Mean Blood Velocity Research Articles

Influence Of Cardiac Output Response To The Onset Of Exercise On Cerebral Blood Flow

It is reported that the changes in cardiac output (Q) contribute to cerebral blood flow (CBF) regulation at rest and even during steady-state exercise. At the onset of cycling exercise, cardiac output (Q) increases acutely and largely via muscle pump, which may cause a larger elevation in CBF than an adequate value. However, the relationship between Q and CBF at the onset of exercise remains unknown. PURPOSE: The purpose of the present study was to examine whether onset exercise-induced large increase in Q contributes to CBF regulation at the onset of exercise. METHODS: In 11 young healthy participants, Q, mean arterial pressure (MAP), and mean blood velocities of middle and posterior cerebral arteries (MCA Vm and PCA Vm, respectively) were continuously measured during a 3-min light cycling exercise at 20 W on the ergometer. RESULTS: At the onset of exercise, Q increased acutely to the peak (P < 0.001), while MCA Vm and PCA Vm had two nadir and peak responses, but these CBF changes were not significant (MCA Vm and PCA Vm; P = 0.461 and P = 0.125, respectively). The change in Q was correlated with that of MCA Vm or PCA Vm from resting baseline to the steady-state exercise (r = 0.371, P = 0.008 and r = 0.418, P = 0.003, respectively). However, interestingly, the change in Q was not correlated with that of MCA Vm or PCA Vm at the onset of exercise (P = 0.223 and P = 0.151, respectively). CONCLUSION: These findings indicate that the change in Q does not contribute to CBF regulation at the onset of exercise for protecting cerebral vasculature against a large and acute elevation in Q at the onset of exercise.

Ingestion of carbonated water increases middle cerebral artery blood velocity and improves mood states in resting humans exposed to ambient heat stress

Sugar-free carbonated water is consumed worldwide. The consumption of carbonated water is high in summer, when the heat loss responses of sweating and skin vasodilation are activated, and thermal perceptions (thermal sensation and comfort) and mood states are negatively modulated. However, whether ingesting carbonated water under ambient heat exposure modulates cerebral blood flow index, heat loss responses, thermal perceptions, and mood states remains to be determined. In this study, 17 healthy, habitually active, young adults (eight women) ingested 4 °C noncarbonated or carbonated water under 37 °C ambient heat-stressed resting conditions. Both drinks increased the middle cerebral artery mean blood velocity, an index of cerebral blood flow, and mean arterial pressure, with carbonated water exhibiting higher elevations than noncarbonated water (P < 0.05). However, the heart rate, sweat rate, and skin blood flow during and after drinking remained unchanged between the two conditions (P > 0.05). The thermal sensation and comfort after drinking remained unchanged between the two conditions (P > 0.05); but, a drink-induced reduction in sleepiness was higher, and drink-induced elevations in motivation and exhilaration were higher after ingesting carbonated water than those after ingesting noncarbonated water (P < 0.05). The analyses suggest that in humans under ambient heat-stressed resting conditions, ingestion of cold carbonated water increases the cerebral blood flow index, blood pressure, motivation, and exhilaration, whereas it decreases sleepiness relative to ingestion of noncarbonated cold water. However, ingestion of cold carbonated water fails to modulate thermoregulatory responses and thermal perception as opposed to noncarbonated cold water.

Thigh-length graduated compression stocking cannot increase blood velocity of the common femoral vein in patients awaiting total hip arthroplasty

ObjectivesGraduated compression stocking (GCS) is one of the mechanical prophylaxes commonly used for deep vein thrombosis (DVT). The present study was designed to observe the effects of graduated compression stockings on the vein deformation and hemodynamics of lower limbs in patients awaiting total hip arthroplasty (THA).MethodsThe lower extremity veins of 22 patients awaiting THA were examined by ultrasound, when they rested in supine position with or without thigh-length GCS. The deformation parameters we measured included antero-posterior (AP) diameters, latero-medial (LM) diameters, and cross-sectional area (CSA) of great saphenous vein (GSV), posterior tibial vein (PTV), popliteal vein (PV), gastrocnemius vein (GV), and superficial femoral vein (SFV). We measured peak velocity and mean velocity of GSV, common femoral vein (CFV), junction of GSV and CFV to represent for hemodynamics of veins.ResultsSignificant compression was observed in almost all measured veins with the use of thigh-length GCS, while it was unable to significantly compress GSV in latero-medial diameter. The mean latero-medial diameter reductions for GSV, PTV, GV, PV and SFV were 19.4, 30.2, 43.2, 29.7 and 20.4%, respectively. GCS significantly compressed antero-posterior diameter of GSV, PTV, GV, PV and SFV by 43.4, 33.3, 42.1, 37.5, and 27.8%, respectively. The mean reduction of cross-section area was 44.8% for GSV, 49.6% for PTV, 60.0% for GV, 57.4% for PV, and 36.2% for FV. No significant changes were observed in the mean blood velocity of GSV, CFV, and junction. GCS was able to significantly reduce peak velocity of CFV (17.6 ± 5.6 cm/s to 16.1 ± 6.0 cm/s) and junction (23.3 ± 9.5 cm/s to 21.3 ± 9.7 cm/s), while it did not change the peak velocity of GSV.ConclusionThigh-length GCS is sufficient to compress lower extremity veins in patients awaiting THA in supine position with the greatest compression in GV, while it was unable to significantly increase blood velocity of common femoral vein or GSV. GCS may prevent DVT through more than simply increasing blood flow. Further studies are needed to determine the specific effects of GCS.

