The oxygen uptake efficiency slope and its value in the assessment of cardiorespiratory functional reserve.

Oxygen uptake efficiency slope is a new index of cardiorespiratory functional reserve derived from the logarithmic relation between oxygen uptake (VO(2)) and minute ventilation during incremental exercise. The oxygen uptake efficiency slope represents how effectively oxygen is extracted and taken into the body from the air, and then ventilated. The physiologic backgrounds of the index are based on: 1) the development of metabolic acidosis that is controlled by the distribution of blood to the skeletal muscles; 2) the physiologic dead space that is affected by the perfusion to the lungs; and 3) arterial carbon dioxide partial pressure. One of the greatest advantages of the oxygen uptake efficiency slope is that it can be calculated by exercise data of submaximal levels. Another advantage is that it is mathematically determined from a set of gas analysis data and, therefore, is completely an objective measurement. Moreover, the oxygen uptake efficiency slope is shown to be highly reproducible. Clinical applications of the oxygen uptake efficiency slope have been reported initially from a population of pediatric patients with heart disease, then from adult patients with chronic heart failure, and finally from elite endurance athletes. Further applications are expected with the use of this sophisticated index. (c)2000 by CHF, Inc.