Search results
Results from the WOW.Com Content Network
The normal relaxed state of the lung and chest is partially empty. Further exhalation requires muscular work. Inhalation is an active process requiring work. [4] Some of this work is to overcome frictional resistance to flow, and part is used to deform elastic tissues, and is stored as potential energy, which is recovered during the passive process of exhalation, Tidal breathing is breathing ...
The concentration of oxygen in the air (mmols O 2 per liter of air) therefore decreases at the same rate as the atmospheric pressure. [26] At sea level, where the ambient pressure is about 100 kPa , oxygen constitutes 21% of the atmosphere and the partial pressure of oxygen ( P O 2 ) is 21 kPa (i.e. 21% of 100 kPa).
The alveolar oxygen partial pressure is lower than the atmospheric O 2 partial pressure for two reasons.. Firstly, as the air enters the lungs, it is humidified by the upper airway and thus the partial pressure of water vapour (47 mmHg) reduces the oxygen partial pressure to about 150 mmHg.
Natural air includes 21% oxygen, which is equivalent to F I O 2 of 0.21. Oxygen-enriched air has a higher F I O 2 than 0.21; up to 1.00 which means 100% oxygen. F I O 2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity, [2] but there are applications when up to 100% is routinely used.
Older units cycled for a period of about 20 seconds and supplied up to 5 litres per minute of 90+% oxygen. Since about 1999, units capable of supplying up to 10 L/min have been available. Classic oxygen concentrators use two-bed molecular sieves; newer concentrators use multi-bed molecular sieves.
Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather . If the entire mass of the atmosphere had a uniform density equal to sea-level density (about 1.2 kg/m 3 ) from sea level upwards, it would terminate abruptly at an altitude of 8.50 ...
It is worthwhile to note that pressures may often be expressed in units of distance such as feet when diving. For this, note that descending 33 ft in salt water or 33.9 ft in fresh water results in a change of 1 atm, so distance and pressure are used interchangeably in this context.
Normal air comprises in crude numbers 80 percent nitrogen N 2 and 20 percent oxygen O 2. Both molecules are small and non-polar (and therefore non-associating). We can therefore expect that the behaviour of air within broad temperature and pressure ranges can be approximated as an ideal gas with reasonable accuracy.