Hemodynamic Changes In Response Research Articles

Hemodynamic response varies across tactile stimuli with different temporal structures.

Tactile stimuli can be distinguished based on their temporal features (e.g., duration, local frequency, and number of pulses), which are fundamental for vibrotactile frequency perception. Characterizing how the hemodynamic response changes in shape across experimental conditions is important for designing and interpreting fMRI studies on tactile information processing. In this study, we focused on periodic tactile stimuli with different temporal structures and explored the hemodynamic response function (HRF) induced by these stimuli. We found that HRFs were stimulus‐dependent in tactile‐related brain areas. Continuous stimuli induced a greater area of activation and a stronger and narrower hemodynamic response than intermittent stimuli with the same duration. The magnitude of the HRF increased with increasing stimulus duration. By normalizing the characteristics into topographic matrix, nonlinearity was obvious. These results suggested that stimulation patterns and duration within a cycle may be key characters for distinguishing different stimuli. We conclude that different temporal structures of tactile stimuli induced different HRFs, which are essential for vibrotactile perception and should be considered in fMRI experimental designs and analyses.

Hemodynamic Changes in Response to Aerobic Exercise: Near-infrared Spectroscopy Study.

This study aimed to determine the neurophysiological mechanisms underlying the effects of aerobic exercise, which influence brain O2 consumption, on cognitive enhancement. Sixteen healthy men were asked to complete a 2-back test at rest and after moderate and high-intensity aerobic exercise. During the 2-back test, hemodynamic changes within the prefrontal cortex were assessed using high-density functional near-infrared spectroscopy. Scores of the 2-back test, regardless of the exercise intensity, were positively correlated with the hemodynamic changes within the right and left dorsolateral prefrontal cortex (DLPFC). During an 2-back test, there were differences in the hemodynamic changes within the DLPFC with moderate and high-intensity exercise conditions. In the 2-back condition, the accumulated oxyhemoglobin within the right DLPFC after moderate intensity exercise was 7.9% lower than that at baseline, while the accumulated oxyhemoglobin within the left DLPFC was 14.6% higher than that at baseline after high-intensity exercise. In response to the 2-back test, the accumulated oxygenated hemoglobin within the left DLPFC after high-intensity exercise increased more significantly than that observed after moderate intensity exercise. These results show that the right DLPFC consumes O2 more efficiently in response to moderate intensity aerobic exercise than in response to high-intensity aerobic exercise.

Hemodynamic Scaling of Task-Induced Signal Changes in Tumor Subjects.

Background: FMRI signal amplitude can change during stimulus presentation due to underlying neural function and hemodynamic responses limiting the accuracy of fMRI in pre-surgical planning. To account for these changes in fMRI activation signal, we used breath-hold tasks to mimic hemodynamic changes in brain tumor subjects and scaled the activation response.Methods: Motor and/or language fMRI was performed in 21 subjects with brain tumor. A breath-hold task was also performed in these subjects to obtain the hemodynamic response changes independent of neural changes. The task activation signals were calibrated on a voxel wise basis for all the subjects. Direct cortical stimulation was used to verify the scaled results of task-based fMRI.Results: After scaling for the hemodynamic response function (HRF) on a voxel wise basis, the spatial extent of the scaled activation was more clustered together and appeared to minimize false positives. Similarly, accounting for the underlying canonical HRF, the percentage increase of active voxels after scaling had lower standard non-deviation suggesting that the activation response across voxels were more similar.Conclusion: Although preliminary in nature, this study suggests that the variation in hemodynamic changes can be calibrated using breath-hold in brain tumor subjects and can also be used for other clinical cases where the underlying HRF has been altered.

Tracking Changes in Frontal Lobe Hemodynamic Response in Individual Adults With Developmental Language Disorder Following HD tDCS Enhanced Phonological Working Memory Training: An fNIRS Feasibility Study.

