Simulation of Respiratory Mechanics

The dynamic relationship between respiratory muscle effort and the consequent changes in lung volume is investigated. A mathematical simulation based on the structures that form the connection between these two variables makes it possible to lump the contribution from all respiratory muscles into a single time-varying driving force. When this force is applied to the system model, the appropriate lung volume pattern results. The simulation results indicate the accuracy of the model and the validity of the lumped muscle force assumption. In addition, the system model adequately describes abnormal conditions such as decreased lung compliance and increased airway resistance. The results of this simulation suggest that the modeling technique is extremely useful in describing and analyzing complex respiratory system interactions.     

Whole Body Mechanics of Stealthy Walking in Cats

The metabolic cost associated with locomotion represents a significant part of an animal''s metabolic energy budget. Therefore understanding the ways in which animals manage the energy required for locomotion by controlling muscular effort is critical to understanding limb design and the evolution of locomotor behavior. The assumption that energetic economy is the most important target of natural selection underlies many analyses of steady animal locomotion, leading to the prediction that animals will choose gaits and postures that maximize energetic efficiency. Many quadrupedal animals, particularly those that specialize in long distance steady locomotion, do in fact reduce the muscular contribution required for walking by adopting pendulum-like center of mass movements that facilitate exchange between kinetic energy (KE) and potential energy (PE) [1]–[4]. However, animals that are not specialized for long distance steady locomotion may face a more complex set of requirements, some of which may conflict with the efficient exchange of mechanical energy. For example, the “stealthy” walking style of cats may demand slow movements performed with the center of mass close to the ground. Force plate and video data show that domestic cats (Felis catus, Linnaeus, 1758) have lower mechanical energy recovery than mammals specialized for distance. A strong negative correlation was found between mechanical energy recovery and diagonality in the footfalls and there was also a negative correlation between limb compression and diagonality of footfalls such that more crouched postures tended to have greater diagonality. These data show a previously unrecognized mechanical relationship in which crouched postures are associated with changes in footfall pattern which are in turn related to reduced mechanical energy recovery. Low energy recovery was not associated with decreased vertical oscillations of the center of mass as theoretically predicted, but rather with posture and footfall pattern on the phase relationship between potential and kinetic energy. An important implication of these results is the possibility of a tradeoff between stealthy walking and economy of locomotion. This potential tradeoff highlights the complex and conflicting pressures that may govern the locomotor choices that animals make.     

Iterative Integral Parameter Identification of a Respiratory Mechanics Model

ABSTRACT: BACKGROUND: Patient-specific respiratory mechanics models can support the evaluation of optimal lung protective ventilator settings during ventilation therapy. Clinical application requires that the individual's model parameter values must be identified with information available at the bedside. Multiple linear regression or gradient-based parameter identification methods are highly sensitive to noise and initial parameter estimates. Thus, they are difficult to apply at the bedside to support therapeutic decisions. METHODS: An iterative integral parameter identification method is applied to a second order respiratory mechanics model. The method is compared to the commonly used regression methods and error-mapping approaches using simulated and clinical data. The clinical potential of the method was evaluated on data from 13 Acute Respiratory Distress Syndrome (ARDS) patients. RESULTS: The iterative integral method converged to error minima 350 times faster than the Simplex Search Method using simulation data sets and 50 times faster using clinical data sets. Established regression methods reported erroneous results due to sensitivity to noise. In contrast, the iterative integral method was effective independent of initial parameter estimations, and converged successfully in each case tested. CONCLUSION: These investigations reveal that the iterative integral method is beneficial with respect to computing time, operator independence and robustness, and thus applicable at the bedside for this clinical application.     

Mathematical Modeling of Respiratory System Mechanics in the Newborn Lamb

In this paper, a mathematical model of the respiratory mechanics is used to reproduce experimental signal waveforms acquired from three newborn lambs. As the main challenge is to determine specific lamb parameters, a sensitivity analysis has been realized to find the most influent parameters, which are identified using an evolutionary algorithm. Results show a close match between experimental and simulated pressure and flow waveforms obtained during spontaneous ventilation and pleural pressure variations acquired during the application of positive pressure, since root mean square errors equal to 0.0119, 0.0052 and 0.0094. The identified parameters were discussed in light of previous knowledge of respiratory mechanics in the newborn.     

