USMLE Pretest Physiology 14th Edition Questions

E-D = ERV

160. A healthy 30-year-old woman is referred for a life insurance physical exam. History reveals that she has never smoked and vesicular breath sounds are heard at the periphery of the lung with auscultation. In the patient's spirometry tracing below, the expiratory reserve volume (ERV) equals which of the following?

.21*380 = 80 mmHg

161. A group of third-year medical students accompanied a medical mission team to Peru, South America. After arriving at the airport in Bolivia, they hiked to a remote mountain village in the Andes at an elevation of 18,000 ft. With a barometric pressure of 380 mm Hg at this altitude, what would be the resulting PO2 of the dry inspired air?

The answer is c The measured PaO2 will be higher and the measured PaCO2 will be lower than the patient's actual blood gas values.

162. A 28-year-old man is admitted to the emergency department with multiple fractures suffered in a car accident. Arterial blood gases are ordered while the patient is breathing room air. After the first-year resident obtains an arterial blood sample from the patient, the glass plunger slides back, drawing an air bubble into the syringe before it is handed to the blood gas technician for analysis. How does exposure to room air affect the measured values of PO2 and PCO2 in arterial blood? a. The measured values of both PaO2 and PaCO2 will be higher than the patient's actual values. b. The measured values of both PaO2 and PaCO2 will be lower than the patient's actual values. c. The measured PaO2 will be higher and the measured PaCO2 will be lower than the patient's actual blood gas values. d. The measured PaO2 will be lower and the measured PaCO2 will be higher than the patient's actual blood gas values. e. The measured values of PaO2 and PaCO2 will accurately reflect the actual values.

The answer is a. In pulmonary fibrosis, the diffusing capacity of the lung is decreased due to an increase in the thickness of the diffusional barrier, as predicted by Fick law of diffusion. Pulmonary fibrosis is characterized by a decrease in lung compliance and an increase in lung elastic recoil ("stiff" lungs), which results in findings typical of a restrictive impairment. Pulmonary function test values characteristic of a restrictive impairment include a decrease in all lung volumes and capacities and a ratio of the FEV1 to the total FVC that is normal or increased. Airway radius is decreased, and thus airway resistance is increased, at lower lung volumes, but in restrictive disorders, the airway resistance is normal when corrected for lung volume in contrast to obstructive disorders, in which an increased airway resistance is a hallmark of the functional imp airment . Decreased lung compliance Increased recoil Normal resistance when corrected for lung volume

163. A 68-year-old woman with pulmonary fibrosis presents with a complaint of increasing dyspnea while performing activities of daily living. She is referred for pulmonary function testing to assess the progression of her disease. Which of the following laboratory values is consistent with her diagnosis? a. Decreased diffusing capacity of the lung b. Increased residual volume c. Decreased forced expiratory volume exhaled in 1 second (FEV1)/forced vital capacity (FVC) d. Increased lung compliance e. Increased airway resistance corrected for lung volume

The answer is b. A pulmonary thromboembolism results in areas of the lung that are ventilated, but not perfused, yielding ratios of infinity and an increase in alveolar dead space. When the ratio equals∞, the PAO2 of the affected alveoli will be the same as that in the humidified inspired air because atmospheric air enters the alveoli via the process of ventilation, but no gas exchange takes place because the alveoli are not perfused. Areas of the lung that are perfused but not ventilated constitute areas of shunting (venous admixture), characterized as a ratio equal to 0, and having PAO2 values that equilibrate with the mixed venous blood.

164. A 34-year-old woman presents in the emergency department with tachypnea and shortness of breath of acute onset. The history reveals that she has been taking oral contraceptives for 9 years. A lung scan demonstrates a perfusion defect in the left lower lobe. Which of the following occurs if the blood flow to alveolar units is totally obstructed by a pulmonary thromboembolism? a. The ratio of the alveolus equals zero. b. The PO2 of the alveolus will be equal to that in the inspired air. c. The PO2 of the alveolus will be equal to the mixed venous PO2. d. There will be an increase in shunting (venous admixture) in the lung. e. There will be a decrease in alveolar dead space.

Z - In pulmonary edema, the abnormal accumulation of fluid in the lungs causes a restrictive pulmonary impairment characterized by decreased lung compliance. X - emphysema The increase in airway resistance in asthma is not associated with an increase (or decrease) in lung compliance. In emphysema, alveolar septal departitioning causes the destruction of elastic fibers, which decreases the elastic recoil of the lungs, thereby increasing lung compliance (curve X). Emphysematous changes in the lungs also occur in aging. An L/S ratio ≥2 indicates normal biochemical maturation of the lung in utero, with normal surfactant production and lung compliance (normal curve). If the L/S ratio is less than 2, such as may occur in preterm infants, there is an increased incidence of respiratory distress syndrome of the newborn, a restrictive impairment that would be characterized by curve Z.

166. A hospitalized patient has tachypnea and significantly labored respirations requiring mechanical ventilation. Based on the pressure-volume curve of the lungs shown as curve Z in the figure below, which of the following is the most likely diagnosis for the patient?

The answer is b When air enters the pleural space due to interruption of the pleural surface through either the rupture of the lung or a hole in the chest wall, the pressure in the pleural space becomes atmospheric, the lung on the affected side collapses because of the lung's tendency to recoil inward, and the chest wall on the affected side recoils outward. With collapse of the lung, the v/q ratio on the affected side decreases. The trachea shifts toward the affected lung in a spontaneous pneumothorax and away from the affected lung in a tension pneumothorax.

