Changes In Mean Velocity Research Articles

Time-Lapse Cross-Well Monitoring of CO2 Sequestration Using Coda Wave Interferometry

In this study, we explored the capability of coda wave interferometry (CWI) for monitoring CO2 storage by estimating the seismic velocity changes caused by CO2 injection. Given that the CWI method is highly efficient, the primary aim of this study was to provide a quick detection tool for the long-term monitoring of CO2 storage safety. In particular, we looked at monitoring with a cross-well geometry. We also expected that CWI could help to reduce the inversion errors of existing methods. Time-lapse upgoing waves and downgoing waves from two-component datasets were utilized to efficiently monitor the area between the wells and provide a quick indication of possible CO2 leakage. The resulting mean velocity changes versus the depth indicated the depth where velocity changes occurred. Combining the upgoing and downgoing wavefields provided a more specific indication of the depth range for changes. The calculated velocity changes were determined using the time shift between the time-lapse wavefields caused by CO2 injection/leakage. Hence, the resulting velocity changes were closely related to the ratio of propagation path length through the CO2 injection/leakage layer over the length of the entire travel path. The results indicated that the noise level and repeatability of the time-lapse datasets significantly influenced the results generated using CWI. Therefore, denoising and time-lapse processing were very important for improving the detectability of any change. Applying CWI to time-lapse cross-well surveys can be an effective tool for monitoring CO2 in the subsurface at a relatively low computational cost. As a highly efficient monitoring method, it is sensitive to changes in the seismic response caused by velocity changes in the subsurface and provides additional constraints on the inversion results from conventional travel time tomography and full waveform inversion.

Effect of Blood Transfusion on Cerebral Hemodynamics and Vascular Topology Described by Computational Fluid Dynamics in Sickle Cell Disease Patients.

The main objective of this study was to demonstrate that computational fluid dynamics (CFD) modeling can be used to study the contribution of covert and overt vascular architecture to the risk for cerebrovascular disease in sickle cell disease (SCD) and to determine the mechanisms of response to therapy such as chronic red blood cell (cRBC) transfusions. We analyzed baseline (screening), pre-randomization and study exit magnetic resonance angiogram (MRA) images from 10 (5 each from the transfusion and observation arms) pediatric sickle SCD participants in the silent cerebral infarct transfusion (SIT) trial using CFD modeling. We reconstructed the intracranial portion of the internal carotid artery and branches and extracted the geometry using 3D Slicer. We cut specific portions of the large intracranial artery to include segments of the internal carotid, middle, anterior, and posterior cerebral arteries such that the vessel segment analyzed extended from the intracranial beginning of the internal carotid artery up to immediately after (~0.25 inches) the middle cerebral artery branching point. Cut models were imported into Ansys 2021R2/2022R1 and laminar and time-dependent flow simulation was performed. Change in time averaged mean velocity, wall shear stress, and vessel tortuosity were compared between the observation and cRBC arms. We did not observe a correlation between time averaged mean velocity (TAMV) and mean transcranial Doppler (TCD) velocity at study entry. There was also no difference in change in time average mean velocity, wall shear stress (WSS), and vessel tortuosity between the observation and cRBC transfusion arms. WSS and TAMV were abnormal for 2 (developed TIA) out of the 3 participants (one participant had silent cerebral infarctions) that developed neurovascular outcomes. CFD approaches allow for the evaluation of vascular topology and hemodynamics in SCD using MRA images. In this proof of principle study, we show that CFD could be a useful tool and we intend to carry out future studies with a larger sample to enable more robust conclusions.

Increase and Decrease in Velocity and Force During Exercise with a Hybrid Robotic-FES Rehabilitation System.

