breathlessness , disability , and exercise tolerance were assessed in 26 patients with severe chronic airflow limitation ( forced expiratory volume in one second ( fev1 ) less than or equal to 1 litre ) divided into two groups -- 15 patients who were normocapnic ( pressure of arterial carbon dioxide ( paco2 ) less than 5.5 kpa ( less than 41.4 mm hg ) ) , and 11 patients who were hypercapnic ( paco2 greater than 6 kpa ( greater than than 45.1 mm hg ) ) .
C0013404
breathlessness
C0007012
carbon dioxide