We investigated the effect changes in end-expiratory lung volume (EEV(L)) had on the response to progressive hypercapnia (CO2-response curve) in eight open-chest, anesthetized dogs, in order to clarify the role that vagal lung mechanoreceptors have in altered respiratory drive during permissive hypercapnia. The dogs were ventilated using a positive-pressure ventilator driven by phrenic neural activity. Systemic arterial CO2 tension (Pa(CO2)) was elevated by increasing the fraction of CO2 delivered to the ventilator. EFV(L) was altered from approximated functional residual capacity ('FRC') to 1.5 and 0.5 'FRC' by changing positive end-expiratory pressure. Although the tidal volume (V(T))-Pa(CO2) and inspiratory time (T(I))- Pa(CO2) relationships were not affected, decreasing EEV(L) from 1.5 'FRC' to 'FRC' and then to 0.5 'FRC' caused a significant (p < 0.01) upward shift in the CO2-response curves for minute ventilation (V̇(I)) and frequency (f), and a significant (p < 0.01) downward shift in the CO2-response curve for expiratory time (TE). We conclude that these shifts were explained by a decrease in the inhibitory activity of slowly adapting pulmonary stretch receptors (PSRs) as EEVL was lowered. In addition, increases in EEVL from 0.5 'FRC' to 1.5 'FRC' caused a significant (p < 0.05) increase in the apneic threshold, which we attribute to an inhibitory effect on central drive caused by increased PSR activity.
|Original language||English (US)|
|Number of pages||7|
|Journal||American Journal of Respiratory and Critical Care Medicine|
|State||Published - 1998|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine