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ASSOCIATION OF ARTERIAL PRESSURE OSCILLATIONS WITH MUSCLE SYMPATHETIC NERVE ACTIVITY (MSNA) DURING CENTRAL HYPOVOLEMIA

We have previously demonstrated (Crit Care Med 36:1892, 2008) that spectral power at the high frequency of the R‐R interval (RRIHF) is inversely correlated with MSNA during progressive hypovolemia induced by lower body negative pressure (LBNP). We tested the hypothesis that oscillations in arterial pressure would also be associated with MSNA during LBNP. Subjects (11 M/5 F; n=16) were instrumented to record ECG, beat‐by‐beat arterial pressure (Finometer) and MSNA (peroneal nerve) during a progressive LBNP protocol taken to the point of tolerance (i.e., presyncope), followed by recovery. Systolic blood pressure (SBP) and R‐R interval oscillations were assessed in the frequency domain with Fourier transform. Application of LBNP caused reductions in R‐R interval and SBP, and progressive increases in MSNA. SBP oscillations increased during LBNP, as indicated by increases in both high frequency (SBPHF; 0.15‐0.4 Hz) and low frequency (SBPLF; 0.04‐0.15) domains, but only at the highest LBNP levels. While RRIHF was strongly and inversely correlated with MSNA (R2 = 0.97), SBPHF and SBPLF were not as highly correlated with MSNA (SBPHF R2 = 0.56, SBPHF R2 = 0.50). These results demonstrate that increases in arterial pressure oscillations during LBNP are not solely attributable to sympathetic activation.