Sietsema, Kathy E; David Geffen School of Medicine at UCLA, Torrance, California.
Rossiter, Harry B.

Seminars in Respiratory & Critical Care Medicine. 44(5):661-680, 2023 Oct.

Aerobic, or endurance, exercise is an energy requiring process supported
primarily by energy from oxidative adenosine triphosphate synthesis. The
consumption of oxygen and production of carbon dioxide in muscle cells are
dynamically linked to oxygen uptake (VO2) and carbon dioxide output (VCO2)
at the lung by integrated functions of cardiovascular, pulmonary,
hematologic, and neurohumoral systems. Maximum oxygen uptake (VO2max) is
the standard expression of aerobic capacity and a predictor of outcomes in
diverse populations. While commonly limited in young fit individuals by
the capacity to deliver oxygen to exercising muscle, (VO2max) may become
limited by impairment within any of the multiple systems supporting
cellular or atmospheric gas exchange. In the range of available power
outputs, endurance exercise can be partitioned into different intensity
domains representing distinct metabolic profiles and tolerances for
sustained activity. Estimates of both VO2max and the lactate threshold,
which marks the upper limit of moderate-intensity exercise, can be
determined from measures of gas exchange from respired breath during
whole-body exercise. Cardiopulmonary exercise testing (CPET) includes
measurement of VO2 and VCO2 along with heart rate and other variables
reflecting cardiac and pulmonary responses to exercise. Clinical CPET is
conducted for persons with known medical conditions to quantify
impairment, contribute to prognostic assessments, and help discriminate
among proximal causes of symptoms or limitations for an individual. CPET
is also conducted in persons without known disease as part of the
diagnostic evaluation of unexplained symptoms. Although CPET quantifies a
limited sample of the complex functions and interactions underlying
exercise performance, both its specific and global findings are uniquely
valuable. Some specific findings can aid in individualized diagnosis and
treatment decisions. At the same time, CPET provides a holistic summary of
an individual’s exercise function, including effects not only of the
primary diagnosis, but also of secondary and coexisting conditions.