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%