Hemodynamic Responses to Oscillatory Thigh Cuff Inflations

Background. In the clinical setting, individuals have varying tolerance to hypovolemia induced by blood loss. Experimental generation of 0.1 Hz oscillations (~10-s cycle) in arterial pressure and cerebral blood flow via oscillatory lower body negative pressure (OLBNP) increases tolerance to this simulated hemorrhage, and protects cerebral tissue oxygenation. However, use of OLBNP as a method of inducing hemodynamic oscillations in the clinical setting is limited as: 1) it is a large and cumbersome technique, and; 2) it induces central hypovolemia, which would only worsen the magnitude of hemorrhage. In this study we evaluated a more clinically applicable method of inducing 0.1 Hz oscillations in arterial pressure and cerebral blood flow, using intermittent inflation of bilateral thigh cuffs. We hypothesized that the amplitude of arterial pressure and cerebral blood flow oscillations at 0.1 Hz would increase in response to repeated thigh cuff inflations at 0.1 Hz when compared with a baseline control condition. Methods. Ten healthy human subjects were tested (6 male, 4 female; 26.8 ± 4.1 y). Middle cerebral artery velocity (MCAv) was measured via transcranial doppler ultrasound, arterial pressure was measured via finger photoplethysmography, and end tidal CO2 (etCO2) was measured via capnography. Following a 10-min baseline period, intermittent thigh cuff inflations at 0.1 Hz and 230 mmHg (5-s inflation, 5-s deflation) were performed for 10-min ("oscillations”). 0.1 Hz oscillatory amplitude of mean arterial pressure and mean MCAv were quantified using Fast Fourier transformation during the last 5-min of baseline and the oscillatory period, and compared via two-tailed paired t-tests. Results. The amplitude of 0.1 Hz oscillations increased during the oscillatory period vs. baseline for mean arterial pressure (baseline: 1.7 ± 1.0 mmHg2 vs. oscillations: 9.0 ± 6.2 mmHg2; P = 0.004) and mean MCAv (baseline: 1.1 ± 0.6 (cm/s)2 vs. oscillations: 3.4 ± 3.1 (cm/s)2; P = 0.04). Absolute mean arterial pressure was similar between baseline and the oscillatory period (baseline: 97.2 ± 8.1 mmHg vs. oscillations: 99.1 ± 15.0 mmHg; P = 0.54), but absolute mean MCAv was lower during the oscillatory period (baseline: 61.7 ± 14.6 cm/s vs. oscillations: 53.2 ± 13.1 cm/s; P = 0.02). This reduction in mean MCAv was most likely due to hypocapnia (indexed by etCO2) induced by pacing the breathing of all subjects at ≥10 breaths/min (baseline: 33.2 ± 4.8 mmHg vs. oscillations 27.2 ± 4.5 mmHg; P = 0.005). Conclusions. Intermittent thigh cuff inflations at 0.1 Hz induced 0.1 Hz oscillations in both arterial pressure and cerebral blood flow when compared to baseline. These findings indicate that intermittent thigh cuff inflations could be developed as a method to induce pulsatile perfusion as a potential new therapy for individuals experiencing major blood loss.