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Effects of Sodium Bicarbonate Administration on the Exercise Tolerance of Normal Subjects Breathing Through Dead Space*

Richard W. Light, MD, FCCP; Ming-Jen Peng, MD; David W. Stansbury; Catherine S. H. Sassoon, MD, FCCP; Judith A. Despars, RN and C. Kees Mahutte, MD, PhD, FCCP

* From the Department of Medicine of the Veterans Administration Medical Center, Long Beach Pulmonary Disease Service, Saint Thomas Hospital and Vanderbilt University, Nashville, TN.

Study objective: The purpose of this study was to determine whether the administration of sodium bicarbonate to normal individuals would increase their PaCO2 and thereby decrease the ventilatory requirements at a given workload.

Design: In this double-blind crossover study, six normal men ingested either 3 mEq/kg NaHCO3 or 1 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 breathing through external dead space (with a volume of approximately 50% of their FEV1), a second exercise test without any external dead space, and an assessment of their respiratory response to hypercapnia.

Results: The administration of the NaHCO3 resulted in a significant increase 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 Hg at rest that persisted during exercise. During exercise periods with the added dead space, the Borg scores were significantly lower at each workload after the subjects received bicarbonate, but the maximal exercise level did not increase. The mean (± SD) slope of the mouth occlusion pressure response to hypercapnia was significantly lower 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 NaHCO3 results in a significant increase in the PaCO2, decreases the ventilation and the Borg score at equivalent workloads, and decreases the hypercapnic response in normal individuals.

Abbreviations:CO2 = carbon dioxide; O2 = oxygen; P0.01 = mouth occlusion pressure at 0.1 s after onset of inspiratory effort; VCO2 = carbon dioxide output; VD/VT = physiological dead space ventilation; VE = minute ventilation; VE/ VCO2 = ventilatory equivalent for CO2; VE/ VO2 = ventilatory equivalent for O2; VO2 = oxygen consumption; VT = tidal volume

Key Words: dead space • exercise • metabolic alkalosis






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