We propose a simple moving-average (MA) model that uses the low-frequency (LF) component of the peroneal muscle sympathetic nerve spike rate (LF(spike rate)) and the high-frequency (HF) component of respiration (HF(Resp)) to describe the LF neurovascular fluctuations and the HF mechanical oscillations in systolic blood pressure (SBP), respectively. This method was validated by data from eight healthy subjects (23-47 yr old, 6 male, 2 female) during a graded tilt (15 degrees increments every 5 min to a 60 degrees angle). The LF component of SBP (LF(SBP)) had a strong baroreflex-mediated feedback correlation with LF(spike rate) (r = -0.69 +/- 0.05) and also a strong feedforward relation to LF(spike rate) [r = 0.58 +/- 0.03 with LF(SBP) delay (tau) = 5.625 +/- 0.15 s]. The HF components of spike rate (HF(spike rate)) and SBP (HF(SBP)) were not significantly correlated. Conversely, HF(Resp) and HF(SBP) were highly correlated (r = -0.79 +/- 0.04), whereas LF(Resp) and LF(SBP) were significantly less correlated (r = 0.45 +/- 0.08). The mean correlation coefficients between the measured and model-predicted LF(SBP) (r = 0.74 +/- 0.03) in the supine position did not change significantly during tilt. The mean correlation between the measured and model-predicted HF(SBP) was 0.89 +/- 0.02 in the supine position. R(2) values for the regression analysis of the model-predicted and measured LF and HF powers indicate that 78 and 91% of the variability in power can be explained by the linear relation of LF(spike rate) to LF(SBP) and HF(Resp) to HF(SBP). We report a simple two-component model using neural sympathetic and mechanical respiratory inputs that can explain the majority of blood pressure fluctuation at rest and during orthostatic stress in healthy subjects.