Middle Cerebral Artery Blood Flow Research Articles

Most High-Intensity Transient Signals Are Not Associated With Specific Surgical Maneuvers.

Mortality after congenital heart defect surgery has dropped dramatically in the last few decades. Current research on long-term outcomes has focused on preventing secondary neurological sequelae, for which embolic burden is suspected. In children, little is known of the correlation between specific surgical maneuvers and embolic burden. Transcranial Doppler ultrasound is highly useful for detecting emboli but has not been widely used with infants and children. Bilateral middle cerebral artery blood flow was continuously monitored from sternal incision to chest closure in 20 infants undergoing congenital heart defect repair or palliative surgery. Embolus counts for specific maneuvers were recorded using widely accepted criteria for identifying emboli via high-intensity transient signals (HITS). An average of only 13% of all HITS detected during an operation were correlated with any of the surgical maneuvers of interest. The highest mean number of HITS associated with a specific maneuver occurred during cross-clamp removal. Cross-clamp placement also had elevated HITS counts that significantly differed from other maneuvers. In this study of infants undergoing cardiac surgery with cardiopulmonary bypass, the great majority of HITS detected are not definitively associated with a specific subset of surgical maneuvers. Among the measured maneuvers, removal of the aortic cross-clamp was associated with the greatest occurrence of HITS. Future recommended research efforts include identifying and confirming other sources for emboli and longitudinal outcome studies to determine if limiting embolic burden affects long-term neurological outcomes.

Aerobic Exercise Acutely Improves Dynamic Cerebral Autoregulation During Brain Activation

PURPOSE: Cognitive function is temporarily improved by acute aerobic exercise, especially clinical high-intensity interval exercise (cHIIE; four 4 min bouts of high-intensity exercise) (Tsukamoto et al. 2016). Meanwhile, dynamic cerebral autoregulation (dCA) is an important cerebrovascular mechanism to maintain relatively constant cerebral blood flow (CBF) against the rapid fluctuations in perfusion pressure, but it is impaired during cognitive tasks (causing brain activation) due to cerebral vasodilation (Ogoh et al. 2018). Although it has been demonstrated that dCA is not changed by aerobic exercise (Tsukamoto et al. 2019), which improves cognitive function (Tsukamoto et al. 2016), the impact of aerobic exercise on the brain activation-induced dCA impairment remains unclear. The purpose of the present study was to investigate the changes in dCA during a cognitive task prior to following different types of aerobic exercise. METHODS: Nine healthy male subjects performed three trials in a randomized crossover order; moderate-intensity continuous exercise (for 40 min), low-volume HIIE (lvHIIE; ten 1 min bouts of high-intensity exercise), and cHIIE protocols. The participants performed a 5 min color-word Stroop task (cognitive task) before, immediately after, and 30 min after each exercise bout. Middle cerebral artery blood flow velocity (Transcranial doppler ultrasonography) and arterial pressure (Finger photosplethysmography) were continuously measured to determine dCA using transfer function analysis, and dCA was estimated at rest and during each cognitive task. RESULTS: Before exercise, transfer function phase in the very low-frequency (VLF) was decreased during cognitive task compared to the resting measurement (P < 0.01), indicating that there was brain activation-induced dCA impairment. However, VLF phase during the cognitive task immediately after exercise was higher than before (P < 0.01) and 30 min (P < 0.01) after exercise regardless of exercise protocol, indicating that dCA impairment during the cognitive task was blunted immediately after exercise. CONCLUSIONS: The brain activation-induced dCA impairment is attenuated immediately after exercise. This result implies that aerobic exercise improves dynamic CBF regulation in response to brain activation during a cognitive task.

