I85PREP
⌘ K
ABA BASIC study materials
ABA BASIC study resources

ABA BASIC practice questions

One question at a time. Build your ABA BASIC understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

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

At sea level, which value is closest to 1 atmosphere of pressure expressed in millimeters of mercury?

  1. 100
  2. 760 Correct answer.
  3. 47
  4. 273

Explanation

Standard atmospheric pressure at sea level supports a mercury column 760 mm high, equivalent to about 101.3 kPa. The other values correspond to unrelated quantities such as alveolar carbon dioxide tension or temperature on the Kelvin scale.

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

Minimum alveolar concentration (MAC) is best defined as which of the following?

  1. The dose producing apnea in half of anesthetized patients
  2. The blood concentration at which 50% of receptors are occupied
  3. The alveolar concentration preventing movement in 50% of subjects Correct answer.
  4. The alveolar concentration that produces unconsciousness in 95% of patients

Explanation

MAC is the alveolar concentration of a volatile agent at one atmosphere that prevents purposeful movement in response to a standard surgical stimulus in 50% of patients. It is used as a measure of relative potency, with lower MAC indicating greater potency.

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

An aspirated foreign body is most likely to lodge in which structure?

  1. Left main bronchus
  2. Trachea at the carina
  3. Right main bronchus Correct answer.
  4. Left lower lobe bronchus

Explanation

The right main bronchus is wider, shorter, and more vertical than the left, so aspirated material preferentially enters it. This anatomic asymmetry explains the classic right-sided distribution of aspirated objects.

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

Which nerve fiber type conducts action potentials most rapidly?

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

Explanation

Conduction velocity rises with fiber diameter and myelination. A-alpha fibers are the largest and most heavily myelinated, so they conduct fastest, whereas C fibers are small and unmyelinated and conduct slowest.

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

Succinylcholine produces neuromuscular blockade through which mechanism?

  1. Inhibition of acetylcholine release from the nerve terminal
  2. Competitive antagonism at the nicotinic receptor
  3. Sustained nicotinic receptor activation Correct answer.
  4. Blockade of voltage-gated sodium channels in the muscle membrane

Explanation

Succinylcholine is a depolarizing blocker that binds nicotinic receptors and keeps them open, causing persistent depolarization and a phase I block. It does not act by competing reversibly with acetylcholine.

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

Neostigmine reverses nondepolarizing neuromuscular blockade by which action?

  1. Blockade of presynaptic calcium channels
  2. Inhibition of acetylcholinesterase Correct answer.
  3. Direct agonism at nicotinic receptors
  4. Increased hepatic metabolism of the blocker

Explanation

Neostigmine inhibits acetylcholinesterase, so acetylcholine accumulates in the synaptic cleft and outcompetes the nondepolarizing blocker. This effect requires functioning acetylcholinesterase and can be limited in deep blocks.

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

An increase in which factor shifts the oxyhemoglobin dissociation curve to the right?

  1. Increased 2,3-diphosphoglycerate Correct answer.
  2. Increased pH
  3. Decreased carbon dioxide tension
  4. Decreased temperature

Explanation

2,3-DPG binds deoxyhemoglobin and stabilizes it, lowering oxygen affinity and shifting the curve rightward so oxygen is released more readily to tissues. Acidosis, hypercapnia, and fever produce similar rightward shifts.

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

In laminar flow through a rigid tube, doubling the radius changes flow by what factor?

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

Explanation

Hagen-Poiseuille flow is proportional to the fourth power of the radius. Doubling the radius therefore raises flow by 2 to the fourth power, or 16-fold, when pressure gradient and viscosity are unchanged.

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

A drug follows first-order kinetics with a half-life of 8 hours. During a constant-rate infusion, what fraction of the final steady-state concentration is reached after 24 hours?

  1. 50%
  2. 96%
  3. 87.5% Correct answer.
  4. 75%

Explanation

Twenty-four hours represents three half-lives. Each half-life closes half of the remaining gap to steady state, so after three half-lives the fraction achieved is 1 minus one-eighth, or 87.5%.

