Nasal cavity modelling

Identical olfactory neurons are located in different places in the cavity, and therefore occupy different positions in the flow path. By using a nasal cavity model, we investigated the influence of the dynamic flow on the sensors response14. The responses from identical fiber optic sensors located... 

Figure 9. A plastic model of a nasal cavity showing the different positions (numbers 1-5) of the sensors. Reprinted with permission from ref. 14. Copyright 2003 American Chemical Society.

During mastication, nonvolatile flavor molecules must move from within the food, through the saliva to the taste receptors on the tongue, and the inside of the mouth, whereas volatile flavor molecules must move from the food, through the saliva and into the gas phase, where they are carried to the aroma receptors in the nasal cavity. The two major factors that determine the rate at which these processes occur are the equilibrium partition coefficient (because this determines the initial flavor concentration gradients at the various boundaries) and the mass transfer coefficient (because this determines the speed at which the molecules move from one location to another). A variety of mathematical models have been developed to describe the release of flavor molecules from oil-in-water emulsions. 

Following the same surgical operation as in the in vivo model, the drug remaining in the nasal cavity can be recovered at a predetermined time and analyzed in this simple model. This method is useful for evaluating both the absorption and the degradation of peptides. 

Plowchalk DR, Andersen ME, Bogdanffy MS. 1997. Physiologically based modelling of vinyl acetate uptake, metabolism, and intracellular pH changes in the rat nasal cavity. Toxicol. Appl. Pharmacol. 142 386 100... 

In addition to small molecules, a number of protein therapeutic agents, such as neurotrophic factors27 and insulin,28 have been successfully delivered to the CNS using IN delivery in a variety of species. The therapeutic benefit of IN delivery of proteins has been demonstrated by Liu et al. in rat stroke models.29 Their studies demonstrated that insulin-like growth factor I (IGF-I) could be delivered to the brain directly from the nasal cavity, even though IGF-I did not cross the BBB efficiently by itself. As a consequence, IN IGF-I markedly reduced infarct volume and improved neurological function following focal cerebral ischemia. Research in... 

Pharmacokinetic models to describe, as a function of formaldehyde air concentration, the rate of formation of formaldehyde-induced DNA-protein cross links in different regions of the nasal cavity have been developed for rats and monkeys (Casanova et al. 1991 Heck and Casanova 1994). Rates of formation of DNA-protein cross links have been used as a dose surrogate for formaldehyde tissue concentrations in extrapolating exposure-response relationships for nasal tumors in rats to estimate cancer risks for humans (EPA 1991a see Section 2. 4.3). The models assume that rates of cross link formation are proportional to tissue concentration of formaldehyde and include saturable and nonsaturable elimination pathways, and that regional and species differences in cross link formation are primarily dependent on anatomical parameters (e g., minute volume and quantity of nasal mucosa) rather than biochemical parameters. The models were developed with data from studies in which... 

Our first task is to build a model where the complex vocal apparatus is broken down into a small number of independent components. One way of doing this is shown in Figure 11.1b, where we have modelled the lungs, glottis, pharynx cavity, mouth cavity, nasal cavity, nostrils and lips as a set of discrete, coimected systems. If we make the assumption that the entire system is linear (in the sense described in Section 10.4) we can then produce a model for each component separately, and determine the behaviour of the overall system fi om the appropriate combination of the components. While of course the shape of the vocal tract will be continuously varying in time when speaking, if we choose a sufficiently short time fi ame, we can consider the operation of the components to be constant over that short period time. This, coupled with the linear assumption then allows us to use the theory of linear time invariant (LTI) filters (Section 10.4) throughout. Hence we describe the pharynx cavity, mouth cavity and lip radiation as LTI filters, and so file speech production process can be stated as the operation of a series of z-domain transfer functions on the input. 

When the velum is lowered during the production of nasals and nasalised vowels, sound enters via the velar gap, propagates through the nasal cavity and radiates through the nose. Hence for a more complete model, we have to add a component for the nasal cavity. This in itself is relatively straightforward to model for a start, it is a static articulator, so doesn t have anywhere near the complexity of shapes that occur in the oral cavity. By much the same techniques we employed above, we can construct an all-pole transfer function for the nasal cavity. 

Beyond this the similarities between the formant s mthesiser and LP model start to diverge. Firstly, with the LP model, we use a single all-pole transfer function for all sounds. In the formant model, there are separate transfer functions in the formant synthesiser for the oral and nasal cavity. In addition a further separate resonator is used in formant synthesis to create a voiced source signal from the impulse train in the LP model the filter that does this is included in the all-pole filter. Hence the formant synthesiser is fundamentally more modular in that it separates these components. This lack of modularity in the LP model adds to the difficulty in providing physical interpretations to the coefficients. 

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