Background: Current research suggests a neurobiological marker of developmental language disorder (DLD) in adolescents and young adults may be an atypical neural profile coupled with behavioral performance that overlaps with that of normal controls. Although many imaging techniques are not suitable for the study of speech and language processing in DLD populations, fNIRS may be a viable option. In this study we asked if fNIRS can be used to identify atypical cortical activation patterns in individual adults with DLD and track potential changes in cortical activation patterns following a phonological working memory training protocol enhanced with anodal HD tDCS stimulation to the presupplementary motor area (preSMA).Objective/Hypothesis: The purpose of this study was two-fold: (1) to determine if fNIRS can be used to identify atypical hemodynamic responses in individual young adults with DLD during active spoken word processing and, (2) to determine if fNIRS can detect changes in hemodynamic response in these same adults with DLD following anodal HD tDCS enhanced phonological working memory training.Methods: Two adult subjects with DLD (female, age 25) completed a total of two sessions of fNIRs working memory task prior to and following one session of a non-word repetition task paired with anodal HD tDCS (1.0 mA tDCS; 20 min) to the preSMA. Standardized z-scores of behavioral measures (accuracy and reaction time) and changes in hemodynamic response during an n-back working memory task for the two participants with DLD was compared to that of a normative sample of 21 age- and gender- matched normal controls (ages 18 to 25) prior to and following phonological working memory training.Results: Individual standardized z-scores for each participant with DLD indicated that prior to training, hemoglobin response in the prefrontal lobe for both participants was markedly different from each other and normal controls. Following training, standard scores showed that the hemodynamic response for both participants moved within normal limits for ROIs.Conclusion: These findings highlight the feasibility of fNIRS to establish individual differences in the link between behavior and neural patterns in single subjects with DLD, as well as track individual differences in changes in brain activity following working memory training.

Design of a wearable four-channel near-infrared spectroscopy system for the measurement of brain hemodynamic responses.

Objectives This work describes the design and development of a four-channel near-infrared spectroscopy system to detect the oxygenated and deoxygenated hemoglobin concentration changes in the brain during various motor tasks. Methods The system uses light-emitting diodes corresponding to two wavelengths of 760nm and 850nm sensitive to deoxygenated and oxygenated hemoglobin concentration changes, respectively. The response is detected using a photodetector with an integrated transimpedance amplifier. The system is designed with four channels for functional near-infrared spectroscopy (fNIRS) signals acquisition. Two experiments were conducted to demonstrate the ability of the system to detect the changes in hemodynamic responses of different tasks. In the first experiment, the hemodynamic changes during motor execution and imagery of right- and left-fist clenching tasks were acquired by the developed system and validated against a standard multichannel NIRS system. In another experiment, the fNIRS signals during rest and motor execution of right-fist clenching task were acquired using the system and classified. Results The results demonstrate the ability of the designed system to detect the brain hemodynamic changes during various tasks. Also, the activation patterns obtained by the developed system with a minimum number of channels are on par with those obtained by the commercial system. Conclusions The developed four-channel NIRS system is user-friendly and has been designed with inexpensive components, unlike the commercially available NIRS instruments that are cumbersome and expensive.

Measuring Changes In Attention Task And Hemodynamic Oxygenation In Post-Concussion Patients Using Functional Near-infrared Spectroscopy

