Premorbid ventilatory response to hypercapnia is not related to resting arterial carbon dioxide tension in hamsters with elastase-induced emphysema

Abstract

Marked variability in resting steady-state arterial PCO2 (PaCO2) values are observed among patients with chronic obstructive pulmonary disease (COPD), independent of severity of their obstructive airways defect. The reasons for the development of hypercapnia in some but not in the others remain unclear. One hypothesis states that the level of morbid resting PaCO2 may be related to the premorbid hypercapnic ventilatory response (HCVR); accordingly, subjects who were relatively insensitive to CO2 breathing (low responders) develop CO2 retention in the face of lung disease. The present study investigated this hypothesis in the hamster model of elastase-induced emphysema. After obtaining steady-state HCVR in 19 unanesthetized unrestrained hamsters, emphysema was induced by intratracheal instillation of pancreatic elastase. Forty-five days later, minute ventilation and PaCO2 measurements were done, and lung function tests were obtained. The slopes of HCVR and morbid PaCO2 values varied from -0.09 to 2.36 ml/min/mmHg inspired PCO2 and 48.7 to 63.1 mmHg, respectively. There were no significant correlations between morbid PaCO2 values and premorbid HCVR or lung function test abnormalities caused by emphysema. These animal model studies do not support the hypothesis that the level of PaCO2 in patients with COPD is related to their premorbid HCVR.