Pulmonary Function Studies: Review By Elizabeth Kelley Buzbee AAS, RRT- NPS, RCP Lone Star college Systems- Kingwood

Identify the indications for PFT

answer according to the AARC CPG, PFT need to be done to: [1] diagnosis restrictive defects, [2] to differentiate between restrictive and obstructive defects, [3] assess the patient’s response to interventions [4] pre-op assessment of patients at risk for pulmonary limitations [5] evaluate pulmonary disability [6] Quantify air trapping; is it getting worse, better

What are the hazards of PFT?

answer According to the AARC CPG, the relative contraindications include [1] untreated pneumothorax [2] hemoptysis [3] unstable hemodynamics [4]aneurysms. – If persons have claustrophobia, upper body paralysis or cast that makes the ‘body box’ impossible, this single test may be deferred.

Identify this type of pulmonary function study

answer This is a flow volume loop used to find both obstructive and restrictive defects. The shape of the curve can give the RCP information about where an obstruction is located: intra-thoracic large airway, large fixed or small airways

Read the FVC of the blue tracing and compare it to the normal one

answer The FVC of the blue tracing on the flow volume loop is 200 ml [the line starts at 100 so we need to subtract that from the end point] The FVC of the normal flow volume loop is 600 ml. The percent of predicted is 200/600 or 33% of predicted There is very severe derangement of the FVC values

Is the blue tracing consistent with a restrictive defect or an obstructive defect?

answer The blue tracing is 33% of predicted which demonstrates a very severe restrictive defect.

Identify the peak inspiratory flow rate of the blue tracing Identify the peak expiratory flow rate of the blue tracing

answer the peak inspiratory flow rate of the blue tracing is about 65 LPM The peak expiratory flow rate is also about 65 LPM

Compare the blue tracing of the PIFR to the normal one Compare the blue tracing of the PEFR to the normal one

answer PIFR is about 80 LPM so 65/80 = 81% predicted or normal PEFR is about 100 LPM so 65/100 is 65% of predicted which is consistent with mild airway obstruction

Discuss the clinical significance of VT that is 50% of predicted.

answer A V T by itself is not too helpful; we could have a restrictive defect or an obstructive one. The most use we get out of this value is during weaning parameters.

Discuss the clinical significance of a FEV1 that is 45% of predicted

answer A FEV1 that is 45% of predicted implies that there is a severe obstructive defect, but we need to see the FVC also If both are down, we may have restrictive defect If FVC is ok, but there is a lower FEV1 then it is clear we have obstruction Calculate the FEV1/FVC. A normal person should be able to exhale 70% of his FVC in the first second

Discuss the clinical significance of a FEV1/FVC that is higher than normal.

answer The person with a FEV1/ FVC that is high may have a normal exhaled flow, but have a low FVC due to a restrictive defect.

Discuss the clinical significance of an elevated FRC.

answer High FRC implies that there is air trapping which is associated with obstructive defects

Discuss the clinical significance of a TLC that is 135% of predicted

answer TLC that is elevated shows significant hyperinflation if the FRC is also higher than normal

If a person’s RV is increased what problems does this imply?

answer An elevated RV implies that there is air- trapping associated with obstructive defects such as asthma, COPD or emphysema

How do we ask a patient to perform the flow volume loop?

answer We ask him to perform a FVC into the computer which will display the graphics We ask him to inhale as deeply as possible from the end expiratory of a normal breath then exhale as completely and as quickly as possible

What is the function of the MVV?

answer The MVV is used to monitor the ability of a patient to maintain rapid and deep breaths over a period of time The person with significant obstruction cannot do this because he will start to air trap The person with restrictive defect will have problems getting a big enough VT with each breath---the most important diagnostic benefit of looking at the MVV is assessing the patient for his ability to tolerate pulmonary rehabilitation

How do we measure a value like the RV that cannot leave the body?

answer To collect the value of the RC which is needed to calculate the FRC, we need to measure this volume indirectly by helium dilution studies or by N2 washout [over several minutes]

What is the function of the single breath N2 washout study

answer In the single-breath N2 washout study we are looking at gas distribution which is directly related to the level of airway obstruction

What is the significance of having a higher TGV by body box than TLC by helium dilution

answer If the body box results in a higher volume than the helium dilution, it is because there are airways that have not been exposed to the other airway—they are completely obstructed

What circumstances can result in decreased diffusion of Carbon monoxide during diffusion studies?

answer Any disorder that results in hypoxemia can result in diffusion defect. If there are no s/s of restrictive or obstructive defects on PFT, but there is diffusion, we worry about disorders such as pulmonary emboli.

Case study # 1 Your patient is a 45 YO Asian male who presents with episodes of SOB associated with weather changes and increased activity. He is tested in the Pulmonary function lab: you see the following: FVC - 63% predicted Slow VC - 88% predicted What does this imply?

answer If the slow VC is higher than the forced VC, we may have an obstructive defect without a restrictive componant

He also has this: – IC – 89% predicted – FRC- 136% predicted – PEFR – 65% predicted – PIFR 91% predicted

answer – IC – 89% predicted- this is WNL and shows that there is no restrictive defect – FRC- 136% predicted- this shows that there is no restrictive defect. But that there is obstructive defect associated with air trapping – PEFR – 65% predicted- the peak flow is decreased showing mild obstructive defect – PIFR 91% predicted is WNL; there is no upper airway obstruction

He has the following data: FEV 1 62% predicted FEV 1 /FVC 67% predicted FEV 25-75% 65% predicted MVV – 54% of predicted

answer FEV 1 62% predicted: implies that there is moderate obstructive defect FEV 1 /FVC 67% predicted: supports this obstructive defect FEV 25-75% 65% predicted- mild obstruction in the smaller airway MVV – 54% of predicted: shows that this patient would have poor exercise tolerance, but could undergo pulmonary rehab

What is your overall impression of this patient?

answer This patient has several indices for mild- moderate obstructive defect with air trapping This patient has no evidence of restrictive defect

Case study #2 Your patient is a 58 YO LAF who presents with the following s/s: She is in considerable respiratory distress at rest with RR 25 BPM, HR 109 with sinus tachycardia. Systemic BP is 156/99. She is afebrile at this time, but has recurrent pneumonias over the last few years. On 12-lead EKG we see right axis deviation.

She has the following PFT: FVC - 49% predicted Slow VC - 49% predicted IC – 50% predicted FRC- 45% predicted

answer FVC - 49% predicted: implies there is might be a severe restrictive or obstructive defect Slow VC - 49% predicted: supports a severe restrictive defect IC – 50% predicted: implies moderate restrictive defect FRC- 45% predicted: implies there is severe restrictive defect

answer The patient has the following parameters on PFT: PEFR – 88% predicted before and after BD: no obstructive defect PIFR 95% predicted no obstructive defect FEV 1 120% predicted: WNL no obstructive defect FEV 1 /FVC 145% predicted: implies there is restrictive defect FEV 25-75% 98% predicted: no obstruction in the small airways MVV – unable to complete

What is your overall impression of this patient?

answer This patient has moderate-severe restrictive defect with no obstruction