The relationship of resting ventilation to mouth occlusion pressure. An index of resting respiratory function

In order to examine the relationship of mouth occlusion pressure (MOP), an index of central inspiratory neuromuscular drive, to age and sex and to resting ventilation (VE), measurements were made in the seated posture in 84 healthy, normal subjects (38 men, 46 women; ages 18-72 years, mean +/- SD = 39.8 +/- 14.5 years) and in 79 patients with either airways obstruction (n = 63) or restrictive lung disease (n = 16). In the normal subjects, there was no significant relationship between age or sex and MOP (expressed as P0.1), which is the mouth pressure developed against a complete occlusion at 0.1 s after the beginning of inspiration, and dP/dtmax, the maximal rate of rise of this pressure; mean +/- SD for P0.1 = 0.75 +/- 0.32 cmH2O, and dP/dtmax = 19.41 +/- 10.10 cmH2O/s. Similarly, there was no significant relationship between age or sex and VE/P0.1 or VE/dP/dtmax. In 99 percent of normal subjects (83 of 84), VE/P0.1 was greater than 8.0 L/min/cmH2O, whereas in only 1 of the 79 patients was the value greater than 7.9 L/min/cmH2O. While the mean values of P0.1 and dP/dtmax were significantly different between normal subjects and patients, there was considerable overlap, whereas the ratio VE/P0.1 or VE/dP/dtmax provided excellent differentiation between normal subjects and patients with lung disease. This index, which is easily measured and requires minimal patient cooperation, provides valuable information in the clinical assessment of ventilatory drive and lung mechanics.