A 48-year-old woman comes to the emergency department with headache, dizziness, and nausea for the past several hours. She has no fever, nasal congestion, or cough but reports that her husband has also been complaining of headache. The patient has been burning wood in the fireplace to warm her house after losing electricity during a snowstorm. Her temperature is 37 C (98.6 F), blood pressure is 135/70 mm Hg, and pulse is 94/min and regular. Physical examination is unremarkable. The substance responsible for this patient’s condition most likely impairs hemoglobin function through which of the following mechanisms?

A group of investigators is researching the changes in oxygen-hemoglobin binding that occur under various clinical conditions.  They are especially interested in situations that alter the shape and position of the oxygen-hemoglobin dissociation curve.  Which of the following processes would most likely cause a shift from the blue curve to the red curve in the graph below?

Scientists studying the principles behind oxygen-hemoglobin dissociation have discovered a way to successfully separate hemoglobin tetramers into individual alpha and beta subunits.  During an experiment, a solution is created that contains only monomeric beta-hemoglobin subunits under physiologic conditions.  If measured, the oxygen dissociation curve of the dissolved beta subunits will most likely resemble which of the following lines?

A 23-year-old healthy man who lives at sea level is attempting to trek to the Mount Everest base camp at an elevation of 5,334 m (17,500 ft).  While hiking, he experiences mild shortness of breath, lightheadedness, headache, and fatigue.  The patient reaches the base camp after 7 days, where he is evaluated at a high-altitude clinic.  He appears exhausted, but physical examination is otherwise unrevealing.  Which of the following physiologic changes has most likely occurred in this patient?

An 81-year-old man comes to the office after an upper respiratory tract infection.  His symptoms have largely resolved except for a mild, nonproductive cough that is especially bothersome at night.  Medical history includes hypertension and knee osteoarthritis.  The patient is still physically active and plays golf on the weekends.  He is a retired insurance executive and has no known environmental exposures.  He has no history of smoking.  Physical examination is unremarkable, and chest x-ray is normal.  Pulmonary function testing is considered in this patient.  Compared to midlife, which of the following changes are most likely expected as a result of normal aging in this patient?

A 34-year-old man travels to Peru to participate in a mountain-climbing expedition.  He has no prior medical problems and takes no medications.  The patient does not use tobacco, alcohol, or illicit drugs.  During his trip, he stays in a high-altitude camp in the mountains at over 4,000 m (13,000 ft) above sea level.  After 2 days at the camp, the patient has blood drawn by the camp’s physician while breathing ambient air.  Which of the following sets of arterial blood gas values is most likely to be seen in this patient?

A 24-year-old healthy college student enrolls into a research study investigating the factors affecting blood oxygen content.  The study is performed at sea level, on room air with no additional oxygen.  A technique is devised to measure the accurate partial pressure of oxygen in the blood as it flows through the circulation.  Blood samples are obtained from the vena cavae, alveolar capillaries, and the aorta.  All data are plotted, and the curve obtained is shown in the graph below.

Which of the following factors most likely explains the change in partial pressure indicated by the arrow?

A 23-year-old man undergoes exercise physiology testing at sea level.  He jogs on a treadmill to achieve a moderate-intensity physical activity level based on a target heart rate of 50%-70% of his estimated maximum heart rate.  An increase in which of the following is expected at the peak of his exertion?

A 6-year-old boy playing in a dusty field in windy weather inhales many small particles that become lodged in his terminal bronchioles.  Which of the following respiratory components is most important in clearing these particles?

 43-year-old man is brought to the emergency department after being found unresponsive by his wife.  She says he was in his usual state of health when she left home a few hours ago.  The patient has a history of depression and type 2 diabetes mellitus.  He was recently laid off from work.  Blood pressure is 100/60 mm Hg and pulse is 64/min.  On physical examination, the patient is responsive to deep sternal rub and has mildly dry mucous membranes.  Arterial blood gas analysis reveals the following:

Which of the following is the most likely current acid-base status in this patient?

The combined compliance of the lung and chest wall of a healthy individual is measured and plotted as shown below.  It is noted that the intrapleural pressure at the end of maximal inspiration is -8 cm H₂0 (marked x).

Which of the following is the best estimate of the intrapleural pressure at the point marked by the black dot?

A 52-year-old man is brought to the emergency department after being found unresponsive on the street.  The patient’s medical history is unknown.  Temperature is 36.2 C (97.2 F), blood pressure is 108/62 mm Hg, and pulse is 72/min.  On physical examination, he is unresponsive to verbal and tactile stimuli but moans to deep sternal rub.  An arterial blood gas analysis on room air shows a partial pressure of oxygen of 60 mm Hg.  The partial pressure of oxygen in his alveoli is calculated to be 68 mm Hg.  Which of the following is the most likely cause of this patient’s symptoms?

A 64-year-old man is evaluated for worsening dyspnea on exertion.  He has a 40-pack-year smoking history.  The lungs are hyperresonant on percussion and there is diffuse wheezing on auscultation.  Chest x-ray reveals a flattened diaphragm with a narrow mediastinum, and there are decreased bronchovascular markings in the peripheral lung region.  Which of the following lung volume patterns is most likely to be present in this patient?  (Each bar represents total lung capacity with different volumes as marked.)

A 34-year-old man is evaluated due to dyspnea.  The patient undergoes complete pulmonary function testing as well as lung volume measurements.  His pulmonary volume curve (blue line) is compared with a normal individual’s curve (black line) in the illustration below:

Which of the following measures is increased in this patient?