Acute Adolescent Concussion: Cerebrovascular Reactivity, Symptom Burden, And Exercise Response

Cerebral vasoreactivity (CVR) disruptions have been observed following concussion, which may exacerbate concussion-related symptoms. These CVR disruptions may also influence the cerebral blood flow (CBF) responses during aerobic exercise and thus limit exercise capacity post-concussion. PURPOSE: To examine the relationships between concussion-related symptoms, cerebral vasculature’s ability to respond to changes in CO2 (vasoreactivity), and CBF responses during sub-maximal aerobic exercise in adolescents post-concussion. METHODS: : Adolescents less than two weeks post-concussion completed the Post-Concussive Symptom Checklist (PCSC), cerebral vascular assessments, and a modified YMCA exercise protocol. CVR at rest was estimated from the slope (cm/s/mmHg) of the relationship between the increases in breath-by-breath end-tidal CO2 and responses of CBF velocity during an air rebreathing task (i.e., increasing end-tidal CO2). CBF velocity was measured via transcranial Doppler ultrasonography at the M1 segment of the middle cerebral artery unilaterally during the air rebreathing task and during the aerobic exercise test. Only physical and vestibular-related symptoms were included in analysis: headache, nausea, balance problems, dizziness, fatigue, and % activity level. Two stepwise linear regressions were conducted to test (1) if concussion symptoms are related to CVR and (2) if CVR predicted relative change in CBF velocity during the aerobic exercise test. RESULTS: The majority of the variance in CVR was explained by symptoms of nausea, dizziness, as well as current physical activity levels. Age, sex, resting heart rate, balance, and fatigue also contributed to a lesser degree. Exercise caused a significant increase in MCA blood flow (p<0.001). This exercise induced increase in CBF was largely explained by CVR and estimated VO2peak, with resting heart rate, prior concussion(s), and time since injury also contributing. CONCLUSIONS: Our findings suggests that symptom burden is related to disruptions in CVR in adolescents in the early weeks after a concussion. In turn, the cerebral blood flow response to exercise was related to both CVR and aerobic capacity, suggesting that disruptions in CVR may impact exercise tolerance post-concussion.

Arterial and Venous Cerebral Blood Flow Velocities and Their Correlation in Healthy Volunteers and Traumatic Brain Injury Patients.

Few studies have explored the cerebral venous compartment or the correlation between venous and arterial cerebral blood flows. We aimed to correlate cerebral blood flow velocities in the arterial (middle cerebral artery) and venous (straight sinus) compartments in healthy volunteers and traumatic brain injury (TBI) patients. In addition, we determined the normative range of these parameters. A total of 122 healthy volunteers and 95 severe TBI patients of both sexes were included and stratified into 3 age groups as follows: group 1 (aged, 18 to 44 y); group 2 (aged, 45 to 64 y); group 3 (older than 65 y). Transcranial Doppler systolic cerebral blood flow velocity, diastolic cerebral blood flow velocity, and mean cerebral blood flow velocity (FVs, FVd, FVm, respectively) were measured in the middle cerebral artery and peak cerebral venous blood flow velocity (FVVs) was measured in the straight sinus. The arteriovenous correlation was assessed on the basis of a positive relationship between FVs and FVVs. There was an arteriovenous correlation (FVs vs. FVVs) in healthy volunteers (R=0.39, P<0.0001). We found no arteriovenous correlation in the TBI cohort overall, but FVs and FVVs were correlated in age group 1 (R=0.28, P=0.05) and in males (R=0.29, P=0.01). In healthy volunteers, FVs and FVm were significantly higher in males compared with females; and FVs, FVm, FVd, FVVs all increased across the age spectrum. There were no significant differences in any of these parameters in TBI patients. There are age and sex differences in arterial and venous cerebral blood flow velocities in healthy volunteers. Arteriovenous correlation is present in healthy volunteers but absent in TBI patients.

Cerebrovascular reactivity: a new frontier for measuring cognitive health in models of accelerated ageing?

Cerebrovascular reactivity: a new frontier for measuring cognitive health in models of accelerated ageing?

Risk Factors for Delayed Neurocognitive Recovery According to Brain Biomarkers and Cerebral Blood Flow Velocity

