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Network slicing enables the creation of multiple logical independent networks on physical networking infrastructure. Network slice deployment in a Fifth Generation (5G) mobile network can be classified as vertical and horizontal slicing. The paper compares the performance of the two slicing methods through solving two convex optimization problems, considering several smart hospital scenarios that differ from each other based on their medical speciality. The results are used to draw insights on the most appropriate slicing approach for each setup.

Supporting parallel multi-priority data streams is vital for maintaining the quality of service (QoS) in vehicle-to-everything (V2X) communication. Hence, the European telecommunications standard institute (ETSI) has defined four packet types, with varying priority levels, to be used as broadcast packets in such communication. This paper studies the medium access control (MAC) layer performance of IEEE 802.11p and cellular-V2X (C-V2X) Mode 4 using discrete-time Markov chain (DTMC) based models, while considering parallel multi-priority data streams. The overall model consists of four queue models with their respective traffic generators, which are appropriately linked with the DTMCs modeling the MAC layer operations of IEEE 802.11p and C-V2X Mode 4. Closed-form solutions for the steady-state probabilities of the models are obtained, which are then utilized to derive expressions for key performance indicators at the MAC layer. Numerical results are provided to draw insights on the MAC layer performance of the two technologies. IEEE 802.11p is comparatively superior in average delay, and at maintaining fairness among multi-priority data streams, whereas C-V2X Mode 4 exhibits better collision resolution, which leads to its higher throughput. The paper also includes design insights on possible performance enhancements for future releases.

Background: Dopamine is frequently used as inotropic agent in preterm infants. Its cardiovascular actions, as well as effects on neurovascular interactions may be neuroprotective during hypoxic-ischaemic events. Using a preterm lamb model we aimed to test the impact of intravenous dopamine on hypoxic-ischaemic brain injury. Method(s): Nine fetal lambs (91-93d gestation) were instrumented with catheters in carotid artery and jugular vein, and an umbilical cord occluder. Four days after surgery, intravenous dopamine (DA, 10 mug/kg/ min, n = 5) (or saline, n = 4) was commenced. Then a hypoxic-ischaemic insult was induced with umbilical cord occlusion for 25 min. Infusions were continued for another 72 h before euthanasia. Fetal brains were collected for immunohistopathology. Result(s): Dopamine infusion increased fetal heart rate (184 +/- 1 to 203 +/- 1 bpm, P < 0.05) while arterial pressure was unchanged. Three animals in the DA group showed tachycardic response to cord occlusion, while the other two animals showed bradycardic response similar to the saline group. In the periventricular white matter, the saline group had higher number of microglia (lectin positive) than the DA group (10 +/- 3 vs. 6 +/- 2 per 0.04 mm2, P < 0.05). The saline group tended to have shorter myelinated fibre lengths (CNPase) compared with the DA group (15.0 +/- 2.0 vs. 18.4 +/- 5.7 mum respectively, P = ns). No histological differences were evident between DA animals exhibiting a tachycardic or bradycardic response during cord occlusion. Conclusion(s): Intravenous dopamine reduces hypoxic-ischaemic white matter injury in preterm lambs, independent of the cardiovascular response during the hypoxic-ischaemia., F.Y. Wong, Ritchie Centre, MIMR, Monash University, Melbourne, VIC, Australia. E-mail: flora.wong@med.monash.edu.au, CONFERENCE ABSTRACT

Vehicle-to-vehicle (V2V) communication plays a pivotal role in intelligent transport systems (ITS) with cellular-vehicle to everything (C-V2X) and IEEE 802.11p being the two competing enabling technologies. This paper presents multi-dimensional discrete-time Markov chain (DTMC) based models to study the medium access control (MAC) layer performance of the IEEE 802.11p standard and C-V2X Mode 4, considering periodic cooperative awareness messages (CAMs) and event-driven decentralized environmental notification messages (DENMs). Closed-form solutions for the models’ steady-state probabilities are obtained, which are then utilized to derive expressions for several key performance metrics. Numerical results are provided to draw insights on the performance. In particular, a performance comparison between IEEE 802.11p and C-V2X Mode 4 in terms of the average delay, the collision probability, and the channel utilization is presented. The results show that IEEE 802.11p is superior in terms of average delay, whereas C-V2X Mode 4 excels in collision resolution. The paper also includes design insights on possible future MAC layer performance enhancements of both standards.

