Low-pressure area This generates a steady wind blowing toward the land, bringing the moist near-surface air over the oceans with it. Similar rainfall is caused by the moist ocean-air being lifted upwards by mountains, surface heating, convergence at the surface, divergence aloft, or from storm-produced outflows at the surface. However the lifting occurs, the air cools due to expansion in lower pressure, which in turn produces condensation. In winter, the land cools off quickly, but the ocean keeps the heat longer due to its higher specific heat. The hot air over the ocean rises, creating a low-pressure area and a breeze from
Pulse pressure aorta wall. A pulse pressure is considered abnormally low if it is less than 25% of the systolic value. The most common cause of a low (narrow) pulse pressure is a drop in left ventricular stroke volume. In trauma, a low or narrow pulse pressure suggests significant blood loss (insufficient preload leading to reduced cardiac output). If the pulse pressure is extremely low, i.e. 25 mmHg or less, the cause may be low stroke volume, as in Congestive Heart Failure and/or cardiogenic shock. A narrow pulse pressure is also caused by aortic valve stenosis and cardiac tamponade. Usually, the resting