Behavioral thermoregulation US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Behavioral thermoregulation. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Behavioral thermoregulation US Medical PG Question 1: A 50-year-old male is brought to the dermatologist's office with complaints of a pigmented lesion. The lesion is uniformly dark with clean borders and no asymmetry and has been increasing in size over the past two weeks. He works in construction and spends large portions of his day outside. The dermatologist believes that this mole should be biopsied. To prepare the patient for the biopsy, the dermatologist injects a small amount of lidocaine into the skin around the lesion. Which of the following nerve functions would be the last to be blocked by the lidocaine?
- A. Pain
- B. Touch
- C. Temperature
- D. Sympathetic stimulation
- E. Pressure (Correct Answer)
Behavioral thermoregulation Explanation: ***Pressure***
- **Pressure** sensation is mediated by **Aβ fibers**, which are relatively **larger** and **myelinated**, making them more resistant to local anesthetic blockade.
- Nerve fibers are blocked in a specific order, typically starting with smaller, unmyelinated fibers and ending with larger, myelinated fibers.
*Pain*
- **Pain** sensation is primarily carried by **unmyelinated C fibers** and **small myelinated Aδ fibers**, which are among the **first to be blocked** by local anesthetics.
- These fibers have a **high surface-to-volume ratio**, making them more susceptible to the action of lidocaine.
*Touch*
- **Touch** sensation is mediated by a mix of **Aβ and Aδ fibers**; light touch is typically blocked relatively early due to the involvement of smaller fibers.
- However, **crude touch** often persists longer than pain and temperature but is usually blocked before pressure.
*Temperature*
- **Temperature** sensation is primarily carried by **Aδ and C fibers**, making it one of the **earliest sensations to be blocked** by local anesthetic.
- These fibers are generally small and have high sensitivity to local anesthetic agents.
*Sympathetic stimulation*
- **Sympathetic nerve fibers** are typically **small, unmyelinated C fibers** and are generally the **first to be blocked** by local anesthetics.
- This early blockade can lead to **vasodilation** in the area due to the loss of sympathetic tone.
Behavioral thermoregulation US Medical PG Question 2: An infant boy of unknown age and medical history is dropped off in the emergency department. The infant appears lethargic and has a large protruding tongue. Although the infant exhibits signs of neglect, he is in no apparent distress. The heart rate is 70/min, the respiratory rate is 30/min, and the temperature is 35.7°C (96.2°F). Which of the following is the most likely cause of the patient’s physical exam findings?
- A. Autosomal dominant mutation in the SERPING1 gene
- B. Genetic imprinting disorder affecting chromosome 11p15.5
- C. Type I hypersensitivity reaction
- D. Excess growth hormone secondary to pituitary gland tumor
- E. Congenital agenesis of an endocrine gland in the anterior neck (Correct Answer)
Behavioral thermoregulation Explanation: ***Congenital agenesis of an endocrine gland in the anterior neck***
- This description is highly suggestive of **congenital hypothyroidism**, caused by **thyroid dysgenesis** (agenesis or hypoplasia of the thyroid gland).
- Symptoms include **lethargy**, **macroglossia** (large protruding tongue), **hypotonia**, **feeding difficulties**, **umbilical hernia**, and **hypothermia**, all consistent with the clinical picture.
*Autosomal dominant mutation in the SERPING1 gene*
- A mutation in the **SERPING1 gene** causes **hereditary angioedema**, characterized by recurrent episodes of unpredictable swelling in various body parts.
- While swelling can affect the tongue, it is typically episodic, painful, and often triggered, which is not suggested by the chronic lethargy and physical signs described.
*Genetic imprinting disorder affecting chromosome 11p15.5*
- This describes **Beckwith-Wiedemann syndrome**, an overgrowth disorder caused by imprinting defects involving genes like **IGF2**, **H19**, and **CDKN1C** on chromosome 11p15.5.
- Features include **macroglossia**, **macrosomia**, **umbilical hernia**, **hemihyperplasia**, and increased risk of embryonal tumors like **Wilms tumor**.
- However, Beckwith-Wiedemann syndrome does not typically present with profound **lethargy** and **hypothermia** as seen in congenital hypothyroidism.