Deployment of unmanned aerial vehicles (UAVs) as aerial base stations (ABSs) has been considered to be a feasible solution to provide network coverage in scenarios where the conventional terrestrial network is overloaded or inaccessible due to an emergency situation. This article studies the problem of optimal placement of the UAVs as ABSs to enable network connectivity for the users in such a scenario. The main contributions of this work include a less complex approach to optimally position the UAVs and to assign user equipment (UE) to each ABS, such that the total spectral efficiency (TSE) of the network is maximized, while maintaining a minimum QoS requirement for the UEs. The main advantage of the proposed approach is that it only requires the knowledge of UE and ABS locations and statistical channel state information. The optimal 2-dimensional (2D) positions of the ABSs and the UE assignments are found using K-means clustering and a stable marriage approach, considering the characteristics of the air-to-ground propagation channels, the impact of co-channel interference from other ABSs, and the energy constraints of the ABSs. Two approaches are proposed to find the optimal altitudes of the ABSs, using search space constrained exhaustive search and particle swarm optimization (PSO). The numerical results show that the PSO-based approach results in higher TSE compared to the exhaustive search-based approach in dense networks, consuming similar amount of energy for ABS movements. Both approaches lead up to approximately 8-fold energy savings compared to ABS placement using naive exhaustive search.

The enhanced distributed channel access (EDCA) mechanism enables IEEE 802.11p to accommodate differential quality of service (QoS) levels in vehicle-to-vehicle (V2V) communications, through four access categories (ACs). This paper presents multi-dimensional discrete-time Markov chain (DTMC) based model to study the effect of parallel operation of the ACs on the medium access control (MAC) layer performance of ITS-G5 IEEE 802.11p. The overall model consists of four queue models with their respective traffic generators, which are appropriately linked with the DTMCs modeling the operation of each AC. Closed-form solutions for the steady-state probabilities of the models are obtained, which are then utilized to derive expressions for key performance indicators at the MAC layer. An application for a highway scenario is presented to draw insights on the performance. The results show how the performance measures vary among ACs according to their priority levels, and emphasize the importance of analytical modeling of the parallel operation of all four ACs.

Network softwarization enables the novel concept of Local 5G Operator (L5GO) networks, for deploying localized 5G solutions to serve case and location specific communication needs. This paper proposes a L5GO network architecture for delay critical future telehealth services, considering two use cases on augmented reality assisted and robotic aided surgery. The paper compares the latency performance of the proposed L5GO architecture with a traditional legacy network and a network equipped with Multi-access Edge Computing (MEC). The results highlight the unique advantages of utilizing an L5GO to cater the communication needs of delay critical telehealth, compared to a traditional network.

As the comparative pathophysiology of perinatal infection in the fetus and newborn is uncertain, this study contrasted the cerebral effects of endotoxemia in conscious fetal sheep and newborn lambs. Responses to intravenous bacterial endotoxin (lipopolysaccharide, LPS) or normal saline were studied on three consecutive days in fetal sheep (LPS 1 mug/kg, n = 5; normal saline n = 5) and newborn lambs (LPS 2 mug/kg, n = 10; normal saline n = 5). Cerebro-vascular function was assessed by monitoring cerebral blood flow (CBF) and cerebral vascular resistance (CVR) over 12 h each day, and inflammatory responses were assessed by plasma TNF alpha (TNF-alpha), nitrate and nitrite concentrations. Brain injury was quantified by counting both resting and active macrophages in the caudate nucleus and periventricular white matter (PVWM). An acute cerebral vasoconstriction (within 1 h of LPS injection) occurred in both the fetus (DELTACVR +53%) and newborn (DELTACVR +63%); subsequently prolonged cerebral vasodilatation occurred in the fetus (DELTACVR -33%) in association with double plasma nitrate/nitrite concentrations, but not in the newborn. Abundant infiltration of activated macrophages was observed in both CN and PVWM at each age, with the extent being 2-3 times greater in the fetus (P < 0.001). In conclusion, while the fetus and newborn experience a similar acute disruption of the cerebral circulation after LPS, the fetus suffers a more prolonged circulatory disruption, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury.Copyright © 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

