Non-invasive delineation of ventricular tachycardia substrates for cardiac stereotactic body radiotherapy: utility of in-silico pace-mapping

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): EPSRC

Background

Cardiac stereotactive body radiotherapy (CSBRT) is an emerging, non-invasive ablation modality that targets ventricular tachycardia (VT) substrates in patients with limited conventional treatment options. Success of CSBRT hinges primarily on the correct identification of VT targets, which requires non-invasive planning. Current non-invasive, pre-procedure strategies employ multi-electrode electrocardiographic imaging (ECGi). Given its significant cost and potential challenges in detecting endocardial, intramural and/or septal VT sites, there is a need to optimise VT delineation strategies for CSBRT; patient-specific simulations may show promise at guiding such planning non-invasively.

Purpose

We aim to perform non-invasive, in-silico pace-mapping on an image-based computational model to identify VT substrates for CSBRT. We intend to show the utility of our fast computational pipeline - relying on CT imaging data only - to provide further insights on inaccessible, scar-related VT episodes.

Methods

A detailed computational torso model of a CSBRT candidate with incessant VT was generated from CT imaging data. Extracellular content volumes (ECVs) were used to identify different tissue types (healthy, border zone and non-conducting), and scale model tissue conductivities accordingly. In-silico pace-mapping was performed by simulating ~360 paced beats across the LV, and computing corresponding 12-lead ECGs within a fast electrophysiological (EP) simulation environment combining reaction-eikonal and lead field methods. QRS complexes from simulated paced beats were used to construct the virtual correlation pace-map against the measured QRS of the clinically-induced VT, along with a ‘reference-less’ virtual pace-map constructed from neighbouring paced-beat QRSs (within a 20 mm radius). An epicardial activation map of the clinically-induced VT was reconstructed from ECGi measurement, and used for comparison against our virtual pace-maps.

Results

Correlations between simulated paced-beat QRS complexes and the clinically-induced VT QRS were higher in mid-apical, infero-septal segments - segment 9 (85.71%), 10 (87.95%) and 15 (89.58%) - identifying septal origin and pathway of the induced re-entrant circuit. A possible septal VT isthmus was also identified by a high gradient in the virtual reference-less pace-map in segment 9 (> 2.5%/mm). Our in-silico predictions were in agreement with the clinical regions identified for CSBRT (segment 9 and 15), and provided additional information on the 3D and septal dynamics of the VT episode.

Conclusions

Our in-silico pace-mapping study successfully localised VT substrates in a patient unable to receive standard ablative procedures, and provided further clinical insight on the induced VT dynamics. Our rapid in-silico pace-mapping approach may be utilised to support optimal identification of VT target volumes for CSBRT.

Dispersion of repolarization increases after cardiac resynchronization therapy in patients who do not undergo left ventricular reverse remodelling

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Wellcome/EPSRC Centre for Medical Engineering

CardioInsight Inc.

Background

The effect of CRT on dispersion of repolarization and arrhythmic risk is unclear. LV epicardial pacing has been associated with increased dispersion of repolarization, which may be due to altered activation and repolarization sequence. However, while CRT-induced ventricular arrhythmias have been reported, evidence from large clinical trials suggest CRT has a favourable effect on arrhythmic risk, with a lower incidence of arrhythmia in patients who undergo LV reverse remodelling.

Purpose

To investigate the effect of CRT and LV reverse remodelling on dispersion of repolarization using electrocardiographic imaging (ECGi).

Methods

11 patients with heart failure and electrical dyssynchrony underwent ECGi after CRT implant and again at 6 months. Reconstructed epicardial electrograms were used to create maps of activation recovery intervals (ARI), an accepted surrogate for action potential duration, which were corrected for heart rate. LV ARI dispersion was calculated as the standard deviation of ARI across the LV epicardium. The methodology is summarized in figure 1.

Results

Mean age at implant was 74±10 years and 82% of patients were male. 64% had ischaemic aetiology of heart failure, and mean LV ejection fraction was 29±10%. 64% of patients had underlying LBBB, 28% had an RV-paced rhythm and 9% had RBBB. 8 patients had a ≥15% reduction in LV end-systolic volume (LVESV) with CRT at 6 months (volumetric responders). Example ARI maps for 1 patient are shown in figure 2A. There was a significant increase in LV ARI dispersion at 6 months compared to baseline (36.4±7.2ms vs 28.2±7.7ms; P=0.03) [Fig 2B]. In a multiple linear regression analysis, volumetric response was an independent predictor of relative change in LV ARI dispersion from baseline to 6 months (P=0.04). In a sub-analysis, for volumetric responders there was no significant difference in LV ARI dispersion between baseline and CRT at 6 months (36.4 ±6.1 vs 30.1±7.8 ms; P=0.1). In comparison, in volumetric non-responders there was a significant increase in LV ARI dispersion (38.3±1.2 vs 22.6±2.6 ms; P=0.01). The relative change in LV ARI dispersion from baseline to CRT 6-months was greater for volumetric non-responders compared to volumetric responders (70.7 ±21.3% vs 27.0 ±35.4%; P=0.04) [Fig 2C]. There was a moderate negative correlation between relative change in LV ARI dispersion and relative reduction in LVESV (R=-0.5), however this did not meet statistical significance (P=0.12) [Fig 2D].

Conclusion

CRT increases dispersion of repolarization at 6 months. However, this potentially arrhythmogenic effect of epicardial pacing was only observed in CRT non-responders, which is in keeping with previous evidence that LV reverse remodelling reduces risk of ventricular arrhythmia.

Subthreshold delayed afterdepolarizations mediated by reduced tissue conductivity form a substrate for unidirectional block and reentry within the infarcted heart

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): British Heart Foundation, Wellcome Trust

Background

Delayed afterdepolarizations (DADs) due to spontaneous calcium release (SCR) events at the subcellular scale have been associated with arrhythmia formation in the border zone (BZ) of infarcted hearts. DADs may not only summate to form ectopic focal sources but may also inactivate sodium channels forming a substrate for unidirectional conduction block and reentry. The role played by infarct anatomy and altered intracellular coupling in facilitating this phenomenon is not fully understood.

Purpose

To use computational modelling to investigate the role of anatomical properties of the infarct BZ in creating a substrate for DAD-mediated conduction block and reentry.

Methods

MRI data from a porcine post-infarction heart was used to build the computational model. A phenomenological model was used to simulate SCRs in the BZ. Arrhythmia susceptibility was quantified by pacing the model followed by a pause, to see whether DADs would occur, and an extra S2 beat with different coupling intervals (CIs). Tissue conductivity in the BZ was decreased to investigate the effect of uncoupling on DAD-mediated conduction block.

Results

Subthreshold DADs occurring within the infarct BZ inactivated the fast sodium channels which resulted in block of S2 beats. This occurred most readily in narrow isthmuses where electrotonic load was attenuated by the non-conducting scar. DADs rendered the entire isthmus area refractory establishing a substrate for unidirectional block and reentry (see Fig. A). Reduced tissue conductivity in the BZ reduced electrotonic load on cells undergoing DADs. This led to more local tissue depolarization (Vm) as uncoupling prevented current from flowing to neighboring cells at rest (Fig. B-C). Reduced tissue conductivity also enhanced DAD-mediated block by increasing the vulnerable window for reentry initiation (700ms < S2 CI < 900ms as shown in Fig. D).

Conclusion

Subthreshold DADs provide a substrate for arrhythmogenesis in the infarct BZ. Tissue uncoupling enhanced the arrhythmogenic risk by increasing the time window of unidirectional block.

Automated detection of scar-related ventricular tachycardia origins from implanted device electrograms: a combined computational-AI platform

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): EPSRC

Background

Existing strategies that identify ventricular tachycardia (VT) ablation targets either employ invasive and time-consuming electrophysiological (EP) mapping, or non-invasive modalities that utilise standard electrocardiogram (ECG) signals. Success of these pre-procedure ablation approaches in localising re-entrant VTs often relies on VT induction, which could be avoided by utilising recordings of clinical VT episodes stored as electrograms (EGMs) in implanted devices. Such a non-invasive approach that localises VT substrates from EGMs may aid ablation planning, enhancing safety and speed.

