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Biomedical subjects

J Milic-Emili

Publications and source records attributed to J Milic-Emili.

At least 37 records · Page 2Linked to original sources
PubMed2000

Predictors of weaning outcome in chronic obstructive pulmonary disease patients.

Several threshold values for predicting weaning outcome from mechanical ventilation have been proposed. These values, however, have been obtained in nonhomogeneous patient populations. The aim of the present study was to determine the threshold values in chronic obstructive pulmonary disease (COPD) patients and compare them to those reported for nonhomogeneous patient populations. The initial weaning trial included 81 COPD patients. Fifty-three of them underwent a successful weaning trial, whereas 28 failed it. The latter were enrolled into the present investigation, and were restudied during a subsequent successful trial. The weaning indices used were those reported in the literature. The threshold values obtained were within 10% of those reported for a nonhomogeneous patients population only for tidal volume and effective compliance. The classification error was <20% for maximal inspiratory pressure (MIP), occluded inspiratory pressure swing (deltaPI)/MIP, rapid and shallow breathing (respiratory frequency/tidal volume), and compliance, rate, oxygenation, pressure index (CROP), whereas the area under the receiver operating characteristic curves was >0.9 only for deltaPI/MIP and CROP. In conclusion, the threshold values obtained in chronic obstructive pulmonary disease patients who failed the first weaning attempt differed from those previously reported. Although a gold standard weaning index is not available for chronic obstructive pulmonary disease patients, the occluded inspiratory pressure swing/ maximal inspiratory pressure and compliance, rate, oxygenation, pressure index may be candidates for such a role.

Acute Disease↗
PubMed2000

Bedside assessment of respiratory viscoelastic properties in ventilated patients.

Viscoelasticity represents an important component of respiratory mechanics, being responsible, in some cases, for most of the pressure dissipated during breathing. Hitherto the methods available for determining the viscoelastic properties have been simplified, but are still time-demanding and depend on a great deal of calculation. In this study, a simple means of determining respiratory viscoelastic properties during mechanical ventilation was introduced. The viscoelastic constants of the respiratory system, modelled as a Maxwell body, were studied in 17 normal subjects and seven patients with acute lung injury (ALI) using two end-inspiratory occlusions; one with a short inspiratory time (tI) to determine the elastic component of viscoelasticity and the other with a long tI to assess the resistive component of viscoelasticity. The results were reproducible and similar to those provided by the previously described multiple-breath method (MB). The mean+/-SD viscoelastic resistance was 5.31+/-1.50 cm H2O x L(-1) x s with the proposed method and 5.71+/-1.87 cm H2O x L(-1) x s with the MB method in normal subjects, and 8.93+/-2.82 cm H2O x L(-1) x s and 10.36+/-3.13 cm H2O x L(-1), respectively in ALI patients. The mean+/-SD viscoelastic elastance was 3.92+/-0.84 cm H2O x L(-1) and 4.94+/-1.01 cm H2O x L(-1) in normal subjects and 7.08+/-2.01 cm H2O x L(-1) and 8.21+/-1.16 cm H2O x L(-1) in ALI patients, respectively. The mean+/-SD viscoelastic time constant was 1.36+/-0.24 s and 1.17+/-0.34 s in normal subjects and 1.26+/-0.35 s and 1.24+/-0.23 in ALI patients, respectively. The method was easy to perform and applicable at the bedside in clinical routine.

Adult↗
PubMed2000

Volume and time dependence of respiratory system mechanics in normal anaesthetized paralysed humans.

