USMLE Step 1 Respiratory Practice Questions

Which muscle is the primary muscle of quiet inspiration?

• (A) Diaphragm
• (B) External intercostals
• (C) Internal intercostals
• (D) Scalene muscles

What is the definition of Functional Residual Capacity (FRC)?

• (A) Volume of air remaining in the lungs after a normal tidal expiration (ERV + RV)
• (B) Volume of air inhaled or exhaled during a normal breath (TV)
• (C) Maximum volume of air that can be forcefully exhaled after a maximal inspiration (VC)
• (D) Total volume of air the lungs can hold (TLC)

According to Fick's law of diffusion, the rate of gas transfer across the alveolar-capillary membrane is inversely proportional to which factor?

• (A) Membrane thickness
• (B) Partial pressure gradient
• (C) Surface area
• (D) Diffusion coefficient of the gas

A patient presents with hypoxemia (low PaO2) that improves significantly with supplemental oxygen. Ventilation/perfusion (V/Q) scan shows a V/Q ratio approaching zero in the affected lung region. This pattern is most characteristic of:

• (A) Airway obstruction (shunt)
• (B) Pulmonary embolism (dead space)
• (C) Interstitial lung disease
• (D) Emphysema

Which factor causes a right shift in the oxygen-hemoglobin dissociation curve, indicating decreased hemoglobin affinity for oxygen?

• (A) Increased PCO2 (hypercapnia)
• (B) Decreased temperature
• (C) Increased pH (alkalosis)
• (D) Decreased 2,3-BPG

What is the primary form in which carbon dioxide (CO2) is transported in the blood?

• (A) Bicarbonate ions (HCO3-) in plasma
• (B) Dissolved CO2 in plasma
• (C) Bound to hemoglobin (carbaminohemoglobin)
• (D) Carbonic acid (H2CO3)

Obstructive lung diseases, such as COPD and asthma, are typically characterized by:

• (A) Decreased FEV1/FVC ratio
• (B) Increased FEV1/FVC ratio
• (C) Decreased Total Lung Capacity (TLC)
• (D) Increased lung elastic recoil

Which substance, produced by Type II pneumocytes, reduces alveolar surface tension and prevents alveolar collapse?

• (A) Surfactant
• (B) Mucus
• (C) Elastin
• (D) Collagen

The central chemoreceptors located in the medulla oblongata are most sensitive to changes in:

• (A) Arterial PCO2 (via changes in CSF H+)
• (B) Arterial PO2
• (C) Arterial pH
• (D) Venous PO2

What is the definition of anatomical dead space?

• (A) Volume of the conducting airways (nose, pharynx, trachea, bronchi)
• (B) Volume of alveoli that are ventilated but not perfused
• (C) Volume of air remaining in the lungs after maximal expiration
• (D) Volume of air moved during a normal breath

Restrictive lung diseases, such as pulmonary fibrosis, are typically characterized by:

• (A) Decreased Total Lung Capacity (TLC) and decreased FVC
• (B) Increased FEV1/FVC ratio
• (C) Increased lung compliance
• (D) Decreased work of breathing

Which respiratory measurement represents the maximum amount of air that can be forcefully exhaled after a maximal inhalation?

• (A) Vital Capacity (VC)
• (B) Total Lung Capacity (TLC)
• (C) Functional Residual Capacity (FRC)
• (D) Inspiratory Capacity (IC)

Peripheral chemoreceptors, located in the carotid bodies and aortic bodies, are primarily sensitive to changes in:

• (A) Arterial PO2 (hypoxemia)
• (B) Arterial PCO2
• (C) Venous pH
• (D) Cerebrospinal fluid [H+]

In a healthy individual at rest, the ventilation/perfusion (V/Q) ratio is highest in which region of the lung?

• (A) Apex
• (B) Base
• (C) Middle zone
• (D) Hilum

What is the effect of carbon monoxide (CO) on oxygen transport?

• (A) Binds to hemoglobin with high affinity, reducing O2 binding sites AND shifts the O2-Hb curve left
• (B) Binds to hemoglobin with low affinity
• (C) Causes a right shift in the O2-Hb curve
• (D) Increases the amount of dissolved O2 in plasma

Forced Expiratory Volume in 1 second (FEV1) measures:

• (A) The volume of air forcefully exhaled in the first second after a maximal inspiration
• (B) The total volume of air forcefully exhaled after a maximal inspiration
• (C) The volume of air remaining after a normal expiration
• (D) The rate of airflow during middle portion of expiration

Which law states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures exerted by each individual gas?

• (A) Dalton's Law
• (B) Henry's Law
• (C) Boyle's Law
• (D) Charles's Law

During exercise, ventilation increases primarily due to:

• (A) Input from central command and peripheral mechanoreceptors/chemoreceptors
• (B) A significant drop in arterial PO2
• (C) A significant rise in arterial PCO2
• (D) A significant drop in arterial pH

What is the normal approximate value for the alveolar-arterial (A-a) oxygen gradient?

• (A) 5-15 mmHg
• (B) 0 mmHg
• (C) 20-30 mmHg
• (D) 40-50 mmHg

Which condition typically leads to a decrease in lung compliance?