*Type I hypersensitivity reaction*
- A **Type I hypersensitivity reaction** (e.g., anaphylaxis) could cause acute **angioedema** of the tongue, but this would be an acute, rapidly progressing, and life-threatening event.
- The infant's description of being "in no apparent distress" and exhibiting chronic signs like lethargy and hypothermia makes an acute allergic reaction unlikely.
*Excess growth hormone secondary to pituitary gland tumor*
- **Excess growth hormone** (gigantism in children, acromegaly in adults) can cause **macroglossia** and coarse facial features in the long term.
- However, it does not explain the associated **lethargia**, **hypothermia**, and profound developmental delay seen in congenital hypothyroidism in an infant.
Behavioral thermoregulation US Medical PG Question 3: A 20-year-old woman reports to student health complaining of 5 days of viral symptoms including sneezing and a runny nose. She started coughing 2 days ago and is seeking cough medication. She additionally mentions that she developed a fever 2 days ago, but this has resolved. On exam, her temperature is 99.0°F (37.2°C), blood pressure is 118/76 mmHg, pulse is 86/min, and respirations are 12/min. Changes in the activity of warm-sensitive neurons in which part of her hypothalamus likely contributed to the development and resolution of her fever?
- A. Anterior hypothalamus (Correct Answer)
- B. Paraventricular nucleus
- C. Suprachiasmatic nucleus
- D. Lateral area
- E. Posterior hypothalamus
Behavioral thermoregulation Explanation: ***Anterior hypothalamus***
- The **anterior hypothalamus** contains warm-sensitive neurons that detect increases in body temperature and activate mechanisms for heat dissipation, such as sweating and vasodilation.
- In fever, **prostaglandins** increase the set point in the anterior hypothalamus, causing the body to retain heat and increase heat production until the new set point is reached; resolution of fever involves resetting this set point back to normal.
*Paraventricular nucleus*
- The **paraventricular nucleus** is primarily involved in neuroendocrine functions, stress response, and the regulation of appetite and autonomic nervous system.
- It plays a significant role in releasing hormones like **corticotropin-releasing hormone (CRH)** and **oxytocin**, not direct temperature regulation.
*Suprachiasmatic nucleus*
- The **suprachiasmatic nucleus (SCN)** is the body's main biological clock, regulating **circadian rhythms** including the sleep-wake cycle and daily fluctuations in body temperature.
- While it influences the normal diurnal variation in body temperature, it is not directly responsible for the acute regulation of fever.
*Lateral area*
- The **lateral hypothalamus** primarily functions as the "hunger center," stimulating foraging and feeding behavior.
- Damage to this area can lead to **anorexia** and reduced food intake, not impairments in fever response.
*Posterior hypothalamus*
- The **posterior hypothalamus** is primarily involved in heat conservation and production mechanisms, such as shivering and vasoconstriction, in response to cold.
- It contains cold-sensitive neurons and functions to raise body temperature if it falls below the set point, but it is not where the set point itself is regulated in response to pyrogens.
Behavioral thermoregulation US Medical PG Question 4: A 23-year-old man presents to the emergency department brought in by police. He was found shouting at strangers in the middle of the street. The patient has no significant past medical history, and his only medications include a short course of prednisone recently prescribed for poison ivy exposure. His temperature is 77°F (25°C), blood pressure is 90/50 mmHg, pulse is 90/min, respirations are 17/min, and oxygen saturation is 98% on room air. The patient is only wearing underwear, and he is occasionally mumbling angrily about the government. He appears to be responding to internal stimuli, and it is difficult to obtain a history from him. Which of the following is the next best step in management?
- A. Haloperidol IM
- B. Warmed IV normal saline and warm blankets (Correct Answer)
- C. Lorazepam and discontinue steroids
- D. Warm air recirculator
- E. Risperidone and warm blankets
Behavioral thermoregulation Explanation: ***Warmed IV normal saline and warm blankets***
- The patient's core body temperature of **77°F (25°C)** indicates severe **hypothermia**. The immediate priority is to rewarm the patient to prevent further physiological compromise.