167. A 6′3′′ tall, 140-lb, 20-year-old man was watching television when he felt pain in his shoulder blades, shortness of breath, and fatigue. His father noticed how pale he was and took him to the emergency department. The physical exam revealed decreased tactile fremitus, hyperresonance, and diminished breath sounds. A chest x- ray revealed a 55% pneumothorax of the right lung, which was attributed to rupture of a bleb on the surface of the lung. What changes in lung function occur as a result of a pneumothorax? a. The chest wall on the affected side recoils inward. b. The intrapleural pressure in the affected area equals to atmospheric pressure. c. The trachea deviates away from the affected lung. d. There is hyperinflation of the affected lung. e. The ratio on the affected side increases above normal.

The answer is d. VTV = VD + VA VA = VT-VD = 500 - 125 = 375 mL * 15 = 5625

169. A 125-lb, 40-year-old woman with a history of nasal polyps and aspirin sensitivity since childhood presents to the emergency department with status asthmaticus and hypercapnic respiratory failure. She requires immediate intubation and is placed on a mechanical ventilator on an FIO2 of 40%, a control rate of 15 breaths per minute, and a tidal volume of 500 mL. Which of the following is her approximate alveolar ventilation?

The answer is a. During exercise, minute ventilation and alveolar ventilation increase linearly with carbon dioxide production up to a level of about 60% of the maximal workload. Above that level, called the anaerobic threshold, muscle lactate spills into the circulation causing a metabolic acidosis, characterized by a decrease in pH and [HCO3] . The increased [H+] stimulates the peripheral (not central) chemoreceptors to increase alveolar ventilation more proportionally than the increase in carbon dioxide production, resulting in a decrease in PaCO2.

170. A 26-year-old man training for a marathon reaches a workload that exceeds his anaerobic threshold. If he continues running at or above this workload, which of the following will increase? a. Alveolar ventilation b. Arterial pH c. PaCO2 d. Plasma [HCO-3] e. Firing of the central chemoreceptors

The answer is c Because the dead space air does not participate in gas exchange, the entire output of CO2 in the expired gas comes from the alveolar gas. Accordingly, alveolar (and arterial) PCO2 can be expressed in terms of CO2 output and alveolar ventilation according to the following equation: Thus, an increase in alveolar ventilation at a constant rate of carbon dioxide production will lower PACO2 and PaCO2. Hyperventilation increases PAO2 and PaO2, with no change in the alveolar-arterial PO2 difference. The V/q will be normal or increased.

171. A medical student waiting for her first patient interview at the clinical skills center becomes very anxious and increases her rate of alveolar ventilation. If her rate of CO2 production remains constant, which of the following will decrease? a. pH b. PaO2 c. PaCO2 d. V/Q per min e. Alveolar-arterial PO2 difference

The answer is b. An increased velocity of airflow will increase turbulent airflow, as predicted by an increased Reynolds number. Resistance to turbulent airflow exceeds that for laminar airflow, and thus the pressure gradient required for airflow increases when flow is turbulent. Because the velocity of airflow is greatest in the trachea and large airways, the predisposition to turbulent airflow is greater in the central than in the peripheral airways. Airway resistance varies inversely with the fourth power of airway radius, according to Poiseuille law.

173. A 58-year-old woman experiences an acute exacerbation of asthma, which causes her breathing to become labored and faster. As a result, which of the following changes in airflow is expected? a. Flow in the trachea and upper airways will become more laminar. b. The pressure gradient required for airflow will increase. c. The resistance to airflow will decrease. d. The resistance to airflow will increase linearly with the decrease in airway radius. e. Reynolds number will decrease.

The answer is e. Alveolar ventilation is the volume of air entering and leaving the alveoli per minute. Alveolar ventilation is less than the minute ventilation (minute volume) because the last part of each inspiration remains in the conducting airways and does not reach the alveoli. The minute ventilation is the product of tidal volume and respiratory rate (14,400 mL/min). Alveolar ventilation cannot be measured directly but must be calculated by subtracting dead space ventilation from minute ventilation. The ratio of the physiological dead space volume to the tidal volume (VD/VT) can be calculated using the Bohr equation (PaCO2 PECO2/PaCO2), and then multiplied by the VT to yield the dead space volume, which when multiplied by the respiratory rate yields the dead space ventilation (5760 mL/min). Thus, alveolar ventilation in this patient is 8640 mL/min. The adequacy of alveolar ventilation is determined by the alveolar air equation, which states that the PaCO2 is approximately equal to the rate of carbon dioxide production divided by the rate of alveolar ventilation. At a normal rate of alveolar ventilation, PaCO2 is in the normal range of 35 to 45 mm Hg. Assuming a constant rate of carbon dioxide production, a decrease in alveolar ventilation (hypoventilation) causes a higher PaCO2 than normal (ie, >45 mm Hg) and a rate of alveolar ventilation that is greater than normal (hyperventilation) "blows off" excessive CO2 causing PaCO2 to decrease below normal (ie, <35 mm Hg). Thus, in this patient, the PaCO2 of 30 mm Hg indicates that she is hyperventilating. If her increase in alveolar ventilation matched an increased carbon dioxide production, then PaCO2 would be in the normal range.

