Fig. 6

Cardiac and intestinal sympathetic efferent activities shown after analog integration of sympathetic discharges during ventilation (4 min) with a 1.5–2 % carbon monoxide in air (primary tissue hypoxia), and b 8 % oxygen and 92 % nitrogen (arterial hypoxia) in anesthetized artificially ventilated rabbits under neuromuscular blockade (means ± standard errors, n = 8). In each condition, core (rectal, T _re ) temperature did not change; ear skin temperature (T _ear ) increased during both primary tissue and arterial hypoxia, due to suppression of cutaneous sympathetic activity, as confirmed by separate recordings in supplementary experiments (not shown). Changes relative to pre-stimulation activity levels are shown after analog integration of multi-fiber activities from splanchnic (N. splanchn.) and cardiac (cardiac sympath.) sympathetic nerve branches. Effects of primary tissue hypoxia differed from those of arterial hypoxia with respect to the cardiac sympathetic response: during primary tissue hypoxia its increase in activity accompanied that of splanchnic sympathetic activity without significant changes in arterial pressure (Pm _ar ) and heart rate (HF). During arterial hypoxia, cardiac sympathetic activity became reduced, as reflected also by reduction of heart rate, in contrast to the increase in splanchnic activity, and arterial pressure increased. Columns indicate changes in arterial (PaO ₂ ) and venous (PvO ₂ ) oxygen tension. From Iriki and Kozawa [26]