Twenty‐four‐hour non‐invasive monitoring of systemic haemodynamics and cerebral blood flow velocity in healthy humans

Acute short‐term changes in blood pressure (BP) and cardiac output (CO) affect cerebral blood flow (CBF) in healthy subjects. As yet, however, we do not know how spontaneous fluctuations in BP and CO influence cerebral circulation throughout 24 h. We performed simultaneous monitoring of BP, systemic haemodynamic parameters and blood flow velocity in the middle cerebral artery (MCAV) in seven healthy subjects during a 24‐h period. Finger BP was recorded continuously during 24 h by Portapres and bilateral MCAV was measured by transcranial Doppler (TCD) during the first 15 min of every hour. The subjects remained supine during TCD recordings and during the night, otherwise they were seated upright in bed. Stroke volume (SV), CO and total peripheral resistance (TPR) were determined by Modelflow analysis. The 15 min mean value of each parameter was assumed to represent the mean of the corresponding hour. There were no significant differences between right vs. left, nor between mean daytime vs. night time MCAV. Intrasubject comparison of the twenty‐four 15‐min MCAV recordings showed marked variations (P < 0.001). Within each single 15‐min recording period, however, MCAV was stable whereas BP showed significant short‐term variations (P < 0.01). A day–night difference in BP was only observed when daytime BP was evaluated from recordings in the seated position (P < 0.02), not in supine recordings. Throughout 24 h, MCAV was associated with SV and CO (P < 0.001), to a lesser extent with mean arterial pressure (MAP; P < 0.005), not with heart rate (HR) or TPR. These results indicate that in healthy subjects MCAV remains stable when measured under constant supine conditions but shows significant variations throughout 24 h because of activity. Moreover, changes in SV and CO, and to a lesser extent BP variations, affect MCAV throughout 24 h.     

Twenty-four-hour non-invasive monitoring of systemic haemodynamics and cerebral blood flow velocity in healthy humans

Acute short-term changes in blood pressure (BP) and cardiac output (CO) affect cerebral blood flow (CBF) in healthy subjects. As yet, however, we do not know how spontaneous fluctuations in BP and CO influence cerebral circulation throughout 24 h. We performed simultaneous monitoring of BP, systemic haemodynamic parameters and blood flow velocity in the middle cerebral artery (MCAV) in seven healthy subjects during a 24-h period. Finger BP was recorded continuously during 24 h by Portapres and bilateral MCAV was measured by transcranial Doppler (TCD) during the first 15 min of every hour. The subjects remained supine during TCD recordings and during the night, otherwise they were seated upright in bed. Stroke volume (SV), CO and total peripheral resistance (TPR) were determined by Modelflow analysis. The 15 min mean value of each parameter was assumed to represent the mean of the corresponding hour. There were no significant differences between right vs. left, nor between mean daytime vs. night time MCAV. Intrasubject comparison of the twenty-four 15-min MCAV recordings showed marked variations (P < 0.001). Within each single 15-min recording period, however, MCAV was stable whereas BP showed significant short-term variations (P < 0.01). A day-night difference in BP was only observed when daytime BP was evaluated from recordings in the seated position (P < 0.02), not in supine recordings. Throughout 24 h, MCAV was associated with SV and CO (P < 0.001), to a lesser extent with mean arterial pressure (MAP; P < 0.005), not with heart rate (HR) or TPR. These results indicate that in healthy subjects MCAV remains stable when measured under constant supine conditions but shows significant variations throughout 24 h because of activity. Moreover, changes in SV and CO, and to a lesser extent BP variations, affect MCAV throughout 24 h.     