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

A drug is infused at 4 mg/min and reaches a steady-state plasma concentration of 2 mg/L. What is its clearance?

  1. 0.5 L/min
  2. 4 L/min
  3. 2 L/min Correct answer.
  4. 8 L/min

Explanation

At steady state, clearance equals the infusion rate divided by the plasma concentration. Dividing 4 mg/min by 2 mg/L gives 2 L/min.

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

If intracellular potassium is 150 mEq/L and extracellular potassium is 4 mEq/L, the potassium equilibrium potential at 37 degrees Celsius is closest to which value?

  1. -96 mV Correct answer.
  2. -61 mV
  3. +96 mV
  4. -30 mV

Explanation

The Nernst equation at body temperature gives approximately 61 mV times the logarithm of the outside-to-inside potassium ratio. The ratio 4/150 has a log of about -1.57, giving roughly -96 mV, close to the resting membrane potential.

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

Compared with an agent of low blood solubility, an inhaled agent with high blood solubility will do which of the following?

  1. Require a larger inspired partial pressure to achieve the same brain tension
  2. Equilibrate between blood and alveoli more rapidly than low-solubility agents
  3. Show a slower rise in alveolar partial pressure Correct answer.
  4. Produce a more rapid induction of anesthesia in most patients

Explanation

A highly soluble agent is taken up extensively by blood, so the alveolar partial pressure rises slowly toward the inspired value. Because alveolar and brain partial pressures track together, induction is slower for soluble agents.

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

Oxygen consumption is 250 mL/min, arterial oxygen content is 20 mL/dL, and mixed venous oxygen content is 15 mL/dL. What is the cardiac output?

  1. 2.5 L/min
  2. 12.5 L/min
  3. 5 L/min Correct answer.
  4. 10 L/min

Explanation

The Fick principle states that oxygen consumption equals cardiac output times the arteriovenous oxygen content difference. The difference of 5 mL/dL equals 50 mL/L, so 250 mL/min divided by 50 mL/L gives 5 L/min.

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

Clearance of which substance is used to measure glomerular filtration rate?

  1. Renal plasma flow
  2. Effective renal blood flow
  3. Tubular secretory maximum
  4. Glomerular filtration rate Correct answer.

Explanation

Inulin is freely filtered and is neither reabsorbed nor secreted, so its clearance equals the glomerular filtration rate. Creatinine clearance approximates the same value but is less exact.

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

A patient has a prolonged neuromuscular block after a single dose of succinylcholine. Deficiency of which enzyme is most likely responsible?

  1. Catechol-O-methyltransferase
  2. Monoamine oxidase
  3. Acetylcholinesterase
  4. Plasma butyrylcholinesterase Correct answer.

Explanation

Succinylcholine is normally hydrolyzed rapidly by plasma butyrylcholinesterase, also called pseudocholinesterase. Genetically reduced enzyme activity prolongs the depolarizing block well beyond the usual few minutes.

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

Turbulent gas flow is favored by which combination of conditions?

  1. Low flow velocity with a wide tube and high viscosity
  2. High flow velocity, wide tube, low viscosity Correct answer.
  3. High flow velocity with a narrow tube and high viscosity
  4. Low flow velocity with a narrow tube and high viscosity

Explanation

The Reynolds number rises with velocity and tube diameter and falls with viscosity. Higher Reynolds numbers favor turbulence, so high velocity, large diameter, and low viscosity promote it.

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

A cylinder contains 10 L of oxygen at 2000 psi. At constant temperature, what volume would this gas occupy at 500 psi?

  1. 40 L Correct answer.
  2. 10 L
  3. 20 L
  4. 80 L

Explanation

Boyle's law states that pressure times volume is constant at fixed temperature. Scaling from 2000 psi to 500 psi lowers pressure fourfold, so the gas expands fourfold to 40 L.

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

Ketamine produces anesthesia chiefly by acting at which receptor?

