Study on mouth occlusion pressure in normal subjects and patients with obstructive or restrictive lung diseases

Mouth occlusion pressure (P 0.1 ) is the mouth pressure developed against a complete occlusion at 0.1 second after beginning of inspiration from FRC. Consciousness, autogenous reflexes and various lung mechanics do not affect it. We did this study in sequence of arterial blood gas examination, flow-volume curve, body plethysmography, diffusion capacity and measurement of P 0.1 . We divided the subjects into 4 groups such as normal control groups below 35 and above 50 years old, and the patient groups of obstructive and restrictive lung diseases. We measured P 0.1 during breathing of the ambient air and, again during 6% CO 2 -rebreathing with simultaneous measurement of ventilatory parameters such as MV (minute ventilatory volume)/P 0.1 , T i /T t (inspiratory time/total respiratory time), TV/T i , and P 0.1 /TV/T i . During breathing of the ambient air, P 0.1 , MV/P 0.1 and P 0.1 /TV/T i showed a significant difference between the control groups and patient groups, and between the patient groups of obstructive and restrictive diseases. During CO 2 -rebreathing, P 0.1 and P 0.1 /TV/T i showed a significant difference between the control groups and patient groups. P 0.1 and P 0.1 /TV/T i correlated significantly. We did not find any difference between the patients with normal PaO 2 and those with hypoxemia. However, during CO 2 -rebreathing, there was a characteristic change of P 0.1 in the hypercapnic patient group compared with the normocapnic patient group. As a result, P 0.1 and P 0.1 /V T /T i are the valid indices of central inspiratory neuromuscular drive and effectiveness of respiratory muscles contraction. They are useful in the diagnosis of advanced chronic lung diseases that accompany CO 2 retention.