USCA is used.

Non-invasive assessment of brachial artery endothelial vasomotor function: the effect of cuff position on level of discomfort and vasomotor responses

Non-invasive assessment of brachial artery flow-mediated dilation using cuff occlusion of the arm above or below the elbow to stimulate flow is emerging as a highly useful technique to examine endothelial vasomotor function in human subjects. In anticipation of a large-scale investigation, an important issue is the acceptability of the technique to participants. The purpose of this study was to determine the level of discomfort associated with the technique and compare it to the commonly used procedure of venipuncture. Flow-mediated dilation was determined using cuff occlusion of the arm above the elbow and a blood sample was obtained by standard venipuncture from 54 subjects. The level of discomfort for each procedure was assessed and compared using a visual analogue scale and was found to be extremely low. When the occlusion cuff was positioned above the elbow, the discomfort was slightly more severe (1.9+/-1.9 cm) than venipuncture (1.0+/-1.3 cm, p = 0.003). In 27 subjects, the effect of cuff position (above or below the elbow) was compared: the below the elbow position was associated with a reduction in the percentage increase in flow (570+/-280% versus 900+/-560%, p = 0.005), flow-mediated dilation (6.8+/-3.8% versus 9.8+/-5.7%, p = 0.008) and discomfort (1.6+/-0.8 versus 3.7+/-2.2 cm, p = 0.008). When the cuff was located below the elbow, the level of discomfort was equivalent to that associated with venipuncture. Thus, non-invasive assessment of flow-mediated brachial artery dilation is well tolerated and appears to be suitable for a large-scale study of endothelial function.

Lack of gender difference in acetazolamide-induced cerebral vasomotor reactivity in patients suffering from type-1 diabetes mellitus

The aim of the present work was to investigate the impact of gender on resting cerebral blood flow velocity and cerebrovascular reserve capacity among diabetic patients. Middle cerebral artery mean blood flow velocity (MCAV) was measured in 72 patients suffering from type 1 diabetes mellitus at rest and 5, 10, 15 and 20 min after intravenous administration of 1 g acetazolamide. Cerebrovascular reserve was calculated as the maximal percent increase in MCAV after acetazolamide. Resting MCAV and cerebrovascular reserve capacity were compared between males and females. Resting cerebral blood flow velocity was higher in diabetic females than in males (men, 55.0+/-17.0 cm/s; women, 64.4+/-12.6 cm/s, p=0.0094). Cerebrovascular reserve capacity was similar in diabetic women and men (men, 44.0%+/-18.6%; women, 52.6%+/-32.9%, p=0.17). Comparing MCAV and cerebrovascular reserve capacity among the diabetic subgroups with disease duration < or = 10 years and >10 years, we did not detect any differences between women and men. Duration of diabetes was an important factor in determining cerebrovascular reserve capacity in both sexes: long-term diabetic women and men showed lower CRC values than diabetics with < or = 10 years disease duration. Cerebrovascular reserve capacity is similar in diabetic women and men. Taking into consideration that cerebrovascular reserve is normally higher among women, our finding indicates a relatively more serious worsening of cerebral vasodilatory responses in women suffering from type 1 diabetes.

Flow-mediated dilatation

Arterial endothelial dysfunction is one of the key early events in atherogenesis, preceding structural atherosclerotic changes. It is also important in the late stages of obstructive atherosclerosis, predisposing to constriction and/or thrombosis. Endothelial function can be measured in coronary arteries and in the periphery by measuring vasomotor function after intra-arterial infusion of pharmacologic substances which enhance the release of endothelial nitric oxide. The disadvantage of these methods is their invasive nature, which generally makes them unsuitable for studies involving asymptomatic subjects. For this reason, noninvasive tests of endothelial function have been developed. In the most widely used of these, an ultrasound-based method, arterial diameter is measured in response to an increase in shear stress, which causes endothelium-dependent dilatation. Endothelial function assessed by this method correlates with invasive testing of coronary endothelial function, as well as with the severity and extent of coronary atherosclerosis. This noninvasive endothelial function testing has provided valuable insights into early atherogenesis, as well as into the potential reversibility of endothelial dysfunction by various strategies, including pharmacological agents (lipid lowering, ACE inhibition), L-arginine, antioxidants and hormones.

