Pulmonary aspiration in mechanical ventilation occurs despite appropriate inflation of the tracheal tube cuff. After anaesthesiath is can causep ostoperative and, in critically ill patients, ventilator-associated pneumonia. Cuff over-inflation exerts excessive pressure on the tracheal mucosa causing injury. High volume low pressure (HVLP) cuffs permit wall pressure control as the intracuff pressure (CP) is the tracheal wall pressure (TWP). Unfortunately, at the cuff wall, folds and channels and, therefore, fluid leakage occur. Low volume high pressure (LVHP) cuffs develop neither folds nor associated leakage, but TWP is not easily inferred from CP and excessive pressures can result in tracheal injury. This thesis examines the problem of aspiration in a model, in anaesthetised patients and in the critically ill. In the model, protection against leakage resulted from positive end-expiratory pressure and cuff lubrication. Two tracheal cuff prototypes are introduced. Firstly, the compliant HVLP cuff is one with a tapered shape made of highly compliant material. Within the model this produced a circumferential band at the cuff wall without folds thus effectively eliminating channels and leakage. Secondly, the prototype pressure limited cuff (PLC) is a latex LVHP cuff with inflation characteristics such that TWP can be inferred from CP and maintained at an acceptable level. Within the model the PLC prevented leakage at acceptable TWPs. For clinical use a constant pressure inflation device is required to provide uninterrupted protection, although notably HVLP cuffs allow leakage despite this. The PLC prevented dye aspiration in 100% of tracheally intubated critically ill patients compared with 13% of the control HVLP group (p<0.01). A silicone cuff with similar inflation characteristics, yet improved biocompatability and shelf life, prevented dye aspiration in 100% of patients with tracheostomies compared to 0% of the HVLP control group (p=0.001). HVLP cuff lubrication delayed dye aspiration for 1 to 5 days (p<0.05).

Rhythmic collapse and reinflation of tracheal tubes is a form of active ventilation that augments convective gas exchange in multiple orders of insects. The underlying mechanism driving this phenomenon is not known. Among other things, tracheal tube collapse could be caused by either direct impingement of trachea or by a difference of pressure gradients between the intra-tracheal air and the surrounding hemolymph. To determine the relationship between hemolymph pressure and tracheal tube collapse in the ground beetle (Pterostichus commutabulis), we performed direct measurements of hemolymph pressure inside the beetle's prothorax while simultaneously using synchrotron phase contrast imaging to observe morphological changes in the trachea. We observed that a pressure pulse co-occurred with every tube compression observed throughout the body, suggesting that pulses in hemolymph pressure are responsible for tracheal collapse. To assess the effects of the experimental x-ray conditions imposed on the subjects during imaging, hemolymph pressure was also directly measured in the prothorax of beetles less restricted in non-x-ray trials. To compare the pressure patterns in the two experiments, a novel method of identifying and analyzing pressure pulses was developed and applied to the data sets. The comparison provides the first quantitative characterization of a directly measured hemolymph pressure environment, and demonstrates strong similarities in the pressure patterns recorded in both tests. However, pulses occurring during the x-ray experiments exhibited larger average magnitudes. Further video analysis however shows that collapse of the primary tracheal tubes was observed to occur even in the presence of the smallest simultaneously measured pressure pulse (1.01 kPa), suggesting that collapse of the primary tracheal tubes. / Master of Science

The insect respiratory system serves as a model for both robust microfluidic transport and mate- rial design. In the system, the convective flow of gas is driven through local deformations of the tracheal network, a phenomenon that is dependent on the unique structure and material properties of the tracheal tissue. To understand the underlying mechanics of this method of gas transport, we studied the microstructure and material properties of the primary thoracic tracheal tubes of the American cockroach (Periplaneta americana). We performed quasi-static uniaxial tests on the tissue which revealed a nonlinear stress-strain response even under small deformations. A detailed analysis of the tissue's microstructural arrangement using both light and electron mi- croscopy revealed the primary sources of reinforcement for the tissue as well as heterogeneity on the meso-scale that may contribute to the physiological function of the tracheae during respi- ration. Finally, a custom mechanical testing system was developed with which inflation-extension tests on the tracheae were used to gather data on the biaxial elastic response of the tissue over a wide range of physiologically relevant loading conditions. From information gathered about the material microstructure, a robust constitutive model was chosen to quantify the biaxial response of the tracheae. This model will provide a basis from which to simulate the behavior of tracheal net- works in future computational studies. This study gives the first description of the elastic response of the tracheae which is essential for understanding the mechanics of respiration in insects. Thus it brings us closer to the realization of novel bio-inspired microfluidic systems and materials that utilize mechanical principles from the insect respiratory system. / Ph. D.

Abdominal pumping is a widespread behavior in insects. However, there remains ambiguity surrounding the abdominal pumping behavior, both in terms of describing what exactly abdominal pumping is (i.e., if various modes of operation exist) and also what function(s) abdominal pumping serves (and if function is conserved across groups of insects). In some insects respiratory patterns have been correlated with abdominal movements, although the specific mechanical effects of these movements on the animal\'s respiratory system are generally unknown. Conversely, some insects (such as beetles, ants, and crickets) create convection in the respiratory system by compressing their tracheal tubes, yet the underlying physiological mechanisms of tracheal collapse are also unknown. This study aimed to investigate the relationship between abdominal pumping and the compression of tracheal tubes in the darkling beetle, Zophobas morio. I observed the movements of the abdomen and tracheal tubes using synchrotron x-ray imaging and video cameras, while concurrently monitoring CO2 expiration. I identified and characterized two distinct abdominal movements differentiated by the synchrony (the pinch movement) or lack of synchrony (the wave movement) of abdominal tergite movement. Tracheal tube compressions (and corresponding CO2 pulses) occurred concurrently with every pinch movement. This study provides evidence of a mechanistic linkage between abdominal movements and tracheal tube compressions in the ground beetle, Zophobas morio. / Master of Science

grainy head (grh) genes encode a family of transcription factors conserved from fly to human. Drosophila grh is the founding member of this gene family and has multiple functions, including tracheal tube size control, epidermal barrier formation and reconstruction after wounding. To understand the underlying molecular mechanism of grh functions, we tried to isolate its direct targets and analyze their function. We identified ten grh targets by combining bioinformatics and genetics. Grh directly controls the expression of stitcher (stit), which encodes a Ret family receptor tyrosine kinase (RTK), during both development and wound healing. Stit promotes actin cable assembly and induces extracellular signal-regulated kinase (ERK) phosphorylation around the wound edges upon injury. Stit also activates barrier repair genes and its own expression at the wound sites in a Grh-dependent manner. This positive feedback loop ensures efficient epidermal wound repair. In addition, Grh regulates the expression of multiple genes involved in chitin biosynthesis or modification. Most of the genes are required for tracheal tube size control. Two of them, verm and serp, encode related putative luminal chitin deacetylases. The functional analysis of verm and serp identifies an important role of luminal chitin matrix modification in limiting tracheal tube elongation. Therefore, it is very likely that Grh controls tracheal tube size through regulating multiple targets involved in the assembly or modification of luminal chitin matrix. Grh also directly activates the epidermal expression of Peptidoglycan recognition protein LC (PGRP-LC) gene that is required for the induction of antimicrobial peptides (AMPs) upon infection. Furthermore, ectopically expressing Grh is sufficient to induce AMP Cecropin A lacZ reporter (CecA-LacZ) in the embryonic epidermis. These results suggest a new function of Grh in the local immune responses in Drosophila barrier epithelia. / At the time of the doctoral defense, the following papers was unpublished and had a status as follows: Paper 1: Manuscript.