Cerebral blood flow velocity and psychomotor performance during acute hypoxia

INTRODUCTION: The physiological effects of hypoxic environments can help determine safe limits for workers where cognitive and motor performance is important. We investigated the effects of a PIO2 of 15 kPa and 10 kPa on medial cerebral artery blood flow velocity (CBFV) and psychomotor performance. METHODS: Over 3 sessions, each involving 3 separate test batteries, 13 subjects breathed either 21 kPa PIO2 (control), 15 kPa PIO2, or 10 kPa PIO2. The tests measured reaction time, spatial orientation, voluntary repetitive movement, and fine manipulation. CBFV, PETCO2, PETO2, Sa02, and BP were recorded throughout. RESULTS: ANOVA analysis showed that 15 kPa PIO2 did not significantly change psychomotor test performance. The mean number of incorrect responses in the reaction time test significantly increased to 5.6 (SD - 4.0) while breathing 10 kPa PIO2, as did the mean number of errors (7.7 +/- 5.0) in the fine manipulation test. Only 10 kPa PIO2 affected CBFV, causing a significant increase in flow from 50 +/- 6.5 cm x s(-1) to 55 +/- 10.3 cm x s(-1). CBFV significantly increased during three psychomotor tests while breathing air; however, it did not increase further during psychomotor testing in hypoxia. DISCUSSION: A PIo2 of 15 kPa did not affect subject performance, and should not cause operational risk. At 10 kPa PIO2, accuracy and vigilance were slightly affected; however, the reduction in oxygenation was not great enough to cause major decrements. CBFV was not a good indicator of mental stress during hypoxia.     

Cerebral blood flow in patients with normal pressure hydrocephalus

Mean cerebral blood flow (CBF) of the whole brain was measured in 48 patients who underwent cerebrospinal fluid shunt surgery for normal pressure hydrocephalus (NPH) by performing first-pass radionuclide angiography using 99Tcm-hexamethylpropylene amine oxime. Patients were divided according to outcome into an 'excellent' improvement group, a 'good' improvement group, a 'fair' improvement group and a 'poor' improvement group. Patients with excellent and good improvement had a preoperative mean CBF of 40.4 +/- 3.9 ml.100 g-1.min-1 and 37.1 +/- 5.5 ml.100 g-1.min-1, respectively, both of which were significantly (P < 0.005) higher than that in 11 patients who showed fair improvement (30.8 +/- 3.2 ml.100 g-1.min-1) and six patients who showed poor improvement (31.8 +/- 2.5 ml.100 g-1.min-1). Patients with a clinical improvement after shunting had an increased postoperative mean CBF. We conclude that patients with a preoperative mean CBF of over 35 ml.100 g-1.min-1 can show favourable improvement after a shunting procedure, and that the preoperative mean CBF of 32 ml.100 g-1.min-1 can be considered the critical level for treatment.     

Middle cerebral artery blood velocity during running

Running induces characteristic fluctuations in blood pressure (BP) of unknown consequence for organ blood flow. We hypothesized that running‐induced BP oscillations are transferred to the cerebral vasculature. In 15 healthy volunteers, transcranial Doppler‐determined middle cerebral artery (MCA) blood flow velocity, photoplethysmographic finger BP, and step frequency were measured continuously during three consecutive 5‐min intervals of treadmill running at increasing running intensities. Data were analysed in the time and frequency domains. BP data for seven subjects and MCA velocity data for eight subjects, respectively, were excluded from analysis because of insufficient signal quality. Running increased mean arterial pressure and mean MCA velocity and induced rhythmic oscillations in BP and in MCA velocity corresponding to the difference between step rate and heart rate (HR) frequencies. During running, rhythmic oscillations in arterial BP induced by interference between HR and step frequency impact on cerebral blood velocity. For the exercise as a whole, average MCA velocity becomes elevated. These results suggest that running not only induces an increase in regional cerebral blood flow but also challenges cerebral autoregulation.     

