Hepa

Hepa may refer to:

HEPA

High-efficiency particulate arrestance (HEPA), also sometimes called high-efficiency particulate arresting or high-efficiency particulate air, is a type of air filter. Filters meeting the HEPA standard have many applications, including use in medical facilities, automobiles, aircraft and homes. The filter must satisfy certain standards of efficiency such as those set by the United States Department of Energy (DOE). To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size of 0.3 µm.

Function

HEPA filters are composed of a mat of randomly arranged fibres. The fibres are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting its functions are fibre diameter, filter thickness, and face velocity. The air space between HEPA filter fibres is typically much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect and impractical. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibres can not pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles. These particles are trapped (they stick to a fibre) through a combination of the following three mechanisms:

Hepoxilin

Hepoxilins (HxA3 and HxB3) are nonclassic eicosanoid hormones involved in inflammation.

History

Hepoxilins were identified and named in Canada in 1984 by CR Pace-Asciak and JM Martin.

Biochemistry

They derive from arachidonic acid via oxidation by the enzyme 12-lipoxygenase. Hepoxilins are differentiated from closely related eicosanoids, the leukotrienes and the lipoxins, in that hepoxilins have no conjugated double bonds. Corresponding trioxlins A4 and B4 are formed by the same pathway from EPA Two, more recently described hepoxins, 11(S)-hydroxy-14(S),15(S)-epoxy-5(Z),8(Z),12(E)-eicosatrienoic acid and 13(R)-hydroxy-14(S),15(S)-epoxy-5(Z),8(Z),11(Z)-eicosatrienoic acid, termed respectively 14,15-HXA₃ and 14,15-HXB₃ are made by 15-lipoxygenase-1 with 15(S)-hydroperoxy-eicosatetraenoic acid as an intermediate; 14,15-HXA₃ may then be further metabolized by glutathione transferases to 11(S),15(S)-dihydroxy-14(R)-glutathionyl-(5Z),8(Z),12(E)eicosatrienoic acid (14,15-HXA₃C) which is then further metabolized to 11(S),15(S)-dihydroxy-14(R)-cysteinyl-glycyl-(5Z),8(Z),12(E)eicosatrienoic acid (14,15-HXA₃D). The latter two hepoxilins are analogous to eoxins and leukotrienes and presumed to share the same glutatione transferase and peptidase pathways in their formation (see 15-Hydroxyicosatetraenoic acid).