Purpose

Our goal is to automate scar-related VT localisation by utilising EGM recordings of VT episodes from implanted devices. To achieve this, deep-learning algorithms will be trained on computational data to return VT sites of origin from implanted device EGMs. Ultimately, we intend to utilise this computational-artificial intelligence (AI) framework to detect ablation targets of clinical VT episodes and guide pre-procedure ablation planning non-invasively.

Methods

A comprehensive library of ECGs and EGMs from simulated paced beats (~15000) and scar-related VTs (500) was generated across five detailed torso models within a fast EP computational environment, combining reaction-eikonal and lead field methods. ECG (or EGM) traces from simulated paced beats were used to initially pre-train two convolutional neural network (CNN) long short-term (LSTM) attention-based architectures. Subsequently, signals of the in-silico, re-entrant VTs were used to re-train the networks to output the sites of origin of these episodes in a standardised ventricular coordinate space. Finally, the retrained CNN architectures were tested on re-entrant VTs of unseen models, and median localisation errors (LEs) were estimated against known VT origins from simulations.

Results

The performance of the networks to localise scar-related VT episodes was asserted for each torso model. When a torso model was only seen during initial training on simulated paced beats, implanted device EGMs and ECGs successfully localised VT sources with LEs 10.04 – 16.36 mm and 10.05 – 12.79 mm, respectively. When a torso model was not seen during pacing or VT training, recreating potential clinical application settings where ECGs or EGMs of clinical VTs would be the only inputs to the networks, LEs ranged 12.42 - 22.79 mm and 12.41 - 19.68 mm for EGM and ECG-based testing, respectively.

Conclusions

Our study successfully detected VT ablation substrates with accuracy that could be beneficial in clinical ablation settings. The proposed computational-AI framework may be used to automate the localisation of scar-related VTs from clinical ECGs or EGM recordings from implanted devices, ultimately aiding ablation planning.

Making seawalls multifunctional: The positive effects of seeded bivalves and habitat structure on species diversity and filtration rates

The marine environment is being increasingly modified by the construction of artificial structures, the impacts of which may be mitigated through eco-engineering. To date, eco-engineering has predominantly aimed to increase biodiversity, but enhancing other ecological functions is arguably of equal importance for artificial structures. Here, we manipulated complexity through habitat structure (flat, and 2.5 cm, 5 cm deep vertical and 5 cm deep horizontal crevices) and seeding with the native oyster (Saccostrea glomerata, unseeded and seeded) on concrete tiles (0.25 m × 0.25 m) affixed to seawalls to investigate whether complexity (both orientation and depth of crevices) influences particle removal rates by suspension feeders and colonisation by different functional groups, and whether there are any ecological trade-offs between these functions. After 12 months, complex seeded tiles generally supported a greater abundance of suspension feeding taxa and had higher particle removal rates than flat tiles or unseeded tiles. The richness and diversity of taxa also increased with complexity. The effect of seeding was, however, generally weaker on tiles with complex habitat structure. However, the orientation of habitat complexity and the depth of the crevices did not influence particle removal rates or colonising taxa. Colonisation by non-native taxa was low compared to total taxa richness. We did not detect negative ecological trade-offs between increased particle removal rates and diversity and abundance of key functional groups. Our results suggest that the addition of complexity to marine artificial structures could potentially be used to enhance both biodiversity and particle removal rates. Consequently, complexity should be incorporated into future eco-engineering projects to provide a range of ecological functions in urbanised estuaries.

P321Subthreshold delayed afterdepolarizations form a substrate for conduction block in the infarcted heart

Funding Acknowledgements

National Institute for Health Research; British Heart Foundation; and The Wellcome Trust and Engineering and Physical Sciences Research Council.

Background

Delayed afterdepolarizations (DADs) due to spontaneous calcium (Ca) release (SCR) events from the sarcoplasmic reticulum have been implicated with a variety of arrhythmias. Such SCR events have also been reported in cells that survive in the infarct border zone (BZ). While the potential of Ca-mediated DADs to become suprathreshold and propagate in the form of ectopic beats has been well characterized, the role of subthreshold DADs in arrhythmia formation in the infarcted heart remains to be elucidated.

Purpose

To use computational modelling to investigate whether subthreshold Ca-mediated DADs may form a substrate for conduction block and reentry in the BZ. Our hypothesis is that subthreshold DADs can hinder local tissue excitability in critical infarct BZ regions by inactivating the fast sodium current (INa), leading to temporary unidirectional conduction block providing a trigger for arrhythmogenesis.

Methods

We developed an idealized infarct model of the left ventricle. The infarct region consisted of a non-conducting scar transcended by an isthmus of cells that survived myocardial infarction (border zone). These cells were made prone to Ca-mediated DADs described by a phenomenological model of SCR events. The model was pre-paced at the apex followed by a 1500ms-pacing pause to see whether DADs would emerge. An extra beat with a longer coupling interval (CI) was then applied. The following electrophysiological changes resulting from remodeling processes in the isthmus were simulated to assess their contribution to the arrhythmogenic potential of subthreshold DADs: INa loss-of-function due to a (2.5mV and 5mV) negative-shift in the steady-state channel inactivation; 50% reduction in tissue conductivity; and increased levels of fibrosis (up to 50%).

Results

On average, Ca-mediated DADs reached their maximum value 1065ms after the last paced beat (Fig. A). Despite this, in the default electrophysiological setup, simulations with extra beats with 1000ms > CI > 1100ms did not result in conduction block in any of the experiments. When repeated with combined changes of reduced tissue conductivity and fibrosis, subthreshold DADs were still unable to create a substrate for block. However, when combined with a 5mV-shift in INa inactivation, block at isthmus’ mouth proximal to the stimulus site was detected for extra beats 1010 ms ≥ CI ≥ 1070ms (see Fig. B). The cause of block was due to a subthreshold DAD occurring just prior to the arrival of the extra beat. All blocked beats degenerated into reentry.

Conclusions

Under most physiological conditions, subthreshold DADs are unlikely to provide a substrate for unidirectional block. However, under conditions of decreased excitability, subthreshold DADs can hinder tissue excitability in the infarcted region leading to conduction block and reentry.

Abstract Figure. DAD-mediated conduction block in the BZ

221Evaluating the ability of different substrate mapping techniques to identify scar-related ventricular tachycardia circuits using computational modelling

Funding Acknowledgements

National Institute for Health Research; British Heart Foundation; and The Wellcome Trust and Engineering and Physical Sciences Research Council.

Background

Accurate identification of targets for catheter ablation therapy of ventricular tachycardias (VTs) in the postinfarction heart remains a significant challenge. Identification of such targets often requires VT-induction to delineate the entry/exit points of the reentrant circuit sustaining the VT. However, inducibility may not be possible due to hemodynamic instability. In this scenario, substrate ablation strategies can still be performed to uncover the arrhythmogenic substrate during sinus or paced rhythm. However, substrate mapping may fail to accurately delineate the reentrant circuit resulting in VT recurrence after the procedure.

Purpose

To use computer simulations to compare the ability of different electroanatomical maps constructed following typical substrate ablation strategies to identify the VT exit site.

Methods

An image-based computational model of the porcine post-infarction left ventricle was constructed to simulate VT and paced rhythm. Electroanatomical maps were constructed based on the following features extracted from electrograms computed on the endocardial surface: activation time (AT), bipolar electrogram amplitude, signal fractionation and the reentry vulnerability index (RVI - a metric combining activation and repolarization timings to identify tissue susceptibility to reentry). Potential ablation targets during substrate mapping were compared for: highest 5% AT gradient; lowest 5% bipolar signal amplitudes; areas with fragmented signals (more than one peak); and lowest 5% RVI. The minimum distance, d, between the manually identified VT exit site and the targets was measured.

Results

The RVI performed better than the other metrics at detecting the VT exit site (see Figure). The minimum distance between sites of lowest RVI and the exit site was 3.2mm compared to 13.1mm and 15.9mm in traditional AT and voltage maps, respectively. As the scar was not transmural, parameters derived from all electrograms (including those located on dense scar regions) were used to construct the electroanatomical maps. This improved the performance of the RVI significantly, making it more specific than the other metrics as can be seen in the Figure.

