The negative expiratory pressure (NEP) method was used to detect expiratory flow limitation at rest and at different exercise levels in 4 normal subjects and 14 patients with chronic obstructive pulmonary disease (COPD). This method does not require performance of forced expirations, nor does it require use of body plethysmography. It consists in applying negative pressure (-5 cmH2O) at the mouth during early expiration and comparing the flow-volume curve of the ensuing expiration with that of the preceding control breath. Subjects in whom application of NEP does not elicit an increase in flow during part or all of the tidal expiration are considered flow limited. The four normal subjects were not flow limited up to 90% of maximal exercise power output (Wmax). Five COPD patients were flow limited at rest, 9 were flow limited at one-third Wmax, and 12 were flow limited at two-thirds Wmax. Whereas in all patients who were flow limited at rest the maximal O2 uptake was below the normal limits, this was not the case in most of the other patients. In conclusion, NEP provides a rapid and reliable method to detect expiratory flow limitation at rest and during exercise.

Two new methods, application of negative pressure at the airway opening during expiration (NEP) and reduction of flow resistance by bypassing the expiratory line of the ventilator by exhaling into the atmosphere (ATM), were used to detect expiratory flow limitation in 12 semirecumbent (45 degree) mechanically ventilated patients, seven with chronic airway obstruction (CAO). An increase of expiratory flow with NEP or ATM, relative to the preceding control breath, was taken as indicating absence of expiratory flow limitation. By contrast, the portion of the tidal expiration over which there was no change in flow with NEP or ATM was considered as flow-limited. With NEP, nine patients exhibited flow limitation, six (all with CAO) were flow-limited over most of the tidal expiration (> 70% VT), and three at < 60% VT. Although the results with NEP and ATM were in general in good agreement, in the three non-flow-limited patients the ATM method gave erroneous results. Six patients were also studied supine, including two who were not flow-limited when semirecumbent: both became flow-limited when supine. We conclude that NEP provides a simple method to detect flow limitation in mechanically ventilated patients. The supine position enhances flow limitation.

We conclude that on ZEEP, tidal FL is common in ARDS patients and is associated with greater regional PEEPi inhomogeneity than in NFL patients. With PEEP of 10 cm H2O, flow limitation with concurrent cyclic dynamic airway compression and re-expansion and the risk of "low lung volume injury" were absent in all patients. In FL patients, PEEP induced a significant increase in PaO2, mainly because of the reduction of regional PEEPi inequality, whereas in the NFL group, arterial oxygenation was improved satisfactorily because of alveolar recruitment.

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We investigated the effect of mouthpiece design on maximum static expiratory (PEmax) and inspiratory (PImax) mouth pressures. We measured PEmax from total lung capacity (TLC) and PImax from residual volume (RV) in 21 healthy volunteers, and in 40 patients referred for respiratory muscle testing. We compared two different mouthpieces, a semi-rigid plastic flanged type fitting inside the lips, and a 4 cm diameter rubber tube held against the lips. The tube mouthpiece gave significantly higher values for PEmax (p less than 0.02) in all subjects. PImax was also significantly higher (p less than 0.005) with the tube mouthpiece in subjects who recorded normal pressures. We conclude that maximum pressures are obtained in all normal subjects with the rubber tube mouthpiece, and that differences in quoted normal ranges of maximum static respiratory pressures reflect in part the design of the mouthpiece and the way in which it was used.

