Respiratory Function Tests Fiona Gilmour SHO 03/06/04

Respiratory Function Tests n Mechanical Function –Spirometry –Lung Volumes –Diffusion Capacity n Gas Exchange Function –Arterial Blood Gases

Use? n Do not predict individual risk of pulmonary complications –Smoking –Exercise tolerance –Type of surgery n 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 n Most useful for monitoring response to therapy/ following progress of disease

n Validity depends on –Co-operation and technique of patient –Experience of operator –Quality of equipment n Various patterns overlap so difficult to interpret

Spirometry

Lung Volumes n V T = volume breathed in and out in relaxed breathing n IRV = extra volume that can be inhaled with maximum effort n ERV = extra volume expired with maximum effort n IRV+V T +ERV = Vital capacity (VC) n ERV+RV = Functional residual capacity (FRC)

Spirometry 2 n FEV 1 = volume exhaled in 1 second n FVC = total forced volume exhaled n FEV 1 /FVC% n PEF = Peak expiratory flow during forced expiration n All values compared to predicted values based on –Age –Sex –Height +/or weight –Race

Spirometry 3 n Specific disease patterns can be seen based on these values –Obstructive –Restrictive n Normal FEV1/FVC is 80% n If obstructive picture found response to bronchodilators is measured

Spirometry 4

Expiratory Flow n Measured on spirometer or peak flow meter n Compared with predicted values n Reduced values indicate airflow obstruction n If diary kept indicates current fitness n Maximum flow rates at different stages of VC can also be measured –indicates small airway function n PEF <200L/min effective cough is difficult

Diffusion Capacity n Carbon monoxide diffusing capacity (DLCO) is rate of transfer of CO from inspired gas to pulmonary capillary (transfer factor) n Indicates health of alveolar-capillary membrane n Useful for evaluation of Emphysema n Does not indicate gas exchange n Measured by single breath test n RV can be measured at the same time using Helium

Relevance to Thoracic n Need to assess cardiorespiratory reserve n Can estimate post op lung function n Needs to be considered in context of patients health and proposed resection n 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. n Post op estimate FEV 1 <800L or FVC < 15ml/kg increases risk, difficult to cough and may need ventilation n Post op estimate = Pre op value x (5 - no.lobes resected) / 5 n Goal is post op value FEV 1 > 35% predicted n Minimum pre op FEV 1 –Pneumonectomy >55% –Lobectomy >40% –Wedge >35%