Gas Exchange Models for a Flexible Insect Tracheal System (original) (raw)
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Microscale Gaseous Slip Flow in the Insect Trachea and Tracheoles
An analytical investigation into compressible gas flow with slight rar-efactions through the insect trachea and tracheoles during the closed spiracle phase is undertaken, and a complete set of asymptotic analytical solutions is presented. We first obtain estimates of the Reynolds and Mach numbers at the channel terminal ends where the tracheoles directly deliver respiratory gases to the cells, by comparing the magnitude of the different forces in the compressible gas flow. The 2D Navier–Stokes equations with a slip boundary condition are used to investigate compressibility and rarefied effects in the trachea and tracheoles. Expressions for the velocity components, pressure gradients and net flow inside the trachea are then presented. Numerical simulations of the tracheal compressible flow are performed to validate the analytical results from this study. This work extends previous work of Arkilic et al. (J Microelectromech Syst 6(2):167–178, 1997) on compressible flows through a microchannel. Novel devices for microfluidic compressible flow transport may be invented from results obtained in this study.
Proceeding of Sixth International Symposium on Turbulence and Shear Flow Phenomena
The central airways of the lung are a complex system of bifurcations and pipes. In the case of artificial ventilation support with the necessity of using airway management devices (i.e. endotracheal tubes) the complexity of the system even increases and a complete understanding of the ventilation and oxygenation mechanisms is of major interest in order to ensure protective oxygenation and ventilation of the patient. Numerical investigations on the influence of endotracheal tubes on the flow revealed that thesel tubes have an important impact within the trachea and accordingly in the central airways of the lung. A parametric study on the effect of the tube's level of detail on the resulting flow regime showed that it is necessary to model not only the tube's ending but also the bending which is essential for the development of secondary flows. A comparison of numerical data generated with a turbulent and a laminar Navier-Stokes solver revealed that for the indistinct, potentially transitional flow in the airways with endotracheal tube the simulations with turbulence model are more promising but in terms of computational costs more expensive.
Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle
Journal of Experimental Biology, 2008
Rhythmic tracheal compression is a prominent feature of internal dynamics in multiple orders of insects. During compression parts of the tracheal system collapse, effecting a large change in volume, but the ultimate physiological significance of this phenomenon in gas exchange has not been determined. Possible functions of this mechanism include to convectively transport air within or out of the body, to increase the local pressure within the tracheae, or some combination thereof. To determine whether tracheal compressions are associated with excurrent gas exchange in the ground beetle Pterostichus stygicus, we used flow-through respirometry and synchrotron x-ray phase-contrast imaging to simultaneously record CO(2) emission and observe morphological changes in the major tracheae. Each observed tracheal compression (which occurred at a mean frequency and duration of 15.6+/-4.2 min(-1) and 2.5+/-0.8 s, respectively) was associated with a local peak in CO(2) emission, with the start of each compression occurring simultaneously with the start of the rise in CO(2) emission. No such pulses were observed during inter-compression periods. Most pulses occurred on top of an existing level of CO(2) release, indicating that at least one spiracle was open when compression began. This evidence demonstrates that tracheal compressions convectively pushed air out of the body with each stroke. The volume of CO(2) emitted per pulse was 14+/-4 nl, representing approximately 20% of the average CO(2) emission volume during x-ray irradiation, and 13% prior to it. CO(2) pulses with similar volume, duration and frequency were observed both prior to and after x-ray beam exposure, indicating that rhythmic tracheal compression was not a response to x-ray irradiation per se. This study suggests that intra-tracheal and trans-spiracular convection of air driven by active tracheal compression may be a major component of ventilation for many insects.
