more information on the 'best treatment' of surgical and trauma patients. Ultimately, it should be in everyone's interest to interpret the existing data on medical topics objectively and neutrally, without rushing to premature, far-reaching conclusions which could confuse physicians and even render future therapy with potentially life-saving drugs impossible.

End-expiratory air trapping due to obstructive airway disease can be estimated through the measurement of intrinsic positive end-expiratory pressure PEEPi. The influence of breathing-frequency and use of expiratory muscles on PEEPi were measured in 10 normal and 10 chronic bronchitic patients (COPD). Insignificant control values of PEEPi increased to measurable values at high breathing rate in normal subjects. Control values were higher in COPD patients and increased at fast breathing rate. When corrected for the use of expiratory muscles according to simultaneous gastric pressure drop, PEEPi decreased in COPD, but still increased at high rate. We conclude that modifying the respiratory rate can increase PEEPi values independently of the severity of airway obstruction and the use of expiratory muscles. Before estimating the pathological value of a PEEPi measurement or evaluating the effects of a treatment, we always need to know the simultaneous breathing frequency.

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Background: In clinical practice, patients have different inspiratory behaviors during noninvasive pressure support ventilation (PSV): some breathe quietly, others actively help PSV by an additional effort, and others even resist the inspiratory pressure of PSV. Objective: What is the influence of patient collaboration (inspiratory behavior) on the efficiency of PSV? Methods: We ventilated 10 normal subjects with nasal PSV (inspiratory/expiratory: 10/0 and 15/5 cm H₂O) and measured their flow and volume with a pneumotachograph and their esophageal and gastric pressures during three different respiratory voluntary behaviors: relaxed inspiration, active inspiratory work and resisted inspiration. Results: When compared with relaxed inspiration with 10/0 cm H₂O PSV: (1) an active inspiratory effort increased tidal volume (from 789 ± 356 to 1,046 ± 586 ml; p = 0.006), minute ventilation (from 10.40 ± 4.45 to 15.77 ± 7.69 liters/min; p < 0.001), transdiaphragmatic work per cycle (from 0.55 ± 0.33 to 1.72 ± 1.40 J/cycle; p = 0.002) and inspiratory work per cycle (from 0.14 ± 0.20 to 1.26 ± 1.01 J/cycle; p = 0.003); intrinsic positive end-expiratory pressure (PEEP_i) increased from 1.23 ± 1.02 to 3.17 ± 2.30 cm H₂O; p = 0.002); (2) a resisted inspiration decreased tidal volume (to 457 ± 230 ml; p = 0.007), minute ventilation (to 6.93 ± 3.04 liters/min; p = 0.028) along with a decrease in transdiaphragmatic work but no change in PEEP_i. Data obtained during a bilevel PSV of 15/5 cm H₂O were similar to those obtained with the 10/0 cm H₂O settings. Conclusions: Active inspiratory effort increases ventilation during PSV at the expense of an increased breathing work and PEEP_i. Resisted inspiration inversely decreases inspiratory work and ventilation with no air trapping. These differences between inspiratory behaviors could affect the expected beneficial effects of PSV in acutely ill patients.

Non-invasive ventilation (NIV) is more and more used. Some failures of the technique have been reported, and efforts are needed to understand them. Collaboration (inspiratory behaviour) of the patient during NIV could play a role in the success of this technique. We have studied the influence of this one on the efficiency of NIV. While ventilating 10 stable chronic obstructive pulmonary disease patients with a nasal pressure support ventilation (PSV), we measured their flow and volume with a pneumotachograph and oesophageal and gastric pressures during three different respiratory voluntary behaviours: relaxed inspiration, active inspiratory effort and resisted inspiration. We showed that when compared with the relaxed inspiration: (a) Active inspiratory effort increases slightly minute ventilation from 14.8 +/- 4.7 to 15.41 +/- 4.19 during PSV 10/0 without change of breathing frequency but with an important increase of inspiratory work (W(OB)) from 14.47 +/- 9.43 to 28.55 +/- 25.35 J/min (P=0.008). PEEPi increases with active behaviour during PSV but not during BiPAP. (b) A resisted inspiration decreases inspiratory work (to 7.53 +/- 8.6 J/min) at the price of a decrease of the minute ventilation to 11.47 +/- 4.20 l/min (P=0.06). Results of ventilation, PEEPi and work parameters were identical during the bilevel pressure support (15/5 cm H2O). The aims of NIV being to increase ventilation and unload the inspiratory muscles, our results suggest that during NIV, a relaxed spontaneous breathing is preferable. These differences between the inspiratory behaviours could affect the expected benefits of PSV in acutely ill patients.