Early rehabilitation is beneficial for stroke patients, but it is often delayed since the patients are often bedbound due to their general condition. New robotic rehabilitation devices such as ROBERT® enable patients to exercise even while bedbound. During pilot testing of an automated FES-delivery system combined with ROBERT®, we observed both increased and decreased exerted velocity and interaction force during repetitive exercising with the system. The goal of the current study was thus to investigate the extent of both potentiation and fatigue, as assessed in the velocity and interaction force produced in response to repetitive robotic-FES exercising. Eight healthy subjects completed 50 repetitions of leg-press exercises using the hybrid robotic-FES system. For individual subjects, significant changes were found for both mean and maximal velocities and interaction forces exerted during the exercise. Roughly half of the subjects had an increase in maximal velocity and interaction force during the exercise, and half exhibited an increase in mean velocity, whereas three subjects had an increase in mean interaction force during the exercise. The changes in mean velocity were in the range of -40.6 to 30.9% and for the maximal velocity they were in the range of -21.9 to 22.0%. The changes for mean interaction force were in the range of -5.8 to 11.0%, while for the maximal interaction force, they were in the range of -7.8 to 14.4%. These changes might pose significant challenges for future developments of hybrid robotic-FES rehabilitation systems, as the system must be able to comply with the observed changes, and appropriately adapt to them in order to maintain efficacy and safety.

Impact of inlet and outlet opening height variation on the air quality and ventilation efficiency in the on-top wind catcher buildings: A CFD simulation

This paper examines the role of wind-catcher height on the quality of ventilation inside the building. The base sample in this study includes a single-zone isolated building combined into a one-sided wind catcher as an inlet. Difference between inlet and outlet opening height is considered as an independent variable and ventilation quality and efficiency are considered as dependent variables. The results showed that by increasing the height of opening as a wind-catcher in the inlet facade, the airflow rate increases, the velocity decreases and the age of air increases. By increasing the height of the outlet opening, as a window from the floor to the ceiling of the room, there is no noticeable change in mean velocity, mean age of air and airflow rate. However, by transforming the outlet opening form a window to an on-top wind-catcher, the mean velocity and airflow rate decrease and the mean age of air increase. Also, by increasing the height of the wind catcher on the outlet facade, the ventilation efficiency increases too. High-resolution 3D steady RANS CFD simulations of cross ventilation are performed for all case studies.

Analysis of the impact of the South-to-North water diversion project on water balance and land subsidence in Beijing, China between 2007 and 2020

After operating the middle route of South-to-North Water Diversion Project (SNWDP), the total water transfer to Beijing has exceeded 5.0 km3, bringing significant changes to the water use structure of Beijing. This article compiles historic data from 2007 to 2020 to analyze changes in water circulation, groundwater level, climate factors and subsidence patterns in Beijing following implementation of the middle SNWDP. It is found that the main current pressure on Beijing's water supply has come from improved living standards, the gradual popularization of water-using appliances, and a rapid development of the accommodation and catering industries. An InSAR time series approach was used to map subsidence in Beijing between 2007 and 2020 using satellite images from Sentinel-1A/B, Radarsat-2 and ALOS-1. Climate factors including precipitation and evapotranspiration were estimated using the Penman-Monteith-Leuning Evapotranspiration V2 (PML_V2) product. By compiling ground subsidence data for Beijing and corresponding climate data, the impact of the SNWDP and climate factors on groundwater levels and ground subsidence in Beijing were examined We identified three periods to characterize the changes of surface displacement after implementation of the SNWDP as a) the pre-effect stage, b) the effective stage, and c) the post-effective stage. The contribution of the SNWDP was apparent at the second stage, alleviating the problem of land subsidence to some extent. The ease of subsidence at different stages are accounted for 4%, 26.5%, and 41.7%, respectively, in terms of the mean velocity changes. Based on the result of some general circulation models. Precipitation in the Beijing region is expected to increase over the next decade, implying a greater likelihood of rapid groundwater recovery. However, although groundwater is expected to recover in the long run, climate extremes in the future could possibly challenge the success of SNWDP during certain dry periods.

Proof-of-Concept of the Virtual Reality Comprehensive Balance Assessment and Training for Sensory Organization of Dynamic Postural Control.