4D magnetic resonance velocity mapping of blood flow patterns in the aorta in young vs. elderly normal subjects.

Four-dimensional magnetic resonance MR velocity mapping was developed to study normal flow patterns in the thoracic aorta using time-resolved cardiac gated three-directional velocity data. Sixteen normal subjects were studied, one young group (average age 31 years) and one group with elderly people (average age 72 years). Blood flowed in a right-handed helix from the ascending aorta to the aortic arch. A straight flow pattern or a left-handed helix was seen in the descending aorta. Blood flow was never parabolic. Blood flowed forward in early systole, retrograde in mid-to-end systole, and forward again in diastole in all subjects as a basic pattern. Continuous retrograde flow over a long distance was not seen, but blood entered a retrograde flow column at various levels. In young people blood passed from the aortic valve to the mid-descending aorta in less than one heartbeat. In people in their sixties it took two heartbeats and in people older than 78 years, it took three heartbeats. The maximum systolic forward velocities were higher in young subjects than in elderly while the retrograde velocities were lower. J. Magn. Reson. Imaging 1999;10:861-869.     

Four-dimensional magnetic resonance velocity mapping of blood flow patterns in the aorta in patients with atherosclerotic coronary artery disease compared to age-matched normal subjects

PURPOSE: To test the hypothesis that age and atherosclerotic coronary artery disease (CAD) may influence aortic blood flow patterns. MATERIALS AND METHODS: A total of 21 patients with CAD, 37-86 years old, were studied, together with 20 age-matched normal subjects. Time-resolved, three-direction velocity data over an entire volume were obtained with sequential single-slice two-dimensional cardiac-gated magnetic resonance (MR) velocity-encoded phase-contrast sequences. RESULTS: In both normal subjects and CAD patients, the time it took for particles to travel from aortic valve to descending aorta was significantly longer in the elderly age group than in the younger (37-46 years old). This time was significantly longer in patients than in normal subjects. Systolic velocities were significantly higher in young normal subjects than in elderly normal subjects, and significantly lower in CAD patients than in age-matched normal subjects. Retrograde velocity was higher in CAD patients than in normal subjects, and higher in elderly CAD patients than in young. CONCLUSION: CAD patients have abnormal blood flow patterns in the aorta compared with age-matched normal subjects, especially young patients ages 37-46. The aging process has a similar effect on blood flow patterns as atherosclerosis. Ascending aorta flow is chaotic in some very elderly normal subjects and in CAD patients of all ages. Chaotic aortic flow may result in reduced blood flow into the coronary arteries.     

First pass evaluation of blood velocity in the pulmonary artery.

Studying the kinetics of blood flow in the pulmonary artery using non-invasive techniques may be an important tool in assessing the prognosis of lung diseases. The aim of this study was to ascertain dynamic parameters of pulmonary blood flow, particularly the velocity of a small bolus of a radioactive tracer after intravenous injection. Since the shape and distribution pattern of the bolus changes substantially from frame to frame, common image processing techniques for motion detection or other techniques, such as accumulation of subtracted images, segmentation and spectral analysis with temporal/spatial filtering, are unable to properly evaluate the motion of the bolus. However, the passage of the bolus from the arm to the lungs was visualized with good contrast through acquisition of a first pass sequence of scintigraphic images. The wave form of the bolus becomes increasingly complex as it progresses towards the pulmonary artery. In the proposed method the time-activity curves for each pixel are displayed. It is assumed that the peaks of the maximum counts in these curves correlate with the time after injection that the bolus takes to cross each pixel (bolus head). The bolus head contains information on time, space and activity, and allows the velocity of the studied fluid to be calculated. We demonstrated a mean velocity through the pulmonary artery trunk in resting patients of approximately 11 cm/s, with a mean residence time of 0.5 s.     

Cerebral blood flow response pattern during balloon test occlusion of the internal carotid artery.