Current concussion assessment protocols rely on clinical functioning and thus may not be sensitive to underlying neural deficits. PURPOSE: The purpose of this study was to measure hemodynamic response changes using functional near-infrared spectroscopy (fNIRS) in asymptomatic, post-concussion participants (CON) compared to healthy controls (CTL). METHODS: CON participants (n=9, age=18.44±1.51 years, sex=66% female) diagnosed with a concussion at a Midwestern emergency department were recruited from 2018-2019. CTL participants (n=22, age=23.63±4.55 years, sex=54% female) were recruited through electronic postings and classroom announcements. During the first study visit, participants completed a demographics questionnaire, pain and symptom severity scores, and an attention task. Participants were then fitted for a silicon headband with two fNIRS diode arrays consisting of eight emitters and ten detectors over each hemisphere’s temporal and frontal cortices, superior and middle temporal regions and the parietal cortex. The computerized behavioral attention task consisted of 144 trials spread over six 24-trial task blocks. Mean accuracy (%) and reaction times (s) were recorded, while the fNIRS device measured hemoglobin response. After the first visit, participants were monitored daily for symptom resolution, and completed a second lab visit once symptom count and severity scores reached normative baseline values. Behavioral and neuroimaging fNIRS data from the attention task were analyzed using independent t-tests, with alpha levels set to p<0.05. RESULTS: Once asymptomatic, attention task analyses yielded no significant differences between CON and CTL groups for both mean reaction time (0.003±0.040s, p=0.953) and accuracy (-0.50±0.40%, p=0.47). Analysis of fNIRS data indicated hyperactivity in the pre-frontal cortex, temporal lobe and frontotemporal region of the CON group’s left hemisphere compared to the CTL group (q<0.05, false discovery rate corrected). CONCLUSIONS: Our results suggest post-concussion participants may require additional cognitive resources during attentional tasks in order to maintain normative vigilance. Researchers should continue to evaluate hemodynamic changes, and how these effects may influence making a safe return to activity decision.

Comparison of the resistive indices obtained in the uterine artery and the ophthalmic artery in preeclamptic and normotensive patients in Doppler US.

IntroductionPreeclampsia is a medical condition characterized by hypertension and proteinuria during pregnancy, with the symptoms generally manifesting in the 3rd trimester. Hypertension brings hemodynamic changes; it is therefore expected that arterial blood flow velocity waveforms will be different in the uterine and ophthalmic arteries in preeclampsia. Vascular changes do occur in preeclampsia, which in turn induces hemodynamic changes.AimTo compare mean values of the resistive index of the ophthalmic and uterine arteries in patients with preeclampsia and normotensive individuals in Doppler US.MethodsIn this cross-sectional observational study, ultrasound of the uterine and ophthalmic arteries was performed in 60 pregnant women in the 2nd and 3rd trimester of pregnancy to compare the resistive index of these arteries in preeclamptic and normotensive individuals. All the patients, i.e. 30 preeclamptic and 30 normotensive pregnant women, took part in this study voluntarily. The study was approved by the institutional review board (IRB) of the University of Lahore.ResultsThe mean resistive index of the uterine artery was 0.50 ± 0.08 in normotensive participants and 0.64 ± 0.09 in preeclamptic women, with the p-value <0.001. The mean resistive index of the ophthalmic artery was 0.70 ± 0.05 in normotensive participants and 0.63 ± 0.04 in preeclamptic women, with the p-value <0.001.ConclusionsThere was a significant negative correlation between the resistive index of the uterine and ophthalmic arteries among the patients with preeclampsia and a significant positive correlation among normotensive individuals. Preeclampsia could be easily diagnosed with Doppler ultrasound based on hemodynamic changes in response to vascular changes in the ophthalmic and uterine arteries.

Developmental maturation of inhibitory control circuitry in a high-risk sample: A longitudinal fMRI study

BackgroundThe goal of this work was to characterize the maturation of inhibitory control brain function from childhood to early adulthood using longitudinal data collected in two cohorts. MethodsFunctional MRI during a go/no-go task was conducted in 290 participants, with 88 % undergoing repeated scanning at 1- to 2-year intervals. One group entered the study at age 7–13 years (n = 117); the other entered at age 18–23 years (n = 173). 33.1 % of the sample had two parents with a substance use disorder (SUD), 43.8 % had one parent with an SUD, and 23.1 % had no parents with an SUD. 1162 scans were completed, covering ages 7–28, with longitudinal data from the cohorts overlapping across ages 16–21. A marginal model with sandwich estimator standard errors was used to characterize voxel-wise age-related changes in hemodynamic response associated with successful inhibitory control. ResultsThere was significant positive linear activation associated with age in the frontal, temporal, parietal, and occipital cortices. No clusters survived thresholding with negative linear, positive or negative quadratic, or positive or negative cubic contrasts. ConclusionsThese findings extend previous cross-sectional and small-scale longitudinal studies that have observed positive linear developmental trajectories of brain function during inhibitory control.

