Mechanics in rats by end-inflation occlusion and single-breath methods

Biological impact of restrictive and liberal fluid strategies at low and high PEEP levels on lung and distal organs in experimental acute respiratory distress syndrome

Background: Fluid regimens in acute respiratory distress syndrome (ARDS) are conflicting. The amount of fluid and positive end-expiratory pressure (PEEP) level may interact leading to ventilator-induced lung injury (VILI). We therefore evaluated restrictive and liberal fluid strategies associated with low and high PEEP levels with regard to lung and kidney damage, as well as cardiorespiratory function in endotoxin-induced ARDS.

Methods: Thirty male Wistar rats received an intratracheal instillation of Escherichia coli lipopolysaccharide. After 24 h, the animals were anesthetized, protectively ventilated (V_T = 6 ml/kg), and randomized to restrictive (5 ml/kg/h) or liberal (40 ml/kg/h) fluid strategies (Ringer lactate). Both groups were then ventilated with PEEP = 3 cmH₂O (PEEP3) and PEEP = 9 cmH₂O (PEEP9) for 1 h (n = 6/group). Echocardiography, arterial blood gases, and lung mechanics were evaluated throughout the experiments. Histologic analyses were done on the lungs, and molecular biology was assessed in lungs and kidneys using six non-ventilated animals with no fluid therapy.

Results: In lungs, the liberal group showed increased transpulmonary plateau pressure compared with the restrictive group (liberal, 23.5 ± 2.9 cmH₂O; restrictive, 18.8 ± 2.3 cmH₂O, p = 0.046) under PEEP = 9 cmH₂O. Gene expression associated with inflammation (interleukin [IL]-6) was higher in the liberal-PEEP9 group than the liberal-PEEP3 group (p = 0.006) and restrictive-PEEP9 (p = 0.012), Regardless of the fluid strategy, lung mechanical power and the heterogeneity index were higher, whereas birefringence for claudin-4 and zonula-ocludens-1 gene expression were lower in the PEEP9 groups. Perivascular edema was higher in liberal groups, regardless of PEEP levels. Markers related to damage to epithelial cells [club cell secreted protein (CC16)] and the extracellular matrix (syndecan) were higher in the liberal-PEEP9 group than the liberal-PEEP3 group (p = 0.010 and p = 0.024, respectively). In kidneys, the expression of IL-6 and neutrophil gelatinase-associated lipocalin was higher in PEEP9 groups, regardless of the fluid strategy. For the liberal strategy, PEEP = 9 cmH₂O compared with PEEP = 3 cmH₂O reduced the right ventricle systolic volume (37%) and inferior vena cava collapsibility index (45%).

Conclusion: The combination of a liberal fluid strategy and high PEEP led to more lung damage. The application of high PEEP, regardless of the fluid strategy, may also be deleterious to kidneys.

Measurement of pleural pressure swings with a fluid-filled esophageal catheter vs pulmonary artery occlusion pressure

PURPOSE

Pleural pressure measured with esophageal balloon catheters (Peso) can guide ventilator management and help with the interpretation of hemodynamic measurements, but these catheters are not readily available or easy to use. We tested the utility of an inexpensive, fluid-filled esophageal catheter (Peso) by comparing respiratory-induced changes in pulmonary artery occlusion (Ppao), central venous (CVP), and Peso pressures.

METHODS

We studied 30 patients undergoing elective cardiac surgery who had pulmonary artery and esophageal catheters in place. Proper placement was confirmed by chest compression with airway occlusion. Measurements were made during pressure-regulated volume control (VC) and pressure support (PS) ventilation.

RESULTS

The fluid-filled esophageal catheter provided a high-quality signal. During VC and PS, change in Ppao (∆Ppao) was greater than ∆Peso (bias = -2 mm Hg) indicating an inspiratory increase in cardiac filling. During VC, ∆CVP bias was 0 indicating no change in right heart filling, but during PS, CVP fell less than Peso indicating an inspiratory increase in filling. Peso measurements detected activation of expiratory muscles, development of non-west zone 3 lung conditions during inspiration, and ventilator-triggered inspiratory efforts.

CONCLUSIONS

A fluid-filled esophageal catheter provides a high-quality, easily accessible, and inexpensive measure of change in pleural pressure and provided insights into patient-ventilator interactions.

The Effects of Prone with Respect to Supine Position on Stress Relaxation, Respiratory Mechanics, and the Work of Breathing Measured by the End-Inflation Occlusion Method in the Rat

PURPOSE

The working hypothesis is that the prone position with respect to supine may change the geometric configuration of the lungs inside the chest wall, thus their reciprocal mechanical interactions, leading to possible effects on stress relaxation phenomena and respiratory mechanics.

METHOD

The effects of changing body posture from supine to prone on respiratory system mechanics, particularly on stress relaxation, were investigated in the rat by the end-inflation occlusion method.