This paper proposes a multi-dimensional Markov model to evaluate the medium access control (MAC) layer performance of 3GPP cellular vehicle to everything (V2X) Mode 4. The Mode 4 specifications enable quality of service guarantees in a decentralized manner, without the connectivity of a cellular base station, and therefore, ideal for V2X messaging in intelligent transportation systems (ITS). To this end, periodic cooperative aware messages (CAMs) and event triggered decentralized environmental notification messages (DENMs) are considered in the paper. The discrete time Markov model consists of a node model, a queue model, and traffic generators for CAM and DENM packets that are dependent and solved in closed form and iteratively. The model is applied to a highway scenario to provide insights on the average delay, the collision probability, and the channel utilization in Mode 4. The results show that Mode 4 has been partially over-specified for ITS applications and able to serve CAMs and DENMs conveniently. However, there exists locally optimal combinations of CAM and DENM intervals that can lead to lower average delay.

Modularisation in mechanical, electrical and plumbing (MEP) in construction has become more prevalent along with mass customisation of buildings during the last decade. However, it is currently accomplished only for smaller systems where integrated packaged units are used in heating, ventilation and air conditioning (HVAC) and other building services installations. The term ‘optimum modularity’ is rarely used in the field due to extensive use of packaged systems. Packaged units are limited to external plant room installations and hardly used in building internal installations such as in basements due to difficulties in assembly and job-site delivery. In this study, an efficient method is developed which leads to the minimum total assembly and installation cost of building services systems. The method identifies the optimum sets of modules and module division points based on assembly cost and capacity weight of lifting equipment. It is shown that the optimum modularity for a system is highly dependent on the module weight and the module division point.

Study Objectives: The aim of this study was to compare the oxygen desaturation index (ODI) generated by two different sleep software systems. Method(s): Participants undergoing diagnostic polysomnography for suspected obstructive sleep apnea underwent simultaneous oximetry recording using the ResMed ApneaLink Plus device (AL) and Compumedics Profusion PSG3 system (Comp). The ODI was calculated by the algorithms in the respective software of each system. To determine if differences were due to algorithm or recording devices, the Comp software was also used to generate ODI values using oximetry data from the AL. Result(s): In 106 participants, there was good correlation but poor agreement in the ODI generated by the two systems. AL ODI values tended to be higher than Comp ODI values, but with significant variability. For ODI4%, bias was 4.4 events/h (95% limits of agreement -5.8 to 14.6 events/h). There was excellent correlation and agreement when the same oximetry raw data was analyzed by both systems. For ODI4%, bias was 0.03 events/h (95% limits of agreement -2.7 to 2.8 events/h). Similar results were evident when the ODI3% was used. Conclusion(s): There is a clinically significant difference in ODI values generated by the two systems, likely due to device signal processing, rather than difference in ODI calculation algorithms.

Mechanical, Electrical and Plumbing (MEP) work in high-rise construction can be very challenging due to the different crews involved during installation. Conflicts between the crews generally cause delays in project schedule and result in additional cost due to rework. This study will identify the MEP conflicts in high-rise construction through observations made by the author during the time spent in case study projects. This study focuses on the use of Modular MEP systems in high-rise construction to eliminate the current conflicts. Traditional MEP construction process was reviewed to identify changes to the process when using modular MEP systems. Challenges in implementing modular MEP in high- rise construction is discussed and an implementation strategy is proposed. Role of Building Information Modelling (BIM) in modular MEP construction is highlighted in the study and its involvement during different stages of the modularisation process is discussed.

Prefabrication of houses is a growing industry in Australia. Although prefabrication does not negatively affect the building quality, the potential to provide acceptable indoor environment quality with high energy efficiency is still a topic of argument. Effective passive design strategies are necessary to achieve low-energy buildings with satisfactory indoor environment quality. The building envelope parameters such as materials, openings and shadings highly affect the heat transfer, air exchange and light transmission between outside and indoor environment. Shading, one of the passive envelope design strategies, can reduce cooling energy while improving the indoor thermal comfort. However, the effects on daylighting and thermal performance depend on the climate conditions, and the size, location and orientation of the shading device. The performance benchmarks of prefabricated houses have not been well documented in the literature. The aim of this paper is to investigate the effects of shading design options on thermal and daylighting performance of a typical modular house in Melbourne. EnergyPlus and Radiant simulation engines have been employed in this study. By quantifying the performance, the appropriate shading design for the typical modular house in Melbourne could be identified.