The effect of cardiac output on the pharmacokinetics and pharmacodynamics of propofol during closed-loop induction of anesthesia

Background and objectiveIntraoperative hemodynamic stability is essential to safety and post-operative well-being of patients and should be optimized in closed-loop control of anesthesia. Cardiovascular changes inducing variations in pharmacokinetics may require dose modification. Rigorous investigational tools can strengthen current knowledge of the anesthesiologists and support clinical practice. We quantify the cardiovascular response of high-risk patients to closed-loop anesthesia and propose a new application of physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) simulations to examine the effect of hemodynamic changes on the depth of hypnosis (DoH). MethodsWe evaluate clinical hemodynamic changes in response to anesthesia induction in high-risk patients from a study on closed-loop anesthesia. We develop and validate a PBPK-PD model to simulate the effect of changes in cardiac output (CO) on plasma levels and DoH. The wavelet-based anesthetic value for central nervous system monitoring index (WAVCNS) is used as clinical end-point of propofol hypnotic effect. ResultsThe median (interquartile range, IQR) changes in CO and arterial pressure (AP), 3 min after induction of anesthesia, are 22.43 (14.82-36.0) % and 26.60 (22.39-35.33) % respectively. The decrease in heart rate (HR) is less marked, i.e. 8.82 (4.94-12.68) %. The cardiovascular response is comparable or less enhanced than in manual propofol induction studies. PBPK simulations show that the marked decrease in CO coincides with high predicted plasma levels and deep levels of hypnosis, i.e. WAVCNS < 40. PD model identification is improved using the PBPK model rather than a standard three-compartment PK model. PD simulations reveal that a 30% drop in CO can cause a 30% change in WAVCNS. ConclusionsSignificant CO drops produce increased predicted plasma concentrations corresponding to deeper anesthesia, which is potentially dangerous for elderly patients. PBPK-PD model simulations allow studying and quantifying these effects to improve clinical practice.

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English

The effect of demographic characteristics on anxiety and hemodynamic response during intubation in patients undergoing septoplasty

Aim: To investigate whether the demographic characteristics of patients scheduled for septoplasty had an effect on their trait and preoperative state anxiety and hemodynamic response caused by endotracheal intubation. Material and Methods: In our prospective observational study, after the demographic characteristics of the patients were recorded, the State-Trait Anxiety Inventory (STAI) was administered three times to measure preoperative trait (STAI-1), preoperative state (STAI-2) and postoperative state (STAI-3) anxiety. The preoperative basal hemodynamic parameters were noted. The percentage changes in the hemodynamic responses of the patients during intubation (systolic arterial pressure, diastolic arterial pressure, and mean arterial pressure) were evaluated. The relationship between the severity of anxiety and hemodynamic changes was investigated.Results: Preoperative state anxiety was present in 85% of the patients (STAI-2≥50). The mean STAI-1 score was found to be statistically significantly lower in men (42.81) than in women (45.46) (p=0.005). The mean STAI-2 score, showing preoperative state anxiety, was statistically significantly lower in males (53.89) than in females (57.72) (p=0.001). The mean STAI-2 score was 58.05 in patients aged 45 and over and 54.15 in those under 45 years (p0.001). In addition, the percentage changes in hemodynamic response were significantly higher in the group aged 45 and over (systolic arterial pressure: 16.32 mm-Hg, diastolic arterial pressure: 23.88 mm-Hg, mean arterial pressure: 20.34 mm-Hg) (p0.001).Conclusion: In this study, we observed that preoperative state anxiety was more prevalent in elderly and female patients, and the vital changes during endotracheal intubation were seen at a higher rate in elderly patients.

