Conscious but not thinking-Mind-blanks during visuomotor tracking: An fMRI study of endogenous attention lapses.

Attention lapses (ALs) are complete lapses of responsiveness in which performance is briefly but completely disrupted and during which, as opposed to microsleeps, the eyes remain open. Although the phenomenon of ALs has been investigated by behavioural and physiological means, the underlying cause of an AL has largely remained elusive. This study aimed to investigate the underlying physiological substrates of behaviourally identified endogenous ALs during a continuous visuomotor task, primarily to answer the question: Were the ALs during this task due to extreme mind-wandering or mind-blanks? The data from two studies were combined, resulting in data from 40 healthy non-sleep-deprived subjects (20M/20F; mean age 27.1 years, 20-45). Only 17 of the 40 subjects were used in the analysis due to a need for a minimum of two ALs per subject. Subjects performed a random 2-D continuous visuomotor tracking task for 50 and 20 min in Studies 1 and 2, respectively. Tracking performance, eye-video, and functional magnetic resonance imaging (fMRI) were recorded simultaneously. A human expert visually inspected the tracking performance and eye-video recordings to identify and categorise lapses of responsiveness as microsleeps or ALs. Changes in neural activity during 85 ALs (17 subjects) relative to responsive tracking were estimated by whole-brain voxel-wise fMRI and by haemodynamic response (HR) analysis in regions of interest (ROIs) from seven key networks to reveal the neural signature of ALs. Changes in functional connectivity (FC) within and between the key ROIs were also estimated. Networks explored were the default mode network, dorsal attention network, frontoparietal network, sensorimotor network, salience network, visual network, and working memory network. Voxel-wise analysis revealed a significant increase in blood-oxygen-level-dependent activity in the overlapping dorsal anterior cingulate cortex and supplementary motor area region but no significant decreases in activity; the increased activity is considered to represent a recovery-of-responsiveness process following an AL. This increased activity was also seen in the HR of the corresponding ROI. Importantly, HR analysis revealed no trend of increased activity in the posterior cingulate of the default mode network, which has been repeatedly demonstrated to be a strong biomarker of mind-wandering. FC analysis showed decoupling of external attention, which supports the involuntary nature of ALs, in addition to the neural recovery processes. Other findings were a decrease in HR in the frontoparietal network before the onset of ALs, and a decrease in FC between default mode network and working memory network. These findings converge to our conclusion that the ALs observed during our task were involuntary mind-blanks. This is further supported behaviourally by the short duration of the ALs (mean 1.7 s), which is considered too brief to be instances of extreme mind-wandering. This is the first study to demonstrate that at least the majority of complete losses of responsiveness on a continuous visuomotor task are, if not due to microsleeps, due to involuntary mind-blanks.

Attenuating the Pressor Response to Laryngoscopy and Endotracheal Intubation in Controlled Hypertensives: The Effect of Combining Lidocaine and Magnesium Sulphate.

BACKGROUND: Laryngoscopy and intubation result in a pressor response which may be deleterious especially in hypertensives, resulting in potentially harmful effects. Many drugs have been used to attenuate this undesirable pressor response to laryngoscopy and intubation in hypertensives; amongst them are magnesium alone in different doses or in combination with lidocaine. However, drug combinations have been found to be more effective than single drug therapy. OBJECTIVE: This study compared the different doses of magnesium sulphate and its combination with lidocaine for the attenuation of the pressor response. METHODS: A prospective, randomized, double-blinded study. Nighty-six controlled hypertensives (ASA physical status II) scheduled for elective surgery under general anaesthesia and who required endotracheal intubation were recruited and randomized into either Group I (they received 30mg/kg of IV MgSO4 plus 1.5mg/kg of 2% lidocaine) or Groups II and III who received 30mg/kg and 40mg/kg of IV MgSO4 alone, respectively. The outcome was the change in the systolic blood pressure (SBP) from the baseline following administration of study medication and after laryngoscopy and endotracheal intubation. The side effects of study medication and changes in serum magnesium level prior to and after 30 minutes of administering study medication were documented. RESULTS: The post-intubation SBP was attenuated in patients in groups I and III only. However, five patients in group III had hypotension. Serum magnesium levels were higher than their respective baseline values in all the groups. CONCLUSION: The combination of 1.5 mg/kg of 2% lidocaine and 30 mg/kg of MgSO4 is more effective than 30 mg/kg of MgSO4 alone and even MgSO4at the higher dose of 40 mg/kg.

