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Respir Med. 2003 Apr;97(4):415-20.

A simple noninvasive pressure-time index at the mouth to measure respiratory load during acute exacerbation of COPD A comparison with normal volunteers.

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  • 1Servicio de Neumología, Hospital Clínico Universitario, Valencia, Spain.


We assessed the validity of the pressure-time index (PTI) measured at the mouth as a noninvasive and simplified alternative to conventional tension-time index for assessing respiratory load and inspiratory muscle force reserve. PTI was measured within 48 h of hospital admission and at 24 h before discharge in 37 consecutive patients with acute exacerbation of chronic obstructive pulmonary disease (COPD) using the equation PTI = (P(awo)/MIP)(T(I)/T(T)) 100, where P(awo) is the mean airway pressure measured at the mouth, MIP the maximal inspiratory pressure, and T(I)/T(T) the inspiratory time (T(I)) to total cycle length (T(T)) ratio. Controls were 30 normal volunteers with similar anthropometric features. Mean (+/- SD) PTI values were significantly higher in COPD patients (0.29 +/- 0.10) than in controls (0.11 +/- 0.04) (P < 0.001) primarily because MIP and T(I)/T(T) were significantly lower and P(awo) was higher in the COPD population than in controls. As a result of improvement of the respiratory condition, PTI values were significantly lower at discharge (0.20 +/- 0.10 vs. 0.29 +/- 0.10, P < 0.001) due to a drop in P(awo) and an increase in MIP. The accuracy of different PTI cutpoints was assessed by comparison of the receiver operating characteristics curves. Best cutpoint values for differentiating COPD patients on admission and at hospital discharge from controls were 0.13 (positive predictive value 76%) and 0.17 (positive predictive value 92%) respectively. Noninvasive PTI measured at the mouth provides a valid and easy method for assessing respiratory muscle load and reserve. Changes in PTI values reflect functional improvement following treatment of acute exacerbation of COPD.

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