RESULTS

In the prone with respect to supine position, an increment of the frictional resistance of the airway (from 0.13 ± 0.01 to 0.19 ± 0.02 cm H2O/l sec(-1), p < 0.05) and a decrement of the stress relaxation-linked pressure dissipation (from 0.51 ± 0.05 to 0.45 ± 0.05 cm H2O/l sec(-1), p < 0.01) were found. Respiratory system elastance and total resistive pressure dissipation did not change significantly. Accordingly, a significant increase of the frictional "ohmic" mechanical inspiratory work of breathing and a decrease of the visco-elastic work of inspiration were demonstrated, while no significant changes occurred for the total mechanical work of breathing and its total resistive and elastic components.

CONCLUSION

It is concluded that postural changes affect the visco-elastic characteristics of the respiratory system and the related stress relaxation phenomena by influencing the disposition and relation of the lungs inside the chest wall and their relative geometrical configuration, and the interaction phenomena of the constitutive parenchymal structures, i.e., elastin and collagen fibers. Since the prone position resulted in no serious or disadvantageous respiratory system mechanical derangement, it is suggested it may be usefully applied in nursing or for therapeutic goals.

Lung volume reduction surgery for native lung hyperinflation following single-lung transplantation for emphysema: which patients?

OBJECTIVES

Lung transplantation is an established treatment for patients with advanced emphysema. Double-lung transplantation is favoured to avoid complications following single-lung transplantation, including native lung hyperinflation. Nonetheless, single-lung transplantation continues due to limited donor organ availability. The aim of this study was to evaluate the pre-operative assessment, surgical techniques and outcomes in patients undergoing lung volume reduction surgery for native lung hyperinflation.

METHODS

Eight patients underwent lung volume reduction surgery for native lung hyperinflation between October 2008 and April 2011. Symptoms, pre-operative evaluation, peri-operative morbidity, length of stay, pulmonary function and survival were examined. The mean follow-up was 17 months.

RESULTS

Participants underwent high resolution CT and bronchoscopy with transbronchial biopsy and bronchial washings to exclude alternative causes for deterioration in pulmonary function tests. V/Q scan was performed to assess the contribution of each lung to overall function. Measurement of inspiratory airflow resistance in each lung was performed in one case. Seven patients underwent multiple wedge resections and one underwent bilobectomy. All patients survived to hospital discharge, and mean length of stay was 13.9 days. Functional improvement was demonstrated in all cases at follow-up, with a mean percentage increase of 29.3% in forced expiratory volume in one second and 21.6% in forced vital capacity. Symptomatic improvement was also reported by all patients post-operatively.

CONCLUSIONS

Lung volume reduction surgery for native lung hyperinflation is an effective treatment strategy with an acceptable level of surgical risk. Patient selection, however, remains vital. The non-anatomical multiple wedge excision technique used here was as effective as anatomical lung volume reduction surgery used in other series. With regard to pre-operative assessment, the measurement of single-lung inspiratory airflow resistance is of particular interest. We feel that this may provide an additional method of differentiating between native lung hyperinflation and obliterative bronchiolitis prior to surgery, thus improving patient selection.

Mechanics of the lung in the 20th century

Major advances in respiratory mechanics occurred primarily in the latter half of the 20th century, and this is when much of our current understanding was secured. The earliest and ancient investigations involving respiratory physiology and mechanics were frequently done in conjunction with other scientific activities and often lacked the ability to make quantitative measurements. This situation changed rapidly in the 20th century, and this relatively recent history of lung mechanics has been greatly influenced by critical technological advances and applications, which have made quantitative experimental testing of ideas possible. From the spirometer of Hutchinson, to the pneumotachograph of Fleisch, to the measurement of esophageal pressure, to the use of the Wilhelmy balance by Clements, and to the unassuming strain gauges for measuring pressure and rapid paper and electronic chart recorders, these enabling devices have generated numerous quantitative experimental studies with greatly increased physiologic understanding and validation of mechanistic theories of lung function in health and disease.

Effect of the oestral cycle on respiratory mechanics in the rat

AIM

To assess the effect of the oestral cycle on the respiratory mechanics of the rat.

METHODS

We measured the main mechanical respiratory parameters, namely respiratory system and lung resistances and compliances, by the end-inflation occlusion method on two populations of female rats, during proestrous-oestrous and metaoestrous-diestrous phases.

RESULTS

Inflation-deflation loops of the lungs were found to be statistically higher in rats during metaoestrous-diestrous phase. No other statistically significant difference was found in the measured mechanical respiratory parameters.

CONCLUSION

Our results suggest that the naturally occurring fluctuations in serum sexual hormone levels during the sexual cycle influence the lung's hysteresis but do not influence the respiratory system and lung resistances or static compliances. A possible effect of female sexual hormones on surfactant activity is also suggested.