CONTEXTE: La laryngoscopie et l'intubation entraînent une réponse pressive, qui peut être délétère, surtout chez les hypertendus, entraînant des effets potentiellement dangereux. De nombreux médicaments ont été utilisés pour atténuer cette réponse pressive indésirable à la laryngoscopie et à l'intubation chez les hypertendus, parmi lesquels le magnésium seul à différentes doses ou en association avec la lignocaïne. Cependant, les associations de médicaments se sont avérées plus efficaces qu'un traitement médicamenteux unique. OBJECTIF: Cette étude a comparé les différentes doses de sulfate de magnésium et son association avec la lidocaïne pour l'atténuation de la réponse pressive. MÉTHODES: Une étude prospective, randomisée, en double aveugle. Six hypertendus contrôlés (statut physique ASA II) prévus pour une chirurgie élective sous anesthésie générale et nécessitant une intubation endotrachéale ont été recrutés et randomisés dans le groupe I, ils ont reçu 30mg/kg de MgSO4 1V plus I,5mg/kg de lidocaïne à 2%, les groupes II et III ont reçu respectivement 30mg/kg et 40mg/kg de MgSO4 IV seul. Les résultats étaient les changements de la pression artérielle systolique (PAS) par rapport à la ligne de base après l'administration du médicament étudié et après la laryngoscopie et l'intubation endotrachéale. Les effets secondaires du médicament à l'étude et les changements du taux de magnésium sérique avant et après 30 minutes d'administration du médicament à l'étude ont été documentés. RÉSULTATS: La PAS après intubation a été atténuée chez les patients des groupes I et III seulement. Cependant, cinq patients du groupe III ont présenté une hypotension. Les niveaux de magnésium sérique étaient plus élevés que leurs valeurs de base respectives dans tous les groupes. CONCLUSION: L'association de 1,5 mg/kg de lidocaïne à 2 % et de 30 mg/kg de MgSO4 est plus efficace que 30 mg/kg de MgSO4 seul et même à la dose supérieure de 40 mg/kg. Mots clés: Sulfate de magnésium, Lidocaïne, Laryngoscopie et intubation endotrachéale, Réponse hémodynamique, Taux sériques de MgSO4.

Changes in visual cortical function in moderately myopic patients: a functional near-infrared spectroscopy study.

PURPOSE: To investigate haemoglobin oxygenation in the visual cortex of myopic patients using functional near-infrared spectroscopy (fNIRS). METHODS: The experiment consisted of two parts. Part 1 examined functional changes in the visual cortex before and after refractive correction in myopic patients. Subjects were divided into normal controls, uncorrected and corrected myopes. Part 2 examined functional changes in the visual cortex caused by lens-induced myopia in normal subjects, and whether this activity recovered after a period of rest. Here, subjects were divided into three groups: emmetropes, lens-induced myopia and a rest group. The rest group completed a test with the uncorrected eye following lens removal and 5 min of rest. The visual stimulus was a black and white checkerboard. fNIRS was used to detect changes in oxyhaemoglobin content within the visual cortex. The original fNIRS data were analysed using MATLAB to obtain the ß values (the visual cortical activity response caused by the task); these were used to calculate Δß, which represents the degree of change in oxygenated haemoglobin caused by visual stimulation. RESULTS: The Δß value measured in each single channel or only in the region of interest (ROI) was significantly higher in the emmetropic control group than the uncorrected myopic group. After optical correction, the responses of myopic subjects approached those of the emmetropes and were not significantly different. If myopia was induced in emmetropic subjects by imposing defocus with positive lenses, a decline in functional activity was observed similar that observed in uncorrected myopes. Activity recovered after the lenses were removed. CONCLUSIONS: Myopic defocus reduced the level of haemoglobin oxygenation in the visual cortex, but activity could be restored by optical correction.

Tailored haemodynamic response function increases detection power of fMRI in awake dogs (Canis familiaris).

