Skills: Monitoring Ventilation (DP IB Biology: SL)

• The volume of air within the lungs of an individual will change depending on their level of activity
  • When at rest, breathing is shallow and slow
  • When exercising, breathing is deeper and more frequent

• The volume of air breathed in and out during normal breathing is the tidal volume
  • Normal breathing here refers to a breath that does not involve forced expiration

• The ventilation rate is the number of breaths taken per minute
• A piece of equipment called a spirometer can be used to create a trace to show the volume changes in the lungs

Practical 6: Monitoring of ventilation in humans at rest and after mild and vigorous exercise

• It is possible to investigate the effect of exercise on ventilation using the following variables
• Dependent variable: The ventilation parameter that is measured
  • This could be the ventilation rate, the tidal volume, or a combination of both
  • These measurements can be taken using a variety of methods, e.g. Basic observations such as counting breaths to measure ventilation rate
  • A data logger such as an inflatable chest belt and pressure sensor to measure ventilation rate
  • A spirometer can measure both ventilation rate and tidal volume

• Independent variable: The type or intensity of exercise
  • The type of exercise could include a range from inactive e.g. lying down, to very active e.g. sprinting, and everything in between
  • E.g. the intensity of the exercise could be measured by increasing speed on a treadmill

Apparatus

• Stop watch
• Inflatable chest belt and pressure sensor OR spirometer

Method: Using an inflatable chest belt

1. Taking breathing measurements using an inflatable chest belt and pressure sensor
2. The person (subject) being examined breathes in and out with a chest belt placed around the thorax, that has had air pumped into it
3. As the subject breathes the pressure sensor logs the changes in pressure due to ventilation; the data logged can be viewed on a computer
4. From the data collected, the rate of ventilation can be deduced
5. The subject then repeats steps 1-4 after a period of exercise
   • The type or intensity of exercise should be specified

6. The subject then repeats step 5 several more times after exercise of different specified type or intensity e.g., gradually increasing in intensity
7. A repeat of all measurements should be taken and several subjects should be tested in order to collect reliable results

Method: Using a spirometer

1. Taking breathing measurements using a spirometer
2. The subject being examined breathes in and out through the spirometer after a period of rest
3. As the subject breathes through the spirometer, a trace is drawn on a rotating drum of paper, or a graph is formed digitally which can be viewed on a computer
4. From this trace, the subject’s tidal volume and breathing rate can all be calculated
5. The person then completes steps 1-4 after a period of exercise
   • The type or intensity of exercise should be specified

6. The subject then repeats step 5 several more times after exercise of different specified type or intensity e.g., gradually increasing in intensity
7. A repeat of all measurements should be taken and several subjects should be tested in order to collect reliable results

Using a spirometer to monitor ventilation

Analysis

• The effect of exercise on ventilation can be seen in the spirometer trace below

• Exercise can be seen to increase the rate of ventilation resulting in more breaths taken per minute
• It is also evident that after exercise the tidal volume of the person has increased, which means more air is breathed in and out in each breath
• After exercise, both tidal volume and ventilation rate eventually return to resting values