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Paced Auditory Serial Addition Test
The Paced Auditory Serial Addition Test (PASAT) is a neuropsychological test in which digits heard at a fixed pace are added in pairs, used in brain injury and multiple sclerosis.
Pacemaker failure
Pacemaker failure is the malfunction of an implanted cardiac pacemaker, its leads, or its programming so that it fails to keep an adequate heart rate.
Pacemaker implantation
Pacemaker implantation, also called permanent pacemaker implantation, is a surgical procedure placing a pulse generator and leads under the skin to treat slow heart rhythms, with nearly one million implants yearly.
Pacemaker neuron
A pacemaker neuron is a neuron that generates rhythmic bursts of action potentials independently of synaptic input, driving circadian rhythms in the suprachiasmatic nucleus and respiration in the preBötzinger complex.
Pacemaker syndrome
Pacemaker syndrome: iatrogenic symptoms from ventricular pacing causing AV dyssynchrony, first described 1969; incidence 2-80%; treated by reprogramming or dual-chamber upgrade.
Pachira aquatica
Pachira aquatica, the Guiana-chestnut or money tree, is a wetland Bombacoideae tree from Mexico to South America; type of its genus, edible seeds, braided houseplant form, Least Concern.
Pachycephala
Pachycephala (whistlers) is the largest genus of Pachycephalidae, Australo-Papuan in origin, spanning the Indo-Pacific; includes the Golden Whistler complex, the world's most geographically variable bird species with over 70 subspecies.
Pachycephalosaurus
Pachycephalosaurus, the thick-headed lizard, a Late Cretaceous North American dome-skulled herbivorous dinosaur (69–66 Ma, ~3 m, 450 kg); known for head-butting debate and Dracorex/Stygimoloch growth-stage synonymy.
Pachycereus
Pachycereus, Mexican columnar cactus genus (Britton & Rose 1909) with five accepted species including the giant cardón Pachycereus pringlei, up to 20 m tall, bat-pollinated, native only to Mexico.
Pachydermoperiostosis
Pachydermoperiostosis, or primary hypertrophic osteoarthropathy (Touraine-Solente-Gole syndrome), is a rare hereditary disorder with digital clubbing, pachydermia, and periostosis, caused by HPGD or SLCO2A1 mutations elevating prostaglandin E2.
Pachydiscus
Pachydiscus, an extinct Late Cretaceous ammonite genus (Zittel, 1884; type species Ammonites neubergicus von Hauer, 1858) of the family Pachydiscidae, ranging Santonian to latest Maastrichtian worldwide; P. neubergicus marks the base of the Maastrichtian Stage.
Pachymeningitis
Pachymeningitis, also called hypertrophic pachymeningitis in its fibrotic form, is inflammation and thickening of the dura mater (ICD-11 8E41) caused by infection, autoimmune disease including ANCA and IgG4-related disease, or cancer, diagnosed by MRI and dural biopsy.
Pachyonychia congenita
Pachyonychia congenita (PC), also called Jadassohn-Lewandowsky or Jackson-Lawler syndrome, is a rare autosomal dominant keratin disorder from KRT6A/B/C, KRT16, or KRT17 mutations, causing thick nails, painful plantar calluses, cysts, and oral leukokeratosis, with no cure.
Pachyptila
Pachyptila is a genus of small seabirds called prions in the petrel family Procellariidae, abundant around the Southern Ocean and known for variation in bill width between filter-feeding and pursuit-feeding species.
Pachyrhizus
Pachyrhizus is a genus of five Neotropical legume species known as yam beans, three cultivated for their edible tuberous roots, including the Mexican species jicama.
Pachyrhizus erosus
Pachyrhizus erosus, jicama or yam bean (Mexican turnip, bang kuang), is a Mexican-Central American climbing legume grown for its edible starchy storage root; its rotenone-rich seeds are toxic but used as insecticide.
Pacific black duck
Pacific black duck (Anas superciliosa), also called grey duck, a brown dabbling duck of Australia, New Guinea, New Zealand, and Pacific islands, threatened mainly by hybridization with the introduced mallard.
Pacific giant salamander
Pacific giant salamander, genus Dicamptodon (Dicamptodontidae), large semi-aquatic salamanders of the Pacific coast from British Columbia to California and northern Idaho; four species, Threatened in Canada, forest-stream habitat.
Pacific Islands Forum Fisheries Agency enforcement operations
The Pacific Islands Forum Fisheries Agency enforcement operations coordinate satellite tracking, aerial patrols, and patrol boats among 17 Pacific members to police illegal fishing across about 27.5 million square kilometers.
Pacific Northwest oyster industry
Pacific Northwest oyster industry: Pacific, Kumamoto, and Olympia oyster aquaculture in Puget Sound, Willapa Bay, and coastal British Columbia; Washington leads U.S. farmed bivalve production, shaped by hatcheries, ocean acidification, and tribal treaty rights.
Pacific Northwest Research Station
Pacific Northwest Research Station (PNW), USDA Forest Service research unit founded 1925, headquartered in Portland, Oregon; first director Thornton T. Munger; 11 labs, 12 experimental forests; slated for closure in 2026 reorganization.
Pacific Northwest tree octopus
Pacific Northwest tree octopus (Octopus paxarbolis), a fictitious arboreal cephalopod invented in 1998 by satirist Lyle Zapato on zapatopi.net; a documented Internet hoax preserved by the Library of Congress and widely used in media-literacy education.
Pacific oyster
Pacific oyster (Magallana gigas, formerly Crassostrea gigas), Japanese or Miyagi oyster: cupped oyster native to northwest Pacific Asia, the world's most cultivated oyster, introduced to 66 countries; protandrous hermaphrodite releasing up to 200 million eggs; genus name change from Crassostrea remains contested.
Pacific razor clam
Pacific razor clam (Siliqua patula), a fast-burrowing surf-zone bivalve from Alaska to California; supports major recreational and commercial fisheries in Washington, Oregon, and Alaska, often closed by domoic acid and saxitoxin biotoxin events.
Pacific sleeper shark
Pacific sleeper shark (Somniosus pacificus), a large deep-water North Pacific sleeper shark reaching 7 m, sister species of the Greenland shark; slow-swimming, Near Threatened, bycatch-caught, olfactory-driven predator of fish, squid, and marine mammals.
PACIFIC trial (NCT02125461)
PACIFIC (NCT02125461) is AstraZeneca's phase 3 trial of consolidation durvalumab (MEDI4736) after chemoradiotherapy in unresectable stage III NSCLC; it doubled median PFS (16.8 vs 5.6 months) and established the PACIFIC regimen as standard of care.
Pacifier
Pacifier (soother, dummy): silicone or latex teat with shield and ventilation holes for infant non-nutritive sucking. Reduces SIDS risk (OR 0.39), linked to otitis media and malocclusion; AAP, AAPD, and ACM guidance conflict on timing.
PACIFIER trial
PACIFIER (RisoR Crest Everolimus Eluting Stent trial, NCT07098195) is a Poly Medicure-sponsored, single-arm, open-label, multicentre study of 2,000 patients in India and Italy assessing target lesion failure at 360 days for a biodegradable-polymer everolimus-eluting cobalt-chromium stent.
Pacing-induced cardiomyopathy
Pacing-induced cardiomyopathy (PICM) is left ventricular systolic dysfunction caused by chronic right ventricular pacing, affecting about 12% of pacemaker patients and presenting as heart failure.
Pack rat
Pack rat (woodrat, genus Neotoma): North American herbivorous rodent known for building stick houses and middens and collecting shiny objects; 23 species, middens used to reconstruct ancient climates.