Biomedical subjects

J Milic-Emili

Publications and source records attributed to J Milic-Emili.

At least 73 records · Page 4Linked to original sources

PubMed1996

Mean airway pressure as an index of mean alveolar pressure.

Mean airway pressure (Pao) has been advocated as a useful index for monitoring hemodynamic performance and risk for barotrauma during mechanical ventilation. This is based on the assumption that Pao closely reflects mean alveolar pressure (Palv). In the present study we have compared Pao with Palv in 12 sedated, paralyzed, mechanically ventilated patients. External PEEP ranged from 0.3 to 8.9 cm H2O. Palv was estimated by measuring Pao after rapid flow interruptions made at different points in time of the breathing cycle, using a modification of the method of Fuhrman and coworkers (4). All subjects exhibited intrinsic PEEP (PEEPi), which ranged from 0.5 to 9.4 cm H2O. A significant negative correlation (p < 0.001) was found between Pao/Palv and PEEPi. On average, at PEEPi of 10 cm H2O, Pao underestimated Palv by about 50%. We conclude that Pao cannot be taken as an index of Palv in patients who exhibit dynamic hyperinflation and PEEPi caused by expiratory flow limitation.

Adult↗

PubMed1996

Effects of bronchomotor tone and gas density on time dependence of forced expiratory vital capacity maneuver.

It has been shown that in normal subjects and chronic obstructive pulmonary disease (COPD) patients the maximal expiratory flows and FEV1 are significantly higher if the FVC maneuver is preceded by a rapid inspiration without an end-inspiratory pause (maneuver 1) compared with a slow inspiration with an end-inspiratory pause of approximately 5 s (maneuver 2). This time dependency of FVC was attributed primarily to loss of lung recoil (stress relaxation) during breath-holding at TLC, in association with time constant inequality within the lungs, and changes in bronchomotor tone. To examine the role of bronchomotor tone on time dependency of FVC, 11 COPD and 10 asthmatic patients performed FVC maneuvers 1 and 2 before and after administration of a bronchodilator drug (salbutamol). In addition, using the same approach, the effects of changing airway resistance per se were assessed in another group of 10 COPD patients and 10 normal subjects, while breathing air and after equilibration with 80% helium in oxygen. Main findings were: peak expiratory flow (PEF), FEV1, and maximal midexpiratory flow rate (MMF) were significantly larger with maneuver 1 than 2; after salbutamol administration and during helium-oxygen breathing, all indices increased significantly with both maneuvers but the relative differences between maneuvers 1 and 2 were unchanged. We conclude that time dependency of maximal expiratory flow-volume (MEFV) curves, as indexed by PEF, FEV1, and MMF, is largely independent of bronchomotor tone and gas density, and probably reflects mainly stress relaxation of the respiratory tissues. The relevance of time dependency of FVC maneuver in the assessment of bronchodilator response and density dependence is discussed.

Adult↗

PubMed1996

Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease.

The purpose of this study was to assess whether expiratory flow limitation (FL), as measured by applying negative pressure at the mouth during tidal expiration, is a better predictor of dyspnea than routine spirometry measurements. The study population consisted of 117 ambulatory patients with COPD. Dyspnea was assessed according to the ATS-DLD respiratory Questionnaire. Expiratory flow limitation was measured in supine and sitting positions, and expressed as a percentage of the expired control tidal volume affected by flow limitation (FL, % VT). Using Spearman's rank correlation (rs), we found that the correlation of dyspnea scale with FL was stronger (rs > 0.5) than with FVC (rs < -0.3) or FEV1 (rs < -0.4) in both positions. In a multiple regression analysis FL remained the best predictor of dyspnea scale even after adjustment for FEV1 (% pred). Finally, FL was almost as sensitive as FEV1 (% pred) but much more specific in assessing the severity of dyspnea scale. These findings suggest that expiratory flow limitation as measured by the negative expiratory pressure technique may be more useful in the evaluation of dyspnea in patients with COPD than spirometry measurements.

