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Anesthesia Board study materials
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Anesthesia Board practice questions

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Question 1Basic Sciences (physics, physiology, pharmacology, pathophysiology)

At sea level, which value is closest to one atmosphere of pressure?

  1. 47 mmHg
  2. 100 mmHg
  3. 760 mmHg Correct answer.
  4. 380 mmHg

Explanation

One atmosphere equals 760 mmHg, which is also 101.3 kPa. This is the reference pressure for partial-pressure calculations in respiratory physiology.

Question 2Basic Sciences (physics, physiology, pharmacology, pathophysiology)

The short duration of action of succinylcholine is primarily due to which process?

  1. Redistribution into fat
  2. Rapid plasma ester hydrolysis Correct answer.
  3. Renal tubular secretion
  4. Hepatic first-pass metabolism

Explanation

Succinylcholine is rapidly hydrolyzed by plasma butyrylcholinesterase to inactive metabolites, so neuromuscular block terminates within minutes.

Question 3Basic Sciences (physics, physiology, pharmacology, pathophysiology)

When fully saturated, approximately how much oxygen is bound per gram of hemoglobin?

  1. 20 mL
  2. 0.3 mL
  3. 1.34 mL Correct answer.
  4. 0.003 mL

Explanation

The Hüfner constant states that 1 g of fully saturated hemoglobin binds about 1.34 mL of oxygen. Multiplying by hemoglobin concentration gives the oxygen-carrying capacity of blood.

Question 4Basic Sciences (physics, physiology, pharmacology, pathophysiology)

For laminar flow through a cylindrical tube, doubling the radius changes flow by what factor?

  1. 16 Correct answer.
  2. 2
  3. 8
  4. 4

Explanation

Poiseuille's law states that flow is proportional to the fourth power of the radius when other factors are constant. Doubling the radius therefore increases flow by 2^4, or 16-fold.

Question 5Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which lung volume cannot be measured by simple spirometry?

  1. Expiratory reserve volume
  2. Residual volume Correct answer.
  3. Tidal volume
  4. Inspiratory reserve volume

Explanation

Residual volume is the air remaining after maximal expiration and cannot be exhaled into a spirometer. It is measured by gas dilution, nitrogen washout, or body plethysmography.

Question 6Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which change shifts the oxyhemoglobin dissociation curve to the right?

  1. Increased temperature Correct answer.
  2. Decreased 2,3-diphosphoglycerate
  3. Presence of fetal hemoglobin
  4. Alkalosis

Explanation

Increased temperature, acidosis, hypercapnia, and increased 2,3-DPG reduce hemoglobin oxygen affinity and shift the curve right. A rightward shift favors oxygen unloading at the tissues.

Question 7Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which agent is a direct vasodilator that can cause cyanide toxicity when infused for prolonged periods?

  1. Phenylephrine
  2. Ephedrine
  3. Norepinephrine
  4. Sodium nitroprusside Correct answer.

Explanation

Sodium nitroprusside releases nitric oxide and cyanide, and prolonged infusion can produce cyanide accumulation. It is metabolized to thiocyanate, which is cleared renally.

Question 8Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which law states that the amount of gas dissolved in a liquid is proportional to its partial pressure?

  1. Henry's law Correct answer.
  2. Charles's law
  3. Fick's law
  4. Dalton's law

Explanation

Henry's law relates dissolved gas concentration to partial pressure through the solubility coefficient. This principle underlies uptake and elimination of inhaled anesthetics.

Question 9Basic Sciences (physics, physiology, pharmacology, pathophysiology)

The minimum alveolar concentration (MAC) of an inhaled anesthetic is defined as the alveolar concentration that produces which effect?

  1. Prevents movement in 95% of patients
  2. Prevents movement in 50% of patients Correct answer.
  3. Produces unconsciousness in 50% of patients
  4. Causes apnea in 50% of patients

Explanation

MAC is the ED50 for immobility in response to a standard surgical stimulus. It is used to compare potency among volatile anesthetics.

Question 10Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Hypoxic pulmonary vasoconstriction primarily serves to do which of the following?

  1. Reduce right ventricular afterload
  2. Divert blood away from poorly ventilated alveoli Correct answer.
  3. Increase airway resistance
  4. Increase pulmonary blood flow to poorly ventilated alveoli

Explanation

Hypoxic pulmonary vasoconstriction constricts small pulmonary arteries in poorly ventilated lung units. This redirects blood toward better-ventilated alveoli and improves ventilation-perfusion matching.