Functional magnetic resonance imaging (fMRI) of awake and unrestrained dogs (Canis familiaris) has been established as a novel opportunity for comparative neuroimaging, promising important insights into the evolutionary roots of human brain function and cognition. However, data processing and analysis pipelines are often derivatives of methodological standards developed for human neuroimaging, which may be problematic due to profound neurophysiological and anatomical differences between humans and dogs. Here, we explore whether dog fMRI studies would benefit from a tailored dog haemodynamic response function (HRF). In two independent experiments, dogs were presented with different visual stimuli. BOLD signal changes in the visual cortex during these experiments were used for (a) the identification and estimation of a tailored dog HRF, and (b) the independent validation of the resulting dog HRF estimate. Time course analyses revealed that the BOLD signal in the primary visual cortex peaked significantly earlier in dogs compared to humans, while being comparable in shape. Deriving a tailored dog HRF significantly improved the model fit in both experiments, compared to the canonical HRF used in human fMRI. Using the dog HRF yielded significantly increased activation during visual stimulation, extending from the occipital lobe to the caudal parietal cortex, the bilateral temporal cortex, into bilateral hippocampal and thalamic regions. In sum, our findings provide robust evidence for an earlier onset of the dog HRF in two visual stimulation paradigms, and suggest that using such an HRF will be important to increase fMRI detection power in canine neuroimaging. By providing the parameters of the tailored dog HRF and related code, we encourage and enable other researchers to validate whether our findings generalize to other sensory modalities and experimental paradigms.

Comparison of Esmolol and Dexmedetomidine Infusion in Attenuating Haemodynamic and Blood Glucose Response to Laryngoscopy and Intubation: A Single Blinded Study.

BACKGROUND: This study aims to compare the effect of infusions of two agents, dexmedetomidine and esmolol, with the control group in attenuating the haemodynamic stress response and neuroendocrine modulation surrogated by capillary blood glucose (BG) during the procedures. METHODS: Sixty patients aged 18-70 years old who underwent elective surgeries involving endotracheal intubation were randomised into three groups of equal size: i) control; ii) dexmedetomidine and iii) esmolol. Heart rate (HR) was measured at baseline (T0), after drug administration (T1), after induction of anaesthesia (T2), immediately after intubation (T3), and 3 min, 5 min and 10 min after intubation (T4, T5 and T6). BG was measured pre-operatively and 30 min post-intubation. RESULTS: Two-way repeated-measures analysis of variance showed significant time [within-group changes, F(3.2, 182.5) = 30.39, P < 0.001], treatment [between-group differences regardless of time, F(2, 57) = 50.24, P < 0.001] and interaction [between-group differences based on time, F(6.4, 182.5) = 37.65, P < 0.001] effects on HR. A significantly higher HR was observed in the control group compared to the dexmedetomidine and esmolol groups from T2 to T6. BG exhibited a significant time effect [F(1, 57) = 41.97, P < 0.001] with no significant treatment and interaction effects. All three groups showed a significant increase in BG from baseline. CONCLUSION: Both dexmedetomidine and esmolol are equally effective in attenuating haemodynamic responses to laryngoscopy and intubation. However, both do not significantly modulate neuroendocrine stress.

Optimising neonatal fMRI data analysis: Design and validation of an extended dHCP preprocessing pipeline to characterise noxious-evoked brain activity in infants.

The infant brain is unlike the adult brain, with considerable differences in morphological, neurodynamic, and haemodynamic features. As the majority of current MRI analysis tools were designed for use in adults, a primary objective of the Developing Human Connectome Project (dHCP) is to develop optimised methodological pipelines for the analysis of neonatal structural, resting state, and diffusion MRI data. Here, in an independent neonatal dataset we have extended and optimised the dHCP fMRI preprocessing pipeline for the analysis of stimulus-response fMRI data. We describe and validate this extended dHCP fMRI preprocessing pipeline to analyse changes in brain activity evoked following an acute noxious stimulus applied to the infant's foot. We compare the results obtained from this extended dHCP pipeline to results obtained from a typical FSL FEAT-based analysis pipeline, evaluating the pipelines' outputs using a wide range of tests. We demonstrate that a substantial increase in spatial specificity and sensitivity to signal can be attained with a bespoke neonatal preprocessing pipeline through optimised motion and distortion correction, ICA-based denoising, and haemodynamic modelling. The improved sensitivity and specificity, made possible with this extended dHCP pipeline, will be paramount in making further progress in our understanding of the development of sensory processing in the infant brain.

