give some effects of atmospheric pressure
Answers
Explanation:
Atmospheric pressure is an indicator of weather. When a low-pressure system moves into an area, it usually leads to cloudiness, wind, and precipitation. High-pressure systems usually lead to fair, calm weather. A barometer measures atmospheric pressure, which is also called barometric pressure.
Answer:
Direct Effect:
This has two mechanisms.
(a) An increase in pressure proportionately increases the number of IR absorbing C02 molecules and thereby increases the C02 signal. A 1% increase in pressure causes a 1% relative increase in the C02 signal. This effect is eliminated by calibrating the capnometer with a known partial pressure of the C02 gas (mmHg = vol% * atmospheric pressure) using a commercially available calibrating gas. Given such a calibration, the capnometer will display CO2 concentrations within its measurement cuvette as partial pressure, regardless of changes in the atmospheric pressure.1 However, if the capnometer is calibrated in volume percent, then FC02 readings will need to be corrected for changes in atmospheric pressure (a 1% increase in pressure produces a 1% relative increase in FC02 value).2
(b) Changes in pressure also produce a second effect (alteration of intermolecular forces) exerted by C02 molecules, which alters the IR absorption. An increase in pressure by 1% results in a relative increase in the signal by 0.5 to 0.8% which can produce a small error.2,3
Maximal changes in the atmospheric pressure caused by changes in the weather are of the order of 20 mmHg. This would result in a change in PC02 of less than 0.5 to 0.8 mmHg (measurement range of PC02, 30-40 mmHg). Therefore, in routine clinical use, corrections for changes in atmospheric pressure are unnecessary.2 However, in studies in which precision is needed corrections for variations in barometric pressure are useful. Increases in the sampling flow rate of side-stream C02 sensors result in a reduction of pressure at the airway and lower apparent C02 measurements. However, if the unit is calibrated at the average prevailing atmospheric pressure and sampling flow does not change, the unit should be sufficiently accurate for clinical measurements. Further, application of PEEP (positive end expiratory pressure) increases the C02 reading. A PEEP of 20 cm H20 increases the C02 reading by 1.5 mmHg.1 Some units measure the pressure in their sensor and automatically adjust the C02 reading accordingly.1,3,4
INDIRECT EFFECT
The indirect effect of atmospheric pressure on the PCO2 values results when an analyzer reports measurements in volume percent. In conjunction with measurements of arterial blood gas tensions, it is preferable to record the readings as PCO2(mmHg) and not as volume percent. The atmospheric pressure at the time of measurement must be known to compute a PC02 value (mmHg = FC02 * atmospheric pressure).1 However, if the atmospheric pressure at the time of measurement differs from the atmospheric pressure at the time of calibration, then the observed FC02 readings should be corrected for the two components of "direct effect" of atmospheric pressure changes before computing the PC02 value.2,3