The purpose of the present investigation was to assess the effect of large tidal volumes and mean lung volumes on the viscoelastic properties of the respiratory system in normal humans; and to verify if in this case the results could be satisfactorily described by a simple linear viscoelastic model of the respiratory system. Twenty-eight subjects (7 females), aged 14-28 yrs, were studied before orthopaedic surgery on the lower limbs. None were obese, or had clinical evidence of cardiopulmonary disease. The interrupter conductance and the viscoelastic constants of the respiratory system were assessed using the rapid end-inspiratory airway occlusion method during mechanical ventilation with tidal volumes up to 3 L and applied end-expiratory pressures up to 23 cmH2O. It was found that the interrupter conductance increased linearly with lung volume over a larger range than used previously; and the viscoelastic resistance and time constant did not change over the entire range of tidal volumes and end-expiratory pressures studied. In conclusion, in normal anaesthetized, paralysed subjects a simple linear viscoelastic model satisfactorily described the viscoelastic behaviour of the respiratory system over the whole range of volume studied.

Adolescent↗
PubMed2000

Performance of forced expiratory manoeuvre in children.

The negative expiratory pressure (NEP) method has been previously used to assess the performance of forced vital capacity (FVC) manoeuvre in normal adults. The aim of the present study is to assess whether flow limitation is achieved during FVC manoeuvres in children aged 6-14 yrs. NEP (-10 cmH2O) was successfully applied in 177 normal children, the portion of FVC over which expiratory flow did or did not change with NEP being taken as effort-dependent and effort-independent, respectively. In all children peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) increased with NEP, indicating that PEF was in the effort-dependent portion of FVC. This portion decreased significantly with age (50-20% of FVC from 6-14 yrs). It is suggested that this mainly reflects the poorer coordination of specialized motor acts in younger children because of incomplete morphological and functional maturation of the relevant central nervous system (CNS) mechanisms. The results indicate that most unexperienced children aged 6-14 yrs can perform acceptable forced vital capacity manoeuvres, eventually achieving flow limitation over a portion of the forced vital capacity that increases with age. The negative expiratory pressure method can be used for online assessment of the performance of forced vital capacity manoeuvres and evaluation of treatment-related effects.

Adolescent↗
PubMed2000

Intrinsic positive end-expiratory pressure in mechanically ventilated patients with and without tidal expiratory flow limitation.

OBJECTIVE: To assess static intrinsic positive end-expiratory pressure (PEEPi,st) and expiratory flow limitation (FL) in 32 consecutive mechanically ventilated patients with acute respiratory failure (ARF), using a commercial ventilator with an incorporated device that allows the application of a negative expiratory pressure (NEP). DESIGN: Prospective clinical study. SETTING: Multidisciplinary intensive care unit of a university hospital. PATIENTS: Thirty-two consecutive ventilated patients with ARF of various etiologies. INTERVENTIONS: Evaluation of respiratory mechanics, PEEPi,st, and FL from pressure, flow, and volume traces provided by the ventilator. MEASUREMENTS: Peak airway pressure, PEEPi,st, dynamic elastance, and interrupter resistance were measured in relaxed patients in a supine position. Comparison of tidal flow-volume curves before and during the application of an NEP of 5 cm H2O was used to assess tidal expiratory FL. RESULTS: Twelve of 32 patients studied exhibited tidal expiratory FL, which was detected by the absence of increase in expiratory flow despite application of an NEP over the entire or part of the baseline expiratory flow-volume curve. All patients exhibited PEEPi,st, which amounted to 1.2 +/- 0.9 cm H2O (mean +/- SD) in the 20 non-FL patients and 7.1 +/- 2.8 cm H2O in the 12 FL patients (p < 0.00001). The majority of patients with ARF resulting from underlying lung disease (11 of 13) had FL and a PEEPi,st > 4 cm H2O, whereas in patients with ARF of extrapulmonary origin, PEEPi,st was always < 4 cm H2O and only one grossly obese patient exhibited FL. Based on multiple regression analysis, in non-FL patients, PEEPi,st correlated significantly only with minute ventilation, whereas in FL patients PEEPi,st correlated significantly with peak airway pressure. CONCLUSIONS: Because all the patients exhibited PEEPi,st and 12 of 32 patients (38%) also had FL, the authors conclude that the assessment of these variables at the bedside could provide useful information concerning respiratory mechanics in mechanically ventilated patients.