Grip forces exerted against stationary held objects during gravity changes

 In the present study, grip forces exerted against a stationary held object were recorded during parabolic flights. Such flight maneuvers induce changes of gravity with two periods of hypergravity, associated with a doubling of normal terrestrial gravity, and a 20 s period of microgravity. Accordingly, the object’s weight changed from being twice as heavy as normally experienced and weightless. Grip-force recordings demonstrated that force control was seriously disturbed only during the first experience of hyper- and microgravity, with the grip forces being exceedingly high and yielding irregular fluctuations. Thereafter, however, grip force traces were smooth, the force level was scaled to the object’s weight under normal and high-G conditions, and the grip force changed in parallel with the weight during the transitions between hyper- and microgravity. In addition, during weightlessness, when virtually no force was necessary to stabilize the object, a low force was established, which obviously represented a reasonable safety margin for preventing possible perturbations. Thus, all relevant aspects of grip-force control observed under normal gravity conditions were preserved during gravity changes induced by parabolic flights. Hence, grip-force control mechanisms were able to cope with hyper- and microgravity, either by incorporating relevant receptor signals, such as those originating from cutaneous mechanoreceptors, or by adequately including perceived gravity signals into control programs. However, the adaptation to the uncommon gravity conditions was not complete following the first experience; finer tuning of the control system to both hyper- and microgravity continued over the measurement interval, presumably with a longer observation period being necessary before a stable performance can be reached. Received: 23 April 1998 / Accepted: 20 December 1998     

Towards increased data transmission rate for a three-class metabolic brain–computer interface based on transcranial Doppler ultrasound

In this study, we conducted an offline analysis of transcranial Doppler (TCD) ultrasound recordings to investigate potential methods for increasing data transmission rate in a TCD-based brain–computer interface. Cerebral blood flow velocity was recorded within the left and right middle cerebral arteries while nine able-bodied participants alternated between rest and two different mental activities (word generation and mental rotation). We differentiated these three states using a three-class linear discriminant analysis classifier while the duration of each state was varied between 5 and 30 s. Maximum classification accuracies exceeded 70%, and data transmission rate was maximized at 1.2 bits per minute, representing a four-fold increase in data transmission rate over previous two-class analysis of TCD recordings.     

Real-time continuous neuromonitoring combines transcranial cerebral Doppler with near-infrared spectroscopy cerebral oxygen saturation during total aortic arch replacement procedure: a pilot study

The purpose of this investigation was to use combined transcranial cerebral Doppler (TCD) and near-infrared spectroscopy cerebral oxygen saturation (NIRS) during total aortic arch replacement (TAAR) to monitor middle cerebral artery blood flow velocity and regional cerebral oximetry (rSO(2)) changes to provide a clinical basis for protective measures that may decrease injury of the central nervous system. Consecutive 12 adult patients underwent deep hypothermic circulatory arrest (DHCA) and antegrade selective cerebral perfusion (ASCP) during TAAR. A TCD probe was placed at the temporal windows after induction of anesthesia and the NIRS probe placed on the forehead of patients to collect perioperative, intraoperative, and postoperative hemodynamic parameters, and cerebral blood flow (CBF) and rSO(2) during cardiopulmonary bypass (CPB). In this retrospective case series, all patients survived, and there were no postoperative neurologic complications. There was no significant correlation between the mean arterial pressure and rSO(2). The middle cerebral artery mean velocity (VmMCA) and rSO(2) were significantly correlated, and main pump flow significantly correlated with rSO(2). After ASCP, VmMCA, rSO(2), and venous oxygen saturation were significantly lower than before ASCP, but VmMCA and rSO(2) returned to pre-CPB levels postoperatively. After off pump, the flow of ASCP showed a significant positive correlation with VmMCA and rSO(2). During DHCA when ASCP flow was lower than 5 ml/kg/min, TCD could not detect the MCA blood flow signal. When the flow of ASCP was above keeping around 10 ml/kg/min, MCA CBF velocity was maintained and rSO(2) > 45%. The combination of TCD and NIRS can be effective in monitoring brain function during DHCA with ASCP and may provide a guide for decreasing brain injury during the TAAR procedure.     

The carotid artery as an alternative site for dynamic autoregulation measurement: an inter-observer reproducibility study

The internal carotid artery (ICA) has been proposed as an alternative site to the middle cerebral artery (MCA) to measure dynamic cerebral autoregulation (dCA) using transcranial Doppler ultrasound (TCD). Our aim was to test the inter-operator reproducibility of dCA assessment in the ICA and the effect of interaction amongst different variables (artery source × operator × intra-subject variability). Two operators measured blood flow velocity using TCD at the ICA and MCA simultaneously on each side in 12 healthy volunteers. The autoregulation index (ARI) was estimated by transfer function analysis. A two-way repeated measurements ANOVA with post-hoc Tukey tested the difference between ARI by different operators and interaction effects were analysed based on the generalized linear model. In this healthy population, no significant differences between operator and no interaction effects were identified amongst the different variables. This study reinforced the validity of using the ICA as an alternative site for the assessment of dCA. Further work is needed to confirm and extend our findings, particularly to disease populations.     

