(Chest. 2003;123:1625-1632.)
© 2003
American College of Chest Physicians
Time Course of Expiratory Flow Limitation in COPD Patients During Acute Respiratory Failure Requiring Mechanical Ventilation*
Valentina Alvisi, MD;
Anna Romanello, MD;
Michel Badet, MD;
Sandrine Gaillard, MD;
Francois Philit, MD and
Claude Guérin, MD
* From the Department of Anesthesiology (Drs. Alvisi and Romanello), University of Ferrara, Ferrara, Italy; and Service de Réanimation Médicale et Assistance Respiratoire (Drs. Badet, Gaillard, Philit, and Guérin), Hôpital de la Croix-Rousse, Lyon, France.
Correspondence to: Claude Guérin, MD, Service de Réanimation Médicale et Assistance Respiratoire, Hôpital de la Croix-Rousse, 103 grande rue de la Croix-Rousse, 69004 Lyon, France; e-mail: claude.guerin{at}chu-lyon.fr
 |
Abstract
|
|---|
Study objectives: (1) To determine the incidence of expiratory flow limitation (FL) at ICU admission, at the time of extubation, and at ICU discharge in intubated patients with COPD receiving mechanical ventilation for acute respiratory failure (ARF); and (2) to assess the feasibility of inspiratory capacity (IC) as an indication of pulmonary dynamic hyperinflation in this setting.
Design: Prospective, observational pilot study with physiologic measurements performed at ICU admission and during the weaning process driven by the clinician. A 60-min T-tube trial was initiated once criteria for weaning were present. The decision to extubate or reventilate patients was made by the clinician at the end of this session. Assessment of failure or success of T-tube trials was performed independently.
Setting: A 25-bed ICU of a tertiary teaching university hospital.
Patients: Over a 13-month period, 25 intubated patients with COPD receiving mechanical ventilation for ARF were included.
Interventions: None.
Measurements and results: At ICU admission, FL assessed by the negative expiratory pressure test was measured under passive ventilatory conditions at the baseline ventilatory settings, on zero end-expiratory pressure, and in a semirecumbent position. During weaning, FL, respiratory pattern, and IC were measured during T-tube trials, before extubation, 1 h after extubation, and at ICU discharge. At ICU admission, 24 of 25 patients presented FL with, on average, 73 ± 22% of the tidal volume. Ten patients were unavailable for follow-up due to death (n = 6) unplanned extubation (n = 3), or refusal (n = 1), so that only 15 patients completed the whole protocol (all 15 patients were extubated). For these 15 patients, the incidence of FL was 93% at ICU admission, 47% before extubation, and 40% at ICU discharge. IC was significantly greater at ICU discharge than before extubation (36 ± 11% predicted vs 44 ± 12% predicted, p < 0.01) and in successful T-tube trials compared with unsuccessful T-tube trials (38 ± 13% predicted vs 24 ± 8% predicted, p < 0.01).
Conclusions: The incidence of expiratory FL is high in patients with COPD receiving mechanical ventilation, and is reduced during aggressive therapy when the patient is placed on mechanical ventilatory support and the time that weaning begins during the ICU stay. IC was lower in patients in whom weaning was unsuccessful. Further large-scale studies are required to confirm these preliminary results.
Key Words: COPD • expiratory flow limitation • mechanical ventilation
|
Introduction
|
|---|
Expiratory flow limitation (FL) is a condition during which expiratory flow cannot be increased by increasing the driving pressure gradient, ie, the difference between lung elastic recoil pressure and atmospheric pressure.1
Expiratory FL is a major determinant of dyspnea in patients with stable COPD.2
In COPD patients with acute respiratory failure (ARF), the incidence of expiratory FL is expected to be very high. Characterizing expiratory FL in these patients is important to judiciously enable the external positive end-expiratory pressure (PEEP) to be selected so as to avoid any overdistension of the lung. According to the waterfall theory,3
increasing pressure downstream from the site of small airway closure or collapse should not decrease expiratory flow and, hence, should not induce a further rise in lung volume once a critical pressure threshold, above which pulmonary hyperinflation is increased, is reached. In COPD patients with ARF, dynamic pulmonary hyperinflation is the main factor explaining the increased work of breathing,4
ventilator dependency,5
and one of the major respiratory determinants for weaning failure.6
The determination of dynamic pulmonary hyperinflation is, however, not easy to perform in an ICU. The measurement of intrinsic PEEP (PEEPi), as an indication of the dynamic pulmonary hyperinflation, requires insertion of an esophageal balloon and assessment of the abdominal muscles that can be recruited during expiration.7
It has been shown, however, that changes in inspiratory capacity (IC) reflect the change in pulmonary hyperinflation, the greater the IC the lower the end-expiratory lung volume, assuming a constant total lung capacity.8
Therefore, we performed this prospective pilot study in intubated patients with COPD receiving mechanical ventilation for an episode of ARF, with the following aims: (1) to evaluate the incidence of expiratory FL at ICU admission, (2) to evaluate the time course of expiratory FL during management in the ICU, and (3) to evaluate the feasibility of IC measurement as a marker of dynamic pulmonary hyperinflation and the role of the value of IC in weaning trials. Our working hypotheses for this setting were as follows: (1) expiratory FL is very frequent at ICU admission and should improve with successful management, and (2) weaning failure is associated with lower values of IC than those associated with weaning success.
|
Materials and Methods
|
|---|
Patients
From January 1, 2000, to January 31, 2001, all consecutive intubated patients with COPD receiving mechanical ventilation were prospectively screened at admission to our 25-bed ICU. The inclusion criteria for the prospective cohort were as follows: (1) COPD diagnosed from clinical history, chest radiographs, and airflow obstruction on pulmonary function tests; (2) age > 18 years; (3) intubation and mechanical ventilation required for ARF as a result of exacerbation; and (4) informed consent obtained from next of kin. Patients were excluded if they were receiving invasive mechanical ventilation postoperatively, were hemodynamically unstable (systolic arterial pressure < 90 mm Hg), or had thoracic drainage; those for whom the cause of decompensation was acute cardiogenic edema or pneumonia; those receiving noninvasive mechanical ventilation; or those for whom informed consent was not obtained. Our institutional ethics committee approved the protocol for this study.
Measurement Set-up
Airflow was measured using a Fleisch 2 pneumotachograph (Hans Rudolph model 37000; Hans Rudolph; Kansas City, MO) attached at the proximal end of the endotracheal tube and connected to a differential pressure transducer (DP55 ± 5 cm H2O; Validyne; Northridge, CA). The pneumotachograph was linear over the experimental range of airflow ± 2.5 L/s. Pressure at the airway opening (Pao) was measured from a port inserted between the endotracheal tube and the pneumotachograph and connected to another pressure transducer (DP55 ± 100 cm H2O; Validyne) via a rigid polyethylene tube (1.7 mm inner diameter). Change in lung volume was evaluated by numerical integration of the airflow signal. The airflow, volume, and Pao signals were amplified (AC bridge amplifier, ABC module; Raytech Instruments; Vancouver, BC, Canada), low-pass filtered at 50 Hz, sent to a 16-bit analog-to-digital converter (Direc Physiologic Recording system; Raytech Instruments) installed on a personal computer (100 MHz), and sampled at 200 Hz (Direc Digital recording system software version 3.3; Raytech Instruments). The digitized airflow, volume, and Pao signals were continuously displayed on the computer screen. Records were monitored with respect to time and also as flow/volume loops. The recordings were stored on a computer hard disk in Direc format. Subsequently Direc signals were converted into Anadat signals and analyzed using Anadat software (Anadat-Labdat 5.1; RHT-InfoDat; Montreal, QC, Canada). Airflow and Pao were calibrated before each study.