Vasomotor hyporeactivity in the anterior cerebral artery during motor activation in Huntington's disease patients

This experiment used functional transcranial Doppler ultrasonography to demonstrate that blood flow velocity in the anterior cerebral artery is hyporeactive in Huntington's disease (HD) patients during maze testing (P<0.05). These vascular changes are due to tracing, as opposed to problem solving, components of the maze task. Using logistic regression, the reactivity of the ACA during activation is able to categorize patients as being either gene negative, or positive, for HD (P=0.0007). The possible role that nitric oxide/peroxynitrite may play in this phenomena is discussed.

The impact of coronary artery disease on the coronary vasomotor response to nonionic contrast media

BACKGROUND

Coronary artery disease (CAD) alters the vasomotor response to a variety of pharmacological agents. We tested the hypothesis that CAD also has an impact on the coronary vasomotor response to radiologic contrast media.

METHODS AND RESULTS

We performed quantitative coronary angiography in 42 patients without angiographic evidence of CAD and 38 patients with CAD in the left coronary artery. Angiographically smooth coronary segments (n=235) were analyzed for changes on luminal diameters and coronary venous oxygen saturation in response to 3 media: the nonionic dimer iodixanol, the nonionic monomer iopromide, and the ionic agent ioxaglate. In subjects without CAD, we assessed the effects of intracoronary administration of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine and of the cyclooxygenase inhibitor indomethacin on such changes. Iodixanol induced coronary vasodilation in subjects without CAD (8.8+/-8.6%, P<0.001). Patients with CAD exhibited no significant diameter changes in segments >/=20 mm apart from a stenosis (4.7+/-9.4%, P=NS) and significant constriction in segments <20 mm from a stenosis (-3.8+/-4.6%, P<0. 05). Similar results were obtained with iopromide, but no changes were found with ioxaglate. All contrast media induced transient (<35 seconds) increases in coronary venous oxygen saturation in all subjects. Indomethacin, but not N(G)-monomethyl-L-arginine, blunted the vasodilating effect of iodixanol and iopromide (by 80% and 76%, respectively; P<0.001).

CONCLUSIONS

Nonionic contrast media induce a vasodilatory response in normal vessels not by a mechanism involving increased flow or endothelial nitric oxide synthesis, but rather by depending on preserved vascular cyclooxygenase activity. CAD changes normal epicardial vasodilatory response into vasoconstriction.

A longitudinal study of vessel wall properties in normotensive and hypertensive renal transplant recipients

The mechanisms responsible for reduced arterial distensibility in renal transplant recipients remain to be evaluated. The present longitudinal study was aimed to evaluate the effect of hypertension on the evolution of vessel wall properties in renal transplant recipients. The mechanical properties of the common carotid artery were determined in 24 normotensive and 24 treated hypertensive renal transplant recipients 6-12 weeks after transplantation. The measurements were repeated after 2 years. Arterial distension was determined by using a multigate pulsed Doppler system, blood pressure (BP) was measured by a mercury sphygmomanometer. BP was 127 +/- 3/80 +/- 2 mm Hg at entry and 133 +/- 3/82 +/- 2 mm Hg after 2 years in the normotensive group, 146 +/- 4/90 +/- 3 mm Hg at entry and 145 +/- 3/87 +/- 2 mm Hg after 2 years in the hypertensive group (P < 0.01, normotensives vs hypertensives). The distensibility coefficient (DC) decreased significantly after 2 years in the hypertensive group (DC 18.3 +/- 1.3 10(-3)/kPa before, 15.1 +/- 1.2 10(-3)/kPa after 2 years, P < 0.05) whereas no significant change was observed in the normotensive group (DC 19.0 +/- 1.4 10(-3)/kPa before, DC 17.8 +/- 1.3 10(-3)/kPa after 2 years, NS). There was a significant correlation between the change of the distensibility coefficient after 2 years and mean arterial pressure (n = 48, r = 0.42, P < 0.01). The results show that the decrease of arterial distensibility after 2 years is accelerated in hypertensive renal transplant recipients despite effective anti-hypertensive treatment. Since BP levels were not different at entry into the study and after 2 years, differences in distending pressure along cannot explain the more pronounced decrease of arterial distensibility over time in hypertensive renal transplant recipients.

