Lung Function and High Resolution Computed Tomography in Sickle Cell Disease.

Adults with sickle cell disease (SCD) may develop sickle chronic lung disease which appears to be a complication of chronic hemolysis and repeated episodes of pulmonary vaso-occlusion. Pulmonary function tests have usually been used to document the severity of lung disease in SCD, but some patients cannot successfully undertake such examinations. Recently, high resolution computed tomography (HRCT) has been shown to be of value in the evaluation of patients with diffuse lung diseases. Assessment of lung disease in SCD by HRCT, however, has not been fully explored. The study sets out to investigate the relationship of any pulmonary function abnormalities in adults with SCD to a non-invasive measure of hemolysis and findings on HRCT. The study population consisted of 33 Hb SS subjects (12 males) with a median age of 36 (range 17–67) years, median height of 167 (range 53–188) cm, and median weight of 69 (range 52–92) kg.

Pulmonary function was assessed by measurements of lung volumes, spirometry, gas transfer and oxygen saturation, and hemolysis by measurement of end-tidal carbon monoxide (ETCO). The degree of a lobar volume loss and ground glass opacification and prominence of central vessels on HRCT were quantitatively assessed.

There was a wide variation in the lung function of the cohort. Nine patients had a restrictive lung function abnormality, five an obstructive abnormality and four a mixed restrictive/obstructive abnormality. Twenty-seven of the patients completed assessment of ETCO levels. ETCO levels correlated positively with bilirubin levels (r_s=0.66, p=0.0002) and the absolute reticulocyte count (r_s=0.70, p=0.0002), and negatively with hemoglobin (r_s=−0.51, p=0.008). ETCO levels negatively correlated with FEV₁ (p=0.006), VC_pleth (p=0.006), sGaw (p=0.04) and S_pO₂ (p=0.007). A reticular pattern, lobar volume loss and prominent central vessels were the three most common abnormalities on HRCT. FEV₁ (p<0.05), FVC (p<0.005) and TLC (p=0.008) correlated with HRCT findings, particularly lobar volume loss. Lobar volume loss, prominent central vessels and a reticular pattern/ground glass opacification were all present on HRCT in 12 of 18 subjects with a restrictive, obstructive or mixed defect.

Our results suggest that non-invasive assessment of hemolysis and/or HRCT examination might facilitate identification of SCD patients with respiratory function impairment. More of the patients had abnormalities on HRCT than on lung function testing, which suggests that HRCT is a more sensitive detector of respiratory abnormalities than lung function testing. This hypothesis merits testing by serially assessing SCD patients to determine if those with only HRCT abnormalities subsequently develop lung function abnormalities.