The Wagner-Nelson Method Can Generate an Accurate Gastric Emptying Flow Curve from 13CO2 Data Obtained by a 13C-Labeled Substrate Breath Test

Background: In pharmacokinetics, the Wagner-Nelson (W-N) method can accurately estimate the rate of drug absorption from its urinary elimination rate. A stable isotope (¹³C) breath test attempts to estimate the rate of absorption of ¹³C, as an index of gastric emptying rate, from the rate of pulmonary elimination of ¹³CO₂. The time-gastric emptying curve determined by the breath test is quite different from that determined by scintigraphy or ultrasonography. In this report, we have shown that the W-N method can adjust the difference. Methods: The W-N equation to estimate gastric emptying from breath data is as follows: the fractional cumulative amount of gastric contents emptied by time t = A_breath(t)/A_breath(∞) + (1/0.65)·d[A_breath(t)/A_breath(∞)]/dt, where A_breath(t) = the cumulative recovery of ¹³CO₂ in breath by time t and A_breath(∞) = the ultimate cumulative ¹³CO₂ recovery. The emptying flow curve generated by ultrasonography was compared with that generated by the W-N method-adjusted breath test in 6 volunteers. Results: The emptying curves by the W-N method were almost identical to those by ultrasound. Conclusions: The W-N method can generate an accurate emptying flow curve from ¹³CO₂ data, and it can adjust the difference between ultrasonography and the breath test.