Control models, respiratory

This article reviews and evaluates the existing work related to respiratory regulation with particular emphasis on the control models which... 

This review is not an exhaustive survey, but rather focuses on principal advances and existing limitations. For additional insight there are several reviews on the physiological aspects of respiratory control (I, 2, 3, 4, 5) and respiratory control models (6, 7, 8). A brief review of the important physiological observations related to mechanisms of control, the stimuli, and the receptors is included. This information is the physiological background for the discussions of respiratory control models. 

Although the assumption of such a control mechanism involving reference values for the controlled variables is intuitively attractive, the existence of such reference values is still questioned (26). However, in most respiratory control models to date such a servomechanistic regulation is generally used only recently have other performance criteria been suggested (26). 

Table I summarizes the important existing respiratory control models. Each model is made up of certain structural elements (1) lungs, (2) body tissues, (3) blood-gas relations, (4) ventilatory control law, and (5) blood flow and blood flow distribution control laws. The models differ mainly in the treatment of the last four elements.

In a continuation of the early work of Grodins and co-workers, Grodins and James (30) presented a respiratory control model which like... 

Additional respiratory control models have recently been reported by Milhom and Reynolds (42) and Duflin (49), Milhoms model is similar to his previous model except that a peripheral sensor compartment is added, and the central H+ sensor is located beneath the surface of the medulla. The depth of the central sensor was adjusted (effectively adjusting the diffusional time lag) to provide close agreement between computed and experimental ventilatory responses to C02 inhalation. When the model is applied to CSF perfusion, good agreement is reported. 

In earlier researches [8], it was suggested that normal ventilatory responses to CO2, exercise inputs, and mechanical loading could be predicted by the minimization of a controller objective function consisting of total chemical and mechanical cost of breathing. The optimal respiratory control model was later proposed and verified by optimizing a quadratic inspiratory neural drive [9]. The optimal instantaneous airflow and lung volume were derived based on a lumped-parameter RC model [10] for the relation between respiratory neural and mechanical outputs. 

Three usually seen airflow, including sinusoidal, square, and descending wave, in mechanical ventilation are modeled as the inspiratory flow pattern during CMV mode and volume-targeted mechanical ventilation in this paper. Instead of optimizing the pressure profile, the airflows waveforms will be optimized in current study through the optimal respiratory control model. 

Among those respiratory control models under studied during the past years, possible optimality principle has... 

This paper modeled sinusoidal, square, and descending airflow waveforms and control parameters in CMV, and implemented an optimal control model for respiratory systems. Simulations were performed under resistive and elastic loading. In Fig. 4, we may find the optimal airflow profiles of sinusoidal (left), square (middle), and descending (right) model of no load (solid line), which was compared with that of CRL (top) and CEL (bottom). 

Hawthorne, A., et al. (1987) Models for estimating organic emissions from building materials formaldehyde example. Atmos. Environ. 21, No. 2. Lewis, R. G., et al. (1986) Monitoring for non-occupational exposure to pesticides in indoor and personal respiratory air. Presented at the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN. 

The major respiratory factors in the control of ozone uptake are the morphology (including the mucus layer), the respiratory flow, the physical and chemical properties of mucus, and the physical and chemical properties of ozone. The next two sections discuss models of the morphology and the air and mucus flow. The physical and chemical properties of bronchial secretions have been reviewed by Barton and Lourenco and Charman et al. The relevant physical and chemical properties of ozone, are its solubility and diffusivity in mucus and water and its reaction-rate constants in water, mucus, and tissue. 

Among other predictions, the integrated model reveals that as work rate is varied, commensurate increases in the rate of mitochondrial ATP synthesis are effected by changes in concentrations of available ADP and inorganic phosphate. In other words, mitochondrial respiratory control is achieved in vivo by substrate feedback control. The predicted relationship between substrates and work rate is plotted in Figure 7.14. Model predictions are compared to data obtained from NMR spectroscopy of exercising flexor forearm muscle in healthy human subjects [106],... 

A variety of in vitro toxicity tests have been developed to model the effects of toxins on living cells or tissues. In these tests, a carrier medium (such as fetal bovine serum) containing given concentrations, or doses, of a particular toxin are added to cell cultures (cell lines). Various indicators of toxicity, cell morphology transformation, or cell prohferation are then measured after specified periods of time. The cell types used in a particular study can be chosen to approximate the types of cells that would be affected during acmal exposure, such as respiratory cells or tissues. Toxicity indicators include, for example, measures of the percent of viable cells remaining at the end of the test (compared to a control line with no added toxin), and the concentrations various cytokines or other cytoplasmic enzymes induced from the cells by the toxin. Uncertainties with the in vitro toxicity tests include how comparable their results are to those of in vivo toxicity tests, and how well they reproduce actual physiological conditions and processes in the human body (Johnson and Mossman, 2001). 

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