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.'et tianics of Rcspiration: Flow-Volume

RESPIRATORY PHYSIOLOGY

V high lung vołumes, ratę of airflow dunng expiration inereases pro-gressivcly with inucasing effort. At intcrmcdiate and Iow lung vol-airflow rearhes maximal levek after only modeli effort is cxort «f and thereafter inereases no further despile inereasiog effort

Dctcrminanl

At lung voiumes greater than 75% of VC, airflow inereases progressóely with inereasing pleural pressure. Airflow Is effort dependent. At volumes helów 75% of VC. airflow tevels otf as płcural pressurc excecds atmospherie pressure. Thereafter, airflow ts effort independent, because further inereases In pleural pressure result in no further rise in ratę of

; of Maximal Expiratory

jrwet of maximal airflow contraction of expiratory muscles at a given lung *-me raiscs pleural pressurc abovc atmosphenc level 1+20 cm H₂0). Alveolar -"•urr Kum of pleural pressurc and lung recoil pressure) is yet higher 1—30 cm Airway pressure falls progressiveły from alveolus to airway oponing in en ommg resistance. At equal pressure point of airway, pressure within an way pressure surrounding it (pleural pressure). Beyond rhk point, as intr.ilumin.il —-surę drops further, bclow pleural pressure. airway will be compressed

With further inereases in expiratory effort, at same lung volume, pleural pressure is greater and alveolar pressure is correspondingK higher. Tali In airway pressure and location of equal pressure point are unchanged, but beyond equal pressure point, intrathoracic airways will be compressed to a greater degree by higher pleural pressure. Once maximal airflow is achieved, further inereases in pleural pressure prpducc proportional inereases in resistance of segment downstream from equal pressure point, so ratę of airflow doe< not change

Figurę 5.12 FlowVoi.ume Relationships_

*wrlow varies as a function of pressure and lung volume. Tlie highesl rales of airflow are seen at high lung yolumes.

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