PURPOSETo evaluate the risk of temporary or permanent internal carotid artery occlusion.METHODSIn 156 patients intraarterial balloon test occlusion in combination with a stable xenon-enhanced CT cerebral blood flow study was performed before radiologic or surgical treatment. All 156 patients passed the clinical balloon test occlusion and underwent a xenon study in combination with a second balloon test. Quantitative flow data were analyzed for absolute changes as well as changes in symmetry.RESULTSFourteen patients exhibited reduced flow values between 20 and 30 mL/100 g per minute, an absolute decrease in flow, and significant asymmetry in the middle cerebral artery territory during balloon test occlusion. These patients would be considered at high risk for cerebral infarction if internal carotid artery occlusion were to be performed. With one exception they belonged to a group (class I) of 61 patients who showed bilateral or ipsilateral flow decrease and significant asymmetry with lower flow on the side of occlusion. The other 95 patients, who showed a variety of cerebral blood flow response patterns including ipsilateral or bilateral flow increase, were at moderate (class II) or low (class III) stroke risk. In contrast to these findings, exclusively qualitative flow analysis failed to identify the patients at high risk: a threshold with an asymmetry index of 10% revealed only 16% specificity whereas an asymmetry index of 45% showed only 61% sensitivity for detection of low flow areas (< 30 mL/100 g per minute).CONCLUSIONFor achieving a minimal hemodynamic related-stroke rate associated with permanent clinical internal carotid artery occlusion we suggest integration of a thorough analysis of quantitative cerebral blood flow data before and during balloon test occlusion.     

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360–557 mL/min (mean [± standard deviation], 465 mL/min ± 52); internal carotid arteries, 132–367 mL/min (mean, 265 mL/min ± 60); external carotid arteries, 113–309 mL/min (mean, 186 mL/min ± 51); vertebral arteries from 133–308 mL/min (mean, 244 mL/min ± 43); and cerebral circulation, 546–931 mL/min (mean, 774 mL/min ± 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P =.007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.     

Cerebral lactate production and blood flow in acute stroke.

Eight stroke patients were examined serially in the acute phase and 1 week and 2-4 weeks after stroke with water-suppressed proton magnetic resonance spectroscopy. The time courses of lactate level and regional cerebral blood flow were studied. A high lactate level was found in the acute phase. The lactate content decreased to barely detectable levels during the following 3 weeks, while regional blood flow increased during this period. The inverse relationship between lactate level and cerebral blood flow suggests that lactate plays no substantial role in the vasodilatation underlying the hyperemia that follows reperfusion. The amount of lactate present in the acute phase reflects the severity of ischemia in the affected region. The lactate level was still above normal in the subacute phase with hyperemia, suggesting lactate production through aerobic glycolysis. Thus, the lactate level in the subacute phase probably does not reflect the degree of anaerobic glycolysis in hypoxic neuronal tissue.     

军事飞行人员正常高值血压的调查研究

目的 调查正常高值血压在军事飞行人员中的分布及与心血管疾病危险因素的相关性,为进一步预警及干预提供理论依据.方法 随机抽取健康军事飞行人员340例,其中正常血压196例、正常高值血压144例,对不同飞行时间和机种分组之间进行比较,并对两组飞行人员的年龄、体质量指数(body mass index,BMI)、血清总胆固醇...     

Cerebral blood flow-related signal changes during breath-holding.