Conclusions

Among all metrics investigated here, the RVI identified the vulnerable region closest to VT exit site. This finding suggests that activation-repolarization metrics may improve the detection of pro-arrhythmic regions without having to induce VT. Moreover, the RVI may be particularly well suited for detecting vulnerable regions within non-transmural scars.

Abstract Figure. VT and Substrate Mapping

P532Endocardial pacing is less arrhythmogenic than conventional epicardial pacing when pacing in proximity to scar in patients with ischemic heart failure

Funding Acknowledgements

WT 203148/Z/16/Z; MR/N011007/1; RE/08/003; PG/15/91/31812; PG/16/81/32441

Background

Endocardial pacing has been shown to improve response to cardiac

resynchronization therapy (CRT) in comparison to conventional epicardial pacing and the

physiological activation, endocardium to epicardium, is proposed to make it less arrhythmogenic.

However, the relative arrhythmic risk of endocardial and epicardial pacing has not been

systematically investigated. Pacing in proximity to scar increases susceptibility to arrhythmogenesis

during epicardial pacing. Whether this is also the case during endocardial pacing is currently

unknown.

Purpose

We investigate 1) whether endocardial pacing is less arrhythmogenic than epicardial

pacing, 2) whether pacing location relative to scar plays a role in arrhythmogenesis during

endocardial pacing, and 3) whether these findings could be explained by the direction of the

transmural action potential duration (APD) gradient.

Methods

We used computational models of ischemic heart failure and patient-specific (n = 24) left ventricular anatomy and scar morphology to simulate repolarization during endocardial and

epicardial pacing. Pacing locations were selected 0.2-3.5cm from a scar. We ran simulations with a

20ms transmural APD gradient, as found in heart failure, from the epicardium to endocardium

(physiological) and with this gradient inverted. We computed the volume of high

(>3ms/mm) repolarization gradients (HRG) within 1cm around a scar, as a surrogate for arrhythmia

risk, and analysed these with ANOVA and Tukey-Kramer post-hoc tests.

Results

Simulations with a physiological APD gradient predict that endocardial pacing creates a

smaller (34%) volume of HRG around (1cm) a scar compared to epicardial pacing when

pacing 0.2cm from scar (Figure 1-A). The volume of HRG decreases (P < 0.05) with distance

from scar for epicardial pacing but not endocardial pacing (Figure 1-A). Inverting the

transmural APD gradient, inverts the trend observed with a physiological gradient. In this case, the

volume of HRG is unaffected by pacing location during epicardial pacing, whereas it decreases (19%)

with the distance from scar for endocardial pacing. This is illustrated

in the regions highlighted in yellow in Figure 1 for endocardial pacing at 0.2 and 3.5cm from a scar

with a physiological (B) and an inverted (C) gradient.

Conclusions

Endocardial pacing is less arrhythmogenic (purpose 1) than conventional epicardial

pacing when pacing in proximity to scar and is also less susceptible to pacing location relative to scar

(purpose 2). The direction of the transmural APD gradient offers a mechanistic explanation for

reduced susceptibility to arrhythmogenesis during endocardial pacing compared to epicardial pacing

(purpose 3). Endocardial pacing is an attractive alternative to conventional epicardial pacing in

patients with scar, as it allows pacing in proximity to scar while avoiding increasing arrhythmogenic

risk in patients with ischemic heart failure.

Abstract Figure.

Urban blue: A global analysis of the factors shaping people's perceptions of the marine environment and ecological engineering in harbours

Marine harbours are the focus of a diverse range of activities and subject to multiple anthropogenically induced pressures. Support for environmental management options aimed at improving degraded harbours depends on understanding the factors which influence people's perceptions of harbour environments. We used an online survey, across 12 harbours, to assess sources of variation people's perceptions of harbour health and ecological engineering. We tested the hypotheses: 1) people living near impacted harbours would consider their environment to be more unhealthy and degraded, be more concerned about the environment and supportive of and willing to pay for ecological engineering relative to those living by less impacted harbours, and 2) people with greater connectedness to the harbour would be more concerned about and have greater perceived knowledge of the environment, and be more supportive of, knowledgeable about and willing to pay for ecological engineering, than those with less connectedness. Across twelve locations, the levels of degradation and modification by artificial structures were lower and the concern and knowledge about the environment and ecological engineering were greater in the six Australasian and American than the six European and Asian harbours surveyed. We found that people's perception of harbours as healthy or degraded, but not their concern for the environment, reflected the degree to which harbours were impacted. There was a positive relationship between the percentage of shoreline modified and the extent of support for and people's willingness to pay indirect costs for ecological engineering. At the individual level, measures of connectedness to the harbour environment were good predictors of concern for and perceived knowledge about the environment but not support for and perceived knowledge about ecological engineering. To make informed decisions, it is important that people are empowered with sufficient knowledge of the environmental issues facing their harbour and ecological engineering options.

Building blue infrastructure: Assessing the key environmental issues and priority areas for ecological engineering initiatives in Australia's metropolitan embayments

Ecological engineering principles are increasingly being applied to develop multifunctional artificial structures or rehabilitated habitats in coastal areas. Ecological engineering initiatives are primarily driven by marine scientists and coastal managers, but often the views of key user groups, which can strongly influence the success of projects, are not considered. We used an online survey and participatory mapping exercise to investigate differences in priority goals, sites and attitudes towards ecological engineering between marine scientists and coastal managers as compared to other stakeholders. The surveys were conducted across three Australian cities that varied in their level of urbanisation and environmental pressures. We tested the hypotheses that, relative to other stakeholders, marine scientists and coastal managers will: 1) be more supportive of ecological engineering; 2) be more likely to agree that enhancement of biodiversity and remediation of pollution are key priorities for ecological engineering; and 3) identify different priority areas and infrastructure or degraded habitats for ecological engineering. We also tested the hypothesis that 4) perceptions of ecological engineering would vary among locations, due to environmental and socio-economic differences. In all three harbours, marine scientists and coastal managers were more supportive of ecological engineering than other users. There was also greater support for ecological engineering in Sydney and Melbourne than Hobart. Most people identified transport infrastructure, in busy transport hubs (i.e. Circular Quay in Sydney, the Port in Melbourne and the Waterfront in Hobart) as priorities for ecological engineering, irrespective of their stakeholder group or location. There were, however, significant differences among locations in what people perceive as the key priorities for ecological engineering (i.e. biodiversity in Sydney and Melbourne vs. pollution in Hobart). Greater consideration of these location-specific differences is essential for effective management of artificial structures and rehabilitated habitats in urban embayments.

Image-Based Personalization of Cardiac Anatomy for Coupled Electromechanical Modeling

Computational models of cardiac electromechanics (EM) are increasingly being applied to clinical problems, with patient-specific models being generated from high fidelity imaging and used to simulate patient physiology, pathophysiology and response to treatment. Current structured meshes are limited in their ability to fully represent the detailed anatomical data available from clinical images and capture complex and varied anatomy with limited geometric accuracy. In this paper, we review the state of the art in image-based personalization of cardiac anatomy for biophysically detailed, strongly coupled EM modeling, and present our own tools for the automatic building of anatomically and structurally accurate patient-specific models. Our method relies on using high resolution unstructured meshes for discretizing both physics, electrophysiology and mechanics, in combination with efficient, strongly scalable solvers necessary to deal with the computational load imposed by the large number of degrees of freedom of these meshes. These tools permit automated anatomical model generation and strongly coupled EM simulations at an unprecedented level of anatomical and biophysical detail.

Image-Based Personalization of Cardiac Anatomy for Coupled Electromechanical Modeling

Computational models of cardiac electromechanics (EM) are increasingly being applied to clinical problems, with patient-specific models being generated from high fidelity imaging and used to simulate patient physiology, pathophysiology and response to treatment. Current structured meshes are limited in their ability to fully represent the detailed anatomical data available from clinical images and capture complex and varied anatomy with limited geometric accuracy. In this paper, we review the state of the art in image-based personalization of cardiac anatomy for biophysically detailed, strongly coupled EM modeling, and present our own tools for the automatic building of anatomically and structurally accurate patient-specific models. Our method relies on using high resolution unstructured meshes for discretizing both physics, electrophysiology and mechanics, in combination with efficient, strongly scalable solvers necessary to deal with the computational load imposed by the large number of degrees of freedom of these meshes. These tools permit automated anatomical model generation and strongly coupled EM simulations at an unprecedented level of anatomical and biophysical detail.

