Liebermeister’s rule
Liebermeister’s Rule:
🔹 Definition
Liebermeister’s rule states that in fever, the heart rate increases by approximately 8–10 beats per minute (bpm) for every 1°C rise in body temperature above normal.
🔹 Normal Relationship
- At 37°C (normal temperature): HR ~70–80 bpm
- At 38°C: HR expected ~90 bpm
- At 39°C: HR expected ~100–110 bpm
- At 40°C: HR expected ~110–120 bpm
🔹 Clinical Use
- Helps clinicians estimate whether the pulse is appropriate for the degree of fever.
- Deviation from Liebermeister’s rule can indicate pathology.
🔹 Exceptions
- Relative Bradycardia (Faget sign): Fever without expected tachycardia → seen in typhoid fever, brucellosis, yellow fever, Legionnaires’ disease, drug fever, tularemia.
- Exaggerated Tachycardia: Can occur in thyrotoxicosis, myocarditis, severe dehydration, shock.
✅ Summary:
Liebermeister’s rule = +8–10 bpm HR per 1°C fever rise.
Faget sign is a notable exception (fever + relative bradycardia).
Q1. Faget sign refers to:
Faget sign is the dissociation of fever with relative bradycardia.
Q2. Relative bradycardia means:
Relative bradycardia is defined as pulse lower than expected rise predicted by Liebermeister’s rule.
Q3. Which rule predicts normal HR rise with fever?
Liebermeister’s rule: HR rises 8–10 bpm per 1°C rise in body temperature.
Q4. Which infection classically shows Faget sign?
Typhoid fever is the classical condition with fever + relative bradycardia.
Q5. Faget sign is also known as:
Faget sign = pulse–temperature dissociation.
Q6. Which vector-borne disease shows Faget sign?
Yellow fever is classically associated with relative bradycardia.
Q7. Mechanism of Faget sign is thought to involve:
Mechanism: direct toxin/cytokine effect on conduction or vagal dominance.
Q8. Which bacterial zoonosis shows Faget sign?
Brucellosis can show fever with relative bradycardia.
Q9. Another bacterial cause of Faget sign is:
Tularemia is associated with relative bradycardia.
Q10. Atypical pneumonia with Faget sign is most likely due to:
Legionnaires’ disease shows Faget sign.
Q11. Which parasitic disease sometimes shows relative bradycardia?
Some cases of malaria (esp. falciparum) can show Faget sign.
Q12. Drug fever can be associated with:
Drug-induced fever may show pulse–temperature dissociation.
Q13. Which of the following is NOT classically linked to Faget sign?
Influenza shows proportional tachycardia, not Faget sign.
Q14. The clinical importance of Faget sign is:
Faget sign is a useful clinical clue for specific infections.
Q15. Who described Faget sign?
Jean Charles Faget described this clinical sign in yellow fever.
Q16. In yellow fever, the presence of Faget sign is considered:
It is a characteristic clue, though not absolutely pathognomonic.
Q17. In typhoid, Faget sign appears typically in:
Relative bradycardia is seen in early febrile phase of typhoid.
Q18. Which condition is most useful to differentiate using Faget sign?
Faget sign helps in narrowing diagnosis of typhoid, yellow fever etc. against other febrile states.
Q19. Which vector is associated with two infections showing Faget sign (typhoid excluded)?
Yellow fever via Aedes; tularemia via ticks and other vectors.
Q20. The absence of expected tachycardia in fever suggests:
Pulse–temperature dissociation is the definition of Faget sign.
| Feature | Normal Fever Response (Liebermeister’s Rule) |
Faget Sign (Relative Bradycardia) |
|---|---|---|
| Pulse–Temperature Relation | HR ↑ ~8–10 bpm for each 1°C rise | HR does not rise as expected |
| Example at 39°C | HR ~100–110 bpm | HR ~80–90 bpm |
| Mechanism | Sympathetic activation | Direct pathogen/toxin effect or vagal influence |
| Typical Causes | Most febrile illnesses | Typhoid fever, Yellow fever, Brucellosis, Tularemia, Legionella, Drug fever, Malaria |
| Clinical Use | Predicts appropriate HR response | Clue to specific infectious diseases (pulse–temperature dissociation) |