Hemodynamic responses to strength exercise with blood flow restriction in small muscle groups

The aim of this study was to analyze the acute hemodynamic responses to strength exercise with blood flow restriction involving small muscle groups. The sample consisted of 10 male volunteers (22.6 ± 2.07 years, 1.78 ± 0.06 m, 76.32 ± 13.36 kg) who randomly performed two experimental protocols involving the elbow flexion exercise with the dominant arm: strength exercise of the elbow flexors with blood flow restriction (EFBFR) and strength exercise of the elbow flexors without blood flow restriction (EEF). A cross-over design with a seven to ten days interval between the experimental protocols was used. Systolic blood pressure (SBP), diastolic (DBP) and mean (MAP), pulse pressure (PP), heart rate (HR) and double product (DP) were evaluated at rest, immediately after exercise and at 15 minutes of recovery. SBP, DBP and MAP presented a significant increase (p <0.05) immediately after EFBFR when compared to the protocol without blood flow restriction, returning to rest values at the 15 minutes of recovery. DBP significantly reduced (p <0.05) in the recovery period only in the EFBFR experiment and HR increased post-effort in both experiments. The PP and DP did not change between the different times, regardless of the protocol.The results of the present study allow us to conclude that strength exercise with BFR involving small muscle groups was more efficient than exercise without BFR to promote acute changes in hemodynamic responses and that BFR did not represent a cardiovascular risk considering its effects on PP.

Hemodynamic changes in women with symptoms of supine hypotensive syndrome.

Supine positioning during late pregnancy causes the gravid uterus to compress the inferior vena cava, resulting in dramatic hemodynamic changes. The maintenance of placental perfusion requires maternal circulatory and autonomic adaptations. Women with supine hypotensive syndrome (defined as a drop in systolic blood pressure of anything between 15 and 30mmHg or an increase in heart rate of 20 bpm, with or without symptoms) may have reduced ability to compensate for the effects of supine positioning. Twelve womenwith uncomplicated pregnancies and no symptoms of supine hypotension (normal) and 10 women withuncomplicated pregnancies who reportedsymptoms of supine hypotension between 34 and 38weeks' gestation underwent magnetic resonance imaging in the supine and left lateral positions. Phase contrast images were evaluated to measure blood flow through the aorta, inferior vena cava, superior vena cava and azygos vein. Women with symptoms of supine hypotension showed significant reductions in azygos venous flow rate compared with the normal group (-0.15 (-0.30 to -0.01)L/min). Those with symptoms showed no statistically significant compensatory changes in heart rate compared with the normal group (heart rate change 4.5 (-3.1 to 12.1) bpm).Hemodynamic changes in response to positioning were similar across both groups including: a reduction in inferior vena cava blood flow, reduction in cardiac output and an increase in azygos blood flow. Maternal hemodynamic adaptations were found to be consistent across groups irrespective of whether the women had symptoms of supine hypotension. In both groups a reduction in blood flow through the inferior vena cava occurred in the supine position with a subsequent reduction in cardiac output. Both groups showed a compensatory increase in blood flow through the azygos vein in order to partially compensate for this. Taking into account the effect of maternal position, women with symptoms were found to have reduced azygos flow compared with asymptomatic women. There was a significant increase in heart rate when the women were supine than when they were in the left lateral position.

Acute effects of combined Bacopa, American ginseng and whole coffee fruit on working memory and cerebral haemodynamic response of the prefrontal cortex: a double-blind, placebo-controlled study

ABSTRACT Objective: This study assessed whether a multi-ingredient herbal supplement containing Bacopa monniera (BM), Panax quinquefolius ginseng (PQ) and whole coffee fruit extract (WCFE) could enhance cognitive performance and cerebral-cortical activation during tasks of working memory and attention. Method: In a randomised, double-blind, placebo-controlled, between-group study, 40 healthy adults between 18–60 years (M = 34.46 SD = 12.95) completed tasks of working memory and attention at baseline and 45 min post active or placebo supplement consumption. During the cognitive testing, changes in hemodynamic response in the prefrontal cortex (PFC) were continuously measured using functional near-infrared spectroscopy (fNIRS). Results: Working memory task performance on the N-back task was significantly improved following active supplement consumption compared to placebo in terms of accuracy (p < .01) and response time (p < .05). Improved performance was associated with a reduction of PFC activation (p < .001) related to effortful mental demand, reflecting increased neural efficiency concomitant with improved cognitive performance. The effects were independent of background demographics variables and changes in blood glucose response and mood. Discussion: This is the first report of acute effects on cognitive performance in healthy adults following intake of a combined, multi-ingredient herbal supplement with concomitant changes in cerebral haemodynamic response. The potential synergistic effects of polyphenolic compounds on neurocognitive function and fNIRS use in nutritional intervention studies, poses a significant increase in the capacity to understand the effects of dietary compounds on the brain.

