Pulmonary Volumes and capacity measures Flashcards
LO109:To link the key functional and morphological features of the pathology of chronic bronchitis and emphysema to its clinical signs and symptoms.
Label this spirometry diagram
Define tidal volume
VT represents the volume of inspired or expired air with each normal breath. Appoximately 500ml in normal adult male
Define inspiratory reserve volume
IRV is the additional volume of air that can be inspired over and above VT with full force. It is equal to approximately 3000ml
Define Expiratory reserve volume
ERV is the maximum volume of additional gas that can be expired with forceful expiration above tidal expiration. Normally about 1100ml
Define Residual volume
RV is the volume of air that remains in the lung after most forceful expiration. Normally around 1200ml.
RV cannot be directly measured through spirometry.
A measure of Functional residual capacity (FRC) can be taken using helium dilution technique and then RV can be calculated using the measure of Expiratory reserve volume (ERV) taken from spirometry with the following calculation
RV=FRC-ERC
Define inspiratory capacity
IC is the volume of air that can be taken in when starting at normal expiratory distention (normally about 3500ml). This can be calculated
IC=VT +IRV
Where VT is tidal volume and IRV is inspiratory reserve volume.
Define Vital Capacity
VC is the amount of air someone can expel from their lungs after first filling them to the maximum capacity.
VC = IRV+VT+ERV
IRV = Inspiratory reserve volume
VT=Tidal Volume
ERV = Expiratory Reserve Volume
Also
VC=IC+ERV
Define Functional Residual Capacity
FRC is the volume of air left in the lungs at the end of tidal expiration. This includes both the expiratory reserve volume (forced additional expiration) and the residual volume (that cannot be measured with spirometry, but represents the volume of air that remains in the lungs after maximum expiration)
FRC = ERV+RV
FRC is normally approximately 2300ml
Describe how Functional Residual Capacity is measured.
FRC is measured using the helium dilution method. This involves taking a spirometer of known volume filled with air mixed with helium of a known volume. The person then breathes out normally so that what remains in the lungs is Functional Residual Capacity (FRC). The person then breathes from the helium spirometer and the helium mix is then diluted by the FRC such that the degree of dilution enables the FRC to be calculated
FRC=(Initial concentration of helium/final concentration of helium)*Initial volume of the spirometer
Define the total lung capacity
TLC is the maximum volume to which the lungs can be expanded with maximum effort. This includes residual volume and vital capacity.
TLC = VC+RV
Alternatively it is the inspiratory capacity and the functional residual capacity
TLC = IC+FRC
Again it is obvious that TLC requires both spirometry and helium dilution method to establish the RV or FRC.
Define minute respiratory rate
This is the total amount of new air moved into the respiratory system each minute
= respiratory rate * Tidal volume
normally 12*500ml
approx 6L/min
At a maximum VT can equal VC (4600ml) and resp rate can reach 40+ giving a minute resp rate approaching 200L/min. Most people cannot reach half-2/3 this level for longer than a minute.
Define dead space and its role in alveolar ventilation
The conducting zone of the respiratory airways do not engage in gas exchange, but nonetheless are filled with gases with each breath. This means a certain portion of the air is not involved in alveolar ventilation or useful for gas exchange. To work out alveolar ventilation it is therefore necessary to subtract the volume of deadspace air from the tidal volume.
VA (Volume of alveolar ventilation/min)= Freq RR * (VT-VD)
How is deadspace measured?
Subject fills lungs with pure oxygen. What is expired is then monitored for nitrogen content. Dead space air is expired first and as it has not been involved in gas exchange it will be pure oxygen, then alveolar air will start to mix with the deadspace air and the nitrogen content will start to rise until it reaches a plateau representing pure alveolar air. The grey area of the curve respresents the deadspace
VD= Gray area * VE/Pink area + Gray area
What is the difference between anatomical and physiological deadspace?
Physiological deadspace includes alveoli that themselves are not participating in gas exchange due to poor perfusion. Anatomical deadspace is the just the conducting airways that are not involved in gas exchange.
What is maximum expiratory flow and it’s clinical relevance?
This is the maximum flow that the airflow will reach follow expiration at maximum force. The airflow peaks and cannot increase any further even with greater effort as the expiration force not only acts on the air in the airways, but also on the airways and alveoli resulting in a collapse in the bronchioles such that airflow cannot increase with the increased pressure. Measured by taking a maximum breath in then expiring as quickly as possible. Peak expiratory flow is reached early on in the expiration.
Constricted lungs show a pattern of reduced total lung capacity, reduced residual volume and significantly reduced peak expiratory flow as the more full the lungs are the greater peak expiratory flow can be reached. Examples of constricted lung diseases: Fibrotic disease such as TB, Silicosis and chest wall constriction - Kyphosis, scoliosis and fibrotic pleurisy.
Obstructed lung disease show increased TLC and RV, but significantly reduced maximum expiratory flow. Obstructed lug diseases include - asthma and emphysema.
What is Forced expiratory vital Capacity and forced expiratory volume (1 second) and their clinical relevance?
Max inspiration followed by max expiration and the difference between the two is Forced Vital Capacity (FVC).
A measure can also be taken of the amount of air expired in the first second.
In normal and obstructed lungs there may be a small difference in the FVC, but the more pronounced difference is in the FEV1. In normal longs the % of FVC expired in the first second is 80% and will be >80% in a obstructed lung.
FEV1/FVC%
What it this and what is it used for?
Mini-wright peak flow meter.
Take maximum breath in and then max breath out with maximum force to give a measure of greatest level of flow achieved. Frequently used in obstructive respiratory disease such as asthma or COPD
