Ventilation-Perfusion Ratio: The ratio of alveolar ventilation to simultaneous alveolar capillary blood flow in any part of the lung. (Stedman, 25th ed)Pulmonary Embolism: Blocking of the PULMONARY ARTERY or one of its branches by an EMBOLUS.Krypton Radioisotopes: Unstable isotopes of krypton that decay or disintegrate emitting radiation. Kr atoms with atomic weights 74-77, 79, 81, 85, and 87-94 are radioactive krypton isotopes.Laser-Doppler Flowmetry: A method of non-invasive, continuous measurement of MICROCIRCULATION. The technique is based on the values of the DOPPLER EFFECT of low-power laser light scattered randomly by static structures and moving tissue particulates.Pulmonary Gas Exchange: The exchange of OXYGEN and CARBON DIOXIDE between alveolar air and pulmonary capillary blood that occurs across the BLOOD-AIR BARRIER.Hindlimb: Either of two extremities of four-footed non-primate land animals. It usually consists of a FEMUR; TIBIA; and FIBULA; tarsals; METATARSALS; and TOES. (From Storer et al., General Zoology, 6th ed, p73)Technetium Tc 99m Aggregated Albumin: A gamma-emitting radionuclide imaging agent used for the diagnosis of diseases in many tissues, particularly in cardiovascular and cerebral circulation.Perfusion Imaging: The creation and display of functional images showing where the blood flow reaches by following the distribution of tracers injected into the blood stream.Ischemia: A hypoperfusion of the BLOOD through an organ or tissue caused by a PATHOLOGIC CONSTRICTION or obstruction of its BLOOD VESSELS, or an absence of BLOOD CIRCULATION.Noble Gases: Elements that constitute group 18 (formerly the zero group) of the periodic table. They are gases that generally do not react chemically.Perfusion: Treatment process involving the injection of fluid into an organ or tissue.Pulmonary Circulation: The circulation of the BLOOD through the LUNGS.Lung: Either of the pair of organs occupying the cavity of the thorax that effect the aeration of the blood.Xenon Radioisotopes: Unstable isotopes of xenon that decay or disintegrate emitting radiation. Xe atoms with atomic weights 121-123, 125, 127, 133, 135, 137-145 are radioactive xenon isotopes.Ventilation: Supplying a building or house, their rooms and corridors, with fresh air. The controlling of the environment thus may be in public or domestic sites and in medical or non-medical locales. (From Dorland, 28th ed)Blood Gas Analysis: Measurement of oxygen and carbon dioxide in the blood.Respiration, Artificial: Any method of artificial breathing that employs mechanical or non-mechanical means to force the air into and out of the lungs. Artificial respiration or ventilation is used in individuals who have stopped breathing or have RESPIRATORY INSUFFICIENCY to increase their intake of oxygen (O2) and excretion of carbon dioxide (CO2).Pulmonary Ventilation: The total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Partial Pressure: The pressure that would be exerted by one component of a mixture of gases if it were present alone in a container. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Pulmonary Artery: The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs.Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.Administration, Inhalation: The administration of drugs by the respiratory route. It includes insufflation into the respiratory tract.Respiratory Function Tests: Measurement of the various processes involved in the act of respiration: inspiration, expiration, oxygen and carbon dioxide exchange, lung volume and compliance, etc.Anoxia: Relatively complete absence of oxygen in one or more tissues.High-Frequency Ventilation: Ventilatory support system using frequencies from 60-900 cycles/min or more. Three types of systems have been distinguished on the basis of rates, volumes, and the system used. They are high frequency positive-pressure ventilation (HFPPV); HIGH-FREQUENCY JET VENTILATION; (HFJV); and high-frequency oscillation (HFO).Dictionaries, MedicalDictionaries as Topic: Lists of words, usually in alphabetical order, giving information about form, pronunciation, etymology, grammar, and meaning.Church of Jesus Christ of Latter-day Saints: A group of religious bodies tracing their origin to Joseph Smith in 1830 and accepting the Book of Mormon as divine revelation. (from Merriam-Webster's Collegiate Dictionary, 10th ed)Physiology: The biological science concerned with the life-supporting properties, functions, and processes of living organisms or their parts.Nigeria: A republic in western Africa, south of NIGER between BENIN and CAMEROON. Its capital is Abuja.UtahDoxapram: A central respiratory stimulant with a brief duration of action. (From Martindale, The Extra Pharmocopoeia, 30th ed, p1225)Flail Chest: A complication of multiple rib