174. A 27-year-old woman at 30 weeks of gestation goes to the obstetrician for a prenatal visit. During the visit, she expresses concern that she has been breathing faster than usual. Lab results revealed the following: Based on the data, what conclusions can you draw about the level of the patient's alveolar ventilation? a. Alveolar ventilation exceeds her minute ventilation. b. Alveolar ventilation is inadequate due to rapid, shallow breathing. c. Alveolar ventilation is less than her dead space ventilation. d. Alveolar ventilation matches the increased CO2 production during pregnancy. e. Alveolar ventilation is greater than normal.

The answer is c. Pulmonary surfactant increases lung compliance by lowering alveolar surface tension. As a result, the pressure gradient needed to inflate the alveoli decreases, as does the work of breathing. Although surfactant replacement therapy has proven to be beneficial in respiratory distress syndrome of the newborn, surfactant replacement therapy is not currently recommended in acute respiratory distress syndrome based on clinical evidence against efficacy of the therapy.

175. A newborn of 28 weeks of gestation develops respiratory distress syndrome. Mechanical ventilation on 100% O2 with 10 cm H2O of positive end-expiratory pressure (PEEP) does not provide sufficient oxygenation. After porcine surfactant is instilled via a fiberoptic bronchoscope, the PaCO2, fraction of inspired oxygen (FIO2), and shunting improve impressively. The improvements in respiratory function occurred because surfactant increased which of the following? a. Alveolar surface tension b. Bronchiolar smooth muscle tone c. Lung compliance d. The pressure gradient needed to inflate the alveoli e. The work of breathing

The answer is a Cigarette smoking is the major cause of COPD. In obstructive lung diseases, the increase in airway resistance causes a decrease in expiratory flow rates and "air-trapping," which results in an increased residual volume, and thus total lung capacity. This hyperinflation pushes the diaphragm into a flattened position. Asbestosis and pulmonary fibrosis are restrictive lung diseases, in which curve C would be the typical MEFV curve. Decreased effort would decrease flow rates during the effort-dependent portion of a MEFV curve, but not during the effort-independent portion.

176. In the maximal expiratory flow-volume curves below, curve A would be typical of which of the following clinical presentations? a. A 75-year-old man who has smoked two packs of cigarettes per day for 60 years. His breath sounds are decreased bilaterally and his chest x-ray shows flattening of the diaphragm. b. A 68-year-old man who presents with a dry cough that has persisted for 3 months. His chest x-ray shows opacities in the lower and middle lung fields. The man states that he was exposed to asbestos for approximately 10 years when he worked in a factory in his 30s. c. A 57-year-old woman with pulmonary fibrosis who presents to the emergency room with shortness of breath. d. An 84-year-old woman with a history of myocardial infarction who reports shortness of breath that worsens in the recumbent position. e. A healthy, 22-year-old man getting his army enlistment physical exam. He has never smoked, but is tired that morning, and does not use much effort while exhaling.

The answer is b. The afferent pathway from the carotid body chemoreceptors is the Hering nerve, a branch of cranial nerve IX, the glossopharyngeal nerve. The vagus nerve constitutes the afferent pathway from the aortic baroreceptors, the J receptors, the irritant airway receptors, and the rapidly adapting stretch receptors mediating the Hering-Breuer inflation reflex.

177. A 14-year-old adolescent girl presents with a lump in the neck. Fine needle aspiration biopsy reveals acinic cell carcinoma of the parotid gland. During the parotidectomy, there is compression injury of the glossopharyngeal nerve. As a result, which of the following respiratory reflexes will be impaired? a. Aortic baroreceptor reflex b. Carotid body chemoreceptor reflex c. Hering-Breuer inflation reflex d. Irritant airway reflex e. Juxta pulmonary capillary (J) receptor reflex

The answer is a The answer is a. (Barrett, pp 649-653. Levitzky, pp 181-184.) Alveolar hypoventilation (as evidenced by the higher-than-normal value of PaCO2) is a type of hypoxic hypoxia or hypoxemia (as evidenced by the decreased PaO2). Anemic hypoxia is characterized by a decreased concentration of hemoglobin (anemia) or a reduction in the saturation of hemoglobin with oxygen (SaO2) expected for a given PaO2, as would occur in carbon monoxide poisoning or methemoglobinemia. Stagnant hypoxia is characterized by a decreased cardiac output; in this patient, cardiac output, calculated as is 5 L/min, which is normal. In histotoxic hypoxia, oxygen extraction is impaired, and thus CaO2 - CvO2 would be less than normal and SvO2 would be greater than normal.