Aged↗

PubMed1996

Effect of pattern of preceding inspiration on FEV1 in asthmatic children.

In adults, both peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) are significantly influenced by the time course of the inspiration preceding the forced expiration. The aim of this study was to evaluate the effects of three different inspiratory manoeuvres on PEF, FEV1, and forced vital capacity (FVC) in asthmatic children. Twenty five symptomless asthmatic children performed forced expiration preceded by three different inspiratory manoeuvres, which consisted of: a rapid inspiration with a 2 s end-inspiratory breathhold (Manoeuvre No. 1); a rapid inspiration without an end-inspiratory breathhold (Manoeuvre No. 2); and a slow inspiration lasting about 5 s with an end-inspiratory breathhold of at least 4 s (Manoeuvre No. 3). All manoeuvres were performed in a randomly assigned sequence each morning for three consecutive days. In each session, the manoeuvres were repeated three times and the highest value was chosen. Both FVC and FEV1 obtained with Manoeuvre No. 3 were significantly lower than the corresponding values obtained with Manoeuvre Nos. 1 and 2. The mean (SD) FVC values were 2.76 (0.66) L with Manoeuvre No. 1, 2.67 (0.58) L with Manoeuvre No. 2 and 2.52 (0.52) L with Manoeuvre No. 3. The corresponding values of FEV1 were 2.25 (0.53), 2.22 (0.53) and 2.07 (0.44) L, respectively. By contrast, the values of PEF, obtained with a portable peak flow meter, were similar with the three different inspiratory manoeuvres. The results of this study show that in symptomless asthmatic children the preceding inspiratory manoeuvre may influence forced vital capacity and forced expiratory volume in one second. Hence, in order to reduce variability due to interference by physiological factors and so improve reproducibility of pulmonary function tests, the inspiratory manoeuvres must be accurately standardized.

Asthma↗

PubMed1996

Effect of different inspiratory maneuvers on FEV1 in patients with cystic fibrosis.

The time course of inspiration has been shown to have a significant influence on the subsequent maximal expiratory flows and timed forced expiratory volumes in healthy adults and those with COPD. The purpose of this study was to evaluate the effect of two different inspiratory maneuvers on the spirogram in 15 patients with cystic fibrosis, aged 13 to 35 years, who had mild to moderate airway obstruction. Patients performed a forced expiratory maneuver either after a rapid inspiration without an end-inspiratory pause or after a slow inspiration with a 4-s end-inspiratory pause. Flow-time and volume-time curves were measured by a pneumotachograph. The mean values of FVC, FEV1, and peak expiratory flow were significantly larger by 11%, 13%, and 26%, respectively, after the rapid inspiration without an end-inspiratory pause compared to the slow inspiration with the end-inspiratory pause. This discrepancy probably reflects differences in effective elastic recoil pressure between the two maneuvers. Although the nature of this phenomenon is not fully understood, our results show that for spirometry in patients with cystic fibrosis, the preceding inspiratory maneuver influences the results. An important corollary is that this inspiratory maneuver should be standardized.

Adolescent↗

PubMed1995

Carbon dioxide responsiveness in COPD patients with and without chronic hypercapnia.

To ascertain whether and to what extent the reduced ventilatory response to a hypercapnic stimulus in chronic obstructive pulmonary disease (COPD) patients depends on a blunted chemoresponsiveness of central origin or to mechanical impairment, we studied two groups of COPD patients without (group A) and with (group B) chronic hypercapnia, but with similar degrees of airway obstruction and hyperinflation. The study was performed on 17 patients (9 normocapnic and 8 hypercapnic). Six age-matched normal subjects (group C) were also studied as a control. During a CO2 rebreathing test, ventilation (VE), mouth occlusion pressure (P0.1), and the electromyographic activity of diaphragm (Edi) were recorded and then plotted against end-tidal carbon dioxide tension (PCO2). Inspiratory muscle strength was significantly lower in the hypercapnic group (group B) compared to normocapnic group (A), and in these groups compared to the control group (C). Both patient groups exhibited significantly lower delta VE/delta PCO2 than the control group. In hypercapnics, delta P0.1/delta PCO2 was significantly lower than in normocapnics and control group, whilst mouth occlusion pressure as % of maximal inspiratory pressure delta P0.1 (% MIP)/delta PCO2 did not differ significantly among the three groups. delta Edi/delta PCO2 increased from C to A. At a PCO2 of 8.65 kPa, VE was similar in the normocapnic and control group, but lower in hypercapnics; Edi was similar in hypercapnic and control group; but greater in normocapnics. P0.1(% MIP) did not differ significantly among groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1995