Cardiovascular and Orthostatic Responses to a Festive Meal Associated With Alcohol in Young Men.

Aim: Sharing a festive meal associated with alcohol is quite common. While the cardiovascular changes occurring after meal ingestion of different nutrient composition has been well-established, the effects of ingesting a festive versus a standard meal accompanied with alcohol are less clear. Here, we compared the postprandial hemodynamics, cutaneous and psychomotor performance responses after ingestion of a classical Swiss festive meal [cheese fondue (CF)] versus a light ready-meal [Nasi Goreng (NG)], both accompanied with white wine.Methods: In a randomized cross over design, we examined in 12 healthy young men, the continuous cardiovascular, cutaneous, and reaction time responses to ingestion of cheese fondue versus a standard meal at rest (sitting position) and hemodynamic changes in response to orthostatic challenge (active standing) in pre- and postprandial phases.Results: Breath alcohol concentration after wine ingestion was similar after both meal types. Compared to the standard meal, consumption of CF induced higher increases in heart rate (HR), cardiac output (CO), double product (DP) and cardiac power output (CPO), greater vasodilation, and rises in skin blood flow and skin temperature. Greater increases in HR, DP, and mean blood pressure (MBP) were observed during orthostatic challenges with CF compared to NG. A two-choice reaction time task revealed similar reaction times with both meals, suggesting no influence of meal composition on psychomotor performance.Conclusion: In sitting position, CF ingestion induced a more important cardiovascular load compared to NG. Although the dose of alcohol and the festive meal used here did not lead to orthostatic hypotension, eating CF induced a greater cardiometabolic load suggesting that hemodynamic reserves have been encroached during active standing. This may impede the cardiovascular capacity during physical exercise or stress situations, particularly in elderly subjects who are at greater risk for postprandial hypotension and cardiovascular diseases.

The Role of EEG-fMRI in Studying Cognitive Network Alterations in Epilepsy.

Brain functions do not arise from isolated brain regions, but from interactions in widespread networks necessary for both normal and pathological conditions. These Intrinsic Connectivity Networks (ICNs) support cognitive processes such as language, memory, or executive functions, but can be disrupted by epileptic activity. Simultaneous EEG-fMRI can help explore the hemodynamic changes associated with focal or generalized epileptic discharges, thus providing information about both transient and non-transient impairment of cognitive networks related to spatio-temporal overlap with epileptic activity. In the following review, we discuss the importance of interictal discharges and their impact on cognition in different epilepsy syndromes. We explore the cognitive impact of interictal activity in both animal models and human connectivity networks in order to confirm that this effect could have a possible clinical impact for prescribing medication and characterizing post-surgical outcome. Future work is needed to further investigate electrophysiological changes, such as amplitude/latency of single evoked responses or spontaneous epileptic activity in either scalp or intracranial EEG and determine its relative change in hemodynamic response with subsequent network modifications.

Delta-9-tetrahydrocannabinol intoxication is associated with increased prefrontal activation as assessed with functional near-infrared spectroscopy: A report of a potential biomarker of intoxication