Background and Objectives: The aim of this study is to identify risk factors for the development of delayed neurocognitive recovery (dNCR). Materials and Methods: 140 patients underwent neurocognitive evaluations (Adenbrooke, MoCa, trial making, and CAM test) and middle cerebral artery (MCA) blood flow velocity (BFV) measurements, one day before cardiac surgery. BFV was re-evaluated after anesthesia induction, before the beginning, middle, end, and after cardiopulmonary bypass (CPB) and postsurgery. To measure glial fibrillary acidic protein (GFAP) and neurofilament heavy chain (Nf-H), blood samples were collected after anesthesia induction, 24 and 48 h after the surgery. Neurocognitive evaluation was repeated 7–10 days after surgery. According to the results, patients were divided into two groups: with dNCR (dNCR group) and without dNCR (non-dNCR group). Results: 101 patients completed participation in this research. GFAP increased in both the non-dNCR group (p < 0.01) and in the dNCR group (p < 0.01), but there was no difference between the groups (after 24 h, p 0.342; after 48 h, p 0.273). Nf-H increased in both groups (p < 0.01), but there was no difference between them (after 24 h, p = 0.240; after 48 h, p = 0.597). MCA BFV was significantly lower in the dNCR group during the bypass (37.13 cm/s SD 7.70 versus 43.40 cm/s SD 9.56; p = 0.001) and after surgery (40.54 cm/s SD 11.21 versus 47.6 cm/s SD 12.01; p = 0.003). Results of neurocognitive tests correlated with CO2 concentration (Pearson’s r 0.40, p < 0.01), hematocrit (r 0.42, p < 0.01), MCA BFV during bypass (r 0.41, p < 0.01), and age (r −0.533, p < 0.01). The probability of developing dNCR increases 1.21 times with every one year of increased age (p < 0.01). The probability of developing dNCR increases 1.07 times with a decrease of BFV within 1 cm/s during bypass (p = 0.02). Conclusion: Risk factors contributing to dNCR among the tested patients were older age and middle cerebral artery blood flow velocity decrease during bypass.

Cerebral macro- and microcirculatory blood flow dynamics in successfully treated chronic hypertensive patients with and without white mater lesions

The mechanisms of high blood pressure (HBP) -related brain pathology progression remain relatively unclear. We investigated whether lowering BP in chronic HBP patients normalizes cerebral perfusion dynamics at resistance vessel and capillary levels. Sixty-seven patients with HBP and 49 age- and sex-matched healthy controls underwent simultaneous recordings of middle cerebral artery blood flow velocity (CBFV), BP, and end-tidal CO2 concentration. Thirty-four controls and 28 patients underwent additional near-infrared spectroscopy recordings (oxygenated [O2Hb] and deoxygenated [HHb] hemoglobin). Degree of microcirculatory white matter lesions was graded by Fazekas scale. Dynamic cerebral autoregulation (dCA) was assessed by transfer function analysis. BP was successfully lowered (patients = 89 ± 15 mm Hg, controls = 87 ± 17), but cerebrovascular resistance was higher in BP patients (p < 0.05). BP-CBFV phase was lower in very low frequency (VLF) (left/right: 48 ± 20°/44 ± 17; controls: 61 ± 20/60 ± 21; p < 0.001) and low frequency (LF) (34 ± 14/35 ± 14; controls: 48 ± 20/44 ± 17; p < 0.05) ranges. Gain was higher in VLF range (in %/ mm Hg 0.56 ± 0.44/0.59 ± 0.49; controls: 0.32 ± 0.29/0.34 ± 0.32; p ≤ 0.005). BP-CBFV phase and gain did not differ across Fazekas groups. Across all patients, the capillary phases and gains (CBFV-[O2Hb], CBFV-[HHb]) were comparable to controls. Successfully treated chronic HBP results in normal brain capillary hemodynamics while the resistance vessel state is disturbed (phase decrease, gain increase).

Imaging transcranial Doppler ultrasound to measure middle cerebral artery blood flow: the importance of measuring vessel diameter.

Cerebral blood flow (CBF) is commonly inferred from blood velocity measurements in the middle cerebral artery (MCA), using nonimaging, transcranial Doppler ultrasound (TCD). However, both blood velocity and vessel diameter are critical components required to accurately determine blood flow, and there is mounting evidence that the MCA is vasoactive. Therefore, the aim of this study was to employ imaging TCD (ITCD), utilizing color flow images and pulse wave velocity, as a novel approach to measure both MCA diameter and blood velocity to accurately quantify changes in MCA blood flow. ITCD was performed at rest in 13 healthy participants (7 men/6 women; 28 ± 5 yr) with pharmaceutically induced vasodilation [nitroglycerin (NTG), 0.8 mg] and without (CON). Measurements were taken for 2 min before and for 5 min following NTG or sham delivery (CON). There was more than a fivefold, significant, fall in MCA blood velocity in response to NTG (∆-4.95 ± 4.6 cm/s) compared to negligible fluctuation in CON (∆-0.88 ± 4.7 cm/s) (P < 0.001). MCA diameter increased significantly in response to NTG (∆0.09 ± 0.04 cm) compared with the basal variation in CON (∆0.00 ± 0.04 cm) (P = 0.018). Interestingly, the product of the NTG-induced fall in MCA blood velocity and increase in diameter was a significant increase in MCA blood flow following NTG (∆144 ± 159 ml/min) compared with CON (∆-5 ± 130 ml/min) (P = 0.005). These juxtaposed findings highlight the importance of measuring both MCA blood velocity and diameter when assessing CBF and document ITCD as a novel approach to achieve this goal.

