Impedance cardiogramにおける肺循環関与部分の究明

Effect of hemodynamic changes in pulmonary circulation on the impedance cardiogram

　Impedance cardiographyは，循環系の無侵襲的計測法として注目されてきた。心拍出量の測定のみならず，各種心疾患での波形解析による診断^15,18,21）や，心機能の予備力判定に応用されつつある^14）。しかるにその個々の波形の成因については，未だ充分解明されていない。

　従来は，研究の主眼が左心機能に向けられてきたが，impedance cardiogramには左心系だけでなく，右心系の変化も含まれていると考えられる^12）。著者はimpedance cardiogramの中，肺循環動態が関与する部分を明らかにする為に，左房内にバルーンを挿入し，左房負荷に伴う肺うっ血がΔZの拡張期波に影響を及ぼすことをすでに証明した^6）。

An artificial transthoracic bypass between the left ventricle and the auricle was made on 11 mongrel dogs. A regurgitation of blood from the ventricle to the auricle was measured with an electro-flow meter placed in the bypass circuit. Pulmonary artery pressure was measured with an electro-manometer through a Swan-Ganz flow-directing-catheter. By opening or closing the bypass a hemodynamic condition similar to the one in mitral insufficiency was instantly produced or reversed to normal.

As the hemodynamic load on the pulmonary circulation increased, the ΔZ was of the impe-dance cardiogram changed from a high peak to a bimodal curve or to a plateau. These features became more prominent when hypoxia was in-duced along with an opening of the bypass. The changes in the ΔZ wave were mainly attribut-able to a rise in its diastolic phase. The ratios of the height of the diastolic ΔZ wave over the height of the systolic ΔZ correlated well with the changes in pulmonary artery pressure. Under moderate hypoxia, 7 dogs with normal heart and pulmonary artery pressure, did not manifest any changes in their impedance cardiogram.