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The Glossary contains terms commonly associated with ventilators, the community, and respiratory physiology. Click on a hyperlinked letter to view the entries that begin with that letter, then scroll down in the window to find the word you are looking for.

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Rapid Shallow Breathing Index

(RSBI) Respiratory rate (frequency) divided by tidal volume. The units are typically bpm/L. This calculation was developed as a weaning parameter, but its predictive reliability has not been proven.

The RSBI is measured by attaching a hand-held spirometer to the endotracheal tube and recording the respiratory rate and average tidal volume over one minute, though some ventilators will calculate this value for you.

For more information, see Yang KL. Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991;324(21):1445-50.

RAW Airway Resistance - The ratio of the change in the pressure difference between the airway opening and the alveoli, to the change in flow through the airway, for breathing frequencies up to panting, assuming that the compliance of the airways is normal.
RC Respiratory Care - A clinical support specialty concerned with the application of treatments for respiratory diseases, trauma and dysfunction.
Reactance When applied to a pneumatic system such as the lungs, reactance is a mathematical expression of the combined effects of compliance, inertance and frequency.
Relative Humidity The ratio of the amount of water vapor contained in air to the maximum amount air could hold at the same temperature and pressure, expressed as percent.
Resistance In a pneumatic system with constant, unidirectional flow, the resistance is the ratio of the pressure difference along a conduit to the flow through it. This same definition can be applied during oscillatory flow, such as breathing, if it can be shown or assumed that the effects of the compliance of the conduit and compressibility and inertance of the gas in it are negligible at the (breathing) frequencies being considered. If these conditions do not hold, then the effects of these factors on the pressure difference must be eliminated either experimentally or mathematically before the ratio is calculated.
Respirator A term that has been used in the past for ventilator.
Respiratory Rate RR - See Frequency (of Breathing).
Resuscitator A portable device used in emergency situations to ventilate the lungs of individuals to adequately breathe on their own. These devices may be either manually or gas powered.
Rise Time The time required for a variable to change from its baseline value to a given percentage (usually 90%) of its intended final value.
RSBI see Rapid Shallow Breathing Index
RT Respiratory Therapy - (See RC - Respiratory Care.)
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