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Physics, Pharmacology and Physiology for Anaesthetists - 7

Tĩnh tuân thủ thường cao hơn so với việc tuân thủ năng động bởi vì có thời gian cho khối lượng và cân bằng áp lực giữa phổi và hệ thống đo lường. Khối lượng đo được có xu hướng tăng lên và áp lực đo có xu hướng giảm, cả hai | Compliance and resistance Compliance The volume change per unit change in pressure ml.cmH2O 1 or l.kPa 1 . Lung compliance When adding compliances it is their reciprocals that are added as with capacitance so that 1 CTOTAL 1 cCHEST 1 clung where CCHEST is chest compliance 1.5-2.0l.kPa-1 or 150-200 ml.cmH2O 1 CLUNG is lung compliance 1.5-2 l.kPa 1 or 150-200 ml.cmH2O 1 and CTOTAL is total compliance 7.5-10.0 l.kPa 1 or 75-100 ml.cmH2O 1 . Static compliance The compliance of the lung measured when all gas flow has ceased ml.cmH2O 1 orl.kPa 1 . Dynamic compliance The compliance of the lung measured during the respiratory cycle when gas flow is still ongoing ml.cmH2O 1 or l.kPa 1 Static compliance is usually higher than dynamic compliance because there is time for volume and pressure equilibration between the lungs and the measuring system. The measured volume tends to increase and the measured pressure tends to decrease both of which act to increase compliance. Compliance is often plotted on a pressure-volume graph. Resistance The pressure change per unit change in volume cmH2O.ml 1 orkPa.l 1 . Lung resistance When adding resistances they are added as normal integers as with electrical resistance Total resistance Chest wall resistance lung resistance Compliance and resistance 143 Whole lung pressure-volume loop This graph can be used to explain a number of different aspects of compliance. The axes as shown are for spontaneous ventilation as the pressure is negative. The curve for compliance during mechanical ventilation looks the same but the x axis should be labelled with positive pressures. The largest curve should be drawn first to represent a vital capacity breath. Inspiration The inspiratory line is sigmoid and therefore initially flat as negative pressure is needed before a volume change will take place. The mid segment is steepest around FRC and the end segment is again flat as the lungs are maximally distended and so poorly compliant in the face of further .