- 4k Downloads
The alveolar air is fully saturated with water vapor at core body temperature while ambient air is cooler and contains less water. This gradient in heat and water vapor pressure is maintained along the nose and upper airways. They function as a counter current heat and moisture exchanger. The inspired air gains heat and water vapor from the upper airway lining which is partly recovered when the expired gas looses heat and water condenses back to the airway surface. This recovery occurs because the upper airway temperature remains below core body temperature during expiration. Breathing is associated with a net heat and water loss because the expired air temperature is higher than ambient temperature under normal circumstances. The losses must be replenished by the airway epithelium which in turn is supplied by the bronchial circulation. It is unknown under which circumstances the capacity of the airway lining to humidify cold and dry gas becomes overcharged. This capacity is likely different in health and disease. Water transport through the mucosa into the aqueous layer of the airway lining is possibly rate limiting.
KeywordsEndotracheal Tube Core Body Temperature Absolute Humidity Heated Wire Full Saturation
- Dreyfuss D, Djedaini K, Gros I, Mier L, Le Bourdelles G, Cohen Y, Estagnasie P, Coste F, Boussougant Y (1995) Mechanical ventilation with heated humidifiers or heat and moisture exchangers: effects on patient colonization and incidence of nosocomial pneumonia. Am J Respir Crit Care Med 151:986–992PubMedGoogle Scholar
- Institute A N S (1979) Standard for humidifiers and nebulizers for medical use. ASI Z79.9–1979:8Google Scholar
- Schiffmann H, Rathgeber J, Singer D, Harms K, Bolli A, Zuchner K (1997) Airway humidification in mechanically ventilated neonates and infants: a comparative study of a heat and moisture exchanger vs. a heated humidifier using a new fast-response capacitive humidity sensor. Crit Care Med 25:1755–1760PubMedCrossRefGoogle Scholar
- Schiffmann H, Singer S, Singer D, von Richthofen E, Rathgeber J, Zuchner K (1999) Determination of airway humidification in high-frequency oscillatory ventilation using an artificial neonatal lung model. Comparison of a heated humidifier and a heat and moisture exchanger. Intensive Care Med 25:997–1002PubMedCrossRefGoogle Scholar