• (A) Pulmonary fibrosis
• (B) Emphysema
• (C) Asthma
• (D) Aging

What is the physiological consequence of a large physiological dead space (e.g., due to pulmonary embolism)?

• (A) Wasted ventilation and potential hypercapnia
• (B) Increased diffusion capacity
• (C) Decreased work of breathing
• (D) Improved oxygenation

The respiratory center, controlling the basic rhythm of breathing, is located primarily in the:

• (A) Medulla oblongata
• (B) Pons
• (C) Cerebellum
• (D) Hypothalamus

How does the body primarily compensate for metabolic acidosis?

• (A) Hyperventilation (respiratory compensation)
• (B) Hypoventilation (respiratory compensation)
• (C) Renal retention of H+
• (D) Renal excretion of HCO3-

Which factor has the greatest effect on airway resistance?

• (A) Radius of the airway
• (B) Length of the airway
• (C) Viscosity of the gas
• (D) Turbulence of airflow

What is the approximate partial pressure of oxygen (PO2) in dry inspired air at sea level?

• (A) 160 mmHg
• (B) 100 mmHg
• (C) 150 mmHg
• (D) 21 mmHg

The chloride shift (Hamburger phenomenon) involves the exchange of which ions across the red blood cell membrane?

• (A) Bicarbonate (HCO3-) out, Chloride (Cl-) in
• (B) Chloride (Cl-) out, Bicarbonate (HCO3-) in
• (C) Sodium (Na+) out, Potassium (K+) in
• (D) Potassium (K+) out, Sodium (Na+) in

Hypoxia-induced pulmonary vasoconstriction is a mechanism that primarily serves to:

• (A) Divert blood flow away from poorly ventilated alveoli
• (B) Increase overall pulmonary blood flow
• (C) Decrease pulmonary vascular resistance
• (D) Improve oxygen delivery to systemic tissues

What happens to intrapleural pressure during a normal quiet inspiration?

• (A) Becomes more negative
• (B) Becomes less negative (more positive)
• (C) Remains unchanged
• (D) Equals atmospheric pressure

Which lung capacity cannot be measured by simple spirometry?

• (A) Functional Residual Capacity (FRC)
• (B) Vital Capacity (VC)
• (C) Inspiratory Capacity (IC)
• (D) Expiratory Reserve Volume (ERV)

Diffusion limitation of gas exchange across the alveolar-capillary membrane is most likely to occur under which condition?

• (A) Exercise at high altitude
• (B) Resting at sea level
• (C) Breathing 100% oxygen
• (D) Pulmonary fibrosis at rest

What is the primary mechanism by which the lungs excrete acid from the body?

• (A) Exhalation of carbon dioxide (CO2)
• (B) Secretion of H+ into the airways
• (C) Reabsorption of bicarbonate from alveoli
• (D) Production of ammonia

Cheyne-Stokes respiration, an abnormal breathing pattern characterized by cycles of crescendo-decrescendo breathing followed by apnea, is often associated with:

• (A) Congestive heart failure or neurological disease
• (B) Opioid overdose
• (C) Diabetic ketoacidosis
• (D) Asthma exacerbation

What term describes the tendency of the lungs to return to their resting volume after being stretched?

• (A) Elastic recoil
• (B) Compliance
• (C) Resistance
• (D) Surface tension

In which condition would you expect to find an increased FEV1/FVC ratio?

• (A) Pulmonary fibrosis (a restrictive disease)
• (B) Chronic bronchitis (an obstructive disease)
• (C) Asthma (an obstructive disease)
• (D) Emphysema (an obstructive disease)

The volume of gas that dissolves in a liquid is directly proportional to its partial pressure above the liquid. This is described by:

• (A) Henry's Law
• (B) Dalton's Law
• (C) Boyle's Law
• (D) Laplace's Law

What effect does parasympathetic stimulation have on the airways?

• (A) Bronchoconstriction and increased mucus secretion
• (B) Bronchodilation and decreased mucus secretion
• (C) Bronchodilation and increased mucus secretion
• (D) Bronchoconstriction and decreased mucus secretion

Where is airway resistance highest in the respiratory tract?

• (A) Medium-sized bronchi
• (B) Trachea
• (C) Terminal bronchioles
• (D) Alveoli

A patient's arterial blood gas shows: pH 7.25, PaCO2 60 mmHg, HCO3- 26 mEq/L. This represents:

• (A) Acute respiratory acidosis
• (B) Metabolic acidosis
• (C) Respiratory alkalosis
• (D) Metabolic alkalosis

Which part of the brain contains the apneustic and pneumotaxic centers that help modulate the output of the medullary respiratory centers?

• (A) Pons
• (B) Medulla oblongata
• (C) Cerebellum
• (D) Midbrain

Calculation of the A-a gradient requires knowledge of alveolar PO2 (PAO2). The simplified alveolar gas equation is PAO2 = PIO2 - (PaCO2 / R). What does 'R' represent?

• (A) Respiratory quotient (CO2 produced / O2 consumed)
• (B) Airway resistance
• (C) Lung compliance
• (D) Gas constant