Changes In Blood Flow Velocity Research Articles

Neurovascular Reactivity in Patients with Acute Ischemic Stroke

OBJECTIVE: We aimed to assess the motor evoked blood flow velocity (BFV) changes in both middle cerebral arteries (MCA) using transcranial Doppler (TCD) monitoring in patients with acute ischemic strokes and healthy subjects. METHODS: Eighty-two patients with acute territorial infarction in the MCA territory, 83 patients with acute lacunar infarction in MCA territory and 21 control subjects were investigated. A long term TCD monitoring device was used for the simultaneous recording of both MCA during 10 cycles of 20 seconds while the subjects performed hand gripping with a frequency of one per second, and subsequently 20 seconds when they were resting to assess BFV changes on activated cortical motor areas. Neurovascular reactivity was defined as a relative increase in blood flow velocities which were calculated as the percentage change in baseline value. RESULTS: Hand gripping showed a marked rise in the blood flow velocities in both MCAs in all subjects (p<0.001 for all vessels). Patients with territorial infarction had significantly lower neurovascular reactivity (15.0%±9.5) than those of patients with lacunar infarction (19.9%±11.5 p<0.007). CONCLUSION: Our results suggest that unilateral cerebrovascular ischemic events can affect blood flow in both MCAs in patients with acute ischemic events in the MCA territory, and neurovascular reactivity was preserved in patients with lacunar stroke in contrast to territorial stroke.

Ankle positions and exercise intervals effect on the blood flow velocity in the common femoral vein during ankle pumping exercises

[Purpose] The aim of this study was to identify the most effective method of performing ankle pumping exercises. [Subjects and Methods] The study subjects were 10 men. We measured time-averaged maximum flow velocity and peak systolic velocity in the common femoral vein using a pulse Doppler method with a diagnostic ultrasound system during nine ankle pumping exercises (three different ankle positions and three exercise intervals). Changes of blood flow velocity during ankle pumping exercises with different ankle positions and exercise intervals were compared. [Result] Peak systolic velocity of the leg-up position showed significantly lower values than those of the supine and head-up positions. For all exercise intervals, the increased amount of blood flow velocity in the leg-up position was significantly lower than that in the head-up and supine positions. [Conclusion] Ankle positions and exercise intervals must be considered when performing effective ankle pumping exercises.

Effect of elastic stockings and ankle positions on the blood velocity in the common femoral vein.

[Purpose] The aim of this study was to identify how to effectively use elastic stockings. [Subjects and Methods] Ten young healthy men participated in this study. Time-averaged maximum flow velocity in the common femoral vein was measured for 20 seconds using a pulse Doppler method with a diagnostic ultrasound system under six conditions (three different positions and with and without stockings). Changes of blood flow velocity were compared. [Results] Elastic stockings did not affect the blood flow velocity in the common femoral vein. For both the with stockings condition and without stockings condition, the time-averaged maximum flow velocity in the head-up position was significantly lower than that in the supine and leg-up positions. Time-averaged maximum flow velocity showed no significant difference between the supine position and leg-up position. [Conclusion] Elastic stockings did not affect the blood flow velocity in the common femoral vein, but ankle positions did affect it. Further studies of patients with venous insufficiency are needed.

Changes in left ventricular function and coronary blood flow velocity during isocapnic hypoxia: A cardiac magnetic resonance imaging study

Changes in left ventricular function and coronary blood flow velocity during isocapnic hypoxia: A cardiac magnetic resonance imaging study

Human recombinant erythropoietin gradient dosage influence on ischemic and reperfusion liver injury

We investigate influence of human recombinant erythropoietin different dosage on blood flow velocity and morphological changes in liver during ischemic and reperfusion injury. It was proved what optimal preconditioning dosage is 50 IU/kg.