Haemodynamic responses to simulated long working hours in different age groups.

OBJECTIVES: This study aimed to clarify haemodynamic responses of different age groups to simulated long working hours. METHODS: Men of three age groups participated in this study (16 in their 30s (mean 33.9±2.7 years old), 15 in their 40s (45.5±2.9) and 16 in their 50s (54.1±2.7)). All participants conducted 12 45-min personal computer-based tasks from 09:00 to 22:00. Nine 10-min to 15-min breaks between task periods, a 1-hour break at noon, and a 50-min break in the evening were provided. Haemodynamic responses were measured during task periods. All participants had normal resting systolic blood pressure (SBP <140 mm Hg) and diastolic blood pressure (DBP<90 mm Hg), which were measured before tasks started in the morning. Two-way repeated-measures analysis of variances and multiple comparisons (Bonferroni) were conducted. RESULTS: No haemodynamic indices were significantly different among groups at baseline. Compared with baseline, SBP was almost unchanged for the 30s group but increased for the 40s and 50s groups during task periods. The 50s group showed higher SBP compared with the 30s group especially in the latter half of the working hours (p<0.05). In addition, the 50s group also showed higher total peripheral resistance (TPR) than the 30s group (p<0.1). CONCLUSION: The 50s group showed higher SBP and TPR responses than the 30s group, especially in the latter half of working hours. These results suggest that older workers might suffer more cardiovascular damage related to long working hours.

Force related hemodynamic responses during execution and imagery of a hand grip task: A functional near infrared spectroscopy study.

We examined force related hemodynamic changes during the performance of a motor execution (ME) and motor imagery (MI) task by means of multichannel functional near infrared spectroscopy (fNIRS). The hemodynamic responses of fourteen healthy participants were measured while they performed a hand grip execution or imagery task with low and high grip forces. We found an overall higher increase of [oxy-Hb] concentration changes during ME for both grip forces but with a delayed peak maximum for the lower grip force. During the MI task with lower grip force, the [oxy-Hb] level increases are stronger compared to the MI with higher grip force. The facilitation in performing MI with higher grip strength might thus indicate less inhibition of the actual motor act which could also explain the later increase onset of [oxy-Hb] in the ME task with the lower grip force. Our results suggest that execution and imagery of a hand grip task with high and low grip forces, leads to different cortical activation patterns. Since impaired control of grip forces during object manipulation in particular is one aspect of fine motor control deficits after stroke, our study will contribute to future rehabilitation programs enhancing patient's grip force control.

Using Functional Near Infrared Spectroscopy (fNIRS) to Study Dynamic Stereoscopic Depth Perception.

The parietal cortex has been widely implicated in the processing of depth perception by many neuroimaging studies, yet functional near infrared spectroscopy (fNIRS) has been an under-utilised tool to examine the relationship of oxy- ([HbO]) and de-oxyhaemoglobin ([HbR]) in perception. Here we examine the haemodynamic response (HDR) to the processing of induced depth stimulation using dynamic random-dot-stereograms (RDS). We used fNIRS to measure the HDR associated with depth perception in healthy young adults (n = 13, mean age 24). Using a blocked design, absolute values of [HbO] and [HbR] were recorded across parieto-occipital and occipital cortices, in response to dynamic RDS. Control and test images were identical except for the horizontal shift in pixels in the RDS that resulted in binocular disparity and induced the percept of a 3D sine wave that 'popped out' of the test stimulus. The control stimulus had zero disparity and induced a 'flat' percept. All participants had stereoacuity within normal clinical limits and successfully perceived the depth in the dynamic RDS. Results showed a significant effect of this complex visual stimulation in the right parieto-occipital cortex (p < 0.01, η(2) = 0.54). The test stimulus elicited a significant increase in [HbO] during depth perception compared to the control image (p < 0.001, 99.99 % CI [0.008-0.294]). The similarity between the two stimuli may have resulted in the HDR of the occipital cortex showing no significant increase or decrease of cerebral oxygenation levels during depth stimulation. Cerebral oxygenation measures of [HbO] confirmed the strong association of the right parieto-occipital cortex with processing depth perception. Our study demonstrates the validity of fNIRS to investigate [HbO] and [HbR] during high-level visual processing of complex stimuli.

