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Figure 2 Power spectral density during control tilt (A) and saline tilt (B). During the control tilt, upon assumption of the upright position, there was a significant increase in low frequency power (0.03 to 0.15 Hz) with a decrease in high frequency power (0.16 to 0.50 Hz). Despite continued upright positioning, there was a progressive decline in low frequency power. After the administration of normal saline, low frequency power progressively increased during the remainder of upright positioning.