Global ground strike point characteristics in negative downward lightning flashes – Part 1: Observations

Information about lightning properties is important in order to advance the current understanding of lightning, whereby the characteristics of ground strike points (GSPs) are in particular helpful to improving the risk estimation for lightning protection. Lightning properties of a total of 1174 negative downward lightning flashes are analyzed. The high-speed video recordings are taken in different regions, including Austria, Brazil, South Africa and the USA, and are analyzed in terms of flash multiplicity, duration, interstroke intervals and ground strike point properties. According to our knowledge this is the first simultaneous analysis of GSP properties in different regions of the world applying a common methodology. Although the results vary among the data sets, the analysis reveals that a third of the flashes are single-stroke events, while the overall mean number of strokes per flash equals 3.67. From the video imagery an average of 1.56 GSPs per flash is derived, with about 60 % of the multiple-stroke flashes striking the ground in more than one place. It follows that a ground contact point is struck 2.35 times on average. Multiple-stroke flashes last on average 371 ms, whereas the geometric mean (GM) interstroke interval value preceding strokes producing a new GSP is about 18 % greater than the GM value preceding subsequent strokes following a pre-existing lightning channel. In addition, a positive correlation between the duration and multiplicity of the flash is presented. The characteristics of the subset of flashes exhibiting multiple GSPs is further examined. It follows that strokes with a stroke order of 2 create a new GSP in 60 % of the cases, while this percentage quickly drops for higher-order strokes. Further, the possibility of forming a new lightning channel to ground in terms of the number of strokes that conditioned the previous lightning channel shows that approximately 88 % developed after the occurrence of only one stroke. Investigating the time intervals in the other 12 % of the cases when two or more strokes re-used the previous lightning channel showed that the average interstroke time interval preceding a new lightning channel is found to be more than twice the time difference between strokes that follow the previous lightning channel.

CN Tower current wavefront parameters

This work is focused on the establishment of comprehensive statistics concerning the characteristics of the lightning current measured at the CN Tower during five years (1992-1996). Negative lightning currents are characterized with two distinguished impulses: short risetimes’ impulses, and impulses with substantially larger risetimes and larger current peaks in comparison with fast impulses. The slower negative current impulses were found to occur either in single stroke flashes or as first strokes in multiple stroke flashes, suggesting that they may belong to downward-initiated lightning to the CN Tower. The statistical analysis illustrates that there is a substantial difference in current wavefront parameter of ordinary negative fast wavefront impulses and those for slow wavefront negative impulses. The obtained statistics are very important for building lightning protection means against direct strikes to power lines, substation and communication equipments, as well as against lightning occurring in their vicinities.

Multi-Stroke Lightning Interaction with Wiring Harness: Experimental Tests and Modelling

This paper presents the obtained results of experimental tests and modelling of lightning disturbances that were propagated in a model of aircraft cable bundle and caused by multiple lightning return-strokes interactions. The work is a continuation of previous research, which was concerned mainly with the interaction of lightning discharge with a single return-stroke. The section of the cable harness arranged above the metal plate was investigated. In one of its wires, a multiple-stroke current representing indirect lightning effects was injected from an impulse current generator dedicated to avionics immunity tests. Overvoltages induced at the ends of other wires surrounded by a braided shield, as well as the influence of line parameters and shield grounding condition on the shape and level of observed transients, were examined. The computer simulation results match the measurement data with satisfactory accuracy, and therefore, the presented model can be used to estimate indirect lightning effects in the wiring harness of avionics.

Global ground strike point characteristics in negative downward lightning flashes – part 1: Observations

Lightning properties of a total of 1174 negative downward lightning flashes are analyzed. The high-speed video recordings are taken in different regions around the world, including Austria, Brazil, South Africa and USA, and are analyzed in terms of flash multiplicity, duration, interstroke intervals and ground strike point (GSP) properties. Although the results vary among the data sets, the analysis reveals that a third of the flashes are single-stroke events, while the overall mean number of strokes per flash equals 3.67. From the video imagery an average of 1.56 GSPs per flash is derived, with about 60 % of the multiple stroke flashes striking ground in more than one place. It follows that the channel creating a GSP is re-used by a factor of 2.3. Multiple-stroke flashes last on average 371 ms, whereas the geometric mean (GM) interstroke interval value preceding strokes producing a new GSP is about 18 % greater than the GM value preceding subsequent strokes following a pre-existing channel. In addition, a positive correlation between the duration and multiplicity of the flash is presented. The characteristics of the subset of flashes exhibiting multiple GSPs is further examined. It follows that strokes with stroke order of two create a new GSP in 60 % of the cases, while this percentage quickly drops for higher order strokes. Further, the possibility to form a new channel to ground in terms of the number of strokes that conditioned the previous channel shows that approximately 88 % developed after the occurrence of only one stroke. Investigating the time intervals in the other 12 % of the cases when two or more strokes re-used the previous channel showed that the average interstroke time interval preceding a new channel is found to be more than twice the time difference between strokes that follow the previous channel.

