Deflation Compliance Research Articles

Mouse lung mechanical properties under varying inflation volumes and cycling frequencies

Respiratory pathologies alter the structure of the lung and impact its mechanics. Mice are widely used in the study of lung pathologies, but there is a lack of fundamental mechanical measurements assessing the interdependent effect of varying inflation volumes and cycling frequency. In this study, the mechanical properties of five male C57BL/6J mice (29–33 weeks of age) lungs were evaluated ex vivo using our custom-designed electromechanical, continuous measure ventilation apparatus. We comprehensively quantify and analyze the effect of loading volumes (0.3, 0.5, 0.7, 0.9 ml) and breathing rates (5, 10, 20 breaths per minute) on pulmonary inflation and deflation mechanical properties. We report means of static compliance between 5.4–16.1 µl/cmH2O, deflation compliance of 5.3–22.2 µl/cmH2O, percent relaxation of 21.7–39.1%, hysteresis of 1.11–7.6 ml•cmH2O, and energy loss of 39–58% for the range of four volumes and three rates tested, along with additional measures. We conclude that inflation volume was found to significantly affect hysteresis, static compliance, starting compliance, top compliance, deflation compliance, and percent relaxation, and cycling rate was found to affect only hysteresis, energy loss, percent relaxation, static compliance and deflation compliance.

Effect of Albuterol on Expiratory Resistance in Mechanically Ventilated Patients

In mechanically ventilated patients with COPD, the response of the expiratory resistance of the respiratory system (expiratory R(RS)) to bronchodilators is virtually unknown. To examine the effect of inhaled albuterol on expiratory R(RS), and the correlation of albuterol-induced changes in expiratory R(RS) with end-inspiratory resistance and the expiratory flow-volume relationship. We studied 10 mechanically ventilated patients with COPD exacerbation, before and 30 min after administration of albuterol. We obtained flow-volume curves during passive expiration, divided the expired volume into 5 equal volume slices, and then calculated the time constant and dynamic effective deflation compliance of the respiratory system (effective deflation C(RS)) of each slice via regression analysis of the volume-flow and post-occlusion volume-tracheal pressure relationships, respectively. For each slice we calculated expiratory R(RS) as the time constant divided by the effective deflation C(RS). Albuterol significantly decreased the expiratory R(RS) (mean expiratory R(RS) 42.68 ± 17.8 cm H(2)O/L/s vs 38.08 ± 16.1 cm H(2)O/L/s) and increased the rate of lung emptying toward the end of expiration (mean time constant 2.51 ± 1.2 s vs 2.21 ± 1.2 s). No correlation was found between the albuterol-induced changes in expiratory R(RS) and that of end-inspiratory resistance. Only at the end of expiration did albuterol-induced changes in the expiratory flow-volume relationship correlate with changes in expiratory R(RS) in all patients. In patients with COPD, albuterol significantly decreases expiratory resistance at the end of expiration. In mechanically ventilated patients, neither inspiratory resistance nor the whole expiratory flow-volume curve may be used to evaluate the bronchodilator response of expiratory resistance.

Impact of Mechanical Ventilation on the Developing Airway

After completing this article, readers should be able to: 1. Explain why immature infants are at a greater risk for mechanical ventilation-induced airway damage than are more mature infants. 2. Describe the effect of ventilatory pressures on components of the airway. 3. Delineate how mechanical ventilation disrupts airway mechanics. 4. Characterize how mechanical ventilation affects immature airway smooth muscle. 5. Describe techniques of optimizing ventilation to minimize respiratory damage. Although the air passages take on a mature appearance well before a fetus is viable, they undergo significant maturational changes in late gestation. During development, the airways are more susceptible to damage. In fact, although controversy still surrounds the pathogenesis of bronchopulmonary dysplasia (BPD) and other neonatal airway complications, it appears that the duration and higher pressures of mechanical ventilation, along with the use of oxygen, are related to the development of airway-related problems in preterm infants. As a result, because of their greater need for ventilatory assistance, very preterm infants are at substantially increased risk of airway damage. With recent and continuing advancements in neonatal care, a growing number of immature infants survive premature births. One of the primary hurdles that must be overcome in these infants is respiratory system immaturity. In this context, an understanding of the embryologic development and physiologic maturation of the respiratory system is imperative. The respiratory system can be subdivided grossly into the airways and the lung parenchyma. Developmental changes in the mechanical properties of these two components predispose the immature airway to injury. The immature lung is a relatively noncompliant structure. During neonatal development, lung compliance increases with lung maturity. However, the opposite is true for airways. Immature airways are relatively more compliant than their mature counterparts, with airway maturation resulting in a decrease in airway compliance. This produces an interesting predicament when contemplating the administration of mechanical ventilation …

Mechanism of lobar alveolar pressure decline during forced deflation in canine regional emphysema.