Influence of high‐intensity interval training to exhaustion on the directional sensitivity of the cerebral pressure‐flow relationship in young endurance‐trained men

We previously reported subtle dynamic cerebral autoregulation (dCA) alterations following 6 weeks of high‐intensity interval training (HIIT) to exhaustion using transfer function analysis (TFA) on forced mean arterial pressure (MAP) oscillations in young endurance‐trained men. However, accumulating evidence suggests the cerebrovasculature better buffers cerebral blood flow changes when MAP acutely increases compared to when MAP acutely decreases. Whether HIIT affects the directional sensitivity of the cerebral pressure‐flow relationship in these athletes is unknown. In 18 endurance‐trained men (age: 27 ± 6 years, VO2max: 55.5 ± 4.7 ml·kg−1·min−1), we evaluated the impact of 6 weeks of HIIT to exhaustion on dCA directionality using induced MAP oscillations during 5‐min 0.05 and 0.10 Hz repeated squat‐stands. We calculated time‐adjusted changes in middle cerebral artery mean blood velocity (MCAv) per change in MAP (ΔMCAvT/ΔMAPT) for each squat transition. Then, we compared averaged ΔMCAvT/ΔMAPT during MAP increases and decreases. Before HIIT, ΔMCAvT/ΔMAPT was comparable between MAP increases and decreases during 0.05 Hz repeated squat‐stands (p = 0.518). During 0.10 Hz repeated squat‐stands, ΔMCAvT/ΔMAPT was lower during MAP increases versus decreases (0.87 ± 0.17 vs. 0.99 ± 0.23 cm·s−1·mmHg−1, p = 0.030). Following HIIT, ΔMCAvT/ΔMAPT was superior during MAP increases over decreases during 0.05 Hz repeated squat‐stands (0.97 ± 0.38 vs. 0.77 ± 0.35 cm·s−1·mmHg−1, p = 0.002). During 0.10 Hz repeated squat‐stands, dCA directional sensitivity disappeared (p = 0.359). These results suggest the potential for HIIT to influence the directional sensitivity of the cerebral pressure‐flow relationship in young endurance‐trained men.

Influence of cardiac output response to the onset of exercise on cerebral blood flow.

Change in cardiac output (Q) contributes to cerebral blood flow (CBF) regulation at rest and even during steady-state exercise. At the onset of cycling exercise, Q increases acutely and largely via muscle pump. The purpose of the present study was to examine whether onset exercise-induced a large increase in Q contributes to CBF regulation at the onset of exercise. In 20 young healthy participants (10 males and 10 females), Q, mean arterial pressure (MAP), and mean blood velocities of middle and posterior cerebral arteries (MCA Vm and PCA Vm) were continuously measured during light cycling exercise for 3min. At the onset of exercise, Q increased acutely to the peak (P < 0.001), while the CBF peak responses were not significantly higher than the values during the steady-state exercise (MCA Vm and PCA Vm; P = 0.183 and P = 0.101, respectively). The change in Q was correlated with that of MCA Vm or PCA Vm from resting baseline to the steady-state exercise (r = 0.404, P < 0.001 and r = 0.393, P < 0.001, respectively). However, the change in Q was not correlated with that of MCA Vm or PCA Vm at the onset of exercise (P = 0.853 and P = 0.893, respectively). Any sex differences in the onset response of peripheral and cerebral hemodynamics to exercise were not observed. These findings suggest that the acute change in Q does not contribute to CBF regulation at the onset of exercise for protecting cerebral vasculature against a large and acute elevation in Q at the onset of exercise.

Prediction of Fetal Growth Restriction for Fetal Umbilical Arterial/Venous Blood Flow Index Evaluated by Ultrasonic Doppler under Intelligent Algorithm

The empirical wavelet transform (EWT) algorithm was applied in ultrasound to explore the predictive value for fetal growth restriction (FGR) in fetal arteriovenous indexes. 142 pregnant women who received prenatal ultrasonic examination and delivered were selected. They were classified into control group and FGR group. There were 102 patients with normal pregnancy in the control group, and 40 patients with delayed fetal growth in the FGR group. The extended triple collocation (ETC) algorithm was employed to divide the Fourier spectrum of signals adaptively, and the constructed small filter banks were classified into corresponding intervals. The instantaneous frequency was analyzed, and the arterial blood flow indexes of the two groups were compared. The results showed that the time-frequency analysis method under EWT had lower normalization error and higher accuracy. The inner diameter and cross-sectional area of FGR were remarkably smaller than those of the control group, and the differences were statistically significant (P < 0.05). There were no significant differences in mean blood flow and mean blood velocity between the control group and FGR group (P > 0.05). The arterial blood flow parameters of the systolic flow velocity (VS) and the diastolic flow velocity (VD) in the FGR group were notably lower than those in the control group, and the differences were significant (P < 0.05). In conclusion, the frequency principal component extracted by EWT algorithm was less disturbed by noise, which could accurately and effectively evaluate fetal arteriovenous blood flow indexes and predict FGR.

