The nose is the front line defender of the respiratory system. Unsteady simulations in three-dimensional models have been developed to study transport patterns in the human nose and its overall air-conditioning capacity. The results suggested that the healthy nose can efficiently provide about 90% of the heat and the water fluxes required to condition the ambient inspired air to near alveolar conditions in a variety of environmental conditions and independent of variations in internal structural components. The anatomical replica of the human nose showed the best performance and was able to provide 92% of the heating and 96% of the moisture needed to condition the inspired air to alveolar conditions. A detailed analysis explored the relative contribution of endonasal structural components to the air-conditioning process. During a moderate breathing effort, about 11% reduction in the efficacy of nasal air-conditioning capacity was observed.

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Evaluation of the fluid flow pattern in a non-pregnant uterus is important for understanding embryo transport in the uterus. Fertilization occurs in the fallopian tube and the embryo (fertilized ovum) enters the uterine cavity within 3 days of ovulation. In the uterus, the embryo is conveyed by the uterine fluid for another 3 to 4 days to a successful implantation site at the upper part of the uterus. Fluid movements within the uterus may be induced by several mechanisms, but they seem to be dominated by myometrial contractions. Intra-uterine fluid transport in a sagittal cross-section of the uterus was simulated by a model of wall-induced fluid motion within a two-dimensional channel. The time-dependent fluid pattern was studied by employing the lubrication theory. A comprehensive analysis of peristaltic transport resulting from symmetric and asymmetric contractions is presented for various displacement waves on the channel walls. The results provide information on the flow field and possible trajectories by which an embryo may be transported before implantation at the uterine wall.

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The nasal cavity is the main passage for air flow between the ambient atmosphere and the lungs. A preliminary requisite for any investigation of the mechanisms of each of its main physiological functions, such as filtration, air-conditioning and olfaction, is a basic knowledge of the air-flow pattern in this cavity. However, its complex three-dimensional structure and inaccessibility has traditionally prevented a detailed examination of internal in vivo or in vitro airflow patterns. To gain more insight into the flow pattern in inaccessible regions of the nasal cavity we have conducted a mathematical simulation of asymmetric airflow patterns through the nose. Development of a nose-like model, which resembles the complex structure of the nasal cavity, has allowed for a detailed analysis of various boundary conditions and structural parameters. The coronal and sagittal cross-sections of the cavity were modeled as trapezoids. The inferior and middle turbinates were represented by curved plates that emerge from the lateral walls. The airflow was considered to be incompressible, steady and laminar. Numerical computations show that the main air flux is along the cavity floor, while the turbinate structures direct the flow in an anterior-posterior direction. The presence of the turbinates and the trapezoidal shape of the cavity force more air flux towards the olfactory organs at the top of the cavity.

How do infants extract milk during breast-feeding? We have resolved a century-long scientific controversy, whether it is sucking of the milk by subatmospheric pressure or mouthing of the nippleareola complex to induce a peristaltic-like extraction mechanism. Breast-feeding is a dynamic process, which requires coupling between periodic motions of the infant's jaws, undulation of the tongue, and the breast milk ejection reflex. The physical mechanisms executed by the infant have been intriguing topics. We used an objective and dynamic analysis of ultrasound (US) movie clips acquired during breast-feeding to explore the tongue dynamic characteristics. Then, we developed a new 3D biophysical model of the breast and lactiferous tubes that enables the mimicking of dynamic characteristics observed in US imaging during breastfeeding, and thereby, exploration of the biomechanical aspects of breast-feeding. We have shown, for the first time to our knowledge, that latch-on to draw the nipple-areola complex into the infant mouth, as well as milk extraction during breast-feeding, require development of time-varying subatmospheric pressures within the infant's oral cavity. Analysis of the US movies clearly demonstrated that tongue motility during breast-feeding was fairly periodic. The anterior tongue, which is wedged between the nipple-areola complex and the lower lips, moves as a rigid body with the cycling motion of the mandible, while the posterior section of the tongue undulates in a pattern similar to a propagating peristaltic wave, which is essential for swallowing.submental ultrasound | sucking pressure | computational model | fluid-structure interaction B reast-feeding is strongly publicized and encouraged by many societies and communities. It is well accepted that breast milk provides the infant both nutrients and immunities required for growth and development during the first months after birth. It is less known that breast-fed infants exercise and prepare their orofacial muscles for future tasks of speaking and chewing (1), and also have higher oxygen saturation than bottle-fed infants (2). Breast-feeding is the outcome of a dynamic synchronization between oscillation of the infant's mandible, rhythmic motility of the tongue, and the breast milk ejection reflex that drives maternal milk toward the nipple outlet. First, the infant latches onto the breast and nipple so that the nipple, areola, and underlying mammary tissue and lactiferous ducts are drawn into the infant's mouth with the nipple tip extended as far as the hard-soft palate junction (HSPJ). Then, the infant moves its mandible up and down, compressing the areola and the underlying lactiferous ducts with its gums in a suckling process that extracts the milk into its mouth (3, 4). Simultaneous with compression, spontaneous undulating motions of the infant tongue channel the milk posteriorly and trigger the swallowing reflex (5). During breast-feeding, suckling, swallowing, and breathing are coordinated by the central nervous system in a way that allows for...

