To develop new methods for studying correlations between the performance and outcome of resuscitation efforts in real-world clinical settings using data recorded by automatic devices, such as automatic external defibrillators (AEDs), and to explore effects of shock timing and chest compression depth in the field.
In 695 records of AED use in the pre-hospital setting, continuous compression data were recorded using AEDs capable of measuring sternal motion during compressions, together with timing of delivered shocks and the electrocardiogram. In patients who received at least one shock, putative return of spontaneous circulation (P-ROSC) was defined as a regular, narrow complex electrical rhythm > 40 beats/min with no evidence of chest compressions at the end of the recorded data stream. Transient return of spontaneous circulation (t-ROSC) was defined as the presence of a post-shock organized rhythm > 40 beats/min within 60s, and sustained > or = 30 s. 2x2 contingency tables were constructed to examine the association between these outcomes and dichotomized time of shock delivery or chest compression depth, using the Mood median test for statistical significance.
The probability of P-ROSC for first shocks delivered < 50 s (the median time) after the start of resuscitation was 23%, versus 11% for first shocks > 50 s (p=0.028, one tailed). Similarly, the probability of t-ROSC for shorter times to shock was 29%, compared to the 15% for delayed first shocks (p=0.016). For shocks occurring > 3 min after initiation of rescue attempts, the probability of t-ROSC with pre-shock average compression depth > 5 cm was more than double that with compression depth < 5 cm (17.7% vs. 8.3%, p=0.028). For shocks > 5 min, the effect of deeper compressions increased (23.4% versus 8.2%, p=0.008).
Much can be learned from analysis of performance data automatically recorded by modern resuscitation devices. Use of the Mood median test of association proved to be sensitive, valid, distribution independent, noise-resistant and also resistant to biases introduced by the inclusion of hopeless cases. Efforts to shorten the time to delivery of the first shock and to encourage deeper chest compressions after the first shock are likely to improve resuscitation success. Such refinements can be effective even after an unknown period of preceding downtime.
"In any case, incorporating a CPR artifact filter to current AEDs is more complex than using algorithms that directly analyze the corrupt ECG [5, 6]. Filtering techniques based on the CD signal require the use of external CPR quality devices [40, 41] or modified defibrillation pads [42, 43] to record the acceleration signal. Alternatively other reference signals can be used, such as the thoracic impedance recorded through the defibrillation pads . "
[Show abstract][Hide abstract] ABSTRACT: Interruptions in cardiopulmonary resuscitation (CPR) compromise defibrillation success. However, CPR must be interrupted to analyze the rhythm because although current methods for rhythm analysis during CPR have high sensitivity for shockable rhythms, the specificity for nonshockable rhythms is still too low. This paper introduces a new approach to rhythm analysis during CPR that combines two strategies: a state-of-the-art CPR artifact suppression filter and a shock advice algorithm (SAA) designed to optimally classify the filtered signal. Emphasis is on designing an algorithm with high specificity. The SAA includes a detector for low electrical activity rhythms to increase the specificity, and a shock/no-shock decision algorithm based on a support vector machine classifier using slope and frequency features. For this study, 1185 shockable and 6482 nonshockable 9-s segments corrupted by CPR artifacts were obtained from 247 patients suffering out-of-hospital cardiac arrest. The segments were split into a training and a test set. For the test set, the sensitivity and specificity for rhythm analysis during CPR were 91.0% and 96.6%, respectively. This new approach shows an important increase in specificity without compromising the sensitivity when compared to previous studies.
BioMed Research International 05/2014; 2014(5):872470. DOI:10.1155/2014/872470 · 3.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Noticeable difference in pulsed second breakdown performance have appeared in high-frequency power transistors operated in the vicinity of BVCEO. Devices with thin, lightly doped epitaxial collector regions show second breakdown at much lower currents than many devices having the same base and emitter structure but thick epitaxial collector regions. However, some of the latter devices also have low second breakdown currents. The early second breakdown can be predicted in terms of the negative resistance seen at the collector terminal with the base open. This negative resistance leads to internal instability and current crowding. At high voltages, the collector negative resistance is electrical in nature and does not depend on heating effects with consequent time lags (although these will introduce a further negative resistance), so that the instability it introduces builds up very rapidly. It is caused by local reverse base current producing increased forward bias on the emitter junction as it flows through the sheet resistance of the base layer. Two effects modify the collector negative resistance, giving rise to considerable differences in second breakdown performance. One of these effects is the avalanche breakdown occurring at the edge of the shallow diffused planar collector-base junction. If this breakdown occurs at a lower voltage than that required to make M > 1/¿, where M is the avalanche multiplication factor for the collector junction under the emitter, no negative resistance appears and the transistor shows a high second breakdown current.
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