Question 11Basic Sciences (physics, physiology, pharmacology, pathophysiology)

An E-cylinder contains approximately 660 L of oxygen. At a flow of 6 L/min, approximately how long will it last?

  1. 110 min Correct answer.
  2. 90 min
  3. 220 min
  4. 60 min

Explanation

Dividing the cylinder contents by the flow gives 660 L ÷ 6 L/min = 110 minutes. This estimate assumes the cylinder is full and flow is constant.

Question 12Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which drug is a competitive antagonist at the mu-opioid receptor?

  1. Morphine
  2. Remifentanil
  3. Naloxone Correct answer.
  4. Fentanyl

Explanation

Naloxone competitively blocks mu-opioid receptors and reverses opioid-induced respiratory depression and analgesia. The other listed drugs are mu-opioid agonists.

Question 13Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A patient with severe COPD has chronic hypercapnia and a pH of 7.36. Which compensatory change is expected?

  1. Decreased plasma bicarbonate
  2. Acute hyperventilation
  3. Increased plasma bicarbonate Correct answer.
  4. Increased plasma chloride without bicarbonate change

Explanation

Chronic respiratory acidosis is compensated by renal retention of bicarbonate, which raises plasma bicarbonate and returns pH toward normal. This adaptation develops over days to weeks.

Question 14Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Malignant hyperthermia is most often caused by a mutation in which structure?

  1. Ryanodine receptor type 1 Correct answer.
  2. Voltage-gated sodium channel
  3. Beta-2 adrenergic receptor
  4. Nicotinic acetylcholine receptor

Explanation

Malignant hyperthermia is usually linked to mutations in the skeletal muscle ryanodine receptor type 1. Triggering agents cause uncontrolled calcium release from the sarcoplasmic reticulum.

Question 15Basic Sciences (physics, physiology, pharmacology, pathophysiology)

According to Bernoulli's principle, as fluid velocity increases in a narrowed vessel, lateral pressure does which of the following?

  1. Increases
  2. Decreases Correct answer.
  3. Oscillates randomly
  4. Remains unchanged

Explanation

Bernoulli's principle reflects conservation of energy: as kinetic energy increases with velocity, lateral pressure falls. This relationship explains pressure drops at points of narrowing in a flowing system.

Question 16Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which benzodiazepine is frequently used for induction of anesthesia because of its rapid onset after intravenous injection?

  1. Diazepam
  2. Lorazepam
  3. Chlordiazepoxide
  4. Midazolam Correct answer.

Explanation

Midazolam is water soluble, rapidly crosses the blood-brain barrier, and has a short context-sensitive half-time after infusion. These properties make it useful for intravenous sedation and induction.

Question 17Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A patient has a heart rate of 80 beats/min and a stroke volume of 60 mL. What is the cardiac output?

  1. 6.0 L/min
  2. 4.8 L/min Correct answer.
  3. 3.6 L/min
  4. 2.4 L/min

Explanation

Cardiac output is heart rate multiplied by stroke volume: 80 beats/min × 60 mL/beat = 4800 mL/min, or 4.8 L/min.

Question 18Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Anesthetic A has a blood-gas partition coefficient of 0.5, and Anesthetic B has a coefficient of 2.0. Which has faster alveolar-to-blood equilibration and induction?

  1. Anesthetic A Correct answer.
  2. It cannot be determined from these coefficients
  3. Anesthetic B
  4. Both equilibrate at the same rate

Explanation

A lower blood-gas partition coefficient means lower blood solubility, so the blood partial pressure rises more quickly toward the alveolar partial pressure. This speeds equilibration with the brain and induction.

Question 19Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Renal blood flow is maintained over a range of arterial pressures primarily by which mechanism?

  1. Antidiuretic hormone release
  2. Myogenic and tubuloglomerular feedback Correct answer.
  3. Sympathetic vasoconstriction alone
  4. Efferent arteriolar constriction alone

Explanation

Renal autoregulation depends mainly on the myogenic response of afferent arterioles and tubuloglomerular feedback from the macula densa. Together these keep renal blood flow and glomerular filtration relatively stable.

Question 20Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which volatile anesthetic undergoes the least hepatic metabolism?

  1. Desflurane Correct answer.
  2. Sevoflurane
  3. Enflurane
  4. Halothane

Explanation

Desflurane is the least metabolized volatile anesthetic, with only about 0.02% undergoing biotransformation. This minimizes concerns about metabolic products and organ toxicity.

Question 21Basic Sciences (physics, physiology, pharmacology, pathophysiology)

For a highly protein-bound acidic drug, which change is most likely in a patient with severe hypoalbuminemia?

  1. Higher total plasma concentration with unchanged free fraction
  2. Higher free fraction and greater tissue uptake Correct answer.
  3. Lower free fraction and reduced tissue uptake
  4. Reduced hepatic clearance because no drug is filtered

Explanation

Less albumin binding leaves more unbound drug, which can distribute into tissues and produce a greater pharmacologic effect. Total plasma concentration often falls even though the free fraction rises.

Question 22Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A cylinder reads 1000 psig at 27°C. If it cools to 7°C, what is the approximate pressure? (Assume ideal gas behavior and constant volume.)

  1. 700 psig
  2. 1120 psig
  3. 1000 psig
  4. 930 psig Correct answer.

Explanation

At constant volume, absolute pressure is proportional to absolute temperature. Converting to absolute values, about 1015 psia at 300 K becomes about 947 psia at 280 K, or roughly 930 psig.

Question 23Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A patient with a large right-to-left intrapulmonary shunt has hypoxemia that responds poorly to 100% oxygen. Which best explains this?

  1. Shunt blood bypasses ventilated alveoli Correct answer.
  2. Oxygen diffusion across the alveolar membrane is impaired
  3. Supplemental oxygen paradoxically increases the shunt fraction
  4. Shunted blood leaves the lungs fully saturated with oxygen

Explanation

In a true shunt, blood bypasses ventilated alveoli and mixes with oxygenated blood without participating in gas exchange. Because the shunted blood never contacts a high alveolar oxygen tension, supplemental oxygen cannot fully correct the hypoxemia.

Question 24Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which statement about the context-sensitive half-time of remifentanil is correct?

  1. It shortens with longer infusions
  2. It varies unpredictably with infusion duration
  3. It lengthens progressively with longer infusions
  4. It stays essentially constant Correct answer.

Explanation

Remifentanil is metabolized by nonspecific plasma and tissue esterases, so its offset is largely independent of infusion duration. This contrasts with drugs that accumulate in peripheral compartments.

Question 25Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Using the Fick principle, a patient has an oxygen consumption of 250 mL/min, an arterial oxygen content of 20 mL/dL, and a mixed venous oxygen content of 15 mL/dL. What is the cardiac output?

  1. 2.5 L/min
  2. 10 L/min
  3. 5 L/min Correct answer.
  4. 16.7 L/min

Explanation

The arteriovenous oxygen difference is 5 mL/dL, or 50 mL/L. Dividing oxygen consumption by this difference gives 250 mL/min ÷ 50 mL/L = 5 L/min.

Question 26Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which gas law states that, at constant temperature, the volume of a fixed amount of gas is inversely proportional to its pressure?

  1. Gay-Lussac's law
  2. Boyle's law Correct answer.
  3. Avogadro's law
  4. Charles's law

Explanation

Boyle's law describes the inverse relationship between pressure and volume for a fixed mass of gas when temperature is held constant, so that the product of pressure and volume is constant. Charles's law relates volume to absolute temperature, Gay-Lussac's law relates pressure to temperature, and Avogadro's law relates volume to the number of moles.

Question 27Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Functional residual capacity is calculated as the sum of which two volumes?

  1. Expiratory reserve volume and residual volume Correct answer.
  2. Vital capacity and residual volume
  3. Tidal volume and residual volume
  4. Inspiratory capacity and tidal volume

Explanation

Functional residual capacity is the volume of gas remaining in the lungs at the end of a normal expiration, which is the sum of expiratory reserve volume and residual volume. It represents the balance point between the outward recoil of the chest wall and the inward recoil of the lungs.

Question 28Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Succinylcholine produces skeletal muscle paralysis primarily by which mechanism?

  1. Competitive antagonism at the nicotinic acetylcholine receptor
  2. Persistent depolarization of the motor end plate Correct answer.
  3. Blockade of presynaptic acetylcholine release
  4. Irreversible inhibition of acetylcholinesterase

Explanation

Succinylcholine is a depolarizing neuromuscular blocker that binds nicotinic receptors and maintains the end plate in a depolarized state, so the voltage-gated sodium channels remain inactivated and the muscle cannot be re-excited. The initial depolarization produces visible fasciculations before flaccid paralysis develops.