Blood-Flow Velocity in Glaucoma Patients Measured with the Retinal Function Imager

ABSTRACT Purpose: Circulatory abnormalities in the retina, optic nerve and choroid have been detected by various technologies in glaucoma patients. However, there is no clear understanding of the role of blood flow in glaucoma. The purpose of this study was to compare retinal blood-flow velocities using the retinal function imager (RFI) between glaucoma and healthy subjects. Materials and Methods: Fifty-nine eyes of 46 patients with primary open-angle glaucoma (POAG), 51 eyes of 31 healthy individuals and 28 eyes of 23 patients with glaucomatous optic neuropathy (GON) but normal perimetry were recruited for this study. Three eyes of 2 patients in the glaucoma group and 2 eyes of 1 patient in the GON group had normal pressure at the time of diagnosis. Eighty-three percent of the glaucoma patients and 73% of the patients in the GON group were treated with anti-glaucoma medications. All patients were scanned by the RFI. Differences among groups were assessed by mixed linear models. Results: The average venous velocity in the GON group (3.8 mm/s) was significantly faster than in the glaucoma (3.3 mm/s, p = 0.03) and healthy (3.0 mm/s, p = 0.005) groups. The arterial velocity in the GON group was not different from any of the other study groups (4.7 mm/s). The arterial and venous velocity in the POAG eyes was not different than in the healthy eyes (arterial: 4.3 versus 4.2 mm/s, p = 0.7; venous: 3.3 versus 3.0 mm/s, p = 0.3). A subgroup of 13 glaucoma patients who had perimetric glaucoma in 1 eye and normal visual field (VF) in the fellow eye showed a trend of lower velocity in the glaucoma eyes. Conclusions: Changes in retinal blood-flow velocity were detected only in the pre-perimetric state, but not in perimetric glaucoma. These findings might represent early dysregulation in the retinal vasculature.

Age-related changes in aortic 3D blood flow velocities and wall shear stress: Implications for the identification of altered hemodynamics in patients with aortic valve disease.

To investigate age-related changes in peak systolic aortic 3D velocity and wall shear stress (WSS) in healthy controls and to investigate the importance of age-matching for 3D mapping of abnormal aortic hemodynamics in bicuspid aortic valve disease (BAV). 4D flow MRI (fields strengths = 1.5-3T; resolution = 2.2-3.9 × 1.7-2.6 × 2.2-4.0 mm(3) ; Venc = 150-250 cm/s; TE/TR/FA = 2.3-2.8/4.7-5.4msec/7-15°) was performed in 56 controls (age range: 19-78 years) and in two BAV patient groups each consisting of 10 subjects (group 1: 20-29 years, group 2: 52-57 years). Heat maps showing abnormal 3D velocity and WSS were created for the BAV patients by comparison with an age-matched and with an unmatched control group. The fraction of the aorta exposed to abnormal velocity/WSS was calculated relative to the total aortic volume/surface. Significant inverse relationships between age and healthy velocity/WSS were found (R(2) = 0.32/0.39, P < 0.001). For BAV group 1, abnormally elevated velocity/WSS was overestimated when compared with older controls (51-60 years) than when correctly age-matched (∼25 ± 14% vs. ∼8 ± 5%). For BAV group 2, abnormally decreased velocity/WSS was overestimated when compared with younger controls (21-30 years) than when correctly age-matched (∼9 ± 7% vs. 1 ± 1%). Significant correlations exist between age and peak systolic velocity and WSS. Therefore, robust age-matching is important when creating abnormal 3D aortic velocity and WSS maps for patients with BAV.

Correlations between endothelial function in the systemic and cerebral circulation and insulin resistance in type 2 diabetes mellitus.

