Respiratory Function Tests

Fiona Gilmour

SHO

03/06/04

Respiratory Function Tests

Mechanical Function– Spirometry– Lung Volumes– Diffusion Capacity

Gas Exchange Function– Arterial Blood Gases

Use? Do not predict individual risk of pulmonary

complications– Smoking– Exercise tolerance– Type of surgery

Those who benefit pre-op– Equivocal clinical or CXR findings to aid Dx– Functional ability cannot be assessed eg Physically

disabled– Thoracic resections - specific requirements

Most useful for monitoring response to therapy/ following progress of disease

Validity depends on– Co-operation and technique of patient– Experience of operator– Quality of equipment

Various patterns overlap so difficult to interpret

Spirometry

Lung Volumes

VT = volume breathed in and out in relaxed breathing

IRV = extra volume that can be inhaled with maximum effort

ERV = extra volume expired with maximum effort

IRV+VT+ERV = Vital capacity (VC)

ERV+RV = Functional residual capacity (FRC)

Spirometry 2

FEV1 = volume exhaled in 1 second FVC = total forced volume exhaled FEV1/FVC% PEF = Peak expiratory flow during forced expiration All values compared to predicted values based on

– Age

– Sex

– Height +/or weight

– Race

Spirometry 3

Specific disease patterns can be seen based on these values– Obstructive– Restrictive

Normal FEV1/FVC is 80% If obstructive picture found

response to bronchodilators is measured

Spirometry 4

Obstructive Restrictive

FEV1 Reduced + Reduced FVC Reduced Reduced + FEV1/FVC% Reduced ++ Normal/High VC Normal/reduced Reduced ++ FRC Normal Reduced RV High Reduced TLC High Reduced

Expiratory Flow

Measured on spirometer or peak flow meter Compared with predicted values Reduced values indicate airflow obstruction If diary kept indicates current fitness Maximum flow rates at different stages of VC can

also be measured– indicates small airway function

PEF <200L/min effective cough is difficult

Diffusion Capacity

Carbon monoxide diffusing capacity (DLCO) is rate of transfer of CO from inspired gas to pulmonary capillary (transfer factor)

Indicates health of alveolar-capillary membrane Useful for evaluation of Emphysema Does not indicate gas exchange Measured by single breath test RV can be measured at the same time using

Helium

Relevance to Thoracic

Need to assess cardiorespiratory reserve Can estimate post op lung function Needs to be considered in context of patients health

and proposed resection 3 Groups

– Fit, good exercise tolerance, normal spirometry

– major med probs, min ex tol, grossly abnormal spirometry

– Mod coexisting disease, reduced ex tol, abnormal spirometry

Cont.

Post op estimate FEV1 <800L or FVC < 15ml/kg increases risk, difficult to cough and may need ventilation

Post op estimate = Pre op value x (5 - no.lobes resected) / 5

Goal is post op value FEV1 > 35% predicted Minimum pre op FEV1

– Pneumonectomy >55%

– Lobectomy >40%

– Wedge >35%