Introduction 1 2 3 lactate base excess bicarbonate heart rate respiratory parameters 2 2 4 In this study we evaluated and compared three consecutive time periods in each of which a different parameter was used for monitoring the exercise intensity and adjusting the workload in order to obtain a submaximal exercise test. Initially HR monitoring was used; in the second period exercise intensity monitoring and adjustment were guided by monitoring of RQ. In the final period exercise intensity was monitored by serial rapid lactate measurements. Subjects and methods 3 1 3 2 Exercise was performed on an electromagnetically braked bicycle ergometer (Lode, Groningen, Netherlands). Monitoring exercise intensity and adjusting the workload W max 5 W max W max First period: HR-triggered tests maxpred maxpred maxpred 6 Second period: Respiratory gas exchange ratio (RQ)-triggered tests The workload adjustments were guided by measurement of the RQ, aiming for an RQ of 1.0 in the last 4–5 min of the exercise episode. This RQ was chosen as it indicates the anaerobic threshold Third period: Lactate-triggered tests t 1 Table 1 Algorithm for lactate-guided exercise intensity adjustments W max W max t t W max W max 2 In the third period (rapid serial lactate triggering) the test was performed at the gastroenterology function department; HR was monitored, but respiratory parameters were not monitored. Arterial blood samples for determination of base excess (BE), bicarbonate (blood gas analyzer; Radiometer ABL520, Copenhagen, Denmark), and lactate (enzymatic assay; Cobas Fara; Roche Diagnostics, Branchburg, NJ, USA) were drawn, in parallel with the 10-min tonometry interval, before and immediately at the end of the 10-min exercise episode. Rapid serial lactate measurements were performed using a small portable lactate analyzer (Accutrend; Roche Diagnostics, Almere, the Netherlands), specifically developed for use during exercise testing. Using this device, measurement results were available within 60 sec after blood sampling. 1 Fig. 1 Relationship between arterial lactate concentration after exercise and BE decrease at the end of the exercise period  max t>1 max maxpred maxpred t>80 Statistics P Results HR triggering maxpred maxpred 2 Table 2 Resulting exercise intensities for the three triggering regimes  Exercise level  (BE decrease, <3 mM) (BE decrease, 3–7 mM) (BE decrease, >7 mM) Triggering method Low Target High HR (39 tests) 3 (8%) 27 (69%) * RQ (84 tests) 8 (10%) 74 (88%) 2 (2%) Lactate (55 tests) ** * 3 (5%) Note * P ** P max t r r P 2 max Fig. 2 max max maxpred  RQ triggering In 84 tests RQ triggering was used. In 67 (80%) of these tests the target RQ of 1.0 was reached while the mean RQ in the last 4 min was 1.0 ± 5%. In 11 tests (13%) the target RQ was not reached and in 6 tests (7%) the mean RQ in the last 4 min exceeded the target RQ by more than 5%. Of the eight tests with a low exercise level, the target RQ was not reached in four. In both tests with a too high exercise intensity, the mean RQ in the last 4 min was >1.05. max t r r P max t P 3 max Lactate triggering t t Arterial lactate vs BE decrease and bicarbonate decrease r r P 1 Comparison accuracy of exercise tonometry at low, target, and high exercise levels 1 P Fig. 3 max  False-negative tonometry results were found in 10 of all 178 tests (6%). Low exercise levels did not result in an increase in false-negative tonometry tests: in only 2 of 10 (5%) false-negative tests was the exercise level too low; 1 test was RQ-triggered, the other lactate-triggered. P The sensitivity and specificity of tonometry exercise testing for gastrointestinal ischemia did not differ among the three groups (82% and 73%, respectively). Discussion For optimal diagnostic accuracy, the exercise level in gastric exercise tonometry can be monitored and adjusted by RQ measuring or, alternatively, by serial arterial lactate measurement. Although the latter resulted in more tests with lower than desired exercise levels, this had no influence on diagnostic accuracy. 3 7 8 9 10 1 11 12 Triggering on RQ measurements resulted in the highest proportion of tests within the target range but has disadvantages. It requires a pulmonary function laboratory with specific devices for measurement of exhaled carbon dioxide and inhaled oxygen, making the test expensive and more complicated. The advantage of RQ monitoring in minimizing the proportion of below-target exercise level did not result in a lower number of false-negative tests in this study. 13 In conclusion, by using RQ and serial lactate measurements, adequate exercise levels for gastric exercise tonometry can be achieved. Rapid lactate measurements and the presented algorithm for gastric exercise tonometry are feasible for daily clinical practice.