Normal developmental changes in carotid artery diameter measured by echo-tracking

We examined the developmental changes in carotid arterial diameter and its change with pulsatile pressure in infants and children using the phase-locked echo-tracking method. The mean, maximum systolic, and minimum diastolic carotid arterial diameter and pulsating diameter changes were measured in 95 healthy children aged 1 month to 13 years. The mean, maximum, and minimum carotid arterial diameter increase significantly and exponentially with age, body weight, height, and body surface area, and the correlation coefficient was highest with body surface area. The change in carotid arterial diameter with pulse pressure increased gradually until 2 to 3 years of age. Our results suggest that the maturational changes in carotid diameter and the dynamic changes in the diameter reflect changes in the carotid-cerebral circulatory system. The noninvasive measurement of the carotid diameter and pulsating diameter changes by a phase-locked echo-tracking method is useful for examining carotid-cerebral circulatory disorders.

Transcranial Doppler in 178 patients before, during, and after carotid endarterectomy

From July 1991 to March 1995, 178 patients who underwent 198 carotid surgical repairs were investigated preoperatively, intraoperatively, and postoperatively by transcranial Doppler sonography (TCD). Preoperative TCD evaluation showed stenosis of the middle cerebral artery (MCA) in 4 patients (2.2%), siphon stenosis in 3 (1.6%), incomplete circle of Willis in 23 (12.9%), a decrease of mean blood flow velocity more than 70% of the basal value during digital common carotid compression in 31 (17.9%), and a critical reduction of vasomotor reactivity (no significant increase of mean blood flow velocity in the MCA during breath-holding test) in 34 (19.1%). Nine patients (5%) had surgery without preoperative angiography. In those patients the indication for surgery was based on color Doppler imaging and TCD investigations. Ninety surgical procedures were carried out under general anesthesia and 188 under locoregional anesthesia. In 37 surgeries (31.7%) a shunt was inserted. The use of a shunt was based on a decrease of mean blood flow velocity in the MCA below 50% of the basal value under general anesthesia or loss of consciousness combined with a decrease of mean blood flow velocity in the MCA higher than 70% of the basal value when locoregional anesthesia was employed. Intraoperative TCD monitoring showed a decrease of mean blood flow velocity in the MCA due to shunt malfunction in (8.3%) of 36 surgeries, turbulence of blood flow during declamping in 79 procedures (39.8%), and microembolic events in 10 patients (5%) that were related to one transient and one permanent neurological deficit. Another permanent deficit occurred in a patient without TCD signs. After surgery, TCD reliably detected an early asymptomatic occlusion of the carotid artery, hyperperfusion syndrome in 12 (6.0%), and an increase of vasomotor reactivity in 10 (29.4%) of 34 surgeries.

[The venous valve: non-invasive imaging of its functioning]

B Mode and TM mode Imaging are useful tools to illustrate directly the venous valve motion. Using B Mode, venous valve are echogenic with a particular kinetic as regards its topography. So it's possible to determine in TM Mode a "pseudo-cardiac" valvular motion (jugular vein) and a "pseudo-diaphragmatic" motion for the lower limbs veins. Valvular motion assures unidirectional venous flow.