The Synthesis of 5-Ethoxycarbonyl-1,2-dimethyl-1,2,3,6-tetrahydropyridine

The title compound has been synthesised by Dieckmann cyclisation of 2-ethoxycarbonylethyl 1-ethoxycarbonyl-2-propylmethylamine, followed by reduction and dehydration.

How useful are port surveys focused on target pest identification for exotic species management?

Monitoring surveys are an important tool for detecting new arrivals of exotic species, for documenting patterns of invasion, and exotic species impacts. Faced with time and cost constraints, these surveys are increasingly focused on lists of target pest species, identified as being most likely to arrive and cause significant harm. We used the national survey of Australian international ports for introduced marine pests as a case study to assess: (1) the taxonomic rigor of surveys focused on detection of target species; and (2) how the ability of port surveys to inform invasion patterns is dependent on taxonomic approach. Our analysis of the 46 available reports revealed common sub-optimal taxonomic practices that compromised their utility to identify abiotic conditions that are good predictors of biological invasion. Thus, although surveys for target species may provide information on the distribution of a handful of species, they may fail to do much else.

Arrhythmic risk biomarkers for the assessment of drug cardiotoxicity: from experiments to computer simulations

In this paper, we illustrate how advanced computational modelling and simulation can be used to investigate drug-induced effects on cardiac electrophysiology and on specific biomarkers of pro-arrhythmic risk. To do so, we first perform a thorough literature review of proposed arrhythmic risk biomarkers from the ionic to the electrocardiogram levels. The review highlights the variety of proposed biomarkers, the complexity of the mechanisms of drug-induced pro-arrhythmia and the existence of significant animal species differences in drug-induced effects on cardiac electrophysiology. Predicting drug-induced pro-arrhythmic risk solely using experiments is challenging both preclinically and clinically, as attested by the rise in the cost of releasing new compounds to the market. Computational modelling and simulation has significantly contributed to the understanding of cardiac electrophysiology and arrhythmias over the last 40 years. In the second part of this paper, we illustrate how state-of-the-art open source computational modelling and simulation tools can be used to simulate multi-scale effects of drug-induced ion channel block in ventricular electrophysiology at the cellular, tissue and whole ventricular levels for different animal species. We believe that the use of computational modelling and simulation in combination with experimental techniques could be a powerful tool for the assessment of drug safety pharmacology.

Modulation of shock-end virtual electrode polarisation as a direct result of 3D fluorescent photon scattering

Due to the large transmural variation in transmembrane potential following the application of strong electric shocks, it is thought that fluorescent photon scattering from depth plays a significant role in optical signal modulation at shock-end. For the first time, a model of photon scattering is used to accurately synthesize fluorescent signals over the irregular geometry of the rabbit ventricles following the application of such strong shocks. A bidomain representation of electrical activity is combined with finite element solutions to the photon diffusion equation, simulating both the excitation and emission processes, over an anatomically-based model of rabbit ventricular geometry and fiber orientation. Photon scattering from within a 3D volume beneath the epicardial optical recording site is shown to transduce differences in transmembrane potential within this volume through the myocardial wall. This leads directly to a significantly modulated optical signal response with respect to that predicted by the bidomain simulations, distorting epicardial virtual electrode polarization produced at shock-end. Furthermore, we show that this degree of distortion is very sensitive to the optical properties of the tissue, an important variable to consider during experimental mapping set-ups. These findings provide an essential first-step in aiding the interpretation of experimental optical mapping recordings following strong defibrillation shocks.

2-(Anilinomethyl)imidazolines as alpha(1)-adrenoceptor agonists: the identification of alpha(1A) subtype selective 2'-carboxylic acid esters and amides

2-(Anilinomethyl)imidazolines with 2'-esters or 2'-amides are potent agonists of the cloned human alpha(1)-adrenoceptors in vitro. The size and shape of the ortho substituent can have significant effects on the potency, efficacy, and subtype selectivity of these 2-(anilinomethyl)imidazolines. alpha(1A)-subtype selective agonists have been identified.

Comparison of surgical outcomes between teaching and nonteaching hospitals in the Department of Veterans Affairs

OBJECTIVE

To determine whether the investment in postgraduate education and training places patients at risk for worse outcomes and higher costs than if medical and surgical care was delivered in nonteaching settings.

SUMMARY BACKGROUND DATA

The Veterans Health Administration (VA) plays a major role in the training of medical students, residents, and fellows.

METHODS

The database of the VA National Surgical Quality Improvement Program was analyzed for all major noncardiac operations performed during fiscal years 1997, 1998, and 1999. Teaching status of a hospital was determined on the basis of a background and structure questionnaire that was independently verified by a research fellow. Stepwise logistic regression was used to construct separate models predictive of 30-day mortality and morbidity for each of seven surgical specialties and eight operations. Based on these models, a severity index for each patient was calculated. Hierarchical logistic regression models were then created to examine the relationship between teaching versus nonteaching hospitals and 30-day postoperative mortality and morbidity, after adjusting for patient severity.

RESULTS

Teaching hospitals performed 81% of the total surgical workload and 90% of the major surgery workload. In most specialties in teaching hospitals, the residents were the primary surgeons in more than 90% of the operations. Compared with nonteaching hospitals, the patient populations in teaching hospitals had a higher prevalence of risk factors, underwent more complex operations, and had longer operation times. Risk-adjusted mortality rates were not different between the teaching and nonteaching hospitals in the specialties and operations studied. The unadjusted complication rate was higher in teaching hospitals in six of seven specialties and four of eight operations. Risk adjustment did not eliminate completely these differences, probably reflecting the relatively poor predictive validity of some of the risk adjustment models for morbidity. Length of stay after major operations was not consistently different between teaching and nonteaching hospitals.

CONCLUSION

Compared with nonteaching hospitals, teaching hospitals in the VA perform the majority of complex and high-risk major procedures, with comparable risk-adjusted 30-day mortality rates. Risk-adjusted 30-day morbidity rates in teaching hospitals are higher in some specialties and operations than in nonteaching hospitals. Although this may reflect the weak predictive validity of some of the risk adjustment models for morbidity, it may also represent suboptimal processes and structures of care that are unique to teaching hospitals. Despite good quality of care in teaching hospitals, as evidenced by the 30-day mortality data, efforts should be made to examine further the structures and processes of surgical care prevailing in these hospitals.

Recertification of respiratory therapists' intubation skills one year after initial training: an analysis of skill retention and retraining

Allied health personnel and nonanesthesiologist physicians often undergo training in tracheal intubation but then may actually use the skill relatively infrequently. This study assessed retention of skills one year after initial training and identified specific areas of knowledge critical to successful performance of intubation. Eleven respiratory therapists on the staff of a 253-bed hospital, each of whom had been trained one year previously in airway management, were evaluated. Prior to returning to the operating room for skills assessment and recertification, each respiratory therapist took a 21-question written exam. Therapists then went to the operating room and a trained observer (anesthesiologist) monitored the intubations performed to see whether critical steps were followed, while a second observer monitored a checklist of skills performed. The attending anesthesiologist recertified the therapist only when all steps were correctly performed and the intubation was successful. There was a poor correlation (r = -0.25, p > 0.1) between the number of intubations performed by the therapists for emergencies in the previous year and the number of intubations needed to be recertified. There was a negative correlation (r = -0.8, p < 0.05) between the score on the written test and the number of intubations required for recertification-a higher score meant fewer intubations were needed to achieve recertification. First-pass success occurred significantly more frequently if all skills tested were performed correctly (50/75 first-pass successes had all skills performed correctly vs 10/28 for failed first-pass, p < 0.01). The most common errors were levering the blade on the upper teeth (12/91) and tube not inserted from the right side of the mouth (28/104). When the blade was levered, 8 of 10 intubations failed. When the tube was not inserted from the right side of the face, 6 of 12 failed. The useful findings of this study are: (1) occasional performance of intubation did not ensure skill maintenance; (2) cognitive and procedural abilities correlated, suggesting benefits to study as well as to practical training; and (3) two specific mistakes were associated with a high incidence of failure.