A simple method to detect expiratory flow limitation during spontaneous breathing.

Patients with severe chronic obstructive pulmonary disease (COPD) often exhale along the same flow-volume curve during quiet breathing as during a forced expiratory vital capacity manoeuvre, and this has been taken as indicating flow limitation at rest. To obtain such curves, a body plethysmograph and the patient's co-operation are required. We propose a simple technique which does not entail these requirements. It consists in applying negative pressure at the mouth during a tidal expiration (NEP). Patients in whom NEP elicits an increase in flow throughout the expiration are not flow-limited. In contrast, patients in whom application of NEP does not elicit an increase in flow during most or part of the tidal expiration are considered as flow-limited. Using this technique, 26 stable COPD patients were studied sitting and supine. Eleven patients were flow-limited both seated and supine, eight were flow-limited only when supine, and seven were not flow-limited either seated or supine. Only 5 of 19 patients who were flow-limited seated and/or supine had severe ventilatory impairment (forced expiratory volume in one second (FEV1) < 40% predicted). We conclude that the NEP technique provides a simple, rapid, and reliable method for detection of expiratory flow limitation in spontaneously breathing subjects, which does not require the patient's co-operation, and can be applied in different body positions both at rest and during muscular exercise. Our results also indicate a high prevalence of flow limitation in COPD patients at rest, particularly when supine.

Aged↗

PubMed1994

Chest wall interrupter resistance in anesthetized paralyzed humans.

Tracheal (Ptr) and esophageal (Pes) pressure and flow were measured in 12 supine anesthetized paralyzed normal subjects aged 16-22 yr. The subjects were ventilated with a fixed inflation volume (range 0.57-0.62 liter) and with different constant flows ranging between 0.24 and 1.12 l/s. A rapid airway shutter (closing time 10-15 ms) was used to briefly occlude (0.4-0.9) the airways at end inspiration for 33-44 consecutive breaths. At each flow level, Ptr and Pes records obtained during end-inspiratory occlusions were ensemble averaged to allow for the cardiac artifacts. The interrupter resistances of the chest wall and respiratory system were assessed as the rapid fall in Pes and Ptr with occlusion divided by the flow preceding the occlusion. Interrupter resistances of both the chest wall and lung were independent of flow and averaged 0.4 +/- 0.1 and 1.5 +/- 0.4 (SD) cmH2O.s.l-1, respectively. The contribution of the chest wall to the total interrupter resistance was approximately 27% at flows < or = 1 l/s.

Adolescent↗

PubMed1994

Volume-pressure curve of the respiratory system predicts effects of PEEP in ARDS: "occlusion" versus "constant flow" technique.