Expiratory FL Measurement
Expiratory FL was assessed by the negative expiratory pressure (NEP) test, which has previously been described.2
The NEP could be applied either during controlled mechanical ventilation9
or spontaneous breathing.10
Measurement Timing
It was planned to obtain measurements during the first 24 h after intubation and onset of mechanical ventilation, during the T-tube trials, before and 1 h after extubation, and at ICU discharge.
Procedure
Measurements at the Onset of Invasive Mechanical Ventilation:
Patients were sedated using continuous IV infusion of midazolam, 0.2 mg/kg; and/or were paralyzed with a continuous IV infusion of atracurium, 0.3 to 0.6 mg/kg; and received mechanical ventilation in volume-controlled mode with a squared inflation flow. The measurements were performed using the baseline ventilatory settings selected by the clinician, on zero end-expiratory pressure (ZEEP), with the same ventilator, with a low-compliant circuit, used specifically for this study (Horus; Taema, France). During the experiments, the humidifier was omitted from the ventilatory circuit. Patients were investigated in a semirecumbent position. After any secretions in the trachea had been removed by gentle suctioning, the set-up was inserted. Respiratory mechanics were assessed by the standard airway occlusion technique using a 3-s end-expiratory occlusion followed by a 5-s end-inspiratory occlusion performed using specific buttons on the ventilator.11
The resistance and static elastance of the respiratory system were computed using standard formulas.11
For the computation of interrupter resistance of the respiratory system, the errors caused by the closing time of the ventilator valve were corrected as previously described.12
The change in lung volume from the end-expiratory lung volume during mechanical ventilation to the relaxation volume of the respiratory system (change in functional residual capacity [FRC]) was measured by prolonging the expiratory duration up to the point at which flow reached zero, and no total PEEP (PEEPt) could be detected from an end-expiratory pause. Finally, the NEP test was performed by applying a negative pressure of - 3 to - 4 cm H2O at the airway opening during expiration. Three NEP tests were performed, each separated by 10 baseline cycles.
Measurements During Weaning:
The weaning process was driven by the clinician in charge according to standard recommendations13
for the current study. Once criteria for weaning were present, patients underwent a 60-min T-tube trial. They were then disconnected from the ventilator and allowed to breath spontaneously in a semirecumbent position at the same fraction of inspired oxygen as during mechanical ventilation. After 5 min of spontaneous breathing, baseline respiratory rate (f), transcutaneous oxygen saturation, cardiac rate, systolic arterial BP, and anxiety were measured. During the T-tube trial, patients were followed up, for the purpose of this study, by a research fellow who noted the time that each of the following events occurred: f > 35 breaths/min for > 5 min, transcutaneous oxygen saturation < 88% for > 5 min, cardiac rate > 140 beats/min or increased by > 20% from baseline, systolic arterial BP > 180 mm Hg or < 90 mm Hg, and agitation. At the end of this T-tube trial, the physician in charge decided to either reconnect or extubate the patient on the basis of their clinical judgement and/or occurrence of any of the above events. Just before either extubation or reconnection to the ventilator, a 1-min acquisition of airflow and Pao signals was performed, followed by three NEP tests at the same negative pressure as during mechanical ventilation. Finally, two IC maneuvers were performed in which the patients were asked to make a further maximal effort in addition to maximal inspiration.8
The clinician was unaware of the values of the measurements. In the event of extubation, the same measurements were repeated 1 h later. In the event of reconnection to the ventilator, the same measurements were performed during the additional T-tube trials over the following days until extubation. Measurements were also performed at the time of ICU discharge. All measurements were made at least 4 h after the use of bronchodilators. During the study, a physician and a nurse not involved in the protocol were always present to provide patient care.