Accurate quantification of the impact of visual, somatosensory, and vestibular systems on postural control may inform tailor-made balance intervention strategies. The aim of this proof-of-concept study was to determine the safety, sense of presence, system usability, and face validity of a newly developed Virtual Reality Comprehensive Balance Assessment and Training (VR-ComBAT) in healthy young individuals. The VR-ComBAT included six balance condition: (1) stable surface with fixed virtual reality (VR) surroundings; (2) stable surface with blacked out VR surroundings; (3) stable surface with VR visual conflict; (4) unstable surface with fixed VR surroundings; (5) unstable surface with blacked out VR surroundings; and (6) unstable surface with VR visual conflict. Safety was evaluated using the number of adverse events, including scores on the Simulator Sickness Questionnaire. Sense of presence was evaluated using the igroup Presence Questionnaire (iPQ). System usability was assessed using the Systems Usability Scale (SUS). Friedman analyses with post hoc Wilcoxon Signed Rank tests were employed to demonstrate face validity by quantifying center of pressure (COP) changes in mean distance, mean velocity, and mean frequency in the anteroposterior (AP) and mediolateral (ML) direction across the six conditions. Twenty-three participants (27.4 ± 8.0 years old; 13 women) reported no adverse events. Participants scores on average 44.9 ± 9.6 on the iPQ and 79.7 ± 9.9 on the SUS. Post hoc analyses showed significant changes in COP-based measures when compared to baseline. The mean frequency change of COP showed direction-dependence in which increased frequency change in AP was observed while decreased change in ML was noted. The VR-ComBAT provides a safe, feasible, and cost-effective VR environment that demonstrates consistent sensory re-weighting between visual, somatosensory, and vestibular systems. Future studies should investigate whether VR-ComBAT can be used to inform precision rehabilitation of balance and fall prevention in older adults without and with neurological conditions.

Sensitivity of the iLOAD® Application for Monitoring Changes in Barbell Velocity Following Power- and Strength-Oriented Resistance Training Programs.

To evaluate the sensitivity of the iLOAD® application to detect the changes in mean barbell velocity of complete sets following power- and strength-oriented resistance training (RT) programs. Twenty men were randomly assigned to a power training group (countermovement jump and bench press throw at 40% of the 1-repetition maximum [1RM]) or strength training group (back squat and bench press at 70% to 90% of 1RM). Single sets of 10 repetitions at 25% and 70% of 1RM during the back squat and bench press exercises were assessed before and after the 4-week RT programs simultaneously with the iLOAD® application and a linear velocity transducer. The power training group showed a greater increment in velocity performance at the 25% of 1RM (effect size range = 0.66-1.53) and the 70% of 1RM (effect size range = 0.11-0.30). The percent change in mean velocity after the RT programs highly correlated between the iLOAD® application and the linear velocity transducer for the back squat (r range = .85-.88) and bench press (r range = .87-.93). However, the iLOAD® application revealed a 2% greater increase in mean velocity after training compared to the linear velocity transducer. The iLOAD® application is a cost-effective, portable, and easy-to-use tool which can be used to detect changes in mean barbell velocity after power- and strength-oriented RT programs.

The effects of Kinesiology Tape on static postural control in individuals with functional ankle instability

ObjectiveTo investigate if applying Kinesiology Tape (KT) on the unstable ankle may improve static postural control in individuals with Functional ankle instability. DesignA repeated measured study. Participants performed a series of static quiet bipedal and unipedal stances on a force platform. Measurements were taken at three different times: baseline or no tape, immediately and 24 h after the taping application with the tape remaining on the ankle. SettingA university’s psychomotor laboratory. ParticipantsTwenty young adults with Functional ankle instability aged from 18 to 30 years old. Outcome measures: Postural control was assessed by four measures derived from the centre of pressure data: Area of 95% Confidence ellipse, standard deviation of displacements, mean velocity and mean power frequency. The analysis of variance (ANOVA) was performed to determine any significant improvement in postural control over time due to KT. ResultsOnly minor changes in mean velocity and MPF in unipedal stances were observed immediately after KT application. However, the overall results indicated statistically insignificant improvements in postural control neither immediately after KT application nor after 24 h. ConclusionResults suggest that the use of KT did not affect bipedal and unipedal stances of individuals with functional ankle instability.

Perioperative CTEPH patient monitoring with 2D phase-contrast MRI reflects clinical, cardiac and pulmonary perfusion changes after pulmonary endarterectomy.