BACKGROUND AND PURPOSE: In the past, functional MR imaging techniques have been used successfully to determine cerebrovascular reactivity (CVR) to various stimuli, complementing the arsenal of functional brain investigations feasible with MR imaging. While previous studies have focused on blood oxygenation changes under vasodilatory stress, the aim of this study was to assess regional cerebral blood flow (rCBF) changes during breath-holding by using a flow-sensitive alternating inversion recovery (FAIR) imaging technique. METHODS: In six healthy volunteers, FAIR images were acquired during alternating periods of breath-holding and breathing at 40-second intervals after inspiration and at 30-second intervals after expiration, for a total dynamic scanning time of 10 minutes. To quantify the rCBF changes, we obtained 2.5-minute baseline samples during normal breathing. RESULTS: Repeated challenges of breath-holding induced an overall rise in rCBF. In general, rCBF changes were greatest in gray matter and were insignificant in white matter. Using the mean values of the baseline images collected before breath-holding to calculate the rCBF changes, we found that quantitative analysis yielded an rCBF increase of 47% to 87% after breath-holding. The rCBF changes clearly depended on the breath-holding duration and technique; however, for one given breath-holding paradigm the results showed relatively small interindividual variability. CONCLUSION: rCBF changes during a simple vascular challenge can be detected and quantified by means of functional MR imaging at 1.5 T. Noninvasive assessment of CVR could become a useful clinical tool to identify persons with impaired CVR.     

Cerebral blood volume alterations during fractional pneumoencephalography.

Simultaneous and continuous measurements of the cerebral blood volume (CBV), cerebrospinal fluid (CSF) and blood pressure were carried out in six patients during fractional pneumoencephalography in order to examine intracranial volumetric interactions. Three patients (Group A) showed normal encephalographic findings, and in three patients (Group B) communicating hydrocephalus with convexity block was found encephalographically. In all patients the injection of air was followed by an immediate increase of CSF pressure and blood pressure and a concomitant decrease of CBV. The initial CSF pressure was invariably re-established within 3 to 3.5 min. During this time interval the CBV of the patients of Group B decreased significantly and 30 percent more than that of Group A. Furthermore, after restoration of the original CSF pressure, CBV returned to its initial level in all patients of Group A, whereas it remained unchanged or showed a further decrease in the patients of Group B. Removal of an amount of CSF corresponding to half of the amount of injected air was followed by a significant reactive hyperemic response in two normal patients. The intracranial volumetric alterations during fractional pneumoencephalography are discussed in detail with respect to the underlying physiologic mechanisms and are suggested as a model for acute and low pressure hydrocephalus.     

Phalangeal US velocity discriminates between normal and vertebrally fractured subjects

The purpose of this study was to evaluate the diagnostic sensitivity of phalangeal bone ultrasound velocity of the hand in the diagnosis of osteoporosis and to compare this technique to bone mineral density (BMD) measurement at the lumbar spine assessed by dual X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). We investigated US velocity at the distal metaphysis of the proximal phalanx and spinal BMD in 101 women. Fifty-nine were healthy (mean age 50 ± 11.6 years) and 42 were osteoporotic (mean age 65 ± 6.6 years) with documented vertebral fractures. In the healthy population the relation with age was, respectively, r = –0.73 (p < 0.0001) for quantitative US (QUS), r = –0.74 (p < 0.0001) for QCT and r = –0.48 (p < 0.01) for DXA. Both US and DXA were correlated with QCT: r = 0.74 and r = 0.77 (p < 0.0001), respectively. Correlation of QUS and DXA was r = 0.56 (p < 0.0001). Phalangeal US velocity and spinal BMD (QCT and DXA) values discriminate healthy from osteoporotic women. Age-adjusted logistic regression analysis of the data showed standardized odds ratios (OR) for vertebral fracture to be similar for US and DXA (OR = 1.8 and 1.5, respectively) and stronger for QCT (OR = 2.9). Phalangeal US velocity reflects age-related bone loss and differentiates between healthy and osteoporotic subjects. Received: 28 August 1998; Revision received: 24 December 1998; Accepted: 28 December 1998     

MR-based coronary artery blood velocity measurements in patients without coronary artery disease