Prefabrication is a sought after area in the AEC industry for manufacture of building components in an off-site controlled environment. Although, most of the structural element such as panels and modules are efficiently prefabricated and assembled onsite, prefabrication of complete mechanical, electrical and plumbing (MEP) systems is not achieved in many cases. This is mainly due to the limitations during assembly of different systems, poor implementation of building information modelling (BIM) and lack of standards for offsite manufacturing. The research will introduce the concept of Design for Excellence (DFX) which is currently used efficiently in the automotive, aerospace and shipbuilding industries. Applications of the DFX concept for building services in residential buildings were studied. This paper presents the overall concept of holistic approach to arrive at an optimum solution for design integrated building services systems for prefabricated buildings.

Background: As the comparative pathophysiology of perinatal infection is uncertain, this study contrasted the cerebral effects of endotoxemia in conscious fetal sheep and newborn lambs. Method(s): Responses to intravenous endotoxin (lipopolysaccharide, LPS) or normal saline (NS) were studied on 3 consecutive days in fetal sheep (LPS 1 mug/kg, n = 5; NS n = 5) and newborn lambs (LPS 2 mug/kg, n = 10; NS n = 5). Cerebrovascular function was assessed by monitoring cerebral blood flow and cerebral vascular resistance (CVR) over 12 hr each day, and inflammatory responses were assessed by plasma nitrate/nitrite concentrations. Brain injury was quantified by counting macrophages in the caudate nucleus (CN) and periventricular white matter (PVWM). Result(s): An acute cerebral vasoconstriction occurred in both the fetus (DELTACVR +53%) and newborn (DELTACVR +63%); subsequently prolonged cerebral vasodilatation occurred in the fetus (DELTACVR -33%) in association with doubled plasma nitrate/nitrite concentrations, but not in the newborn. Abundant infiltration of activated macrophages was observed in both CN and PVWM at each age, with the extent being 2-3 times greater in the fetus. Conclusion(s): While the fetus and newborn experience a similar acute disruption of the cerebral circulation after LPS, the fetus suffers a more prolonged circulatory disruption, a greater infiltration of activated macrophages, and an exaggerated susceptibility to brain injury.

Introduction: The oxygen desaturation index (ODI) is increasingly being used either for the diagnosis of obstructive sleep apnoea (OSA) or in determining the risk for cardiovascular disease in patients with OSA. However, different programs utilise different algorithms to calculate the ODI. The aim of this project was to compare the ODI generated by two different programs. Method(s): Participants undergoing a diagnostic sleep study for suspected OSA underwent simultaneous oximetry recording using both the ApneaLink portable device (AL) and Compumedics laboratory sleep study system (Comp). The ODI was automatically calculated by the respective software programs. To determine if any differences were due to algorithm or recording devices, the Compumedics software was used to generate ODI values using the oximetry data recorded by the ApneaLink device. Pearson's correlation was assessed and Bland-Altman plots were used to analyse agreement between the two programs. Result(s): N = 116. Ten participants had to be excluded due to technical issues. The Compumedics program tended to generate lower ODI values than the ApneaLink program, but with significant variability. For ODI4%, correlation of ODI-AL v ODI-Comp (matched for recording time) had r = 0.96 (P < 0.001; 95%CI 0.94 - 0.97). For agreement, bias = 4.4 with AL reading higher (95% limits -5.8 to 16.6). For ODI3%, correlation was similar, but agreement was poorer with AL reading higher (bias = 7.1; 95% limits -6.4 to 20.6) as shown in Figure 1. There was excellent agreement between ODI-AL and ODIComp when AL data was analysed using the Compumedics software. For ODI4%, correlation had r = 0.998 (P < 0.001; 95%CI 0.9974 - 0.9988). For agreement, bias = 0.03 (95% limits -2.7 to 2.8), suggesting the main source of discrepancy was not due to the different algorithms used by the different programs. Similar results were evident for ODI3%. Discussion(s): There is a clinically significant difference in ODI values generated by th

