Regional structure-function correlations in chronic obstructive lung disease measured with positron emission tomography.

BACKGROUND

Positron emission tomography, performed with isotopes of very short half life, can be used to relate local lung tissue density to local ventilation and to the ventilation:perfusion ratio. This method has been used in 10 patients with severe chronic airflow obstruction and differing values for carbon monoxide transfer factor (TLCO) and transfer coefficient (KCO).

METHODS

Ventilation (VA) and the ventilation:perfusion ratio (V/Q), lung density, and blood volume were measured regionally in a single transaxial section at mid-heart level with the patients in a supine position. Alveolar volume, extravascular tissue lung density, and perfusion (Q) were derived. Twenty five regions with abnormalities in the ventilation images were analysed.

RESULTS

Tissue density showed a negative correlation with the ratio V/Q (r = 0.55) and a positive correlation with Q (r = 0.59) and blood volume (r = 0.65). In four patients with a low carbon monoxide transfer factor (TLCO) and transfer coefficient (KCO) < 50% predicted many regions with low VA had low tissue density and normal or high V/Q. On the other hand, in four patients with TLCO and KCO > 50% predicted many regions with low VA had normal or high tissue density and low values of V/Q. The other two patients had patterns between these two extremes. Individual ratios between mean values of tissue density and V/Q had a positive correlation with KCO (% pred; r = 0.79).

CONCLUSIONS

These findings link structural differences with distinctive functional patterns; they reinforce the view that bronchial inflammation or oedema predominate in some patients with chronic airflow obstruction, whereas alveolar destruction is the major feature in others.