Effect on Middle Cerebral Artery Blood Flow of Nicardipine Hydrochloride of Acute Intracerebral Hemorrhage: Transcranial Doppler Sonography Study

Effect on Middle Cerebral Artery Blood Flow of Nicardipine Hydrochloride of Acute Intracerebral Hemorrhage: Transcranial Doppler Sonography Study

Human cerebrovascular responses to diving are not related to facial cooling.

What is the central question of this study? Does facial cooling-mediated stimulation of cutaneous trigeminal afferents associated with the diving response increase cerebral blood flow or are factors associated with breath-holding (e.g. arterial carbon dioxide accumulation, pressor response) more important in humans? What is the main finding and its importance? Physiological factors associated with breath-holding such as arterial carbon dioxide accumulation and the pressor response, but not facial cooling (trigeminal nerve stimulation), make the predominant contribution to diving response-mediated increases in cerebral blood flow in humans. Diving evokes a pattern of physiological responses purported to preserve oxygenated blood delivery to vital organs such as the brain. We sought to uncouple the effects of trigeminal nerve stimulation on cerebral blood flow (CBF) from other modifiers associated with the diving response, such as apnoea and changes in arterial carbon dioxide tension. Thirty-seven young healthy individuals participated in separate trials of facial cooling (FC, 3min) and cold pressor test (CPT, 3min) under poikilocapnic (Protocol 1) and isocapnic conditions (Protocol 2), facial cooling while either performing a breath-hold (FC+BH) or breathing spontaneously for a matched duration (FC-BH) (Protocol 3), and BH during facial cooling (BH+FC) or without facial cooling (BH-FC) (Protocol 4). Under poikilocapnic conditions neither facial cooling nor CPT evoked a change in middle cerebral artery blood flow velocity (MCA vmean ; transcranial Doppler) (P>0.05 vs. baseline). Under isocapnic conditions, facial cooling did not change MCA vmean (P>0.05), whereas CPT increased MCA vmean by 13% (P<0.05). Facial cooling with a concurrent BH markedly increased MCA vmean (Δ23%) and internal carotid artery blood flow (ICAQ ; duplex Doppler ultrasound) (Δ26%) (P<0.001), but no change in MCA vmean and ICAQ was observed when facial cooling was accompanied by spontaneous breathing (P>0.05). Finally, MCA vmean and ICAQ were similarly increased by BH either with or without facial cooling. These findings suggest that physiological factors associated with BH, and not facial cooling (i.e. trigeminal nerve stimulation) per se, make the predominant contribution to increases in CBF during diving in humans.

Cardio-respiratory, oxidative stress and acute mountain sickness responses to normobaric and hypobaric hypoxia in prematurely born adults.

We compared the effects of hypobaric and normobaric hypoxia on select cardio-respiratory responses, oxidative stress and acute mountain sickness (AMS) severity in prematurely born individuals, known to exhibit blunted hypoxic ventilatory response. Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840m; PiO2:90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; PiO2:90.6 (0.9) mmHg; FiO2:0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO2), heart rate (HR) and blood pressure were measured before and every 2h during the exposures. Ventilatory responses and middle cerebral artery blood flow velocity (MCAv) were assessed at rest and during submaximal cycling before and at 4 and 8h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points. HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO2 as compared to NH with no significant differences in the ventilatory parameters, HR or blood pressure. No significant differences between conditions were found in resting or exercising MCAv and measured oxidative stress markers. Significantly lower values of ferric-reducing antioxidant power (P = 0.037) were observed during HH as opposed to NH. AMS severity was higher at 8h compared to baseline (P = 0.002) with no significant differences between conditions. These data suggest that, in prematurely born adults, 8-h exposure to hypobaric, as opposed to normobaric hypoxia, provokes greater reductions in systemic oxygenation and antioxidant capacity. Further studies investigating prolonged hypobaric exposures in this population are warranted. NCT02780908 (ClinicalTrials.gov).