A new pulsatile flow visualization method using a photochromic dye with application to Doppler ultrasound

A nonintrusive method for the visualization of pulsatile flow velocity profiles is described. The method is based on the use of a photochromic dye that is added to the fluid being studied and a nitrogen laser which excites the dye producing a marker “line” whose movement can be photographed. A microcomputer is used as a system controller, to coordinate the system timing and to manage the data transfer. The method used for analysis of the photographs to determine the velocity profiles is described. Examples are presented of instantaneous velocity profiles obtained from velocity waveforms that are similar to those of the femoral artery. In addition, application of the system for studying the relationship between Doppler ultrasound spectral recordings and flow velocity profiles is discussed.     

Enhanced cerebral CO2 reactivity during strenuous exercise in man

Light and moderate exercise elevates the regional cerebral blood flow by ~20% as determined by ultrasound Doppler sonography (middle cerebral artery mean flow velocity; MCA V _mean). However, strenuous exercise, especially in the heat, appears to reduce MCA V _mean more than can be accounted for by the reduction in the arterial CO₂ tension (P _aCO₂). This study evaluated whether the apparently large reduction in MCA V _mean at the end of exhaustive exercise relates to an enhanced cerebrovascular CO₂ reactivity. The CO₂ reactivity was evaluated in six young healthy male subjects by the administration of CO₂ as well as by voluntary hypo- and hyperventilation at rest and during exercise with and without hyperthermia. At rest, P _aCO₂ was 5.1±0.2 kPa (mean ± SEM) and MCA V _mean 50.7±3.8 cm s⁻¹ and the relationship between MCA V _mean and P _aCO₂ was linear (double-log slope 1.1±0.1). However, the relationship became curvilinear during exercise (slope 1.8±0.1; P<0.01 vs. rest) and during exercise with hyperthermia (slope 2.3±0.3; P<0.05 vs. control exercise). Accordingly, the cerebral CO₂ reactivity increased from 30.5±2.7% kPa⁻¹ at rest to 61.4±10.1% kPa⁻¹ during exercise with hyperthermia (P<0.05). At exhaustion P _aCO₂ decreased 1.1±0.2 kPa during exercise with hyperthermia, which, with the determined cerebral CO₂ reactivity, accounted for the 28±10% decrease in MCA V _mean. The results suggest that during exercise changes in cerebral blood flow are dominated by the arterial carbon dioxide tension.     

偏头痛患者脑动脉变异及脑血流动力学特征

目的:观察偏头痛患者脑动脉变异及脑血流动力学特征,探讨偏头痛的病因及可能的发病机制。方法:对68例偏头痛患者行全脑血管造影检查,观察其脑血管的发育、变异情况,并进行分类;经颅多谱勒检测双侧大脑前、中、后动脉血流速度。结果:大脑后动脉发育异常29例,大脑前动脉发育异常17例,颈内动脉发育异常2例;总变异率为70.59%。经颅多谱勒显示发育异常侧脑血流速度减慢。结论:脑动脉变异引起的脑血流动力学改变可能是导致偏头痛发生的主要机制。     

Differences between middle cerebral artery blood velocity waveforms of young and postmenopausal women

OBJECTIVE: We characterized middle cerebral artery (MCA) blood flow velocity waveforms measured by transcranial Doppler ultrasonography in premenopausal (26.6 +/- 6.1 years, mean +/- SD) and postmenopausal (54.0 +/- 3.6 years) women, of whom six were receiving hormone therapy (PM-HT) and seven were not (PM-non-HT). We hypothesized that feature points on MCA waveforms are altered in postmenopausal women compared with those in young women. DESIGN: A short protocol involved maintaining end-tidal PO2 at euoxia (88 mm Hg) and end-tidal PCO2 at 1.5 mm Hg above eucapnic values using a dynamic end-tidal forcing system. Doppler data for the velocity spectral outline (Vp) were collected every 10 ms, and velocity waveform analyses were done on a beat-by-beat basis. Waveform features were identified over each cardiac cycle, including the average Vp (VCYC), maximum acceleration (AMAX), and the ratio of the velocity at the reflected wave and the velocity at peak systole (VR:VMAX). RESULTS: VCYC was unchanged between premenopausal and postmenopausal women (69.4 +/- 9.6 and 67.5 +/- 11.1 cm/s, respectively). AMAX was significantly higher (P = 0.007) in premenopausal women (987.9 +/- 280.7 cm/s) compared with postmenopausal women (743.1 +/- 100.3). Conversely, VR:VMAX was significantly smaller (P < 0.001) in premenopausal women (0.90 +/- 0.09) compared with postmenopausal women (1.11 +/- 0.05). In postmenopausal women, the reflected wave is higher than the maximum velocity at peak systole, suggesting the presence of a shoulder in the MCA waveform. CONCLUSIONS: Further investigations are required to assess whether this waveform analysis can provide insight into pathophysiologic changes in cerebral hemodynamics with aging.     

