Search PubMed⌕ Search

Biomedical subjects

J Milic-Emili

Publications and source records attributed to J Milic-Emili.

At least 127 records · Page 7Linked to original sources
PubMed1989

Flow and volume dependence of expiratory resistance in anesthetized cats.

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36-48 ml, the isovolume pressure-flow relationships of the lung and respiratory system were studied. The expiratory pressure was altered between 3 and -12 cmH2O for single tidal expirations. Isovolume pressure-flow plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear in all cases, fitting Rohrer's equation: P = K1V + K2V2, where P is the resistive pressure loss, K1 and K2 are Rohrer's coefficients, and V is flow. Values of K1 and K2 declined with lung inflation, consistent with the volume dependence of pulmonary (RL) and respiratory system resistances (Rrs). During lung deflation against atmospheric pressure, RL and Rrs tended to remain constant through most of expiration, resulting in a nearly linear volume-flow relationship. In the presence of a fixed respiratory system elastance, the shape of the volume-flow profile depended on the balance between the volume and the flow dependence of RL and Rrs. However, the flow dependence of RL and Rrs indicates that their measured values will be affected by all factors that modify expiratory flow, e.g., respiratory system elastance, equipment resistance, and the presence of respiratory muscle activity.

Airway Resistance↗
PubMed1989

Submaximal exercise in emphysema and malnutrition at two levels of carbohydrate and fat intake.

Eight malnourished patients with emphysema (EMPH) and eight malnourished patients without evidence of lung disease (MLAN) received an infusion of 5% dextrose plus electrolytes (D5W) for 48 h and were then randomly assigned to a hypercaloric diet with either 53% of the calories as carbohydrate (CB) or with 55% as fat (FB) for the 1st wk, maintaining a constant protein intake. The alternate diet was given the following week. Ventilation and gas exchange were measured during supine cycle ergometry at 0, 12, and 25 W during the D5W, CB, and FB diet periods. At each exercise intensity, the EMPH group demonstrated a 12-15% greater O2 consumption, a lower respiratory quotient, and an O2 debt larger than that of the MALN group. Resting ventilation was higher during the CB than FB regimen in both groups of patients, but during the CB diet the EMPH group had a more exaggerated ventilatory response than the MALN group. The results demonstrate that EMPH patients have an unusual metabolic pattern during hypercaloric feeding and exercise. Furthermore in EMPH patients a FB regimen does not appear to create the additional stress on the respiratory system during exercise that is generated with a CB regimen.

Adult↗
PubMed1989

Viscoelastic behavior of lung and chest wall in dogs determined by flow interruption.

Pulmonary and chest wall mechanics were studied in six anesthetized paralyzed dogs, by use of the technique of rapid airway occlusion during constant flow inflation. Analysis of the pressure changes after flow interruption allowed us to partition the overall resistance of the lung (Rl) and chest wall (Rw) and total respiratory system (Rrs) into two components, one (Rinit) reflecting in the lung airway resistance (Raw), the other (delta R) reflecting primarily the viscoelastic properties of the pulmonary and chest wall tissues. The effects of varying inspiratory flow and inflation volume were interpreted in terms of frequency dependence of resistance, by using a spring-and-dashpot model previously proposed and substantiated by Bates et al. (Proc. 9th Annu. Conf. IEEE Med. Biol. Soc., 1987, vol. 3, p. 1802-1803). We observed that 1) Raw and Rw,init were nearly equal and small relative to Rl and Rw (both were unaffected by flow); 2) Rrs,init decreased slightly with increasing volume; 3) both delta Rl and delta Rw decreased with increasing flow and increased with increasing lung volume. These changes were manifestations of frequency dependence of delta R, as it is predicted by the model; 4) Rrs, Rl, and Rw followed the same trends as delta R. These results corroborate data previously reported in the literature with the use of different techniques to measure airways and pulmonary tissue resistances and confirm that the use of Rl to assess bronchial reactivity is problematic. The interrupter techniques provides a convenient way to obtain Raw values, as well as analogs of lung and chest wall tissue resistances in intact dogs.