178. A 30-year-old woman is admitted to the emergency department with dyspnea, tachycardia, confusion, and other signs of hypoxia. The following laboratory data were obtained while the patient was breathing room air: Which of the following is the most appropriate classification of the patient's hypoxia? a. Hypoxic hypoxia (hypoxemia) b. Anemic hypoxia c. Stagnant (hypoperfusion) hypoxia d. Histotoxic hypoxia e. Carbon monoxide poisoning

179. The answer is b.

179. A 63-year-old woman is required to undergo pulmonary function testing as part of a life insurance health assessment. The occupational medicine physician orders the testing to be done in both the upright and supine positions. In the upright position, which of the following variables will be lower in the apex compared with the base of the lung? A. PaCO2 B. Lung compliance C. Pulmonary vascular resistance (PVR) D. Resting lung volume (functional residual capacity [FRC]) E. V/Q min ratio

The answer is c. (Le, p 549. Levitzky, pp 90-91.) PVR is calculated as: PVR = (DeltaP/q - MPAP)-M LAP/ Pulmonary blood flow = 35-15 mmhg / 4 L/min = 5 mmhg/L/min

181. A 67-year-old man who is a candidate for cardiac transplantation undergoes cardiac catheterization to assess his hemodynamic status. Findings include: Pulmonary artery pressure (PAP) = 35 mm Hg Cardiac output = 4 L/min Left atrial pressure (LAP) = 15 mm Hg Right atrial pressure = 10 mm Hg Which of the following values is his PVR? a. 0.16 L/min/mm Hg b. 0.2 L/min/mm Hg c. 5 mm Hg/L/min d. 6.25 mm Hg/L/min

The answer is b. Hemoglobin has 240 × greater affinity for carbon monoxide than for oxygen. Thus, in carbon monoxide poisoning, the amount of dissolved oxygen, as reflected by the PaO2, may be normal, but the saturation of hemoglobin with oxygen will be lower than expected for a given PaO2. In anemia, hemoglobin concentration is reduced, but the saturation of hemoglobin O2 is normal. Hypoventilation, v/q mismatch with low v/q units, and right-to-left shunting are all causes of hypoxemia (decreased PaO2).

182. A 36-year-old woman is found comatose at her home and is life-flighted to the nearest regional medical center. Blood gases reveal a normal PaO2 but a lower-than- normal arterial O2 saturation. Which of the following conditions is most consistent with the findings? a. Anemia b. Carbon monoxide poisoning c. Hypoventilation d. Low ratio e. Right-to-left shunt

The answer is a. Reversibility of airway obstruction is assessed by the change in expiratory flow rate before and after administration of a bronchodilator drug, such as a β2-adrenergic agonist, which increases airway radius, thereby decreasing airway resistance and increasing expiratory airflow as predicted by Poiseuille law. Increasing the effort of muscular contraction on exhalation would increase expiratory airflow on the effort-dependent portion of the MEFV curve, but not the effort-independent portion, as delineated in the figure below. Regardless of increased effort, flow rates decrease during the effort-independent portion of a maximal expiration due to dynamic compression of the airways by the positive intrapleural pressure generated by a forced (active) expiration .

183. A 22-year-old male presents with a nonproductive cough, wheezing, and dyspnea. While doing a FVC maneuver, he generated curve 1 in the figure below. After receiving an aerosolized medication, he generated curve 2 while repeating the vital capacity 10 minutes later. Compared to curve 1, the greater flow rates measured after exhaling 3 L on curve 2 can be attributed to an increase in which of the following? a. Airway radius b. Airway resistance c. Dynamic compression of the airways d. Effort exerted in contracting the expiratory muscles e. Intrapleural pressure

The answer is c In CHF, left ventricular dysfunction increases left ventricular end-diastolic pressure, which raises LAP, pulmonary venous pressure, and pulmonary capillary pressure, which is the hydrostatic pressure tending to drive fluid movement out of the pulmonary capillaries, according to Starling law. Thus, pulmonary edema, generally limited to the interstitium of the lungs, is a hallmark of CHF. All of the other responses would act to decrease fluid movement out of the capillary, in accordance with Starling law.

185. A 62-year-old man with congestive heart failure (CHF) develops increasing shortness of breath in the recumbent position. A chest x-ray reveals cardiomegaly, horizontal lines perpendicular to the lateral lung surface indicative of increased opacity in the pulmonary septa, and lung consolidation. Pulmonary edema in CHF is promoted by which of the following? a. Decreased pulmonary capillary permeability b. Decreased pulmonary interstitial oncotic pressure c. Increased pulmonary capillary hydrostatic pressure d. Increased pulmonary capillary oncotic pressure e. Increased pulmonary interstitial hydrostatic pressure

The answer is c Destruction of the alveolar septa in emphysema causes a loss of pulmonary capillaries, which decreases the surface area available for diffusion, and therefore decreases the rate of diffusion in accordance with Fick law. Alveolar septal departitioning with destruction of pulmonary capillaries results in enlargement of the air spaces distal to the terminal bronchioles and an increase in alveolar dead space, that is, alveoli that are ventilated but not perfused. Elastic fibers are also found in the alveolar septa. In emphysema, the destruction of elastic fibers decreases lung elastic recoil and increases lung compliance. The loss of elastic recoil increases intrapleural pressures, which decreases transmural pressure across the noncartilaginous airways (less radial traction), which decreases airway caliber and increases airway resistance in accordance with Poiseuille law. In addition, the loss of elastic recoil impairs the ability to oppose dynamic compression of the airways. As a result, dynamic compression occurs closer to the alveoli during forced expirations, resulting in air trapping and an increase in residual volume and total lung capacity.

