II. Pathophysiology

  1. Predisposing conditions alter heat balance
  2. See Temperature Regulation

III. Causes: Increased endogenous heat load

  1. Vigorous Exercise or overexertion
  2. Sympathomimetic drugs (see below)
  3. Caffeine

IV. Causes: Increased Exogenous Heat load

V. Causes: Decreased Heat Dissipation

  1. Exogenous cause
    1. Humidity
      1. Evaporation of sweat stops at 75% humidity (and sweating has no cooling effect at 95% humidity)
    2. Occlusive or excessive clothing
  2. Endogenous cause
    1. Dehydration
    2. Lack of acclimatization
    3. Poor physical conditioning
    4. Healed burns
    5. Sunburn
    6. Dermatitis
    7. Sweat Gland Dysfunction
    8. See Medications Predisposing to Heat Illness

VI. Causes: Other predisposing factors for abnormal heat balance

  1. Medications Predisposing to Heat Illness
  2. Prior Heat Stroke
  3. Concurrent infection
    1. Upper Respiratory Infection
    2. Gastroenteritis
  4. Age over 65 years
    1. Myocardial dysfunction
    2. Vascular disease
    3. Decreased muscle mass
    4. Decreased skin blood supply
    5. Renal Insufficiency
    6. Chronic illness
    7. Decreased mobility
  5. Children (especially tightly bundled infants)
    1. See Enclosed Vehicle Excessive Heat
    2. Generate greater metabolic heat during activity and at rest (higher basal metabolic rate)
    3. Slower acclimitization
    4. Decreased sweat response and capacity
    5. Increased surface area to body mass ratio (greater heat absorption)
    6. Decreased Blood Volume to redistribute to the periphery
    7. Immature Hypothalamus (less able to Temperature regulate)
  6. Comorbid medical condition
    1. Anorexia
    2. Cystic Fibrosis
    3. Diabetes Insipidus
    4. Poorly controlled Diabetes Mellitus
    5. Obesity
    6. Hypokalemia
    7. Sickle Cell Trait or Sickle Cell Anemia

VII. References

  1. Czerkawski (1996) Your Patient Fitness 10(4): 13-20
  2. Salinas and Ruttan (2017) Crit Dec Emerg Med 31(9): 3-10
  3. Sandor (1997) Physician SportsMed, 25(6):35-40
  4. Barrow (1998) Am Fam Physician 58(3):749-56 [PubMed]
  5. Hett (1998) Postgrad Med 103(6):107-20 [PubMed]
  6. Wexler (2002) Am Fam Physician 65(11):2307-20 [PubMed]

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