Countdown before voluntary exercise induces muscle vasodilation with baroreflex-mediated decrease in muscle sympathetic nerve activity in humans.

We examined whether a countdown (CD) before voluntary cycling exercise induced prospective vascular adjustment for the exercise and, if so, whether and how muscle sympathetic nerve activity (MSNA) was involved in the responses. Young men performed voluntary cycling in a semirecumbent position (n = 14) while middle cerebral artery blood flow velocity (VMCA; Doppler ultrasonography), heart rate (HR), arterial pressure (AP; finger photoplethysmography), oxygen consumption rate (V̇o2), oxygen saturation in the thigh muscle (; near-infrared spectrometry), cardiac output (CO; Modelflow method), and total peripheral resistance (TPR) were measured (experiment 1). Another group underwent the same exercise protocol but used only the right leg (n = 10) while MSNA (microneurography) was measured in the peroneal nerve of the left leg (experiment 2). All subjects performed eight trials with a ≥5-min rest between trials. In four trials randomly selected from the eight trials, exercise onset was signaled by a 30-s CD, whereas in the remaining four trials, exercise was started without CD. We found that CD first increased VMCA, HR, CO, and mean AP, and then decreased TPR and increased and V̇o2 (experiment 1; all P < 0.021). Furthermore, the CD-induced increase in mean AP decreased total MSNA and burst frequency (experiment 2; both P < 0.048) through the baroreflex, with decreased TPR and increased (experiment 2; both P < 0.001). The vasodilation and increased V̇o2 continued after the start of exercise. Thus CD before starting exercise induced the muscle vasodilatory response with a concomitant reduction in MSNA through the baroreflex to accelerate aerobic energy production after the start of exercise.NEW & NOTEWORTHY Prospective cardiovascular adjustment occurs before starting voluntary exercise, increasing heart rate and arterial pressure followed by muscle vasodilation; however, the precise mechanisms and significance for this vasodilation remain unknown. We found that during the countdown before starting exercise cerebral blood flow velocity increased, followed by increases in heart rate and arterial pressure, which suppressed MSNA through baroreflex, resulting in thigh muscle vasodilation to increase oxygen consumption rate, which might make it easier to start exercise.

Cardiovascular disease risk is associated with middle cerebral artery blood flow velocity in older adults.

The aim of this study was to evaluate the relationship of cardiovascular disease (CVD) on middle cerebral blood flow velocity (MCAv) at rest and during exercise. A secondary aim was to explore the relationship between MCAv and 1) the presence of white matter lesions and 2) cognitive function. We recruited individuals who were cognitively normal older adults. CVD risk was assessed by the Pooled Cohort atherosclerotic cardiovascular disease (ASCVD) risk score. Transcranial Doppler ultrasound measured middle cerebral artery at rest and during a bout of moderate intensity exercise. We quantified white matter lesions from MRI and cognitive function outcomes included executive function, language, processing speed, and attention. Seventy-two participants 70.1 ± 4.7 years of age completed the study protocol. ASCVD risk score was significantly associated with resting and exercise MCAv (p<0.01) but not associated with white matter lesions (p>0.468). We observed a significant association between resting and exercise MCAv and language processing (p=0.010) but not other cognitive domains. In cognitively normal older adults, higher ASCVD risk score was associated with blunted resting and exercise MCAv and with lower language processing performance. These results highlight the need for CVD risk management to maintain optimal brain health.