186. A 76-year-old patient with emphysema presents for his annual pulmonary function testing to assess the progression of his disease. As a result of alveolar septal departitioning in emphysema, there is a decrease in which of the following? a. Airway resistance b. Alveolar dead space c. Diffusing capacity d. Lung compliance e. Total lung capacity

189. The answer is a The elevated LAP, which is normally approximately 5 mm Hg, is indicative of an increase in left ventricular preload. Plotting LAP (preload) and cardiac output in the cardiac function curves below demonstrates that cardiac contractility has decreased since the previous admission. PVR, calculated as (mean PAP − mean LAP)/cardiac output, is (35 - 20)/3 = 5 mm Hg/L/min, which is higher than normal [(15 − 5 mm Hg)/5 L/min = 2 mm Hg/L/min]. PAWP measured with a Swan-Ganz catheter is an index of the pulmonary capillary hydrostatic pressure. Normal PAWP is ≤12 mm Hg. An elevated PAWP of 25 mm Hg is indicative of an increased pulmonary capillary hydrostatic pressure, which will drive fluid movement out of the pulmonary capillaries according to Starling law, thereby decreasing net fluid reabsorption into the pulmonary capillaries.

189. A person with CHF and progressive shortness of breath is admitted to the hospital for cardiac transplantation surgery. Hemodynamic recordings made with a Swan-Ganz catheter were as follows: Mean pulmonary artery pressure (PAP): 35 mm Hg Mean left atrial pressure (LAP): 20 mm Hg Pulmonary artery wedge pressure (PAWP): 25 mm Hg Cardiac Output: 3 L/min On a previous admission, the patient's LAP was 15 mm Hg and cardiac output was 4 L/min. What can be deduced from these data? a. Cardiac contractility is lower than on the previous admission. b. Left ventricular preload is lower than on his previous admission. c. Net fluid absorption into the pulmonary capillaries is increased. d. Pulmonary capillary hydrostatic pressure is lower than normal. e. Pulmonary vascular resistance is lower than normal at present.

The answer is e. The alveoli at the apex of the lung are larger than those at the base, so their compliance is less. Because the compliance is reduced, less inspired gas goes to the apex than to the base. Also, because the apex is above the heart, less blood flows through the apex than through the base. However, the reduction in airflow is less than the reduction in blood flow, so that the ratio at the top of the lung is greater than it is at the bottom. The increased ratio at the apex makes PACO2 lower and PAO2 higher than they are at the base.

201. A 72-year-old man with CHF, paroxysmal nocturnal dyspnea, and orthopnea is referred for pulmonary function test in the supine and upright positions. Which of the following is higher at the apex of the lung than at the base when a person is upright? a. Blood flow b. Lung compliance c. PaCO2 d. Ventilation e. V/Q ratio

202. The answer is a Lymph flow is proportional to the amount of fluid filtered out of the capillaries. The amount of fluid filtered out of the capillaries depends on the Starling forces and capillary permeability. Increasing capillary oncotic pressure directly decreases filtration by increasing the hydrostatic (osmotic) force drawing water into the capillary. Increasing capillary pressure, capillary permeability, and interstitial protein concentration (oncotic pressure) all directly increase lymph flow. When venous pressure is increased, the capillary hydrostatic pressure is increased and, again, capillary filtration is increased. Lymph flow is normally approximately 2 to 3 L per day.

202. A 65-year-old smoker develops a squamous cell bronchogenic carcinoma that metastasizes to the tracheobronchial and parasternal lymph nodes. The chest x-ray is consistent with accumulation of fluid in the pulmonary interstitial space. Flow of fluid through the lymphatic vessels will be decreased if there is an increase in which of the following? a. Capillary oncotic pressure b. Capillary permeability c. Capillary pressure d. V per min/Q per min e. Central venous pressure f. Interstitial protein concentration

The answer is A Respiratory muscles consume oxygen in proportion to the work of breathing. The work of breathing is equal to the product of the change in volume for each breath and the change in pressure necessary to overcome the resistive work of breathing and the elastic work of breathing. Resistive work includes work to overcome tissue as well as airway resistance; thus, a decreased airway resistance will decrease the work of breathing and the oxygen consumption of the respiratory muscles. A decreased lung compliance would increase the elastic work of breathing. An increase in respiratory rate or tidal volume increases the work of breathing.

204. A 57-year-old woman presents with dyspnea on exertion. Pulmonary function studies with plethysmography demonstrate an increased resting oxygen consumption and work of breathing. Which of the following will decrease the oxygen consumption of the respiratory muscles? a. A decrease in airway resistance b. A decrease in diffusing capacity of the lung c. A decrease in lung compliance d. An increase in rate of respiration e. An increase in tidal volume

206. The answer is c When the pleura and hence the lung-chest wall system are intact, the inward elastic recoil of the lung opposing the outward elastic recoil of the chest wall results in a subatmospheric (negative) pressure within the pleural space. When one reaches lung volumes in excess of approximately 70% of the total lung capacity, the chest wall recoil is also inward.

206. A 48-year-old coal miner complains of shortness of breath and a productive cough. He has smoked one to two packs of cigarettes per day since he was 16 years old. Pulmonary function studies are ordered, including an esophageal balloon study to measure intrapleural pressures. Normally, intrapleural pressure is negative throughout a tidal inspiration and expiration because of which of the following? a. The lungs have the tendency to recoil outward throughout a tidal breath. b. The chest wall has the tendency to recoil inward throughout a tidal breath. c. The lungs and chest wall recoil away from each other throughout a tidal breath. d. The lungs and chest wall recoil in the same direction throughout a tidal breath. e. A small volume of air leaves the pleural space during a tidal breath.