Adolescent↗
PubMed2000

Expiratory flow limitation and intrinsic positive end-expiratory pressure at zero positive end-expiratory pressure in patients with adult respiratory distress syndrome.

It has been suggested that in patients with adult respiratory distress syndrome (ARDS), intrinsic positive end-expiratory pressure (PEEPi) is generated by a disproportionate increase in expiratory flow resistance. Using the negative expiratory pressure (NEP) technique, we assessed whether expiratory flow limitation (EFL) and PEEPi were present at zero PEEP in 10 semirecumbent, mechanically ventilated ARDS patients. Because bronchodilators may decrease airway resistance, we also investigated the effect of nebulized salbutamol on EFL, PEEPi, and respiratory mechanics in these patients, and in seven patients we measured the latter variables in the supine position as well. In the semirecumbent position, eight of the 10 ARDS patients exhibited tidal EFL, ranging from 5 to 37% of the control tidal volume (VT), whereas PEEPi was present in all 10 subjects, ranging from 0.4 cm H(2)O to 7.7 cm H(2)O. The onset of EFL was heralded by a distinct inflection point on the expiratory flow-volume curve, which probably reflected small-airway closure. Administration of salbutamol had no statistically significant effect on PEEPi, EFL (as %VT), or respiratory mechanics. EFL (%VT) and PEEPi were significantly higher in the supine position than in the semirecumbent position, whereas the other respiratory variables did not change. Our results suggest that in the absence of externally applied PEEP, most ARDS patients exhibit EFL associated with small-airway closure and a concomitant PEEPi.

Adult↗
PubMed2000

Noninvasive assessment of inspiratory muscle function during exercise.

The use of esophageal and gastric balloons limits measurement of the tension-time index of inspiratory muscles (TTI) during exercise. The aim of this study was to assess whether a noninvasive tension-time index, TT(0.1), given by P(0.1)/PI(max) x TI/Ttot (where P(0.1) is mouth occlusion pressure, PI(max) is maximal inspiratory pressure, and TI/Ttot is duty cycle) could reliably assess TTI during exercise. In seven healthy young men and nine patients with COPD we measured TT(0.1) and TTI (i.e., Pes/Pes(max) x TI/Ttot where Pes is mean esophageal pressure and Pes(max) is maximal static Pes) at rest and during an incremental exercise test. A significant linear correlation (p < 0.02) was found between TT(0.1) and TTI in all normal subjects and patients with COPD. An equation for estimating TTI from TT(0.1) was established for each group. In the normal subjects there was good agreement between estimated and observed data. In five additional normal males studied prospectively, the agreement was also satisfactory and reproducible. In the COPD patients the agreement was poor. In conclusion, in young healthy subjects the changes in TT(0.1) during exercise reflect the changes in TTI, allowing satisfactory estimation of TTI from noninvasive measurements of TT(0.1).

Adult↗
PubMed2000

Flow limitation and dynamic hyperinflation during exercise in COPD patients after single lung transplantation.