To evaluate the feasibility of MR-based coronary blood velocity measurements (MRvenc) in patients without coronary artery disease (CAD). Eighty-three patients with angiographically excluded CAD received MRvenc of the proximal segments of both coronary arteries (CAs). Using a retrospectively ECG-gated breath-hold phase-contrast FLASH sequence with high temporal resolution, flow data were technically acquirable in 137/166 (83%) CAs. Quantification and analysis of blood velocities in systole and diastole of both CAs were performed. Biphasic velocity profiles were found in 83/100 CAs. Median systolic and diastolic velocities differed significantly in LCA (19 cm/s, 24 cm/s; P<0.0001) and RCAs (14 cm/s, 16 cm/s; P<0.01). The diastolic/systolic velocity ratio was calculated in LCAs and RCAs with a median of 1.3 and 1.1, respectively. The velocity profiles of the remaining CAs were monophasic (17 CAs) or revealed severe alterations of the physiologic velocity profile with reduced flow undulations and steady velocities (37 CAs). Optimized clinical MRvenc is feasible to quantify blood velocities in the CAs. Potential indications are (1) non-invasive monitoring of patients after aortic valve reconstruction as well as (2) detection of asymptomatic CAD patients.     

Cerebral blood flow velocity by transcranial Doppler during a vertical-rotating table simulation of the push-pull effect

BACKGROUND: The push-pull effect (PPE) has been suspected of causing many aircraft accidents. The perfusion and then withdrawal of cerebral blood during the PPE may change the state of the cerebral blood vessel. HYPOTHESIS: During head-down tilt (HDT) cerebral vasoconstriction occurs in response to the elevated perfusion pressure to maintain cerebral blood flow, and during subsequent head-up tilt (HUT) the increased resistance of the cerebral blood vessel recovers slowly. METHODS: Ten healthy male non-pilots were exposed to the following protocol using a rotating-table to simulate the push-pull maneuver: HUT (+1 Gz) for 1 min followed by transition to HDT (-1 Gz) 10 s followed by transition to HUT (+1 Gz) 1 min. Cerebral blood flow velocity and pulsatility indices in the left middle cerebral artery were continually measured with a transcranial Doppler (TCD) instrument. RESULTS: Mean blood flow velocity (Vm) increased significantly by 10%, during the first 5 s of HDT, recovered to baseline during HDT 5 10 s, and remained unchanged during subsequent HUT. Systolic blood flow velocity (Vs) increased by 9% during HDT 5-10 s and 11% during HUT 0-5 s. Diastolic blood flow velocity (Vd) decreased by -9% during HDT 5-10 s, and -22% during HUT 0-5 s. Vs-Vd increased by 26% during HDT 5 10 s, and 41%, during HUT 0-5 s. Pulsatile indices (PI) and resistance index (RI) increased by 26%) and 15% during HDT 5-10 s, and by 40% and 27% during HUT 0-5 s, respectively. Vs, Vs-Vd, PI, and RI remained at the higher level, and Vd remained at the lower level to HDT 15-20 s. CONCLUSIONS: The results indicate that cerebral vasoconstriction occurred to prevent brain over-perfusion during HDT. During HUT, the elevated resistance of the cerebral vessel remained at the higher level for about 20 s, and may have worsened the cerebral perfusion from exposure to +Gz. This may be one of the mechanisms of PPE.     

沙格列汀对改善2型糖尿病患者血压的效果及其作用机制

 目的 观察沙格列汀改善2型糖尿病(type 2 diabetes mellitus, T2DM)患者血压的效果, 并探讨其心血管保护作用的机制。方法 选取血糖控制不佳而血压控制平稳的T2DM 78例, 随机分为治疗组43例和对照组35例, 两组在原有口服药物基础上, 治疗组加用沙格列汀, 对照组增加原有药物剂量或加用其他降糖药。治疗3个月后, 观察两组治疗前后血糖、糖化血红蛋白(HbA₁c)、体重指数(BMI)及血压变化。结果 两组治疗后空腹血糖(fasting plasma glucose, FPG)、餐后血糖(postprandial glucose, PPG)、HbA₁c较前均明显下降(P<0.05);治疗组收缩压(SBP)[ (133.9±16.5) mmHg vs (125.2±13.4) mmHg, P<0.01]、24 h平均收缩压较治疗前明显下降[ (125.2±11.7) mmHg vs(116.6±8.6)mmHg, P<0.01], 但对照组以上指标较治疗前无明显变化。Spearman相关分析显示治疗组血压下降与空腹、餐后血糖及HbA₁c下降均无关。结论 沙格列汀不仅能降低T2DM患者血糖, 而且对血压也具有改善作用。     

