Effects of helium-oxygen on respiratory mechanics, gas exchange, and ventilation-perfusion relationships in a porcine model of stable methacholine-induced bronchospasm

Protein composition of bronchoalveolar lavage fluid and airway surface liquid from newborn pigs

The airway mucosa and the alveolar surface form dynamic interfaces between the lung and the external environment. The epithelial cells lining these barriers elaborate a thin liquid layer containing secreted peptides and proteins that contribute to host defense and other functions. The goal of this study was to develop and apply methods to define the proteome of porcine lung lining liquid, in part, by leveraging the wealth of information in the Sus scrofa database of Ensembl gene, transcript, and protein model predictions. We developed an optimized workflow for detection of secreted proteins in porcine bronchoalveolar lavage (BAL) fluid and in methacholine-induced tracheal secretions [airway surface liquid (ASL)]. We detected 674 and 3,858 unique porcine-specific proteins in BAL and ASL, respectively. This proteome was composed of proteins representing a diverse range of molecular classes and biological processes, including host defense, molecular transport, cell communication, cytoskeletal, and metabolic functions. Specifically, we detected a significant number of secreted proteins with known or predicted roles in innate and adaptive immunity, microbial killing, or other aspects of host defense. In greatly expanding the known proteome of the lung lining fluid in the pig, this study provides a valuable resource for future studies using this important animal model of pulmonary physiology and disease.

Experimental animal models of muscle wasting in intensive care unit patients

The muscle wasting and loss of muscle function associated with critical illness and intensive care have significant negative consequences for weaning from the respirator, duration of hospital stay, and quality of life for long periods after hospital discharge. There is, accordingly, a significant demand for focused research aiming at improving our understanding of the mechanisms underlying the impaired neuromuscular function in intensive care unit (ICU) patients. However, the study of generalized muscle weakness in critically ill ICU patients is further complicated by the coexistence of multiple independent factors, such as different primary diseases, large variability in pharmacologic treatment, collection of muscle samples several weeks after admission to the ICU, and exposure to causative agents. This has led to the design of specific animal models mimicking ICU conditions. These models have often been used to study the mechanisms underlying the paralysis and muscle wasting associated with acute quadriplegic myopathy in ICU patients. This short review aims at presenting existing and recently introduced experimental animal models mimicking the conditions in the ICU (i.e., models designed to determine the mechanisms underlying the muscle wasting associated with ICU treatment).

A porcine model of acute quadriplegic myopathy: a feasibility study

BACKGROUND

The mechanisms underlying acute quadriplegic myopathy (AQM) are poorly understood, partly as a result of the fact that patients are generally diagnosed at a late stage of the disease. Accordingly, there is a need for relevant experimental animal models aimed at identifying underlying mechanisms.

METHODS

Pigs were mechanically ventilated and exposed to various combinations of agents, i.e. pharmacological neuromuscular blockade, corticosteroids and/or sepsis, for a period of 5 days. Electromyography and myofibrillar protein and mRNA expression were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), confocal microscopy, histochemistry and real-time polymerase chain reaction (PCR).

RESULTS

A decreased compound muscle action potential, normal motor nerve conduction velocities, and intact sensory nerve function were observed. Messenger RNA expression, determined by real-time PCR, of the myofibrillar proteins myosin and actin decreased in spinal and cranial nerve innervated muscles, suggesting that the loss of myosin observed in AQM patients is not solely the result of myofibrillar protein degradation.

CONCLUSION

The present porcine AQM model demonstrated findings largely in accordance with results previously reported in patients and offers a feasible approach to future mechanistic studies aimed at identifying underlying mechanisms and developing improved diagnostic tests and intervention strategies.

Model-based detection of partially obstructed endotracheal tube*

OBJECTIVES

A five-element lumped pulmonary model was developed to estimate respiratory mechanics automatically and noninvasively. The model was applied to diagnose obstructed endotracheal tube. Events like bronchospasm and stiff chest wall were also tested to determine the specificity of the diagnosis. Cases with positive end-expiratory pressure were also included in the analysis to see the effects of positive end-expiratory pressure on the model.

DESIGN

Randomized controlled animal study.

SETTING

University department of anesthesiology.

SUBJECTS

Ten anesthetized, paralyzed, and mechanically ventilated mongrel dogs (19-45 kg) of either gender.

INTERVENTIONS

Two levels of upper airway obstruction were induced in ten dogs by partially constricting the endotracheal tube. Acute bronchial constriction was produced in five dogs by injecting methacholine through a central venous catheter. In the same five dogs, the chest wall was stiffened by wrapping a pressure cuff around the chest. Positive end-expiratory pressure was also applied as a separate event in these five animals.

MEASUREMENTS AND MAIN RESULTS

Airway pressure and flow were continuously recorded at the mouth. Model parameters were iteratively identified until the root mean square error between respiratory impedance (obtained from airway pressure and flow) and model-predicted impedance (calculated using Ohm's law) was minimum. The peak inspiratory pressure increased and the peak expiratory flow rate decreased with increasing levels of partial obstruction. The value of the model parameters R(1) and C(2) increased and C(1) decreased with partial obstructed endotracheal tube, whereas R(1) increased and L and C(2) decreased with bronchospasm. With stiff chest wall, R(2) increased and C(2) decreased. With positive end-expiratory pressure, the L parameter decreased and no significant change in other model parameters was observed. Obstructed endotracheal tube is indicated if R(1) increased > or =30%, C(1) decreased > or =10%, and C(2) increased > or =10% from baseline. The test results using 45 events, including control, three complications, and positive end-expiratory pressure, show that when the model is used to diagnose obstructed endotracheal tube, the method has a sensitivity of 90% and specificity of 97%.

CONCLUSIONS

During an obstructed endotracheal tube, model parameters change such that the event can be diagnosed noninvasively, automatically, and accurately. The model differentiates between upper airway obstruction and complications like bronchospasm and stiff chest wall.