PFT detects the impairment and assesses the effect of treatment and progress in the disease. It is done to assess the lung capacity, and it determines how quickly the lung can move air in and out. Spirometry is the common lung function test.
In respiratory function test, lung volume, gas exchange capacity and airway, narrowing is quantified and compared with normal values adjusted for age and gender. The most convenient home monitor test is peak flow meter, but values are an effort dependent.
Abbreviations used in PFT.
X FEV1 forced expiratory volume in 1 second
X FVC forced vital capacity.
X VC vital capacity
X PEF peak expiratory flow.
X TLC total lung capacity
X FRC functional residual capacity
X RV residual volume
X TLCO Gas transfer factor for carbon monoxide
X DLCO diffusing capacity for carbon monoxide
X KCO transfer coefficient for carbon monoxide
Measurement of gas transfer factor.
The gas transfer factor may be thought of as the conductance of the lungs for the gas being studied. It forms the useful overall estimate if the ability of the lungs to exchange gases and is of particular value in interstitial lung disease, sarcoidosis and emphysema. It is normally estimated by measuring the uptake of carbon monoxide from a single breath of a 0.3% mixture in air.
Arterial blood gas analysis
Modern automatic analysers give a rapid direct read out of PaO2(Partial pressure of arterial oxygen) , PaCO2( Partial pressure of carbon dioxide in the blood) and H ion concentration in arterial blood, often supplemented by derived variables, which may be of value in assessment of hypoxemia or acid base balances, which may be of value in assessment of hypoxemia.
PATTERNS OF ABNORMAL VENTILATORY CAPACITY TEST | OBSTRUCTIVE | RESTICTIVE |
| FEV1 | DECRESED | DECREASED |
| VC | DECREASED/NORMAL | DECREASED |
| FEV1/VC | DECREASED | NORMAL/INCREASED |