Introduction: Obstructive sleep apnoea (OSA) has been previously thought of as a homogenous disorder characterised by continuous and repetitive upper airway obstruction during sleep. However, recent published research demonstrates that OSA patients experience different severities of obstruction when lying in different body positions. In such patients, the positional dependence of OSA suggests the underlying pathophysiological mechanisms responsible for upper airway obstruction are also altered by position. Recent evidence suggests that OSA is not simply due to poor upper airway anatomy, but is also due to 1) an inability of the pharyngeal muscles to hold open or stiffen the airway during sleep, 2) an oversensitive ventilatory control system (i.e. high loop gain), 3) a low respiratory arousal threshold, 4) a low lung volume. To date we do not know how body position is likely to alter these 4 phenotypical traits Methods: Patients with an apnea and hypopnea index (AHI) >30/hr on polysomnography were selected. Patients were studied on 2 nights one week apart. One study was conducted with the subject supine (head also supine). The other study was performed with the patient lying in the right lateral position with the head in the Frankfort plane as comfort allowed. Patients were under continuous video monitoring and were repositioned if they moved from the prescribed position. In addition to basic demographic and anthropomorphic features lung volume was measured using a nitrogen washout technique in the seated, lateral decubitus and supine positions. On the study night patients were fitted with a nasal CPAP mask. While the patient was asleep, a sleep physician (SJ) monitored the PSG montage in real time. The OSA traits were measured as described by Wellman and colleagues. Result(s): 5 patients have been studied to date and their data are included in the table below. Conclusion(s): The improvements seen in the phenotype traits in the lateral position are largely due to imp

Aim Dopamine is used as an inotropic medication in preterm infants. The preterm human blood brain barrier (BBB) is permeable to intravascular dopamine, and the impact of exogenous dopamine on the preterm brain remains unknown. The preterm lamb model may be suitable for studying the cerebral impact of dopamine therapy whether its BBB permeability is similar to preterm human infants. We aimed to examine BBB permeability to exogenous dopamine in the preterm lamb, by measuring dopamine levels in the cerebrospinal fluid (CSF). Methods Nine preterm foetal lambs (125-130 days, term = 147 days) were given either dopamine at 10 mug/kg/min (dopamine, n = 4) or saline (control, n = 5). CSF, and plasma samples were taken for dopamine assay. Results The median (range) baseline CSF dopamine level for the combined control and dopamine groups (n = 9) was 0.10(0.03-0.16) ng/mL, and baseline plasma dopamine was 0.30(0.13-0.84) ng/mL. The dopamine lambs showed increase in CSF dopamine to 3.91(1.87-11.35) ng/mL with plasma dopamine increased to 14.2 (9.1-57.9) ng/mL. No change was found in the control lambs. Conclusion In the preterm lamb, the BBB permeability and pharmacokinetics to dopamine infusion are similar to findings in the preterm human infant, supporting applicability of the preterm lamb model for studying effects of dopamine infusion in the preterm human brain. ©2013 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.

Background: Dopamine is frequently used as inotropic agent in preterm infants. Its cardiovascular actions, as well as effects on neurovascular interactions may be neuroprotective during hypoxic-ischaemic events. Using a preterm lamb model we aimed to test the impact of intravenous dopamine on hypoxic-ischaemic brain injury. Method(s): Nine fetal lambs (91-93d gestation) were instrumented with catheters in carotid artery and jugular vein, and an umbilical cord occluder. Four days after surgery, intravenous dopamine (DA, 10 mug/kg/ min, n = 5) (or saline, n = 4) was commenced. Then a hypoxic-ischaemic insult was induced with umbilical cord occlusion for 25 min. Infusions were continued for another 72 h before euthanasia. Fetal brains were collected for immunohistopathology. Result(s): Dopamine infusion increased fetal heart rate (184 +/- 1 to 203 +/- 1 bpm, P < 0.05) while arterial pressure was unchanged. Three animals in the DA group showed tachycardic response to cord occlusion, while the other two animals showed bradycardic response similar to the saline group. In the periventricular white matter, the saline group had higher number of microglia (lectin positive) than the DA group (10 +/- 3 vs. 6 +/- 2 per 0.04 mm2, P < 0.05). The saline group tended to have shorter myelinated fibre lengths (CNPase) compared with the DA group (15.0 +/- 2.0 vs. 18.4 +/- 5.7 mum respectively, P = ns). No histological differences were evident between DA animals exhibiting a tachycardic or bradycardic response during cord occlusion. Conclusion(s): Intravenous dopamine reduces hypoxic-ischaemic white matter injury in preterm lambs, independent of the cardiovascular response during the hypoxic-ischaemia.