Derivation and Application of a Tool to Estimate Benefits From Multiple Therapies That Reduce Recurrent Stroke Risk

Background and Purpose— Lowering blood pressure and cholesterol, antiplatelet/antithrombotic use, and smoking cessation reduce risk of recurrent stroke. However, gaps in risk factor control among stroke survivors warrant development and evaluation of alternative care delivery models that aim to simultaneously improve multiple risk factors. Randomized trials of care delivery models are rarely of sufficient duration or size to be powered for low-frequency outcomes such as observed recurrent stroke. This creates a need for tools to estimate how changes across multiple stroke risk factors reduce risk of recurrent stroke. Methods— We reviewed existing evidence of the efficacy of interventions addressing blood pressure reduction, cholesterol lowering, antiplatelet/antithrombotic use, and smoking cessation and extracted relative risks for each intervention. From this, we developed a tool to estimate reductions in recurrent stroke risk, using bootstrapping and simulation methods. We also calculated a modified Global Outcome Score representing the proportion of potential benefit (relative risk reduction) achieved if all 4 individual risk factors were optimally controlled. We applied the tool to estimate stroke risk reduction among 275 participants with complete 12-month follow-up data from a recently published randomized trial of a healthcare delivery model that targeted multiple stroke risk factors. Results— The recurrent stroke risk tool was feasible to apply, yielding an estimated reduction in the relative risk of ischemic stroke of 0.36 in both the experimental and usual care trial arms. Global Outcome Score results suggest that participants in both arms likely averted, on average, 45% of recurrent stroke events that could possibly have been prevented through maximal implementation of interventions for all 4 individual risk factors. Conclusions— A stroke risk reduction tool facilitates estimation of the combined impact on vascular risk of improvements in multiple stroke risk factors and provides a summary outcome for studies testing alternative care models to prevent recurrent stroke. Registration— URL: https://www.clinicaltrials.gov ; Unique identifier: NCT00861081.

Bypassing the Closest Stroke Center for Thrombectomy Candidates

Background and Purpose— Patients with acute ischemic stroke who have large vessel occlusion benefit from direct transport to a comprehensive stroke center (CSC) capable of endovascular therapy. To avoid harm for patients without large vessel occlusion from delayed access to intravenous thrombolysis (IVT), it has been suggested to only redirect patients with high likelihood of large vessel occlusion for whom the additional delay to intravenous thrombolysis (IVT) caused by transport to the CSC is below a certain threshold. However, which threshold achieves the greatest clinical benefit is unknown. Methods— We used mathematical modeling to calculate additional-delay-to-IVT thresholds associated with the greatest reduction in disability-adjusted life years in abstracted 2-stroke center and multiple-stroke center scenarios. Model parameters were extracted from recent meta-analyses or large prospective cohort studies. Uncertainty was quantified in probabilistic and 2-way univariate sensitivity analyses. Results— Assuming ideal treatment time performance metrics, transport to the nearest CSC was the preferred strategy irrespective of additional delay-to-IVT when the transfer time between primary stroke center and CSC was <40 minutes (95% credible interval: 25–66 minutes); otherwise, the optimal additional delay-to-IVT-threshold ranged from 28 to 139 minutes. In multiple-stroke center scenarios, optimal additional-delay-to-IVT thresholds were 30 to 54 minutes in urban and 49 to 141 minutes in rural settings; use of optimal thresholds as compared with a 15 minute-threshold saved 0 to 0.11 and 0 to 0.37 disability-adjusted life years per triage case, respectively. Assuming slower treatment times at primary stroke centers and CSCs yielded longer permissible additional delays. Conclusions— Our results suggest that patients with acute ischemic stroke with suspected large vessel occlusion should be redirected to a CSC if the additional delay to IVT is <30 minutes in urban and 50 minutes in rural settings.

Predictors of Neurological Outcome of Arterial Ischemic Stroke in Children

Stroke is an important cause of mortality and morbidity in children. The aim of the study was to evaluate long-term neurological outcome in children with arterial ischemic stroke (AIS) and explore predictive factors that affect poor outcome. Fifty-six patients aged between 1 month and 17 years who were treated at M. Iashvili Children's Central Hospital, Tbilisi, Georgia, with an onset of stroke from 2007 to 2017 were included. To explore predictive factors of outcome, the following data were collected: demographic characteristics, risk factors, he presenting signs, radiological features, and presence of stroke recurrence. Neurological status at discharge and long-term neurological outcome at least 1 year after stroke was evaluated according to Pediatric Stroke Outcome Measure subscale. The reported outcome after childhood stroke was variable with long-term neurological deficits in one-third of patients (30.4%). The neurological outcome was worse in males, in patients with multiple stroke episodes, and in those with infarctions involving a combination of cortical and subcortical areas. Pediatric AIS carries the risk of long-term morbidity, and neuroimaging has a predictive influence on outcome.