Effects of biomechanical properties of blood on surface tension-driven flows in superhydrophilic channels

Surface tension-driven microfluidic flows offer low-cost solutions for blood diagnostics due to the pump-less flow handling. Knowledge of the influence of the biomechanical properties of blood on such flows is key to design such devices; however, a systematic examination of that influence is lacking in the literature. We report on the effects of specific hemorheological factors for flows in a superhydrophilic microchannel. Whole human blood and erythrocyte suspensions in phosphate buffer and dextran solutions were tested. Heat-treated counterparts of the aforementioned samples were produced to alter the deformability of the cells. The flow of the samples was imaged and characterized using micro-particle image velocimetry and tracking techniques to probe the effects of hematocrit, and erythrocyte aggregation and deformability. Meniscus velocities, velocity profiles in the channel, and local and bulk shear rates were derived. The mean velocity of blood was affected by the increasing sample viscosity and the reduced erythrocyte deformability as expected. The increased erythrocyte aggregation appeared to affect more the shape of the velocity profiles in the normal, compared to the heat-treated samples. Very high shear rates are observed in the early stages of the flow, suggesting high erythrocyte disaggregation, persisting sufficiently strong until the flow reaches the end of the channel.

Middle Cerebral Artery Pulsatility Index is Elevated in Chronic Kidney Disease

IntroductionCKD patients exhibit an increased risk of cerebrovascular disease such as stroke, transient ischemic attacks, and cerebral small vessel disease. One mechanism that may contribute to this risk is increased cerebrovascular stiffness and augmented pulsatility of blood flow into the cerebral microcirculation. Middle cerebral artery pulsatility index (MCA PI) provides an indirect measure of cerebrovascular stiffness and can be measured with transcranial Doppler (TCD) ultrasonography. Prior work suggests that MCA PI is elevated in CKD patients following stroke, but it remains unclear if MCA PI is elevated in CKD patients without a history of cerebrovascular disease. Moreover, whether MCA PI correlates with central (aortic) arterial stiffness in CKD remains unknown. We hypothesized that MCA PI would be elevated in CKD patients stages III‐IV compared to controls without CKD matched for age, race, sex, diabetes and hypertension. Furthermore, we hypothesized that MCA PI would correlate with central arterial stiffness and estimated glomerular filtration rate (eGFR) in CKD.Methods13 CKD participants stages III‐IV (mean eGFR=38±3 ml/min/1.73m2) and 10 controls without CKD (age=60±2y) underwent measurement of middle cerebral artery blood velocity via TCD during 5 minutes of seated rest. MCA PI was averaged over the 5 minute period and calculated as MCA PI = (peak systolic blood velocity – diastolic blood velocity)/(mean blood velocity). In CKD, central arterial stiffness was measured via carotid‐femoral pulse wave velocity (cfPWV) after 5 minutes of supine rest. MCA PI was compared between CKD vs CON via 2‐tailed, independent sample T‐tests and the relationships between MCA PI, cfPWV, and eGFR CKD were examined via linear regression.ResultsMCA PI was elevated in CKD compared to CON (0.91±0.06 vs 0.73±.04, P=0.04) and was associated with cfPWV (R=0.72, P=0.01). However, we observed no relationship between MCA PI and eGFR in CKD (P=0.83).DiscussionIn support of our hypothesis, MCA was elevated in CKD compared to controls and was associated with central arterial stiffness. These findings suggest that cerebrovascular stiffness is elevated in CKD patients without a history of cerebrovascular disease, and that MCA PI correlates with central arterial stiffness in CKD. Increases in cerebrovascular stiffness and subsequent flow pulsatility may comprise one mechanism of cerebrovascular disease risk in CKD. Future work should clarify the relationship between MCA PI and severity of renal disease in a larger cohort, and examine the prognostic value of MCA PI as a predictor of future cerebrovascular disease burden in CKD.