Background: Bedside assessments of cerebral oxygenation are sought to monitor cerebral injury in patients undergoing intensive care. Spatially resolved spectroscopy measures tissue oxygenation index (TOI, %) which reflects mixed cerebral arterial and venous oxygenations. We aimed to evaluate arterial and venous components of TOI (cerebral arterial to venous volume ratio [A:V ratio]) in the newborn lamb brain using cerebral arterial and venous blood samples, and to investigate the impact of acute hypoxemia on the A:V ratio and TOI. METHOD(S):: Nine lambs were ventilated with varied inspired oxygen to generate arterial oxygen saturations between 25% and 100%. Cerebral arterial and venous oxygen saturations analyzed using cooximeter of arterial and superior sagittal sinus blood were used to estimate TOI (TOIcox), assuming cerebral A:V ratio of 25:75. TOIcox was compared with the TOI measured by spatially resolved spectroscopy (TOIsrs). Actual cerebral arterial and venous volume fractions were reestimated using TOIsrs = cerebral arterial volume fraction* cerebral arterial oxygen saturation + cerebral venous volume fraction*cerebral venous oxygen saturation. Result(s): Median (range) TOIsrs was 48.5% (32.0-64.1%), and TOIcox was 48.4% (13.7-74.4%), and the two were significantly correlated (R = 0.77). The mean difference between TOIsrs and TOIcox was 2.4% (limits of agreement +/- 18.1%). The TOIsrs - TOIcox difference varied with oxygen saturations, with TOIsrs higher than TOIcox at low saturations, and lower at high saturations. Cerebral arterial volume fraction was 22.9-27.5% in normoxia and markedly increased in hypoxemia. Conclusion(s): TOI corresponds with cerebral oxygenation. The variable agreement of TOIsrs with TOIcox may reflect changes in cerebral A:V ratio due to arterial oxygenation-related vasoreactivity. © 2010, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins.

The impact of endotoxemia on cerebral endothelium and cerebral blood flow (CBF) regulation was studied in conscious newborn lambs. Bacterial endotoxin [LPS, 2 mug/kg iv] was infused on 3 consecutive days. Cerebrovascular function was assessed by monitoring CBF and cerebral vascular resistance (CVR) over 12 h each day and by the endothelium-dependent vasodilator bradykinin (BK) (n = 10). Inflammatory responses were assessed by plasma tumor necrosis factor-alpha (TNF-alpha, n = 5). Acutely, LPS disrupted the cerebral circulation within 1 h, with peak cerebral vasoconstriction at 3 h (CBF -28 and CVR +118%, P < 0.05) followed by recovery to baseline by 12 h. TNF-alpha and body temperature peaked ~1 h post-LPS. BK-induced vasodilatation (CVR -20%, P < 0.05) declined with each LPS infusion, was abolished after 3 days, and remained absent for at least the subsequent 5 days. Histological evidence of brain injury was found in four of five LPS-treated newborns. We conclude that endotoxin impairs cerebral perfusion in newborn lambs via two mechanisms: 1) acute vasoconstriction (over several hours); and 2) persistent endothelial dysfunction (over several days). Endotoxin-induced circulatory impairments may place the newborn brain at prolonged risk of CBF dysregulation and injury as a legacy of endotoxin exposure. Copyright © 2010 the American Physiological Society.