209. The answer is b. Respiratory muscle paralysis causes an acute, uncompensated respiratory acidosis. The primary disturbance is an elevation in arterial PCO2 due to alveolar hypoventilation from the impaired mechanics of breathing. The hypercapnia lowers the ratio of HCO3 to dissolved CO2 in the plasma, and thus lowers the pH according to the Henderson-Hasselbalch equation. In acute respiratory acidosis, the plasma HCO3 concentration increases 1 mmol/L for every 10 mm Hg increase in PaCO2 due to intracellular buffering. In chronic respiratory acidosis (eg, in COPD), the kidneys compensate for the acidosis by increasing the net excretion of H+, which increases the plasma HCO3 by 0.4 mmol/L for every mm Hg increase in PaCO2, which helps return the pH back into the normal range (choice c). The interpretation of choice a is metabolic acidosis, in which there is a lower than normal pH due to a primary decrease in plasma HCO3, with compensatory hyperventilation that decreases arterial PCO2. Choice d represents acute respiratory alkalosis, in which hyperventilation lowers arterial PCO2 and increases arterial pH; plasma HCO3 decreases 0.2 mmol/L for every mm Hg decrease in PaCO2 due to intracellular buffering. Choice e is compensated metabolic alkalosis.

209. Several months after recovering from mononucleosis, a 26-year-old man develops weakness and tingling in both legs. Three days later, he is hospitalized when his legs become paralyzed. A conduction block in the peripheral Aβ, sensory fibers and the finding of autoantibodies to Schwann cell gangliosides confirm the diagnosis of Guillain-Barré syndrome. The next day the weakness and paralysis ascended to his upper extremities and trunk. Stat arterial blood gas results indicated the need for mechanical ventilation. Which of the following sets of values is consistent with acute respiratory muscle paralysis?

210. The answer is c. (Le, p 550. Levitzky, pp 23, 171-173. Longo, p 278.) Kyphoscoliosis is a deformity of the spine involving both lateral displacement (scoliosis) and anteroposterior angulation (kyphosis), which decrease the compliance of the chest wall. Decreased chest wall compliance and respiratory muscle weakness cause inadequate alveolar ventilation, which leads to an accumulation of carbon dioxide and a decrease in arterial pH (respiratory acidosis). Restrictive impairments are characterized by a decrease in all lung volumes and capacities, but a normal or increased ratio of FEV1 to FVC.

210. A 37-year-old woman is admitted to the hospital with severe kyphoscoliosis and respiratory muscle weakness. Which of the following physiological variables is most likely decreased in this patient? a. Airway resistance b. Alveolar surface tension c. Arterial carbon dioxide tension d. Chest wall compliance e. FEV1/FVC

213. The answer is d (Levitzky, pp 65-67, 73-75, 171-172.) A decrease in alveolar ventilation results in an increased PaCO2. Alveolar hypoventilation in this patient is likely due to shallow breathing from abdominal pain or depressed respirations secondary to pain medication. A decrease in metabolic activity would decrease the rate of production of carbon dioxide (VCO2), which would decrease PaCO2, assuming that alveolar ventilation does not change. V/q inequality causes hypoxemia, and thus reflex hyper-ventilation. At a constant tidal volume and respiratory rate, a decrease in the dead space volume would increase alveolar ventilation, and thus lower the PaCO2.

213. An 83-year-old woman is found unresponsive by her son approximately 3 hours after she returned to her hospital room following gall bladder surgery. The nurse reported that the patient had asked for her pain medications and said she was going to rest for a while. Arterial blood gases reveal hypercapnia and hypoxemia. Which of the following is the most likely cause of the high arterial PCO2 ? a. Decreased alveolar dead space b. Decreased metabolic activity c. Hypoventilation d. Hypoxemia e. inequality

214. The answer is c. (Levitzky, pp 90-102, 105-107.) Increasing cardiac output causes PVR to passively decrease due to two mechanisms— distention of perfused vessels and recruitment of more parallel vascular beds. Cardiac output is often elevated in septic shock, which differentiates it from hypovolemic and cardiogenic shock. Decreasing alveolar PO2 causes hypoxic pulmonary vasoconstriction and a rise in PVR. Increasing alveolar PCO2 or pulmonary artery H+ concentration also causes PVR to rise. The sympathetic nervous system exerts little effect on PVR under physiologic conditions, but stimulation of sympathetic nerves will constrict the pulmonary vessels, causing increased PVR. At high lung volumes, the pulmonary capillaries ("alveolar" vessels) are stretched and compressed causing an increased PVR; this is true with spontaneous respirations and occurs even more so with positive pressure ventilation.

