新製品 非観血心拍出量計

Physiol. Meas. 27 (2006) 817–827 doi:10.1088/0967-3334/27/9/005
Impedance cardiography revisited
G Cotter1, A Schachner2, L Sasson2, H Dekel2 and Y Moshkovitz3
1 Divisions of Clinical Pharmacology and Cardiology, Duke University Medical Center, Durham,
NC, USA
2 Angela & Sami Sharnoon Cardiothoracic Surgery Department, Wolfson Medical Center, Israel
3 Department of Cardiac Surgery, Assuta Hospital, Petah Tikva, Israel
E-mail: gad.cotter@duke.edu
Received 7 February 2006, accepted for publication 9 June 2006
Published 5 July 2006
Online at stacks.iop.org/PM/27/817
Abstract
Previously reported comparisons between cardiac output (CO) results in
patients with cardiac conditions measured by thoracic impedance cardiography
(TIC) versus thermodilution (TD) reveal upper and lower limits of agreement
with two standard deviations (2SD) of approximately ±2.2 l min−1, a 44%
disparity between the two technologies. We show here that if the electrodes
are placed on one wrist and on a contralateral ankle instead of on the chest, a
configuration designated as regional impedance cardiography (RIC), the 2SD
limit of agreement between RIC and TD is ±1.0 l min−1, approximately
20% disparity between the two methods. To compare the performances of
the TIC and RIC algorithms, the raw data of peripheral impedance changes
yielded by RIC in 43 cardiac patients were used here for software processing
and calculating the CO with the TIC algorithm. The 2SD between the TIC
and TD was ±1.7 l min−1, and after annexing the correcting factors of the
RIC formula to the TIC formula, the disparity between TIC and TD further
declined to ±1.25 l min−1. Conclusions: (1) in cardiac conditions, the RIC
technology is twice as accurate as TIC; (2) the advantage of RIC is the use
of peripheral rather than thoracic impedance signals, supported by correcting
factors.
Keywords: cardiac output measurements, thoracic bioimpedance, whole-body
bioimpedance, impedance cardiography
Introduction
Three basic technologies are currently in use for impedance cardiography (ICG): (1) the
thoracic ICG (TIC), where the electrodes are placed on the root of the neck and the lower
part of the chest, being the dominant method in the market (Patterson et al 1964, Kubicek
0967-3334/06/090817+11$30.00 © 2006 IOP Publishing Ltd Printed in the UK 817
818 G Cotter et al
et al 1966, 1974); (2) the whole-body ICG (ICGWB), where four pairs of electrodes are used,
one pair on each limb (Tischenko 1973, Koobi et al 1999); (3) the regional ICG (RIC), a
technology which is used by the NICaS (noninvasive cardiac system). In this technology,
which is the subject of this report, only two pairs of electrodes are used, performing best
when placed on one wrist and on the contralateral ankle (Cohen et al 1998, Cotter et al 2004,
Torre-Amione et al 2004).
Two comprehensive reviews of the literature on clinical experience in measuring the
cardiac output (CO) by TIC determined that in patients with cardiac conditions the TIC-CO
results are unreliable (Raaijmakers et al 1999, Handelsman 1991). According to Patterson
(1985) andWang et al (2001), a number of sources in the chest, such as the lungs, vena cava, and
systemic and pulmonary arterial vasculatures, generate systolic impedance reductions, while
the heart generates signals of increased impedance. In addition to thesemultifarious sources of
Z,4 variations in the electrical conductivities between the sources of impedance changes and
the TIC electrodes (Kim et al 1988, Kauppinen et al 1998), and between the various impedance
sources (Wtorek 2000) have been described. These model experimentations indicated that
the thoracic Z is not a reliable signal for calculation of the SV due to the multiple sources
of dZ/dt (Kim et al 1988, Wang and Patterson 1995, Kauppinen et al 1998, Wtorek 2000),
providing the explanations for the above-mentioned unsatisfactory clinical results obtained by
TIC (Raaijmakers et al 1999, Handelsman 1991).
In this report, an attempt is made to define the differences between the peripheral and
thoracic impedance signals, and based on this, to explain the differences in the performance
of RIC and TIC.
As we are capable of saving raw data from the wrist–ankle (peripheral) impedance
signals, we were able to use the peripheral impedance waveforms and base impedance values
to calculate stroke volumes, using various algorithms that have been associated with TIC
calculations. This enabled us to prove that (1) the performance of RIC is twice as accurate
as reported TIC results; (2) the reasons for this are as follows: (a) the impedance changes
which are yielded by the limb electrodes are more suitable than the impedance changes of
the thoracic electrodes for calculating the stroke volume and (b) the use of properly designed
coefficients improved the accuracy of the CO results by at least an additional 25%.
Methods
The data for this project were gathered from two patient series. In both, comparisons were made
between cardiac output results measured by the NICaS versus thermodilution. One series,
which was studied in hospital A, consisted of 30 patients who were studied immediately upon
arrival at the ICU following an open heart operation. In 11 (36%), despite the intravenous
administration of adrenalin, cardiac index (CI) was lower than 2.5 l min−1 m−2. The second
series included 13 cases of acute heart failure that were studied in hospital B. CI was lower
than 2.5 l min−1 m−2 in seven (54%), and in the combined group of 43 cases of the two
hospitals, it was lower than 2.5 l min−1 m−2 in 18 (43%).
The purpose of this study was to use peripheral impedance waveforms to calculate stroke
volume by means of four different ICG algorithms and to compare each of these SV values
with the thermodilution SV result.
Of the 55 and 31 studies conducted in hospitals A and B, respectively, raw data were
successfully retrieved from only the last 30 consecutive patients of hospital A and the last 13
4 In the ICGWB and RIC, where the impedance changes are depicted in the periphery, the impedance value is
automatically converted into the real parts (R0 and R) of the measured impedance signals (Lamberts et al 1984).

