Ch7-notes

Ch7-notes - Mechanics of Breathing-Ch 7 Questions 1 How much power does it take to run a mechanical respirator 2 Is there a difference in power

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Mechanics of Breathing-Ch 7 Questions: 1. How much power does it take to run a mechanical respirator? 2. Is there a difference in power consumption between constant pressure and constant flow modes? Normal human breathing at rest only involves the diaphragm muscle which is located at the separation of the thorax and abdominal cavity. The diaphragm is dome shaped and flattens during contraction leading to creation of a negative pressure within the lungs. Air then flows through the trachea and fills the lungs . The lungs and chest wall are elastic structures which are stretched in proportion to lung volume. This makes it possible to expire just by passive relaxation. For more forceful inspiration and expiration other muscles can be used. Note the external intercostal muscle arrangement between the ribs which raise the ribs when contracted and aid inspiration. Internal intercostal muscles lower the ribs and are expiratory in action. Both intercostal muscles also attach to the spinal column. The abdominal muscles when contracted push abdominal contents inward and can create a large expiratory flow for activity like coughing. The simplest engineering model is shown below as an electrical circuit model or the associated differential equation.
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P = R dV/dt + C V dV/dt = - V/(RC) + P/R This model is useful in understanding normal and artificial respiration. In normal breathing driving pressure is due to the diaphragm which can be thought of as a piston pump pulling the thoraco-abdominal separation downward. The input pressure would be negative with the ground point corresponding to mouth pressure. This pressure is opposed by
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This note was uploaded on 02/15/2012 for the course BME 403 taught by Professor Yamashiro during the Spring '07 term at USC.

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Ch7-notes - Mechanics of Breathing-Ch 7 Questions 1 How much power does it take to run a mechanical respirator 2 Is there a difference in power

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