The effects of positive end-expiratory pressure (PEEP) on static ("rapid airway occlusion" technique) and dynamic ("constant flow" technique) volume-pressure (V-P) curves were studied in 19 patients with adult respiratory distress syndrome (ARDS). To describe the shape of both curves, the nonlinear coefficient of a second-order polynomial equation fitted to the static (static nonlinear coefficient) and dynamic (dynamic nonlinear coefficient) V-P curves on zero end-expiratory pressure (ZEEP) was used. Two distinct patterns were observed: (1) in ten patients, the static and dynamic V-P curves on ZEEP exhibited a convex shape with a progressive decrease in slope with increasing inflation volume (nonlinear coefficients: negative). In these patients PEEP induced a volume displacement along the static and dynamic V-P curves on ZEEP (hyperinflation). (2) In nine patients, the static and dynamic V-P curves on ZEEP showed a concave shape with a progressive increase in slope with increasing volume (nonlinear coefficients: positive) and PEEP shifted both curves upward along the volume axis (alveolar recruitment). A correlation (p < 0.0001) between static and dynamic nonlinear coefficients was found at all levels of PEEP. Both static and dynamic nonlinear coefficients on ZEEP were correlated (p < 0.0001) with the amount of lung volume recruited with PEEP, and the variations of cardiac index (CI), O2 delivery (DO2), right-to-left venous admixture (Qs/Qt), and PaO2 with PEEP. Besides, the effects of PEEP on Cl, DO2, Qs/Qt, and PaO2 were less pronounced (p < 0.001) in patients with convex V-P curves than in patients with concave V-P curves.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1994

Detection of expiratory flow limitation during mechanical ventilation.

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.

Aged↗

PubMed1994

Dependence of maximal flow-volume curves on time course of preceding inspiration in patients with chronic obstruction pulmonary disease.

Thirteen patients with chronic obstructive pulmonary disease (COPD) performed forced vital capacity (FVC) maneuvers either immediately after a rapid inspiration (maneuver 1) or after a slow inspiration with a 4- to 6-s end-inspiratory pause (maneuver 2). Seated in a body plethysmograph, they breathed through a pneumotachograph. Inspirations were initiated from resting end-expiratory lung volume. Abdominal muscle activity was recorded by means of surface electrodes. With maneuver 1: (1) expiratory flows were 20 to 40% larger in the volume range 10 to 95% FVC; (2) peak expiratory flow was on average 30% higher; and (3) FEV1, expressed as percent of FVC, increased by about 8%. No substantial differences in the pattern of abdominal muscle activity occurred between maneuvers. The dependence of maximal flow-volume curves on the time course of the preceding inspiration is probably related in part to the viscoelastic elements present within the respiratory system, which, stretched during rapid inspirations, increase the effective elastic recoil during the FVC maneuver 1. This cannot occur with maneuver 2, because of stress relaxation of the viscoelastic elements during the 4- to 6-s breathhold preceding the FVC maneuver. Other factors (e.g., time constant inequality) might also be involved. In any case, the results imply that the inspiratory maneuver prior to FVC must be standardized.

Abdominal Muscles↗

PubMed1993

Flow resistance in mechanically ventilated patients with severe neurological injury.

In 5 mechanically ventilated patients with severe neurological injury (SNI), we measured the respiratory system's flow resistance (Rrs) over a range of inspiratory flows between 0.2 to 2 L/s, at inflation volumes (delta V) ranging from 0.1 to 1 L. Under baseline ventilatory conditions (V = 1 L/s; delta V = 0.95 L), we also partitioned Rrs into airway resistance (Raw) and the additional resistance offered by the tissues of the lung and chest wall (delta Rrs). At all inflation volumes, Rrs decreased hyperbolically with increasing flow but was higher than in normal anesthetized paralyzed subjects (N). At V of 1 L/s and delta V of 0.5 L, Rrs was significantly greater in SNI than in N (7.7 +/- 1.5 v 4.2 +/- 0.5 cm H2O/L/s; P < .01). This discrepancy was due to higher Raw in SNI. Indeed, at V of 1 L/s, Raw (mean +/- SEM) was significantly higher in SNI than in N (4.0 +/- 0.9 v 2.4 +/- 0.2 cm H2O/L/s; P < .001), whereas delta Rrs did not differ significantly. The increased Raw in SNI was due to the fact that these patients were therapeutically hyperventilated (PaCO2 = 30.4 +/- 4.2 mm Hg) and as a result their airways were bronchoconstricted. We conclude that in the intensive care unit setting, hyperventilated patients with severe neurological injury can not be considered to be adequate controls in terms of Rrs and Raw, because hypocapnia induces an increase of Raw and consequently also in Rrs (= Raw+delta Rrs).