Effects of uni- and bilateral phrenicotomy on active and passive respiratory mechanics in rats

Eighteen spontaneously breathing anesthetized rats were selected to belong to three groups: control (C), unilateral (U), and bilateral phrenicotomy (B). Eight days after surgery, the passive and active mechanical properties of the respiratory system, the shape of the occlusion pressure wave, the decay of inspiratory muscle activity during expiration and control of breathing were analysed. Passive and active elastances increased significantly from C to U and from U to B. Passive and active time constants decreased either in uni- or bilateral phrenicotomies. Passive and active resistances remained unaltered. The intensity of respiratory drive increased from C to U and B. In conclusion, uni- and bilateral phrenicotomies increase the elastic load of the respiratory system, because of both its passive and active components, which raised the respiratory neuromuscular drive of the remaining muscles. Consequently, minute ventilation remained unchanged. The higher frequency was allowed for, by a shorter time constant of the respiratory system and by a faster decay of post-inspiratory muscle activity.

Eosinophils increase lung microvascular permeability via the peroxidase-hydrogen peroxide-halide system. Bronchoconstriction and vasoconstriction unaffected by eosinophil peroxidase inhibition

Eosinophils have been implicated as effector cells in producing vascular and bronchial constriction and increased microvascular permeability in the lung. Hypohalous acids produced by the eosinophil peroxidase (EPO)-hydrogen peroxide (H2O2)-halide system are stable cytotoxic oxidants. We measured the effects of EPO inhibition in activated eosinophils on vascular permeability, assessed using the capillary filtration coefficient (Kf,c), vascular resistance (Rt,vasc), and airway resistance (Raw) in isolated rat lungs perfused with 5% bovine albumin in Kreb's solution. Eosinophils were harvested by bronchoalveolar lavage of Toxicara canis-infected rats. Infusion of 2 x 10(6) phorbol myristate acetate (PMA)-activated cells produced a 3.3-fold increase in Rt,vasc at 30 min, primarily caused by small vessel constriction, a 2.5-fold increase in Raw at 150 min, and a 1.8-fold increase in Kf,c at 90 min. Inhibition of EPO using 3-amino-1,2,4-triazole (3-AT) prevented the increases in Kf,c, but not those in eosinophil superoxide production, Rt,vasc, or Raw. Addition of 2 mM sodium bromide as preferential EPO substrate caused Kf,c, but not Rt,vasc, or Raw, to increase significantly (2.5-fold) compared with activated eosinophils alone. Thus, the acute changes in microvascular permeability were modulated by activity of the EPO-H2O2-Halide system, but the increased vascular and bronchial resistances were mediated through a different pathway.

Evoked bronchoconstriction: testing three methods for measuring respiratory mechanics

In order to assess the usefulness of methods for noninvasive study of respiratory mechanics in intubated patients better, we studied 16 anesthetized paralyzed mechanically ventilated guinea pigs previously sensitized with ovalbumin. Respiratory system elastance and resistance were determined in control and acute antigen exposed (AAE) animals by the end-inflation occlusion method (EIOM), the single-breath method (SBM), and the interrupter technique (IT). In control group, total respiratory system resistance and elastance were constant over tidal volume range and the three methods provided similar results. In AAE group elastance was also constant throughout tidal volume and measured by SBM and IT was, respectively, 93.4 and 57.9% higher than in control group. The relationships between resistive pressure and expiratory flow became curvilinear with an upward convexity. IT underestimated both elastance and resistance measurements in AAE group. Using EIOM the determination of the homogeneous and uneven components of respiratory resistance was possible in control animals, whereas in AAE group resistance was entirely represented by its uneven component.

Expiratory mechanics before and after uncomplicated heart surgery

In 12 mechanically ventilated anesthetized paralyzed patients undergoing cardiac surgery for either coronary bypass or for correcting valvular dysfunction volume, airflow, tracheal, esophageal, and transpulmonary pressures were measured. Respiratory system elastance and resistance were partitioned into their lung and chest wall components throughout tidal relaxed expiration. Measurements were performed prior to thoracotomy and just after rib cage closure. Before surgery, patients with valvular disease had significantly higher respiratory system and lung elastances and resistances than those with ischemic heart disease. After surgery, patients with valvular disease showed a decrease in respiratory system and lung resistances. Surgery strikingly modified chest wall resistive properties in both groups. Postoperatively, the mechanical properties of the respiratory system were very similar in valvular and ischemic patients.

Vagal influences on respiratory mechanics, pressures, and control in rats

In eight spontaneously breathing anesthetized rats airflow, volume, and tracheal pressure were measured. The passive and active mechanical properties of the respiratory system, the shape of the tracheal occlusion pressure wave (Potr), the decay of inspiratory muscle pressure during expiration, and parameters related to the control of breathing were computed both before and after bilateral cervical vagotomy. Pre- and post-vagotomy values of passive elastance, resistance, and time constant were similar. Active mechanics disclosed an increase of elastance and a decrease in resistance and in the time constant after vagotomy. The time course of Potr showed a downward concavity and was not modified by vagotomy in the range of control inspiratory times, whereas the shape of inspiratory muscle pressure decay during expiration was changed. The present data help to explain why after vagotomy the load-compensatory mechanisms are less effective.