Epidural naloxone reduces intestinal hypomotility but not analgesia of epidural morphine

PURPOSE

Epidural morphine is associated with decreased bowel motility and increased transit time. Low doses of intravenous naloxone reduce morphine-induced pruritus without reversing analgesia, but the effect of epidural naloxone on bowel motility has not been studied. Therefore we evaluated bowel motility and analgesia when naloxone was co-administered with morphine into the epidural space.

METHODS

Forty-three patients having combined thoracic epidural and general anesthesia for subtotal gastrectomy were randomly assigned to one of two study groups. All received a bolus dose of 3 mg epidural morphine at the beginning of surgery, followed by a continuous epidural infusion containing 3 mg morphine in 100 ml bupivacaine 0.125% with either no naloxone (control group, n = 18) or a calculated dose of 0.208 microg x kg(-1) x hr(-1) of naloxone (experimental group, n = 25) for 48 hr. We measured the time to the first postoperative passage of flatus and feces to evaluate the restoration of bowel function, and visual analog scales (VAS) for pain during rest and movement. Scores were assessed at 2, 4, 8, 16, 24, 36 and 48 hr postoperatively.

RESULTS

The experimental group had a shorter time to the first postoperative passage of flatus (5 1.9 +/- 1 6.6 hr vs 87.0 +/- 19.5 hr, P < 0.001 ) and feces (95.3 +/- 25.0 hr vs 132.9 +/- 29.4 hr, P < 0.001). No differences were found in either resting or active VAS between the two groups.

CONCLUSION

Epidural naloxone reduces epidural morphine-induced intestinal hypomotility without reversing its analgesic effects.

Effects of fenoterol and ipratropium on respiratory resistance of asthmatics after tracheal intubation

We have studied the effects of a beta-agonist, fenoterol, and a cholinergic antagonist, ipratropium, on post-intubation total respiratory system resistance (Rrs) in asthmatics who developed increased Rrs after tracheal intubation. Sixteen stable asthmatics in whom Rrs increased after intubation were allocated randomly to receive either 10 puffs of fenoterol (group F) or 10 puffs of ipratropium (group IB) via a metered dose inhaler 5 min after intubation. Anaesthesia was induced and maintained with propofol i.v. Rrs was recorded before treatment and again 5, 15 and 30 min after treatment. Rrs decreased significantly from pretreatment values by mean 53 (SD 8)%, 53 (7)% and 58 (6)% at 5, 15 and 30 min, respectively, in group F, but declined by only 12 (6)%, 15 (4)% and 17 (5)% in group IB. At all times after treatment, patients in the fenoterol group had significantly lower Rrs values than those in the ipratropium group. We conclude that increased Rrs after tracheal intubation in asthmatics can be reduced effectively by treatment with fenoterol. A secondary finding of our study was that even after induction of anaesthesia with propofol, patients with a history of asthma may develop high Rrs.

Epidural naloxone reduces pruritus and nausea without affecting analgesia by epidural morphine in bupivacaine

PURPOSE

To determine whether epidural naloxone preserved analgesia while minimizing side effects caused by epidural morphine.

METHODS

Eighty patients undergoing combined epidural and general anesthesia for hysterectomy were randomly assigned to one of four groups. All received 2 mg epidural morphine bolus one hour before the end of surgery and a continuous epidural infusion was started containing 4 mg morphine in 100 ml bupivacaine 0.125% with either no naloxone (Group 1, n = 20), 0.083 microg x kg(-1) x hr(-1) of naloxone (Group 2, n = 20), 0.125 microg x kg(-1) x hr(-1) of naloxone (Group 3, n = 20) or 0.167 microg x kg(-1) x hr(-1) of naloxone (Group 4, n = 20). Analgesia and side effects were evaluated by blinded observers.

RESULTS

The combination of epidural morphine and bupivacaine provided good analgesia. Eight hours after the end of surgery, the pain score in the group receiving the highest dose of naloxone was lower than in the control group (VAS 1.2 vs. 2.0, P<0.05) but there was less pruritus in the high-dose naloxone group (itching score 1.3 vs. 1.9, P<0.05). Pain scores were no different in any of the naloxone groups from the control group. Itching was less in both of the higher dose naloxone groups (P<0.05 at 8, 16, and 32 hours). The incidence of vomiting in the control group was 40% vs. 5% for high dose naloxone group (P<0.05).

CONCLUSIONS

Epidural naloxone reduced morphine-induced side effects in dose-dependent fashion without reversal of the analgesic effect.

Endotracheal intubation, but not laryngeal mask airway insertion, produces reversible bronchoconstriction

BACKGROUND

Tracheal intubation frequently results in an increase in respiratory system resistance that can be reversed by inhaled bronchodilators. The authors hypothesized that insertion of a laryngeal mask airway would be less likely to result in reversible bronchoconstriction than would insertion of an endotracheal tube.

METHODS

Fifty-two (45 men, 7 women) patients were randomized to receive a 7.5-mm (women) or 8-mm (men) endotracheal tube or a No. 4 (women) or No. 5 (men) laryngeal mask airway. Anesthesia was induced with 2 microg/kg fentanyl and 5 mg/kg thiopental, and airway placement was facilitated with 1 mg/kg succinylcholine. When a seal to more than 20 cm water was verified, respiratory system resistance was measured immediately after airway placement. Inhalation anesthesia was begun with isoflurane to achieve an end-tidal concentration of 1% for 10 min. Respiratory system resistance was measured again during identical conditions.

RESULTS

Among patients receiving laryngeal mask airways, the initial respiratory system resistance was significantly less than among patients with endotracheal tubes (9.2+/-3.3 cm water x 1(-1) x s(-1) [mean +/- SD] compared with 13.4+/-9.6 cm water x 1(-1) x s(-1); P < 0.05). After 10 min of isoflurane, the resistance decreased to 8.6+/-3.6 cm water x 1(-1) x s(-1) in the endotracheal tube group but remained unchanged at 9.1+/-3.3 cm water x 1(-1) x s(-1) in the laryngeal mask airway group. The decrease in respiratory system resistance in the endotracheal tube group of 4.7+/-7 cm water x 1(-1) x s(-1) was highly significant compared with the lack of change in the laryngeal mask airway group (P < 0.01).

CONCLUSIONS

Resistance decreased rapidly only in patients with endotracheal tubes after they received isoflurane, a potent bronchodilator, suggesting that reversible bronchoconstriction was present in patients with endotracheal tubes but not in those with laryngeal mask airways. A laryngeal mask airway is a better choice of airway to minimize airway reaction.

Cough during emergence from isoflurane anesthesia

We evaluated the effects of smoking history and albuterol treatment on the amplitude and frequency of cough during emergence from anesthesia. Before induction of anesthesia, 68 patients were randomized to receive two puffs of a placebo or two puffs of albuterol via a metered dose inhaler. Anesthesia was then induced with thiopental, fentanyl, and succinylcholine. The patients' tracheas were intubated with an 8.0 mm-endotracheal tube, and isoflurane administration was initiated. At the end of surgery, isoflurane was discontinued, and the pressure in the endotracheal tube cuff was monitored via the pilot balloon while the end-tidal isoflurane concentration was recorded. Of the 68 patients, 52 coughed before responding to command, but the incidence did not differ between smokers and nonsmokers (33 of 43 vs 19 of 25), nor did it differ between albuterol-treated and untreated patients. There was no difference in the frequency or amplitude of coughs between smokers and nonsmokers, nor did albuterol affect either variable. The mean end-tidal concentration at which cough first occurred was 0.30%+/-0.02%, and only 5% of patients coughed at values >0.6%. We conclude that 1) cough is frequent during emergence; 2) smoking does not affect emergence cough; 3) albuterol treatment does not affect emergence cough; and 4) patients are unlikely to cough at end-tidal values of isoflurane >0.6%.

