Respiratory Mechanics: The physical or mechanical action of the LUNGS; DIAPHRAGM; RIBS; and CHEST WALL during respiration. It includes airflow, lung volume, neural and reflex controls, mechanoreceptors, breathing patterns, etc.Lung Compliance: The capability of the LUNGS to distend under pressure as measured by pulmonary volume change per unit pressure change. While not a complete description of the pressure-volume properties of the lung, it is nevertheless useful in practice as a measure of the comparative stiffness of the lung. (From Best & Taylor's Physiological Basis of Medical Practice, 12th ed, p562)Airway Resistance: Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow.Lung Volume Measurements: Measurement of the amount of air that the lungs may contain at various points in the respiratory cycle.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 Gas Exchange: The exchange of OXYGEN and CARBON DIOXIDE between alveolar air and pulmonary capillary blood that occurs across the BLOOD-AIR BARRIER.Positive-Pressure Respiration: A method of mechanical ventilation in which pressure is maintained to increase the volume of gas remaining in the lungs at the end of expiration, thus reducing the shunting of blood through the lungs and improving gas exchange.Expiratory Reserve Volume: The extra volume of air that can be expired with maximum effort beyond the level reached at the end of a normal, quiet expiration. Common abbreviation is ERV.Work of Breathing: RESPIRATORY MUSCLE contraction during INHALATION. The work is accomplished in three phases: LUNG COMPLIANCE work, that required to expand the LUNGS against its elastic forces; tissue resistance work, that required to overcome the viscosity of the lung and chest wall structures; and AIRWAY RESISTANCE work, that required to overcome airway resistance during the movement of air into the lungs. Work of breathing does not refer to expiration, which is entirely a passive process caused by elastic recoil of the lung and chest cage. (Guyton, Textbook of Medical Physiology, 8th ed, p406)Air Pressure: The force per unit area that the air exerts on any surface in contact with it. Primarily used for articles pertaining to air pressure within a closed environment.Ventilators, Mechanical: Mechanical devices used to produce or assist pulmonary ventilation.Tidal Volume: The volume of air inspired or expired during each normal, quiet respiratory cycle. Common abbreviations are TV or V with subscript T.Respiratory Distress Syndrome, Adult: A syndrome characterized by progressive life-threatening RESPIRATORY INSUFFICIENCY in the absence of known LUNG DISEASES, usually following a systemic insult such as surgery or major TRAUMA.Lung: Either of the pair of organs occupying the cavity of the thorax that effect the aeration of the blood.Respiratory Muscles: These include the muscles of the DIAPHRAGM and the INTERCOSTAL MUSCLES.Respiratory Physiological Phenomena: Physiological processes and properties of the RESPIRATORY SYSTEM as a whole or of any of its parts.Mechanics: The branch of physics which deals with the motions of material bodies, including kinematics, dynamics, and statics. When the laws of mechanics are applied to living structures, as to the locomotor system, it is referred to as BIOMECHANICAL PHENOMENA. (From Dorland, 28th ed)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.Functional Residual Capacity: The volume of air remaining in the LUNGS at the end of a normal, quiet expiration. It is the sum of the RESIDUAL VOLUME and the EXPIRATORY RESERVE VOLUME. Common abbreviation is FRC.Oscillometry: The measurement of frequency or oscillation changes.Prone Position: The posture of an individual lying face down.Pulmonary Ventilation: The total volume of gas inspired or expired per unit of time, usually measured in liters per minute.Inhalation: The act of BREATHING in.Exhalation: The act of BREATHING out.Thorax: The upper part of the trunk between the NECK and the ABDOMEN. It contains the chief organs of the circulatory and respiratory systems. (From Stedman, 25th ed)Pneumoperitoneum, Artificial: Deliberate introduction of air into the peritoneal cavity.Thoracic Wall: The outer margins of the thorax containing SKIN, deep FASCIA; THORACIC VERTEBRAE; RIBS; STERNUM; and MUSCLES.Blood Gas Analysis: Measurement of oxygen and carbon dioxide in the blood.Respiration: The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration (= OXYGEN CONSUMPTION) or cell respiration (= CELL RESPIRATION).Elasticity: Resistance and recovery from distortion of shape.Ventilator Weaning: Techniques for effecting the transition of the respiratory-failure patient from