These tests check how well air/oxygen enter and moves within the airways.
The common PFTs are –
Spirometry
Diffusion studies
Body plethysmography.
Among these three, spirometry is most commonly used to diagnose COPD.
Blood gas measurements are made to evaluate the patients acid/base balance and oxygenation.
PH is a measurement of free hydrogen ion concentration in the blood. It is determined by the ratio of acids and bases present and levels indicates whether blood is normal, acidic or alkaline.
Normal Blood Gas Values
Normal PH – 7.40 Acidosis < 7.35 Alkalosis - > 7.45 Oxygen saturation – 95% or more Bicarbonate – 22-26 m Eq/L Partial atmospheric Oxygen (PaO2) - 80-100 torr Partial atmospheric CO2 (PaCO2) 35-45 torr
When PaCO2 is evaluated and pH falls abruptly, it is associated with acute respiratory failure.
When PaO2 is less than 60 torr and PaCo2 is elevated but PH is near normal, it indicates chronic changes.
In COPD, despite normal food intake, there is an imbalance between energy intake and expenditure. There is an increase in the REE (Resting energy expenditure). There is increased catabolism and muscle protein breakdown along with pronounced systemic inflammation.
The greater the severity of airflow obstruction, the higher the weight loss. This leads to impairment of lung structure, disturbances in defence mechanism and in decreased exercise tolerance.
Last modified: Saturday, 5 November 2011, 10:44 AM
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