Effects on Respiratory and Circulatory Dynamics

There are exceptions and variations to the general clinical rule that muscle relaxants depress respiration and have no effect on circulation.Variation may be attributed to differences in animal species, in individual response, in muscle affected, in drug used and in dose employed.Conclusions about muscle relaxants derived from animal experiments cannot always be assumed to apply to man.The “respiratory sparing” action of a muscle relaxant cannot be relied upon in any individual patient. Facilities for adequate artificial respiration must always be available when any dose of any muscle relaxant drug is administered.Muscle relaxants affect circulation by inhibition of parasympathetic and sympathetic ganglia, by anticholinesterase activity and by release of histamine.     

Effects of the Menopause Transition on Body Fatness and Body Fat Distribution

Objective : The menopause transition increases cardiovascular and metabolic disease risk, partly because of the adverse effects of estrogen deficiency on the plasma lipid-lipoprotein profile and cardiovascular function. This increased cardiovascular and metabolic disease risk may also be partially mediated by increased body fat, increased intraabdominal adipose tissue accumulation, or both. The objective of this mini-review is to summarize studies that have investigated the relationships among the menopause transition, body fatness, and body fat distribution. Research Methods and Procedures : A review of cross-sectional and longitudinal studies on menopause that examined body fatness and body fat distribution. Results : Cross-sectional reports show that the menopause transition is related to modest increases in body mass index or total fatness, although not all studies found significant effects. Increased central adiposity appears to be related to menopause, independent of advancing age, but these results are methodology dependent. An independent effect of menopause on central body fatness was noted by the use of techniques such as DEXA or computed tomography, whereas studies using circumference measures showed discrepant results. Longitudinal studies showed that the menopause transition accelerated the increase in central adiposity, although no studies quantified changes in intra-abdominal fat by imaging techniques. Discussion : Thus, additional longitudinal studies using more accurate measures of adiposity are needed to critically examine the effects of the menopause transition on total and central body fatness. Collectively, previous studies suggest that menopause is related to modest increase in total fatness and accelerated accumulation of central body fat that exceeds changes normally attributed to the aging process. These changes may increase the risk for cardiovascular and metabolic disease in aging women.     

Effects of Ipomeamarone on Respiratory Enzyme System in Mitochondria

Ipomeamarone inhibited oxidation and phosphorylation in tightly coupled rat liver mitochondria. The inhibition of the oxygen uptake was higher when either β-hydroxybutyrate or α-ketoglutarate was supplied as the substrate than when succinate was used. In mitochondrial preparations which had been uncoupled, inhibitions of the electron transport chain from β-hydroxybutyrate to cytochrome c, and of the enzymes succinate cytochrome c oxidoreductase and β-hydroxybutyrate dehydrogenase were observed. Ipomeamarone inhibited also the ATP-inorganic phosphate exchange reaction, but did not act as an uncoupler; it repressed 2, 4-dinitropheaol-induced oxygen uptake.     

Mechanics of Microtubules: Effects of Protofilament Orientation

Microtubules are hollow cylindrical polymers of the protein tubulin that play a number of important dynamic and structural roles in eukaryotic cells. Both in vivo and in vitro microtubules can exist in several possible configurations, differing in the number of protofilaments, helical rise of tubulin dimers, and protofilament skew angle with respect to the main tube axis. Here, finite element modeling is applied to examine the mechanical response of several known microtubule types when subjected to radial deformation. The data presented here provide an important insight into microtubule stiffness and reveal that protofilament orientation does not affect radial stiffness. Rather, stiffness is primarily dependent on the effective Young's modulus of the polymerized material and the effective radius of the microtubule. These results are also directly correlated to atomic force microscopy nanoindentation measurements to allow a more detailed interpretation of previous experiments. When combined with experimental data that show a significant difference between microtubules stabilized with a slowly hydrolyzable GTP analog and microtubules stabilized with paclitaxel, the finite element data suggest that paclitaxel increases the overall radial flexibility of the microtubule wall.