Characterisation and Comparison of Acute Haemodynamic, Cardiac Biochemical and Hormonal Response to Different Ventricular Pacing Sites in the Normal Heart.

BACKGROUND: Acute cardiac response to right ventricular pacing is unknown. We aimed to assess the acute haemodynamic, biochemical and hormonal response to asynchronous right ventricular pacing and investigate whether there is a difference between an apical and outflow tract site. METHODS: In 21 patients with normal cardiac function, haemodynamics, brain natriuretic peptide and high sensitive troponin T were measured in response to 10minutes of pacing at each site in a randomised crossover fashion and compared. RESULTS: Pacing both sites there were significant increases in pulmonary capillary wedge pressures (p<0.001) and QRS width (p< 0.01). In comparison to baseline, apical pacing demonstrated significant (p<0.05) increases in arterial peptide and troponin levels and venous peptide levels. Outflow tract pacing compared to baseline demonstrated significant (p<0.05) increases in arterial peptide and venous, arterial and coronary sinus troponin. There were no significant differences in responses between sites. CONCLUSION: Asynchronous right ventricular pacing demonstrated significant increases in filling pressures, cardiac hormonal and biochemical response above baseline with very short durations of pacing (10minutes). There was no difference in response between sites. These findings imply that even very short periods of right ventricular based pacing are potentially deleterious.

Cortical excitability and the shape of the haemodynamic response.

Individual differences in the temporal dynamics of the haemodynamic response can reflect cortical excitation and can reveal underlying cortical physiology. Here, we show differences in the shape of the haemodynamic response that are dependent on stimulus parameters. Two sets of visual stimuli were used varying in parameters that are known to manipulate the haemodynamic response in the visual cortex. We measured the oxyhaemoglobin response using near infrared spectroscopy. The first set of stimuli comprised chromatic square-wave gratings that varied with respect to the separation in the CIE UCS chromaticities of the alternating bars. The gratings with large separations in chromaticity evoked an oxyhaemoglobin response with greater amplitude, consistent with greater activation of the visual cortex. The second set of stimuli comprised horizontal achromatic gratings that (1) were static, (2) drifted at a constant velocity towards fixation, or (3) reversed direction every half spatial cycle to create a vertical vibrating motion. Although the three types of grating had a similar effect on the amplitude of the oxyhaemoglobin response, the moving gratings (2 and 3) evoked a steeper decrease in oxyhaemoglobin concentration after stimulus-offset. The steeper slope appears to reflect the post-stimulus undershoot and the slope may provide a correlate of cortical excitability when the amplitude of the haemodynamic response has saturated.

Haemodynamic response associated with both ictal and interictal epileptiform activity using simultaneous video electroencephalography/near infrared spectroscopy in a within-subject study.

This paper reports the findings from a pilot study of four patients with medically refractory epilepsy undergoing pre-surgical evaluation with ages ranging from 5 to 17 years. Video electroencephalography recordings and data from a near infrared spectroscopy cerebral/somatic oximeter were gathered and related to electrographic seizure onset and offset as determined by a paediatric epileptologist. All four patients showed haemodynamic changes associated with epileptiform activities. The increased blood flow clearly coincided with epileptiform activity and continued to increase as the epileptiform activity built up. Regional cerebral oxygen saturation increased in the epileptogenic focus, perhaps due to loss of cerebrovascular autoregulation. These findings reinforce that near infrared spectroscopy can potentially be used in a wide spectrum of patients with epilepsy regardless of the underlying brain pathology.

Comparison of the Magnesium Sulphate With Paracetamol Combination vs the Fentanyl With Lignocaine Combination in Attenuating the Hemodynamic Response During Laryngoscopy and Intubation: A Prospective, Double-Blinded Randomized Controlled Study.