Adult↗

PubMed1993

Does alveolar recruitment occur with positive end-expiratory pressure in adult respiratory distress syndrome patients?

We studied the effects of positive end-expiratory pressure (PEEP) (2 to 14 cm H2O) on alveolar recruitment (Vrec), static respiratory compliance, and end-expiratory lung volume (EELV) in nine sedated, paralyzed, mechanically ventilated adult respiratory distress syndrome patients. Positive end-expiratory pressure was applied in increasing and decreasing steps of 2 cm H2O. Flow, tidal volume, and airway pressure were measured. We used the rapid airway occlusion technique to determine static end-inspiratory elastic recoil pressure of the respiratory system (Pst, rs) and intrinsic PEEP (PEEPi). The changes in EELV were measured with respiratory inductive plethysmography. Alveolar recruitment was estimated as the difference in lung volume between PEEP and zero end-expiratory pressure (ZEEP) for the same end-inspiratory Pst, rs (20 cm H2O). We found that (1) Vrec with PEEP up to 14 cm H2O was in general rather small and was absent in two patients; (2) all patients exhibited PEEPi at ZEEP (5.6 +/- 1.0 cm H2O) and little change in EELV and Vrec was achieved until the external PEEP exceeded PEEPi; (3) if end-inspiratory Pst, rs is high at ZEEP, there is little or no alveolar recruitment with PEEP; and (4) Vrec and EELV were slightly higher during stepwise deflation than stepwise inflation with PEEP, except at ZEEP where EELV did not change after inflation-deflation runs with PEEP.

Adult↗

PubMed1993

Oxygen delivery-consumption relationship in adult respiratory distress syndrome patients: the effects of sepsis.

The oxygen consumption-delivery relationship (VO2/DO2) was studied in 15 sedated paralyzed patients with the adult respiratory distress syndrome (ARDS) due to multiple trauma and in whom sepsis was absent. Different levels (0 to 15 cm H2O) of positive end-expiratory pressure (PEEP) were applied. Oxygen delivery was calculated from cardiac index (thermodilution technique) and arterial oxygen content measurements. Oxygen consumption was calculated using Fick's equation. Regression lines were obtained for each patient. Oxygen supply dependency was defined as a significant (P < .05) relationship between changes in VO2 and DO2 with PEEP. Results were compared with those obtained in 18 ARDS patients in whom ARDS was due to sepsis. In nonseptic ARDS patients no significant relationship between changes in VO2 and DO2 with PEEP was found within the experimental range of DO2 on zero end-expiratory pressure (ZEEP) (347 to 845 mL/min/m2). None of these patients had multiple organ system failure (MOSF), and 73% survived. In ARDS patients in whom sepsis was present, supply dependency was present only when DO2 on ZEEP ranged between 330 and 640 mL/min/m2. All these patients developed MOSF and died. When DO2 on ZEEP ranged between 686 and 951 mL/min/m2 in septic ARDS patients, the supply dependency phenomenon was absent and only three patients developed MOSF and died (70% survivors). In almost all patients PEEP reduced DO2 and therefore worsened O2 balance by either increasing O2 extraction ratio and approaching the critical threshold for supply dependency or dismissing DO2 from the range of non-supply dependency.

Adult↗

PubMed1993

Lung and chest wall mechanics in mechanically ventilated COPD patients.