Background-The measurement of effective alveolar carbon dioxide tension (PACo2eff) is still a matter of debate. It has, however, become common practice to use arterial instead ofalveolar CO2 tension for computing alveolar oxygen tension (PAo2) and physiological dead space, not only in normal subjects but also in patients. The purpose of this study was to estimate alveolar CO2 tension during spontaneous breathing with a new bedside technique which is simple and non-invasive, and to compare these values with arterial CO2 tension measured in normal subjects and patients with chronic airways obstruction. Methods -The subjects breathed quietly through the equipment assembly (mouthpiece, monitoring ring, Fleisch transducer head) connected to a pneumotachograph and a fast response infrared CO2 analyser. The method is a computerised calculation of the volume weighted effective alveolar CO2 tension obtained from the simultaneously recorded expiratory flow and CO2 concentration versus time curves. An arterial blood sample was taken to measure PaCo2 for comparison during the study. Results -The results showed a mean difference (PAco2eff-Paco2) of -0 205 kPa in 20 normal subjects and -0'460 kPa in 46 patients. The 95% confidence interval of the bias was -0-029 to -0*379kPa in normal subjects and -0*213 to -0 707 kPa in patients. The limits of agreement between PAco2eff and PaCo2 were 0*526 to -0 935 in normal subjects and 1170 to -2-088 in patients. Conclusions -The volume weighted effective alveolar Pco2 in normal subjects and patients with chronic airways obstruction is lower than the arterial Pco2 and is recommended as a better estimate in the classical equations for estimating dead space and intrapulmonary shunt. (Thorax 1995;50:240-244) Keywords: alveolar CO2 tension, alveolar-arterial Pco2 difference, chronic airways obstruction, spontaneous breathing.The estimation of effective alveolar carbon dioxide tension is still a matter of debate because the available methodology is not widely accepted. In most classical calculations alveolar carbon dioxide tension (PACo2) has been assumed to be equivalent to arterial blood CO2 tension (Paco2) in normal subjects.' '°It has also become common in clinical practice and in research work to use arterial CO2 tension as a substitute for alveolar CO2 tension for the computation of alveolar oxygen tension (PAo2) and of the physiological dead space/tidal volume ratio (VDphysNVT) .l2 56 2 11 The aim of this study was to estimate effective alveolar CO2 tension during tidal breathing with a new and simple technique and to compare these values with arterial CO2 tension in both normal subjects and patients with chronic airways obstruction. Methods THEORETICAL CONSIDERATIONSThe method is based on the computation of the effective CO2 concentration in the expired air at the mouth (FECO2efI) and the dead space/ tidal volume ratio (VD/VT) on the VE/time

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The effects of pulmonary rehabilitation in cystic fibrosis are well documented, but the effectiveness of interval exercise training remains unexplored. The aim of this study was to investigate whether interval exercise (IE) could be as beneficial as continuous exercise (CLE) in terms of improvement in functional capacity, peripheral muscle strength, and quality of life. We studied 24 Caucasian, ambulatory, adult, cystic fibrosis patients. Patients underwent a structured, outpatient, hospital-based pulmonary rehabilitation program for 12 weeks. Patients were randomised either to 30 min high-intensity IE (100% WRmax for 30 s alternated with 40% WRmax for 30 s; n=12) or 30 min moderate intensity CLE (70% WRmax; n=12). Interventions were balanced to provide the same overall training work load. Assessment was performed at baseline and following completion of the rehabilitation program. Functional capacity was assessed by the 6MWT, peripheral muscle strength was measured by the quadriceps isometric force and the Cystic Fibrosis Questionnaire-Revised (CFQ-R) was used to assess patient reported outcomes. The 6MWT was significantly improved equally in the IE Group (by 45 m; pre: 538±70, post: 583±83 m; p<0.001) and in CLE Group (by 48 m; pre: 516±57, post: 564±55 m; p=0.001). Improvement in quadriceps muscle strength was significantly greater in the IE group (pre: 37.9±13.1, post: 45.2±14.2 Kg; p=0.024) compared to CLE (pre: 40.0±12.2, post: 45.4±9.3 Kg; p=0.072). The CFQ-R was improved in both groups for the domains of “physical functioning” (IE Group pre: 52.8±14.5, post: 64.6±11.9; CLE Group pre: 60.4±11.2, post: 67.4±13.1; p=0.034) and “body image” (IE Group pre: 81.5±8.5, post: 88.1±7.3; CLE Group pre: 74.1±10.7, post: 80.7±9.7; p=0.046). Average training arterial oxygen saturation and Borg dyspnoea scores during exercise training indicated that the IE Group compared to the CLE Group exhibited higher oxygen saturation (94±1 vs. 91%±1%; p=0.002) and lower intensity of dyspnoea (3.8±0.7 vs. 5.9±0.8; p<0.001).In conclusion,within the pulmonary rehabilitation setting, IE is equally effective to CLE in improving functional capacity and aspects of quality of life, but is superior to CLE in improving peripheral muscle strength. Furthermore, it can be applied to CF patients with lower dyspnoea sensations and lower arterial desaturation, thus qualifying as a safer alternative training strategy.