Central Command Related Changes in Anterior Cerebral Artery Blood Velocity and Prefrontal Oxygenation at the Onset of Moderate Voluntary Hand‐Grip Exercise

Recently, it has been identified that volitionally initiated finger tapping, which is a “very light motor effort” physical activity, elicits greater increases in mean anterior cerebral artery blood velocity (ACAmean), ACA vascular conductance index (ACAvci) and prefrontal oxygenation (Oxy‐Hb) responses compared to a cued start. These findings suggest that differences in ACAmean and prefrontal Oxy‐Hb responses between the exercise initiation modes may be related to central command. However, it remains unknown if similar responses are observed at the onset of voluntary exercise of a “moderate motor effort”. Therefore, the purpose of this study was to determine ACAmean, ACAvci and prefrontal Oxy‐Hb responses during dynamic hand grip exercise at 40% of maximal voluntary contraction (MVC) during two exercise initiation modes (voluntary or cued start). ACAmean, ACAvci, and prefrontal Oxy‐Hb were measured in seven participants (4 females and 3 males; aged 26 ± 3 years) at baseline (‐30 sec to ‐20 sec prior to initiation of exercise), pre‐exercise (‐20 sec to 0 sec) and the onset of exercise (0 sec to 15 sec) of each exercise initiation condition. Participants perceived exertion Borg Scale rating for the 40%‐MVC was 11.5 (median). A two‐way repeated measures ANOVA was conducted for the variables of interests. A significant factor interactions was identified for ACAmean ((F(2,12) = 5.02, p=0.03)) and Oxy‐Hb ((F(2,12) = 5.86, p= 0.02)). Post hoc test revealed that a voluntary start to hand grip exercise increased ACAmean by 2.6±1.0 cm/s (p=0.002) v.s. 0.7± 2.0 cm/s for a cued start (p=0.3) and increased Oxy‐Hb by 11.6±10.7 µM (p=0.02) v.s. 2.9±9.5 µM for a cued start (p=0.7) at the onset of exercise when compared to baseline. Furthermore, there was tendency in ACAvci to also increase with voluntary start by 3.9%±6.0 (p=0.06) vs. cued start 0.43% ± 6.0 p=0.57 from baseline to the initial onset of exercise. These primary findings suggest that moderate dynamic hand grip exercise elicits similar anterior cerebral blood flow and prefrontal oxygenation responses previously observed and thus, showing similar metabolic demands as finger‐tapping.

Acute Impact of JUUL Electronic Cigarette use on Cerebral Vascular Vasodilator Responsiveness

BackgroundCardiovascular disease is a major cause of death among cigarette smokers and is responsible for ~30% of heart disease related mortality in the U.S each year. Although cigarette smoking rates have declined in recent years, the use of electronic cigarettes (e‐cigarettes) continues to gain popularity in the U.S. and have generated widespread debate within the public health community, mostly due to the lack of scientific evidence regarding their safety and impact on health and behavior. The increasing rates of e‐cigarette use in the U.S have been largely attributed to the recent emergence of the high‐nicotine‐delivery pod‐based devices such as JUUL. Unlike e‐cigarettes, the literature surrounding the health impact of combustible cigarette smoking is well developed with overwhelming evidence of an adverse impact on various cardiovascular outcomes including impaired cerebral perfusion/vascular function. However, the impact of e‐cigarettes on cerebral vascular function remains to be elucidated, representing a major knowledge gap and research priority.HypothesisThis study tested the hypothesis that acute e‐cigarette vaping (JUUL) will impair cerebral vascular function as indexed by the cerebral vasodilatory responsiveness to a hypercapnic stimulus.MethodsA total of 16 adult smokers (mean age=25±5 yrs.) participated in this pilot study which occurred following an overnight fast. Cerebral vascular function was assessed as the hyperemic response to rebreathing‐induced hypercapnia before and ~45 min following a vaping session (10 puffs; 3s each, separated by 30s intervals). Heart rate (ECG), respiration (Pneumotrace), beat‐to‐beat blood pressure (Finometer), middle cerebral artery mean blood velocity (MCAv ‐ transcranial Doppler) and breath‐by‐breath end‐tidal carbon dioxide concentration (PETCO2‐ capnograph) were continuously measured. Cerebral vascular conductance index (CVCi) was calculated as MCAv / mean arterial pressure. Cerebral vasodilatory responsiveness was assessed as % increase in CVCi (%CVCi) during the highest common magnitude of hypercapnia achieved during the pre‐ and post‐vaping trials.ResultsAll CVCi data are reported at the highest common magnitude of hypercapnia achieved during the pre‐ and post‐vaping sessions (ΔPETCO2Pre: 13±2 mmHg, ΔPETCO2 Post: 12±2 mmHg; P=0.11). Cerebral vascular function/vasodilatory responsiveness, as assessed by the CVCi response to the hypercapnic challenge was significantly blunted following the vaping session (Pre: +52±25%, Post: +42±14%; P=0.04).ConclusionsOur preliminary results suggest that e‐cigarette vaping using JUUL acutely impairs cerebral vascular function as indexed by cerebral vasodilatory responsiveness to a hypercapnic challenge. These findings highlight the need for longitudinal studies to assess the long‐term impact of JUUL use on cerebral vascular function as well as other indices of cardiovascular health.

Cerebral haemodynamics during arrhythmia in health, ischaemic heart disease and heart failure with reduced ejection fraction, and in a preclinical swine model.