Airway Resistance↗
PubMed1989

Respiratory mechanics in anesthetized paralyzed humans: effects of flow, volume, and time.

The effects of inspiratory flow rate and inflation volume on the resistive properties of the total respiratory system were investigated in 16 anesthetized paralyzed humans by using the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rmin,rs) and of the effective additional resistance (delta Rrs) as the result of viscoelastic pressure dissipations within the pulmonary and chest wall tissues. We observed that 1) at fixed inflation volume, Rmin,rs increased linearly with increasing flow although delta Rrs decreased according to an exponential function; 2) at fixed inflation flow, Rmin,rs decreased with increasing inflation volume although there was a concomitant increase in delta Rrs. This behavior could be explained in terms of a spring-and-dashpot model incorporating 1) the standard resistance and elastance and 2) a spring-and-dashpot in parallel with standard elastance, reflecting the stress adaptation units within the thoracic tissues.

Adolescent↗
PubMed1989

Comparison of the constant flow and occlusion methods for assessment of bronchoconstriction in guinea-pigs.

Assessments of total respiratory compliance (C) and conductance (G) with the constant inspiratory flow and the occlusion methods were compared in the basal state and during histamine or serotonin induced bronchoconstriction in 22 normal, anaesthetized, paralysed, mechanically ventilated guinea-pigs. In the basal state, no significant difference was found between the C and G values measured by both methods. During drug-induced bronchoconstriction, small but significant differences were observed between the respiratory parameters measured by the two methods, and expressed as the percentage ratio (R) to the corresponding basal values (respectively RCCF and RCOC, and RGCF and RGOC). This discrepancy, which was independent of the drug and of the dose, was probably attributable to a modification of the visco elastic properties of the lung due to either the mechanical ventilation or the infused drug. Nevertheless, this study demonstrates that both methods can be considered as equivalent for bronchoconstriction assessment because very strong correlations were found between RCCF and RCOC (r = 0.96, p less than 0.001) and between RGCF and RGOC (r = 0.97, p less than 0.001), and because the slopes of the linear relationships were not significantly different from unity in both cases.

Animals↗
PubMed1988

Inspiratory effort and occlusion pressure in triggered mechanical ventilation.

We have studied eleven patients ventilated in the assisted mode during recovery from acute respiratory failure. We have measured the effort required to trigger the pressure demand valve for 3 different ventilators, and have measured the occlusion pressure as an index of neuromuscular inspiratory drive. We found a delay in the opening of the demand valve, as previously described by other authors. We also found a close correlation between the effort required to open the demand valve and the occlusion pressure. We conclude that the inspiratory effort required to open the demand valve, in the assist mode, is greater than the preset trigger level and that it is well correlated with the neuromuscular inspiratory drive. This inspiratory effort against the closed demand valve, allows the measurement of the occlusion pressure.

Aged↗
PubMed1988

Respiratory compliance and resistance in mechanically ventilated patients with acute respiratory failure.

The purpose of this study was noninvasive assessment of respiratory compliance and resistance in mechanically ventilated patients with acute respiratory failure (ARF). To this end, flow, change in lung volume, and airway pressure were measured at the proximal tip of the endotracheal tubes in twenty nine critically ill unselected patients. Eleven had acute exacerbation of chronic obstructive pulmonary disease (COPD), 8 had adult respiratory distress syndrome (ARDS) and 10 had ARF of various etiologies. Static compliance (Cst,rs), 'intrinsic' PEEP (PEEPi), as well as minimum and maximum resistance (Rrs,min and Rrs,max, respectively) were obtained with end-inspiratory and end-expiratory airway occlusions. We found that: (1) PEEPi was present in all patients with COPD (up to 11.4 cmH2O) and it was not uncommon in patients with ARF without history of chronic airway disease (up to 4.1 cmH2O). (2) Without correction for PEEPi average Cst,rs was not significantly different between ARDS and COPD patients, whereas the average corrected compliance was significantly lower in ARDS patients. (3) Substantial frequency-dependence of resistance was exhibited not only by COPD patients, but also by ARDS patients.