Data Analysis
The respiratory pattern was determined from the airflow signal as the tidal volume (VT), f, inspiratory time (TI), expiratory time, and total duration of cycle (TTOT). From these measurements, the mean inspiratory flow (VT/TI), duty cycle (TI/TTOT), and f/VT ratios were computed. Assessment of FL was performed by superimposing the expiratory airflow/VT loop generated with NEP with that obtained immediately before, without NEP.9
If the expiratory flow with NEP was higher than under control condition, the subject was classified as having no FL (NFL). If, on the contrary, all or part of the expiratory flow/volume curve was superimposed on the control curve, the subject was classified as having FL. The extent of FL was quantified as the fraction of the control VT with FL (FL, percentage of VT).
The T-tube trial was classified as being successful when none of the clinical events prospectively recorded occurred at any time during the trial. The T-tube trial was classified as being a failure when at least one of the clinical events occurred at any time during the trial. This classification was independent of the decision of the physician in charge to reconnect or extubate the patient.
Statistical Analysis
The consecutive breaths over the 1-min recording were averaged to obtain the respiratory pattern. The values for the three NEP tests were averaged. The highest value of IC was used, and the IC was expressed as a percentage of the predicted value. The predicted values of IC were computed as the difference between predicted total lung capacity and predicted FRC. The predicted values were those of Morris et al.14
The values were expressed as mean ± SD. Comparisons were made by Wilcoxon signed-rank test or rank-sum test, as appropriate. A p value < 0.05 was considered statistically significant. Statistical analyses were performed using SigmaStat software (SigmaStat for Windows, version 2.03; SPSS; Chicago, IL).
|
Results
|
|---|
During the study period, 25 patients were included (Table 1
). The mean values of vital capacity, FEV1, and FEV1/vital capacity ratio were 68 ± 19%, 39 ± 22%, and 55 ± 19% of the predicted values, respectively. In all patients, the respiratory mechanics and expiratory FL were assessed at ICU admission during invasive, controlled mechanical ventilation. However, the whole protocol was not performed for six patients who died before extubation, in three patients who underwent unplanned extubation, and in one patient who refused to continue. Hence, 15 patients completed the schedule from ICU admission to ICU discharge.
View this table:
[in this window]
[in a new window]
|
Table 1. Clinical and Anthropometric Characteristics, and Severity at ICU Admission of 25 Intubated Patients with COPD Receiving Mechanical Ventilation
|
|
Respiratory Mechanics and Expiratory Flow at ICU Admission
The average baseline ventilatory settings of the 25 patients receiving ZEEP at ICU admission are given in Table 2
. At these settings, the static elastance of the respiratory system was 18.4 ± 5.5 cm H2O/L, and values for total, interrupter, and additional airflow resistances for the respiratory system were 2.16 ± 5.5 cm H2O/L/s, 9.5 ± 4.4 cm H2O/L/s, and 12.1 ± 6.5 cm H2O/L/s, respectively. The average value of PEEPt was 6.5 ± 3.4 cm H2O. This was associated with pulmonary hyperinflation as reflected by the 
FRC of 0.40 ± 0.27 L (Table 3
). In all patients but one (patient 10), expiratory FL on ZEEP was detected, resulting in a 96% incidence of expiratory FL on ICU admission (Table 3)
. Expiratory FL was present, on average, > 73 ± 22% of VT (range, 19 to 100%; Table 3
). In the 24 patients with FL, the extent of FL was weakly correlated with the PEEPt (r = 0.42, p < 0.05).
View this table:
[in this window]
[in a new window]
|
Table 2. Baseline Ventilatory Settings Under Controlled Mechanical Ventilation at ZEEP at ICU Admission of 25 Patients With COPD
|
|
Time Course
The delay from ICU admission to extubation was 11 ± 7 days, and that from ICU admission to ICU discharge was 21 ± 23 days. All but 1 of the 15 patients who completed the protocol were successfully extubated. One patient was reintubated 4 days after extubation and underwent tracheostomy for long-term, domiciliary mechanical ventilation. All 15 patients were alive at ICU discharge, 5 to 98 days after ICU admission.
