Effects of sodium bicarbonate administration on the exercise tolerance of normal subjects breathing through dead space

Study objective: The purpose of this stud,. was to determine whether the ad ministration of sodium bicarbonate to normal individuals would increase the ir PaCO2 and thereby decrease the ventilatory requirements at a given workl oad. Design: In this double-blind crossover study, sis normal men ingested eithe r 3 mEq/kg NaHCO3 or I mEq/kg NaCl once a day for 5 days, in addition to 40 mg of furosemide and 40 mEq KCl. After each 5-day treatment, the subjects underwent a symptom-limited maximal bicycle ergometer exercise test while b reathing through external dead space (with a volume of approximately 50% of their FEV1), a second exercise test without any external dead space, and a n assessment of their respiratory response to hypercapnia. Results: The administration of the NaHCO3 resulted in a significant increas e in the arterial HCO3- from 20.8 to 24.0 mEq/L and a significant increase in the PaCO2 from 31.7 to 36.9 mm Ng at rest that persisted during exercise , During exercise periods with the added dead space, die Borg scores were s ignificantly lower at each workload after the subjects received bicarbonate , but the maximal exercise level did not increase, The mean (+/- SE) slope of the mouth occlusion pressure response to hypercapnia was significantly l ower after the administration of NaHCO3 than after NaCl, respectively: 0.73 +/- 0.41 vs 1.27 +/- 0.97 cm H2O/mm Hg. Conclusion: From this study we conclude that the administration of NnHCO(3) results in a significant increase in the PaCO2, decreases the ventilation and the Borg score at equivalent workloads, and decreases the hypercapnic r esponse in normal individuals.