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

Explanation

Ketamine is a noncompetitive antagonist at the NMDA subtype of glutamate receptor, which accounts for its dissociative anesthetic and analgesic effects. It does not act primarily through GABA-A receptors like propofol or volatile agents.

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

Hypoxic pulmonary vasoconstriction serves which purpose?

  1. Divert blood from poorly ventilated lung units Correct answer.
  2. Reduce oxygen delivery to the systemic circulation
  3. Lower pulmonary artery pressure during hypoxia
  4. Increase pulmonary blood flow to hypoxic areas

Explanation

Alveolar hypoxia constricts adjacent pulmonary arterioles, redirecting blood away from poorly ventilated regions toward better-ventilated lung. This improves ventilation-perfusion matching and limits systemic hypoxemia.

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

The diaphragm receives its motor innervation from which spinal roots?

  1. C3-C5 Correct answer.
  2. C1-C3
  3. C5-C7
  4. T1-T4

Explanation

The phrenic nerve arises from cervical roots C3, C4, and C5 and supplies the motor innervation of the diaphragm. Preservation of these roots is essential for spontaneous ventilation in patients with cervical spinal injury.

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

Two alveoli have equal surface tension but different radii. According to Laplace's law, the smaller alveolus does which of the following?

  1. Has a lower collapsing pressure
  2. Requires no surfactant to remain stable
  3. Has the same collapsing pressure as the larger one
  4. Has a higher collapsing pressure Correct answer.

Explanation

Laplace's law states that pressure equals twice the surface tension divided by the radius. With equal surface tension, a smaller radius generates a higher collapsing pressure, which is why surfactant is needed to equalize alveolar stability.

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

Which opioid has a context-sensitive half-time that remains essentially constant regardless of infusion duration?

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

Explanation

Remifentanil is cleared by nonspecific plasma and tissue esterases, so its offset is independent of infusion duration and its context-sensitive half-time stays near 3 to 4 minutes. Drugs relying on redistribution and hepatic metabolism show progressively longer offset after prolonged infusions.

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

A patient has sodium 140 mEq/L, chloride 105 mEq/L, bicarbonate 25 mEq/L, and albumin 2.0 g/dL. Which statement about the anion gap is correct?

  1. The gap is low-normal, but albumin correction makes it high Correct answer.
  2. The measured anion gap is normal and no correction for albumin is needed in this setting
  3. The measured anion gap is clearly elevated, indicating an unmeasured anion such as lactate
  4. The anion gap cannot be interpreted meaningfully when the serum albumin is low

Explanation

The measured anion gap is 140 minus 130, or 10, which appears normal. Because each 1 g/dL fall in albumin lowers the gap by about 2.5, correcting for an albumin of 2.0 raises the value to roughly 15, revealing an occult elevated gap.

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

Gas flows steadily through a horizontal tube that narrows at a constriction. A side-hole manometer at the constriction, compared with one in the wide segment, will read which pressure?

  1. A lower pressure than in the wide segment Correct answer.
  2. The same pressure as in the wide segment
  3. A higher pressure than in the wide segment
  4. A pressure equal to atmospheric pressure

Explanation

By the Bernoulli principle, fluid velocity increases at a constriction and lateral pressure falls correspondingly, assuming negligible viscous losses. This pressure drop at a narrowing underlies Venturi meters and Bernoulli-type nebulizers.

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

A patient's hemoglobin falls from 15 to 7.5 g/dL while arterial oxygen saturation stays at 100% and cardiac output is unchanged. Oxygen delivery changes by approximately what amount?

  1. 75% decrease
  2. 25% decrease
  3. 50% decrease Correct answer.
  4. No change

Explanation

Oxygen delivery equals cardiac output times arterial oxygen content, and content is dominated by the hemoglobin-bound fraction. Halving hemoglobin roughly halves arterial oxygen content, so delivery falls by about 50% when output and saturation are unchanged.

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

Which pharmacologic property is defined as the dose of a drug required to produce a given effect?