Among the 15 patients who completed the follow-up, the proportion of patients with expiratory FL decreased dramatically from 93% at ICU admission to 47% on the day of extubation, and to 40% at ICU discharge (Fig 1
). As compared with ICU admission, the extent of expiratory FL was significantly lower at the time of both extubation and ICU discharge (Fig 1)
.
View larger version (14K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. Time course of expiratory FL in 15 intubated patients with COPD receiving mechanical ventilation. Top: proportion of patients with expiratory FL. Bottom: mean ± SD values of the extent of FL. *p < 0.001 as compared with values at ICU admission.
|
|
During ICU stay, no significant changes in breathing patterns were observed (Fig 2
). The IC was significantly higher at the time of ICU discharge than at the time of extubation (Fig 3 ).
View larger version (28K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. Time course of mean values of VT (top left), f (top right), mean inspiratory flow (bottom left), and TI/TTOT (bottom right) in 15 intubated patients with COPD receiving mechanical ventilation. BE = before extubation; AE = after extubation; discharge = ICU discharge. Bars are SD.
|
|
View larger version (9K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3. Time course for mean values of IC in 15 intubated patients with COPD receiving mechanical ventilation. *p < 0.01 as compared with values at discharge. See Figure 2
legend for definition of abbreviations. Bars are SD.
|
|
Successful vs Failed T-Tube Trial Sessions
All 15 patients who completed the entire study were extubated; 3 of them were extubated after the first T-tube trial, 9 of them were extubated after the second T-tube trial, 2 of them were extubated after the third T-tube trial, and the remaining patient was extubated after the fourth T-tube trial. In total, 31 T-tube trials were performed: 19 classified as successful and 12 classified as failures. As shown in Table 4
, the values of IC, FL, and respiratory-pattern variables were not different between the first three T-tube trials and were also similar for the 12 patients who completed two consecutive T-tube trials. However, between successful and failed sessions for all the T-tube trials, f/VT values were 72 ± 39 breaths/min/L vs 130 ± 68 breaths/min/L (p < 0.01), FL values were 30 ± 39% of VT vs 35 ± 41% of VT (p > 0.05), and IC values were 38 ± 13% predicted vs 24 ± 8% predicted (p < 0.01) [Fig 4
]. The values of VT/TI and TI/TTOT were not different between the two groups.
View larger version (10K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4. Individual patient values for f/VT (top), FL (percentage of VT) [middle], and IC (percentage of predicted) [bottom] in the 31 failed or successful T-tube trial sessions. *p < 0.001 vs success.
|
|
|
Discussion
|
|---|
The main findings of this prospective, observational, pilot study in patients with COPD receiving invasive mechanical ventilation for ARF are as follows: (1) the incidence of expiratory FL on ICU admission is very high, (2) expiratory FL was reversed in most patients during ICU stay, and (3) IC was found to be associated with a successful T-tube trial.
The high incidence of FL in this setting was an expected finding. A similarly high incidence of FL was recently reported for intubated patients with COPD receiving mechanical ventilation.16
Our sample size is relatively small because the use of invasive mechanical ventilation in patients with COPD currently admitted to our ICU has markedly decreased with the increased use of noninvasive mechanical ventilation in this setting. Therefore, the patients included in the present investigation are probably selected patients. The present measurements were performed in patients in a semirecumbent position, which is known to reduce the occurrence of FL relative to a supine position.9
The high rate of FL in patients with COPD found by Lourens et al16
was observed with the patients in a supine position. The high incidence of FL found at ICU admission in semirecumbent patients with COPD in our study is suggestive of very severe illness, which may also explain why they received invasive mechanical ventilation. The extent of FL at ICU admission in our study was only weakly correlated with PEEPt, a result also observed in intubated patients receiving mechanical ventilation for ARF from various origins.17
In this latter study, however, PEEPt, was significantly higher in patients with FL than in patients with NFL.17
Due to the high rate of FL at ICU admission, we were unable to make this comparison in our study.