mechanical ventilation to spontaneous ventilation, while meeting the criteria that tidal volume be above a given threshold (greater than 5 ml/kg), respiratory frequency be below a given count (less than 30 breaths/min), and oxygen partial pressure be above a given threshold (PaO2 greater than 50mm Hg). Weaning studies focus on finding methods to monitor and predict the outcome of mechanical ventilator weaning as well as finding ventilatory support techniques which will facilitate successful weaning. Present methods include intermittent mandatory ventilation, intermittent positive pressure ventilation, and mandatory minute volume ventilation.Total Lung Capacity: The volume of air contained in the lungs at the end of a maximal inspiration. It is the equivalent to each of the following sums: VITAL CAPACITY plus RESIDUAL VOLUME; INSPIRATORY CAPACITY plus FUNCTIONAL RESIDUAL CAPACITY; TIDAL VOLUME plus INSPIRATORY RESERVE VOLUME plus functional residual capacity; or tidal volume plus inspiratory reserve volume plus EXPIRATORY RESERVE VOLUME plus residual volume.Pressure: A type of stress exerted uniformly in all directions. Its measure is the force exerted per unit area. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Positive-Pressure Respiration, Intrinsic: Non-therapeutic positive end-expiratory pressure occurring frequently in patients with severe airway obstruction. It can appear with or without the administration of external positive end-expiratory pressure (POSITIVE-PRESSURE RESPIRATION). It presents an important load on the inspiratory muscles which are operating at a mechanical disadvantage due to hyperinflation. Auto-PEEP may cause profound hypotension that should be treated by intravascular volume expansion, increasing the time for expiration, and/or changing from assist mode to intermittent mandatory ventilation mode. (From Harrison's Principles of Internal Medicine, 12th ed, p1127)Spirometry: Measurement of volume of air inhaled or exhaled by the lung.Biomechanical Phenomena: The properties, processes, and behavior of biological systems under the action of mechanical forces.Lung Diseases, Obstructive: Any disorder marked by obstruction of conducting airways of the lung. AIRWAY OBSTRUCTION may be acute, chronic, intermittent, or persistent.Respiratory Distress Syndrome, Newborn: A condition of the newborn marked by DYSPNEA with CYANOSIS, heralded by such prodromal signs as dilatation of the alae nasi, expiratory grunt, and retraction of the suprasternal notch or costal margins, mostly frequently occurring in premature infants, children of diabetic mothers, and infants delivered by cesarean section, and sometimes with no apparent predisposing cause.Respiratory Insufficiency: Failure to adequately provide oxygen to cells of the body and to remove excess carbon dioxide from them. (Stedman, 25th ed)Forced Expiratory Volume: Measure of the maximum amount of air that can be expelled in a given number of seconds during a FORCED VITAL CAPACITY determination . It is usually given as FEV followed by a subscript indicating the number of seconds over which the measurement is made, although it is sometimes given as a percentage of forced vital capacity.Anesthesia, General: Procedure in which patients are induced into an unconscious state through use of various medications so that they do not feel pain during surgery.Monitoring, Physiologic: The continuous measurement of physiological processes, blood pressure, heart rate, renal output, reflexes, respiration, etc., in a patient or experimental animal; includes pharmacologic monitoring, the measurement of administered drugs or their metabolites in the blood, tissues, or urine.Postoperative Period: The period following a surgical operation.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.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.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Pulmonary Disease, Chronic Obstructive: A disease of chronic diffuse irreversible airflow obstruction. Subcategories of COPD include CHRONIC BRONCHITIS and PULMONARY EMPHYSEMA.Mechanical Processes: The behaviors of materials under force.Stress, Mechanical: A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area.Infant, Newborn: An infant during the first month after birth.Quantum Theory: The theory that the radiation and absorption of energy take place in definite quantities called quanta (E) which vary in size and are defined by the equation E=hv in which h is Planck's constant and v is the frequency of the radiation.Torsion, Mechanical: A twisting deformation of a solid body about an axis. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.