Main Types of Temperature Curves
Based on diurnal fluctuation ranges, four classic types of temperature charts are distinguished:
- Continuous fever (febris continua): diurnal variations remain within 1 °C. Typical for conditions such as lobar (pneumococcal) pneumonia and typhoid fever.
- Remitting fever (febris remittens): fluctuations exceed 1 °C, but levels never drop back to normal. Frequently accompanies various viral infections.
- Intermittent fever (febris intermittens): the range is 1–2 °C. The key feature is a brief return to normal temperature for several hours followed by a new spike.
- Hectic fever: a severe pattern characterized by sharp recurrent daily fluctuations greater than 2–3 °C with rapid drops. Seen in sepsis, severe tuberculosis, and purulent processes (e.g., liver or lung abscesses).
Classification by Elevation Level
Depending on the degree of temperature elevation, fever is divided into four groups:
- Subfebrile (mild) — from normal up to 38 °C.
- Febrile (moderate) — from 38 to 39 °C.
- Pyretic (high) — from 39 to 41 °C.
- Hyperpyretic (excessive) — over 41 °C.
Further elevation (above 41–42 °C) is blocked by the endogenous antipyretic system, which prevents organism death.
Stage of Temperature Decline (st. decrementi)
Once the primary pyrogen (e.g., microbes or non-infectious agents) is eliminated, the production of leukocytic cytokines drops. In the cold-sensitive neurons of the anterior hypothalamus, the biochemical cascade is inhibited: the activity of phospholipase A2 and cyclooxygenase decreases, lowering levels of prostaglandin E2 and cAMP. Neuronal excitability decreases, and the thermoregulatory center's set point returns to the normal range.
Temperature decline occurs in two forms:
- Lytic decline (lysis): gradual, taking several days. This is the most favorable and frequent scenario for the body.
- Critical decline (crisis): a rapid drop within a few hours. It is accompanied by a sharp activation of heat loss—profuse sweating and marked dilatation of cutaneous arterioles. It carries the risk of a drop in blood pressure and circulatory collapse due to a sharp decrease in venous return to the heart.
Metabolic Shifts
Fever demands massive energy expenditure to supply actively functioning organs with oxygen and substrates. Under the influence of the sympathoadrenal, hypothalamic-pituitary-adrenal, and thyroid systems, the basal metabolic rate predictably increases. The Q10 effect also operates, directly accelerating chemical reactions via thermal stimulation.
- Carbohydrate metabolism: glycogenolysis and glycolysis sharply increase. Glucose oxidation is active, but its energy efficiency remains low.
- Lipid metabolism: due to carbohydrate energy deficits, a compensatory, robust lipolysis is triggered. This is especially prominent during a prolonged second stage of fever. Enhanced fat breakdown leads to the accumulation of ketone bodies and worsening acidosis.
- Protein metabolism: proteolysis (protein breakdown) intensifies, clinically manifesting as a negative nitrogen balance.