Effects of end tidal pressure of carbon dioxide on central drive and respiratory response in patients with chronic obstructive pulmonary disease

Objective To evaluate the effects of end tidal pressure of carbon dioxide (PETCO2) at different levels on the central drive and respiratory response in patients with chronic obstructive pulmonary disease (COPD). Methods After the completion of a pulmonary function test, 13 moderate COPD patients in stable stage and 10 healthy volunteers were studied with a CO2 rebreathing method by improving PETCO2 from 45 mm Hg to 70 mm Hg. The parameters of the central drive and respiratory response were monitored continuously and calculated at different PETCO2 levels. Results The experiment duration was respectively (8.5±1.6) rain in the COPD group and (16.3±3.2) min in the normal group when PETCO2 reached 70 mm Hg. Both groups experienced a linear increase in respiratory rate(RR), and the RR of normal group was higher than that of the COPD group. When PETCO2 was increased from 45 mm Hg to 55 mm Hg, the COPD group resulted in a linear increase in the tidal volume (VT) and minute ventilation (VE); VT increased from (0.68±0.25) L to (1.04±0.44) L and VE increased from (10.59±3.36) L/min to (20.13±4.52) L/min. But when PETCO2 was 55-70 mm Hg, VT and VE appeared a plat in the COPD group, while VT and VE maintained a linear increase in the normal group and higher than those of the COPD group. The ratio ofinspiratory time to duration of one breath (Ti/Ttot) was higher in the normal group than in the COPD group (P<0.05), while the Borg scale scores were lower in the normal group than in the COPD group (P<0.05). Both groups showed a linear increase in mean inspiratory volume per second (VT/T1) and root mean square (RMS), but when PETCO2 was increased from 65 mm Hg to 70 mm Hg, VT/T1 in the COPD group, it was obviously lower than that in the normal group (P<0.05). While RMS in the COPD group was higher than that in the normal group on different PETCO2 levels (P<0.05). COPD group showed a parabolic change in VE/RMS, which was significantly lower than that in the normal group (P<0.001). Conclusion During the early stage of CO2 rebreathing, the respiratory response and central drive of COPD patients show a linear increase, but during late stage, the ventilation appears a plat and ventilation-central coupling is obviously abnormal. The normal group shows a linear increase in respiratory response and central drive, in which respiratory response is higher and central drive is lower than in COPD group. Key words: Chronic obstructive pulmonary disease;  End tidal pressure of carbon dioxide;  Central drive;  Respiratory response