Figure 4. Median (red) and individual (grey) wavelet power spectra of skin and muscle sympathetic neurograms before heating.

The strongest periodicity in skin sympathetic nerve activity (A) was at the respiratory frequency. A rhythm at the cardiac frequency was present, but was not prepossessing. The arrow points to the second harmonic of the respiratory frequency. The strongest periodicity in muscle sympathetic activity (B) was at the cardiac frequency. These median data also show oscillations at the respiratory frequency and ∼0.1 Hz.