Question 29Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Sharp, well-localized pain is transmitted primarily by which nerve fibers?

  1. C fibers
  2. A-delta fibers Correct answer.
  3. A-alpha fibers
  4. A-beta fibers

Explanation

A-delta fibers are thinly myelinated fibers with fast conduction velocities that carry the initial sharp, discriminative component of pain. C fibers are unmyelinated, conduct slowly, and mediate dull, poorly localized, lingering pain.

Question 30Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Pulse oximetry estimates arterial oxygen saturation by applying which principle?

  1. Piezoelectric effect
  2. Raman scattering
  3. Doppler shift
  4. Beer-Lambert law Correct answer.

Explanation

The Beer-Lambert law relates the absorption of light to the concentration of an absorbing substance in a path, and pulse oximetry uses the differing absorption spectra of oxyhemoglobin and deoxyhemoglobin at two wavelengths to compute saturation. The pulsatile component is used to isolate the arterial signal from venous and tissue absorption.

Question 31Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which non-depolarizing neuromuscular blocker undergoes degradation by Hofmann elimination, making its duration largely independent of hepatic and renal function?

  1. Vecuronium
  2. Pancuronium
  3. Cisatracurium Correct answer.
  4. Rocuronium

Explanation

Cisatracurium undergoes Hofmann elimination, a spontaneous pH- and temperature-dependent chemical degradation in plasma, and is also minimally metabolized by nonspecific esterases. This makes its recovery relatively independent of hepatic and renal clearance.

Question 32Basic Sciences (physics, physiology, pharmacology, pathophysiology)

In a healthy adult, which fluid compartment contains the largest volume of water?

  1. Transcellular fluid volume
  2. Intracellular fluid volume Correct answer.
  3. Interstitial fluid volume
  4. Plasma volume

Explanation

Total body water is about 60% of body weight, of which roughly two-thirds is intracellular and one-third is extracellular. The intracellular compartment is therefore the largest, with plasma and interstitial fluid making up the much smaller extracellular space.

Question 33Basic Sciences (physics, physiology, pharmacology, pathophysiology)

According to Poiseuille's law, reducing the radius of an airway by half while other factors remain constant changes resistance by what factor?

  1. Twofold increase
  2. Fourfold increase
  3. Sixteenfold increase Correct answer.
  4. Eightfold increase

Explanation

Poiseuille's law states that resistance is inversely proportional to the fourth power of the radius. Halving the radius therefore multiplies resistance by 2 to the fourth power, which is 16.

Question 34Basic Sciences (physics, physiology, pharmacology, pathophysiology)

At 37°C, the equilibrium potential for potassium across a membrane with intracellular [K+] of 140 mmol/L and extracellular [K+] of 4 mmol/L is closest to which value?

  1. -94 mV Correct answer.
  2. -61 mV
  3. +94 mV
  4. -20 mV

Explanation

The Nernst equation gives an equilibrium potential of about 61 mV multiplied by the logarithm of the outside-to-inside potassium ratio. Since the ratio is approximately 0.029, whose logarithm is about -1.54, the resulting potential is roughly -94 mV, indicating that the inside is negative relative to the outside.

Question 35Basic Sciences (physics, physiology, pharmacology, pathophysiology)

For a drug with a high hepatic extraction ratio, systemic clearance is best described by which statement?

  1. It approximates hepatic blood flow Correct answer.
  2. It equals the glomerular filtration rate
  3. It is limited chiefly by plasma protein binding
  4. It is independent of changes in hepatic blood flow

Explanation

When extraction across the liver is nearly complete, essentially all drug presented in the portal and arterial blood is removed in a single pass, so clearance is limited by delivery, that is, by hepatic blood flow. Protein binding has little impact on clearance for such high-extraction drugs because bound and unbound fractions equilibrate during passage.

Question 36Basic Sciences (physics, physiology, pharmacology, pathophysiology)

The time constant of an alveolar unit is the product of which two variables?

  1. Elastance and resistance
  2. Resistance and volume
  3. Compliance divided by resistance
  4. Compliance and resistance Correct answer.

Explanation

The time constant of a lung unit describes how quickly it fills or empties and equals compliance multiplied by resistance. One time constant corresponds to about 63% of filling or emptying, and units with long time constants require more time to equilibrate with alveolar pressure.

Question 37Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Coronary perfusion pressure of the left ventricle is calculated as which difference?

