Pressure is the force per unit area applied on a surface in a direction perpendicular to that surface.
Pressure can also be described as a form of potential energy in a fluid. The maximum pressure of the fluid medium obtained during propagation of an ultrasonic pulse.
The negative peak pressure is the peak rarefaction pressure attained during the negative portion of a propagating ultrasound pulse in a medium such as tissue.
Sound pressure can be measured using a microphone in air and a hydrophone in water. The SI unit for sound pressure is the Pascal.
Blood pressure is the pressure exerted by the blood on the walls of the blood vessels.

See also Rarefactional Pressure, Low Intensity Pulsed Ultrasound, and Projector.

Sound pressure is reported on a logarithmic scale called sound-pressure level, expressed in decibel (dB) referenced to the weakest audible 1 000 Hz sound pressure of 2*10-5 Pascal (20 mP). Sound level meters contain filters that simulate the ear's frequency response. The most commonly used filter provides what is called 'A' weighting, with the letter 'A' appended to the dB units, i.e. dBA.

The rarefactional pressure is the amplitude of a negative instantaneous sound pressure in an ultrasound beam. Rarefaction is the reduction in pressure of the medium during the acoustic cycle.

See also Mechanical Index.

(Osm) A unit of osmotic pressure used in physical chemistry, cell biology, and medicine.
Definition: 1 osmole is the osmotic pressure of a one molar solution (that is, a solution with a concentration of one mole per liter of solvent) of a substance that does not dissociate.
If chemical solutions are separated by a semipermeable membrane (a membrane that resists the passage of dissolved substances but permits the passage of the solvent, usually water), then the solvent will diffuse across the membrane to equalize the concentrations. This process is called osmosis.
Solutions with higher concentrations of dissolved substances are said to have higher osmotic pressure than solutions having lower concentrations; thus the solvent moves from an area of low osmotic pressure to an area of higher osmotic pressure.
Osmotic pressure depends on the total number of dissolved particles, so for a substance that dissociates into two ions, such as ordinary salt (sodium chloride), a one molar solution has an osmotic pressure of 2 osmoles. In practice, most measurements are in milliosmoles (mOsm). Typical values range from 20 mOsm for fresh water through 290 mOsm for typical human blood plasma to 1010 mOsm for salt water from the open ocean.

See also Part Per Million, and Mole.

Dobutamine stress echocardiography is a variation of exercise echocardiography to unmask coronary artery blockages. During this test, the heart is stressed by infusing dobutamine. Dobutamine is commonly used to treat patients with low blood pressure, to improve circulation and as a diagnostic testing agent. Dobutamine increases the heart rate and blood pressure and the degree to which the heart contracts. It therefore mimics the effects of exercise for patients who are unable to exercise to a sufficient degree.
The examination starts with the resting transthoracic echocardiogram. After that, dobutamine is infused at a low dose. Following, the dose is increased every three minutes to increase the heart rate and cardiac contractions. At each of these three-minute stages, the heart is scanned using transthoracic echocardiography. An electrocardiogram has to be continuously recorded and blood pressure automatically checked every three minutes.
Disconcerting and stress-related sensations of the patient is to expect during infusion of dobutamine and does not represent any harmful effect. As soon as the infusion is completed, it is discontinued and usually within five to ten minutes the heart rate and blood pressure will return to the levels before starting the exam. Only qualified staff with specific training should perform this test. As for all types of cardiovascular stress testing, all of the necessary equipment and medicines to treat complications must be available in the stress testing room.