Background: Dopamine is frequently used as inotropic agent in preterm infants. Its actions on alpha- and beta-adrenergic and dopaminergic receptors may possibly modify cardiovascular responses during hypoxic-ischaemic events. Using a preterm lamb model we aimed to test the impact of intravenous dopamine on cardiovascular parameters during hyoxicischaemia. Method(s): Six preterm fetal lambs (93 d gestation) were instrumented with catheters in carotid artery and jugular vein, and an inflatable umbilical cord occluder. Post-operatively continuous ECG and blood pressure were recorded, with daily arterial blood gases. After 4 days of recovery period, intravenous dopamine (or saline at same infusion rate) was commenced at 10 mug/kg/min. A hypoxic-ischaemic insult was induced with umbilical cord occlusion for 25 min. Dopamine was continued for another 72 hours before both ewe and foetus were euthanised. Result(s): Averaged baseline fetal heart rate (FHR) and mean arterial blood pressure (MAP) were similar between lambs given saline (control, 190 bpm and 38.7 mm Hg) and dopamine (DA, 196 bpm and 31.9 mm Hg), with no significant change after dopamine infusion was started. FHR of control group dropped significantly throughout cord occlusion to a nadir of 69.2 bpm and MAP dropped to nadir of 17.6 mm Hg (p < 0.001). In contrast, in DA group, FHR was elevated during cord occlusion to maximum of 260.3 bpm (p < 0.001), with no significant change in MAP. Conclusion(s): Intravenous dopamine modifies systemic cardiovascular response to severe hypoxic-ischaemia in preterm lambs. Whether other inotropic agents would have similar effects, and the corresponding impact on end organ injury remain to be clarified.

Objectives: The significance of blood pressure variability (BPV) for cerebral oxygenation in extremely preterm infants has not been explored, though BPV may well be associated with end organ injury. We hypothesized that increased BPV in sick preterm infants, by exceeding the cerebral autoregulatory capacity, is associated with cerebral oxygenation changes which closely follow the blood pressure fluctuations. We assessed the autoregulatory capacity in the early postnatal period, by determining the correlation between BPV (mmHg2) and coherence of mean arterial blood pressure (MABP mmHg) and cerebral oxygenation (tissue oxygenation index, TOI %). Study Design: Thirty-two preterm infants of mean gestational age of 26.3 (+/-1.5) weeks were studied on the first 3 postnatal days. Spectral analysis (Coherence and transfer-function gain analysis) was used to calculate coherence of MABP and TOI; BPV was quantified using power spectral density of MABP. Result(s): Overall, maximum Coherence showed a trend for positive correlation with BPV (n = 32, p = 0.06). Infants identified as clinically unstable with documented brain injury (n = 7) had high Coherence values at low BPV. Separate analysis of stable infants (excluding the 7 critically ill infants) revealed a significant association between maximum Coherence and BPV (n = 25, p = 0.006). Conclusion(s): Fluctuation in cerebral oxygenation is closely associated with increased BPV in preterm infants undergoing intensive care. Moreover, in the critically sick preterm infant, blood pressure-dependent variations in cerebral oxygenation occur even with relatively lower BPV, suggesting they have severely impaired autoregulation, and placing them at greater vulnerability to cerebral injury arising from blood pressure fluctuations. © 2012 Wong et al.

Background: Cerebral blood flow (CBF)-metabolism coupling (FMC) is a fundamental regulatory mechanism of the mature brain, varying CBF to sustain cerebral metabolic rate of oxygen (CMRO2) and maintain cerebral oxygen extraction (OE). Previous studies suggest that FMC is immature in the preterm brain, predisposing to cerebral hypoxia. Dopamine is a natural neurotransmitter involved in mediating mature FMC, and is commonly used as inotropic agent in preterm infants. Using a lamb model we tested the impact of intravenous dopamine on FMC in the preterm brain, while manipulating CMRO2 using selective brain hypothermia. Method(s): Five preterm lambs (125-130 days gestation) were partially delivered by Caesarean section. Selective brain hypothermia was achieved by circulating ice-cold water in the pharynx with target brain temperature down to 25degreeC, measured by a fine thermistor placed beneath the dura. Cerebral arterial and venous oxygen saturations (CSaO2 and CSvO2) were analysed using blood samples from the carotid artery and superior sagittal sinus, and were used to estimate OE (OE=CSaO2-CSvO2,%). In three lambs, brain hypothermia was repeated with dopamine infusion at 20mcg/kg/min. Result(s): Mean brain temperature was reduced from 38.4 to 26.5degreeC, with no significant change in core temperature, heart rate and arterial blood pressure. Mean (SD) maximum change in OE during brain hypothermia was 11.4%, and reduced to -4.6% in lambs given dopamine infusion (P <= 0.05). Conclusion(s): Selective brain hypothermia uncouples CBF and cerebral metabolism, as indicated by increased cerebral oxygen extraction, without changes in systemic cardiovascular parameters. Dopamine infusion reduces the change in cerebral oxygen extraction during hypothermia, suggestive of an improvement in cerebral flow-metabolism coupling.