  1. Therapeutic index
  2. Efficacy
  3. Bioavailability
  4. Potency Correct answer.

Explanation

Potency expresses the dose (or concentration) needed to produce a specified effect, so a more potent drug produces the same effect at a lower dose. It is read from the position of the dose-response curve along the x-axis.

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

Activation of a Gs-coupled receptor produces which immediate intracellular effect?

  1. Release of calcium from the sarcoplasmic reticulum
  2. Opening of ligand-gated chloride channels
  3. Increased adenylyl cyclase activity Correct answer.
  4. Increased phospholipase C activity

Explanation

Gs proteins stimulate adenylyl cyclase, raising intracellular cyclic AMP and activating protein kinase A. This is the classic beta-adrenergic and many peptide hormone signaling pathway.

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

The phase 0 upstroke of a ventricular myocyte action potential is produced by which ionic event?

  1. Chloride influx through GABA-gated channels
  2. Potassium efflux through delayed rectifier channels
  3. Calcium influx through L-type channels
  4. Rapid sodium influx through fast channels Correct answer.

Explanation

Ventricular muscle phase 0 is generated by opening of fast voltage-gated sodium channels, producing a rapid inward sodium current. The calcium current contributes chiefly to the phase 2 plateau.

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

The cricothyroid muscle is innervated by which nerve?

  1. External branch of the superior laryngeal nerve Correct answer.
  2. Recurrent laryngeal nerve
  3. Internal branch of the superior laryngeal nerve
  4. Hypoglossal nerve

Explanation

The external branch of the superior laryngeal nerve supplies the cricothyroid, the only intrinsic laryngeal muscle innervated above the vocal cords. This nerve is at risk during ligation of the superior thyroid artery.

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

In blood, the largest fraction of carbon dioxide is transported in which form?

  1. Bicarbonate Correct answer.
  2. Carbaminohemoglobin
  3. Carbonic acid
  4. Dissolved carbon dioxide

Explanation

About 70% of carbon dioxide carried in blood is in the form of bicarbonate generated by carbonic anhydrase within red cells. Dissolved CO2 and carbamino compounds account for most of the remainder.

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

Which drug acts primarily as a direct alpha-1 adrenergic agonist?

  1. Phenylephrine Correct answer.
  2. Clonidine
  3. Isoproterenol
  4. Dobutamine

Explanation

Phenylephrine is a direct-acting agonist with essentially pure alpha-1 activity, producing arteriolar and venous constriction with reflex bradycardia. It has negligible beta activity at usual doses.

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

Within the physiologic range, an increase in left ventricular end-diastolic volume produces which change?

  1. Decreased myocardial oxygen consumption
  2. Increased stroke volume Correct answer.
  3. No change in stroke work
  4. Decreased stroke volume

Explanation

The Frank-Starling relationship states that increasing preload stretches the myocardium and increases force of contraction, raising stroke volume and stroke work. This occurs without a change in sympathetic tone.

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

Aspirin produces its antiplatelet effect through irreversible inhibition of which enzyme?

  1. Cyclooxygenase-1 Correct answer.
  2. Lipoxygenase
  3. Phosphodiesterase
  4. Xanthine oxidase

Explanation

Aspirin acetylates cyclooxygenase-1 in platelets, blocking thromboxane A2 synthesis for the life of the platelet because platelets cannot make new enzyme. This underlies its use in coronary and cerebrovascular disease.

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

A 70-kg patient receives 500 mg of a drug intravenously, and the resulting plasma concentration is 25 mg/L. Assuming immediate complete mixing and negligible elimination, what is the apparent volume of distribution?

  1. 200 L
  2. 50 L
  3. 20 L Correct answer.
  4. 5 L

Explanation

Apparent volume of distribution equals dose divided by plasma concentration, so 500 mg divided by 25 mg/L is 20 L. It is a proportionality constant relating amount of drug in the body to plasma concentration.

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

A drug given orally has a hepatic extraction ratio of 0.9. Which finding is expected?