Internal carotid artery blood flow response to cognitive task is similar between young and older adults

Previous studies reported that the increase in the middle cerebral artery blood flow velocity during cognitive task was greater in older adults than in young adults, suggesting age‐related differences in cerebral blood flow responses to cognitive task. However, previous studies utilized transcranial Doppler ultrasound and thereby information regarding arterial diameter, blood volume flow, and vascular conductance was lacking. On the other hand, Doppler ultrasonography can assess blood volume flow in the internal carotid artery (ICA), which provides the blood supply to a large portion of the cerebral cortex. To date, it remains to be determined whether ICA blood flow response to cognitive task is different between young and older adults. The present study examined the ICA blood flow and blood pressure (BP) responses to 20 s of task switching in 6 young (30 ± 3 yr) and 6 older (66 ± 3 yr) subjects. The ICA blood flow and BP did not change significantly during task switching in young subjects. In older subjects, significant ICA blood flow response was not found, while BP increased (p&lt;0.05) slightly and transiently during the first 10 s of the task. In both subjects, vascular conductance of the ICA was unaltered during task switching. Our present findings suggest that the ICA blood flow response to task switching was similar between young and older subjects.Support or Funding InformationGrant‐in‐Aid for Research Activity start‐up from the Japan Society for the Promotion of Science (19K24333)

Dantrolene Improves Cerebral Perfusion More than Nimodipine in a Rat Model of Cerebral‐induced Vasospasm

A cerebral vasospasm (CVSP) is a potent vasoconstriction of the cerebral vasculature, and the primary cause of morbidity and mortality following a hemorrhagic stroke. The middle cerebral artery (MCA) is one of the most common locations affected by CVSPs. Experimental evidence shows that the ryanodine receptor inhibitor dantrolene may be as effective as the Ca+2 channel blocker nimodipine in reducing vasospasms in the systemic vasculature. To determine if this effect also extends to the cerebral vasculature, we used a rat model of cerebral‐induced vasospasms to investigate the effects of intravenously administered dantrolene (2.5 mg/kg) and nimodipine (1 mg/kg) on cerebral blood flow velocity in the MCA. Blood flow velocity was measured in the MCA seven days after vasospasm‐induction, using a PeriFlux 5000 Laser Doppler System. Measurements were performed 30 minutes before and one hour after either dantrolene or nimodipine administration. In addition, hemodynamic parameters (i.e., systolic, diastolic, and mean blood pressures; heart rate) were measured before and after administration of the drugs. Dantrolene decreased MCA blood flow velocity by 35% (from 364.7± 60 to 231.0 ± 34 perfusion units), whereas nimodipine reduced this parameter by only 14% (N=6, P&lt;0.05). For both dantrolene and nimodipine, the hemodynamic parameters remained unchanged (N=6, P&gt;0.05, when compared to results before drug administration). Our results suggest that 2.5 mg/kg dantrolene is more effective than 1 mg/kg nimodipine in reducing vascular reactivity and improving cerebral blood perfusion in the MCA, without altering systemic hemodynamic parameters. Therefore, dantrolene may provide a promising therapy for the management of CVSP and its complications.Support or Funding InformationThis work was supported by Grants from the National Institute of Health (MBRS‐RISE Grant R25GM061838), the NIMHD‐CCRHD‐RCMI Program (U54‐MD007600), and the Anesthesiology Department of the University of Puerto Rico‐School of Medicine.

The influence of blood flow velocity changes to postoperative cognitive dysfunction development in patients undergoing heart surgery with cardiopulmonary bypass.

The aim of this study was to compare blood flow velocity changes in the middle cerebral artery before, during and after heart surgery with cardiopulmonary bypass for patients with and without postoperative cognitive dysfunction. A total of 100 patients, undergoing elective coronary artery bypass grafting or/and valve surgery enrolled in the study. A neurocognitive test evaluation included Adenbrooke, Mini-Mental State Examination and Trial Making test before and 7-10 days after surgery. Middle cerebral artery mean blood flow velocity was evaluated 1 day before the surgery, after anaesthesia induction, before cardiopulmonary bypass, at the beginning, ending and after cardiopulmonary bypass, and post surgery in intensive care unit. Blood samples for glial fibrillary acidic protein were measured after anaesthesia induction, 24 hours and 48 hours after surgery. According to neurocognitive tests results patients were divided in to two groups: patients with and without postoperative cognitive dysfunction. Of the 100, 86 patients completed investigation. After induction, blood flow velocity of the middle cerebral artery was lower in postoperative cognitive dysfunction group (41.2; min 27.91, max 49.47) than in the H group (41.2, min 21.9, max 84.3) p = 0.034, and during cardiopulmonary bypass, blood flow velocity of the middle cerebral artery was lower in the postoperative cognitive dysfunction group (37.35, min 26.6, max 44.02) than the H group (42.3, min 20.1, max 86.5), p = 0.001. After the surgery, blood flow velocity of the middle cerebral artery was lower in the postoperative cognitive dysfunction group (40.7, min 29.7, max 50.4) than in the H group (45.3, min 34.12, max 59.88), p = 0.05. Results of cognitive tests had weak correlation (rho, 0.391) with middle cerebral artery's blood flow velocity after anaesthesia induction (p = 0.001) and during bypass (p = 0.018). The receiver operating characteristic analysis showed that the blood flow velocity of the middle cerebral artery during bypass (area under the curve = 0.735) was a fair predictor for postoperative cognitive dysfunction (p = 0.001). No significant correlations were found among glial fibrillary acidic protein, middle cerebral artery blood flow velocity, and cognitive tests results. Middle cerebral artery's blood flow velocity was decreased after anaesthesia induction and during cardiopulmonary bypass for patients with postoperative cognitive dysfunction comparing with their blood flow velocity preoperatively. Blood flow velocity during bypass has diagnostic value for postoperative cognitive dysfunction. Brain biomarker glial fibrillary acidic protein is not helpful in diagnosing postoperative cognitive dysfunction.

