Lung Volume and Spirometers

• Spirometers measure lung function (spirometry - ‘measure breath’); a chamber of medical-grade oxygen/air that floats on a tank of water, a spirometer trace has a series of peaks and troughs, peak to peak is one breath
• Can be used to measure the volume and speed of inhalation and exhalation; useful to do an assessment for asthma, pulmonary fibrosis, cystic fibrosis, emphysema, and COPD
• Breathing is “Pulmonary Ventilation”; (pulmonary - related to the lungs), for air to enter the thorax, its pressure has to be lower than atmospheric pressure, at rest lungs need to be ventilated with about 6.0dm^3 of air a minute
• Concentration of new air entering the alveoli with each breath is small compared to the total alveolar air volume (~6.0dm^3)
• Forced breathing out: Contraction of abdominal wall muscles forces the diaphragm up even further; depressing ribcage decreases chest volume - some help from internal intercostals, latissimus dorsi, and abdominal muscles
• Tidal Volume: Volume of air inhaled or exhaled in one breath (~0.5dm^3 at rest), meaning the composition of air in the alveoli does not change drastically, in addition, the lungs never empty completely; residual volume
• Vital Capacity: Max volume of air that can be forced out of the lung (using the diaphragm, ribs, internal intercostal muscles, and abdominal) after the deepest possible inhalation
• Residual Volume: Volume of air that always remains in the lungs, even after a maximum exhalation, this is the air that cannot be removed from the airways and alveoli (~1.5dm^3 then in norml exhalation: ~2.5dm^3)
• Dead Space: Part of the residual volume air that is not available for gas exchange since it remains permanently in the trachea, bronchi and bronchioles
• Ventilation Rate/Breathing Rate: Number of breaths per minute ~ at rest 16-17 breaths min^-1
• Pulmonary Ventilation: Total volume of air moved into the lungs in one minute (dm^3 min^-1); Pulmonary Ventilation = Tital Volume x Ventilation Rate (PV = TVxBR)
• Precautions when using a spirometer: maintain a constant temperature (temperature affects gas volume), ensure that the apparatus is airtight (no leaks, lips sealed around the mouthpiece) and be cautious about the subject’s health