A canine model of unilobar papain-induced emphysema was used to examine the extent to which differences in alveolar pressures (PA) would develop between an emphysematous right lower lobe (RLL) and normal left lower lobe (LLL) during forced vital capacity (FVC) deflation. RLL and LLL PA (PARLL and PALLL, respectively) were measured by the alveolar capsule technique. During forced deflation, PA and lobar flows were determined between 95 and 20% FVC. A choke point common to both lower lobes was observed at > 40% FVC. The results showed that deflation compliance (C) was altered for the RLL such that <90% lobar vital capacity, CRLL > CLLL, whereas >90% lobar vital capacity, CRLL < CLLL. At 95 and 90% FVC, the initial RLL PA decline was greater than that for the LLL (P < 0.05). However, large differences in PA were prevented because of the effect of interdependence of regional expiratory flow (IREF). IREF caused a relative decrease in RLL flows and increase in LLL flows that limited PA differences. Between 80 and 50% FVC, as CRLL became greater than CLLL, and because of the initial effect of IREF, PARLL was approximately PALLL. At < and = 40% FVC, without IREF, lobar differences in PA widened. These findings indicate that IREF may affect the dynamics of flow limitation in regional lung disease.

Improved determination of static compliance by automated single volume steps in ventilated patients

A new method for determination the static compliance of the respiratory system is described ("static compliance by automated single steps"--SCASS). In 12 ventilated patients pressure/volume (P/V) curves were determined by automated repetitive occlusion (6 s) at single volume steps and compared to the conventional syringe method (SM). All measurements were corrected for effects of temperature, humidity and pressure (THP). SM was found to be significantly influenced by intrapulmonary gas exchange causing an effective mean volume deficit of 217.4 +/- 65.7 ml (BTPS) at the end of the deflation. In contrast to that, the short duration of occlusion in SCASS minimize the gas exchange effects. The methodical differences between both methods result in overestimation of the inflation compliance in the uncorrected SM (SMuncorr: 83.4 +/- 12.6; SCASS: 76.0 +/- 11.9 ml/cmH2O. p less than 0.01) and underestimation of the deflation compliance resp. (SMuncorr: 58.3 +/- 7.5; SCASS: 79.1 +/- 15.0 ml/cmH2O. p less than 0.005). In contrast to the P/V curves by SM no significant hysteresis was found by SCASS. Gas exchange seems to be the main reason for the hysteresis. Even after correcting gas exchange and THP effects a significant hysteresis remained. The SCASS method avoids these problems and allows furthermore an accurate checking of leaks.

Respiratory mechanics of the piglet during the first month of life

Piglets at 3, 14, and 30 days of age were studied to assess the postnatal changes in lung, chestwall, and total respiratory system compliance associated with normal growth. Static deflation compliance of the lung and total respiratory system increased significantly with age; there was no change in chestwall compliance. When normalized for body weight or lung volume, all measures of compliance tended to decrease with postnatal age. Measures of lung and chestwall compliance obtained with an end-inspiratory occlusion technique were less than the static compliance measures, but demonstrated the same relative changes with postnatal maturation. Chestwall compliance at 3 days of age was only 1.3 times greater than lung compliance and there was no significant change in this ratio with postnatal age. In contrast to the trend for the human infant, the piglet's chestwall at 3 days of age is stiff relative to the lung and does not become stiffer with age over the first 4 weeks of life.

Pressure-volume curve of total respiratory system in acute respiratory failure. Computed tomographic scan study.

To investigate the relationship between lung anatomy and pulmonary mechanics in acute respiratory failure (ARF), 20 patients with ARF underwent computerized tomography (CT) at 3 levels of positive end-expiratory pressure (PEEP) (5, 10, and 15 cm H2O). The static pressure-volume curve of the total respiratory system and the lung volumes (helium dilution method) were also measured. By knowing the lung volumes and analyzing the CT number frequency distribution, a quantitative estimate of normally aerated, poorly aerated, and nonaerated lung tissue was obtained at each level of PEEP. The recruitment was defined as the percent increase of normally aerated tissue from 5 to 15 cm H2O. We found that the different compliances (starting compliance, inflation compliance, and deflation compliance) were correlated only with the amount of normally aerated tissue present in the range of pressures explored by a given compliance (5 cm H2O for starting compliance and 15 cm H2O for inflation and deflation compliances). No relationship was found between the compliances and the poorly aerated and nonaerated tissue. The specific compliance was in the normal range, whereas the amount of recruitment was related to the ratio of inflation compliance to starting compliance. Our data suggest that (1) the pressure-volume curve parameters in ARF investigate only the residual healthy zones of the lung and do not directly estimate the "amount" of disease (poorly or nonaerated tissue), (2) the pressure-volume curve may allow an estimate of the anatomic recruitment, and (3) the residual normally aerated zones of the ARF lung seem to maintain a normal intrinsic elasticity.