Insulin resistance is associated with endothelial dysfunction in type 2 diabetes mellitus, which can lead to impaired vascular reactivities of both systemic and cerebral circulations. Appropriate 'correction' of vascular reactivity results for non-endothelium-dependent systemic effects avoids misinterpretation of endothelial function. Therefore, we 'corrected' vascular reactivity results and explored the potential correlations between systemic vascular reactivity, cerebrovascular reactivity and insulin resistance. In 34 patients, 'systemic vascular reactivity' was assessed by quantifying reactive hyperaemia. Cerebrovascular reactivity was assessed by quantifying changes in cerebral blood flow velocity during hypercapnia. To minimize the influence of non-endothelium-dependent systemic effects on vascular reactivity results, 'corrected systemic vascular reactivity' was calculated by normalizing systemic vascular reactivity using the measurements from the contralateral side; and cerebrovascular reactivity results were corrected by calculating percentage and absolute changes in cerebrovascular conductance index ('percent cerebrovascular conductance index' and 'delta cerebrovascular conductance index', respectively). Insulin resistance was estimated by homeostatic model assessment. Correlation between conventional cerebrovascular reactivity and systemic vascular reactivity was not significant. But correlations between 'corrected systemic vascular reactivity' and 'percent cerebrovascular conductance index' (r = 0.51; p = 0.002) and 'corrected systemic vascular reactivity' and 'delta cerebrovascular conductance index' (r = 0.50; p = 0.003) were significant. Among all vascular reactivity parameters, only 'delta cerebrovascular conductance index' was significantly correlated with homeostatic model assessment of insulin resistance (r = -0.38; p = 0.029). In conclusion, endothelial function in the systemic and cerebral circulations is moderately correlated, provided that vascular reactivity estimates are corrected for non-endothelium-dependent influences.

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

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

V6. Language lateralization – A comparison of three non-invasive methods in healthy adults

Introduction Language lateralization is crucial in the presurgical evaluation of epilepsy patients to avoid damage to eloquent cortex and to diminish risks of post-surgical language problems. Several non-invasive tools exist to determine language dominance. The gold standard is the invasive Wada-Test. We applied three different, non-invasive methods for language lateralization in healthy adults to determine their concordance. Dichotic listening (DL) test, functional transcranial Dopplersonography (fTCD) and functional magnetic resonance imaging (fMRI) were used. Additionally, acoustically evoked potentials (AEP) were analyzed to prove normal physiology of hearing. Methods fTCD measures the task-dependant relative blood flow velocity changes in both medial cerebral arteries (word generation). Hemispheric differences are calculated and a laterality index (LI) with its standard error of the mean (SEM) are calculated with the program Average©. The fMRI data using the same word generation paradigm were analyzed using Feat of the FSL© package. The calculated fMRI Images were coregistered to the anatomical images. A laterality index was calculated for each subject. DL was used by presenting two rhyme words simultaneously to both ears. The ear contralateral to the language dominant side usually recognizes more words. A leftsided dominance thus leads to more right ear points (REP) and vice versa. A Lambda-Index is given. In all modalities, a positive LI means left-sided language dominance. Results Twenty-three subjects (Age range: 17–39 years, mean 25.6 ± 4.7 SD; 14 female) underwent all three methods. 21 were strongly right-handed (EHI ≥ 70). In 17/23 (74%) fTCD and fMRI were condordant (16 left, 1 no lateralization). Notably, seven subjects had low activation during fMRI which did not lead to lateralization while those seven however had left lateralization during fTCD. In 15 cases (65%) both fTCD and DL lateralized to the left side. Four subjects lateralized to the left during fTCD and showed no lateralization in DL, either due to no lateralization pattern or high stimulus domincane. Two were typical in fTCD and atypical in DL. Only one subject failed to lateralize during fTCD and showed typical lateralization in DL. The correlation for fTCD and fMRI was medium (r = .454, p = .029). DL results did not correlate with either fTCD or fMRI. AEP showed no abnormalities in hearing. The AEP did not correlate with either DL, fTCD or fMRI. Discussion FTCD, fMRI and DL are easily applicable in healthy participants and mostly concordant for lateralization of language dominance. However, language lateralization was achievd in most patients with fTCD, supporting its value for clinical routine. Arguably, the direct feedback of the examiner during fTCD might have enhanced activation and motivation. This study calls for close monitoring and feedback enhancing during DL and fMRI. For better comparison of DHT and fMRI a Wernicke-paradigm should be used in future studies.