By use of the technique of rapid airway occlusion, the effects of inspiratory flow, volume, and time on lung and chest wall mechanics were investigated in 10 chronic obstructive pulmonary disease (COPD) patients mechanically ventilated for acute respiratory failure. We measured the interrupter resistance (Rint), which in humans reflects airway resistance; the additional resistances due to time constant inequality and viscoelastic pressure dissipations within the lungs (delta RL) and the chest wall; and the static and dynamic elastances of lung and chest wall. We observed that 1) static elastances of lung and chest wall in COPD patients were similar to those of normal subjects; 2) Rint of the lung was markedly increased and flow dependent in COPD patients, whereas Rint of the chest wall was negligible as in normal subjects; and 3) in COPD patients, delta RL was markedly increased at all inflation flows and volumes, reflecting increased time constant inequalities within the lungs and/or altered viscoelastic behavior. The results imply increased dynamic work due to Rint and delta RL and marked time dependency of pulmonary resistance and elastance in COPD patients.

Aged↗

PubMed1993

Dependence of maximal flow-volume curves on time course of preceding inspiration.

Thirteen normal subjects, sitting in a body plethysmograph and breathing through a pneumotachograph, performed forced vital capacity maneuvers after a rapid inspiration without or with an end-inspiratory pause (maneuvers 1 and 2) and after a slow inspiration without or with an end-inspiratory pause (maneuvers 3 and 4), the pause lasting 4-6 s. Inspirations were initiated close to functional residual capacity. At all lung volumes, expiratory flow was larger with maneuver 1 than with any other maneuver and, over the upper volume range, larger with maneuver 3 than with maneuver 4, whereas it was similar for maneuvers 2 and 4. Relative to corresponding values with maneuver 4, peak expiratory flow was approximately 16 and approximately 4% larger with maneuvers 1 and 3, respectively, whereas forced expiratory volume in 1 s increased by approximately 5% only with maneuver 1. The time dependence of maximal flow-volume curves is consistent with the presence of viscoelastic elements within the respiratory system (D'Angelo et al. J. Appl. Physiol. 70: 2602-2610, 1991).

Adult↗

PubMed1993

Partitioning of work of breathing in mechanically ventilated COPD patients.

In 10 sedated paralyzed mechanically ventilated chronic obstructive pulmonary disease (COPD) patients, we measured the inspiratory mechanical work done per breath on the respiratory system (WI,rs). We measured the tracheal and esophageal pressures to assess the lung (L) and chest wall (W) components of WI and used the technique of rapid airway occlusion during constant-flow inflation to partition WI into static work [Wst, including work due to intrinsic positive end-expiratory pressure (WPEEPi)], dynamic work due to airway resistance, and the additional resistance offered by the respiratory tissues. Although the patients were hyperinflated, the slope of the static volume-pressure relationships of the lung did not decrease with inflation volume up to 0.8 liter. WI,W was similar in COPD patients and normal subjects. All components of WI,L were higher in COPD patients. The increase in Wst,rs was due entirely to WPEEPi. Our data suggest that, during spontaneous breathing, COPD patients would probably develop inspiratory muscle fatigue, unless continuous positive airway pressure were applied to reduce WPEEPi.

Acute Disease↗

PubMed1993

Modelling of passive expiration in patients with adult respiratory distress syndrome.

The time-course of volume change during passive expiration preceded by an end-inspiratory hold was studied with a biexponential model in six adult respiratory distress syndrome (ARDS) patients. We measured the initial volumes and time constants of the fast (tau 1), and the slow (tau 2) compartments of expiration, as well as the static elastance of the respiratory system. The results were compared to those of 11 normal subjects. We observed that: 1) the biexponential model fitted closely the volume decay; 2) the fast compartment was responsible for 81 +/- 7% (ARDS) versus 84 +/- 10% (controls) of the total volume exhaled, with tau 1 = 0.35 +/- 0.11 s (ARDS) versus 0.50 +/- 0.22 s (controls); 3) the slow compartment contributed only 19 +/- 6% (ARDS) versus 16 +/- 7% (controls), with tau 2 = 4.67 +/- 2.38 s (ARDS) versus 3.27 +/- 1.54 s (controls); and 4) static elastance was higher in ARDS patients. The findings could be explained in terms of a four parameter viscoelastic model of the respiratory system.

Adolescent↗