Systemic leakage of 15 micron radioactive microspheres over a period of 24 hours, in awake late-pregnant guinea pigs.

The present study was designed to determine the reliability of regional blood flow measurements with 15 microns radioactive microspheres, when 24 h have elapsed between reference sampling and sacrifice. The study was performed in 12 chronically-instrumented late-pregnant guinea pigs. The fraction of microspheres recovered from the lungs was consistently higher, by about 2% of the cardiac output after such a 24-h period, as compared to microsphere experiments performed immediately prior to sacrifice. This finding suggests dislodgement of radioactive particles from the systemic circulation between the time of completion of reference sampling and the subsequent 24 h. No correlation could be demonstrated between the change in lung fraction and the change in any organ fraction in particular. Therefore, it is highly unlikely that the microspheres accumulated in the lungs over this period originate from the placenta or any other specific organ. It is concluded that in the awake late-pregnant guinea pig, the 2% loss of microspheres from the systemic circulation during the 24 h following reference sampling, does not invalidate the cardiac output distribution derived.