Life: The Excitement of Biology
Ventilatory movements were recorded in four species of lepidopteran pupae, as large as 11.5g (Pseudosphinx tetrio) and as small as 0.0015g (Phyllonorycter strigulatella). The ventilatory movements and ventilatory extracardiac pulsations in haemocoelic pressure were monitored by several electronic methods (strain-gauge recording of abdominal movements, recording of pulsations in haemocoelic pressure, thermographic recording of heartbeat, microrespirographic recording of O2 consumption and CO2 output, and nanoanemometric recording of inspirations and expirations through individual spiracles). It appears that all investigated insect pupae, whether large or small, carefully avoided breathing based on gaseous diffusion. Instead, the pupae actively ventilated their tracheal systems, exchanging respiratory gases and preventing respiratory water loss. Further, it was found that larvae and pupae of Cossus cossus, which were used circa 100 years ago as experimental evidence for creating the well-known "Krogh´s diffusion theory of insect respiration", exhibited beautiful concerts of previously overlooked ventilatory abdominal movements and ventilatory extracardiac pulsations. These results conflict with the indicated diffusion theory, which claimed that these insects did not need to exhibit ventilatory movements at all. Unfortunately, the diffusion theory has persisted until the present due to the lack of exact experimental data. The evidence that we now provide by means of advanced electronic methods shows a widespread occurrence of ventilatory movements. Even immobile insect pupae with low respiratory metabolism exhibit distinctive ventilatory movements. The movements are quite inconspicuous, occurring in the range of micrometers or nanometers, which obviously were imperceptible to earlier investigators. These results confirm our previous findings of human-like insect breathing, based on convective inhalation and exhalation of air driven by the respectively decreased or increased haemocoelic pressure. The results further confirm the control of insect respiration by an autonomic (brain independent), neuroendocrine system known as the coelopulse system, which consists of the nervous centre located in the mesothoracic ganglion of the ventral nerve cord, the neuromotoric spiracular nerves and the intersegmental or dorsoventral abdominal muscles. The system functions as the abdominal
Airway mechanics, gas exchange, and blood flow in a nonlinear model of the normal human lung
Journal of Applied Physiology
Airway mechanics, gas exchange, and blood flow in a nonlinear model of the normal human lung. .-A model integrating airway/lung mechanics, pulmonary blood flow, and gas exchange for a normal human subject executing the forced vital capacity (FVC) maneuver is presented. It requires as input the intrapleural pressure measured during the maneuver. Selected model-generated output variables are compared against measured data (flow at the mouth, change in lung volume, and expired O 2 and CO 2 concentrations at the mouth). A nonlinear parameterestimation algorithm is employed to vary selected sensitive model parameters to obtain reasonable least squares fits to the data. This study indicates that 1) all three components of the respiratory model are necessary to characterize the FVC maneuver; 2) changes in pulmonary blood flow rate are associated with changes in alveolar and intrapleural pressures and affect gas exchange and the time course of expired gas concentrations; and 3) a collapsible midairway segment must be included to match airflow during a forced expiration. Model simulations suggest that the resistances to airflow offered by the collapsible segment and the small airways are significant throughout forced expiration; their combined effect is needed to adequately match the inspiratory and expiratory flow-volume loops. Despite the limitations of this lumped single-compartment model, a remarkable agreement with airflow and expired gas concentration measurements is obtained for normal subjects. Furthermore, the model provides insight into the important dynamic interactions between ventilation and perfusion during the FVC maneuver. ventilation; perfusion; convective-diffusion transfer; parameter estimation; pulmonary function testing 1447 http:/www.jap.org Address for reprint requests: J.
Discontinuous Gas Exchange in Insects: A Clarification of Hypotheses and Approaches
Physiological and Biochemical Zoology, 2006
Many adult and diapausing pupal insects exchange respiratory gases discontinuously in a three-phase discontinuous gas exchange cycle (DGC). We summarize the known biophysical characteristics of the DGC and describe current research on the role of convection and diffusion in the DGC, emphasizing control of respiratory water loss. We summarize the main theories for the evolutionary genesis (or, alternatively, nonadaptive genesis) of the DGC: reduction in respiratory water loss (the hygric hypothesis), optimizing gas exchange in hypoxic and hypercapnic environments (the chthonic hypothesis), the hybrid of these two (the chthonic-hygric hypothesis), reducing the toxic properties of oxygen (the oxidative damage hypothesis), the outcome of interactions between O 2 and CO 2 control set points (the emergent property hypothesis), and protection against parasitic invaders (the strolling arthropods hypothesis). We describe specific techniques that are being employed to * This paper was prepared as an overview of a symposium session presented at "measure respiratory water loss in the presence or absence of the DGC in an attempt to test the hygric hypothesis, such as the hyperoxic switch and H 2 O/CO 2 regression, and summarize specific areas of the field that are likely to be profitable directions for future research.