Magnetic resonance imaging (MRI) is an emerging tool for diagnosis and treatment monitoring of chronic thromboembolic pulmonary hypertension (CTEPH). The current study aims to identify central pulmonary arterial hemodynamic parameters that reflect clinical, cardiac and pulmonary changes after PEA. 31 CTEPH patients, who underwent PEA and received pre- and postoperative MRI, were analyzed retrospectively. Central pulmonary arterial blood flow, lung perfusion and right heart function data were derived from MRI. Mean pulmonary arterial pressure (mPAP) and 5-month follow-up six-minute walk-distance (6MWD) were assessed. After PEA, mPAP decreased significantly and patients achieved a higher 6MWD. Central pulmonary arterial blood flow velocities, pulmonary blood flow (PBF) and right ventricular function increased significantly. Two-dimensional (2D) phase-contrast (PC) MRI-derived average mean velocity, maximum mean velocity and deceleration volume changes after PEA correlated with changes of 6MWD and right heart ejection fraction (RVEF). Deceleration volume is a novel 2D PC MRI parameter showing further correlation with PBF changes. In conclusion, 2D PC MRI-derived main pulmonary hemodynamic changes reflect changes of RVEF, PBF and 5-month follow-up 6MWD and may be used for future CTEPH patient monitoring after PEA.

Respiratory Fluctuation of Peak Systolic Velocities in the Carotid Doppler Waveforms of Patients With Obstructive Airway Disease: Evidence of Pulsus Paradoxus With Experimental Validation.

To characterize fluctuations in peak systolic velocities (PSVs) in Doppler waveforms of the carotid artery in patients with and without obstructive airway disease and in volunteers subjected to incremental levels of airway resistance in an experimental model. The PSV variation in common carotid waveforms was measured in 100 patients who had had a carotid ultrasound examination and no respiratory or carotid disease. This was compared to that of patients who had this study during an admission for acute exacerbation of chronic obstructive pulmonary disease (COPD). The PSV variation was correlated with pulmonary function testing. In addition, 14 healthy volunteers were asked to breathe through 5 resistors. Simultaneous recordings were made of Doppler waveforms in the common carotid artery, cardiac activity, and respiration. Peak systolic velocity changes from inspiration to expiration were calculated. Of the 100 patients without respiratory disease, the magnitude of the PSV variation averaged 6.3 cm/s. Of the 33 patients with COPD, the PSV variation averaged 16.5 cm/s. Nineteen of the 33 patients with COPD had concurrent pulmonary function testing; there was a statistically significant correlation between the PSV variation and forced vital capacity and forced expiratory volume indices. For the volunteers, mean velocity changes were 7.1, 6.6, 8.3, 15.1, and 16.1 cm/s for 0.00-, 2.15-, 3.27-, 3.58-, and 5.77-cm H2 O/L/s levels of breathing resistance, respectively. There was a statistically significant relationship between an increasing airway load and the decline in PSV during inspiration (P = .02). The PSV variation is greater in patients with increased airway resistance. Similar changes are evident in volunteers breathing into resistors. These findings likely reflect pulsus paradoxus.

Development and Evaluation of Maze-Like Puzzle Games to Assess Cognitive and Motor Function in Aging and Neurodegenerative Diseases.

There is currently a need for engaging, user-friendly, and repeatable tasks for assessment of cognitive and motor function in aging and neurodegenerative diseases. This study evaluated the feasibility of a maze-like Numberlink puzzle game in assessing differences in game-based measures of cognition and motor function due to age and neurodegenerative diseases. Fifty-five participants, including young (18–31 years, n = 18), older (64–79 years, n = 14), and oldest adults (86–98 years, n = 14), and patients with Parkinson’s (59–76 years, n = 4) and Huntington’s disease (HD; 35–66 years, n = 5) played different difficulty levels of the Numberlink puzzle game and completed usability questionnaires and tests for psychomotor, attentional, visuospatial, and constructional and executive function. Analyses of Numberlink game-based cognitive (solving time and errors) and motor [mean velocity and movement direction changes (MDC)] performance metrics revealed statistically significant differences between age groups and between patients with HD and older adults. However, patients with Parkinson’s disease (PD) did not differ from older adults. Correlational analyses showed significant associations between game-based performance and movement metrics and performance on neuropsychological tests for psychomotor, attentional, visuospatial, and constructional and executive function. Furthermore, varying characteristics of the Numberlink puzzle game succeeded in creating graded difficulty levels. Findings from this study support recent suggestions that data from a maze-like puzzle game provide potential “digital biomarkers” to assess changes in psychomotor, visuoconstructional, and executive function related to aging and neurodegeneration. In particular, game-based movement measures from the maze-like puzzle Numberlink games are promising as a tool to monitor the progression of motor impairment in neurodegenerative diseases. Further studies are needed to more comprehensively establish the cognitive validity and test–retest reliability of using Numberlink puzzles as a valid cognitive assessment tool.

