PHGY 312 Lecture Notes - Lecture 4: Time Constant, Ibm System P, Total Pressure
24 May 2016
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Total pressure required inflating the r system o. Ptotal = (volume x elastance) + (flow x resistance) If we increase tidal volume a lot, the elastic work will be very high! Better to breathe a little less deeply and have a faster ventilation rate. Elastic work is high as tidal volume increases (low f) Determined by the pressure accumulated during inspiration and mechanical properties of the system. Time for passive expiration depends on the mechanical time constant. Exp time long enough to let tau deflate the lung. If it"s a shorter exp time, frc starts to increase! They beat the time constant, don"t allow full expiration and end expiratory level goes up. Birds like to expand their sacs by breathing fast. Fibrotic patients have a short time constant (exhale faster, cannot inhale much) Emphysema patients have a long time constant (exhale slower, inhales lots) Retaining co2 if they can"t breathe out enough.
