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Titolo:
THE EFFECT OF CHANGING EXCITATION-FREQUENCY ON PARALLEL CONDUCTANCE IN DIFFERENT-SIZED HEARTS
Autore:
WHITE PA; BROOKES CIO; RAVN HB; STENBOG EE; CHRISTENSEN TD; CHATURVEDI RR; SORENSEN K; HJORTDAL VE; REDINGTON AN;
Indirizzi:
ROYAL BROMPTON & NATL HEART HOSP,DEPT PAEDIAT CARDIOL,SYDNEY ST LONDON SW3 6NP ENGLAND ROYAL BROMPTON & NATL HEART HOSP,DEPT PAEDIAT CARDIOL LONDON SW3 6NP ENGLAND ROYAL BROMPTON & NATL HEART HOSP,DEPT ADULT CARDIOL LONDON SW3 6NP ENGLAND AARHUS UNIV HOSP,INST EXPT CLIN RES DK-8000 AARHUS DENMARK AARHUS UNIV HOSP,DEPT CARDIOL DK-8000 AARHUS DENMARK
Titolo Testata:
Cardiovascular Research
fascicolo: 3, volume: 38, anno: 1998,
pagine: 668 - 675
SICI:
0008-6363(1998)38:3<668:TEOCEO>2.0.ZU;2-2
Fonte:
ISI
Lingua:
ENG
Soggetto:
PRESSURE-VOLUME RELATIONSHIPS; IMPEDANCE CATHETER; STROKE VOLUME; OCCLUSION;
Keywords:
PIG; NEONATAL; ADULT; LEFT VENTRICLE; CONDUCTANCE CATHETER; SALINE WASH-IN; PARALLEL CONDUCTANCE; DUAL FREQUENCY EXCITATION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
23
Recensione:
Indirizzi per estratti:
Citazione:
P.A. White et al., "THE EFFECT OF CHANGING EXCITATION-FREQUENCY ON PARALLEL CONDUCTANCE IN DIFFERENT-SIZED HEARTS", Cardiovascular Research, 38(3), 1998, pp. 668-675

Abstract

Objective: An important component of the ventricular volume measured using the conductance catheter technique is due to parallel conductance (Vc), which results from the extension of the electric field beyond the ventricular blood pool. parallel conductance volume is normally estimated using the saline dilution method (Vc(saline dilution)), in which the conductivity of blood in the ventricle is transiently increasedby injection of hypertonic saline. A simpler alternative has been reported by Gawne et al, [12], Vc(dual frequency) is estimated from the difference in total conductance measured at two exciting frequencies and the method is based on the assumption that parallel conductance is mainly capacitive and hence is negligible at low frequency. The objective of this study was to determine whether the dual frequency techniquecould be used to substitute the saline dilution method to estimate Vcin different sized hearts. Methods: The accuracy and linearity of a custom-built conductance catheter (CC) system was initially assessed invitro. Subsequently, a CC and micromanometer were inserted into the left ventricle of seven 5 kg pigs (group 1) and six 50 kg pigs (group 2). Cardiac output was determined using thermodilution (group 1) and anultrasonic flow probe (group 2) from which the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using saline dilution were performed at frequencies in the range of 5-40 kHz. All measurements were made at end-expiration. Finally, Vc was estimated from the change in end-systolic conductance between 5 kHz and 40 kHz using the dual frequency technique of Gawne et al. [12]. Results: There was no change in measured volume of a simple insulated cylindricalmodel when the stimulating frequency was varied from 5-40 kHz, Vc(saline dilution) varied significantly with frequency in group 1 (8.63 +/-2.74 ml at 5 kHz; 11.51 +/- 2.65 ml at 40 kHz) (p = 0.01). Similar results were obtained in group 2 (69.43 +/- 27.76 ml at 5 kHz; 101.24 +/- 15.21 ml at 40 kHz) (p < 0.001). However, the data indicate that theresistive component of the parallel conductance is substantial (Vc at0 Hz estimated as 8.01 ml in group 1 and 62.3 ml in group 2). There was an increase in alpha with frequency in both groups but this did notreach significance. The correspondence between Vc(dual frequency) andVc(saline dilution) methods was poor (group 1 R-2 = 0.69; group 2 R-2= 0.22). Conclusion: At a lower excitation frequency of 5 kHz a smaller percentage of the electric current extends beyond the blood pool soparallel conductance is reduced. While parallel conductance is frequency dependent, it has a substantial resistive component. The dual frequency method is based on the assumption that parallel conductance is negligible at low frequencies and this is clearly not the case. The results of this study confirm that the dual frequency technique cannot beused to substitute the saline dilution technique. (C) 1998 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 10/07/20 alle ore 14:41:51