Neuronavigated microvascular Doppler sonography for intraoperative monitoring of blood flow velocity changes during aneurysm surgery – A feasible monitoring technique

Introduction and aim of the studyThe intraoperative microvascular Doppler sonography (iMDS) is a well-established tool in vascular surgery for blood flow velocity (BFV) monitoring, capable of detecting vessel occlusion. However, identification of subtotal vessel compromise is more difficult, since the measured BFV may substantially vary with changing insonation angles and insonated vessel segments. To keep these parameters constant we combined neuronavigation with iMDS (niMDS). The question was if niMDS allows the detection of subtotal vessel compromise in aneurysm surgery. MethodsDuring surgery, the 3-dimensional reconstruction of the CT-angiography, which was obtained routinely prior to surgery, was displayed by the neuronavigational system. Prior to clipping, neuronavigation was used to define target point and trajectory, which, by coupling the neuronavigational pointer with the Doppler probe, correspond to the insonated vessel segment and the insonation angle. After clipping, for each vessel segment, the same trajectory was used for all consecutive measurements. The mean BFVs pre- and post-clipping were documented. ResultsWe performed 82 BFV-measurements in 39 aneurysm surgeries. Mean deviation between pre- and post-clipping BFV values was 2.12cm/s. There was a significant correlation between the mean BFV values before and after clipping (r=0.45 [95% CI 17–66%]; p=0.002). One patient experienced new neurological deficits due to occlusion of a perforating vessel that was not insonated. ConclusionThe study could not answer the question if niMDS can detect BFV changes after clipping indicating vessel compromise, as no subtotal vessel occlusion occurred in the 39 operations. However, we proofed that niMDS-measured BFVs only varied minimally in uncompromised vessels pre- and post-clipping, suggesting that vessel compromises might be easily detected during aneurysm surgery.

Effect of acupuncture at Lièquē ( LU 7) on vertebral-basilar artery hemodynamics in patients with cervical vertigo

ObjectiveTo explore the therapeutic efficacy and mechanism of acupuncture at Lièquē (▪ LU 7) in treatment of cervical vertigo (CV). MethodsForty CV patients met the inclusion criteria were enrolled and treated with acupuncture at bilateral LU 7 points, once daily with 10 times as a course. The changes of blood flow velocity in bilateral vertebral artery and basilar artery were observed through transcranial doppler sonography (TCD) before treatment, after deqi with acupuncture and after a course of treatment, respectively. The scores and therapeutic efficacy on clinical symptoms were assessed according to CV symptoms and the functional assessment scale as well as the Criteria for Diagnosis and Curative Effect in TCM Syndromes before treatment and after a course of treatment. ResultsBefore treatment, after deqi and after a course of treatment, the blood flow velocity of basilar artery (BA), left vertebral artery (LVA) and right vertebral artery (RVA) in 22 patients with a decreased blood flow velocity were respectively 23.20±4.84 vs 26.30 ±4.17 vs 29.20 ±4.20 (mm/s, BA), 21.65 ± 3.62 vs 24.20 ± 2.89 vs 26.40 ± 3.62 (mm/s, LVA) and 21.90±3.04 vs 24.25±3.01 vs 26.50±3.95 (mm/s, RVA); while in 18 patients with an increased blood flow velocity were respectively 39.94 ± 8.24 vs 35.17 ± 4.84 vs 32.06 ± 3.49 (mm/s, BA), 41.83 ± 5.64 vs 37.28 ± 2.32 vs 35.61 ± 2.09 (mm/s, LVA) and 37.11 ± 9.83 vs 32.22 ± 6.13 vs 28.11 ± 4.12 (mm/s, RVA). Except that the difference of blood flow velocity of RVA was not significant in patients with an increased blood flow velocity before treatment and after deqi (P> 0.05), the Vm of all vessels in 40 patients was improved after deqi with acupuncture and a course of treatment (P<0.01, P<0.05). According to CV symptoms and the functional assessment scale, before treatment and after a course of treatment, the scores were 15.68 ±5.35 and 26.30 ±3.76, respectively, indicating that after a course of treatment, the symptoms were significantly improved (P< 0.01). According to the Criteria for Diagnosis and Curative Effect in TCM Syndromes, after a course of treatment, the total effective rate was 100% (40/40) and the cured rate was 55.0% (22/40). ConclusionAcupuncture at LU 7 not only improves the blood supply of vertebral-basilar artery in CV patients, but also has a significant curative effect on improving the clinical symptoms.