214. A 29-year-old man with AIDS presents with a painful, red, swollen area on top of his shin, which is warm to the touch. He has a fever, tachypnea, and tachycardia, and is hospitalized and started on IV antibiotics. His condition progresses rapidly to septicemia and septic shock. He is transported to the ICU, intubated, and started on mechanical ventilation. A Swan-Ganz catheter is inserted to monitor pulmonary hemodynamics and lung fluid balance. Which of the following conditions will cause a decrease in PVR? a. Alveolar hypoxia b. Decreased pH in the pulmonary artery c. Increased cardiac output d. Inflation of the lungs to total lung capacity e. Sympathetic stimulation of the pulmonary vessels

215. The answer is a.. (Barrett, pp 666-669. Levitzky, pp 228-233). During moderate aerobic exercise, oxygen consumption and CO2 production increase, and alveolar ventilation increases in proportion. Thus, PaCO2 (and PaO2) does not change. Arterial pH and blood lactate concentration are also normal during moderate aerobic exercise, but during anaerobic exercise, which is reached at workloads that exceed approximately 60% of the maximal workload (called the anaerobic threshold), there is increased production of muscle lactic acid, which spills over into the circulation, causing an increase in the concentration of arterial lactate and a decrease in the pH of the blood.

215. A healthy 32-year-old woman undergoes pulmonary exercise stress testing prior to starting a training regimen in preparation for her first marathon. Normally, during moderate aerobic exercise, which of the following occurs? a. Alveolar ventilation increases b. Arterial pH decreases c. Arterial lactate level increases d. PaCO2 decreases e. PaO2 increases

216. The answer is d (Levitzky, pp 130-140. Longo, pp 456, 898-900.) The diffusing capacity is the volume of gas transported across the lung per minute per mm Hg partial pressure difference. Diffusing capacity is measured by measuring the transfer of oxygen or carbon monoxide across the alveolar-capillary membrane. Because the partial pressure of oxygen and carbon monoxide is affected by their chemical reactions with hemoglobin, as well as their transfer through the membrane, the diffusing capacity of the lung is determined both by the diffusing capacity of the membrane itself and by the reaction with hemoglobin. Increases in the diffusing capacity can be produced by increasing the concentration of hemoglobin within the blood (polycythemia). The approach to the patient with polycythemia includes determination of not only hematocrit but also red cell mass, erythropoietin levels, arterial oxygen saturation, and hemoglobin's affinity for oxygen in order to distinguish among the various causes. The diffusing capacity of the membrane can be calculated by rearranging Fick law of diffusion, and is related to the ratio of the surface area available for diffusion and the thickness of the alveolar-capillary interface. The area available for diffusion is decreased by alveolar-septal departitioning in emphysema and by obstruction of the pulmonary vascular bed by pulmonary emboli. The thickness of the diffusional barrier is increased by interstitial fibrosis and by interstitial or alveolar edema found in CHF.

216. A 56-year-old woman presents to her physician complaining of fatigue, headaches, and dyspnea on exertion. She states that she sometimes gets blue lips and fingers when she tries to exercise. Pulmonary function tests reveal an increase, rather than a decrease, in the diffusing capacity of the lung. Which of the following conditions best accounts for an increase in the diffusing capacity? a. CHF b. COPD c. Fibrotic lung disease d. Polycythemia e. Pulmonary embolism

217. The answer is e. (Kaufman, p 272. Levitzky, pp 153-154, 183.) The decrease in arterial oxygen saturation caused by carbon monoxide poisoning reduces the oxyhemoglobin and thus total arterial oxygen contents but does not reduce the amount of oxygen dissolved in the plasma, which determines the arterial oxygen tension. Carbon monoxide is odorless and tasteless, and dyspnea and respiratory distress are late signs, which is the reason why it is so important to install carbon monoxide detectors in homes and businesses. Respiratory distress becomes manifest with severe tissue hypoxia and anaerobic glycolysis, which leads to lactic acidosis. The decrease in arterial pH stimulates ventilation via the peripheral chemoreceptors. The resultant hyperventilation decreases arterial (and CSF) PCO2, causing CSF pH to rise. Carboxyhemoglobin has a cherry-red color.

217. A 49-year-old farmer develops headache and becomes dizzy after working on a tractor in his barn. His wife suspects carbon monoxide poisoning and brings him to the emergency department where he complains of dizziness, lightheadedness, headache, and nausea. The patient's skin is red, he does not appear to be in respiratory distress, and denies dyspnea. Blood levels of carboxyhemoglobin are elevated. Which of the following best explains the absence of respiratory signs and symptoms associated with carbon monoxide poisoning? a. Blood flow to the carotid body is decreased b. Arterial oxygen content is normal c. Cerebrospinal fluid (CSF) pH is normal d. Central chemoreceptors are depressed e. Arterial oxygen tension is normal

218. The answer is e. (Levitzky, pp 20-28.) Lung compliance is an index of lung distensibility or the ease with which the lungs are expanded; thus, compliance is the inverse of elastic recoil. Compliance is defined as the ratio of change of lung volume to the change in pressure required to inflate the lung (∆V/∆P). Compliance decreases in patients with pulmonary edema or surfactant deficiency and increases when there is a loss of elastic fibers in the lungs, such as occurs in patients with emphysema and with aging.

218. A 68-year-old patient with shortness of breath is referred for pulmonary function testing, including lung volumes, flow-volume curves, and lung compliance. Which of the following statements best characterizes lung compliance? a. It decreases with advancing age. b. It increases when there is a deficiency of surfactant. c. It increases in patients with pulmonary edema. d. It is equivalent to ∆P/∆V. e. It is inversely related to the elastic recoil properties of the lung.

