Capacities are two or more volumes added together These are measured with a spirometer This is estimated, based on height and age These are calculated FRC = ERV + RV TLC = RV + ERV + TV + IRV
You don’t need to memorize the normal numbers, just the definitions • Respiratory Cycle: A single cycle of inhalation and exhalation • Respiratory rate: number of breaths per minute (usually about 12-18; children higher 18-20). • Tidal Volume: normal breath in and out. Usually about 500 ml. • Inspiratory Reserve Volume: take in a normal breath, stop, now inhale as much more as you can. In other words, this is the amount of air that can be forcefully inhaled after a normal inhalation. • Expiratory Reserve Volume (Expiratory capacity): take a normal breath in, a normal breath out, then breathe out the most you can. In other words, this is the amount of air that can be forcefully exhaled after a normal exhalation. This is the air needed to perform the Heimlich maneuver. The maneuver decreases the thoracic cavity volume, causing increased pressure in lungs. That causes forced air with high pressure to be expelled from the lungs. • Residual volume: The amount of air left in your lungs after you exhale maximally. This air helps to keep the alveoli open and prevent lung collapse. This is estimated based on height and age.
You don’t need to memorize the normal numbers, just the definitions • Vital capacity: The volume of air a patient can exhale maximally after a forced inspiration. Maximum deep breath in, then exhale as much as possible. Vital capacity divided by expiratory reserve volume should be 80%. If it is lower than that, the person has either obstructive or restrictive lung disease. To tell which one, look at VC. If it is normal, it is obstructive. If it is low, they have restrictive lung disease. • Total Lung Capacity (TLC): the sum of all lung volumes • Inspiratory Capacity: amount of air for a deep breath in after normal exhalation • Functional residual capacity: amount of air left in your lungs after a normal exhale. You have to calculate this: • FRC = ERV + residual volume. • In COPD, their FRC increases. • They have a barrel chest • The lungs don’t have as much recoil, have decreased tidal volume, cannot exhale enough
You don’t need to memorize the normal numbers, just the definitions • Dead Space: Area where air fills the passageways and never contributes to gas exchange. Amounts to about 150 ml. • Minute Respiratory Volume (MRV): tidal volume x respiratory rate. This calculation does not take into account the volume of air wasted in the dead space. A more accurate measurement of respiratory efficiency is alveolar ventilation rate. • Alveolar Ventilation Rate (AVR) AVR = (TV – Dead Space) x Respiratory Rate Summary of lung calculations FRC = ERV + RV TLC = RV + ERV + TV + IRV MRV = TV x RR AVR = (TV – Dead Space) x RR You DO need to know these formulas.