Do hematocrit and serum fibrinogen influence transcranial Doppler measurements?

To investigate the effect of hematocrit and serum fibrinogen on transcranial Doppler ultrasound (TCD) measurements, we performed, TCD tests and measured hematocrit and serum fibrinogen concentrations in 112 healthy adult volunteers. The mean velocities of the middle cerebral (r = -.37, p < .0001), internal carotid at siphon (r = -.14, p < .05) and cervical level (r = -.14, p < .05), vertebral (r = -.21, p < .005) and the basilar artery (r = -.33, p < .001) were significantly and inversely correlated with hematocrit, while serum fibrinogen weakly affected the mean velocities of the internal carotid artery. The subjects with low hematocrit (< or = 40%) showed significantly higher mean velocities of the middle cerebral, vertebral and basilar arteries than those with high hematocrit (> 40%). Considering the influence of the subject''s age and gender, hematocrit is the strongest factor influencing the velocities of the middle cerebral and the basilar artery. These results suggest that hematocrit is an important variable for TCD measurements of the cerebral blood velocities and should be taken into account in TCD application.     

TCD血流动力学指标评价急性脑梗死患者认知功能损伤程度的价值

目的 探讨经颅多普勒超声（TCD）检查评价急性脑梗死（ACI）后患者认知功能受损的价值。方法 选取2015年5月~2019年4月我院收治的ACI后合并认知功能障碍的患者110例设为认知障碍组,ACI后认知功能正常患者110例设为ACI组,比较两组的大脑中动脉（MCA）平均血流速度（Vm）、阻力指数（RI）、搏动指数（PI）、MCA的屏气指数（BHI）、不同程度认知障碍患者Vm、RI、PI、BHI测定值及认知障碍患者的MCA的Vm、RI、PI、BHI测定值与MoCA评分的关系。结果 认知障碍组的PI测定值高于ACI组,差异具有统计学意义（P＜0.05）;认知障碍组的BHI测定值、MoCA评分低于ACI组,差异具有统计学意义（P＜0.05）;两组Vm、RI测定值比较,差异无统计学意义（P＞0.05）;中度认知障碍患者的PI测定值高于轻度认知障碍患者,差异具有统计学意义（P＜0.05）;中度认知障碍患者BHI测定值、MoCA评分低于轻度认知障碍患者,差异具有统计学意义（P＜0.05）;认知障碍组PI测定值与MoCA评分呈负相关（r=-0.492,P=0.000）;认知障碍组的BHI测定值与MoCA评分呈正相关（r=0.507,P=0.000）;两组Vm、RI与MoCA评分无相关性（r=-0.084、-0.107,P=0.226、0.214）。结论 ACI患者认知功能障碍患者MCA的PI指数升高、BHI降低,TCD血流动力学指标用于评价ACI患者发生认知功能损害具有一定的临床价值。     

The effect of blood pressure calibrations and transcranial Doppler signal loss on transfer function estimates of cerebral autoregulation

There are methodological concerns with combined use of transcranial Doppler (TCD) and Finapres to measure dynamic cerebral autoregulation. The Finapres calibration mechanism ("physiocal") causes interruptions to blood pressure recordings. Also, TCD is subject to signal loss due to probe movement. We assessed the effects of "physiocals" and TCD signal loss on transfer function estimates in recordings of 45 healthy subjects. We added artificial "physiocals" and removed sections of TCD signal from 5 min Finapres and TCD recordings. We also compared transfer function results from 5 min time series with time series as short as 1 min. Accurate transfer function estimates can be achieved in the 0.03-0.07 Hz band using beat-by-beat data with linear interpolation, while data loss is less than 10s. At frequencies between 0.07 and 0.5 Hz, transfer function estimates become unreliable with 5s of data loss every 50s. 2s data loss only affects frequency bands above 0.15Hz. Finally, accurate transfer function assessment of autoregulatory function can be achieved from time series as short as 1min, although gain and coherence tend to be overestimated at higher frequencies.     