IMPLICATIONS

Most patients cough as they awaken from general anesthesia given via an endotracheal tube. In our study population, cough was frequent but generally did not occur until the end-tidal concentration of isoflurane was <0.6%. Smokers were no more likely to cough than nonsmokers, and the beta-adrenergic agonist albuterol did not prevent cough.

The identification and characterization of microsatellites in the compact genome of the Japanese pufferfish, Fugu rubripes: perspectives in functional and comparative genomic analyses

Fugu rubripes (Fugu) has one of the smallest recorded vertebrate genomes and is an economic tool for comparative DNA sequence analysis. Initial characterization of 128 kb of Fugu DNA attributed the compactness of this genome, in part, to a sparseness of repetitive DNA sequence compared with mammalian genomic sequences. This paper describes a new and comprehensive analysis in which 501 theoretically possible microsatellites with a repeat unit of one to six bases were used to query two orders of magnitude more Fugu DNA (i.e. 11.338 Mb). A total of 6042 microsatellites were identified and categorized. In decreasing order, the 20 most frequently occurring microsatellites are AC, A, C, AGG, AG, AGC, AAT, AAAT, ACAG, ACGC, ATCC, AAC, ATC, AGGG, AAAG, AAG, AAAC, AT, CCG and TTAGGG. The 20 most frequently occurring microsatellites represent 81.79% of all microsatellites identified. Our results indicate that one microsatellite occurs every 1.876 kb of DNA in Fugu, 11.55% of the microsatellites are detected in open reading frames that are predicted protein coding regions. With respect to the proportion of microsatellites present in open reading frames and the total abundance (bp) of all microsatellites, the genome of Fugu is similar to the genome of many other vertebrate species. Previous estimates performed indicate that approximately 1% of many vertebrate genomes are comprized of microsatellite sequences. However, many differences prevail in the abundance and frequency of the individual microsatellite classes. Many of the frequently occurring microsatellites in Fugu are known to code in other species for regions in proteins such as transcription factors, whilst others are associated with known functions, such as transcription factor binding sites and form part of promoter regions in DNA sequences of genes. Therefore, it is likely that such repeats in genomes have a role in the evolution of genes, regulation of gene expression and consequently the evolution of species.

Red-blood-cell augmentation of hypoxic pulmonary vasoconstriction: hematocrit dependence and the importance of nitric oxide

Red blood cells (RBCs) are known to augment hypoxic pulmonary vasoconstriction (HPV). To determine whether this phenomenon is hematocrit (Hct) dependent and related to alterations of either nitric oxide (NO) or adenosine metabolism, we studied mechanically ventilated, pump-perfused lungs from euthanized New Zealand White rabbits. Lungs were perfused in situ in a recirculating manner at constant flow; perfusates consisted of Krebs-Henseleit buffer or buffer plus washed RBCs at a Hct of 10% or 30%. HPV was quantitated as the increase in pulmonary artery pressure (Ppa) from baseline after 5 min of hypoxia. In three experimental sets, we studied the effects of Hct on HPV and expired NO, the effects of nitric oxide synthase (NOS) inhibition, and the effects of adenosine receptor blockade. HPV was greater at a higher Hct, and expired NO varied inversely with Hct and decreased with hypoxia. NOS inhibition eliminated RBC-dependence of HPV. Adenosine-receptor blockade did not affect the RBC-dependence of HPV. We conclude that HPV is dependent on Hct, and that this phenomenon may be related to scavenging of NO but not adenosine by RBCs.

Reference cDNA library facilities available from European sources

cDNA libraries are the cornerstone of efforts to identify the relatively small regions of genomes that are responsible for biological effects. Gene hunter seeking candidate genes, via a variety of approaches, ultimately focus on the cloning, sequencing, and expression of cDNAs. Assistance is now available to researchers in the form of genome programs, whose initial goals include assembly of a complete collection of expressed sequences derived from the genome of interest. The concept of reference sets of cDNA libraries is that the aims of genome programs are served most effectively by different laboratories working on a common set of high-quality arrayed cDNA libraries, using different experimental approaches, thereby reducing unnecessary duplication of effort, and maximizing the amount of information that one set of resources can provide.

Effects of intrathecal opioid on extubation time, analgesia, and intensive care unit stay following coronary artery bypass grafting

STUDY OBJECTIVE

To determine if intrathecal opioid decreases time to extubation after coronary artery bypass surgery without compromising postoperative analgesia.

DESIGN

Prospective randomized trial.

SETTING

Veterans Affairs Hospital.

PATIENTS

21 ASA physical status III and IV men scheduled for elective coronary bypass surgery, who had not received medications that would impair anticoagulation at the time of surgery.

INTERVENTIONS

Patients were randomized to receive 10 micrograms/kg morphine and 25 micrograms fentanyl intrathecally preoperatively (n = 12) or no intrathecal opioid (n = 9). The latter group received 25 to 50 micrograms/kg fentanyl and 0.05 to 0.1 mg/kg midaxolam intraoperatively, whereas the intrathecal opioid group received intravenous (i.v.) fentanyl and midazolam only as needed. Both groups were administered i.v. morphine and midazolam postoperatively as needed by intensive care unit (ICU) personnel who were blinded to the treatment group.

MEASUREMENTS AND MAIN RESULTS

For the first 24 hours postoperatively, pain levels (0 = none, to 10 = most severe) and sedation levels (1 = none, to 5 = unconscious) were measured hourly. The time to extubation and discharge from the ICU was recorded. ECG evidence of myocardial ischemia was noted. Pain scores were low for both groups (1.5), but the intrathecal opioid subjects exhibited less sedation than the high-dose fentanyl subjects [means +/- standard deviation (SD) of 2.3 +/- 0.4 vs. 2.8 +/- 0.5, p = 0.03]. Extubation time was 12 hours shorter in the intrathecal opioid group (2.9 +/- 5.3 vs. 14.7 +/- 6.8, p = 0.001). The five subjects with a one day ICU stay were all in the intrathecal opioid group (p = 0.04). The incidence of myocardial ischemia did not differ between the two groups.

CONCLUSIONS

Intrathecal opioid can facilitate early extubation and discharge from the ICU without compromising analgesia or increasing myocardial ischemia.

Reduction in post-intubation respiratory resistance by isoflurane and albuterol

PURPOSE

This study examined the bronchodilating effects of 0.6 MAC and 1.1 MAC isoflurane (ISF) on respiratory system resistance (Rrs) following tracheal intubation and determined whether albuterol supplements that effect.

METHODS

Sixty-seven adult patients were anaesthetized with 2 micrograms.kg-1 fentanyl and 5 mg.kg-1 thiopentone and their tracheas intubated following administration of 1 mg.kg-1 succinylcholine. Respiratory system resistance was measured following intubation and the patients then randomized to receive either 1.1 MAC ISF in oxygen or 0.6 MAC ISF in 50% nitrous oxide and oxygen. Ten minutes later, Rrs was again measured. Patients were then further randomized to receive albuterol or a placebo using incremental doses of 2, 5, and 10 puffs (albuterol puff = 90 micrograms) delivered via a metered dose inhaler at ten minute intervals.

RESULTS

Isoflurane at 1.1 MAC decreased post-intubation Rrs by 23 +/- 5% (mean +/- sem) whereas the decrease was only 7 +/- 5% for 0.6 MAC ISF (P < 0.01). Two puffs of albuterol resulted in a further decrease of 12 +/- 3% (mean +/- sem) in Rrs compared with a 2 +/- 4% decrease in the placebo groups (P < 0.05). Additional puffs of albuterol resulted in no further changes in Rrs.

CONCLUSION

We conclude that following tracheal intubation the reduction in Rrs produced by ISF is highly concentration dependent. Albuterol results in a small further reduction in Rrs.

