Involvement of thoracic nerve afferents in the respiratory response to chest compression.

Chest compression elicits extravagal neural reflexes which can alter the respiratory pattern. Experiments were conducted to determine the source of the afferents responsible for the respiratory response to chest compression (CC). The effects of CC on VT, f, TI, TE, blood gases, end-tidal CO2, and blood pressure were studied in anesthetized, vagotomized dogs and cats. In dogs, thoracic wall afferents were eliminated by thoracic dorsal rhizotomies (TDR) and/or spinal blocks (SB). There were two different respiratory responses to CC. In one (I), Tt decreased and TE increased, resulting in a decreased f. The second (II) resulted in a decreased TI and TE. The I response was still present, but weaker, in animals after TDR (1--4), TDR (5--9), TDR (1--9, T5 or T10 SB and absent in those with T1SB. The II response was still present after TDR ()--4), TDR (5--9), TDR (1--9), or T10SB and absent after T5SB. The results indicate that: (1) afferents responsible for the I response to CC arise from the upper, middle and lower thoracic wall, (2) afferents responsible for the II response arise from the middle and lower thoracic wall, and (3) the responses are not due to changes in chemical drive, blood pressure or lung receptors.