Measuring Lung Capacity

• How do you measure lung volume?

  + peak flow meter measures the rate air is expelled from the lungs

  + a vitalograph draws a graph of air speed (gradient) and the volume of air expelled (line peak) - it measures forced expiratory volume per second
• What does a spirometer do and how does it work?

  + used to measure lung volumes

  + oxygen is inhaled from chamber and carbon dioxide-rich air exhaled passes through soda lime ( mainly calcium hydroxide)

  + allows measurement of oxygen consumption as we can assume that volume of CO2 absorbed by soda lime = volume of O2 absorbed by blood
• Why does the trace of the spirometer slope downwards?

  + total volume of air in chamber decreases

  + person is using up oxygen during aerobic respiration (replace by CO2, absorbed by soda lime)
• What is the inspiratory reserve volume?

  amount extra we can breathe in (over and above tidal volue)
• What is the expiratory reserve volume?

  amount extra you can force out of lungs (above normal tidal volume)
• Which muscles are involved in taking a deep breath in?

  external intercostal muscles and diaphragm contract
• Which muscles are involved in taking a deep breath out?

  internal intercostal and abdominal muscles contract
• What is the vital capacity?

  air volume taken in during deepest inhalation followed by forced exhalation
• What is the vital capacity dependent upon?

  + size of person (height)

  + age and gender

  + level of regular exercise

  + usually around 2.5-5.0 dm3
• What is the residual volume?

  + air left in the lungs you cannot exhale (cannot be measured directly)

  + usually around 0.5 dm3

  + we cannot expel all air from lungs due to rings of cartilage
• What does the counterweight do in a spirometer?

  reduces resistance from the lid when exhaling
• What does the canister of soda lime do in a spirometer?

  removes the carbon dioxide produced
• What is a kymograph?

  trace drawn on revolving drum as lid moves up and dwn
• Which precautions should be taken when using a spirometer?

  + soda lime should be fresh

  + person tested (subject) must be in good health, avoiding medical problems during the experiment

  + mouthpiece must be sterilised to avoid infection

  + water chamber must not be overfilled, as water enters tubes and will be inhaled

  + medical grade O2 to ensure sufficient levels of oxygen in air to be inhaled
• Why does the subject wear a nose clip and why is this necessary?

  + maintains a closed system and collects valid measurements

  + air exhaled/ inhaled in just from in machine (check for leaks)
• What is the tidal volume?

  the volume of air breathed in or out during a normal breath (at rest)