Contour line factors in a weather system. An isobar (from or "baros", meaning 'weight') is a line of equal or constant pressure on a graph, plot, or map; an isopleth or contour line of pressure. More accurately, isobars are lines drawn on a map joining places of equal average atmospheric pressure reduced to sea level for a specified period of time. In meteorology, the barometric pressures shown are reduced to sea level, not the surface pressures at the map locations. The distribution of isobars is closely related to the magnitude and direction of the wind field, and can be used to predict
Alveolar pressure opposite change occurs. The lung alveoli collapse before air is expelled from them, The alveolar pressure rises to about +1 cm H2O. This forces the 500 ml of inspired air out of the lung during 2–3 seconds of expiration. By the end of expiration, the pressure drops gradually and become atmospheric again. Alveolar pressure Alveolar pressure (P) is the pressure of air inside the lung alveoli. When the glottis is opened and no air is flowing into or out of the lungs, alveolar pressure is equal (zero cmH2O). During inspiration, the increased volume of alveoli as a result of lung