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1、Anatomy of the Lower Airway Occlusion of the bronchiole Smooth muscle Foreign body (not shown) Inflammation Lung Volumes & Capacities Total lung capacity (TLC) in a typical adult male is 6 liters Much of inspired air does not enter alveoli Tidal Volume (VT) volume of gas inhaled/exhaled during a sin
2、gle ventilatory cycle Usually 5-7 cc/kg (typically 500 cc) Lung Volumes & Capacities Dead Space Air (VD) Air remaining in air passageways, unavailable for gas exchange (usually 150 cc) Anatomic dead space trachea bronchi Physiologic dead space formed by factors like disease or obstruction Examples:
3、COPD & atelectasis Lung Volumes & Capacities Minute Volume Vmin(minute ventilation) amount of gas moved in and out of respiratory tract per minute (tidal volume - dead space volume) X RR Functional Reserve Capacity (FRC) after optimal inspiration, the optimum amount of air that can be forced from th
4、e lungs in a single exhalation Lung Volumes & Capacities Alveolar Air (alveolar volume) VA Air reaching alveoli for gas exchange Usually 350 cc Inspiratory Reserve (IRV) Amount of gas that can be inspired in addition to tidal volume Expiratory Reserve (ERV) Amount of gas that can be expired after a
5、passive (relaxed) expiration Lung Volumes & Capacities Ventilation Defined as movement of air into & out of lungs Inspiration stimulus from respiratory center of brain (medulla) transmitted via phrenic nerve to diaphragm diaphragm flattens during contraction intercostal muscles contract ribs elevate
6、 and expand results in intrapulmonic pressure (pressure gradient) results in air being drawn into lungs & alveoli inflated Ventilation Expiration Stretch receptors in lungs signal respiratory center via vagus nerve to inhibit inspiration Hering-Breuer Reflex Natural elasticity of lungs passively exp
7、ires air (in non-diseased lung) Control via Pons Apneustic & Pneumotaxic centers Ventilation Chemoreceptors Carotid bodies & Aortic arch Stimulated by PaO2, PaCO2 or pH PaCO2 considered normal neuroregulatory control of ventilations Hypoxic Drive default regulatory control Senses changes in Pa02 Ventilation Other stimulations or depressants to ventilatory drive body temp: w/ fever & w/hypothermia drugs/meds: increase or decrease pain: increases but occasionally decreases emotion: increases acidosis: increases sleep: decreases