[Changes in cerebral vasomotor reactivity in relation to respiratory and metabolic stimuli: an analysis of its behavior in hypertensive and normotensive subjects]

We know that increases in the arterial blood pressure determines changes in the behaviour of the cerebrovascular resistance and also the possible lack of vasomotor reactivity. In order to clarify the pathway of circulatory vasomotor reactivity in arterial hypertension, we carried out a study on a group of hypertensive subjects (20 patients) who were compared to a group of normotensive controls (18 patients). A transcranial doppler (TCD) study was performed with rebreathing tests (apnea and hyperventilation) and it was carried out in both groups of subjects. The TCD was repeated after an administration of sublingual pill of nitroglycerin. In both groups the hyperventilation caused a significant reduction in the velocity peak in the middle cerebral artery (norm.: 84.88 +/- 4.86 cm/sec 60 +/- 5.2 cm/sec; hyperten. 84.50 +/- 7.1 cm/sec 58.80 +/- 5.47 cm/sec) in contrast apnea induced a major increase in the velocities (norm.: 84.88 +/- 4.86 cm/sec 102.50 +/- 4.89 cm/sec; hyperten.: 84.50 +/- 7.1 cm/sec 101.59 +/- 10.6 cm/sec). We noticed a statistical significant difference between the velocities recorded in the different tests (Anova test p < 0.0001). The behaviour of the velocities in the rebreathing tests after nitroglycerin was similar when compared to the same test were performed without the drug. This study suggests that there is no difference in the behaviour of the cerebral reactivity between normotensives and the hypertensive subjects without vascular or cardiac compliance. Finally we would emphasize the role of TCD in the recording changes of cerebrovascular resistances due to pressure or metabolic causes.

Sex-related differences in acetazolamide-induced cerebral vasomotor reactivity

BACKGROUND AND PURPOSE

Cerebral vasomotor reactivity can easily be assessed reliably by measuring vasodilatory response to acetazolamide by transcranial Doppler sonography. The aim of this study was to confirm the hypothesis that female sex is associated with an increased cerebrovascular flow reserve.

METHODS

Blood flow velocity of the middle cerebral artery was measured by transcranial Doppler sonography in 36 healthy sex- and age-matched subjects. After the initial blood flow velocities were recorded, the subjects received 14.3 mg/kg body wt acetazolamide, ie, 1 g/70 kg, intravenously. The measurements were repeatedly performed at 5-minute intervals starting 10 minutes after injection and lasting for 30 minutes. The highest measured flow velocities were used for further analysis.

RESULTS

In both groups mean blood flow velocity increased significantly after acetazolamide (women, from 60.2 +/- 12.5 to 89.9 +/- 14.4 cm/s, P < .006; men, from 54.5 +/- 18.8 to 75.7 +/- 24.5 cm/s, P < .02). The difference in mean blood flow velocity after acetazolamide between groups of women and men was statistically significant (P < .02).

CONCLUSIONS

Female subjects show an increased vasodilatory response to the acetazolamide test compared with men.

Intracranial haemodynamics during vasomotor stress test in unilateral internal carotid artery occlusion estimated by 3-D transcranial Doppler scanner

Seventeen patients, 14 males and 3 females, mean age 64 years (range 45-77 years) with longstanding unilateral occlusion of the internal carotid artery and minimal neurological deficit, were evaluated in order to find criteria for potential benefit of extracranial-intracranial by-pass surgery. 3-D transcranial Doppler was used for estimation of mean velocities and pulsatility index in the middle cerebral artery, anterior cerebral artery and posterior cerebral artery before and after iv injection of 1 g acetazolamide. The anterior cerebral artery was the supplying vessel to the occluded side in 16 patients and mean velocities were significantly (p < 0.001) faster on the occluded (59.3 +/- 14.5 cm sec-1) and nonoccluded (91.6 +/- 29.6 cm sec-1, p < 0.05)) side than those found in the middle cerebral artery (39.2 +/- 13.7 and 50.9 +/- 8.5 cm sec-1). In two patients a decrease of mean velocity after acetazolamide was noted in middle cerebral artery indicating 'steal' effect. In another 4 patients, poor vasomotor response was seen with less than 11% of mean velocity increase in the middle cerebral artery. Differences between posterior cerebral artery on the occluded and nonoccluded side were insignificant as well as those between middle and posterior on the occluded side. Resting values of pulsatility index differed significantly (p < 0.01) only between anterior and posterior cerebral artery on the nonoccluded side.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pulsed Doppler ultrasonography to measure the vasoactive effects of hemoglobin-dextran 10-benzene-tetracarboxylate, a potential erythrocyte substitute]