Background and aims Laryngoscopy and intubation cause an increased sympatho-adrenergic pressor response, which can be detrimental to patients with coronary artery disease, hypertension, etc. Various drugs and manoeuvres have been tried to reduce the pressor response with acceptable results but the quest for the ideal drug still continues. Hence, we planned to compare the effects of magnesium sulfate with paracetamol and fentanyl with lignocaine on attenuating the hemodynamic responses due to direct laryngoscopy and intubation and to note the complications of these drugs. Methods We studied 60 adult patients of the American Society of Anaesthesiologists (ASA) physical status I and II of either sex, scheduled for elective surgery under general anaesthesia. The patients were randomly divided into two groups. Group A received 25 mg/kg magnesium sulphate mixed with paracetamol 1 gram IV (100 ml) given over 10 minutes before induction and Group B received 2 mcg/kg fentanyl and 1.5 mg/kg lignocaine, 3 minutes before intubation. All patients were uniformly pre-medicated, induced, and intubated as per standard protocol. Heart rate (HR) and systemic arterial pressures were recorded at baseline, after study drug infusion, after induction, and 1, 3, 5, 10, and 15 mins after intubation. Hemodynamic parameters were compared using repeated measures analysis of variance (ANOVA). In the post-hoc tests, p value < 0.05 was considered statistically significant. Results We observed the mean pre-op HR (p = 0.161) and mean HR one-minute post-induction (p = 0.144). The percentage change from baseline at one-minute post-induction was 9.7 in Group A and 15.2 in Group B. We observed the mean pre-op mean arterial pressure (MAP) (p = 0.119) and mean MAP one minute post-induction (p = 0.585). The percentage change from baseline at one-minute post-induction was 3.3 in Group A and 2.8 in Group B. The percentage change from baseline was found to be within 15%, for HR in Group A and for systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP in Group B. However, there was no statistically significant difference (p > 0.05) between the mean HR, SBP, DBP, and MAP between the time points. Conclusion In our study, both the combinations of drugs, magnesium sulphate with paracetamol (Group A drugs) and fentanyl with lignocaine (Group B drugs) were found to be equally effective (i.e. neither group was superior to the other) in attenuating the hemodynamic response to laryngoscopy and intubation.

Cerebral haemodynamic response to somatosensory stimulation in preterm lambs and 7-10-day old lambs born at term: Direct synchrotron microangiography assessment.

Neurovascular coupling has been well-defined in the adult brain, but variable and inconsistent responses have been observed in the neonatal brain. The mechanisms that underlie functional haemodynamic responses in the developing brain are unknown. Synchrotron radiation (SR) microangiography enables in vivo high-resolution imaging of the cerebral vasculature. We exploited SR microangiography to investigate the microvascular changes underlying the cerebral haemodynamic response in preterm (n = 7) and 7-10-day old term lambs (n = 4), following median nerve stimulation of 1.8, 4.8 and 7.8 sec durations.Increasing durations of somatosensory stimulation significantly increased the number of cortical microvessels of ≤200 µm diameter in 7-10-day old term lambs (p < 0.05) but not preterm lambs where, in contrast, stimulation increased the diameter of cerebral microvessels with a baseline diameter of ≤200 µm. Preterm lambs demonstrated positive functional responses with increased oxyhaemoglobin measured by near infrared spectroscopy, while 7-10-day old term lambs demonstrated both positive and negative responses. Our findings suggest the vascular mechanisms underlying the functional haemodynamic response differ between the preterm and 7-10-day old term brain. The preterm brain depends on vasodilatation of microvessels without recruitment of additional vessels, suggesting a limited capacity to mount higher cerebral haemodynamic responses when faced with prolonged or stronger neural stimulation.

Searching for the Mechanism of Action of Extremely Low Frequency Electromagnetic Field-The Pilot fNIRS Research.