A 44-year-old man comes to the emergency department due to sudden-onset shortness of breath that started a few hours ago.  Last week, he sustained a crush injury after a motorcycle drove over his left foot, and he has been immobilized since then due to pain.  The patient drinks alcohol occasionally and does not use tobacco or illicit drugs.  Temperature is 36.1 C (97 F), blood pressure is 118/76 mm Hg, pulse is 102/min, and respirations are 28/min.  BMI is 37 kg/m².  On physical examination, heart rhythm is regular with normal S1 and S2.  The lungs are clear to auscultation bilaterally.  The dorsum of the left foot has resolving ecchymoses and swelling compared to when he was evaluated last week.  The right calf is swollen and tender.  Which of the following arterial blood gas values are most likely to be present in this patient?

A 21-year-old man is brought to the emergency department after being found unresponsive in a public restroom.  He has a history of injection drug use.  Temperature is 36.1 C (97 F), blood pressure is 110/70 mm Hg, pulse is 62/min, and respiratory rate is 8/min.  On physical examination, the patient is unconscious with pinpoint pupils.  Endotracheal intubation is performed, and mechanical ventilation is begun.  The ventilator settings are adjusted to provide a minute ventilation of 6.0 L/min.  Calculated alveolar ventilation is 4.2 L/min.  Which of the following most likely accounts for the difference between these 2 parameters?

Researchers are studying the structure and function of hemoglobin.  Arterial and venous blood samples are obtained from enrolled volunteers with no health problems.  Red blood cells are isolated from whole blood by differential centrifugation, and the contents of the intact red blood cells are analyzed.  It is found that the concentration of chloride is much lower in the red blood cells in the arterial sample compared to the venous sample.  The activity of which of the following enzymes is most likely responsible for the observed finding?

A 43-year-old patient comes to the physician due to dyspnea.  The black curve shown below represents the pressure/volume relationship in normal lung tissue.  The blue curve represents the pressure/volume relationship in the patient’s lung tissue.

Which of the following is the most likely cause of this patient’s symptoms?

A 54-year-old man comes to the office due to shortness of breath that has slowly worsened over the last 6 months.  He also has a persistent, nonproductive cough.  The patient does not use alcohol, tobacco, or illicit drugs.  Temperature is 36.8 C (98 F), blood pressure is 132/78 mm Hg, pulse is 74/min, and respirations are 16/min.  Physical examination reveals fine crackles bilaterally on pulmonary auscultation and drumstick-shaped fingers.  Chest x-ray reveals diffuse reticular opacities.  Pulmonary function testing shows decreased FVC, increased FEV1/FVC ratio, and expiratory flow rates that are higher than normal when corrected for lung volume.  This patient’s supernormal expiratory flow rates are best explained by an increase in which of the following parameters?

A researcher is conducting an experiment to determine factors affecting vascular resistance.  Experiment animals are anesthetized, intubated, and attached to a controlled ventilation system.  A catheter is placed into a small artery in various organs in each animal.  The catheter is connected to a manometer for recording pressure and to an oximeter for continuous recording of oxygen saturation.  The fraction of inspired oxygen is gradually changed, and arteriolar resistance is calculated from the manometer readings at regular intervals.  The results shown below were most likely obtained from which of the following organs?

Researchers are studying pulmonary gas exchange in various physiological and pathological states using animal models.  In one experiment, the partial pressure of oxygen (PO₂) in the upper airways is determined to be 150 mm Hg while breathing ambient air at rest.  Analysis of the respiratory gases in a particular lung segment reveals the following:

Which of the following best explains these respiratory gas findings?

A 45-year-old hospitalized man is evaluated for shortness of breath and hypoxemia.  The patient was admitted 3 days ago after a motor vehicle collision.  At that time, evaluation revealed a femur fracture but no other injuries, and the patient underwent open reduction and internal fixation of the fracture.  This morning, he suddenly began experiencing shortness of breath and sharp chest pain.  The patient has no significant medical history and has been receiving morphine for pain control.  He has smoked a pack of cigarettes daily for 15 years and drinks alcohol occasionally.  Temperature is 36.1 C (97 F), blood pressure is 120/70 mm Hg, and pulse is 98/min.  BMI is 42 kg/m².  Chest x-ray is unremarkable, and arterial blood gas analysis on room air shows a pH of 7.51, PaCO₂ of 30 mm Hg, and PaO₂ of 65 mm Hg.  Which of the following is the primary cause of hypoxemia in this patient?

A 56-year-old man comes to the office due to chronic cough and fatigue.  The patient has smoked 2 packs of cigarettes daily since age 18.  Physical examination shows cyanosis and expiratory wheezes scattered throughout the lungs.  During evaluation for long-term oxygen therapy, his respiratory rate decreases shortly after he begins nasal cannular oxygen supplementation.  This patient’s reduced respiratory rate is most likely caused by a sudden decrease in stimulation of which of the following sensory receptors?

A 45-year-old man comes to the emergency department due to severe dyspnea and chest discomfort that began earlier in the day.  The dyspnea has been worsening throughout the day and has been present at rest.  He reports no inciting trauma.  The patient has no other medical conditions and takes no medications.  He has a 20-pack-year smoking history and does not use alcohol or illicit drugs.  Temperature is 36.7 C (98 F), blood pressure is 110/60 mm Hg, and pulse is 96/min.  Arterial blood gas drawn on room air shows an arterial partial pressure of oxygen (PaO₂) of 54 mm Hg and an arterial partial pressure of carbon dioxide (PaCO₂) of 26 mm Hg.  Which of the following processes is most likely occurring in this patient?