The primary psychoactive compound in cannabis, Δ9-tetrahydrocannabinol (THC), binds to cannabinoid receptors (CB1) present in high concentrations in the prefrontal cortex (PFC). It is unknown whether the PFC hemodynamic response changes with THC intoxication. We conducted the first double-blind, placebo-controlled, cross-over study of the effect of THC intoxication on functional near infrared spectroscopy (fNIRS) measures of PFC activation. Fifty-four adult, regular (at least weekly) cannabis users received a single oral dose of synthetic THC (dronabinol; 5–50 mg, dose individually tailored to produce intoxication) and identical placebo on two visits at least one week apart. fNIRS recordings were obtained during a working memory task (N-Back) at three timepoints: before THC/placebo, at 100 min (when peak effects were expected), and at 200 min after THC/placebo administration. Functional data were collected using a continuous-wave NIRS device, with 8 sources and 7 detectors arrayed over the forehead, resulting in 20 channels covering PFC regions. Participants also completed frequent heart rate measures and subjective ratings of intoxication. Approximately half of participants reported significant intoxication. Intoxication ratings were not correlated with dose of THC. Increases in heart rate significantly correlated with intoxication ratings after THC dosing. Results indicated that 100 min after THC administration, oxygenated hemoglobin (HbO) response significantly increased from pre-dose HbO levels throughout the PFC in participants who reported significant intoxication. Changes in HbO response significantly correlated with self-reported intoxication at 100 min after THC administration. Among those who reported intoxication, HbO response decreased at 200 min after THC, when intoxication had largely resolved, compared to the peak THC time point. This study demonstrates that THC intoxication causes increased PFC activity, and fNIRS of the PFC can measure this effect. Increased neural activation in PFC represents a potential biomarker for cannabis intoxication.

APOE gene-dependent BOLD responses to a breath-hold across the adult lifespan.

Age and apolipoprotein E (APOE) e4 genotype are two of the strongest known risk factors for sporadic Alzheimer's disease (AD). Neuroimaging has shown hemodynamic response changes with age, in asymptomatic carriers of the APOE e4 allele, and in AD. In this study, we aimed to characterize and differentiate age- and APOE gene-specific hemodynamic changes to breath-hold and visual stimulation. A further aim was to study whether these responses were modulated by 3-day intake of nitrate, a nitric oxide (NO) source. The study was designed as a randomized, double-blinded, placebo-controlled crossover study, and the study cohort comprised 41 APOE e4 carriers (e3/e4 or e4/e4 genotype) and 40 non-carriers (e3/e3 genotype) aged 30–70 years at enrollment. The participants underwent two scanning sessions, each preceded by ingestion of sodium nitrate or sodium chloride (control). During functional magnetic resonance imaging (fMRI) sessions, participants performed two concurrent tasks; a breath-hold task to probe cerebrovascular reactivity and a visual stimulation task to evoke functional hyperemia, respectively. We found that the blood oxygenation level dependent (BOLD) hemodynamic response to breath-hold was altered in APOE e4 carriers relative to non-carriers. Mid-aged (50–60 years of age) e4 carriers exhibited a significantly increased peak time relative to mid-aged e3 carriers, and peak time for younger (30–40 years of age) e4 carriers was significantly shorter than that of mid-aged e4 carriers. The response width was significantly increased for e4 carriers. The response peak magnitude significantly decreased with age. For the visual stimulation task, we found age-related changes, with reduced response magnitude with age but no significant effect of APOE allele type. We found no effect of nitrate ingestion on BOLD responses evoked by the breath-hold and visual stimulation tasks. The APOE gene-dependent response to breath-hold may reflect NO-independent differences in vascular function.

Differentiating compensatory mechanisms associated with low tolerance to central hypovolemia in women.

Women generally display lower tolerance to acute central hypovolemia than men. The measurement of compensatory reserve (CRM) is a novel metric that provides information about the sum total of all mechanisms that together work to compensate for the relative blood volume deficit. Hemodynamic decompensation occurs with depletion of the CRM (i.e., 0% CRM). In the present study, we hypothesized that the lower tolerance to progressive central hypovolemia reported in women can be explained by a faster reduction rate in CRM compared with men rather than sex differences in absolute integrated compensatory responses. Continuous, noninvasive measures of CRM were collected from 208 healthy volunteers (107 men and 85 women) who underwent progressive stepwise central hypovolemia induced by lower body negative pressure to the point of presyncope. Comparisons revealed shorter ( P < 0.01) times in female participants compared with male participants to reach 30% and 0% CRM. Similarly, the lower body negative pressure level, represented by the cumulative stress index, was less at 30% and 0% CRM in women compared with men ( P < 0.01). Changes in hemodynamic responses and frequency-domain data (oscillations in cerebral blood flow velocity and mean arterial blood pressure) were similar between men and women at 0% CRM ( P > 0.05). We conclude that compensatory responses to central hypovolemia in women were similar to men but were depleted at a faster rate compared with men. The earlier depletion of the compensatory reserve in women appears to be influenced by failure to maintain adequate cerebral oxygen delivery. NEW & NOTEWORTHY We compared hemodynamic and metabolic responses in men and women to experimentally controlled reductions in central blood volume at physiologically equivalent levels of compensatory reserve. We corroborated previous findings that females have lower tolerance to central hypovolemia than males but demonstrated for the first time that compensatory responses are similar. Our findings suggest lower tolerance to central hypovolemia in women results from reaching critical cerebral delivery of oxygen faster than men.

