Negative pressure breathing increases cardiac output and nitrogen elimination in seated subjects

During denitrogenation for rescue, crew members of an internally pressurized disabled submarine (DISSUB) must sit upright, which may hamper venous return, cardiac outputand peripheral circulation. Since negative pressure breathing (NPB) might counteract this problem, denitrogenation was measured in sitting subjects performing NPB. Seven malesubjects completed 125-minute nitrogen (N₂) washouts breathing either 100% oxygen (O₂) or a normoxic gas (21% O₂ in argon) in control conditions and intermittent (I: inspirations only) or continuous (C) NPB at -10 or -15 cmH ₂O. N₂ elimination was measured using a closed rebreathing system. INPB (intermittent) (-15cmH₂O) and CNPB (continous breathing) (-10 and -15cmH₂O) increased cardiac output (CO) 9% during both O₂ and normoxic breathing. Systolic and diastolic blood pressures were unaffected by the CO increase, suggesting a peripheral vasodilatation and enhanced tissue perfusion leading to inreased N₂ elimination. With the CO boost, N₂ washout increased 6% breathing O₂ at -15 cmH₂O CNPB and INPB, while during normoxic breathing there were 6% and 12% increases due to CNBP, -10 and -15 respectively and 6% with -15cmH₂O INPB; breathing 100% O₂ yielding 5% to 15% less N₂ washout than normoxic breathing. Negative pressure breathing during denitrogenation may facilitate decompression in divers and in crew members being rescued from a DISSUB.