Summary
Reasons why venous tracer infusion with arterial sampling [(v-a) mode] has advantages
compared to arterial infusion and venous sampling [(a-v) mode] for studies of blood
lactate kinetics are presented. Arterial tracer infusion can result in biased tracer
input due to streaming and unequal blood flow distribution. The procedure is impractical
for human studies. Venous sampling from the jugular, or any other peripheral or great
vein, provides a sample which may, or may not represent mixed venous systemic blood,
which exists only in the pulmonary artery. Venous sampling will not represent cardiac
lactate metabolism because the coronary arteries drain into the coronary sinus. Venous
sampling, as well as pulmonary artery sampling, will also ignore lactate metabolism
in the lungs which drain into the left atrium from bronchial and pulmonary circulations.
Turnover rates calculated from either venous or arterial specific activities underestimate
true tissue turnover. Correction for either measurement depends on good estimates
of blood flows to lactate exchanging and non-exchanging tissue. Equilibration between
lactate and pyruvate pools does not invalidate the use of tracers to measure lactate
turnover. The (v-a) mode with venous infusion and arterial sampling has advantages
for lactate tracer studies.
Key words
Lactate - Tracers - Kinetics - Glucose