Uterine contractility is generated by contractions of myometrial smooth muscle cells (SMCs) that compose most of the myometrial layer of the uterine wall. Calcium ion (Ca 2ϩ ) entry into the cell can be initiated by depolarization of the cell membrane. The increase in the free Ca 2ϩ concentration within the cell initiates a chain of reactions, which lead to formation of cross bridges between actin and myosin filaments, and thereby the cell contracts. During contraction the SMC shortens while it exerts forces on neighboring cells. A mathematical model of myometrial SMC contraction has been developed to study this process of excitation and contraction. The model can be used to describe the intracellular Ca 2ϩ concentration and stress produced by the cell in response to depolarization of the cell membrane. The model accounts for the operation of three Ca 2ϩ control mechanisms: voltage-operated Ca 2ϩ channels, Ca 2ϩ pumps, and Na ϩ /Ca 2ϩ exchangers. The processes of myosin light chain (MLC) phosphorylation and stress production are accounted for using the cross-bridge model of Hai and Murphy (Am J Physiol Cell Physiol 254: C99 -C106, 1988) and are coupled to the Ca 2ϩ concentration through the rate constant of myosin phosphorylation. Measurements of Ca 2ϩ , MLC phosphorylation, and force in contracting cells were used to set the model parameters and test its ability to predict the cell response to stimulation. The model has been used to reproduce results of voltage-clamp experiments performed in myometrial cells of pregnant rats as well as the results of simultaneous measurements of MLC phosphorylation and force production in human nonpregnant myometrial cells. cellular calcium control mechanisms; myometrial contractions; myosin light chain phosphorylation UTERINE CONTRACTILITY is generated by contractions of the myometrial smooth muscle cells (SMCs) that compose most of the myometrial layer of the uterine wall. In the nonpregnant uterus, synchronous contractions of these SMCs produce changes in the geometry of the uterine fluid-wall interface. These changes induce intrauterine fluid motions that are essential during early phases of reproduction (3,11,28). During parturition, the synchronized contraction of these myocytes generates the forces required to deliver the baby out of the uterus. Depolarization of the cell membrane initiates calcium ion (Ca 2ϩ ) entry into the cells through voltage-operated Ca 2ϩ channels (VOCCs) and thereby a rise in the intracellular Ca 2ϩ concentration (C Ca,i ). The elevated level of C Ca,i allows binding of Ca 2ϩ and calmodulin, thus activating myosin light-chain kinase (MLCK), which phosphorylates a regulatory myosin light chain (MLC) (29,32). This subsequently allows the formation of cross bridges between actin and myosin filaments and the generation of muscle contraction.The excitation-contraction process was studied in both rat and human myometria using the voltage-clamp technique. Stimulation of isolated myocytes using voltage pulses revealed the current-voltage relationship...