Expiratory FL appears to be a reversible phenomenon in the majority of the patients in our study (Fig 1)
. Such a trend has not, to our knowledge, been described previously. To understand how such a high recovery rate could have been observed, we should first of all investigate if there was an overestimation of the absence of FL at the time of extubation. A falsely positive picture of NFL could be due to the presence of leaks. At least two reasons make this possibility unlikely in our study. First, patients were still intubated with a cuff of the endotracheal tube inflated at a similar pressure as that used at ICU admission. Second, the presence of leaks would have been seen in the time course analysis of the airflow and VT tracings as a sustained decrease in end-expiratory lung volume after NEP application.18
Inspection of our records excluded this pattern. Assuming the marked reduction of FL over time in our study is true, at least three contributing factors can be discussed. First, the change from FL to NFL may result from bronchodilation and increasing expiratory reserve volume. The treatment of our patients included large doses of bronchodilating agents, combining anticholinergic and ß2-agonist drugs, administered by inhalation through the endotracheal tube. Since, in our study, measurements were performed at least 4 h after the last inhalation of bronchodilator, the absence of FL could reflect the persisting effect of the drug on the bronchomotor tone. In nonintubated patients with stable COPD, inhaled salbutamol has been shown to reduce pulmonary hyperinflation whereas the FL remained unchanged.19
This can be explained by the lack of any significant bronchoconstriction in the patients in the study reported by Tantucci et al.19
In a similar manner, the reversal of FL in seven patients before extubation in our study could reflect the presence of marked bronchoconstriction at ICU admission. The reduction of VT can itself reverse the FL condition. Low VT induces a reduction in expiratory airflow, which then no longer impinges on the maximal flow. VT was significantly reduced from 0.50 ± 0.13 to 0.40 ± 0.08 L (p = 0.001) between controlled mechanical ventilation at ICU admission and spontaneous breathing during the T-tube trial just before extubation. FL may have also been reversed as a result of the reduction of the inflammation of the small airways by curing the causative infection. It must be noted that none of the patients studied had received inhaled or systemic steroids as part of their treatment.
Many benefits can arise from the reversal of FL, since the patients become less dyspneic2
and increase their expiratory reserve. In our study, dyspnea was, unfortunately, not measured. In our study, all 15 patients who completed the follow-up were extubated after one to four attempts, which may be due to bias since "selected" patients were included, or this favorable outcome could be related to the recovery of FL over time. However, we are unable to draw firm conclusions since there was no control group of patients who could not be extubated. One of the main clinical implications of assessing FL is to help intensive care physicians to select PEEP in patients with COPD in ARF. In spontaneously breathing patients with COPD, several studies have shown that PEEP can reduce the inspiratory work of breathing by offsetting the internal elastic load represented by PEEPi20
21
22
; therefore, facilitation of weaning is expected. The optimal level of PEEP that should be applied for these patients is not known; however, according to the waterfall theory,3
PEEP is theoretically indicated only in patients with expiratory FL. On the basis of our results, PEEP could have been avoided in > 50% of the patients during the weaning process because, at the time of extubation, 8 of the 15 patients no longer had FL. Because work of breathing was not measured in our study, the effect of PEEP in patients with FL and NFL during weaning was, unfortunately, not assessed. Nevertheless, our results indicate that FL should systematically be assessed in these patients before applying PEEP, due to the high prevalence of NFL at the time of extubation.