STUDY OBJECTIVE: Using the negative expiratory pressure (NEP) method, we have previously shown that patients receiving single lung transplantation (SLT) for COPD do not exhibit expiratory flow limitation and have little dyspnea at rest. In the present study, we assessed whether SLT patients exhibit flow limitation, overall hyperinflation, and dyspnea during exercise. METHODS: Expiratory flow limitation assessed by the NEP method and inspiratory capacity maneuvers used to determine end-expiratory lung volume (EELV) and end-inspiratory lung volume (EILV) were performed at rest and during symptom-limited incremental cycle exercise in eight SLT patients. RESULTS: At the time of the study, the mean (+/- SD) FEV(1), FVC, functional residual capacity, and total lung capacity (TLC) amounted to 55 +/- 14%, 67 +/- 12%, 137 +/- 16%, and 110 +/- 11% of predicted, respectively. At rest, all patients did not experience expiratory flow limitation and were without dyspnea. At peak exercise, the maximal mechanical power output and maximal oxygen consumption amounted to 72 +/- 20% and 65 +/- 8% of predicted, respectively, with a maximal dyspnea Borg score of 6 +/- 3. All but one patient exhibited flow limitation and dynamic hyperinflation; the EELV and EILV amounted to 74 +/- 5% and 95 +/- 9% TLC, respectively. The patient who did not exhibit flow limitation during exercise had the lowest dyspnea score. CONCLUSION: Most SLT patients for COPD exhibit expiratory flow limitation and dynamic hyperinflation during exercise, whereas maximal dyspnea is variable.

Aged↗
PubMed1999

Effect of inspiratory flow waveform on work on endotracheal tubes: a model analysis.

OBJECTIVE: This model analysis aimed to predict the impact of different inspiratory flow wave-forms, i. e., constant, sinusoidal, and two linearly decreasing flows, on the resistive work (Wres) performed on endotracheal tubes. DESIGN: Model analysis. RESULTS: Model analysis predicts that: (i) minimal Wres is obtained with the constant flow; (ii) for any given tidal volume/inspiratory duration (V(T)/T(I), mean inspiratory flow), Wres increases with decreasing tube size; (iii) for any given inspiratory flow waveform, Wres increases with increasing V(T)/T(I), being lowest with constant flow. CONCLUSIONS: These findings have major clinical implications: at any given ventilator setting, not only the size of the endotracheal tube but also the inspiratory flow waveform must be taken into account to interpret the values of Wres and hence of the total work of breathing.

Airway Resistance↗
PubMed1999

Expiratory flow limitation during exercise in competition cyclists.

In some trained athletes, maximal exercise ventilation is believed to be constrained by expiratory flow limitation (FL). Using the negative expiratory pressure method, we assessed whether FL was reached during a progressive maximal exercise test in 10 male competition cyclists. The cyclists reached an average maximal O2 consumption of 72 ml. kg-1. min-1 (range: 67-82 ml. kg-1. min-1) and ventilation of 147 l/min (range: 122-180 l/min) (88% of preexercise maximal voluntary ventilation in 15 s). In nine subjects, FL was absent at all levels of exercise (i.e., expiratory flow increased with negative expiratory pressure over the entire tidal volume range). One subject, the oldest in the group, exhibited FL during peak exercise. The group end-expiratory lung volume (EELV) decreased during light-to-moderate exercise by 13% (range: 5-33%) of forced vital capacity but increased as maximal exercise was approached. EELV at peak exercise and at rest were not significantly different. The end-inspiratory lung volume increased progressively throughout the exercise test. The conclusions reached are as follows: 1) most well-trained young cyclists do not reach FL even during maximal exercise, and, hence, mechanical ventilatory constraint does not limit their aerobic exercise capacity, and 2) in absence of FL, EELV decreases initially but increases during heavy exercise.

Adolescent↗
PubMed1999

Respiratory energetics during exercise at high altitude.

The purpose of this study was to assess the effect of high altitude (HA) on work of breathing and external work capacity. On the basis of simultaneous records of esophageal pressure and lung volume, the mechanical power of breathing (Wrs) was measured in four normal subjects during exercise at sea level (SL) and after a 1-mo sojourn at 5,050 m. Maximal exercise ventilation (VEmax) and maximal Wrs were higher at HA than at SL (mean 185 vs. 101 l/min and 129 vs. 40 cal/min, respectively), whereas maximal O2 uptake averaged 2.07 and 3.03 l/min, respectively. In three subjects, the relationship of Wrs to minute ventilation (VE) was the same at SL and HA, whereas, in one individual, Wrs for any given VE was consistently lower at HA. Assuming a mechanical efficiency (E) of 5%, the O2 cost of breathing at HA and SL should amount to 26 and 5.5% of maximal O2 uptake, whereas for E of 20% the corresponding values were 6.5 and 1.4%, respectively. Thus, at HA, Wrs may substantially limit external work unless E is high. Although at SL VEmax did not exceed the critical VE, at which any increase in VE is not useful in terms of body energetics even for E of 5%, at HA VEmax exceeded critical VE even for E of 20%.