Which parameters indicate feed-forward neuromuscular control alterations in functional ankle instability during gait initiation?

To investigate if applying Kinesiology Tape (KT) on the unstable ankle may improve static postural control in individuals with Functional ankle instability.A repeated measured study. Participants performed a series of static quiet bipedal and unipedal stances on a force platform. Measurements were taken at three different times: baseline or no tape, immediately and 24 h after the taping application with the tape remaining on the ankle.A university’s psychomotor laboratory.Twenty young adults with Functional ankle instability aged from 18 to 30 years old. Outcome measures: Postural control was assessed by four measures derived from the centre of pressure data: Area of 95% Confidence ellipse, standard deviation of displacements, mean velocity and mean power frequency. The analysis of variance (ANOVA) was performed to determine any significant improvement in postural control over time due to KT.Only minor changes in mean velocity and MPF in unipedal stances were observed immediately after KT application. However, the overall results indicated statistically insignificant improvements in postural control neither immediately after KT application nor after 24 h.Results suggest that the use of KT did not affect bipedal and unipedal stances of individuals with functional ankle instability.

Abnormal transport behaviors in traveling wave system

In general, for a traveling wave system, a particle always follows the wave with wave velocity or moves in the same direction but with a lower velocity. Here, we investigate transport of an inertial particle in a deterministic traveling wave system subjected to a symmetric periodic signal. Our numerical results indicate that only with the help of the signal, can the particle move against the direction of propagation of the traveling wave, forming an absolutely opposite motion. Without external bias, direction of its mean velocity changes several times with the traveling wave velocity and angular frequency of the signal, i.e., a multiple current reversal phenomenon. In the presence of the external bias, the system experiences nonlinear negative mobility. The intrinsic physical mechanisms and conditions responsible for the occurrence of the anomalous transport phenomena are analyzed in detail.

Measurement of neurovascular coupling in human motor cortex using simultaneous transcranial Doppler and electroencephalography

Objective: Event-related desynchronization (ERD) is a relative power decrease of electroencephalogram (EEG) signals in a specific frequency band during physical motor execution, while transcranial Doppler (TCD) measures cerebral blood flow velocity. The objective of this study was to investigate the neurovascular coupling in the motor cortex by using an integrated EEG and TCD system, and to find any difference in hemodynamic responses in healthy young male and female adults. Approach: Thirty healthy volunteers, aged 20–30 years, were recruited for this study. The subjects were asked to perform a motor task for the duration of a provided visual cue. Simultaneous EEG and TCD recording was carried out using a new integrated system to detect the ERD arising from the EEG signals, and to measure the mean blood flow velocity of the left and right middle cerebral arteries from bilateral TCD signals. Main results: The results showed a significant decrease in EEG power in the mu band (7.5–12.5 Hz) during the motor task compared to the resting phase. It showed significant increase in desynchronization on the contralateral side of the motor task compared to the ipsilateral side. Mean blood flow velocity during the task phase was significantly higher in comparison with the resting phase at the contralateral side. The results also showed a significantly higher increase in the percentage of mean blood flow velocity in the contralateral side of motor task compared to the ipsilateral side. However, no significant difference in desynchronization or change of mean blood flow velocity was found between males and females. Significance: A combined TCD-EEG system successfully detects ERD and blood flow velocity in cerebral arteries, and can be used as a useful tool to study neurovascular coupling in the brain. There is no significant difference in the hemodynamic responses in healthy young males and females.

