L17 Clinical Assessment of Lung Function Flashcards
(37 cards)
Extensively pulmonary function testing can assess four primary aspects of pulmonary function/respiratory system:
Ventilation (including lung mechanics) (bulk movement of gas into and out of lungs),
Gas-exchange (diffusion across alveolar capillary membrane),
Perfusion (quality and quality) (right volume, place, time. no shunts or mismatch)
Respiratory control
Respiratory function testing is performed to assess:
- impact of a pathological or aging (not pathological, natural progression of aging) process
- To tract the progress of a disease process and/or treatment regimen
- Assess degree of interventional risk (capacity to survive (e.g. partial lung removal)) or risk associated with specific activity (scuba diving, police, navy etc. bronchial hyperactivity)
Spirometry (Dynamic Volumes)/ Forced Vital Capacity (FVC)
Spirometry required the concurrent measurement of flow and volume ( and time), during a maximal effort expiration followed be a maximal effort inspiration
Most common lab test of Respiratory volumes
Hardest test to do properly
Overview of Pulmonary Function Tests which are routinely available/required
- Spirometry (Dynamic Volumes- how fast you can get air out of lungs. resistance. pressures of flow)
- Static Lung Volumes (total lung capacity. and divisions (Tidal vol etc))
- D(L(CO)) (Diffusion Capacity) (effectivity of alveolar capillary membrane at exchanging gas b/w plasma and air in alveoli)
- Bronchodilator Response (Responds +vely or -vely to bronchodilator) (if given on different time or different day can get different results)
- Bronchoprovocation Tests (try illicit bronchospasm) (spectrum for degree of stimulus required)
- Cardiopulmonary Exercise testing (produce combined ability to exert yourselves)
Additional Pulmonary Function tests
- Exhaled Nitric Oxide (eNO) (indicates eosinophilic inhalation. common in inflammatory airways disease)
- Maximum Respiratory Pressures (neuronal and muscular systems whether capacble of producing sufficient inspiratory and expiraotry pressures. (motor neuron disease, mysoinia gravis= diminished ability to ventilate)
- Forced Oscillatory Spirometry (non-invasive)
- Ventilatory Response Testing (assess control of ventilation)
- Simulated Cabin Pressure testing (hyprobaric enviro. Lung disease and want to fly. 15% O2 at sea level, can survive that in an aircraft)
- Pulmonary Compliance
- Ambulatory walk tests
- Resting Shunt Assessment (quality and efficiency of blood supply to lung)
Spirometry/FVC Indications
- To establish or confirm diagnosis “obstructive ventilatory defect” (narrow airways)
- Assess effects of intervention
- Preoperative evaluation
- Assessment of “fitness” to participate in various recreational or work related activities
- Assess the impact of work place exposure on airway/lung function
What do we measure from FVC
- Volume: FVC (Force Vital Capacity)
- Instantaneous Flows: peak expiratory flow. FEF25-75 (not used as a diagnostic tool. only repeatability of effort) (FEV1 is used as a diagnostic tool)
- Volumes expired at fixed time periods (FEV1 Force Expired Volume after 1 sec) (FEV 0.5 in pediatric patient (squeeze test. inflate jacket quickly, squeeze air out. 3wks –> 18 years)
- Tragectory expect lung function to change
Changing in Pulmonary Function with Age
cant start at 3 weeks 1. FEV1 -gradual decline of 25ml per year (average) Pulmonary function reaches a Zenith Female: 20-25yrs Male: 25-30yrs *little plateau 2. FEV1: FVC ratio Kink:differential rate of maturation of airways vs lung (start with large airways vs lungs space --> early teens/20's lung volume increases disproportionately to airways leading to larger difference) -varies with age
Normal Flow Volume Loops
Adult
Child: relatively compliant
-as you mature. your lung volume + flows increase with age
Usefulness of spirometry
Subject of assessment of loop is just as useful as object of assessment of numbers
-each different disease has a specific morphology
Flow Volume Loops
- Obstructive: PEF normal. scooped loop
- Obstructive + Gas Trapping: doesn’t get to residual volume
- Restrictive:
a) narrow tall loop. reduced FVC. stiff lung that wants to recoil quickly. Can generate flows just cant inflate well. Fibrotic lung disease.
b) cannot inflate lung at all as lung has been removed (completely normal but only have one). or High transection of thoracic vertebrae (lost a large control of accessory muscles and cannot inflate their lung) (paraplasia)
Very Uncommon: - Variable extrathoracic large airway obstruction. (blow out, upper airway, +ve pressure, but then will collapse upon inspiration/suck in
- Variable intrathoracic large airway obstruction (collapsable airway inside lung) (blow out +ve pressure airway collapses. suck in -ve pressure in airway will open)
4&5 assoc. with tracheal atrasia or valve arrangement (tumour grown into airway and acting like valve) - Fixed large airway obstruction (narrowing/stenosis of airway)
-large goiter. compression on trachea and narrowed
Static Lung Volumes and TLC
Measure all static volumes and capacities of the lung (total lung capacity)
- Plethysmography
- He (helium) dilution
- N2 (nitrogen) wash-out
- most conventional models cant measure residual volume, and hence cannot determine TLC
Indications of Static Lung Volumes and TLC
Measurements of static lung volumes are used to establish of confirm a diagnosis of “restrictive” ventilatory defect
-definition: restrictive diseases require a reduction in TLC (total Lung capacity)
GCC Plethysmograph
whole body. patient sits inside the box
Pressure Transducer + Closed Shutter
The principle of measuring thoracic gas volume (Vtg) using a body plethsmograph is based on Boyl’s aw
P1 x V1= P2 x V2
therefore V1 = (DeltaV/deltaP) x P1
Pant against Closed shutter. panting creates +ve pressure around lung, reduced lung volume
=the volume for any given pressure is directly proportional to the amount of space there was originally
=calculate what the original volume was
If know what total pressure of the system is, can calculate the Volume of gas sitting in lung
30sec
2. Then do Total Lung capacity (max)
and breath out fully to get to Residual volume (min)
Quick. Easy. Repeatable. Tells what you want to know (how much gas can the thorax hold)
Helium Dilution
The He dilution method for measuring FRC (and TLC) uses the conservation of mass principle to measure the total volume of gas in the lung
C1 x V1 = C2 x V2
-conservation of mass
-spirometer with known volume of gas (v1) with known conc of He (C1). attach yourself to this. Breath relatively quickly and deeply.