Velocity of regional blood flow and blood flow in the middle cerebral artery in surgical leg lengthening in patients with congenital and acquired limb shortening

A comparative study of the changes in blood flow velocity in the popliteal artery, arteries of the regenerated bone and the cerebral arteries was performed in 45 patients with congenital and acquired diseases of the limbs at different stages of the Ilizarov surgical lengthening of leg shortened by 3–15 cm. An increase in the regional blood flow was detected in all patients during periods of distraction and fixation. An increase in the blood flow velocity in the middle cerebral artery on the contralateral side by 25% was found only in patients of the first adult age with acquired limb shortening. Based on the results of analyzing the reaction of cerebral arteries in functional test with an additional muscle work, we assumed that the absence of response in congenital diseases is caused by a relative excess of somatic afferentation as a result of the morphological and functional immaturity of the brain regulatory systems.

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

Previous investigations demonstrated that cerebral blood flow was influenced by changes in central blood volume and arterial blood pressure even within the range of cerebral autoregulation (60-150 mmHg). Recently, we found that during acute microgravity (parabolic flight condition), the acute increase in central blood volume decreased gradually arterial blood pressure via the arterial and cardiopulmonary baroreflexes. Despite the acute hypotension and central hypervolemia, steady-state cerebral blood flow was well maintained during this condition. However, the dynamic relationship between central blood volume and cerebrovascular control remains unclear. PURPOSE: The purpose of the present study was to examine dynamic cerebral autoregulation during an acute hypotension with central hypervolemia. METHODS: Nine young healthy subjects voluntarily participated in this study. In order to measure dynamic cerebral autoregulation, change in middle cerebral artery mean blood flow velocity (MCA Vmean) was analyzed during acute hypotension caused by two methods: 1) thigh-cuff occlusion release (without change in central blood volume) and 2) lower body negative pressure (-50 mmHg, LBNP) release (with acute increase in central blood volume). RESULTS: As expected, the thigh-cuff occlusion release caused acute hypotension and decrease in MCA Vmean accordingly, but MCA Vmean returned to the baseline value quickly. LBNP release increased and then decreased arterial blood pressure acutely. During the phase of decreased arterial blood pressure, however, the rate of regulation, as an index of dynamic cerebral autoregulation during LBNP release, was significantly lower than that during cuff release (0.112 ± 0.116 and 0.236 ± 0.053 sec-1, respectively, P=0.030). CONCLUSIONS: These findings suggest that an acute change in central blood volume modifies dynamic cerebral autoregulation.

Clinical research of Yangxue-Qingnao granules on posterior circulation of ischemia