Effects of sildenafil citrate on impedance to flow in the umbilical and fetal middle cerebral arteries in pregnancies at high risk for fetal growth restriction

Objective: To assess whether sildenafil citrate improves blood flow in fetal um- bilical arteries and middle cerebral arteries in pregnancies at high risk for fetal growth restriction. Methods: A quasi-experimental study was carried out at the Department of Ob- stetrics and Gynecology, Suez Canal University Hospital in Ismail- ia over the period from June 2017 to April 2018. Trans-abdominal obstetric ultrasonography (U/S) was done for 30 pregnant women aged24 to 35 years, gestational age ranged between 33- 36 weeks, at high risk for fetal growth restriction (mild pre-eclampsia, diabetes mellitus, history of previous pregnancy with a small for gestational age, stillbirth, severe pre-eclampsia or pregnancies with abnormal umbilical artery indices-above 90th centile). Fetal umbilical and middle cerebral artery blood flow Doppler indices were determined before and 2 and 6 hours after ingestion of sildenafil citrate 20 mg tablet. Results: There was a statistically significant decrease in umbilical artery Dop- pler indices before, two hours and six hours following sildenafil ci- trate therapy in the studied patients (P<0.05) and a statistically signif- icant increase in middle cerebral artery Doppler indices before, two hours and six hours following sildenafil citrate therapy in the studied patients (P<0.05). Conclusions: Sildenafil citrate significantly increases blood flow in the umbilical arteries and normalizes blood flow in fetal middle cerebral arteries in pregnancies at high risk for fetal growth restriction thereby restoring a normal fetal circulation and corrects the “brain sparing” adaptive mechanism.

167: Maternal hyperoxia leads to changes in the fetal aortic isthmus doppler waveform

The doppler velocity pattern in the aortic isthmus (AoI) has been shown to be a valid indicator of cardiac and peripheral circulatory conditions during fetal life. We sought to evaluate changes in the AoI doppler following maternal hyperoxygenation (MH) in utero, during the third trimester of pregnancy. Forty six women with a singleton gestation ≥31 weeks gestational age were prospectively recruited to the study. A fetal echocardiogram was performed on all subjects. Pulsatility index (PI) and Resistance index (RI) were obtained from the AoI. Measurements were also taken of the umbilical artery (UAD), middle cerebral artery (MCA), ductus arteriosus (DA) and pulmonary artery (PA). Doppler measurements were taken at baseline and repeated following MH for 10 minutes at a rate of 12L/min. The median gestational age was 35 [33 – 37] weeks. A decrease in fetal AoI PI following MH was observed (from 2.61 [2.33-2.89] to 2.46 [2.1-2.82], p=0.04). following MH. The resistance index of the AoI decreased from 0.88 to 0.86, p=0.03. There was a decrease in PA PI following hyperoxygenation (from 2.47 [2.11 – 2.80] to 2.08 [1.75 – 2.49], p=0.02). There was no significant change in fetal heart rate or in the resistance indices of the UAD or DA over the study period. There was a significant increase in MCA blood flow, but not in MCA resistance indices. Our findings indicate a reduction in fetal pulmonary vascular resistance with secondary increased fetal pulmonary blood flow in response to MH. This was not achieved at the expense of ductal constriction. There was evidence of improved MCA peak systolic velocity parameters; this was likely due to the positive impact of improved pulmonary venous return on left ventricular preload, leading to improvement of flow in the aorta as demonstrated by the reduced PI in the AoI. The AoI is a fascinating arterial watershed that offers potential to further improve our understanding of fetal hemodynamic physiology. Continued investigation into the use of maternal hyperoxygenation for evaluating fetal cardiovascular physiology is warranted.