219. The answer is c. (Barrett, pp 661, 665-667. Levitzky, pp 207-209.) The central chemoreceptors, located at or near the ventral surface of the medulla, are stimulated to increase ventilation by a decrease in the pH of their extracellular fluid (ECF). The pH of the ECF is affected by the PCO2 of the blood supply to the medullary chemoreceptor area, as well as by the CO2 and lactic acid production of the surrounding brain tissue. The central chemoreceptors are not stimulated by decreases in PaO2 or blood oxygen content but rather depressed by long-term or severe decreases in oxygen supply.

219. A 36-year-old man visits his doctor because his wife has long complained of his snoring, but recently observed that his breathing stops for a couple of minutes at a time while he is sleeping. He undergoes polysomnography and ventilatory response testing to ascertain the extent and cause of his sleep apnea. The activity of the central chemoreceptors is stimulated by which of the following? a. A decrease in the metabolic rate of the surrounding brain tissue b. A decrease in the PO2 of blood flowing through the brain c. An increase in the PCO2 of blood flowing through the brain d. An increase in the pH of the CSF e. Hypoxemia, hypercapnia, and metabolic acidosis

220. The answer is e. (Le, pp 233, 544, 564. Levitzky, pp 32-36, 49-50.) Methacholine is a cholinergic agonist, which causes constriction of bronchial smooth muscle. Bronchoconstriction reduces airway radius, which increases airway resistance, and thus the resistive work of breathing. Methacholine-induced bronchoconstriction decreases the anatomic dead space but has no significant effect on the lung compliance, and thus does not affect the elastic work of breathing.

220. A patient complains of paroxysmal episodes of not being able to catch her breath. When no abnormalities are detected with conventional pulmonary function screening, the pulmonologist orders a methacholine challenge test. Which of the following will increase as a result of stimulating cholinergic receptors on the bronchial smooth muscle? a. Airway diameter b. Anatomic dead space c. Compliance of the lungs d. Elastic work of breathing e. Resistive work of breathing

221. The answer is b. (Levitzky, pp 125-127.) During inspiration, when all alveoli are subjected to essentially the same alveolar pressure, more air will go to the more compliant alveoli in the base of the lung. Because the lungs are essentially "hanging" in the chest, the force of gravity on the lungs causes the intrapleural pressure to increase (become less negative) at the base of the lungs compared to the apex (more negative intrapleural pressure). This also causes the alveoli at the apex of the lung to be larger than those at the base of the lung. Larger alveoli are already more inflated and are less compliant than smaller alveoli. Because of the effect of gravity on blood, more blood flow will go to the base of the lung. Ventilation is about 3 times greater at the base of the lung, but flow is about 10 times greater at the base than at the apex of the lung; therefore, the v/q ratio is lower at the base than at the apex in a normal lung.

221. A 28-year-old woman on oral contraceptives develops tachypnea and reports dyspnea. A ventilation/perfusion scan is ordered to check for pulmonary thromboemboli. Which of the following best explains why, as she takes in a normal inspiration, more air goes to the alveoli at the base of the lung than to the alveoli at the apex of the lung? a. The alveoli at the base of the lung have more surfactant. b. The alveoli at the base of the lung are more compliant. c. The alveoli at the base of the lung have higher ratios. d. There is a more negative intrapleural pressure at the base of the lung. e. There is more blood flow to the base of the lung.

226. The answer is a. (Levitzky, pp 32-40.) As lung volume decreases, intrapleural pressure increases in accordance with Boyle law. The greater intrapleural pressure decreases the radial traction on the airways, thereby decreasing airway diameter and increasing airway resistance. During a forced expiration or at residual volume, the intrapleural pressure actually becomes positive, compressing the airways and increasing their resistance. The vagus nerve constricts airway smooth muscle. Resistances in parallel add as reciprocals. Thus, the large number of small, peripheral airways increases the number of airways arranged in parallel, and lowers the total resistance of the peripheral airways compared to the total cross-section of the central airways.

226. A 43-year-old woman with a history of asthma presents to the emergency department with an acute asthma attack after her bronchodilator inhaler ran out the day before. Airway resistance is greater at which of the following? a. At low lung volumes compared with high lung volumes b. At lower values for Reynolds number c. During inspiration compared with expiration d. In the total cross-section of the small airways compared with the total cross-section of the central airways e. With laminar flow than with turbulent flow

227. The answer is e. (Levitzky, pp 41, 54-59.) A spirometer is an instrument that records the volume of air moved into and out of the lungs during breathing, and therefore can only be used to measure lung volumes and capacities that can be exchanged with the environment. Spirometry can be used to measure the vital capacity, which is the maximal amount of gas that can be expired following a maximal inspiration. Spirometry cannot be used to measure the volume of the gas that remains in the lungs following a maximal expiration (residual volume), and thus cannot directly measure the lung capacities that contain the residual volume, that is, the FRC and the total lung capacity. The peak flow rate is the maximal rate at which the volume of gas is exhaled. The measurement of flow rate requires a pneumotach, an instrument that integrates exhaled volume to derive the flow rate, or by a peak flow meter that patients can use at home, which are calibrated to record exhaled flow rates.

227. A 78-year-old woman presents to her family physician's office with a chief complaint of fatigue and shortness of breath. The doctor indicates that he wants her to go to the hospital to get some pulmonary function tests, but there is one who is able to do in the office. A spirometer can be used to directly measure which of the following? a. FRC b. Peak flow rate c. Residual volume d. Total lung capacity e. Vital capacity