Ventricular arrhythmias are associated with neurological impairment and could represent a source of cerebral hypoperfusion. In the present study, data from healthy individuals (n=11), patients with ischaemic heart disease (IHD; ejection fraction >40%; n=9) and patients with heart failure with reduced ejection fraction (HFrEF; EF = 31 (5)%, n=11), as well as data from swine surgeries, where spontaneous ventricular arrhythmias were observed during cerebrovascular examination (transcranial Doppler ultrasound in humans and laser Doppler in swine) were analysed retrospectively to investigate the effect of arrhythmia on cerebral microvascular haemodynamics. A subset of participants also completed the Montreal Cognitive Assessment (MoCA). Middle cerebral artery mean blood velocity (MCAVmean ) decreased during premature ventricular contraction (PVC) in all groups, and data from swine indicate PVCs reduced cerebral microvascular perfusion. Overall MCAVmean was decreased in the HFrEF vs. control group. Further, %∆MCAVmean /%∆mean arterial pressure during the PVC was greater in the HFrEF vs. control group and was correlated with decreased MoCA scores. Subanalysis of HFrEF data revealed that during bigeminy MCAVmean decreased owing to reductions during irregular beats only. During non-sustained ventricular tachycardia, MCAVmean decreased but recovered above baseline upon return to sinus rhythm. Also, haemodynamic perturbations during and following the PVC were greater in the brachial artery vs. the MCA. Therefore, ventricular arrhythmias decreased indices of cerebral perfusion irrespective of IHD or HFrEF. The relative magnitude of arrhythmia-induced haemodynamic perturbations appears to be population specific and arrhythmia type and organ dependent. The cumulative burden of arrhythmia-induced deficits may exacerbate existing cerebral hypoperfusion in HFrEF and contribute to neurological abnormalities in this population. KEY POINTS: Irregular heartbeats are often considered benign in isolation, but individuals who experience them frequently have a higher prevalence of cerebrovascular and/or cognitive associated disorders. How irregular heartbeats affect blood pressure and cerebral haemodynamics in healthy and cardiovascular disease patients, those with and without reduced ejection fraction, remains unknown. Here it was found that in the absence of symptoms associated with irregular heartbeats, such as dizziness or hypotension, single, multiple non-sustained and sustained irregular heartbeats influence cerebral haemodynamics in a population-specific, arrhythmia-type and organ-dependent manner. Relative deficits in the index of cerebral blood flow normalized to relative deficits in blood pressure were greatest in patients with heart failure with reduced ejection and inversely related with cognitive performance. Chronic arrhythmias may exacerbate existing cerebral hypoperfusion in heart failure with reduced ejection fraction, thereby providing a mechanistic link between otherwise benign irregular heartbeats and cognitive dysfunction, independent of embolism.

Hypercapnia elicits differential vascular and blood flow responses in the cerebral circulation and active skeletal muscles in exercising humans.

The purpose of this study was to investigate the effects of a rise in arterial carbon dioxide pressure (PaCO2) on vascular and blood flow responses in the cerebral circulation and active skeletal muscles during dynamic exercise in humans. Thirteen healthy young adults (three women) participated in hypercapnia and normocapnia trials. In both trials, participants performed a two‐legged dynamic knee extension exercise at a constant workload that increased heart rate to roughly 100 beats min−1. In the hypercapnia trial, participants performed the exercise with spontaneous breathing while end‐tidal carbon dioxide pressure (PETCO2), an index of PaCO2, was held at 60 mmHg by inhaling hypercapnic gas (O2: 20.3 ± 0.1%; CO2: 6.0 ± 0.5%). In the normocapnia trial, minute ventilation during exercise was matched to the value in the hypercapnia trial by performing voluntary hyperventilation with PETCO2 clamped at baseline level (i.e., 40–45 mmHg) through inhalation of mildly hypercapnic gas (O2: 20.6 ± 0.1%; CO2: 2.7 ± 1.0%). Middle cerebral artery mean blood velocity and the cerebral vascular conductance index were higher in the hypercapnia trial than in the normocapnia trial. By contrast, vascular conductance in the exercising leg was lower in the hypercapnia trial than in the normocapnia trial. Blood flow to the exercising leg did not differ between the two trials. These results demonstrate that hypercapnia‐induced vasomotion in active skeletal muscles is opposite to that in the cerebral circulation. These differential vascular responses may cause a preferential rise in cerebral blood flow.

Directional sensitivity of the cerebral pressure-flow relationship in young healthy individuals trained in endurance and resistance exercise.