During the ICU stay in our study, IC increased and, hence, dynamic hyperinflation and the work of breathing should have decreased. The improvement of IC occurred later than the reduction of FL during the ICU stay and was significant only at the time of ICU discharge. In addition, IC was not significantly different between FL and NFL patients. In patients with stable COPD, IC has been reported to be significantly higher in NFL patients than in FL patients.23
The contrasting results between the two studies can be explained by the small number of patients investigated and by the low value of IC recorded in our study. In another study reported by Diaz et al,23
the FL group had a mean IC of 60%, with the lowest IC of 40% of the predicted value. In our patients with FL, these values were 35% and 13%, respectively. Low values of IC may be less useful for distinguishing patients with FL and patients without FL. Moreover, in our study that included very sick patients, the IC maneuver was probably not maximal and, hence, the values of IC were underestimated. We observed lower values of IC after T-tube trial failure than after T-tube trial success. If IC reflects end-expiratory lung volume in these patients, this result is compatible with a markedly higher value for PEEPi found in intubated patients with COPD who failed compared with those who successfully completed the weaning trial.5
Finally, the number of T-tube trials analyzed is too small to be able to provide a threshold value of IC to predict the issue of a weaning trial.
|
Conclusion
|
|---|
In conclusion, the incidence of expiratory FL was very high in patients with COPD receiving invasive mechanical ventilation for ARF in our sample. The incidence of expiratory FL was reduced during aggressive therapy when the patient is placed on mechanical ventilatory support and the time that weaning begins during the ICU stay, so that < 50% of the patients had FL at time of extubation. Therefore, FL should be systematically assessed in this setting to improve the selection of the PEEP value to reduce the work of breathing. IC was lower in patients who failed weaning than those who were successfully weaned. Further large-scale studies are required to confirm these preliminary results.
|
Acknowledgements
|
|---|
The authors thank Professor Milic-Emili for his training with the NEP test, and the nursing staff and physicians of the medical ICU at the Croix Rousse Hospital.
|
Footnotes
|
|---|
Abbreviations: ARF = acute respiratory failure; f = baseline respiratory rate; FL = flow limitation; FRC = functional residual capacity; f/VT = ratio of baseline respiratory rate to tidal volume; IC = inspiratory capacity; NEP = negative expiratory pressure; NFL = no flow limitation; Pao = pressure at the airway opening; PEEP = positive end-expiratory pressure; PEEPi = intrinsic positive end-expiratory pressure; PEEPt = total positive end-expiratory pressure; TI = inspiratory time; TI/TTOT = duty cycle; TTOT = total duration of the respiratory cycle; VT = tidal volume; VT/TI = mean inspiratory flow; = tidal volume; ZEEP = zero end-expiratory pressure
Dr. Alvisi and Dr. Romanello were supported by grants from the Department of Anesthesiology, University of Ferrara, Ferrara, Italy.
This work was supported by grants from Hospices Civils de Lyon.
Received for publication April 16, 2002.
Accepted for publication August 27, 2002.
|
References
|
|---|
- Hyatt, RE (1961) The interrelationship of pressure, flow and volume during various respiratory maneuvers in normal and emphysematous patients. Am Rev Respir Dis 83,676-683[ISI][Medline]
- Eltayara, L, Becklake, MR, Volta, CA, et al Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1996;154,1726-1734[Abstract]
- Tobin, MJ, Lodato, RF PEEP, auto-PEEP and waterfalls. Chest 1989;96,449-451[Free Full Text]
- Coussa, ML, Guérin, C, Eissa, NT, et al Partitioning of work of breathing in mechanically ventilated COPD patients. J Appl Physiol 1993;75,1711-1719[Abstract/Free Full Text]