CO2 supplementation dissociates cerebral oxygenation and middle cerebral artery blood velocity during maximal cycling

This study evaluated whether the reduction of prefrontal cortex oxygenation (ScO₂) during maximal exercise depends on the hyperventilation-induced hypocapnic attenuation of middle cerebral artery blood velocity (MCA V_mean). Twelve endurance-trained males (age: 25 ± 3 years, height: 183 ± 8 cm, weight: 75 ± 9 kg; mean ± SD) performed in three separate laboratory visits, a maximal oxygen uptake (VO₂max) test, an isocapnic (end-tidal CO₂ tension (PetCO₂) clamped at 40 ± 1 mmHg), and an ambient air controlled-pace constant load high-intensity ergometer cycling to exhaustion, while MCA V_mean (transcranial Doppler ultrasound) and ScO₂ (near-infrared spectroscopy) were determined. Duration of exercise (12 min 25 s ± 1 min 18 s) was matched by performing the isocapnic trial first. Pulmonary VO₂ was 90 ± 6% versus 93 ± 5% of the maximal value (P = .012) and PetCO₂ 40 ± 1 versus 34 ± 4 mmHg (P < .05) during the isocapnic and control trials, respectively. During the isocapnic trial MCA V_mean increased by 16 ± 13% until clamping was applied and continued to increase (by 14 ± 28%; P = .017) until the end of exercise, while there was no significant change during the control trial (P = .071). In contrast, ScO₂ decreased similarly in both trials (−3.2 ± 5.1% and −4.1 ± 9.6%; P < .001, isocapnic and control, respectively) at exhaustion. The reduction in prefrontal cortex oxygenation during maximal exercise does not depend solely on lowered cerebral blood flow as indicated by middle cerebral blood velocity.     

A segmented k-space velocity mapping protocol for quantification of renal artery blood plow during breath-holding

Two Important prerequisites for MR velocity mapping of pulsatile motion are synchronization of the sequence execution to the time course of the flow pattern and robustness toward loss of signal in complex flow fields. Synchronization is normally accomplished by using either prospective ECG triggering or so-called retrospective gating. However, if the studied vessel moves periodically in space as a result of respiratory motion, as in the case of renal arteries, a second synchronization with respect to the vessel motion in space may be necessary. One method to overcome this problem is to use the segmented k-space technique, in which the entire data acquisition can be made within a breath-hold by the sampling of several phase-encoding lines within a small time window during each heart cycle. The aim of this study was to investigate the performance of a segmented k-space velocity mapping protocol for renal artery flow determination. The protocol uses 16 phase-encoding lines per heart beat during 16 heart cycles and gives a temporal velocity resolution of 160 msec. Comparison with a conventional ECG-triggered velocity mapping protocol was made in phantoms as well as in volunteers. In our study, both methods showed sufficient robustness toward complex flow in a phantom model. In comparison with the ECG technique, the segmentation technique reduced vessel blurring and pulsatility artifacts caused by respiratory motion, and average flow values obtained in vivo in the left renal artery agreed between the two methods studied. Although presently hampered by a relatively low temporal resolution, velocity mapping with k-space segmentation In combination with breath-holding will benefit from future increased gradient quality, and we assume that in the future the method will become an attractive choice for noninvasive renal artery flow determination.