Fig. 4. Rostral respiratory and autoresuscitative circuits receive ascending excitatory drive from the SOSs.
Triple perfused in situ preparation with independent perfusion of carotid bodies, brainstem (+spinal levels C1 to T3), and thoracic spinal cord (T4 to T13) compartments. (A) Challenge of thoracic compartment alone with hypoxic-hypercapnic perfusate (40-torr PO2, /60-torr PCO2) causes increase in phrenic and g-SNA. (B) Selective cooling (5° to 10°C) of the thoracic segment perfusate (blue) abolishes stimulatory effect of hypoxia/hypercapnia on g-SNA and phrenic activity. (C to F) Quantified data. (G) In three of six preparations, the hypoxic/hypercapnic challenges caused gasps. Amplitude and/or area under the curve indicates activity level. **P < 0.01.