Contrasting geometric and dynamic evolution of lake and land-terminating glaciers in the central Himalaya

Abstract The impact of glacial lake development on the evolution of glaciers in the Himalaya is poorly quantified, despite the increasing prevalence of supraglacial and proglacial water bodies throughout the region. In this study we examine changes in the geometry, velocity and surface elevation of nine lake-terminating and nine land-terminating glaciers in the Everest region of the central Himalaya over the time period 2000 to 2015. The land-terminating glaciers we examined all decelerated (mean velocity change of −0.16 to −5.60 m a−1 for different glaciers), thinned most in their middle reaches, and developed a more gently sloping surface (−0.02 to −0.37° change) down-glacier over the period 2000–2015. The lake-terminating glaciers we examined all retreated (0.46 to 1.42 km), became steeper (0.04 to 8.68° change), and showed maximum thinning towards their termini, but differed in terms of their dynamics, with one group of glaciers accelerating (mean speed-up of 0.18 to 8.04 m a−1) and the other decelerating (mean slow-down of −0.36 m a−1 to −8.68 m a−1). We suggest that these two scenarios of glacier evolution each represent a different phase of glacial lake expansion; one that is accompanied by increasingly dynamic glacier behaviour and retreat, and a phase where glacial lakes have little impact on glacier behaviour that may precede or follow the phase of active retreat. Our observations are important because they quantify the interaction of glacial lake expansion with glacier ice mass loss, and show that increased glacier recession should be expected where a glacial lake has begun to develop.

A Randomized Trial of Oral and Transdermal Rivastigmine for Postural Instability in Parkinson Disease Dementia.

The objective of this study was to compare the efficacy and safety of oral and transdermal rivastigmine for postural instability in patients with Parkinson disease dementia (PDD) who were candidates for a cholinesterase inhibitor. The primary outcome was the change in mean velocity of the center of pressure (CoP) after 6 months. Secondary outcomes included structural parameters of dynamic posturography, clinical rating scales, and adverse events requiring dose reduction. Patients with PDD were randomized in a 1:1 ratio to oral or transdermal rivastigmine with target doses of 6 mg twice daily and 9.5 mg/10 cm daily, respectively. Outcomes were assessed at baseline and 6 months. Results were compared within and between groups. Nineteen patients completed the study (n = 8 oral, n = 11 transdermal). Mean daily doses of 9.4 (±1.5 mg) and 16.4 (±3.6 mg) were achieved in the oral and transdermal groups, respectively. The transdermal group demonstrated a significant 15.8% decrease in mean velocity of CoP (patch: P < 0.05; oral: 10.0% decrease, P = 0.16) in the most difficult scenario (eyes closed with sway-referenced support). There was no difference between groups (P = 0.27). For structural parameters, significant improvements were seen in the mean duration of peaks (patch) and interpeak distance (oral) in the most difficult condition. No changes were observed in clinical rating scales. Six patients experienced nonserious adverse events requiring dose reduction (n = 5 oral; n = 1 transdermal). Rivastigmine may improve certain elements of postural control, notably the mean velocity of CoP. Benefits appear to be more obvious under more taxing sensory conditions.

The Breath-Hold Acceleration Index: A New Method to Evaluate Cerebrovascular Reactivity using Transcranial Doppler.

Cerebrovascular reactivity (CR) is an ideal biomarker to detect cerebrovascular damage. CR can be quantified by measuring changes in cerebral blood flow velocity (CBFV) resulting from a CO2 vasodilatory stimulus, often using the breath-holding index (BHI). In this method, transcranial Doppler (TCD) ultrasound is used to measure CBFV changes in the middle cerebral artery (MCA) during a breath-hold maneuver. Despite its convenience, BHI has high variability. Changing body position may contribute to potential variability. It is important to determine if CR differs with body position. The aims of this study were, first, to propose an alternative, more robust index to evaluate CR using a breath-hold maneuver; second, investigate the effect of body position on CR measured with conventional (BHI) and a new proposed index. Ten healthy young volunteers held their breath for 30 seconds on a tilt table. CR was calculated at five different angles using two indices: the conventional BHI, and the breath-hold acceleration index (BHAI), a new index obtained by linear regression of the most linear portion of the mean velocity change during the breath-hold maneuver. The regression represents acceleration (change in blood flow velocity per unit of time) sampled at each cardiac cycle. The mean coefficient of variation was 43.7% lower in BHAI in comparison with BHI. Neither index was statistically significant between body positions (P > .05). BHAI has less variability in comparison with the conventional standard BHI. Additionally, neither index showed statistical significance in CR based on change in body position.