- **Warmed IV normal saline** and **warm blankets** are essential interventions for **passive external rewarming** and **active core rewarming**, helping to gradually increase the patient's body temperature and stabilize hemodynamic status.
*Haloperidol IM*
- While the patient exhibits agitation and psychotic-like symptoms, addressing severe **hypothermia** is the immediate life-saving priority. Administering an antipsychotic without first stabilizing core temperature could be dangerous.
- Furthermore, **haloperidol** can have sedative effects that might mask the neurological signs of worsening hypothermia or other underlying conditions.
*Lorazepam and discontinue steroids*
- The patient's altered mental status and agitation are likely due to **hypothermia**, not necessarily an adverse effect of **prednisone** or an isolated psychiatric emergency requiring benzodiazepines.
- Discontinuing **steroids** abruptly can lead to **adrenal insufficiency**, which could further complicate the patient's critical condition, especially in the context of stress from severe hypothermia.
*Warm air recirculator*
- A **warm air recirculator** (e.g., forced-air warming blanket) is a form of **active external rewarming**. While beneficial, it is often used in conjunction with or after initiating **active core rewarming** with warmed IV fluids in cases of severe hypothermia.
- Relying solely on external rewarming might not be sufficient to rapidly correct **severe hypothermia** (core temperature < 28°C) and address associated **hemodynamic instability**.
*Risperidone and warm blankets*
- Similar to haloperidol, **risperidone** is an antipsychotic used for agitation and psychosis. However, the patient's primary and life-threatening issue is severe **hypothermia**.
- While **warm blankets** are appropriate for rewarming, addressing the underlying cause of the patient's presentation (hypothermia) takes precedence over immediate pharmacological management of psychiatric symptoms.
Behavioral thermoregulation US Medical PG Question 5: A 33-year-old man presents to the emergency department acutely confused. The patient was found down at a local construction site by his coworkers. The patient has a past medical history of a seizure disorder and schizophrenia and is currently taking haloperidol. He had recent surgery 2 months ago to remove an inflamed appendix. His temperature is 105°F (40.6°C), blood pressure is 120/84 mmHg, pulse is 150/min, respirations are 19/min, and oxygen saturation is 99% on room air. Physical exam is notable for a confused man who cannot answer questions. His clothes are drenched in sweat. He is not making purposeful movements with his extremities although no focal neurological deficits are clearly apparent. Which of the following is the most likely diagnosis?
- A. Heat exhaustion
- B. Nonexertional heat stroke
- C. Neuroleptic malignant syndrome
- D. Malignant hyperthermia
- E. Exertional heat stroke (Correct Answer)
Behavioral thermoregulation Explanation: ***Exertional heat stroke***
- This diagnosis is supported by the patient's presentation of **hyperthermia** (105°F), **tachycardia**, **confusion**, and a history of working at a **construction site** (suggesting physical exertion in a hot environment).
- The patient's **drenched clothes from sweat** indicate the body's initial attempt to cool down, but the extremely high core temperature and confusion signify a failure of thermoregulation.
*Heat exhaustion*
- While heat exhaustion also involves **sweating** and can present with elevated body temperature, the core temperature is typically **below 104°F (40°C)**, and **marked altered mental status** (like severe confusion) is less common or less severe.
- The patient's temperature of 105°F (40.6°C) and profound confusion are more indicative of heat stroke.
*Nonexertional heat stroke*
- Nonexertional (or classic) heat stroke usually affects populations with **compromised thermoregulation** (e.g., elderly, very young, chronically ill) who are exposed to high environmental temperatures **without significant physical exertion**.
- The patient's age (33) and history of working at a construction site make exertional heat stroke more likely than nonexertional.
*Neuroleptic malignant syndrome*
- NMS is characterized by **fever, muscle rigidity** (often "lead pipe" rigidity), **altered mental status**, and **autonomic instability** (including tachycardia and diaphoresis), and is associated with **antipsychotic medications** like haloperidol.
- However, NMS typically develops **gradually over days to weeks**, not acutely. The key differentiator here is the **clear environmental and exertional context** (construction site work), **acute onset** after being found down, and the **absence of characteristic muscle rigidity** that would be prominent in NMS.