Objective To evaluate the curative effect and security of Yangxue-Qingnao granules on posterior circulation ischemia. Methods 52 patients with posterior circulation ischemia from September 2012 to January 2014 in Remin hospital of Wuhan Universityk, were randomly recruited into a control group and a treatment group, with 26 cases in each group. The control group was only treated with flunarizine HCL and Betahistine Mesilate Tablets, while the treatment group was given Yangxue-Qingnao granules based on the control group. The change of clinical symptoms, TCD and cervical vascular ultrasound were observed before and after the treatment. Results After the treatment, the total effective rate of treatment group was significantly different to the control group (96.2% vs. 76.9%; χ2=4.127, P=0.042). The changes of blood flow velocity of vertebral artery, basilar artery and posterior inferior cerebellar artery were all decreased after the treatment in both groups ( t value in the treatment group were 20.624, 13.773, and 9.485 respectively，t value in the control group were 13.203, 9.550, and 5.655, respectively, all P<0.01）, besides such decreases in the treatment group were better than the control group (all P<0.01）. After the treatment, the condition of carotid IMT decrease was significantly better in the treatment group than the control group (the number rate of IMT decrease was (96.2% vs. 69.2%; χ2=5.318, P=0.021). Conclusion Yangxue-Qingnao granules can obviously improve the blood flow velocity and the thickness of IMT in patients with posterior circulation ischemia. The short-term curative effect is obvious. Key words: Brain ischemia; Vertebrobasilar insufficiency; Yangxue-Qingnao granules

The effect of an acute increase in central blood volume on hypercapnia‐induced attenuation in dynamic cerebral autoregulation

It is well established that hypercapnia attenuates dynamic cerebral autoregulation. The impact of central blood volume on cerebral blood flow is controversial. The purpose of the present study was to examine whether hypercapnia‐induced attenuation in dynamic cerebral autoregulation is modified by acute central hypervolemia. Nine young healthy subjects voluntarily participated in this study. In order to measure dynamic cerebral autoregulation during normocapnic and hypercapnic (5%) conditions, the change in middle cerebral artery mean blood flow velocity (MCA Vmean) was analyzed during acute hypotension caused by two methods: 1) thigh‐cuff occlusion release (without change in central blood volume) and 2) lower body negative pressure (‐50 mmHg, LBNP) release (with acute increase in central blood volume). As expected, hypercapnia decreased the rate of regulation, as an index of dynamic cerebral autoregulation (0.236±0.053 and 0.167±0.074 sec‐1, respectively, P=0.025). In contrast, this attenuation was disappeared during central hypervolemia (P=0.574). This phenomenon may be associated with hypervolemia‐induced attenuation of dynamic cerebral autoregulation (P=0.009). These findings suggest that an acute change in central blood volume modifies carbon dioxide‐induced changes in dynamic cerebral autoregulation.

Blood flow velocity measured using the Retinal Function Imager predicts successful ranibizumab treatment in neovascular age-related macular degeneration: early prospective cohort study.

Anti-VEGF treatment has a potent vasoconstrictive effect. Early changes of retinal blood flow velocity (RBFV) measured using the Retinal Function Imager (RFI) combined with indicators of vascular status may help in predicting the visual outcome 1 month post injection in patients with neovascular age-related macular degeneration (nvAMD) under ranibizumab treatment. To develop a simple prediction model based on the change in RBFV 3 days post injection and indicators of a patient's vascular status to assess the probability of a successful visual outcome 1 month post injection. RBFV measured using RFI were prospectively collected pre-injection and 3 days post injection in 18 eyes of 15 patients. Indicators of vascular status (history of hypertension, diabetes mellitus without retinal affection, and smoking) were assessed by medical history. By univariate analyses, parameters associated with visual outcome were weighted (-1 to 6 points). A multivariate logistic regression model with the categorized visual outcome parameter (≥0 letters gained after 1 month) as the dependent variate and the sum score as the independent variate (continuous scale) was used to estimate the score value-specific probabilities of letters gained ≥0 1 month post injection. The indicators of vascular status negatively influenced the likelihood of a letter gain ≥0 whereas an increase in the arterial RBFV strongly increased it. The area under the receiver operating characteristics curve for these parameters investigated was 0.71 (95% CI: 0.43-1.00). Changes in the arterial RBFV following 3 days after ranibizumab injection combined with three indicators of the vascular status identified nvAMD patients with favorable visual outcome accurately.

Apolipoprotein E, carbon dioxide vasoreactivity, and cognition in older adults: effect of hypertension.