What is the central question of this study? Does habitual exercise modality affect the directionality of the cerebral pressure-flow relationship? What is the main finding and its importance? These data suggest the hysteresis-like pattern of dynamic cerebral autoregulation appears present in long-term sedentary and endurance-trained individuals, but absent in resistance-trained individuals. This is the first study to expand knowledge on the directional sensitivity of the cerebral pressure-flow relationship to trained populations. Evidence suggests the cerebrovasculature may be more efficient at dampening cerebral blood flow (CBF) variations when mean arterial pressure (MAP) transiently increases, compared to when it decreases. Despite divergent MAP and CBF responses to acute endurance and resistance training, the long-term impact of habitual exercise modality on the directionality of dynamic cerebral autoregulation (dCA) is currently unknown. Thirty-six young healthy participants (sedentary (n=12), endurance-trained (n=12), and resistance-trained (n=12)) undertook a 5-min repeated squat-stand protocol at two forced MAP oscillation frequencies (0.05 and 0.10Hz). Middle cerebral artery mean blood velocity (MCAv) and MAP were continuously monitored. We calculated absolute (ΔMCAvT /ΔMAPT ) and relative (%MCAvT /%MAPT ) changes in MCAv and MAP with respect to the transition time intervals of both variables to compute a time-adjusted ratio in each MAP direction, averaged over the 5-min repeated squat-stand protocols. At 0.10Hz repeated squat-stands, ΔMCAvT /ΔMAPT and %MCAvT /%MAPT were lower when MAP increased compared with when MAP decreased for sedentary (ΔMCAvT /ΔMAPT : P=0.032; %MCAvT /%MAPT : P=0.040) and endurance-trained individuals (ΔMCAvT /ΔMAPT : P=0.012; %MCAvT /%MAPT P=0.007), but not in the resistance-trained individuals (ΔMCAvT /ΔMAPT : P=0.512; %MCAvT /%MAPT P=0.666). At 0.05Hz repeated squat-stands, time-adjusted ratios were similar for all groups (all P>0.605). These findings suggest exercise training modality does influence the directionality of the cerebral pressure-flow relationship and support the presence of a hysteresis-like pattern during 0.10Hz repeated squat-stands in sedentary and endurance-trained participants, but not in resistance-trained individuals. In future studies, assessment of elite endurance and resistance training habits may further elucidate modality-dependent discrepancies on directional dCA measurements.

Acute Gravitational Stress Selectively Impairs Dynamic Cerebrovascular Reactivity in the Anterior Circulation Independent of Changes to the Central Respiratory Chemoreflex.

Cerebrovascular reactivity (CVR) to changes in the partial pressure of arterial carbon dioxide (PaCO2) is an important mechanism that maintains CO2 or pH homeostasis in the brain. To what extent this is influenced by gravitational stress and corresponding implications for the regulation of cerebral blood flow (CBF) remain unclear. The present study examined the onset responses of pulmonary ventilation (V̇E) and anterior middle (MCA) and posterior (PCA) cerebral artery mean blood velocity (Vmean) responses to acute hypercapnia (5% CO2) to infer dynamic changes in the central respiratory chemoreflex and cerebrovascular reactivity (CVR), in supine and 50° head-up tilt (HUT) positions. Each onset response was evaluated using a single-exponential regression model consisting of the response time latency [CO2-response delay (t0)] and time constant (τ). Onset response of V̇E and PCA Vmean to changes in CO2 was unchanged during 50° HUT compared with supine (τ: V̇E, p = 0.707; PCA Vmean, p = 0.071 vs. supine) but the MCA Vmean onset response was faster during supine than during 50° HUT (τ: p = 0.003 vs. supine). These data indicate that gravitational stress selectively impaired dynamic CVR in the anterior cerebral circulation, whereas the posterior circulation was preserved, independent of any changes to the central respiratory chemoreflex. Collectively, our findings highlight the regional heterogeneity underlying CBF regulation that may have translational implications for the microgravity (and hypercapnia) associated with deep-space flight notwithstanding terrestrial orthostatic diseases that have been linked to accelerated cognitive decline and neurodegeneration.

Transcranial doppler findings in basilar artery dolichoectasia: a case control study

Basilar artery dolichoectasia (BAD) is a disorder characterized by dilatation, elongation and tortuosity of the basilar artery. Transcranial Doppler ultrasound (TCD) is a useful tool that can detect blood flow in intracranial vessels including basilar artery (BA). Few studies have been conducted on blood flow changes in BAD. This study was conducted to evaluate the Doppler parameters in dolichoectatic BA and to assess if there is any difference in TCD findings between stroke and non-stroke BAD patients. A case-control study was conducted on 35 patients diagnosed with BAD (26 male, 9 female) and 35 age- and gender-matched control group (without BAD) at the Middle Euphrates Neuroscience Center, Al-Sader Medical City, Al-Najaf, Iraq. Dolichoectasia was diagnosed on non-enhanced brain CT scan using established imaging criteria according to Dan Deng et al criteria. Doppler flow for control and stroke cases was recorded. The parameters measured on TCD were peak systolic velocity (PSV), end diastolic velocity (EDV) mean blood velocity (MBV), pulsatility index (PI) and resistive index (RI). After logistic regression for adjustment for the significant confounders, there was statistically significant difference in Doppler parameters between both groups including decrease in each of PSV, EDV and MBV while both PI and RI weren’t statistically significant. Among BAD patients, there was statistically significant difference in all TCD parameters between stroke and non-stroke patients (PSV EDV, MBV, PI and RI). BAD was associated with a decrease in flow velocities as measured by TCD. Furthermore, among BAD patients, those with stroke had lower values for all Doppler parameters than non-stroke patients.