The effects of Dextran-Benzene-Tetracarboxylate-Hemoglobin (Dex-BTC-Hb), a chemically-modified hemoglobin-based oxygen carrier, on the vascular tone were compared to those of standard solutions, i.e. the animal's own blood and a 50 milligrams albumin solution, by measuring the carotid blood flow velocity, the mean arterial pressure, the heart rate and respiratory frequency, in anesthetized Hartley guinea pigs after a hemorragic shock. Stroma-free hemoglobin induced 40% hypertension and a 110% rise in blood flow velocity immediately after injection. The velocity was still increased 38%, 3 hours after injection. The calculations of the vascular resistances showed an increase in carotid vascular tone. Dex-BTC-Hb brought about 35% hypertension for two hours with no significant modifications of the vascular tone. These effects are similar to those of the albumin solution. These results indicate that, unlike stroma-free hemoglobin, Dex-BTC-Hb does not significantly affect the vascular tone, probably because of its slight interaction with the factors that regulate vascular tone.

Simultaneous assessment of vasoreactivity using transcranial Doppler ultrasound and cerebral blood flow in healthy subjects

Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their perfusion territories were measured simultaneously in 36 healthy subjects. In 20 subjects, the measurements were first performed under basal conditions and then repeated 15-20 min after an intravenous injection of 1 g of acetazolamide. Reproducibility of simultaneous blood flow and velocity measurements was tested by examining 16 subjects on two occasions under basal conditions with an interval of 20 min. Relatively good reproducibility was found for repeated measurements of velocity and blood flow, being best when side-to-side asymmetry was assessed. The increase in blood flow velocities after acetazolamide was symmetrical (right side, 34.2%; and left side, 35.5%), and the velocity increase was significantly correlated with basal values. The increase in cerebral blood flow was also symmetrical (right side, 29.8%; left side, 30.1%) but not correlated with basal flow values. No significant relationship was found between velocity increase and increase in regional cerebral blood flow. This finding is probably not only due to methodological inaccuracies but may suggest that acetazolamide has an effect on the diameter of the middle cerebral artery or on the magnitude of this artery's perfusion territory. This study supports the use of acetazolamide for assessing cerebral vasoreactivity following the definition of lower limits for velocity and flow increase and for asymmetry of the response.

A comparison of transcranial Doppler and cerebral blood flow studies to assess cerebral vasoreactivity

BACKGROUND AND PURPOSE

The aim of this study was to determine the ability of transcranial Doppler ultrasonography when used to assess cerebral vasoreactivity. The results of this method were compared with regional cerebral blood flow measurements.

METHODS

Forty-three patients with symptoms suggesting cerebrovascular disease took part. Transcranial Doppler findings in the middle cerebral arteries were compared with regional cerebral blood flow in the corresponding perfusion territories before and after acetazolamide administration.

RESULTS

There was a significant positive correlation between the absolute increase in cerebral blood flow in milliliters per 100 g per minute and the percent increase in velocity (r = 0.63). The right-left, side-to-side difference of the acetazolamide response obtained by the two methods also showed a positive correlation (r = 0.80). Control limits obtained from healthy subjects were used for both the blood flow increase (absolute values and asymmetry in absolute values) and the velocity increase (percent increase and asymmetry in percent increase). The two methods then agreed in their evaluation of vasoreactivity in 74 (86%) of the 86 middle cerebral artery perfusion territories; 20 (23%) were assessed by both methods as having a reduced vasodilatory reserve. Eleven hemispheres with a slightly reduced regional cerebral blood flow response to acetazolamide were not detected by transcranial Doppler, whereas all territories with a marked reduction were identified by Doppler. Only one hemisphere with a normal cerebral blood flow increase after acetazolamide administration was assessed by Doppler as having reduced vasoreactivity.

CONCLUSIONS

Transcranial Doppler and the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.