Week 1: Basic Lung Function & Testing Flashcards
Give 4 reasons/uses of measuring lung function
1) aids in diagnosis 2) can be used to measure the response to treatment and without treatment (monitor disease progression) 3) can be done in symptomatic patients and in patients at risk of pulmonary disease (monitor disease) 4) can be used to measure the specific response to certain stimuli in lab and environment (e.g asthmatic to histamine and B2 agonist)
What can be measured in lung function testing and what does it indicate? (Give 3 given in lecture)
Air flow rate (measured by peak flow or by FEV1 on spirometry) gives an idea of airways resistance. Vital capacity gives an indication of the total lung volume Measuring diffusion rate gives an indication of permeability of the alveolar/ capillary membrane and any V/Q mismatch.
What is the peak flow? What are it’s units? How does this differ to FEV1?
Peak flow or the peak expiratory flow rate is the maximum rate of expiration that can be achieved during forced expiration. Measured in L/min. It indicates the resistance of the airways. The measurement relies on 1) bronchial diameter 2) muscle power available for maximal expiratory effort Differs from FEV1 as it can be measured at home using peak flow monitor. FEV1 is a formal measurement of flow rate during spirometry.
Describe how a peak flow monitor would be used
Patient would exhale deeply and then take in a deep breath before placing their lips at the top of the peak flow monitor (which is held horizontally) and producing a forced expiration with maximal expiratory effort. Measurement done 3 times, record highest value.
How could peak flow be used to diagnose and monitor asthma?
Peak flow commonly used to monitor asthma at home. Peak flow measurement done in morning and evening, often see lower value in morning (an) (asthma often sees nocturnal dipping and is worse in early morning) and better values in evening (pm). 20% variability in peak flow measurement is diagnostic of asthma. After treatment begins with preventer (corticosteroid) often see improvement in the PEF value variation.
Spirometry: How available is spirometry? (Reference time/ expense/ specialists) What reference values are available? What two key measurements are taken?
Spirometry most readily available measurement of lung function, does not take long (10-15 mins). Spirometry uses expensive equipment (£800 machine) and requires highly trained technicians. There are standard procedures (internationally accepted criteria) to ensure measurements are reproducible and standard reference values for different populations. Key measurements: FEV1- forced vital capacity in 1 second FVC- forced vital capacity
Describe the lung volumes and capacities that can be measured with spirometry
What is the difference between capacity and volume?
- Tidal volume = volume of air moved in and out of respiratory tract during each ventilatory cycle at rest (quiet respiration).
- Inspiratory reserve volume is additional volume of air that can be forcibly inhaled following normal inspiration, assessed by inspiring maximally
- Expiratory reserve volume is the additional volume of air that can be forcibly exhaled with maximal expiratory effort.
- Vital capacity is the total amount of air moved in and out of the lungs after maximal inspiratory and expiratory effort. ( VC = TV + IRV + ERV).
- Residual volume = volume of air remaining after maximal expiration (FRC - ERV)
- Functional residual capacity (FRC) = volume of air that remains in the lungs after normal expiration during quiet breathing. FRC= RV = ERV
- Total lung capacity = total volume of air in the lungs at the end of maximal inspiration (RV + ERV + IRV + TV = Total lung volume).
- Capacities are 2 or more lung volumes, are fixed and do not change with the pattern of breathing.
How is vital capacity measured?
Vital capacity is measure from maximal inspiration to maximal expiration.
It is a good indicator of total lung capacity (cannot be measured using spirometry as cannot measure residual volume).
What does spirometry measure?
what are the values normally expressed as?
what are normal values affected by (4 factors that will alter recorded values).
- Spirometry measures the volume of air inspired and expired by the lungs by monitoring the change in volume as air is blown in/ sucked out of a known volume of air.
- Spirometry values are normally expressed as the measured value itself and % of predicted value.
- Normal values are affected by age, height, sex, race.
What is a flow volume loop?
What can be measured from a flow volume loop?
- A flow volume is a plot of flow vs volume recorded during spirometry displayed as a continuous loop of inspiration and expiration.
- Plots the volume of air entering the lungs and leaving the lungs during maximal inspiratory and expiratory effort.
- Can give values of forced vital capacity (total volume moved in and out during maximal respiratory effort)
- PEF measured as the peak expiratory flow rate, is the highest point on the expiration curve
- FEV1 is measured by taking the volume change from maximal inspiration to volume left in lungs after 1 second.
Describe the shape of a normal flow- volume loop
- Normal shape shows expiration as a linear upwards stroke, reaching peak expiratory flow, followed by a gradual linear decline as lung volume reduces.
- With reducing lung volume the diameter of the airway reduces leading to increased resistance to flow and therefore reduced flow rate.
- Inspiration seen as standard curve on the bottom of the flow volume loop.
Describe the shape of a flow volume loop with restrictive disease?
- With restrictive disease the forced vital capacity is reduced compared to expected values
- A decrease in forced vital capacity (total volume of air that can be inspired and expired with maximal respiratory effort) is best indication of restrictive disease- however not specific enough for diagnosis alone.
- Therefore flow volume loop is narrowed with a smaller FVC.
- The flow rate is very high in expiratory curve in restrictive disease due to the enhanced effect of elastic recoil. (Loss of expansile chest forces, shifts equilbrium to recoil).
- This can reduce the residual volume as a smaller proportion of air is inspired and a greater proportion of air is expired.
What clinical findings are typical in obstructive disease?
What would show on the spirometry flow volume trace?
- Obstructive diseases reduce the lumen of the airways, which increases the resistance to airflow.
- This means there is more resistance to airflow during expiration which reduces the FEV1.
- The reduction in the volume of air expired, reduces expiratory reserve volume, and can lead to an increase in residual volume (not measured in spirometry).
- Increase in residual volume leads to a hyperinflated barrel chest.
- Increased resistance to airflow leads to airflow becoming turbulent which is heard as an expiratory wheeze.
- On flow volume loop the flow rate is very low in relation to lung volume (reduced FEV1)
- Scooped out appearance after peak expiratory flow due to high resistance, not much volume change.
What is a time volume trace?
What two values does it typically show?
How might it differ in restrictive lung disease?
How might it differ in obstructive lung disease?
- Another form of measurement that can be taken during spirometry, plot of volume (y axis) against time (x axis).
- Shows FEV1 (read off from 1 second up to volume)
- Shows FVC - maximum volume reached.
- A reduced FVC will be seen with restrictive disease as lungs are less compliant (e.g. fibrosis increased stiffness of the lungs). Reduces the total volume that can be inspired and therefore FVC.
- In obstructive disease there is increased resistance to airflow during expiration. These leads to a reduced FEV1 on the time-volume graph and a shallower gradient of expiration up to FVC.
Define FEV1 and FVC
What are normal values for FEV1 and FVC in a healthy person?
- FEV1 = forced expiratory volume in 1 second , is total amount of air expired within 1 second after maximal inspiratory effort followed by maximal expiratory effort.
- FVC = Forced vital capacity, is the total amount of air that can be inspired and expired during maximal respiratory effort. (IRV + TV + ERV).
- Normal FEV1 values are 80% of that predicted
- Normal FVC values are 80% of predicted.