There is an ongoing debate on the benefits of magnetic stimulation in neurological disorders. OBJECTIVES: We aimed to evaluate the influence of magnetic stimulation on blood oxygenation of the motor cortex using functional near-infrared spectroscopy (fNIRS). METHODS: A total of 16 healthy volunteer participants were subjected to four protocols. In the first two protocols, the participants remained at rest without (and then with) magnetic stimulation. In the next two protocols, motor cortex stimulation was achieved using a finger-tapping task, with and without magnetic stimulation. Changes in blood oxygenation levels within the motor cortex were recorded and analysed. RESULTS: No characteristic changes in the blood oxygenation level-dependent responses were observed in resting participants after magnetic stimulation. No statistically significant difference was observed in the amplitude of the fNIRS signal before and after magnetic stimulation. We observed characteristic blood oxygenation level-dependent responses after the finger-tapping task in the second protocol, but not after magnetic stimulation. CONCLUSIONS: Although we did not observe any measurable effect of the magnetic field on the haemodynamic response of the motor cortex, understanding the mechanism(s) of magnetic stimulation may be important. Additional, detailed studies are needed to prove or negate the potential of this medical procedure.

The cerebral haemodynamic response to somatosensory stimulation in preterm newborn lambs is reduced following intrauterine inflammation and dopamine infusion.

BACKGROUND: Neurovascular coupling leads to an increase in local cerebral blood flow and oxygenation in response to increased neural activity. Reduced cerebral functional responses may predispose to tissue hypoxia when neural activity is increased. Intrauterine inflammation, identified clinically as chorioamnionitis, is a major contributor to the neuropathology arising after preterm birth. The impact of chorioamnionitis on the preterm cerebral functional haemodynamic response is unknown. Previously, we have reported that somatosensory stimulation produces predominantly positive cerebral haemodynamic responses (i.e., increased cerebral oxygenation) in preterm lambs, which are reduced with dopamine treatment. As preterm infants born after chorioamnionitis often suffer from hypotension and are treated with dopamine, we aimed to investigate how chorioamnionitis with and without dopamine treatment affect the cerebral haemodynamic response in preterm lambs. METHODS: At 119 days of gestation, intrauterine inflammation was induced by intra-amniotic injection of lipopolysaccharide (LPS) in pregnant ewes. At 126-7 days of gestation (term is ~147 days), these LPS-exposed lambs were delivered and mechanically ventilated. The cerebral functional response was assessed by near infrared spectroscopy as changes in cerebral oxy- and deoxyhaemoglobin (ΔoxyHb, ΔdeoxyHb), following left median nerve stimulation of 1.8, 4.8 and 7.8 s durations without dopamine; and 4.8 and 7.8 s stimulations with intravenous dopamine infusion. RESULTS: Stimulation for 1.8, 4.8 and 7.8 s durations led to negative functional responses (decreased ΔoxyHb) in 5 (62.5%), 5 (62.5%) and 4 (50%) of 8 preterm lambs respectively, while other lambs showed positive responses (increased ∆oxyHb). Dopamine infusion increased baseline tissue oxygenation index (TOI), oxyHb and total Hb. In lambs with a positive functional response, dopamine decreased the evoked ΔoxyHb response, increasing the overall incidence of negative cerebral haemodynamic responses. CONCLUSIONS: Somatosensory stimulation produced mostly negative responses with decreased cerebral oxygenation in preterm lambs exposed to intrauterine inflammation, contrasting with our previous findings of predominantly positive responses in non-inflamed, control, preterm lambs. Dopamine increased baseline cerebral oxygenation, but further increased the incidence of negative functional responses. Impaired neurovascular coupling leading to intermittent localised tissue hypoxia may therefore contribute to the neuropathy in infants with chorioamnionitis, with the risk of injury exacerbated with dopamine treatment.

Dopaminergic neuromodulation has no detectable effect on visual-cue induced haemodynamic response function in the visual cortex: A double-blind, placebo-controlled functional magnetic resonance imaging study.

The aim of this study was to investigate the effect of acute dopamine agonistic and antagonistic manipulation on the visual-cue induced blood oxygen level-dependent signal response in healthy volunteers. Seventeen healthy volunteers in a double-blind placebo-controlled cross-over design received either a dopamine antagonist, agonist or placebo and underwent functional magnetic resonance imaging. Using classical inference and Bayesian statistics, we found no effect of dopaminergic modulation on properties of visual-cue induced blood oxygen level-dependent signals in the visual cortex, particularly on distinct properties of the haemodynamic response function (amplitude, time-to-peak and width). Dopamine-related effects modulating the neurovascular coupling in the visual cortex might be negligible when measured via functional magnetic resonance imaging.