Adult↗
PubMed1999

Effect of negative expiratory pressure on respiratory system flow resistance in awake snorers and nonsnorers.

In spontaneously breathing subjects, intrathoracic expiratory flow limitation can be detected by applying a negative expiratory pressure (NEP) at the mouth during tidal expiration. To assess whether NEP might increase upper airway resistance per se, the interrupter resistance of the respiratory system (Rint,rs) was computed with and without NEP by using the flow interruption technique in 12 awake healthy subjects, 6 nonsnorers (NS), and 6 nonapneic snorers (S). Expiratory flow (V) and Rint,rs were measured under control conditions with V increased voluntarily and during random application of brief (0.2-s) NEP pulses from -1 to -7 cmH(2)O, in both the seated and supine position. In NS, Rint,rs with spontaneous increase in V and with NEP was similar [3.10 +/- 0.19 and 3.30 +/- 0.18 cmH(2)O x l(-1) x s at spontaneous V of 1.0 +/- 0.01 l/s and at V of 1.1 +/- 0.07 l/s with NEP (-5 cmH(2)O), respectively]. In S, a marked increase in Rint,rs was found at all levels of NEP (P < 0.05). Rint,rs was 3.50 +/- 0.44 and 8.97 +/- 3.16 cmH(2)O x l(-1) x s at spontaneous V of 0.81 +/- 0.02 l/s and at V of 0.80 +/- 0.17 l/s with NEP (-5 cmH(2)O), respectively (P < 0.05). With NEP, Rint,rs was markedly higher in S than in NS both seated (F = 8.77; P < 0.01) and supine (F = 9.43; P < 0.01). In S, V increased much less with NEP than in NS and was sometimes lower than without NEP, especially in the supine position. This study indicates that during wakefulness nonapneic S have more collapsible upper airways than do NS, as reflected by the marked increase in Rint,rs with NEP. The latter leads occasionally to an actual decrease in V such as to invalidate the NEP method for detection of intrathoracic expiratory flow limitation.

Adult↗
PubMed1999

Dynamic hyperinflation and flow limitation during methacholine-induced bronchoconstriction in asthma.

Although persistent activation of the inspiratory muscles and narrowing of the glottic aperture during expiration have been indicated as relevant mechanisms leading to dynamic hyperinflation in acute asthma, expiratory flow limitation (EFL) has recently been proposed as a possible triggering factor for increasing endexpiratory lung volume (EELV). To establish whether the attainment of maximal flow rate during tidal expiration could elicit dynamic elevation of EELV, breathing pattern, change in EELV by measuring inspiratory capacity (IC) and occurrence of EFL by the negative expiratory pressure (NEP) method were monitored in 10 stable asthmatic subjects during methacholine-induced, progressive bronchoconstriction in seated position. Change in dyspnoea was scored using the Borg scale. At maximum response forced expiratory volume in one second (FEV1) fell on average by 45+/-2% (p<0.001 versus control), while IC decreased 29+/-2%, (by 0.89+/-0.07 L, (p<0.01 versus control)). Only 2 subjects exhibited EFL at the end of methacholine challenge. In 7 subjects EELV started to increase before the occurrence of EFL. Dyspnoea, which increased from 0.2+/-0.1 to 5.5+/-1.0 (Borg scale) at maximum response (p<0.001), was significantly related to the level of bronchoconstriction as assessed by change in (delta)FEV1 (r=0.72; p<0.001) and to dynamic hyperinflation as measured by deltaIC (r=0.50; p<0.001). However, for both deltaFEV1 and deltaIC the slope of the relationship with increasing dyspnoea was highly variable among the subjects. It is concluded that in acute methacholine-induced bronchoconstriction, dynamic hyperinflation may occur in the absence of expiratory flow limitation and that expiratory flow limitation does not represent the triggering factor to generate dynamic hyperinflation. In these circumstances, dyspnoea appears to be related to the increase in end-expiratory lung volume and not to the onset of expiratory flow limitation.