Adult↗
PubMed1988

Changes in respiratory control induced by amino acid infusions.

We compared the metabolic and respiratory responses to a 4-h infusion of an amino acid solution consisting primarily of branched-chain amino acids (BCAA) to those after a standard amino acid solution in healthy subjects. Both the BCAA solution and the standard amino acid solution increased minute ventilation (mean increase 22%, p less than .001, and 18%, p less than .01, respectively), mean inspiratory flow (19%, p less than .01, and 19%, p less than .05) and oxygen consumption (9%, p less than .02, and 5%, NS). PaCO2 decreased (mean decrease 6%, p less than .01); there was a major increase in the ventilatory response to CO2 inhalation during administration of the BCAA solution but not the standard amino acid solution. Increased plasma norepinephrine concentration (mean increase 75%, p less than .001) during the infusion of the standard amino acid solution but not the BCAA solution suggested increased sympathetic activity. The results demonstrate augmented respiratory effects of amino acid infusions by BCAA enrichment, and a dissociation between the respiratory stimulation, metabolic rate, and sympathetic activity.

Adult↗
PubMed1988

Effect of body posture on respiratory impedance.

The effects of posture on the mechanics of the respiratory system are not well known, particularly in terms of total respiratory resistance. We have measured respiratory impedance (Zrs) by the forced random noise excitation technique in the sitting and the supine position in 24 healthy subjects. Spirometry and lung volumes (He-dilution technique) were also measured in both postures. The equivalent resistance (Rrs), compliance (Crs), and inertance (Irs) were also calculated by fitting each measured Zrs to a linear series model. When subjects changed from sitting to the supine position, the real part of Zrs increased over the whole frequency band. The associated equivalent resistance, Rrs, increased by 28.2%. The reactance decreased for frequencies lower than 18 Hz and increased for higher frequencies. Consequently, Crs decreased by 38.7% and Irs increased by 15.6%. All of these parameter differences were significant (P less than 0.001). A covariance analysis showed that a significant amount of the postural change in Rrs and Crs can be explained by the reduction of functional residual capacity (FRC). This indicates that the observed differences on Zrs can in part be explained be a shift of the operating point of the respiratory system induced by the decrease in the FRC.

Adult↗
PubMed1988

Breathing patterns in anesthetized cats and the concept of minimum respiratory effort.

Theoretical studies dealing with the principle of minimal respiratory effort usually make use of sinusoidal or saw-tooth-like breathing patterns. Recent observations in anesthetized cats have shown that the driving pressure waveform for inspiration can be described by a power function of time and that most of expiration is passive. This driving pressure waveform, however, results in breathing patterns that differ from those described above. For this reason, we have reevaluated in anesthetized cats the principle of minimal respiratory effort by computing optimal duration of inspiration (TI) and optimal tidal volume (VT) for different ventilatory conditions using actual driving pressure waveforms. The results are in qualitative agreement with the experimental observations; i.e., optimal TI decreases and optimal VT increases with increasing minute ventilation. On the average, a good agreement is found between measured and computed values of TI. In some cats, however, there are substantial differences between observed and predicted values of TI, which can probably be ascribed to inaccuracies in the data used in our computations. Despite its limitations, the present model analysis is more realistic than previous ones because actual driving pressure waveforms are used together with actual values of effective inspiratory impedance.

Anesthesia↗
PubMed1988

Effect of lung volume on interrupter resistance in cats challenged with methacholine.

