The Respiratory System Measurement of Lung Function Flashcards
Measurement of Lung Function
Spirometry
-Assessment of lung function
Volume
Flow
-Lung Plethysmograph
-MIR Spirolab
-Wright Flow meter
Oximetry
Respiratory Cycle
Respiratory volume is the term used for various volumes of air moved by or associated with the lungs at a given point in the respiratory cycle. There are four major types of respiratory volumes: tidal, residual, inspiratory reserve, and expiratory reserve
Tidal volume (TV)
is the amount of air that normally enters the lungs during quiet breathing, which is about 500 milliliters.
Expiratory reserve volume (ERV)
is the amount of air you can forcefully exhale past a normal tidal expiration, up to 1200 milliliters for men.
Inspiratory reserve volume (IRV)
is produced by a deep inhalation, past a tidal inspiration. This is the extra volume that can be brought into the lungs during a forced inspiration.
Residual volume (RV)
is the air left in the lungs if you exhale as much air as possible. The residual volume makes breathing easier by preventing the alveoli from collapsing.
inspiratory capacity
inspiratory reserve volume + tidal volume
(IC) is the maximum amount of air that can be inhaled past a normal tidal expiration, is the sum of the tidal volume and inspiratory reserve volume.
functional capacity
expiratory reserve volume +
residual volume
) is the amount of air that remains in the lung after a normal tidal expiration; it is the sum of expiratory reserve volume and residual volume.
vital capacity
inspiratory reserve volume + tidal volume + expiratory reserve volume
is the amount of air a person can move into or out of his or her lungs, and is the sum of all of the volumes except residual volume (TV, ERV, and IRV), which is between 4000 and 5000 milliliters
total lung capacity
is everything
is the sum of all of the lung volumes (TV, ERV, IRV, and RV), which represents the total amount of air a person can hold in the lungs after a forceful inhalation. TLC is about 6000 mL air for men, and about 4200 mL for women.
How Is Residual Volume Measured?
There is no way to measure residual volume directly, but it can be calculated indirectly with a pulmonary function test. Other lung volumes and capacities must first be measured directly, usually with spirometry, before RV can be calculated.
Helium Dilution Test
During a helium dilution test, you would breathe from a container containing a known fraction of helium gas. A spirometer measures the change in the concentration of the gases in the container. This test is conducted in a closed system circuit. It is used less frequently than body plethysmography.
Body Plethysmography
The body plethysmography test measures the total amount of air the lungs can hold. During this test, you would sit inside an airtight plethysmograph booth and breathe through a mouthpiece while pressure and airflow measurements are collected.
As you exhale, the volume of your thoracic cavity can be calculated by recording the change in pressure of the entire chamber.Body plethysmography is the most frequently used method for calculating FRC and residual volume and it yields the most accurate measurements—but it is also the most expensive
Nitrogen Washout
Another closed-circuit test, a nitrogen washout, can also be used to determine FRC, but this method is rarely used.
Lung Plethysmography
Accurate determination of lung volumes
Expensive equipment
Not portable
May be combined with gas dilution methods
Boyle’s Law
Clinical Significance
Residual volume can be used to help diagnose or measure the severity of obstructive lung diseases, such as chronic obstructive pulmonary disease (COPD), asthma, and bronchiectasis. These conditions are characterized by airway inflammation, collapsible airways, expiratory flow obstruction, and air trapping.
In obstructive lung disease, inflammation and decreased elastic recoil cause increased airway resistance and lead to premature small airway closure during expiration. As a result, excess air is trapped and left in the lung after you breathe, leading to an increase in residual volume.
On the other hand, restrictive lung diseases such as pulmonary fibrosis and sarcoidosis, or extrinsic processes like kyphosis and obesity, restrict lung expansion. As a result, less air is retained in the lungs after maximal expiration and therefore less residual air than normal is left in the lungs after expiration.
Electronic spirometry- MIR Spirolab
Portable equipment
Expiratory Flow curve assessed
Patient performance compared with predicted values
-Height: a big person will have big lungs!
-Age: Lung capacity decline with age
-Sex: thoracic dimensions are different Male/Female
-Race
Changes monitored over time (months) or for effect of drugs
Several measurements taken to assure optimum performance
Best values used (it is not an average, it is the best value of 3 performance)
Several measurements taken to assure optimum performance
Best values used (it is not an average, it is the best value of 3 performance)
Forced expiratory volume (FEV1).This is the amount of air expired during the first seconds of the FVC test. - Litres
Peak expiratory flow rate (PEFR).This is the fastest rate that you can force air out of your lungs. L/min
Forced vital capacity (FVC).This is the amount of air exhaled forcefully and quickly after inhaling as much as you can. Liters
FEV1/FVC ratio: declining with age