GABAPENTIN

Introduction: There have been several methods used to prevent or attenuate the adverse hemodynamic changes following endotracheal intubation, but not many studies have been done for the same purpose in patients undergoing nasotracheal intubation. Deepening of anaesthesia, omitting cholinergic premedication, pre-treatment with vasodilators such as nitroglycerine, beta blockers, calcium channel blockers and opioids are few of the different techniques used when trachea is intubated orally or nasally, to blunt significant swings in hemodynamic parameters. We assessed the effectiveness of oral gabapentin to determine changes in hemodynamic response in normotensive patients following nasotracheal intubationwith or without laryngoscopy for elective maxillofacial surgeries. Study Design: Randomized double blind, placebo-controlled clinical trial. Setting: Department of Anesthesia &amp; Intensive Care, Fauji Foundation Hospital Rawalpindi. Period: 18 months after approval from the ethical committee. Material &amp; Methods: Total 130 patients were included in the study. These patients were randomly divided into 2 groups. In Group-A patients were given 800 mg gabapentin and in Group-B patients were given placebo. Heart rate and mean arterial pressures were recorded just before intubation as base line values, and then average readings were taken at 1 minute, 3 minutes, 5 minutes and 10 minutes after intubation. Bradycardia and hypotension were adequately treated with intravenous atropine and vasopressors. Data entry and analysis was done by using SPSS 17. Results: Total 130 patients who underwent elective surgeries were included in the study and divided into 2 groups each group containing 65 patients each. At 1st minute MAP in Group-A (oral gabapentin) and in Group-B (Placebo) was 86.89±4.36 and 98.70±4.39. At 3rd minute MAP in Group-A, in Group-B was 83.40±4.05 and 92.93±4.79. At 5th minute MAP was 82.50±5.00 and 88.03±4.22 and lastly at 10th minute MAP was 79.81±5.37 in Group-A and 83.18±4.77 in Group-B respectively. P-value at 1st, 3rd, 5th and at 10th minutes showed that statistically MAP was different in both treatment groups at the above mentioned time intervals. 1st minute: p-value=0.042, 3rd minute: p-value=0.000, 5th minute: p-value=0.000 and at 10th minute: p-value=0.000. At 1st minute heart rate in Group-A and Group-B was 87.89±1.39 and 93.47±6.88 respectively. At 3rd minute heart rate in Group-A and Group-B was 83.47±5.47 and 89.70±6.76. At 5th minute heart rate was 82.10±5.01 and 84.60±5.91 and lastly at 10th minute heart rate was 78.09±6.79 in Group-A and 77.27±5.34 in Group-B respectively. P -value at 1st, 3rd and 5th minutes showed that statistically heart rate was different in both treatment groups at the above mentioned time intervals. But at 10th minute heart rate was statistically same in both treatment groups. 1st minute: p-value=0.144, 3rd minute: p-value=0.000, 5th minute: p-value=0.011 and at 10th minute: p-value=0.448. Conclusion: According to the results of this study it was observed that oral gabapentin is effective in modifying hemodynamic response to nasotracheal intubation in normotensive patients undergoing elective maxillofacial surgeries. MAP (10th Minute: Group-A vs. Group-B: 0.000) &amp; Heart Rate (10th Minute: Group-A vs. Group-B:0.448)