- Heat stroke is more probable given the immediate occupational exposure and clinical timeline.
*Malignant hyperthermia*
- Malignant hyperthermia is a rare, life-threatening condition associated with exposure to certain **anesthetic agents** (e.g., succinylcholine, volatile anesthetics) or, less commonly, severe exertion in susceptible individuals.
- The patient's recent surgery was two months prior, and there is no mention of current exposure to triggers, making it unlikely to be the immediate cause of his acute presentation.
Behavioral thermoregulation US Medical PG Question 6: A group of investigators is studying thermoregulatory adaptations of the human body. A subject is seated in a thermally insulated isolation chamber with an internal temperature of 48°C (118°F), a pressure of 1 atmosphere, and a relative humidity of 10%. Which of the following is the primary mechanism of heat loss in this subject?
- A. Convection
- B. Evaporation (Correct Answer)
- C. Conduction
- D. Piloerection
- E. Radiation
Behavioral thermoregulation Explanation: ***Evaporation***
- In an environment where the ambient temperature (48°C) is **higher than body temperature**, heat gain by convection, conduction, and radiation occurs. Therefore, **evaporation** of sweat is the only significant mechanism for heat loss.
- The relatively low humidity (10%) at this high temperature facilitates efficient sweat **evaporation**, which cools the body as it converts liquid sweat into water vapor.
*Convection*
- **Convection** involves heat transfer through the movement of air or fluid over the body surface.
- Since the ambient temperature (48°C) is significantly **above body temperature**, the body would gain heat via convection, not lose it.
*Conduction*
- **Conduction** is direct heat transfer between objects in contact.
- As the ambient temperature (48°C) is much **higher than the skin temperature**, the body would actually **gain heat** through conduction from any surfaces it touched if they were at ambient temperature.
*Piloerection*
- **Piloerection** (goosebumps) is a mechanism for minimizing heat loss by trapping a layer of warm air close to the skin.
- This response is activated in **cold environments** to conserve heat, not in hot environments to dissipate it.
*Radiation*
- **Radiation** is heat transfer via electromagnetic waves without direct contact.
- Since the ambient temperature (48°C) is **higher than body surface temperature**, the body would **gain heat** by radiation, not lose it efficiently, from the surrounding environment.
Behavioral thermoregulation US Medical PG Question 7: An 18-year-old man presents to his primary care physician with a complaint of excessive daytime sleepiness. He denies any substance abuse or major changes in his sleep schedule. He reports frequently dozing off during his regular daily activities. On further review of systems, he endorses falling asleep frequently with the uncomfortable sensation that there is someone in the room, even though he is alone. He also describes that from time to time, he has transient episodes of slurred speech when experiencing heartfelt laughter. Vital signs are stable, and his physical exam is unremarkable. This patient is likely deficient in a neurotransmitter produced in which part of the brain?
- A. Hippocampus
- B. Midbrain
- C. Pons nucleus
- D. Hypothalamus (Correct Answer)
- E. Thalamus
Behavioral thermoregulation Explanation: ***Hypothalamus***
- The patient's symptoms of excessive daytime sleepiness, cataplexy (falling asleep with strong emotions like laughter), and hypnagogic hallucinations (sensing someone in the room upon falling asleep) are classic for **narcolepsy**.
- Narcolepsy type 1 is characterized by a significant loss of **orexin (hypocretin)** neurons, a neuropeptide primarily produced in the **lateral hypothalamus** (specifically the lateral and perifornical areas), which plays a crucial role in maintaining wakefulness.
*Hippocampus*
- The **hippocampus** is primarily involved in **memory formation** and spatial navigation.
- Deficiencies in neurotransmitters produced or acting in the hippocampus are typically associated with memory disorders, not narcolepsy.
*Midbrain*
- The **midbrain** contains nuclei involved in dopamine, serotonin, and norepinephrine pathways, which are critical for mood, reward, and sleep-wake regulation.
- While these neurotransmitters influence the sleep-wake cycle, the primary deficiency in narcolepsy type 1 is specifically orexin, which originates from the hypothalamus, not the midbrain.
