Filtration and humidification glossary

	Absolute Humidity (AH)				Describes the water content of air.
	Alveoli				Tiny air sacs in the lungs that allow for rapid gaseous exchange.
	Artificial airway				Plastic or rubber device that can be inserted into the upper or lower respiratory tract to facilitate ventilation or the removal of secretions.
	Atelectasis				Partial collapse or incomplete inflation of the lung.
	Bacteria				Unicellular microorganisms with cell walls but no organelles and an organized nucleus, including some that can cause disease.
	Barotrauma				Injury caused by a change in air pressure, affecting typically the ear or the lung.
	Capillaries				Fine branching blood vessels that form a network between the arterioles and venules.
	Carbon dioxide				A colourless, odourless gas produced by respiration.
	Cardiac output				The amount of blood the heart pumps through the circulatory system in a minute.
	Carina				A ridge of cartilage in the trachea that occurs between the division of the two main bronchi.
	Cilia				Short, microscopic hair-like vibrating structure found in large numbers on the surface of cells in the upper airways.
	Compressible volume				The internal volume of the device and the added mechanical dead space that the use of the device will add to the breathing system.
	Continuous positive airway pressure (CPAP)				A form of positive airway pressure ventilator that supplies continuous pressure to keep the airways open in patients who cannot breathe spontaneously.
	Electrostatic				Relating to charge of electricity that is attracted to the surface of some objects.
	Electrostatic media				Web of Polypropylene fibers with an electrostatic charge. These positive and negative charges enhance the filter's ability to trap microbial contaminants whilst maintaining a relatively low resistance to flow.
	Efficiency				The level of filtration protection or function that the device can deliver. The efficiency of the filter is normally expressed as a reflection of the number of micro organisms that pass through the filter media when it is challenged. This filter is then described as being X% efficient.
	Hepatitis C				Inflammation of the liver due to the hepatitis C virus (HCV), which is usually spread via blood transfusion, haemodialysis and needles.
	HIV				Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV).
	Humidification				The process of increasing the relative humidity of the atmosphere around a patient with aerosol generators or steam inhalers.
	Hydrophobic				Resistance to water. Hydrophobic filter materials repel water, meaning water droplets and condensation stay on the surface of the filter.
	Intrathoracic				Situated or occurring within the thorax.
	Lungs				A pair of organs situated within the ribcage, consisting of elastic sacs with branching passages into which air is drawn, so that oxygen can pass into the blood and carbon dioxide can be removed.
	Mechanical dead space				The compressible/internal volume of devices added to the breathing systems which results in an increase in the volume of the system that is not involved in gas exchange.
	Microbial				Relating to or characteristic of a microorganism, especially a bacterium causing disease or fermentation.
	Microbiologically				Refers to studies or tests relating to bacteria and their effects on humans.
	Mucus membranes				An epithelial tissue that secretes mucus, and lines body cavities and tubular organs including the gut and respiratory passages.
	Nosocomial				Any airborne disease contracted by a patient while under medical care.
	Obstructive				Partial or complete blockage of the breathing passages to the lungs caused by foreign matter, allergic reactions, infections, anatomical abnormalities and trauma.
	PEEP				Abbreviation for positive end-expiratory pressure. Ventilation in which airway pressure is maintained above atmospheric pressure at the end of exhalation by means of a mechanical impedance, usually a valve, within the circuit.
	Pharynx				The membrane-lined cavity behind the nose and mouth, connecting them to the oesophagus.
	Pulmonary oedema				Fluid accumulation in the tissue and air spaces of the lungs.
	Relativity Humidity (RH)				Expressed as a percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature i.e. at 37 degress celsius gas has maximum absolute humidity of 44mg/l. If the humidity content of the gas were only 33mg/l then it would have a relative humidity of 75%.
	Resistance				Airway resistance of the respiratory tract to inhalation and expiration. This is an expression of the amount of effort that is required to make an inspiratory or an expiratory breath.
	Supraglottic airway devices (SADs)				Airway devices used to keep the upper airway open to provide unobstructed ventilation.
	Tidal volume				The volume of gas inhaled and exhaled by the patient during one respiratory cycle. The average for a 70 Kg or 155 lbs adult is 500 ml.
	Tracheal tube				A catheter inserted into the trachea to establish and maintain a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide.
	Tracheostomy tube				A breathing tube inserted into a tracheotomy.
	Viruses				An organisim which causes infection and disease.
	Work of breathing (WOB)				The energy expended to inhale and exhale a breathing gas. In a normal resting state the WOB constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or increased resistance within a breathing system gas flow imposed by breathing apparatus.

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