Abstract 9604: Pulmonary Artery Systolic Blood Pressure Predicted From Cardiac MR Image Data Without Requiring Calibration; A Virtual RHC?

Introduction: Despite decades of initiatives, assessment of absolute pulmonary arterial pressures (PAP) by CMR has remained an elusive goal. We introduce a means to predict the PAP from routine image data easily obtained by CMR. The image data is directly used to calculate the impedance between the LV and the aorta (IMP LV ) and between the RV and the main PA (IMP RV ) which are combined to predict PAP. Methods: Patients (n=33, 82% F), 51 ±12 yrs) with a diagnosis of (PHTN) underwent evaluation by CMR to assess the blood flow through the aorta and PA at the interface to the LV and RV, respectively. Phase velocity mapping flow data at single plane (acquisition time 2min) was used to calculate the previously described and validated impedance for the LV and RV: IMP LV and IMP RV . IMP was calculated using the formula:IMP = (end systolic ejection time) x (mean blood velocity) / (vessel diameter). Systolic PAP was measured during a right heart cath examination performed within one week of the CMR. A multiple linear regression model was generated to predict systolic PAP, with parameters retained with a significance &lt;0.05. Results: The parameters that best predicted the systolic PAP were IMP LV , IMP RV and the distance of the measured IMP LV from the center position of the data range of IMP LV (r = 0.69, p&lt;0.001), Fig 1. The standard major-axis line was fitted to the data (p&lt;0.001). Conclusions: This is the first demonstration of the utility of a CMR-measured left and right ventricular impedance value to directly predict systolic PAP. Critically, the correlation coefficient, identical to Echo, holds over a very wide physiologic range, and has never been demonstrated before by CMR. Of central importance is the distinguishing feature that no calibration of the data is required, thus, unlike typical Echo-derived estimates of PAP or newer implanted pressure monitors, no estimate of CVP or RAP is required. Thus, this is the first-in-man CMR demonstration of a virtual RHC.

Abstract 9605: The Six Minute Walk Test: Right Test, Wrong Interpretation!

Introduction: In patients with pulmonary hypertension (PHTN), after initial hemodynamic assessment, it is common practice to perform the six minute walk test (6MWT). The absolute distance walked represents an integration of pulmonary artery pressure (PAP) and right heart function. Thus, the initial distance walked for each patient is generally used as the benchmark to compare to future 6MWT to assess therapy/prognosis. Here we show that the absolute 6MWT distance (6MWD) is less ambiguously interpreted as the measured impedance between the LV and the aorta. Methods: Patients (n=33, 82% F), age 51± 12yrs) with PHTN (&gt;80% WHO I) underwent CMR to assess phasic blood flow through the aorta at the interface to the LV. CMR- phase velocity mapping flow data at single plane (acquisition time: 2min) was used to calculate the previously described and validated LV impedance (IMP LV ). IMP LV was calculated using the formula: IMP LV = (cardiac beat interval; CL) x (mean blood velocity) / (aortic diameter). Systolic PAP was measured during a right heart cath performed within one week of CMR and at the time of 6MWT. Multiple linear regression models were generated to predict the 6MWT distance. Results: A model predicting 6MWT was generated: systolic PAP, RVEF and age (r= 0.41, with PAP and RVEF not attaining significance). A second model entering IMP LV and age attained significance (r = 0.68, p&lt;0.01). Fig 1. Conclusions: This is the first demonstration of the utility of the 6MWT distance to reflect a uniform measure of the status of the PH patient, less so PAP, even at baseline. The impedance between the LV and the aorta incorporates the dual components of RV and the LV integrated ventricular/arterial function along with the systolic PAP, making it a more fundamental measure of PHTN health status. Thus, despite &gt;50 years of 6MWT used as the cornerstone for PHTN/PAH patients, we now show that this common application is really a predictor of impedance, and in turn, 6MWT was the right test for the wrong reason.

Effect of breath-hold on the responses of arterial blood pressure and cerebral blood velocity to isometric exercise.

The present study examined the effect of breath-hold without a Valsalva maneuver during isometric exercise on arterial blood pressure (ABP) and cerebral blood flow (CBF). Twenty healthy adults (15 men and five women) randomly performed only breath-hold without a Valsalva maneuver (BH), and an isometric handgrip exercise for 30s at 40% of individual maximal voluntary contraction with continuous breathing (IHG) and with breath-hold without the Valsalva maneuver (IHG-BH). Mean ABP (MAP) and blood velocity in the middle (MCA Vmean) and posterior cerebral arteries (PCA Vmean) were continuously measured throughout each protocol. MAP was elevated during the IHG-BH compared with IHG (P < 0.001) and BH (P = 0.001). Similarly, both MCA Vmean and PCA Vmean were higher during IHG-BH compared with IHG and BH (all P < 0.001). Moreover, the relative change in MAP from the baseline was correlated with that in both cerebral blood velocities during the BH (MCA Vmean: r = 0.739, P < 0.001 and PCA Vmean: r = 0.570, P = 0.009) and IHG-BH (MCA Vmean: r = 0.755, P < 0.001 and PCA Vmean: r = 0.617, P = 0.003) condition, but not the IHG condition (P = 0.154 and P = 0.306). These results indicate that during isometric exercise, a breath-hold enhances an exercise-induced increase in MAP and, consequently, MCA Vmean and PCA Vmean.