Measure fluctuations of He conc. at much
When in complete equilibrium (no change in healium conc. Spirometer He conc = Lung He conc.) know what C2 is. V2=V1-V2
Negative= only measures volume of gas that communicates with mouth. if have collapsed airways in different areas it wont work.
Nitrogen wash out
Collect all Nitrogen out of lungs (tends towards 0 know have got all Nitrogen out (little trickles in from circulation))
Inhale 100% O2, collect expirate
Know composition of airway gas: N2 79%. O2 21%. CO2 0%
Composition of alveolar gas: N2 79%. O2 16%. CO2 5%
-Nitrogen composition is same in airways and alveoli (know total amount of No2 comes out and start conc. times = know original vol)
C1 x V1 = C2 x V2
Vn2 / 0.79 = V(FRC)
Negative: a) if there is Gas trapping/poor communication b/w air spaces, doesnt always total vol of gas in thorax. b) If really diseased takes a long time to wash all the gas out (people most interested in doing test on are the worst people to do it on)
Dynamic and Static Lung Volumes
Compare Dynamic and Static lung volumes —> figure out Residual Volume
FRC Function Residual Capacity is the most important lung volume (can increase/decrease if Residual Volume increases and decreases)
-Physiological reasons as to why having a Large Residual volume is really bad
-Spirometry cant see anything wrong as FEV1 hasnt changed.
TLC is relatively less important rarely reach that max
Alveolar Capillary Diffusion Assesment
Single-Breath Carbon Monoxide Diffusing Capacity (D(LCO)) (diffusion of lung forCO2)
Dlco (Tlco)
-Evaluates the transfer of gas from the air spaces into the pulmonary capillaries
Alveolar Capillary Diffusion Assessment Indications
Evaluation and follow up parenchymal lung disease
Differentiating among chronic bronchitis, emphysema (reduced SA), and asthma
Evaluation of pulmonary involvement in systemic diseases
Prediction of arterial desaturation during exercise in some patients with lung disease (is diffusion limited in exercise)
What is D(L(CO))?
Diffusion of the lung for CO2
Fick Equation
dn/dt = -DA (dc/dx)
dn/dt = Rate of diffusion =V.CO
Rate of diffusion = - Diffusion coefficient x Area (concentration gradient/thickness)
Use SA and thickness of alveolar-capillary membrane
D= Diffusion coefficient= constant used for most biological membranes
dc= concentration gradient = (PACO-PCCO)
V.CO= -Dlco x (Paco-Pcco)
=-DA/dx x (Paco-Pcco)
Dlco = V.co/(Paco-Pcco) = Volume of CO2 consumed / average concentration gradient over alveolar-capillary membrane
Alveolar Gases During Diffusion Assessment
Inhale gas trace amounts of methane and CO from residual volume
Methane doesnt undergo gas exchange (doesnt pass through membranes easily)
-Concentration at end of test will be the same as methane at start of test
-if CO was same concentration, CO would have started at same points
-CO change allows to calculate mean driving force over alveolar capillary membrane (Rate calculated using time and Volume) (rate at which capillary is taking up CO2 with respect to pressure driving it)
Alveolar Gases During Diffusion Assessment in a diseased patient
Gas exchange isnt occuring as effectively
difference between expirate CH4 and CO is less (Lines closer and closer together)
-Less gas exchange occuring
Why do use CO in Alveolar Gases During Diffusion Assessment
trace amounts not harmful
- CO follows the same diffusion path as O2 (similar molecular weight)
- The rate of diffusion is much lower than O2 or CO2
- (cannot measure accurately as efficiency of gas exchange /O2 absorption occurs to quickly) (CO is relatively slower) - Amount of CO transported across alveolar capillary membrane is DIFFUSION LIMITED and during the test CO NEVER EQUILIBRIATES with pulmonary capillary plasma
- As haemoglobin binds (200x greater affinity to Hb vs O2) avidly to CO the concentration of CO in the pulmonary capillary plasma can be considered to be Zero (only have to measure partial pressure on alveolar side to know gradient. dont have to use gas in plasma)
Bronchodilator response
The degree to which bronchodilators can ameliorate the effect of airway obstruction can be assessed with PFTs
-Spirometry –> high dose as possble –> measure FEV1
Reversibility is usually indicated by an increase in FEV1 of 12-15% and an increase in FEV1 of 200ml or greater
= =ve positive bronchiodilator response for that day, with that dose, with that type of medication
