Determination of Respiratory Volumes

Determination of Respiratory Volumes

Respiratory volumes, those volumes of air which are exchanged during breathing, are important indicators of the functioning of the respiratory system, and can be measured through the use of a spirometer. We have two styles of spirometer: one has a turbine which rotates as air passes through it, and this rotation is geared down to drives the movement of a needle which indicates the volume of air. The second captures air in an inverted chamber the volume being indicated by the rise of the chamber in a bath of water.

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SPIROMETER OPERATION: Attach a clean mouthpiece, and zero the instrument by rotating the cover so that 0 cc is lined up with the needle.

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The subject should blow hard enough to move the needle, but not so hard as to jam the instrument. The operator should monitor the free movement of the needle as the subject breathes.

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If the needle sticks, try tilting the spirometer, tapping, etc, to insure its free operation. Perform each of the following measurements three times and determine the average of each
Wash the mouth piece when finished and drain in the rack

vital capacity This is best measured by inhaling as deeply as possible, then exhaling through the spirometer until no air remains in the lungs. It is the sum of tidal volume, inspirational volume and expiratory volume, and should equal the sum of the averages of the next three parameters. (Avg = 4800 cc). Perform the test three times, circle the largest of the three as your maximum vital capacity.

tidal volume is the volume of air in easy breathing. We suggest blowing five easy breaths into the spirometer without resetting the dial, and dividing the total by 5. It is difficult to get the spirometer to work smoothly, but don’t give up.
(Avg = 500 cc)

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The wet spirometer is much more dependable than the dry spirometer as it measures the actual volume of air moved.
The tidal volume is much more easily measured with this instrument, although it is harder than you might think to blow one easy breath.  Repeat three times and average.

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Use of a wet spirometer:
Zero to start with.
Place a clean mouthpiece in the end of the pipe.
Blow to produce the volume you are measuring, read the final volume expelled.
How did your wet spirometer vital capacity compare with the data from the dry spirometer?


vital capacity This is best measured by inhaling as deeply as possible, then exhaling through the spirometer until no air remains in the lungs. It is the sum of tidal volume, inspirational volume and expiratory volume, and should equal the sum of the averages of the next three parameters. (Avg = 4800 cc). This is the easiest volume to measure.
tidal volume is the volume of air in easy breathing. We suggest blowing five easy breaths into the spirometer without resetting the dial, and dividing the total by 5. It is difficult to get the spirometer to work smoothly, but don’t give up.
(Avg = 500 cc)
inspiratory capacity is the total volume of air which can be drawn in after exhalation of a tidal volume. Since the spirometer only measures blown air, measure by inhaling as deeply as possible, and expelling until lungs are relaxed at the end of the tidal exhalation.
(Avg = 3600 cc)
inspiratory reserve is the difference between tidal volume and inspirational capacity. Subtract the average tidal from the average inspirational capacity.
(Avg = 3100 cc)
expiratory reserve is total volume of air which can be expelled after exhalation of a tidal volume.
(Avg = 1200 cc)
Record all raw data in your notebook, calculate the average volumes, and report the averages into the class data table. Wash the mouthpieces well with soap and water before and after use.

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