Investigating the Use of Resistance Breathing for the Detection of Acute Hypovolemia
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Introduction: Standard vital signs (e.g., heart rate and blood pressure) lack sensitivity and specificity to detect blood volume status following hemorrhage. Inspiratory resistance breathing has therapeutic potential to increase blood pressure and cardiac output following blood loss. We investigated the potential utility of resistance breathing as a novel method to detect volume loss. We hypothesized that resistance breathing would elicit greater increases in absolute and breath-to-breath amplitude of stroke volume and arterial pressure under hypovolemic vs. normovolemic conditions. Methods: Data were retrospectively analyzed from 23 healthy human subjects aged 23-40 years. Subjects underwent lower body negative pressure (LBNP) protocols to simulate hemorrhage with and without resistance breathing (via an impedance threshold device, ITD). Continuous arterial pressure and stroke volume were measured via finger photoplethysmography. Comparisons of absolute and changes in the breath-to-breath amplitude of arterial pressure and stroke volume were made under 4 conditions: 1) normovolemia; 2) normovolemia + resistance breathing; 3) hypovolemia, and; 4) hypovolemia + resistance breathing. The sensitivity and specificity of breath-to-breath arterial pressure and stroke volume amplitude responses in distinguishing between normovolemia and hypovolemia were assessed via area under the curve (AUC) of receiver operating characteristic (ROC) curves. Results: With resistance breathing the amplitude of systolic arterial pressure (P=0.007), diastolic arterial pressure (P<0.001), and mean arterial pressure (P<0.001) increased during hypovolemia vs. normovolemia, and the amplitude of stroke volume decreased (P=0.002). In distinguishing between normovolemia and hypovolemia, the ROC AUC were >0.86 for breath-by-breath mean, maximum and minimum stroke volume responses, and 0.77 for the amplitude response. The ROC AUC for mean arterial pressure amplitude was 0.88, and 0.64, 0.54, and 0.72 for the mean, maximum and minimum responses. Conclusions: The dynamic responses of arterial pressure and stroke volume with resistance breathing during hypovolemia show promise as a diagnostic tool for detection of hypovolemia in humans.