CO2 transport in normovolemic anemia: complete compensation and stability of blood CO2 tensions

Isovolemic hemodilution does not appear to impair CO2 elimination nor cause CO2 retention despite the important role of red blood cells in blood CO2 transport. We studied this phenomenon and its physiological basis in eight New Zealand White rabbits that were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Isovolemic anemia was induced by simultaneous blood withdrawal and infusion of 6% hetastarch in sequential stages; exchange transfusions ranged from 15-30 ml in volume. Variables measured after each hemodilution included hematocrit (Hct), arterial and venous blood gases, mixed expired PCO2 and PO2, and blood pressure; also, O2 consumption, CO2 production, cardiac output (Q), and physiological dead space were calculated. Data were analyzed by comparison of changes in variables with changes in Hct and by using the model of capillary gas exchange described by Bidani (J. Appl. Physiol. 70: 1686-1699, 1991). There was complete compensation for anemia with stability of venous and arterial PCO2 between Hct values of 36 +/- 3 and 12 +/- 1%, which was predicted by the mathematical model. Over this range of hemodilution, Q rose 50%, and the O2 extraction ratio increased 61% without a decline in CO2 production or a rise in alveolar ventilation. The dominant compensations maintaining CO2 transport in normovolemic anemia include an increased Q and an augmented Haldane effect arising from the accompanying greater O2 extraction.

The effect of isoflurane, halothane, sevoflurane, and thiopental/nitrous oxide on respiratory system resistance after tracheal intubation

BACKGROUND

After tracheal intubation, lung resistance and therefore respiratory system resistance (R[rs]) routinely increase, sometimes to the point of clinical bronchospasm. Volatile anesthetics generally have been considered to be effective bronchodilators, although there are few human data comparing the efficacy of available agents. This study compared the bronchodilating efficacy of four anesthetic maintenance regimens: 1.1 minimum alveolar concentration (MAC) end-tidal sevoflurane, isoflurane or halothane, and thiopental/nitrous oxide.

METHODS

Sixty-six patients underwent tracheal intubation after administration of 2 microg/kg fentanyl, 5 mg/kg thiopental, and 1 mg/kg succinylcholine. Vecuronium or pancuronium (0.1 mg/kg) was then given to ensure paralysis during the rest of the study. Postintubation R(rs) was measured using the isovolume technique. Maintenance anesthesia was then randomized to thiopental 0.25 mg x kg(-1) x min(-1) plus 50% nitrous oxide, or 1.1 MAC end-tidal isoflurane, halothane, or sevoflurane. The R(rs) was measured after 5 and 10 min of maintenance anesthesia. Data were expressed as means +/- SD.

RESULTS

Maintenance with thiopental/nitrous oxide failed to decrease R(rs), whereas all three volatile anesthetics significantly decreased R(rs) at 5 min with little further improvement at 10 min. Sevoflurane decreased R(rs) more than either halothane or isoflurane (P < 0.05; 58 +/- 14% of the postintubation R(rs) vs. 69 +/- 20% and 75 +/- 13%, respectively).

CONCLUSIONS

After tracheal intubation in persons without asthma, sevoflurane decreased R(rs) as much or more than isoflurane or halothane did during a 10-min exposure at 1.1 MAC.

Dexamethasone treatment does not ameliorate subglottic ischemic injury in rabbits

BACKGROUND

Following tracheal intubation, a small proportion of patients develop laryngeal inflammation or tissue necrosis severe enough to result in clinical symptoms. Although corticosteroids are frequently advocated to prevent such injury, human studies have been inconclusive because of the low incidence of the problem. This study developed a rabbit model of endotracheal tube-induced laryngeal injury to test the hypothesis that a corticosteroid, dexamethasone, could ameliorate the inflammation and necrosis.

METHODS

Subglottic injury was induced in 21 anesthetized rabbits by inflating the cuff of an endotracheal tube to 100 mm Hg with the cuff just below the vocal cords. Every 30 min for 2 h, the cuff was deflated, the tube turned 90 degrees, and the cuff then reinflated. After 2 h, the rabbits' tracheas were extubated. Rabbits were divided into two groups: the treatment group received dexamethasone (1 mg/kg) i.v. 1 h prior to extubation with the dose repeated 6 h following extubation; the untreated group received a saline solution placebo. Four additional rabbits were anesthetized for the same period but did not have a tracheal tube inserted. All rabbits were killed 24 h later and the larynxes were harvested. Sections through the larynx at the level of the cricoid cartilage were randomized and submitted blindly to a veterinary pathologist. Larynxes were scored and ranked according to the severity of mucosal inflammation and necrosis, and submucosal hemorrhage, edema, inflammation, and necrosis. Specimens were also evaluated for focal vs diffuse disease.

RESULTS

Injured rabbits demonstrated focal to diffuse mucosal and submucosal inflammation and necrosis. Inflammatory exudates were present in sections from most of the injured rabbits and large sections of the larynxes were denuded of epithelium. There were no differences in injury scores between the treated and untreated rabbits. The four uninjured control rabbits had normal larynxes.

CONCLUSIONS

Two hours of endotracheal tube cuff inflation to 100 mm Hg causes an inflammatory laryngeal injury. The histologic features of the injury are unaltered by treatment with 2 mg/kg dexamethasone.

Comparative effects of thiopentone and propofol on respiratory resistance after tracheal intubation

To compare the effects of propofol and thiopentone on tracheal intubation-induced bronchoconstriction, 37 patients were allocated randomly to anaesthesia with either thiopentone 4 mg kg-1 followed by a 15-mg kg-1 h-1 continuous infusion or propofol 3 mg kg-1 followed by a 9-mg kg-1 h-1 continuous infusion. Intubation was facilitated by vecuronium 0.1-0.2 mg kg-1. Respiratory system resistance (Rrs) was measured by a CP-100 pulmonary function monitor, 5 min after intubation. The 5-min post-intubation Rrs values were significantly lower in the propofol group (8.5 (SD 1.5) cm H2O litre-1 S-1) than in the thiopentone group (10.9 (3.2) cm H2O litre-1 S-1). Thirty minutes after commencing isoflurane-nitrous oxide anaesthesia, Rrs declined by 17.5 (SEM 3.6)% from baseline in the thiopentone group, but by only 1.6 (2.6)% in the propofol group. We conclude that the dose of propofol administered provided more protection against tracheal intubation-induced bronchoconstriction than an induction dose of thiopentone.

Exposures to inhalable and "total" oil mist aerosol by metal machining shop workers

Several recent studies have compared worker personal aerosol exposures as measured by the current method with those obtained by a new approach based on collecting the inhalable fraction, intended to represent all the particles that are capable of entering through the nose and/or mouth during breathing. The present study investigated this relationship for a metal machining facility where aerosols were generated from severely refined, nonaqueous ("straight") cutting oils used during the lathe working of metal rod stock. Workers (n = 23) wore two personal aerosol samplers simulataneously, one of the 37-mm type (for "total" aerosol exposure, E37) and the other of the Institute of Occupational Medicine (IOM) type (for inhalable aerosol exposure, EIOM). The data were analyzed by weighted least squares linear regression to determine the coefficient S in the relation EIOM = S.E37. It was found that S = 2.96 +/- 0.60. This ratio-in which exposure to inhalable aerosol was greater than to "total" aerosol-is consistent with previous observations in other industries. The relative coarsenss of the oil mist aerosol, as estimated by cascade impactor measurements, probably explains the difference between the sampling methods. The collection of large "splash" droplets, may also contribute. Future occupational aerosol standards for metalworking fluids will be based on the new, health-related criteria, and exposures will be assessed on the basis of the inhalable fraction. Results of studies like that described here will enable assessment of the impact on future workplace aerosol exposure assessments of introducing new standards.

Isoflurane anesthesia does not add to the bronchodilating effect of a beta 2-adrenergic agonist after tracheal intubation

This double-blind study investigates whether isoflurane/N2O anesthesia adds to the bronchodilating effect of the beta 2-adrenergic agonist, fenoterol, after an endotracheal tube (ETT)-induced increase in airway resistance. Forty-five patients with ASA physical status I-II were randomly assigned to two groups: fenoterol-treated patients (n = 23) were given three metered-dose inhaler puffs (600 micrograms) of fenoterol 10 min before induction of anesthesia and placebo-treated patients (n = 22) received three puffs of an aerosol containing no medication. Anesthesia was induced with thiopental and vecuronium intravenously. Respiratory system resistance (Rrs) was measured using a CP-100 pulmonary function monitor 5 min after endotracheal intubation. Inhalation anesthesia was then begun using 50% N2O in O2 with end-tidal 1.3% isoflurane. Rrs measurements were repeated at 5, 15, and 30 min after the initiation of inhalation anesthesia. Postintubation Rrs was significantly lower in the fenoterol-treated patients than in the placebo-treated patients. Rrs declined by a mean of 17.1% after 30 min of inhalation anesthesia in the placebo-treated patients but declined by only 1.4% in the fenoterol-treated patients (P < 0.05 for fenoterol provides protection versus placebo). Our results confirm that fenoterol provides protection against ETT-induced increase of airway resistance. However, isoflurane, while a potent bronchodilator, does not add to the effect of fenoterol.