生体電気インピーダンス解析による総体水分量の概算1-3
Robert F Kusshner 医師および Dale A Schoeller 博士
概要
合計58 人の被験者で、生体電気インピーダンス法(BIA)によって測定した総体水分量
(TBW)を、重水素を使用した放射性同位元素希釈法と直接比較した。はじめに、性特異
的方程式および群の方程式を、(各10 人の)肥満男性と非肥満男性、および肥満女性と非
肥満女性の体水分量重回帰分析によって開発した。身長2/抵抗インピーダンスは、最も有意
な変数であり、重水の希釈率(D2O-TBW)を予測するために使用し、かつ体重も変数とし
て使用すると、相関係数R=0.99 および予想標準誤差 = 1.75L が与えられた。方程式によ
って、肥満および非肥満の被験者についても同様にD2O-TBW を予測した。次に、この方
程式を使用して6 人の男性と12 人の女性の混成群であらかじめ検査した。性特異的な方程
式によって、良好な相関係数(0.96 および0.93)、全誤差(2.34 および2.89L)、予測した
平均値と測定したD2O-TBW の間の相違は-1.4±2.05 および-0.48±2.83L と小さく、か
つ、生体電気インピーダンス法はD2O-TBW を正確に予測することができた。BIA によっ
て、体重、身長、および年齢よりも正確にD2O-TBW を予測できることが示唆された。我々
が開発した生体電気インピーダンス法による方程式の信頼性を検証するには、より大規模
な症例数が必要である。 Am J ClinNutr 1986;44:417-424

総体水分量の算出方法の科学的妥当性についての考察
1.総体水分量の正確な算出方法
ヒトの総体水分量の正確な算出方法はなく、比較的正確な算出方法であると考えられ
ている方法は、重水の希釈率から算出する方法であり、この方法は放射線同位元素を
使用するため、研究所レベルでしか使用されていない。そのため、身長、体重、年齢
より簡便に算出する方法などが採用されているが、あくまでも目安として臨床で使用
されているのが現状である。
2.本製品に使用されている総体水分量の算出方法
本製品の総体水分量の算出方法はR. F. Kushner, D. A. Schoeller らがThe American
Jurnal of Clinical Nutrition、Sep 1986, pp 417-424, に発表した生体の交流電流に対
する電気抵抗から算出するアルゴリズム:
総体水分量= 4.96+0.42(Ht2/R)+0.13(Wt)+0.33 (gendaer)* *男性:1、女性:0
である。症例数40 症例で、このアルゴリズムから算出される総体水分量と重水の希釈
率から算出される総体水分量の比較では、相関係数r=0.986、r2=0.97, SEE(Standard
Error of Estimate)=1.748%が得られ、非常に高い相関が示唆された。
3.その他の電気抵抗から算出するアルゴリズム
1990 年以降、電気抵抗から総体水分量を算出する方法と重水の希釈率から算出方法と
の差異について、数多くの発表がされておりその結果を表1に示す。
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