Intracranial flow patterns at increasing intracranial pressure

Summary In the course of a pilot study, changes in intracranial pressure were compared with the transcranial Doppler findings of the middle cerebral artery. The cases of five patients were discussed who developed dissociated brain death in spite of intensive therapeutic measures. The studies showed that changes of the intracranial pressure influenced the flow patterns considerably: at increasing intracranial pressure (decreasing cerebral perfusion pressure) a progressive reduction of the systolic and above all diastolic flow velocities and finally a pendular flow occurred. These changes could be recorded quantitatively by means of the Pourcelot index and the mean flow velocity. Acute changes of the intracranial pressure can be detected at an early stage by noninvasive transcranial Doppler studies and can be followed by adequate intensive therapy.Abbreviations CPP Mean cerebral perfusion pressure - ICP Intracranial pressure - MAP Mean systemic arterial pressure - MCA Middle cerebral artery - MFV Mean flow velocity - pCO₂ Carbon dioxide tension - R Index de résistance=Pourcelot index - TCD Transcranial Doppler Supported by the DFG (SFB 330)     

Impact of age on critical closing pressure of the cerebral circulation during dynamic exercise in humans

Limited information is available regarding cerebral vascular responses to dynamic exercise in older adults. We examined the influence of age on exercise-induced changes in the critical closing pressure (CCP) of the cerebral vasculature. Twelve young and twelve older subjects performed two bouts of steady-state cycling at low and moderate intensities (30 and 50% heart rate reserve). Mean arterial pressure (MAP), middle cerebral artery blood velocity (MCA V) and partial pressure of end-tidal carbon dioxide ( ) were measured. The CCP was estimated by linear extrapolation of pairs of systolic and diastolic blood pressure and MCA V waveforms. Exercise-induced increases in MAP were greater in older subjects (P < 0.01), while mean MCA V (MCA V(mean)) responses to exercise were similar between groups (P = 0.59). The CCP was elevated from rest during low- and moderate-intensity exercise in both groups (moderate exercise: young, +13 ± 2 mmHg and older, +22 ± 2 mmHg; P < 0.01), with the older subjects exhibiting greater increases in CCP during both exercise intensities (moderate exercise: young, +43 ± 9% rest versus older, +153 ± 45% rest; P = 0.04). In contrast, cerebral vascular conductance index (MCA V(mean)/MAP; CVCi) was only decreased during moderate exercise in older subjects (P < 0.01) and CVCi was not altered from rest in young subjects during low- or moderate-intensity cycling. No age-group differences were observed in at rest or during two intensities of exercise (P = 0.40). These data demonstrate that older subjects exhibit larger exercise-induced increases in CCP and decreases in CVCi. Thus, ageing is associated with greater increases in cerebral vascular tone during low- and moderate-intensity dynamic exercise.     

脑动脉硬化的脑电图、脑电地形图和经颅多普勒超声检查的评价研究

目的：探讨脑电图（EEG）、脑电地形图（BEAM）及经颅多普勒超声（TCD）三项检查联合应用于脑动脉硬化的诊断价值。方法：208例诊断为脑动脉硬化的病人,均在发病一周内进行脑电图、脑电地形图及经颅多普勒超声检查。结果：脑电图异常74例,脑电地形图异常125例,经颅多普勒超声异常为100%。脑电图与经颅多普勒超声相比（χ2=25.06,P〈0.001）经处理有极显著差异,脑电地形图与经颅多普勒超声相比（χ2=4.12,P〈0.05）经处理有统计学差异。结论：三项检查联合应用对脑动脉硬化病人进行观察,是判断病变程度性质的重要依据,并可对临床疗效提供一定的参考。为评估脑动脉硬化病人的大脑动脉状况提供有益的信息。     