- Purro, A, Appendini, L, DeGaetano,, et al Physiologic determinants of ventilator dependence in long-term mechanically ventilated patients. Am J Respir Crit Care Med 2000;161,1115-1123[Abstract/Free Full Text]
- Jubran, A, Tobin, MJ Pathophysiologic basis of acute respiratory distress in patients who fail a trial of weaning from mechanical ventilation. Am J Respir Crit Care Med 1997;155,906-915[Abstract]
- Lessard, MR, Lofaso, F, Brochard, L Expiratory muscle activity increases intrinsic positive end-expiratory pressure independently of dynamic hyperinflation in mechanically ventilated patients. Am J Respir Crit Care Med 1995;151,562-569[Abstract]
- Yan, S, Kaminski, D, Sliwinski, P Reliability of inspiratory capacity for estimating end-expiratory lung volume changes during exercise in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1997;156,55-59[Abstract/Free Full Text]
- Valta, P, Corbeil, C, Lavoie, A, et al Detection of expiratory flow limitation during mechanical ventilation. Am J Respir Crit Care Med 1994;150,1311-1317[Abstract]
- Koulouris, NG, Valta, P, Lavoie, A, et al A simple method to detect expiratory flow limitation during spontaneous breathing. Eur Respir J 1995;8,306-313[Abstract]
- Guérin, C, Coussa, ML, Eissa, NT, et al Lung and chest wall mechanics in mechanically ventilated COPD patients. J Appl Physiol 1993;74,1570-1580[Abstract/Free Full Text]
- D’Angelo, E, Calderini, E, Torri, G, et al Respiratory mechanics in anesthetized paralyzed humans: effect of flow, volume and time. J Appl Physiol 1989;67,2556-2564[Abstract/Free Full Text]
- Esteban, A, Frutos, F, Tobin, MJ, et al A comparison of four methods of weaning patients from mechanical ventilation. N Engl J Med 1995;332,345-350[Abstract/Free Full Text]
- Morris, JF, Koski, A, Johnson, LC Spirometric standards for healthy nonsmoking adults. Am Rev Respir Dis 1971;103,57-67[ISI][Medline]
- Le Gall, JR, Lemeshow, S, Saulnier, F A new simplified acute physiology score (SAPS II) based on a European-North American multicenter study. JAMA 1993;270,2957-2968[Abstract]
- Lourens, MS, Berg, BVD, Hoogsteden, HC, et al Detection of flow limitation in mechanically ventilated patients. Intensive Care Med 2001;27,1312-1320[ISI][Medline]
- Armaganidis, A, Stavrakaki-Kallergi, K, Koutsoukou, A, et al Intrinsic positive end-expiratory pressure in mechanically ventilated patients with and without tidal expiratory flow limitation. Crit Care Med 2000;28,3837-3842[CrossRef][ISI][Medline]
- Boczkowski, J, Murciano, D, Pichot, MH, et al Expiratory flow limitation in stable asthmatic patients during resting breathing. Am J Respir Crit Care Med 1997;156,752-757[Abstract/Free Full Text]
- Tantucci, C, Duguet, A, Similovski, T, et al Effect of salbutamol on dynamic hyperinflation in chronic obstructive pulmonary disease. Eur Respir J 1998;12,799-804[Abstract]
- Smith, TC, Marini, J Impact of PEEP on lung mechanics and work of breathing in severe airflow obstruction. J Appl Physiol 1988;65,1488-1499[Abstract/Free Full Text]
- Petrof, B, Legaré, M, Goldberg, P, et al Continuous positive airway pressure reduces work of breathing and dyspnea during weaning from mechanical ventilation in severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1990;141,281-289[ISI][Medline]
- Appendini, L, Patessio, A, Zanaboni, S, et al Physiologic effects of positive end-expiratory pressure and mask pressure support during exacerbations of chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1994;149,1069-1076[Abstract]
- Diaz, O, Villafranca, C, Ghezzo, H, et al Role of inspiratory capacity on exercise tolerance in COPD patients with and without tidal expiratory flow limitation at rest. Eur Respir J 2000;16,269-275[Abstract]
This article has been cited by other articles:
|
|
|
|
 
P. M. A. Calverley and N. G. Koulouris
Flow limitation and dynamic hyperinflation: key concepts in modern respiratory physiology
Eur. Respir. J.,
January 1, 2005;
25(1):
186 - 199.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
Abstract
Introduction
