PS%207_solutions

PS%207_solutions - BIOE 322/BIOS 332 Fundamentals of...

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Page 1 of 3 BIOE 322/BIOS 332 Fundamentals of Systems Physiology Spring 2008 Problem Set #7 Solutions 1. 1.1. Tidal volume = 500 mL Inspiratory capacity = 3500 mL Expiratory reserve volume = 1000 mL Functional residual capacity = 2500 mL Vital capacity = 4500 mL Total lung capacity = 6000 mL 1.2. The volume of the physiologic dead space is estimated with a method based on the P CO2 of expired air (P ECO2 ) that applies the following 3 assumptions: 1) There is no CO2 in inspired air, 2) the physiologic dead space does not participate in gas exchange, therefore, it does not contribute any CO2 to expired air, and 3) all of the CO2 in expired air comes form the exchange of CO2 in functioning alveoli. One problem in comparing the P CO2 of alveolar and expired air is that alveolar air cannot be sampled directly. This problem can be solved, however, because alveolar gas normally equilibrates with pulmonary capillary blood (which becomes systemic arterial blood). Thus, by measuring arterial P CO2 (P aCO2 ), we can determine alveolar P CO2 . Using the abovementioned assumptions, physiologic dead space is calculated as follows: V D = V T * [(P aCO2 – P ECO2 )/P aCO2 ] = (500 mL) * [(40mmHg – 30mmHg)/40mmHg] = 125 mL 1.3. Minute ventilation = V T * f = 500 mL * 12 breaths/min = 6000 mL/min 1.4. Alveolar ventilation (VA) is minute ventilation corrected for physiologic dead space, or: V A = (V T – V D ) * f where V D is physiologic dead space. V A = (500 mL – 125 mL) * 12 breaths/min = 4500 mL/min 1.5. The fundamental relationship in respiratory physiology is an inverse correlation between alveolar ventilation and alveolar PCO2. If CO2 production is constant, the higher the alveolar ventilation, the more CO2 expired and the lower the alveolar PCO2. This relationship is expressed by the alveolar ventilation eqn: V A = V CO2 * K / P ACO2 where P ACO2 is alveolar P CO2 . Rearranging, P ACO2 = V CO2 * K / V A = (200 mL/min) * 863 mmHg / (4500 mL/min) = 38.4 mmHg 2. 2.1. Tidal volume = 500 mL (same before and after bronchodilator) FVC = 2.5 L (during asthma attack), 4.5 L (after treatment) FEV 1 = 1.2 L (during asthma attack), 3.5 L (after treatment) FEV 1 /FVC = 0.48 (during asthma attack), 0.78 (after treatment) Asthma is an obstructive disease that is characterized by inflammation and narrowing of the airways. This narrowing led to increased resistance and decreased airflow. Increases in airway resistance lead to c c c c c c
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PS%207_solutions - BIOE 322/BIOS 332 Fundamentals of...

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