  1. Aortic systolic pressure minus left ventricular systolic pressure
  2. Aortic diastolic pressure minus left ventricular end-diastolic pressure Correct answer.
  3. Aortic diastolic pressure minus right atrial pressure
  4. Aortic mean pressure minus pulmonary capillary wedge pressure

Explanation

Left ventricular myocardial perfusion occurs predominantly during diastole, so the driving pressure is aortic diastolic pressure minus the left ventricular end-diastolic pressure that opposes flow into the subendocardium. Tachycardia and elevated filling pressures reduce this gradient and predispose to subendocardial ischemia.

Question 38Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which condition characteristically produces a metabolic acidosis with a normal anion gap?

  1. Methanol poisoning
  2. Severe diarrhea Correct answer.
  3. Advanced chronic kidney disease
  4. Diabetic ketoacidosis

Explanation

Severe diarrhea causes loss of bicarbonate-rich fluid and is accompanied by chloride retention, producing a hyperchloremic metabolic acidosis with an unchanged anion gap. The unmeasured anions that would widen the gap are not generated in this setting.

Question 39Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Ketamine produces dissociative anesthesia and analgesia chiefly by acting at which receptor?

  1. NMDA receptor Correct answer.
  2. Mu-opioid receptor
  3. Voltage-gated sodium channel
  4. GABA-A receptor

Explanation

Ketamine is a noncompetitive antagonist at the N-methyl-D-aspartate subtype of glutamate receptor, which accounts for its dissociative state, amnesia, and somatic analgesia. This mechanism differs from that of most other intravenous anesthetics, which potentiate inhibitory GABA-A signaling.

Question 40Basic Sciences (physics, physiology, pharmacology, pathophysiology)

For a thin-walled spherical alveolus at a constant distending pressure, wall tension according to the law of Laplace is which of the following?

  1. Inversely proportional to the radius
  2. Independent of the radius
  3. Directly proportional to the radius Correct answer.
  4. Proportional to the square of the radius

Explanation

For a sphere, the law of Laplace gives tension equal to pressure multiplied by radius divided by two, so at constant pressure tension rises with increasing radius. Conversely, at a given wall tension, a smaller sphere generates a higher internal pressure, which is why small alveoli tend to collapse without surfactant.

Question 41Basic Sciences (physics, physiology, pharmacology, pathophysiology)

The Haldane effect describes which phenomenon?

  1. Enhanced oxygen binding in the presence of high carbon dioxide
  2. A leftward shift of the carbon dioxide dissociation curve caused by acidosis
  3. Increased carbon dioxide carrying capacity of oxygenated blood
  4. Greater carbon dioxide carriage by deoxygenated blood Correct answer.

Explanation

The Haldane effect refers to the greater ability of deoxygenated hemoglobin to carry carbon dioxide, largely because reduced hemoglobin binds hydrogen ions and carbon dioxide more avidly. This facilitates carbon dioxide uptake in the tissues and its release in the pulmonary capillaries as hemoglobin becomes oxygenated.

Question 42Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Neostigmine reverses non-depolarizing neuromuscular blockade by which mechanism?

  1. Inhibition of acetylcholinesterase at the neuromuscular junction Correct answer.
  2. Competitive blockade of postsynaptic nicotinic receptors
  3. Displacement of the blocker from plasma protein binding sites
  4. Increased acetylcholine release from the presynaptic nerve terminal

Explanation

Neostigmine inhibits acetylcholinesterase, so acetylcholine accumulates in the synaptic cleft and outcompetes the non-depolarizing blocker for nicotinic receptors. Because the effect depends on acetylcholine availability, reversal is incomplete at deep levels of blockade.

Question 43Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Which change in blood or vessel characteristics most favors turbulent rather than laminar flow?

  1. Decreased fluid density
  2. Increased fluid viscosity
  3. Increased fluid density Correct answer.
  4. Decreased vessel diameter

Explanation

The Reynolds number, which predicts turbulence when it exceeds roughly 2000 to 4000, is proportional to density, velocity, and diameter and inversely proportional to viscosity. Increasing density therefore raises the Reynolds number and promotes turbulent flow.

Question 44Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Cerebral blood flow is most strongly influenced by which of the following over the physiologic range?

  1. Mean arterial pressure between 60 and 150 mmHg
  2. Arterial oxygen tension within the normal range
  3. Hemoglobin concentration
  4. Arterial carbon dioxide tension Correct answer.