*Pons nucleus*
- The **pons** is essential for regulating sleep stages, particularly **REM sleep**, and contains nuclei involved in breathing and motor control.
- While it contributes to sleep architecture, the core pathology of narcolepsy type 1, the loss of orexin-producing neurons, is located higher in the brain, in the hypothalamus.
*Thalamus*
- The **thalamus** acts as a crucial relay station for sensory and motor signals to the cerebral cortex and is involved in regulating consciousness and alertness.
- While it is involved in arousal regulation, it is not the primary site of orexin production, nor is a neurotransmitter deficiency directly from the thalamus the primary cause of narcolepsy.
Behavioral thermoregulation US Medical PG Question 8: A 42-year-old man undergoes therapeutic hypothermia (target temperature 33°C/91.4°F) following cardiac arrest with return of spontaneous circulation. During the cooling phase, he develops shivering, which increases oxygen consumption and interferes with target temperature achievement. He is already on sedation and neuromuscular blockade is being considered. Evaluate the most appropriate management strategy considering both efficacy and safety.
- A. Administer meperidine alone to reduce shivering threshold
- B. Increase sedation and add surface counter-warming of extremities before neuromuscular blockade (Correct Answer)
- C. Abandon therapeutic hypothermia due to complications
- D. Use only mechanical restraints to prevent movement
- E. Immediate neuromuscular blockade without additional measures
Behavioral thermoregulation Explanation: ***Increase sedation and add surface counter-warming of extremities before neuromuscular blockade***
- A **stepwise approach** to shivering is preferred; increasing **sedation** and using **surface counter-warming** reduces the shivering threshold by tricking the hypothalamus into sensing a warmer periphery.
- This strategy minimizes the need for **neuromuscular blockade**, which can mask seizures and prevent accurate **neurological assessment**.
*Administer meperidine alone to reduce shivering threshold*
- While **meperidine** is an effective anti-shivering agent that lowers the shivering threshold, using it **alone** is often insufficient to control vigorous shivering during induction.
- Reliance on a single pharmacologic agent ignores the **multimodal therapy** benefits of physical measures like skin warming and optimized sedation.
*Abandon therapeutic hypothermia due to complications*
- Shivering is a predictable physiological response, not a reason to abandon **Targeted Temperature Management (TTM)**, which provides significant **neuroprotection** post-cardiac arrest.
- Stopping the therapy would deprive the patient of the benefit of reduced **cerebral metabolic rate** and improved survival outcomes.
*Use only mechanical restraints to prevent movement*
- Mechanical restraints are ineffective against the **metabolic consequences** of shivering, such as increased **oxygen consumption** and CO2 production.
- Shivering is a thermoregulatory reflex, and physical restraint does not stop the underlying **thermogenesis** or metabolic demand.
*Immediate neuromuscular blockade without additional measures*
- **Neuromuscular blockade** should be a last resort as it carries risks of **prolonged muscle weakness** and obscures the patient's clinical neurological status.
- It treats the muscular manifestation but lacks the **sedative or analgesic** properties needed to comfort the patient during the cooling process.
Behavioral thermoregulation US Medical PG Question 9: A 72-year-old woman with end-stage renal disease on hemodialysis develops fever (103°F/39.4°C) with rigors during dialysis. Blood cultures from both the dialysis catheter and peripheral site grow gram-positive cocci. Despite appropriate antibiotics and catheter removal, she has persistent fevers of 101-102°F (38.3-38.9°C) for 7 days. She feels better and inflammatory markers are decreasing. Evaluate the most likely explanation for persistent fever.
- A. Appropriate lag in temperature resolution despite adequate treatment (Correct Answer)
- B. Undrained abscess requiring surgical intervention
- C. Drug fever from antibiotic therapy
- D. Inadequate dialysis causing uremic fever
- E. Antibiotic-resistant organism requiring regimen change
Behavioral thermoregulation Explanation: ***Appropriate lag in temperature resolution despite adequate treatment***
- In bacteremia, fever can persist for several days even with effective therapy because **inflammatory cytokines** (like IL-1 and TNF-α) and bacterial products take time to clear from the system.
