Barometer Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced, which were the first form of the modern weather map when created in the 19th century. Isobars, lines of equal pressure, when drawn on such a map, give a contour map showing areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Atmospheric lift caused by low-level wind convergence into the surface brings clouds and sometimes precipitation. The larger the change in pressure, especially if more than 3.5 hPa (0.1 inHg),
Alveolar pressure 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 expansion decrease the intra-alveolar pressure to a value below atmospheric pressure about -1 cmH2O. This slight negative pressure is enough to move 500 ml of air into the lungs in 2 seconds required for inspiration. At the end of inspiration, the alveolar pressure returns to atmospheric pressure (zero cmH2O). During expiration, the