Inspiratory resistance maintains arterial pressure during central hypovolemia: Implications for treatment of patients with severe hemorrhage

OBJECTIVE: To test the hypothesis that an impedance threshold device would increase systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure and delay the onset of symptoms and cardiovascular collapse associated with severe central hypovolemia. DESIGN: Prospective, randomized, blinded trial design. SETTING: Human physiology laboratory. PATIENTS: Nine healthy nonsmoking normotensive subjects (five males, four females). INTERVENTIONS: Central hypovolemia and impending cardiovascular collapse were induced in human volunteers by applying progressive lower body negative pressure (under two experimental conditions: a) while breathing with an impedance threshold device set to open at -7 cm H2O pressure (active impedance threshold device); and b) breathing through a sham impedance threshold device (control). MEASUREMENTS AND MAIN RESULTS: Systolic blood pressure (79 ± 5 mm Hg), diastolic blood pressure (57 ± 3 mm Hg), and mean arterial pressure (65 ± 4 mm Hg) were lower (p < .02) when subjects (n = 9) breathed through the sham impedance threshold device than when they breathed through the active impedance threshold device at the same time of cardiovascular collapse during sham breathing (102 ± 3, 77 ± 3, 87 ± 3 mm Hg, respectively). Elevated blood pressure was associated with 23% greater lower body negative pressure tolerance using an active impedance threshold device (1639 ± 220 mm Hg-min) compared with a sham impedance threshold device (1328 ± 144 mm Hg-min) (p = .02). CONCLUSIONS: Use of an impedance threshold device increased systemic blood pressure and delayed the onset of cardiovascular collapse during severe hypovolemic hypotension in spontaneously breathing human volunteers. This device may provide rapid noninvasive hemodynamic support in patients with hypovolemic hypotension once the blood loss has been controlled but before other definitive therapies are available.