- The clinical improvement and **decreasing inflammatory markers** (like CRP or ESR) are the most reliable indicators of a positive response to treatment, despite the slow normalization of the **hypothalamic set point**.
*Undrained abscess requiring surgical intervention*
- While a persistent fever can indicate an **occult abscess**, this is less likely when the patient reports feeling clinically better and lab trends are improving.
- Persistent bacteremia or clinical worsening, rather than just isolated fever, would typically necessitate intensive imaging for deep-seated **foci of infection**.
*Drug fever from antibiotic therapy*
- Drug fever is a diagnosis of exclusion that usually occurs after **7 to 10 days** of therapy and is often associated with a newly developed rash or eosinophilia.
- In this case, the patient's fever started with a known **bacterial source** (dialysis catheter), making an infectious resolution lag much more probable than a drug reaction.
*Inadequate dialysis causing uremic fever*
- **Uremia** is more commonly associated with **hypothermia** or a blunted febrile response rather than a high persistent fever.
- Modern dialysis efficiently prevents the build-up of metabolic toxins to levels that would trigger a high-grade **febrile state**.
*Antibiotic-resistant organism requiring regimen change*
- Resistance is unlikely here because the patient is showing **clinical improvement** and a downward trend in inflammatory markers, indicating the current regimen is effective.
- If a **resistant organism** were present, you would expect temperatures to remain very high or increase, and blood cultures to remain positive after 48-72 hours of therapy.
Behavioral thermoregulation US Medical PG Question 10: A 19-year-old man at a rave party is brought to the ED with agitation, temperature of 107°F (41.7°C), severe hypertension (180/110 mm Hg), tachycardia, dilated pupils, and diaphoresis. His friends report he took 'Molly.' Despite aggressive cooling, his temperature remains dangerously elevated and he develops rhabdomyolysis. Evaluate the most appropriate additional pharmacologic intervention.
- A. Bromocriptine as a dopamine agonist
- B. Benzodiazepines to reduce CNS and muscular hyperactivity (Correct Answer)
- C. Beta-blockers to control hypertension and tachycardia
- D. Antipyretics to reduce hypothalamic set point
- E. Dantrolene sodium to reduce muscle hypermetabolism
Behavioral thermoregulation Explanation: ***Benzodiazepines to reduce CNS and muscular hyperactivity***
- **MDMA (Ecstasy/Molly)** intoxication causes severe hyperthermia through increased **serotonergic activity**, muscle rigidity, and agitation; **benzodiazepines** are first-line to control agitation and reduce excessive muscle-generated heat.
- Administering **benzodiazepines** also helps manage secondary symptoms like **tachycardia** and **hypertension** by lowering sympathetic outflow.
*Bromocriptine as a dopamine agonist*
- **Bromocriptine** is specifically indicated for **Neuroleptic Malignant Syndrome (NMS)**, which involves dopamine depletion in the hypothalamus and basal ganglia.
- Using it in stimulant or serotonin-mediated toxicity is inappropriate and does not address the primary mechanism of **MDMA**-induced hyperthermia.
*Beta-blockers to control hypertension and tachycardia*
- **Beta-blockers** are generally avoided in stimulant toxicity due to the risk of **unopposed alpha-adrenergic stimulation**, which can worsen **hypertension** and coronary vasoconstriction.
- They do not address the lethal **hyperthermia** or muscle hyperactivity driven by the central nervous system.
*Antipyretics to reduce hypothalamic set point*
- **Antipyretics** like aspirin or acetaminophen are ineffective because the high temperature in **MDMA** toxicity is caused by excess **thermogenesis** (muscle activity), not an altered **hypothalamic set point**.
- Relying on them delays more effective interventions like **evaporative cooling** and sedation.
*Dantrolene sodium to reduce muscle hypermetabolism*
- **Dantrolene** is the specific treatment for **Malignant Hyperthermia** (genetic ryanodine receptor defect) but has limited and controversial evidence in **serotonin syndrome** or MDMA toxicity.
- While it acts on muscle metabolism, **benzodiazepines** should be prioritized to treat the underlying **CNS-mediated agitation** and excessive movement.
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