Reini SA, Fothergill DM, Gasier HG, Horn WG. Propranolol's potential to increase survival time in a disabled submarine. Aviat Space Environ Med 2012; 83:131–5. Background: While awaiting rescue from a disabled submarine, survivors will likely endure an atmosphere of rising CO₂ that will result in CO₂ toxicity once the available emergency CO₂ scrubbing materials are exhausted. Propranolol is a β-blocker that may increase survival time by reducing metabolic CO₂ production (<inline-graphic xlink:href="131inf1.gif"/>co₂). The purpose of this study was to determine if propranolol reduces resting <inline-graphic xlink:href="131inf1.gif"/>co₂ in healthy men. Methods: Eight healthy men completed a counterbalanced, randomized, placebo-controlled, double-blinded crossover study in which each subject received propranolol (40 mg twice daily) or placebo (lactose pill twice daily) over 72 h. The alternate condition was separated by a minimum 96-h washout period. Resting <inline-graphic xlink:href="131inf1.gif"/>co₂, oxygen consumption (<inline-graphic xlink:href="131inf1.gif"/>o₂), ventilation (<inline-graphic xlink:href="131inf1.gif"/>_E), respiration rate (RR), respiratory exchange ratio (RER), mean arterial pressure (MAP), heart rate (HR), and cardiac output (<inline-graphic xlink:href="131inf2.gif"/>) were measured each morning and afternoon. Results: When compared to placebo, propranolol significantly reduced <inline-graphic xlink:href="131inf1.gif"/>co₂ (−6.5%), MAP (−3.6%), HR (−10.4%), and <inline-graphic xlink:href="131inf2.gif"/> (−8.2%); however, there were no significant differences in <inline-graphic xlink:href="131inf2.gif"/>o_2, RR, <inline-graphic xlink:href="131inf1.gif"/>_E, or RER. Discussion: These results show that 40 mg of propranolol taken twice daily reduces resting <inline-graphic xlink:href="131inf1.gif"/>co₂ in healthy men and suggests that this treatment strategy may increase survival time in a disabled submarine scenario.