To investigate the associations between the apolipoprotein E (APOE) ε4 allele, carbon dioxide (CO2 ) vasoreactivity, and cognitive performance and to explore the effect of CO2 vasoreactivity and hypertension on the associations between APOE and cognition. Observational. Community. Older adults (N = 625) enrolled in the Maintenance of Balance, Independent Living, Intellect and Zest in the Elderly of Boston Study. Change in cerebral blood flow velocity in response to CO2 challenge (CO2 ), measured using transcranial Doppler ultrasonography, Trail-Making Test Part B - A (TMT), Hopkins Verbal Learning Test delayed recall (HVLT). APOE-ε4 was associated with lower CO2 vasoreactivity (P = .009) and poorer performance on the TMT (P < .001) and HVLT (P < .001). Having hypertension and APOE-ε4 was associated with worse cognitive and CO2 vasoreactivity measures than having neither or either alone (P < .001 for TMT and HVLT, P = .01 for CO2 vasoreactivity). The association between APOE-ε4 and cognition was only significant if it was present concurrent with low CO2 vasoreactivity, defined as below the median of the sample (APOE by CO2 vasoreactivity interaction: P = .04 for TMT, P = .04 for HVLT). In hypertension, the association between APOE-ε4 and executive function was also only significant in participants with lower CO2 vasoreactivity (P = .005 for APOE by CO2 vasoreactivity). Individuals at risk of Alzheimer's disease (AD) because they have APOE-ε4 may have lower CO2 vasoreactivity, which in turn may be contributing to the observed lower cognitive performance associated with this allele. The cognitive effect of APOE-ε4 is magnified in hypertension and low CO2 vasoreactivity. This study offers evidence that APOE-ε4 may be associated with microvascular brain injury even in the absence of clinical AD.

Inner ocular blood flow responses to an acute decrease in blood pressure in resting humans

Whether inner ocular vessels have an autoregulatory response to acute fluctuations in blood pressure is unclear. We tried to examine the validity of acute hypotension elicited by thigh-cuff release as to assess the dynamic autoregulation in the ocular circulation. Blood flow velocity in the superior nasal and inferior temporal retinal arterioles, and in the retinal and choroidal vasculature were measured with the aid of laser speckle flowgraphy before and immediately after an acute decrease in blood pressure in 20 healthy subjects. Acute hypotension was induced by a rapid release of bilateral thigh occlusion cuffs that had been inflated to 220 mmHg for 2 min. The ratio of the relative change in retinal and choroidal blood flow velocity to the relative change in mean arterial blood pressure (MAP) was calculated. Immediately after cuff release, the MAP and blood flows in the all ocular target vessels decreased significantly from the baseline values obtained before thigh-cuff release. The ratio of the relative change in inner ocular blood flow velocity to that in the MAP exceeded 1% / %mmHg. An explicit dynamic autoregulation in inner ocular vessels cannot be demonstrated in response to an acute hypotension induced by the thigh-cuff release technique.

Shear stress is normalized in glomerular capillaries following ⅚ nephrectomy.

Loss of significant functional renal mass results in compensatory structural and hemodynamic adaptations in the nephron. While these changes have been characterized in several injury models, how they affect hemodynamic forces at the glomerular capillary wall has not been adequately characterized, despite their potential physiological significance. Therefore, we used intravital multiphoton microscopy to measure the velocity of red blood cells in individual glomerular capillaries of normal rats and rats subjected to ⅚ nephrectomy. Glomerular capillary blood flow rate and wall shear stress were then estimated using previously established experimental and mathematical models to account for changes in hematocrit and blood rheology in small vessels. We found little change in the hemodynamic parameters in glomerular capillaries immediately following injury. At 2 wk postnephrectomy, significant changes in individual capillary blood flow velocity and volume flow rate were present. Despite these changes, estimated capillary wall shear stress was unchanged. This was a result of an increase in capillary diameter and changes in capillary blood rheology in nephrectomized rats.