Haemodynamic responses following orotracheal intubation in patients with hypertension---Macintosh direct laryngoscope versus Glidescope®videolaryngoscope.

BACKGROUND AND AIMS: Glidescope®videolaryngoscope (GVL) is a video intubation system with 60° angle blade that provides excellent laryngeal view, does not require alignment of oral, pharyngeal, and laryngeal axes for visualisation of glottis, thus causing less stimulation of orolaryngopharynx. The aim of this study was to compare haemodynamic responses (blood pressure and heart rate) and airway morbidity using the Macintosh direct laryngoscope (MDL) and the Glidescope®videolaryngoscope (GVL) in hypertensive patients. METHODS: Fifty patients with hypertension controlled on antihypertensive medications scheduled for elective surgery under general anaesthesia were randomly assigned to group GVL (n = 25) or group MDL (n = 25). Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP) were recorded at baseline, after induction, pre-intubation, at intubation, 1, 2, 3, 4, and 5 min after intubation. Time to intubation, number of attempts, complications during intubation, and postoperative airway complications (sore throat, hoarseness, dysphagia, and cough) were also recorded. RESULTS: There was a statistically significant increase in SBP, DBP, and MBP at intubation [(P = 0.003, 0.013, 0.03), 1 min (P = 0.001, 0.012, 0.02), 2 min (P = 0.04, 0.02, 0.04), and 3 min (P = 0.02, 0.01)] in the MDL group as compared to GVL group. The time to intubate was significantly greater in the GVL group as compared to MDL group (P = 0.0006). There was no significant difference in the incidence of intraoperative and postoperative airway complications. CONCLUSION: In the hands of an experienced anaesthesiologist, the use of GVL in controlled hypertensive patients is associated with less haemodynamic response as compared to Macintosh Laryngoscope without any increase in airway complications.

The cerebral haemodynamic response to somatosensory stimulation in preterm newborn lambs is reduced with dopamine or dobutamine infusion.

BACKGROUND: In the adult brain, increases in neural activity lead to increases in local blood flow. However, in the preterm neonate, studies of cerebral functional haemodynamics have yielded inconsistent results, including negative responses suggesting decreased perfusion and localised tissue hypoxia, probably due to immature neurovascular coupling. Furthermore, the impact of vasoactive medications, such as dopamine and dobutamine used as inotropic therapies in preterm neonates, on cerebrovascular responses to somatosensory input is unknown. We aimed to characterise the cerebral haemodynamic functional response after somatosensory stimulation in the preterm newborn brain, with and without dopamine or dobutamine treatment. METHODS: We studied the cerebral haemodynamic functional response in 13 anaesthetised preterm lambs, using near infrared spectroscopy to measure changes in cerebral oxy- and deoxyhaemoglobin (ΔoxyHb, ΔdeoxyHb) following left median nerve stimulation using stimulus trains of 1.8, 4.8 and 7.8 s. The 4.8 and 7.8 s stimulations were repeated during dopamine or dobutamine infusion. RESULTS: Stimulation always produced a somatosensory evoked response. Majority of preterm lambs demonstrated positive functional responses (i.e. increased ΔoxyHb) in the contralateral cortex following stimulus trains of all durations. Dopamine increased baseline oxyHb and total Hb, whereas dobutamine increased baseline deoxyHb. Both dopamine and dobutamine reduced the evoked ΔoxyHb responses to 4.8 and 7.8 s stimulations. CONCLUSIONS: Somatosensory stimulation increases cerebral oxygenation in the preterm brain, consistent with increased cerebral blood flow due to neurovascular coupling. Notably, our results show that dopamine/dobutamine reduces oxygen delivery relative to consumption in the preterm brain during somatosensory stimulations, suggesting there may be a risk of intermittent localised tissue hypoxia which has clear implications for clinical practice and warrants further investigation.

Integrals and series related to propagators of neural and haemodynamic waves.

The propagator, or Green function, of a class of neural activity fields and of haemodynamic waves is evaluated exactly. The results enable a number of related integrals to be evaluated, along with series expansions of key results in terms of Bessel functions of the second kind. Connections to other related equations are also noted.