Explanation

Cerebral blood flow changes by roughly 2% to 4% per mmHg of arterial carbon dioxide tension because carbon dioxide dilates cerebral resistance vessels. Oxygen tension exerts little effect until it falls substantially below normal, and mean arterial pressure is held relatively constant by autoregulation across the stated range.

Question 45Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A 70 kg patient is prescribed an infusion of 10 mcg/kg/min of a solution containing 100 mcg/mL. What infusion rate is required?

  1. 4.2 mL/min
  2. 70 mL/min
  3. 7 mL/min Correct answer.
  4. 0.7 mL/min

Explanation

The total dose required each minute is 10 mcg/kg/min multiplied by 70 kg, which equals 700 mcg/min. Dividing this dose by the concentration of 100 mcg/mL gives an infusion rate of 7 mL/min.

Question 46Basic Sciences (physics, physiology, pharmacology, pathophysiology)

According to the Stewart approach to acid-base physiology, an isolated increase in plasma chloride concentration without a change in sodium most likely produces which effect?

  1. A decreased strong ion difference, which produces a metabolic acidosis Correct answer.
  2. No acid-base change, because chloride is a weak acid
  3. A respiratory alkalosis that offsets the chloride load
  4. An increased strong ion difference, which raises pH

Explanation

In the Stewart model, the strong ion difference, calculated mainly as sodium minus chloride, is a primary determinant of pH. Raising chloride without raising sodium narrows the strong ion difference, which increases dissociation of water and lowers pH, producing a hyperchloremic metabolic acidosis.

Question 47Basic Sciences (physics, physiology, pharmacology, pathophysiology)

Cooling observed when a compressed medical gas expands rapidly through a cylinder regulator is best attributed to which phenomenon?

  1. The Joule-Thomson effect, in which a real gas changes temperature during isenthalpic expansion Correct answer.
  2. Charles's law, because volume increases as temperature rises
  3. Adiabatic compression of the gas within the cylinder
  4. Latent heat absorbed during condensation of water vapor

Explanation

Rapid expansion through a restrictive orifice approximates an isenthalpic process, and for many real gases the Joule-Thomson coefficient is positive at cylinder temperatures, so the gas cools. The effect can be clinically important with nitrous oxide and carbon dioxide, which may cause frost or regulator malfunction.

Question 48Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A patient in cardiogenic shock with markedly reduced hepatic blood flow is maintained on a steady infusion of a drug with a high hepatic extraction ratio. What is the most likely effect on the steady-state plasma concentration?

  1. It falls, because metabolism of high-extraction drugs is flow-independent
  2. It rises, because clearance falls in proportion to hepatic blood flow Correct answer.
  3. It depends only on the volume of distribution and not on clearance
  4. It remains unchanged, because high extraction preserves clearance

Explanation

For a high-extraction drug, clearance approximates hepatic blood flow, so a fall in splanchnic perfusion lowers clearance and, at a fixed infusion rate, raises the steady-state concentration. The relationship that steady-state concentration equals infusion rate divided by clearance makes the direction of change predictable.

Question 49Basic Sciences (physics, physiology, pharmacology, pathophysiology)

At lung volumes below functional residual capacity, pulmonary vascular resistance rises primarily because of which mechanism?

  1. Increased blood viscosity at low lung volumes
  2. Compression of alveolar vessels by increased airway pressure
  3. Decreased radial traction on extra-alveolar vessels Correct answer.
  4. A fall in pulmonary artery pressure below left atrial pressure

Explanation

Extra-alveolar vessels are held open by the radial traction of surrounding lung parenchyma, so at low lung volumes this traction diminishes and these vessels narrow, raising pulmonary vascular resistance. Alveolar vessel compression becomes the dominant mechanism at high lung volumes instead.

Question 50Basic Sciences (physics, physiology, pharmacology, pathophysiology)

A 1 mol/L solution of sodium chloride that dissociates completely is separated from pure water by a semipermeable membrane at 37°C. The osmotic pressure generated is closest to which value?

  1. 51 atm Correct answer.
  2. 25 atm
  3. 2 atm
  4. 0.082 atm

Explanation

The van't Hoff equation gives osmotic pressure as the osmotic coefficient times concentration times the gas constant times absolute temperature. With complete dissociation the particle concentration is 2 mol/L, and multiplying by 0.082 L·atm/(mol·K) and 310 K yields approximately 51 atm.