Thoracic impedance of human subjects

Machin, J. W.

doi:10.1007/bf02451918

Cited by 19 publications

(4 citation statements)

References 2 publications

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“…The delivered pulse durations were within the 2 to 10 msec range described for clinical defibrillators by Finlay [11] and within the 4 to 8 msec range we calculated for typical commercially available, damped sine wave defibrillators using published values for output circuit components [12] and for the range of human thoracic resistances (25 to 105 ohms) encountered clinically [13].…”

Section: The Experimental Defibrillatormentioning

confidence: 73%

Therapeutic indices for transchest defibrillator shocks: Effective, damaging, and lethal electrical doses

Babbs

Tacker

VanVleet

et al. 1980

American Heart Journal

155

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Although prospective studies of defibrillator shock overdose cannot be performed in man, the therapeutic indices of various defibrillating current waveforms can be measured in animals. We determined the ratios TD 50 /ED 50 and LD 50 / ED 50 (where TD 50 = median "toxic" or damageinducing dose, ED 50 = median effective or defibrillating dose, and LD 50 = median lethal dose) as measures of the therapeutic index for damped sine wave defibrillator shocks in dogs. Death of an animal and/or any degree of cardiac damage found by gross or microscopic examination were defined as harmful effects of shock, analogous to drug toxicity. In terms of peak current, the ED 50 , TD 50 , and LD 50 were 1.1, 5.8, and 24 amperes/ kg; the therapeutic indices were TD 50 /ED 50 = 5 for morphologic damage and LD 50 /ED 50 = 22 for death. In terms of delivered energy the ED 50 , TD 50 , and LD50 were 1.5, 30, and 470 joules/kg; the therapeutic indices were TD50/ED50 = 20 for damage and LD 50 /ED 50 = 320 for death. These data indicate a reasonable margin of safety for damped sine wave defibrillator shocks in dogs, and are consistent with reported incidences of suspected shock-induced damage in humans.

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Section: The Experimental Defibrillatormentioning

confidence: 73%

Therapeutic indices for transchest defibrillator shocks: Effective, damaging, and lethal electrical doses

Babbs

Tacker

VanVleet

et al. 1980

American Heart Journal

155

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“…The de brillator load impedance, which includes the electrode -skin and the patient transthoracic impedance, determines the delivered current amplitude and energy, and therefore the de brillation success [1 -3]. The role of this parameter has been studied by many investigators [2,4,5]. Lower energy required for de brillation was observed in patients with low transthoracic impedance [6].…”

Section: Introductionmentioning

confidence: 98%

Possibilities for predictive measurement of the transthoracic impedance in defibrillation

Krasteva

Hatib²,

Trendafilova³

et al. 2001

Journal of Medical Engineering & Technology

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Transthoracic electrical defibrillation is administered by high voltages and currents applied through large size electrodes. Therefore, the defibrillator load impedance becomes an essential factorfor the efficacy of the procedure. Attempts at prediction of transthoracic impedance by pre-shock measurement with low-amplitude high-frequency current have yielded apparently promising results. A reassessment was undertaken of the comparison between transthoracic impedance measured over a wide frequency range (bioimpedance spectroscopy) and measured during the shock. An estimation of the possibilities for pre-shock 'prediction ' of the impedance was performed, to allow adequate selection of the defibrillation energy or current with the intention of increasing the possibility for positive results with the first shock. Data were obtained from experimental fibrillation/defibrillation cycles on dogs andfrom cardioversion of atrial fibrillation or flutter in patients. The final results suggest that high-frequency low-amplitude impedance measurements cannot predict the corresponding value during the shock with very high accuracy, as differences up to 15-17% were found using biphasic pulses in patients. However, the method can be used for approximate assessments.

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“…Since the curves all have a similar qualitative shape and the transthoracic impedance is predominantly resistive (21,22) The data derived from discharging six energy levels across 13 dogs were used to evaluate the validity ofEq. 5 according to a general linear model (Statistical Analysis System, SAS Institute, Cary, NC).…”

Section: Resultsmentioning

confidence: 99%

Relationship between canine transthoracic impedance and defibrillation threshold. Evidence for current-based defibrillation.

Lerman¹,

Halperin²,

Tsitlik³

et al. 1987

J. Clin. Invest.

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The electrical parameter used to define defibrillation strength is energy. Peak current, however, may more accurately reflect the field quantities (i.e., electric field strength and current density) that mediate defibrillation and therefore should be a better clinical descriptor of threshold than energy. Though transthoracic impedance is a major determinant of energy-based threshold and is sensitive to operator-dependent changes in impedance (electrode-subject interface), an ideal threshold descriptor should be invariant with respect to these changes in impedance. We therefore compared the relative invariance of energy-and current-based thresholds when transthoracic impedance was altered by one of two methods: (a) change in electrode size (protocol A) or (b) change in electrode force (protocol B). In protocol A, impedance was altered in each dog by a mean of 95%. Energy thresholds determined at both low and high impedance were 44±21 J (mean±SD) and 105±35 J, respectively, P < 0.0001. In contrast, peak current (A) thresholds were independent of transthoracic impedance, 22±5 A (low impedance) vs. 24±6 A (high impedance), P = NS. Energy and current thresholds showed a similar relationship for animals tested in protocol B. Therefore, current-based thresholds, in contrast to energy thresholds are independent of operator-dependent variables of transthoracic impedance and are invariant for a given animal. These results suggest that redefining defibrillation threshold in terms of peak current rather than energy provides a superior method of defibrillation.

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Thoracic impedance of human subjects

Cited by 19 publications

References 2 publications

Therapeutic indices for transchest defibrillator shocks: Effective, damaging, and lethal electrical doses

Therapeutic indices for transchest defibrillator shocks: Effective, damaging, and lethal electrical doses

Possibilities for predictive measurement of the transthoracic impedance in defibrillation

Relationship between canine transthoracic impedance and defibrillation threshold. Evidence for current-based defibrillation.

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