Influence of upper body position on middle cerebral artery blood velocity during continuous positive airway pressure breathing

Continuous positive airway pressure (CPAP) is a treatment modality for pulmonary oxygenation difficulties. CPAP impairs venous return to the heart and, in turn, affects cerebral blood flow (CBF) and augments cerebral blood volume (CBV). We considered that during CPAP, elevation of the upper body would prevent a rise in CBV, while orthostasis would challenge CBF. To determine the body position least affecting indices of CBF and CBV, the middle cerebral artery mean blood velocity (MCA V _mean) and the near-infrared spectroscopy determined frontal cerebral hemoglobin content (cHbT) were evaluated in 11 healthy subjects during CPAP at different body positions (15° head-down tilt, supine, 15°, 30° and 45° upper body elevation). In the supine position, 10 cmH₂O of CPAP reduced MCA V _mean by 9 ± 3% and increased cHbT by 4 ± 2 μmol/L (mean ± SEM); (P < 0.05). In the head-down position, CPAP increased cHbT to 13 ± 2 μmol/L but left MCA V _mean unchanged. Upper body elevation by 15° attenuated the CPAP associated reduction in MCA V _mean (−7 ± 2%), while cHbT returned to baseline (1 ± 2 μmol/L). With larger elevation of the upper body MCA V _mean decreased progressively to −17 ± 3%, while cHbT remained unchanged from baseline. These results suggest that upper body elevation by ∼15° during 10 cmH₂O CPAP prevents an increase in cerebral blood volume with minimal effect on cerebral blood flow.     

Neuroprotective effects of the novel brain-penetrating antioxidant U-101033E and the spin-trapping agent α-phenyl-N-tert-butyl nitrone (PBN)

Literature on the therapeutic efficacy of free radical scavengers suggests that drugs that are able to cross the blood-brain barrier are more effective in protecting the brain from ischemic damage. However, the exact mechanisms by which brain-penetrating antioxidants act have yet not been delineated. We compared the neuroprotective potential of the newly discovered pyrrolopyrimidine U-101033E with that of α-phenyl-N-tert-butyl nitrone (PBN) and investigated their influence on cerebral blood flow. Thirty male Sprague-Dawley rats were subjected to 90 min of middle cerebral artery (MCA) occlusion by an intraluminal filament. Local cerebral blood flow (LCBF) was bilaterally recorded by laser Doppler flowmetry. Neurological deficits were quantified daily. Infarct volume was assessed after 7 days. MCA occlusion reduced ipsilateral LCBF to 20–30% of baseline. After reperfusion, postischemic hyperemia was followed by a decrease in LCBF to about 70% of baseline. There was no difference in LCBF among groups. U-101033E improved neurological function and reduced infarct volume by 52% (P<0.05). Improvement of neurological function and reduction of infarct volume (–25%) in animals treated with PBN was not significant. We conclude that U-101033E has superior neuroprotective properties compared with PBN. Neither drug improves blood flow during ischemia and 1 h of reperfusion. The mechanisms by which these brain-penetrating antioxidants act remain to be clarified. Received: 17 March 1999 / Accepted: 12 July 1999     

脑导纳图与经颅多普勒对缺血性脑血管病患者临床评价

缺血性脑血管病多发于中老年人,常引起脑血管的血液动力学改变.我室利仪及EME公司的TC-2020型经颅多普勒超声仪对47例缺血性脑血管病患者进行脑导纳图及经颅多普勒检测,观察其Ⅰ项指数、Ⅲ相面积、流入时间和颅内血管(ACA、MCA、PCA)的流速、PI值及频谱等指标,并对其血液动力学变化进行综合分析评价.检测结果表明脑导纳图异常率72.3%,TCD异常率80%,进行统计学处理后脑导纳图的三项指标Ⅰ项指数、Ⅲ相面积、流入时间均与对照组有显著差异(P＜0.05);经颅多普勒检测中各项指标Vs、Vm、PI、频谱形态及音频与正常对照组亦有显著差异(P＜0.05).此项结果表明缺血性脑血管病患者有不同程度的动脉硬化、血管顺应性减退、血管阻力增大.因此对脑血管病患者进行脑导纳及经颅多普勒检测可较客观的反应出患者的脑血管硬化程度及脑动脉供血情况,为临床提供了客观的依据与参考.