Validation of insorption by blood analysis with comparisons of systemic and portal venous disappearances of D₂O, Na²⁴, and K⁴²

¹ Sections of Physiology and of Biophysics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

The rates of disappearance D₂O, Na^22/24 and K⁴² from the arterial blood were determined in 17 dogs following rapid injection of the isotopes into the femoral and portal veins. Differences between systemic and portal venous injections were significant during the early phases of the disappearance of the isotopes (P < 0.05). Systemic insorption was simulated by continuous intravenous injection of D₂O, Na²², and K⁴² at known rates into the femoral vein. The appearance of the isotopes in the arterial blood was determined repeatedly during and after their injection. The rate of injection (simulated insorption) was calculated using the mean systemic arterial disappearance rate. The differences between the calculated and actual rates of injection were insignificant. When portal insorption was simulated by constant injection of the isotope into the portal vein, the calculated rate of injection was not significantly different from the actual rate if the mean portal arterial disappearance curve was used in the calculation. When the systemic arterial disappearance curve was utilized, the calculated rate of injection was slightly faster than the actual rate.