Aim: The purpose of this study was to investigate the changes in blood
activity during rest, exercise and recovery, and to assess its influe
nce on left ventricular (LV) volume determination using the count-base
d method requiring blood sampling. Methods: Forty-four patients underw
ent rest-stress radionuclide ventriculography; Tc-99m-human serum albu
min was used in 13 patients (Group I), red blood cells was labeled usi
ng Tc-99m in 17 patients (Group II) in vivo, and in 14 patients (Group
Ill) by modified in vivo/in vitro method. LV volumes were determined
by a count-based method using corrected count rate in blood samples ob
tained during rest, peak exercise and after recovery. Results: In grou
p I at stress, the blood activity decreased by 12.6 +/- 5.4%, p < 0.05
, as compared to the rest level, and increased by 25.1 +/- 6.4%, p < 0
.001, and 12.8 +/- 4.5%, p < 0.05, above the resting level in group II
and III, respectively. This had profound effects on LV volume determi
nations if only one rest blood aliquot was used: during exercise, the
LV volumes significantly decreased by 22.1 +/- 9.6%, p < 0.05, in grou
p I, whereas in groups ii and ill it was significantly overestimated b
y 32.1 +/-: 10.3%, p < 0.001, and 10.7 +/- 6.4%, p < 0.05, respectivel
y. The changes in blood activity between stress and recovery were not
significantly different for any of the groups. Conclusion: The use of
only a single blood sample as volume aliquot at rest in rest-stress st
udies leads to erroneous estimation of cardiac volumes due to signific
ant changes in blood radioactivity during exercise and recovery.