Lung Function Tests Flashcards
what is the function of the respiratory system
- The flow of air in and out of the respiratory system
- Devilry of air to the alveoli where gas exchange takes place
what does spirometry measure
Assess lung function tests
Measure both expired and inspired air
what are the basic 3 related measurements of spirometry
volume
time
flow
what are the positives of spirometry
objective
non-invasive
sensitive to disease
how should the patient be positioned in spirometry
- sit upright
- feet flat on the floor with legs uncrossed
- no use of abdominal muscles for leg position
- loosen tight fitting clothing, if clothing is too tight this can give restrictive pictures on spirometry
what is the technique that should be used in spirometry
- deep breath taken in why still using the mouthpeice
- followed by a further quick full inspiration
- deep breath can be taken in then the mouth is placed tightly around the mouthpiece before a full expiration is performed
- patient asked to completely empty their lungs then take a quick full inspiration followed by a full expiration
what is the quality of spirometry
- have to have an explosive start
- manoeuvre was performed with a maximal inspiration and expiration
- no glottis closure or cessation of airflow occurred
- no coughs
- manoeuvre should meet the end of test criteria (exhaling for 6s with 50ml being exhaled in the last 2s)
define tidal volume
this is the volume of air you move into and out of the lungs during rest subconsciously,
define inspiratory capacity
maximum volume of air inout and out of the lungs in a single respiratory cycle
define forced vital capacity
volume of air that you breath out as hard and fast as possible after the deepest possible breath
define inspiratory reserve volume
volume of air you can draw into your lungs
define expiratory reserve volume
volume of air you can expel from your lungs
define residual volume
volume of air that remains in the lungs even after maximal exhalation
how do you work out forced vital capacity
inspiratory reserve capacity + tidal volume + expiratory reserve volume
what is the PEF
maximal airflow you can achieve during the expiration phase
what are the main determinants in determining the FVC
- Age
- Height
- Sex
- Race
the taller you are the…
greater the lung function
as you age…
your lung function declines
what happens to the PEF in asthma
- it is decreased
why is it important to repeat lung function tests
- lung function might be fine one day and change the next day
asthmatics have xxx lungs
hyper inflated lungs
what happens to the volume flow graph in obstructive lung disease
- hyperinfalted lungs so there is.a greater residual volume then someone with no obstructive comprise therefore the graph shifts to the left
what happens to the volume flow graph in restrictive lung disease
– loss of lung capacity, the residual volume is significantly less than with someone with no respiratory comprise, the volume that they are able to generate in forced vital capacity is also less, thus the loop shifts to the right
what is a normal FEV1/FVC ratio
- FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity
- Values above 70-80% = normal. Age/gender/height adjusted
- Airflow limitation (e.g. Asthma) : ↓FEV1/FVC
describe the difference between FEV1/FVC in asthmatic and COPD
- Although FEV1 is reduced FV is still the similar to someone with no respiratory compromise
- COPD is different as they usually have obstructive airflow that is persistent
what is the limitations of spirometry
- Values above 70-80% = normal. Age/gender/height adjusted
- Airflow limitation (e.g. Asthma) : ↓FEV1/FVC
- Incorrect in some populations = Asian communities
- Misdiagnosis risk? Age-related decline in lung function not because they have obstructive lung disease
- therefore the solution is the 95th percentile for a population - these limits lower normality
what does DLCO/TLCO measure
- Measures how efficient lungs are at exchanging gases
- Ability of lungs to transfer gas from inhaled air to red blood cells
how does the DLCO work
- Diffusing capacity of the lungs for CO (DLCO) – used at 0.3%
- Haemoglobin has a higher affinity for carbon monoxide then oxygen
what is the technique for DLCO
- Single breath hold technique
- Unforced maneous empties the lungs, take a rapid inhalation of CO/helium to total lung capacity, breath hold for 10 seconds and then unforced exhalation for less than 4 seconds
- The sample is exhaled breath
what does DLCO stand for
diffusing capacity of the lungs for carbon monoxide
what are the two important parameters that determine the DLCO
- Lung surface area available for gas exchange
- Rate of capillary blood CO uptake
how do you work out the DLCO
Lung surface area available for gas exchange (Va) X rate of capillary blood CO uptake (Kco)
Why in restrictive lung disease does the DLCO decrease
- ILD: ↓DLCO primarily due to ↓Kco (NB ILD: Fibrosis of Interstitium)
what is DLCO useful for
- Useful for early stage ILD detection before substantial reduction in lung volumes
what are the limitations of the DLCO
Falsely reduced in individuals who fail to inspire to TLC (technique) and Significant variation
describe what exercise tests test assess
- Assess how much exercise a patient is able to manage
- Assess benefit of extra oxygen to help with daily activities
- Assess pre-operative fitness
- Part of a rehabilitation programme
name some exercise tests
6 minute walk
shuttle walk
cardiopulmonary exercise
describe how the 6 minute walk works
- Walk up and down a flat route for 6 minute
- Asses breathless pre and post test
- Blood oxygen saturation levels recordered
describe how the shuttle test works
- Assess distance and speed without taking rest (bleep test)
describe how the cardio-pulmonary exercise test works
- Assess pre-operative fitness/undiagnosed shortenss of breath/poor exercise tolerance cycle ergometer/treadmill
- Increase resistance
Measures
- Oxygen consumtion
- ECG
- SpO2
how do you work out
- vital capacity
- end respiratory volume
- total lung capacity
- inspiratory capacity
- functional residual volume
- expiratory reserve volume
- vital capacity = is calculated by adding the inspiratory reserve volume, the tidal volume and the expiratory reserve volume (IRV + VT + ERV)
- end respiratory volume = measured, total lung capacity (TLC)
- total lung capacity = is calculated by adding the inspiratory reserve volume, the tidal volume, the expiratory reserve volume and the residual volume (IRV + VT + ERV + RV)
- inspiratory capacity = is calculated by adding the tidal volume and the inspiratory reserve volume (VT + IRV)
- functional residual volume = FRC) is calculated by adding the expiratory reserve volume and the residual volume (ERV + RV)
- expiratory reserve volume = (ERV) is a measured value and cannot be calculated
what is the FEV1/FVC in obstructive and restrictive
- raises in restrictive - The lungs could be normal
The ratio may be unaffected whilst both the FEV1 and the FVC have decreased, as occurs in restrictive lung disease - decreases or remains the same in obstructive
This indicates obstructive lung disease
The value FEV1 decreases and therefore the ratio decreases
