The impact of ventricular fibrillation amplitude on successful cardioversion, resuscitation duration, and survival after out-of-hospital cardiac arrest

OBJECTIVE: We sought to examine the incidence of low amplitude ventricular fibrillation and its impact on successful cardioversion, duration of resuscitation, and survival to hospital discharge in patients with out-of-hospital cardiac arrest (OHCA). DESIGN: Retrospective analysis from a statewide registry. SETTING: Victoria, Australia. PARTICIPANTS: Consecutive initial ventricular fibrillation arrests with an emergency medical service (EMS)-attempted resuscitation between 1 February 2019 and 30 January 2020. MAIN OUTCOME MEASURES: Survival to hospital discharge, successful cardioversion, and duration of resuscitation. RESULTS: Of the 471 initial ventricular fibrillation arrests, 429 (91.1%) had sufficient electrocardiogram data for review. The median initial and final ventricular fibrillation amplitude did not differ (0.3 mV; interquartile range [IQR], 0.2–0.5 mV). The final pre-shock amplitude was ≤ 0.1 mV (very fine) and ≤ 0.2 mV (fine) in 22.8% and 37.5% of cases respectively. In a multivariable analysis, only the time between emergency call and first defibrillation was associated with a low initial ventricular fibrillation amplitude ≤ 0.2 mV (adjusted odds ratio [aOR], 1.07; 95% CI, 1.02–1.13; P = 0.004). After adjustment for arrest factors, every 0.1 mV increase in final amplitude was independently associated with survival to hospital discharge (aOR, 1.26; 95% CI, 1.14–1.39; P < 0.001) and initial cardioversion success (aOR, 1.19; 95% CI, 1.07–1.32; P = 0.001). The duration of resuscitation also increased by 1.7 minutes (95% CI, 1.03–2.36; P < 0.001) for every 0.1 mV increase in final amplitude. CONCLUSION: More than one-third of initial ventricular fibrillation OHCA cases were low in amplitude. Comparative international data are needed to better understand how low amplitude ventricular fibrillation rhythms confound the measurement of OHCA interventions and international benchmarks for survival outcomes.

Transmission of vibration and energy through layered and jointed plates subjected to shock excitation

In this article, the vibration and energy transmission characteristics at the multiple interfaces of layered and jointed plates associated with friction are studied as a function of the shock loading amplitude using the established ‘sphere-joint assembled multi-layered plates’ model. The dynamic responses at the multiple interfaces under shock excitation are calculated using finite element analysis. The transmissions of vibration and energy through the multiple interfaces are characterized by the defined vibration and energy transmission ratios. Results show that the acceleration amplitudes at different interfaces increase nonlinearly with the shock amplitude and they are approximated by a third-order polynomial function. The acceleration amplitude nonlinearly decreases along the transmitting interfaces and the maximum attenuation occurs between the first and second transmitting interfaces. A minimum vibration transmission ratio is observed for the range of shock amplitude considered and the value of shock amplitude leading to the minimum is identical for different transmitting interfaces. It is also shown that the energy transmission ratio exhibits a nonlinear behaviour similar to that of the vibration transmission ratio. The expression for determining the shock amplitude resulting in peak energy transmission ratio at the input interface is also presented. Experimental validation is performed, which shows good agreement with numerical results.

The somato-sympathetic reflex in the spontaneous hypertensive rats

In chloralose anesthetized and paralyzed spontaneously hypertensive rats (SHR) a somatosympathetic reflex in the cervical sympathetic trunk elicited by a single electrical shock to forelimb afferent fibres in the median nerve was recorded. It has been shown that the somatosympathetic reflex consists of two responses and following silent period. The А-response evoked by the somatic myelinated afferent fibres stimulation, and C-respon.se elicited by the both stimulation of myelinated and unmyelinated afferent fibres. The silent period occurred with the myelinated fibres stimulation. Its duration was proportional to the electrical shock amplitude. The А-response consisted of four waves, the three of them formed early and late responses.

One-dimensional shock waves in simple materials with memory

Asymptotic evolution laws for plane dilatational shock waves travelling in simple materials with memory are derived in this paper by using two approximation methods. The first method is a combination of singular surface theory and perturbation methods. A system of two coupled first-order ordinary differential equations is derived for the shock amplitude and the amplitude of the accompanying second-order discontinuity. The shock amplitude is assumed to be small, but the accompanying second-order discontinuity may be taken either to be finite or to be small with the shock amplitude. The first case corresponds to the situation in which the duration time of the applied load is small compared with the viscous relaxation time and we show that the evolutionary behaviour of the two discontinuities is strongly affected by material nonlinearity. The second case, however, corresponds to the situation in which the duration time is comparable with the viscous relaxation time and we are able to show that the evolutionary behaviour is as predicted by the linear theory of viscoelasticity. In both cases the corresponding elastic results are obtained on allowing the viscous relaxation time to tend to infinity. The second approximation method is the shock-fitting method applied to a modulated simple wave theory, which is itself an approximation based on a small-amplitude finite-rate assumption equivalent to the first case discussed above. The two approximation methods are shown to yield the same evolution laws within their common range of validity.