Asthma↗
PubMed1999

Flow limitation and dyspnoea in healthy supine subjects during methacholine challenge.

The purpose of this study was to assess whether during standard methacholine (Mch) challenge (concentration up to 128 mg x mL(-1)) healthy supine subjects a) develop tidal expiratory flow limitation (FL) and hyperinflation, and b) whether the onset of tidal FL is associated with dyspnoea. Eight healthy subjects were studied. Dyspnoea was assessed using the Borg scale, FL by the negative expiratory pressure (NEP) method and hyperinflation in terms of decrease in inspiratory capacity (IC). Seven patients became flow limited at Mch doses ranging 4-64 mg x mL(-1), with FL encompassing 34-84% of the control tidal volume. In six of them the onset of tidal FL was associated with little or no dyspnoea and a modest degree of hyperinflation (deltaIC <-0.4 L). In one subject, however, onset of FL was associated with a substantial reduction in IC (0.58 L) and moderately severe dyspnoea. In all of these seven subjects FL was transiently reversed after an IC manoeuvre. In conclusion, the results show that a) most healthy subjects may develop flow limitation and hyperinflation during methacholine challenge in supine position, and b) at onset of flow limitation there is little or no dyspnoea, suggesting that onset of dynamic airway compression per se does not elicit significant dyspnoea. Significant dyspnoea probably only occurs with marked dynamic hyperinflation.

Adult↗
PubMed1999

Flow and volume dependence of respiratory mechanics in anesthetized children.

With the use of constant flow, end-inspiratory airway occlusion, respiratory system resistance (Rrs) can be partitioned into a flow resistive component (Rint) and an additional component (deltaR), reflecting viscoelasticity and time constant inequality. Similarly, respiratory system elastance (Edyn) can be partitioned into static elastance (Est) and elastance due to viscoelasticity and time constant inequality (deltaE). We measured Rrs and Edyn and their subdivisions (Rint and deltaR, Est and deltaE, respectively) and studied their flow and volume dependence in eight otherwise healthy children (median age 3.6 y; range 1.9-5.2 y) undergoing general anesthesia for oral rehabilitation. With a constant inspiratory flow (VI) of approximately 15 mL/s/kg and tidal volume of 12 mL/kg, the mean values of Rrs, Rint, and deltaR were: 0.20, 0.11, and 0.10 cmH2O/mL/s.kg. Under the same conditions, the mean Est and deltaE were: 1.04 and 0.12 cmH2O/mL/kg. With increasing VI and under constant VT, deltaR decreased (p < 0.001) progressively. Rint also decreased paradoxically (p < 0.001). Hence, Rrs decreased (p < 0.001) with increasing VI. Est decreased (p < 0.001) with increasing VI, whereas delta E increased (p < 0.005). With increasing VT and under constant VI, Rint decreased (p < 0.001) and deltaR tended to increase (p = 0.058); Rrs did not change. With increasing VT under constant VI, both Est and deltaE decreased (p < 0.001 and p = 0.001, respectively). Thus, in contrast to the findings in adults, Rint and Est decreased in children with increasing flow and under constant tidal volume, probably reflecting decreased functional residual capacity in anesthetized children, compared with adults. The flow and volume dependence of deltaR and deltaE were similar to those in adults, whereas Rrs did not necessarily follow the direction of changes of deltaR.

Airway Resistance↗