運動耐容能評価の新指標としてΔVO2/work load測定の臨床的意義

The clinical significance ofΔVO2/work load as a new parameter of exercise tolerance

　心疾患患者の心機能面からの重症度評価，薬物治療および外科手術前後の治療効果の判定，さらにリハビリテーション効果やトレーニング効果の判定等，運動負荷試験による心機能評価は多方面に利用されている。このような中で，運動耐容能をできるだけ客観的かつ安全に評価できる指標が求められ，最大酸素摂取量（以下maxV_O2^1,2））や嫌気性代謝閾値（以下AT^1〜6））が広く用いられているがいくつかの問題点も指摘されている。

　今回我々は，運動耐容能評価の新指標の一つとして酸素摂取量であるV_O2の負荷量に対する増加率（以下ΔV_O2／work load　と記す）に着目し，心疾患におけるΔV_O2／work loadの特徴と臨床的意義について検討した。

Progressive bicycle exercise test was performed in 27 patients with chronic heart disease, and ΔV_O2/ work load (ml/min/watt) was measured in order to evaluate exercise tolerance. ΔV_O2/work load was calculated by the following two formulas, and each ΔV_O2/work load was expressed as ΔV_O2 (max) and V_O2 ( 5 min) as shown under.

ΔV_O2(max)=V_O2 (max)-V_O2 (rest)/work load at max.stage

ΔV_O2(5 min)=V_O2 (max)-V_O2 (rest)/work load at 5 min

Simultaneously cardiac output (CO) was measured by Fick's principle and ACO/work load (ml/min/ watt) was calculated.

V_O2 (max) correlated with V_O2 (max) in 27 cardiac patients (r= 0.69, p<0.01). Respiratory compensatory threshold (RCT) was shown in eighteen patients, and in thisroup ΔV_O2 (max) and AV_O2( 5 min) correlated with V_O2 (max) respectively (r= 0.80, p<0.01 ; r= 0. 68, p <0. 02).

ΔV_O2( 5 min) decreased progressively as New York Heart Association functional classification advanced (Class I , 12. 1.± 1. 5 m//min/watt ; Class II , 11. 8 ± 1. 6 ; Class 711, 9. 5 1. 7 ; p<0. 05 between each group other than Class I and ClassII ). ΔV_O2 ( 5 min) cor-related with ΔCO/work load (r= 0. 70, p 0. 01).

Thus V_O2/work load is one of the important para-meters in order to evaluate exercise tolerance in patients with chronic heart disease.