Expiratory volume clamping: a new method to assess respiratory mechanics in sedated infants.

During breathing under sedation via a two-way valve, airflow (V), volume (delta V), and airway pressure (P) were recorded in eight normal (N) infants, seven with reversible obstructive airway disease (ROAD), and seven with chronic lung disease (CLD). Intermittently, expiratory volume clamping (EVC) was applied, involving selective occlusion of the expiratory valve for three to five breaths. The latter produced cumulative increases in delta V that, due to progressive recruitment of the Hering-Breuer reflex, were accompanied by increasing expiratory plateaus in P (i.e., apneas). The resultant passive inflation delta V-P relationships were closely approximated by the expression: delta V = aP2 + bP + c, wherein a represented the pressure-related changes in chord compliance (Crs), b the Crs at P = 0, and c the difference between the dynamic end-expiratory and relaxation volumes of the respiratory system. Relative to N, the ROAD and CLD infants had significantly reduced weight-specific values of a/kg, their b/kg values were increased, whereas the c/kg measurements did not significantly vary. Moreover, for each subject we determined the net Crs/kg obtaining at P = 20 cmH2O (i.e., Crs20/kg), an estimate of the net deflation compliance; the passive respiratory time constant (tau rs) based on the slope of the expired delta V/V relationship; and the respiratory system conductance (Grs/kg). Relative to N, the mean Crs20/kg was significantly reduced only in the infants with CLD and, due to increases in tau rs, both patient groups depicted significantly diminished values of Grs/kg, suggesting the presence of airways obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume/pressure curve of total respiratory system in paralysed patients: artefacts and correction factors.

The volume/pressure (V/P) curve of the total respiratory system in paralysed patients is drawn assuming that volume changes of the respiratory system (delta V resp) equals volume displacement of the measuring apparatus (delta V syr), usually a supersyringe. However, in 93 VP curves we found that O2 removed from the lung-syringe system during the procedure (proportional to the time) largely exceeds the CO2 added to the lung-syringe system (delta V gas). This results in a net loss of volume from the system (delta V resp less than delta V-syr). Deflation compliance, hysteresis area and ratio are significantly affected by this phenomenon. Inflation compliance is less influenced by delta V gas, partially compensated by the intrapulmonary gas expansion due to the temperature changes. We conclude that the parameters computed on the deflation limb of V/P curve are misleading if proper correction of the volume scale is not introduced.

Validation of the plain chest radiograph for epidemiologic studies of airflow obstruction.

The chest radiographs of 125 industrial workers from rural New South Wales were examined for overinflated lungs, with and without attenuated midzonal vessels. Although the mean values of a comprehensive range of pulmonary function tests in the whole group were within normal limits, the nine subjects whose radiographs showed overinflated lungs and attenuated vessels had significantly impaired pulmonary function in comparison with 85 subjects with normal radiographs. The mean values for these nine subjects, expressed as a percentage of the mean value for subjects with normal radiographs, were: forced expiratory volume in 1 second, 75%; total lung capacity, 107%; residual volume, 143%; transpulmonary pressure at maximum inspiration, 60%; static deflation compliance, 158%; lung volume at transpulmonary pressure 10 cm H2O, 132%; transfer factor, 79%; and transfer factor/alveolar volume, 77%. Similar results were obtained by a second observer. Those subjects with overinflation but no vascular attenuation had significantly larger mean values for vital capacity and alveolar volume but no significant difference in total lung capacity or other tests of the mechanical properties of the lungs. Agreement on the presence of a positive sign between the two observers expressed as a percentage of those considered positive by either was 81% for overinflation and 62% for attenuated midzonal vessels. The results indicate that in groups of subjects with normal-average values of pulmonary function, the plain chest radiograph may provide information concerning pulmonary structure that is reflected in tests of function.

The effect of the minimal deflation pressure on lung mechanics in isolated rabbit lungs.

Alterations in the PV relationships of isolated rabbit lungs which are dependent on the minimal deflation pressure (Pmin) have been studied. When Pmin remains positive both inflation and deflation limbs of the PV loop are shifted toward lower transpulmonary (P1) pressures throughout most of the cycle. In addition, Pmin(+) conditions eliminate the deflation inflection and increase deflation compliance at low and mid-lung volumes. Results from indicator washout and spontaneous deflation reveal that Pmin(+) conditions produce a more even inflation of the lung parenchyma and dilate airways at low lung volumes. These effects cause a stabilization of the parenchyma and a delay in airway closure resulting in the increased deflation compliance and a decrease in the trapped gas volume during Pmin(+) conditions. The relevance of Pmin(+) and (−) conditions are discussed for several clinical conditions.