Figure 2. Effects of isocapnic hypoxia on muscle sympathetic nerve activity.

Representative trace for one subject during the post-experimental trial. Traces represent 30 s of data obtained from baseline, hypoxic exposure, and normoxic recovery. Although respiratory (tidal volume, V_T), cardiovascular (mean arterial pressure, MAP), and oxyhaemoglobin saturation (S_aO2) values all returned to baseline values during recovery, muscle sympathetic nerve activity remained elevated. The persistent sympathoexcitation was observed in all subjects for all trials. Note that the partial pressure of carbon dioxide (P_CO2) was maintained at baseline levels throughout experimentation.