CHAPTER 20 • EXERCISE TESTING 119exercise, the PR segment slopes downward and short-
ens in duration at which point the PQ junction
becomes the point of reference for the ST segment.
•J point:The point that distinguishes the QRS com-
plex from the ST segment; the point at which the ST
segment depression is measured.
- ST segment:ST segment level is measured relative to
the PQ junction. If the baseline is depressed, the devi-
ation from that level to the level during exercise or
recovery is measured. The ST segment is measured at
60 or 80 ms after the J point. [At ventricular rates
145 bpm (beats per minute), it is measured at 60 ms
after the J point (ACC/AHA Guidelines for Exercise
Testing, 1997; American Heart Association Scientific
Statement, 2001)].
- VO2max:The greatest amount of oxygen a person can
use while performing dynamic exercise involving a
large part of their muscle mass. This is a function of a
person’s functional aerobic capacity and defines the
limits of the cardiopulmonary system. It is defined by
the Fick Equation which incorporates both heart rate
(HR) and stroke volume (SV):
VO2 max=(HRmax) ×(SVmax) ×(CaO2 max – CvO2 max)VO2max=Max Cardiac Output ×Max Arteriovenous
O 2 diff.•VO2 maxthen is defined by a central component (car-
diac output), which describes the capacity of the heart
to function as a pump, and by peripheral factors (arte-
riovenous-oxygen difference), which describes the
capacity of the lungs to oxygenate the blood delivered
to it and the capacity of the working muscles to
extract this oxygenated blood (Myers, 2001). Many
factors affect each of these variables (Mellion, 1996):
a. HR is affected most importantly by age (220 −age
±12 beats gives a good estimate of maximum HR
or HRmax). HR is also affected by activity type,
body position, fitness, presence of heart disease,
medications, blood volume, and environment
(Hammond and Froelicher, 1985).
b. SV is affected by factors such as genetics, condi-
tioning (heart size), and cardiac disease. In normal
subjects, an increase in both end-diastolic and end-
systolic volume occurs in response to moving from
an upright, at rest position to a moderate level of
exercise. End-systolic volume decreases progres-
sively as exercise intensifies, in order to maintain
SV. At peak exercise, end-diastolic volume may
even decline.
c. Arterial oxygen content is related to the partial
pressure of arterial oxygen, which is determined in
the lung by alveolar ventilation and pulmonary dif-
fusion capacity and in the blood by hemoglobin
content. In the absence of pulmonary disease, arte-
rial oxygen content, and saturation generally
remain similar to resting values throughout exer-
cise, even at high levels (Myers, 2001).
d.Venous oxygen content is determined by the
amount of blood flow directed to the muscle and by
capillary density. Muscle blood flow increases with
exercise not only because of increased cardiac
output, but also by the preferential redistribution of
the cardiac output (>85% of total CO) to the exer-
cising muscle. A decrease in local and systemic
vascular resistance also facilitates greater skeletal
muscle flow. Finally, there is an increase in the
overall number of capillaries with training (Myers,
2001).- Metabolic equivalents (METs):A convenient meas-
ure for expressing oxygen uptake. One MET is a unit
of sitting, resting oxygen requirements (3.5 mL O 2 / kg
body weight/min).
a. 1 MET = Basal O 2 requirements (e.g., sitting)
b.5 METs = Energy cost for activities of daily living
(ADLs), poor prognosis for anginal patients, con-
sider catheterization
c. 10 METs = Same prognosis with medical treat-
ment versus coronary artery bypass grafting
(CABG)
d. 13 METs = Excellent prognosis regardless of other
exercise responses
e. 18 METs = Elite athletes - Myocardial oxygen consumption: The “double
product,” an indirect measurement of myocardial
oxygen consumption, measures the product of maxi-
mum or peak HR and systolic blood pressure. Angina
normally occurs at the same double product rather
than the same external workload. A normal value is
considered greater than 25,000.
PERFORMING THE EXERCISE
STRESS TESTINDICATIONS- The three major cardiopulmonary reasons for EST
relate to diagnosis, prognosis, and therapeutic pre-
scription (ACC/AHA Guidelines for Exercise Testing,
1997; White and Evans, 2001).
CLASSI- Conditions for which there is general consensus that
EST is justified
a. To assist in the diagnosis of coronary artery dis-
ease(CAD) in those adult patients with an inter-
mediate (20–80%) pretest probability of disease