  1. Clearance independent of hepatic blood flow
  2. Oral bioavailability near 10% Correct answer.
  3. Half-life independent of hepatic function
  4. Oral bioavailability near 90%

Explanation

The fraction of drug escaping first-pass hepatic metabolism equals one minus the extraction ratio, so a ratio of 0.9 leaves roughly 10% to reach the systemic circulation. Such drugs have low and variable oral bioavailability.

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

A drug eliminated by zero-order kinetics shows which pattern?

  1. A constant amount removed per unit time Correct answer.
  2. A half-life independent of plasma concentration
  3. A constant fraction removed per unit time
  4. Clearance that rises as concentration rises

Explanation

In zero-order elimination the metabolic pathway is saturated, so a fixed amount of drug is removed per unit time regardless of concentration. As a result, half-life lengthens as the concentration rises.

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

According to Fick's law, doubling the thickness of the alveolar-capillary membrane, with all other factors constant, changes diffusing capacity how?

  1. It decreases to one quarter
  2. It is halved Correct answer.
  3. It doubles
  4. It is unchanged

Explanation

Fick's law states that diffusion is directly proportional to area and the concentration gradient and inversely proportional to membrane thickness. Doubling thickness therefore halves diffusion.

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

Which statement about the critical temperature of a gas is correct?

  1. The temperature at which it behaves as an ideal gas
  2. The highest temperature at which pressure can liquefy it Correct answer.
  3. The temperature at which vapor pressure equals 760 mmHg
  4. The temperature at which it exerts no pressure on its container

Explanation

Critical temperature is the highest temperature above which a substance cannot be liquefied by pressure alone, no matter how much pressure is applied. Oxygen and nitrous oxide have critical temperatures well above room temperature, which is why they exist as liquids in cylinders.

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

A patient with carbon monoxide poisoning has a pulse oximeter reading of 99%. Which best explains this?

  1. Carboxyhemoglobin does not absorb light at either of the two wavelengths used
  2. Carboxyhemoglobin absorbs similarly to oxyhemoglobin at both wavelengths Correct answer.
  3. Carbon monoxide raises the functional hemoglobin concentration
  4. Carbon monoxide causes vasodilation that corrects the reading

Explanation

Conventional pulse oximeters compare absorbance at two wavelengths and cannot distinguish carboxyhemoglobin from oxyhemoglobin, so saturation appears normal despite reduced oxygen content. Co-oximetry is required to detect the abnormality.

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

At low plasma concentrations, the renal clearance of para-aminohippurate is used to estimate which variable?

  1. Filtration fraction
  2. Renal glucose reabsorption
  3. Glomerular filtration rate
  4. Renal plasma flow Correct answer.

Explanation

Para-aminohippurate is filtered and avidly secreted so that nearly all of it is removed in a single pass, making its clearance approximate effective renal plasma flow. Filtration fraction is then calculated as GFR divided by renal plasma flow.

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

In a healthy adult, an acute fall in PaCO2 from 40 to 30 mmHg produces which change in cerebral blood flow?

  1. No change, because of autoregulation
  2. A substantial decrease Correct answer.
  3. An increase only if PaO2 also falls
  4. A substantial increase

Explanation

Cerebral blood flow changes roughly 2 to 4% per mmHg of PaCO2 because carbon dioxide dilates cerebral resistance vessels. Hypocapnia therefore constricts these vessels and reduces flow, which is the basis for hyperventilation to lower intracranial pressure.

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

Adding a competitive antagonist to an agonist produces which change in the agonist dose-response curve?

  1. A leftward shift with unchanged maximal response
  2. A rightward shift with unchanged maximal response Correct answer.
  3. A rightward shift with reduced maximal response
  4. A reduced maximal response with unchanged ED50

Explanation

Competitive antagonism is surmountable: higher agonist concentrations displace the antagonist and restore the full effect, so the curve shifts right without a change in maximum. Only the ED50 increases.

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

When a lumbar epidural is placed in the midline, which structure is penetrated immediately before entering the epidural space?