To examine the effects of changes in lung volume on the magnitude of maximal bronchoconstriction, seven anesthetized, paralyzed, tracheostomized cats were challenged with aerosolized methacholine (MCh) and respiratory system resistance (Rss) was measured at different lung volumes using the interrupter technique. Analysis of the pressure changes following end-inspiratory interruptions allowed us to partition Rss into two quantities with the units of resistance, one (Rinit) corresponding to the resistance of the airways and the other (Rdif) reflecting the viscoelastic properties of the tissues of the respiratory system as well as gas redistribution following interruption of flow. Rinit and Rdif were used to construct concentration-response curves to MCh. Lung volume was increased by the application of 5, 10, and 15 cmH2O of positive end-expiratory pressure. The curve for Rinit reached a plateau in all cats, demonstrating a limit to the degree of MCh-induced bronchoconstriction. The mean value of Rinit (cmH2O.ml-1.s) for the group under control conditions was 0.011 and rose to 0.058 after maximal bronchoconstriction; the volume at which the flow was interrupted was 11.5 +/- 0.5 (SE) ml/kg above functional residual capacity (FRC). It then fell progressively to 0.029 at 21.2 +/- 0.8 ml/kg above FRC, 0.007 at 35.9 +/- 1.3 ml/kg above FRC, and 0.005 at 52.0 +/- 1.8 ml/kg above FRC. Cutting either the sympathetic or parasympathetic branches of the vagi had no significant effect on the lung volume-induced changes in MCh-induced bronchoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1988

Flow and volume dependence of pulmonary mechanics in anesthetized cats.

The effects of inspiratory flow rate and inflation volume on pulmonary mechanics were investigated in six anesthetized-paralyzed cats ventilated by constant-flow inflation. Pulmonary mechanics were assessed using the technique of rapid airway occlusion during constant-flow inflation which allows measurement of the intrinsic pulmonary resistance (RLmin) and of the overall "pulmonary flow resistance" (RLmax), which includes the additional pulmonary pressure losses due to time constant inequalities within the lung and/or stress adaptation. We observed that, at fixed inflation volume, 1) RLmin fitted Rohrer's equation, 2) RLmax was higher at low than intermediate flows, and 3) RLmax-RLmin decreased progressively with increasing flow. At fixed flow, RLmax increased, whereas RLmin decreased with increasing volume. We conclude that during eupneic breathing in cats, the pulmonary flow resistance as conventionally measured includes a significant component reflecting stress adaptation.

Airway Resistance↗
PubMed1988

A theoretical analysis of interrupter technique for measuring respiratory mechanics.

The application of the flow interrupter technique to series and parallel models of the respiratory system is examined theoretically, assuming instantaneous transmission of pressures and incompressible gases in the lung air spaces. The initial pressure change observed immediately after occlusion divided by the preocclusion flow gives an initial resistance (Rinit) equal to that of the airway tree when the model consists of compartments connected in parallel. When the compartments are connected in series, Rinit is the resistance of the most proximal airway only. In general, the initial pressure change is followed by a second slower change, reflecting equilibration of pressures between the compartments. The total postocclusion pressure change divided by the flow gives a steady-state resistance (Rss) whose value depends on the ventilation history before occlusion. When this history consists of a relaxed expiration Rss asymptotes from Rinit to a value higher than the zero-frequency resistance of the model as the expiratory time increases. However, the relative contributions of serial and parallel pendelluft and viscoelasticity to Rss cannot be determined from pressure and flow measurements made at the airway opening. Therefore in disease, the interrupter method does not permit one to say whether ventilation inhomogeneity or alteration in lung tissue properties is the predominant abnormality.

Airway Resistance↗
PubMed1988

Chest wall and respiratory system mechanics in cats: effects of flow and volume.