Abstract P152: Low Memory Recall And High Common Carotid Artery Flow Pulsatility In Non-Dialysis Chronic Kidney Disease Patients

A significant proportion of patients with non-dialysis chronic kidney disease (CKD) present with mild-to-moderate deficits in the cognitive domains of executive function and episodic memory. Excess blood flow pulsatility is damaging to the microvasculature of high-flow, low-resistance organs like the brain and may contribute to the cognitive deficits prevalent among CKD patients. We tested the hypothesis that patients with moderate-to-severe non-dialysis CKD have excess flow pulsatility along their carotid and cerebral vasculature that is associated with deficits in executive function and episodic memory. We recruited 10 non-dialysis CKD patients (age=68±8 yrs; estimated glomerular filtration rate, eGFR=36±18 mL/min/1.73 m 2 ) and 7 healthy age-matched adults (age=65±5 yrs; eGFR=81±17 mL/min/1.73 m 2 ). Global cognitive function was assessed with the Montreal Cognitive Assessment (MoCA). Executive function and episodic memory were assessed using the NIH Toolbox Flanker Inhibitory Control and Attention Test and California Verbal Learning Test III, respectively, and reported as standardized scores (mean=100, SD=15). Pulsatility index [(systolic blood velocity - diastolic blood velocity)/ mean blood velocity] was measured in the common carotid (CCA), internal carotid (ICA), and middle cerebral arteries (MCA) via Doppler and transcranial Doppler ultrasound. Compared to healthy adults, CKD patients did not differ in total brain blood flow (p=0.42) but had lower MoCA (CKD=26±3, Healthy=29±1; p=0.01) and memory recall scores (CKD=92±21, Healthy=110±9; p=0.05). CKD patients did not differ from our healthy control group in executive function (CKD=91±10, Healthy=90±11; p=0.80) but did produce a mean score that was 0.6 SD lower than the NIH Toolbox reference sample. CKD patients had a higher pulsatility index in the CCA (CKD=2.3±0.5, Healthy=1.9±0.3; p=0.05) but not in the ICA (p=0.68) or MCA (p=0.57). CCA pulsatility index was strongly and inversely associated with episodic memory recall scores (r=-0.64, p&lt;0.01, n=17). This data suggests that although the higher CCA flow pulsatility in non-dialysis CKD patients does not appear to be transmitted to the cerebrovasculature, it nevertheless may still be contributing to memory impairments.

Differential Vasomotor Effects of Insulin in the Peripheral and Cerebrovascular Circulations of Healthy Young Adults

Background Insulin-stimulated peripheral and cerebrovascular vasodilation are consistently observed in preclinical animal models. Hyperinsulinemia also has profound vasodilatory effects within the skeletal muscle vasculature in healthy young adults; however, the magnitude of insulin-stimulated cerebrovascular vasodilation in humans remains unclear. We hypothesized insulin-stimulated vasodilation would be observed in both the peripheral and cerebral circulations in healthy young adults. Methods Middle cerebral artery velocity (MCAv) was measured with transcranial Doppler ultrasound in 9 healthy young adults (4M/5F, 28±2 yrs, 24±1 kg/m2) at baseline and following a 60-min hyperinsulinemic (40 mU/m2 body surface area/min), euglycemic infusion. Femoral artery diameter and mean blood velocity were measured by Doppler ultrasound to determine femoral artery blood flow (FBF). Mean arterial blood pressure (MABP) was measured continuously by finger photoplethysmography. Cerebrovascular conductance index (CVCi = MCAv/MABP x 100) and femoral vascular conductance (FVC = FBF/MABP x 100) were calculated. Results Intravenous insulin infusion resulted in an increase in plasma insulin (5±1 to 41±2 µIU/mL, p<0.01) with blood glucose maintained at baseline levels (75±2 to 72±4 mg/dL, p=0.48). MABP was maintained throughout the infusion protocol (85±3 to 88±3 mmHg, p=0.21). There was a significant increase in FBF (134±24 to 184±30 mL/min, p=0.05) and FVC (153±22 to 211±31 mL/min/100 mmHg, p=0.04) during hyperinsulinemia. In contrast, there was no effect of hyperinsulinemia on MCAv (54±3 to 51±3 cm/s, p=0.28) or CVCi (65±5 to 58±3 AU, p=0.14). There was no association between insulin-stimulated peripheral and cerebrovascular vasodilation (R=-0.421, p=0.26). Conclusions Hyperinsulinemia in healthy young adults elicits peripheral vasodilation. Contrary to our hypothesis, following a 60-minute systemic intravenous insulin infusion there is no change in MCAv or CVCi in healthy young adults. These data indicate the cerebral and peripheral vasculature are differentially regulated during hyperinsulinemia.