Investigate the effects of exercise on tidal volume, breathing rate, respiratory minute ventilation and oxygen consumption using data from spirometer traces.
A spirometer is a device which measures breathing and respiration. It can measure breathing rate (number of breaths per minute), tidal volume (volume of gas of one normal breath), respiratory minute ventilation (volume of gas inhaled per minute), and vital capacity (volume of gas of one forced deep breath).
A spirometer consists of a chamber filled with air, connected by tubes and suspended in a tank of water. When the volume of gas changes, the lid of the chamber moves up and down. The chamber contains soda lime to absorb the exhaled carbon dioxide, so changes in the position of the lid are due to changes in the volume of oxygen inhaled/exhaled by the person breathing into the tubes. The person wears a nose clip so that all breathing occurs through the mouth. The graph produced by a spirometer is called a spirograph or spirometer trace.
● Datalogger/computer/kymograph
Find the vertical scale by emptying the chamber, starting the kymograph and then forcing a known volume of air into the chamber. This measures the volume of gas in the chamber, and by reading the trace, the movement of the pen on the kymograph can be calibrated to the actual volume of air.
Find the horizontal scale by setting it to 1 mm per second, using the switch (or as close to 1 mm per second as possible). This is the speed at which the drum turns.
A trained member of staff can fill the spirometer with medical grade oxygen.
Disinfect the mouthpiece and attach it to the tube. Turn the tap so the tube is not attached to the spirometer.
Subject attaches the nose clip and breathes into the tube for a while to practice. When they are comfortable, start the datalogger/kymograph and turn the tap to attach the tube to the spirometer.
Subject takes one forced deep breath and then breathes normally into the spirometer for a duration of 5 minutes maximum.
Disinfectant; Flammable; Keep away from naked flame
Soda Lime; Corrosive; Wear eye protection, avoid contact with skin, keep away from edge of desk
Spirometer; Breathing/circulatory problems; Read manufacturer's notes before using, only use spirometer supervised, don't use with breathing/circulatory issues
● From the calibration of the kymograph, volume of air can be linked to the movement (e.g. in number of squares) of the pen on the kymograph. Therefore, distance can be linked to volume.
● Interpreting the spirometer trace:
○ The tidal volume is the distance from peak to trough, when the subject is breathing normally.
○ The vital capacity is the distance from peak to trough, when the subject takes a forced deep breath.
○ Breathing rate is the number of peaks in a time corresponding to a minute (e.g. total peaks divided by 5).
○ Respiratory minute ventilation is calculated by multiplying breathing rate by tidal volume.
● If the experiment is repeated after exercise (although not during exercise, because a spirometer can create resistance to breathing and therefore isn't safe for use during exercise):
○ Vital capacity remains the same (although can be impacted long-term by regular aerobic exercise).
○ Breathing rate increases.
○ Respiratory minute ventilation increases.
● This is because respiration increases during exercise because of increased muscle contraction. Therefore, more oxygen is required and more carbon dioxide is produced, so breathing rate, tidal volume and therefore respiratory minute ventilation increases to cope with this demand up to the maximum aerobic rate. After this point, minute ventilation will plateau to a maximum and further respiration will be anaerobic.
NB: informed consent should be obtained before anyone uses the spirometer, as they are a participant in scientific research. Anyone should be allowed to refrain from participating or contributing their data, and can stop at any time during the practical.