  1. Ligamentum flavum Correct answer.
  2. Supraspinous ligament
  3. Posterior longitudinal ligament
  4. Dura mater

Explanation

The needle passes skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, and ligamentum flavum before entering the epidural space. The dura lies beyond the epidural space and is penetrated only for a spinal.

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

Afferent impulses from the carotid sinus baroreceptors reach the brainstem through which cranial nerve?

  1. Vagus nerve
  2. Hypoglossal nerve
  3. Facial nerve
  4. Glossopharyngeal nerve Correct answer.

Explanation

The carotid sinus nerve of Hering is a branch of the glossopharyngeal nerve that carries baroreceptor and carotid body chemoreceptor input to the nucleus tractus solitarius. Aortic arch baroreceptors instead travel in the vagus.

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

At the neuromuscular junction, which event directly triggers acetylcholine release from the presynaptic terminal?

  1. Potassium efflux from the nerve terminal
  2. Opening of postsynaptic nicotinic receptors
  3. Calcium influx into the nerve terminal Correct answer.
  4. Sodium influx into the nerve terminal

Explanation

Depolarization of the motor nerve terminal opens voltage-gated calcium channels, and the resulting calcium entry causes vesicular fusion and quantal release of acetylcholine. Magnesium and aminoglycosides impair transmission at this step.

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

Pulmonary end-capillary oxygen content is 20 mL/dL, arterial oxygen content is 18 mL/dL, and mixed venous oxygen content is 14 mL/dL. What is the shunt fraction?

  1. 50%
  2. 33% Correct answer.
  3. 20%
  4. 10%

Explanation

Shunt fraction is calculated as end-capillary minus arterial content divided by end-capillary minus mixed venous content, here 2 divided by 6, or about 33%. The numerator represents blood that bypasses ventilated alveoli.

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

A lung unit has a compliance of 0.05 L/cmH2O and an airway resistance of 4 cmH2O/L per second. What is its time constant?

  1. 20 seconds
  2. 0.2 seconds Correct answer.
  3. 5 seconds
  4. 0.02 seconds

Explanation

The time constant equals compliance multiplied by resistance, here 0.05 L/cmH2O times 4 cmH2O/L per second, or 0.2 seconds. Roughly three time constants are needed for about 95% of a lung unit to empty.

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

A drug has a hepatic extraction ratio of 0.95, and hepatic blood flow is 1.5 L/min. Which statement about its hepatic clearance is correct?

  1. It is about 0.075 L/min and limited by blood flow
  2. It is about 1.4 L/min and sensitive to changes in hepatic blood flow Correct answer.
  3. It is about 0.075 L/min and limited by enzyme activity
  4. It is about 1.5 L/min and independent of protein binding

Explanation

Hepatic clearance equals hepatic blood flow multiplied by the extraction ratio, giving approximately 1.4 L/min. Because extraction is nearly complete, clearance is flow-limited and changes in hepatic perfusion alter it directly.

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

Arterial PCO2 is 40 mmHg and mixed expired PCO2 is 20 mmHg. Using the Bohr equation, what is the dead space fraction (VD/VT)?

  1. 0.75
  2. 0.33
  3. 0.20
  4. 0.50 Correct answer.

Explanation

The Bohr equation gives dead space fraction as arterial minus mixed expired PCO2 divided by arterial PCO2, so 20 divided by 40 equals 0.50. This reflects the fraction of each breath that does not participate in gas exchange.

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

The Haldane effect describes which phenomenon?

  1. Increased carbon dioxide carriage by deoxygenated blood Correct answer.
  2. Decreased carbon dioxide carriage by deoxygenated blood
  3. Increased oxygen binding when pH rises
  4. A rightward shift of the oxygen curve caused by hypercapnia

Explanation

The Haldane effect is the greater ability of deoxygenated hemoglobin to bind carbon dioxide and hydrogen ions. In the tissues, oxygen unloading therefore facilitates CO2 uptake, and in the lung the reverse occurs.