The effects of inspiratory flow rate and inflation volume on the resistive properties of the chest wall were investigated in six anesthetized paralyzed cats by use of the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rw,min) and overall dynamic inspiratory impedance (Rw,max), which includes the additional pressure losses due to time constant inequalities within the chest wall tissues and/or stress adaptation. These results, together with our previous data pertaining to the lung (Kochi et al., J. Appl. Physiol. 64: 441-450, 1988), allowed us to determine Rmin and Rmax of the total respiratory system (rs). We observed that 1) Rw,max and Rrs,max exhibited marked frequency dependence; 2) Rw,min was independent of flow (V) and inspired volume (delta V), whereas Rrs,min increased linearly with V and decreased with increasing delta V; 3) Rw,max decreased with increasing V, whereas Rrs,max exhibited a minimum value at a flow rate substantially higher than the resting range of V; 4) both Rw,max and Rrs,max increased with increasing delta V. We conclude that during resting breathing, flow resistance of the chest wall and total respiratory system, as conventionally measured, includes a significant component reflecting time constant inequalities and/or stress adaptation phenomena.

Animals↗
PubMed1988

Respiratory mechanics during the first day of mechanical ventilation in patients with pulmonary edema and chronic airway obstruction.

We investigated the early changes of respiratory mechanics in mechanically ventilated patients with acute respiratory failure (ARF): 8 patients after acute exacerbation of chronic airway obstruction (CAO), 8 patients with cardiogenic pulmonary edema (CPE), and 8 patients with adult respiratory distress syndrome (ARDS). The patients were studied within the first day from the onset of mechanical ventilation. Flow, changes in lung volume, and airway pressure were measured using the 900C Servo Ventilator. End-inspiratory and end-expiratory occlusions of the airway were performed to obtain respiratory compliance and resistance. We found that: (1) acute exacerbation of CAO was characterized by high respiratory resistance (reflecting in part time-constant inequalities within the lung) and severe pulmonary hyperinflation, with "intrinsic" PEEP (PEEPi) up to 22 cm H2O (mean [SD], 13.5 [6.7] cm H2O); (2) PEEPi, even if not high, was present in almost all patients with pulmonary edema, averaging 3.8 and 3.0 cm H2O in ARDS and CPE, respectively; (3) respiratory resistance was increased in patients with CPE and ARDS who had no history of airway disease; (4) patients with ARDS were characterized also by low compliance (mean [SD], 0.035 [0.005] L/cm H2O) and high resistance, the latter also reflecting a substantial component caused by time-constant inequalities; (5) in all 24 patients, static respiratory compliance (and its reciprocal, elastance) was significantly correlated with the pulmonary oxygenation index, i.e., the PaO2/PAO2 ratio. We conclude that early assessment of respiratory mechanics in mechanically ventilated patients with ARF can provide better understanding of the patients' conditions as well as guidelines for therapeutic approach and weaning attempts.

Airway Resistance↗
PubMed1988

Breathing pattern and load compensatory responses in young scoliotic patients.

The breathing pattern and mouth occlusion pressure developed in 0.1 seconds (P0.1) were measured at rest in sixteen young scoliotic patients in whom the blood gases were within the normal limits. The patients exhibited rapid and shallow breathing. P0.1 was increased above normal, indicating a compensatory increase of neuromuscular inspiratory drive in the face of a stiffer respiratory system. P0.1 (% predicted) correlated positively with the angle of scoliosis. Both duration of inspiration and inspiratory duty cycle correlated negatively with angle of scoliosis and P0.1 (% predicted). On theoretical grounds we show that these changes in breathing pattern are beneficial, both in terms of reducing the energy cost of breathing and preventing the development of inspiratory muscle fatigue.

Adolescent↗
PubMed1987

Effect of posture on ventilation and breathing pattern during room air breathing at rest.

We measured minute ventilation (VE), tidal volume (VT), mean inspiratory flow (VT/TI), and occlusion pressure (P.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for VT, VE, VT/TI, P.1, and effective inspiratory impedance [P.1/(VT/Ti)] were observed in the supine posture. Values for P.1 and P.1/(VT/TI in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P.1 and P.1/(VT/TI) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P.1/(VT/TI) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration.

Adult↗