SKIN SYMPATHETIC-NERVE ACTIVITY END-EFFECTOR FUNCTION DURING SLEEP INHUMANS

Multi-unit sympathetic skin nerve activity (SSA) in the peroneal nerve was recorded together with electrical skin resistance, skin blood flo w and (in some subjects) finger blood pressure during sleep in 22 slee p-deprived healthy subjects. The average strength of sympathetic activ ity in different sleep stages was measured during 5-min periods as the area-under-curve of the integrated neurogram. Stage 2 sleep was reach ed by 15 subjects, stages 3-4 by nine and rapid eye movement (REM) sle ep by six subjects. Non-REM sleep was always associated with an increa sed skin resistance, which was larger in glabrous than in hairy skin ( 293 +/- 48 vs. 175 +/- 14% of awake control level, n = 10, P < 0.05). Skin blood flow also increased during sleep, with a mean maximal incre ase of 397 +/- 179% of the awake control level (n = 11, P < 0.05). In spite of these changes of effector function no significant difference in mean SSA was found between the awake control period and periods of non-REM sleep, but during REM sleep SSA increased with 34% (P < 0.05) compared with the immediately preceding stage 2 period. In stage 2 sle ep, K-complexes were associated with bursts of SSA followed by transie nt changes of skin resistance, blood flow and arterial blood pressure. When both skin resistance and blood flow were recorded within the inn ervation area of the impaled fascicle, single bursts or short periods of increased SSA could be succeeded by increased skin blood flow witho ut concomitant skin resistance change. This indicates the existence of specific sympathetic vasodilator fibres in the skin. Therefore the un changed strength of multiunit SSA during non-REM sleep in the face of increases of skin resistance and blood flow may be a consequence of an increased sympathetic vasodilator nerve activity combined with decrea ses of vasoconstrictor and sudomotor traffic.