Physiological and pathological changes that affect the carbon monoxide diffusing capacity of the lung(DL,CO)
| Extrapulmonary reduction in lung inflation (reduced VA) producing changes in DM or θVc that reduce DL,CO |
| Reduced effort or respiratory muscle weakness |
| Thoracic deformity preventing full inflation |
| Diseases that reduce θVc and thus reduce DL,CO |
| Anaemia |
| Pulmonary emboli |
| Other conditions that reduce θVc and thus reduce DL,CO |
| Hb binding changes (e.g. HbCO, increased FI,O2) |
| Valsalva manoeuvre (increased intrathoracic pressure) |
| Diseases that reduce (in varying degrees) DM and θVc and thus reduce DL,CO |
| Lung resection (however, compensatory recruitment of θVc also exists) |
| Emphysema |
| Interstitial lung disease (e.g. IPF, sarcoidosis) |
| Pulmonary oedema |
| Pulmonary vasculitis |
| Pulmonary hypertension |
| Diseases that increase θVc and thus increase DL,CO |
| Polycythaemia |
| Left-to-right shunt |
| Pulmonary haemorrhage (not strictly an increase in θVc, but effectively an increase in lung Hb) |
| Asthma |
| Other conditions that increase θVc and thus increase DL,CO |
| Hb binding changes (e.g. reduced FI,O2) |
| Muller manoeuvre (decreased intrathoracic pressure as in asthma, resistance breathing) |
| Exercise (in addition, a possible DM component) |
| Supine position (in addition, possibly a slight increase in DM) |
| Obesity (in addition, a possible DM component) |
VA: alveolar volume; DM: membrane conductivity; θ: carbon monoxide (CO)–haemoglobin (Hb) chemical reaction rate; Vc: volume of pulmonary capillary blood; FI,O2: inspired fraction of oxygen; IPF: idiopathic pulmonary fibrosis; Hb: haemoglobin.