fractures, rib and sternum fractures, or thoracic surgery. A portion of the chest wall becomes isolated from the thoracic cage and exhibits paradoxical respiration.Respiratory Insufficiency: Failure to adequately provide oxygen to cells of the body and to remove excess carbon dioxide from them. (Stedman, 25th ed)Encyclopedias as Topic: Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)Motor Neuron Disease: Diseases characterized by a selective degeneration of the motor neurons of the spinal cord, brainstem, or motor cortex. Clinical subtypes are distinguished by the major site of degeneration. In AMYOTROPHIC LATERAL SCLEROSIS there is involvement of upper, lower, and brainstem motor neurons. In progressive muscular atrophy and related syndromes (see MUSCULAR ATROPHY, SPINAL) the motor neurons in the spinal cord are primarily affected. With progressive bulbar palsy (BULBAR PALSY, PROGRESSIVE), the initial degeneration occurs in the brainstem. In primary lateral sclerosis, the cortical neurons are affected in isolation. (Adams et al., Principles of Neurology, 6th ed, p1089)Laparoscopy: A procedure in which a laparoscope (LAPAROSCOPES) is inserted through a small incision near the navel to examine the abdominal and pelvic organs in the PERITONEAL CAVITY. If appropriate, biopsy or surgery can be performed during laparoscopy.Hysterectomy: Excision of the uterus.Cholecystectomy, Laparoscopic: Excision of the gallbladder through an abdominal incision using a laparoscope.Pulmonary Atelectasis: Absence of air in the entire or part of a lung, such as an incompletely inflated neonate lung or a collapsed adult lung. Pulmonary atelectasis can be caused by airway obstruction, lung compression, fibrotic contraction, or other factors.Respiration Disorders: Diseases of the respiratory system in general or unspecified or for a specific respiratory disease not available.Postoperative Complications: Pathologic processes that affect patients after a surgical procedure. They may or may not be related to the disease for which the surgery was done, and they may or may not be direct results of the surgery.Hysterectomy, Vaginal: Removal of the uterus through the vagina.Basement Membrane: A darkly stained mat-like EXTRACELLULAR MATRIX (ECM) that separates cell layers, such as EPITHELIUM from ENDOTHELIUM or a layer of CONNECTIVE TISSUE. The ECM layer that supports an overlying EPITHELIUM or ENDOTHELIUM is called basal lamina. Basement membrane (BM) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. BM, composed mainly of TYPE IV COLLAGEN; glycoprotein LAMININ; and PROTEOGLYCAN, provides barriers as well as channels between interacting cell layers.Capillary Permeability: The property of blood capillary ENDOTHELIUM that allows for the selective exchange of substances between the blood and surrounding tissues and through membranous barriers such as the BLOOD-AIR BARRIER; BLOOD-AQUEOUS BARRIER; BLOOD-BRAIN BARRIER; BLOOD-NERVE BARRIER; BLOOD-RETINAL BARRIER; and BLOOD-TESTIS BARRIER. Small lipid-soluble molecules such as carbon dioxide and oxygen move freely by diffusion. Water and water-soluble molecules cannot pass through the endothelial walls and are dependent on microscopic pores. These pores show narrow areas (TIGHT JUNCTIONS) which may limit large molecule movement.Respiratory Physiological Phenomena: Physiological processes and properties of the RESPIRATORY SYSTEM as a whole or of any of its parts.Pulmonary Alveoli: Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place.Gravitropism: The directional growth of organisms in response to gravity. In plants, the main root is positively gravitropic (growing downwards) and a main stem is negatively gravitropic (growing upwards), irrespective of the positions in which they are placed. Plant gravitropism is thought to be controlled by auxin (AUXINS), a plant growth substance. (From Concise Dictionary of Biology, 1990)Capillaries: The minute vessels that connect the arterioles and venules.Hypoventilation: A reduction in the amount of air entering the pulmonary alveoli.Diffusion: The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially FACILITATED DIFFUSION, is a major mechanism of BIOLOGICAL TRANSPORT.Sleep Apnea, Central: A condition associated with multiple episodes of sleep apnea which are distinguished from obstructive sleep apnea (SLEEP APNEA, OBSTRUCTIVE) by the complete cessation of efforts to breathe. This disorder is associated with dysfunction of central nervous system centers that regulate respiration.Sleep Disorders, Intrinsic: Dyssomnias (i.e., insomnias or hypersomnias) associated with dysfunction of internal sleep mechanisms or secondary to a sleep-related medical disorder (e.g., sleep apnea, post-traumatic sleep disorders, etc.). (From Thorpy, Sleep Disorders Medicine, 1994, p187)