27 Cerebral Autoregulation Associated with Falls in Older Persons with Orthostatic Hypotension?

Abstract Background It is considered well-established that orthostatic hypotension (OH) is associated with falls, population-based studies have found that a large proportion of community-dwelling older adults fulfill the criteria for OH without experiencing falls. It is therefore postulated that older individuals with OH may only experience fall if cerebral autoregulation, which is the mechanism by which the brain blood flow is maintained constant through a autoregulatory range, is impaired. Objective To evaluate the relationship between cerebral autoregulation and OH in older individuals with and without a history of falls. Method Individuals aged 3 60 years were recruited from medical clinics, by word of mouth, and from existing research registries. Baseline sociodemographics, detailed medical history and medication history were obtained. Bilateral middle cerebral artery (MCA) blood flow were recorded using transcranial Doppler ultrasound (TCD) synchronized with non-invasive continuous blood pressure and ECG recordings. Synchronized brain blood flow signals, heart trace and blood pressure signals were first recorded during 10 minutes’ supine rest. Participants were then be asked to perform a standard set of mathematical calculations, a Valsalva maneuver and to stand up from a seated position. Results 36 participants have been evaluated to date (13 fallers, 23 non-Fallers). There is no statistically significant difference in gender, ethnicity or height and weight between groups. Fluctuations in MCA flow velocity were observed with spontaneous fluctuations in blood pressure at rest and with induced blood pressure changes during the challenge maneuvers. Visual inspection of the signals obtained suggested that changes in MCA flow velocity were more marked among fallers and non-fallers. Conclusion Synchronization of cerebral blood flow and continuous blood pressure signals opens up numerous new possibilities in research and clinical practice. Our preliminary findings suggest that cerebral autoregulation does play a role in determining the presence of symptomats in older individuals with OH.

Influence of mild-moderate hypocapnia on intracranial pressure slow waves activity in TBI

BackgroundIn traumatic brain injury (TBI) the patterns of intracranial pressure (ICP) waveforms may reflect pathological processes that ultimately lead to unfavorable outcome. In particular, ICP slow waves (sw) (0.005–0.05 Hz) magnitude and complexity have been shown to have positive association with favorable outcome. Mild-moderate hypocapnia is currently used for short periods to treat critical elevations in ICP. Our goals were to assess changes in the ICP sw activity occurring following sudden onset of mild-moderate hypocapnia and to examine the relationship between changes in ICP sw activity and other physiological variables during the hypocapnic challenge.MethodsICP, arterial blood pressure (ABP), and bilateral middle cerebral artery blood flow velocity (FV), were prospectively collected in 29 adult severe TBI patients requiring ICP monitoring and mechanical ventilation in whom a minute volume ventilation increase (15–20% increase in respiratory minute volume) was performed as part of a clinical CO2-reactivity test. The time series were first treated using FFT filter (pass-band set to 0.005–0.05 Hz). Power spectral density analysis was performed. We calculated the following: mean value, standard deviation, variance and coefficient of variation in the time domain; total power and frequency centroid in the frequency domain; cerebrospinal compliance (Ci) and compensatory reserve index (RAP).ResultsHypocapnia led to a decrease in power and increase in frequency centroid and entropy of slow waves in ICP and FV (not ABP). In a multiple linear regression model, RAP at the baseline was the strongest predictor for the decrease in the power of ICP slow waves (p < 0.001).ConclusionIn severe TBI patients, a sudden mild-moderate hypocapnia induces a decrease in mean ICP and FV, but also in slow waves power of both signals. At the same time, it increases their higher frequency content and their morphological complexity. The difference in power of the ICP slow waves between the baseline and the hypocapnia period depends on the baseline cerebrospinal compensatory reserve as measured by RAP.