Abstract 61: Inspiratory Resistance Maintains Arterial Pressure During Central Hypovolemia: Implications for Treatment of Patients with Severe Hemorrhage.
BACKGROUND: Hemorrhagic shock remains a leading cause of death worldwide. Using lower body negative pressure (LBNP) to induce central hypovolemia and cardiovascular collapse, we tested the hypothesis that an impedance threshold device (ITD) would increase blood pressure and delay the onset of symptoms associated with severe simulated blood loss.
METHODS: Human volunteers (n=9) completed a LBNP protocol with (active) and without (sham) an ITD set to open at −7 cm H2O pressure using a prospective randomized blinded trial design. Continuous non-invasive measures of systolic (SBP), diastolic (DBP), and mean (MAP) arterial blood pressure (BP) (in mmHg) were obtained during a 5 min baseline period followed by 5 min of chamber decompression at −15, −30, −45, and −60 mmHg and additional increments of −10 mmHg every 5 min until onset of cardiovascular collapse.
RESULTS: The average time to cardiovascular collapse was 2,156 ± 156 sec when subjects breathed through the active ITD vs the sham ITD (1,953 ± 106 sec) (P = 0.024). At the time of collapse in the sham group, SBP, DBP, and MAP were higher with the active ITD (102 ± 3, 77 ± 3, and 87 ± 3) vs the sham ITD (79 ± 5, 57 ± 3, and 65 ± 4), respectively (P < 0.02). Elevated BP was associated with 23% higher LBNP tolerance using an active ITD (1639 ± 220 mmHg-min) vs the sham ITD (1328 ± 144 mmHg-min) (P = 0.02). Symptoms, including lightheadedness, diaphoresis, and nausea observed at the time of collapse using the sham ITD were absent at the same time for any given subject with the active ITD.
CONCLUSIONS: Use of an ITD increased blood pressure and delayed the onset of cardiovascular collapse during severe hypovolemic hypotension in spontaneously breathing volunteers. This new device may provide rapid non-invasive hemodynamic support in patients with hypovolemic hypotension once the hemorrhage has been controlled but before other definitive therapies are available.