INFLUENCE OF PHOTOACTIVATED ROSE BENGAL ON MICROCIRCULATION

The study of mean blood velocity changes in rat mesenteric venules (15–30 µm) due to photoactivation (λ = 532 nm, 0,175 W/cm2, 300 s) of i.v. injected Rose Bengal (17 mg/kg) is represented in the article. Using in vivo biomicroscopy the progressive decrease of mean blood velocity both during the laser irradiation and after it was registered. The calculation of thermal effects in the irradiated part of microvessel due to laser absorption by hemoglobin and Rose Bengal showed the rise of temperature was not exceed 0.2оC as compared to initial level. Thus, thermal effect has nearly no significant influence on microvascular disturbances caused by Rose Bengal photoactivation.

Thermodilution-determined Internal Jugular Venous Flow.

Cerebral blood flow (CBF) increases ~20% during whole body exercise although a Kety-Schmidt-determined CBF is reported to remain stable; a discrepancy that could reflect evaluation of arterial vs. internal jugular venous (IJV) flow and/or that CBF is influenced by posture. Here we test the hypothesis that IJV flow, as determined by retrograde thermodilution increases during exercise when body position is maintained. Introducing retrograde thermodilution, IJV flow was measured in eight healthy humans at supine and upright rest and during exercise in normoxia and hypoxia with results compared with changes in ultrasound-derived IJV flow and middle cerebral artery mean velocity (MCA Vmean). Thermodilution determined IJV flow was in reasonable agreement with values established in a phantom (R = 0.59, P < 0.0001) and correlated to the ultrasound-derived IJV flow (n = 7; Kendall τ, 0.28; P = 0.036). When subjects stood up, IJV blood flow decreased by 9% ± 13% (mean ± SD) (219 ± 57 to 191 ± 73 mL·min; P < 0.0001) and the influence of body position was maintained during exercise (P < 0.0001). Exercise increased both IJV flow and MCA Vmean (P = 0.019 and P = 0.012, respectively) and the two responses were similar (P = 0.50). During hypoxia, however, only MCA Vmean responded with a further increase (P < 0.0001). As determined by retrograde thermodilution, IJV flow seems little sensitive to hypoxia, but does demonstrate the about 15% reduction in CBF when humans are upright and, provided that body position is maintained, also the increase in CBF during whole body exercise.

Evidence for hysteresis in the cerebral pressure-flow relationship in healthy men.

The cerebrovasculature is more efficient at compensating for pharmacologically induced transient hypertension versus transient hypotension. Whether this phenomenon exists during nonpharmacologically induced hypertension and hypotension is currently unknown. We compared the percent change in mean velocity in the middle cerebral artery (MCAvmean) per percent change in mean arterial pressure (MAP) (%ΔMCAVmean/%ΔMAP) during transient hypertension and hypotension induced during squat-stand maneuvers performed at 0.05 Hz (20-s cycles) and 0.10 Hz (10-s cycles) in 58 male volunteers. %ΔMCAvmean/%ΔMAP was attenuated by 25% (P = 0.03, 0.05 Hz) and 47% (P < 0.0001, 0.10 Hz) during transient hypertension versus hypotension. Thus, these findings indicate that the brain in healthy men is better adapted to compensate for physiologically relevant transient hypertension than hypotension.NEW & NOTEWORTHY The novel finding of this study is that the change in middle cerebral artery mean flow velocity is attenuated during hypertension compared with hypotension physiologically induced by oscillations in blood pressure in men. These results support that the human brain is more effective at compensating for transient hypertension than hypotension.