Pressures required to move gas through the native airway in the presence of a fenestrated vs a nonfenestrated tracheostomy tube

SUBJECT

It is occasionally desirable for patients with a tracheostomy tube to breathe through their native airway. We hypothesized that capped tracheostomy tubes with cuffs deflated would create substantial additional resistance to airflow without fenestration but would provide minimal resistance to airflow when the tube had a fenestration.

METHODS

Two tracheal models were tested simulating a large (26 mm) and an average (18 mm) trachea. Tests were carried out with fenestrated and nonfenestrated tracheostomy tubes of sizes ranging from No. 4 to No. 10. Negative pressure inspiration was simulated using suction.

RESULTS

With a large trachea or small tubes, the suction required to generate flows of 40 L/min or greater remained less than 5 cm H2O with or without a fenestration. However, with an average-sized trachea and no fenestration, the pressure required to generate flows of 40 L/min or greater exceeded 5 cm H2O and with No. 8 or No. 10 tubes exceeded 20 cm H2O. A fenestration routinely reduced the required pressure to less than 5 cm H2O.

CONCLUSION

The effort required to move gas across the native airway in the absence of a fenestration may be substantial. If a patient is to breathe through a native airway, a fenestrated tube should be used unless the tracheostomy tube is a No. 4.

Comparison of the effects of etomidate, propofol, and thiopental on respiratory resistance after tracheal intubation

BACKGROUND

Tracheal intubation frequently results in reversible bronchoconstriction. Propofol has been reported to minimize this response in healthy patients and in asthma patients, but may be unsuitable for hemodynamically unstable patients for whom etomidate may be preferable. The current study examined respiratory resistance after tracheal intubation after induction with either thiopental, etomidate, or propofol. A supratherapeutic dose of etomidate was used to test the hypothesis that the bronchoconstrictive response could be minimized by deep intravenous anesthesia.

METHODS

Seventy-seven studies were conducted in 75 patients. Anesthesia was induced with either 2.5 mg/kg propofol, 0.4 mg/kg etomidate, or 5 mg/kg thiopental. Respiratory resistance was measured at 2 min after induction.

RESULTS

Respiratory resistance at 2 min was 8.1 +/- 3.4 cmH2O.1(-1).s (mean +/- SD) for patients receiving propofol versus 11.3 +/- 5.3 for patients receiving etomidate and 12.3 +/- 7.9 for patients receiving thiopental (P < or = 0.05 for propofol vs. either etomidate or thiopental).

CONCLUSIONS

Respiratory resistance after tracheal intubation is lower after induction with propofol than after induction with thiopental or after induction with high-dose etomidate.

Characterization of delta opioid receptors in lung cancer using a novel nonpeptidic ligand

Cancer cells are often characterized by the presence of membrane receptors not normally associated with nontransformed cells from the same tissue type. Recent studies have demonstrated increased expression of high-affinity binding sites for opioid receptor-selective ligands in lung cancer cell lines relative to normal lung tissue. We investigated the binding of a nonpeptidic delta opioid receptor ligand in small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells with the aim of developing the ligand as a novel lung cancer imaging agent. The ligand, [3H] (+)-4-[alpha-R)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3- hydroxybenzyl)-N,N-diethylbenzamide ([3H](+)BW373U86), bound with high-affinity [Kd (dissociation constant) = 0.066 +/- 0.012 nM] to membranes prepared from six different SCLC cell lines but not to those from seven NSCLC cell lines, including one mesothelioma. The number of biding sites varied from 10 to 300 fmol/mg membrane protein. Competition binding studies demonstrated displacement of [3H](+)BW373U86 binding by the delta-selective antagonists naltriben and 7-benzylidenenaltrexone but not with the mu- and kappa- selective antagonists D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 and trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]ben zeneacetamide methanesulfonate. Mean apparent Kis for naltriben and 7-benzylidenenaltrexone in membranes from two SCLC cell lines were 0.17 and 3.9 nM, respectively, but were >10 microM for the mu and kappa ligands. The nonselective antagonist naloxone displaced [3H](+)BW373U86 binding with an apparent Ki of approximately 29 nM. On the basis of these data, we believe the lung cancer receptor to be similar, if not identical, to the human brain delta opioid receptor. The lack of high-affinity [3H](+)BW373U86 binding in normal mouse lung membranes suggests a potential role for this ligand as a novel therapeutic or imaging agent.

Effect of anemia on intrapulmonary shunt during atelectasis in rabbits

To elucidate the effects of anemia on intrapulmonary shunt, we studied a model of left lung atelectasis in anesthetized rabbits. In 10 rabbits, isovolemic anemia was produced by sequential hemodilution. Seven control rabbits were followed over time, without hemodilution. Intrapulmonary shunt (Qs/QT) was measured by using blood gas analysis and by quantitation of the percentage of blood flow to the collapsed left lung (QLl/QT) using fluorescent microspheres. In control rabbits, Qs/QT and QLl/QT decreased over time, whereas arterial PO2 increased. In hemodiluted rabbits, there was a trend toward increased Qs/QT and QLl/QT. There were significant differences in the behavior of Qs/QT, QLl/QT, and arterial PO2 between control and hemodiluted rabbits. Hemodynamic parameters, including cardiac output and pulmonary artery pressure, were not different between groups. In a third group of rabbits with pharmacologically induced acidosis but no hemodilution, Qs/QT and QLl/QT decreased over time, and arterial PO2 increased. We conclude that acute isovolemic anemia has a deleterious effect on pulmonary gas exchange, possibly through attenuation of hypoxic pulmonary vasoconstriction.

CD18-independent mechanism of neutrophil emigration in the rabbit lung after ischemia-reperfusion

BACKGROUND

Reperfusion of ischemic lung causes an inflammatory pulmonary vascular injury characterized by increased vascular permeability and migration of inflammatory cells into the alveoli. Migration of neutrophils into the alveolus during reperfusion after 24 hours of unilateral pulmonary artery occlusion has been shown to be in part dependent on the CD18 adhesion molecule on the cell surface. The current study investigated whether reperfusion lung injury after a 1-hour period of complete lung ischemia was CD18 dependent.

METHODS

Eighteen rabbits were assigned to one of three groups. Groups 1 and 2 were subjected to one hour of in situ right hilar occlusion followed by 2 hours of reperfusion. Group 3 was subjected to identical surgical dissection but the right hilum was never occluded. Group 1 rabbits received saline solution (1 mL/kg) before hilar occlusion and group 2 rabbits, monoclonal antibody 60.3, a blocking antibody for the CD18 adhesion molecule on the neutrophil surface (2 mg/kg). In 3 of the antibody-treated rabbits, flow cytometry was performed on blood neutrophils before and after administration of the antibody and 120 minutes after reperfusion.

RESULTS

The rabbits in groups 1 and 2 had significantly increased alveolar neutrophil infiltrate and increased pulmonary vascular resistance compared with the rabbits in group 3. However, there was no significant difference between group 1 (saline solution treated) and group 2 (antibody treated). Antibody treatment did not block migration of neutrophils into the alveoli. Flow cytometry of circulating neutrophils demonstrated that CD18 was upregulated after reperfusion and that CD18 was fully blocked after antibody treatment for the duration of the study.

CONCLUSIONS

We conclude that a 1-hour period of warm ischemia followed by reperfusion results in upregulation of CD18 but that emigration of the neutrophils into the alveoli is not CD18 dependent in this injury.