Using inhaled hyperpolarized 3Helium (3He) and diffusion-weighted magnetic resonance (MR) imaging, anatomically correlated maps of the Apparent Diffusion Coefficient (ADC) of 3He gas, an indirect measurement of the degree of restriction placed upon random motion of 3He atoms within the lung, can be produced. ADC values thus reflect the size of the airspaces, and are greater in emphysema. (D.A. Yablonskiy et al, PNAS 99(5): 2002 pp 3111–3116.). We used ADC measurements as a noninvasive means to explore the effects of surgery for emphysema on airspace structure at the microscopic level, and thus elucidate the anatomical alterations underlying postoperative subjective and physiologic changes.
Six patients undergoing surgical therapy for treatment of severe emphysema were scanned pre- and post-operatively. The resulting mean ADCs were analyzed in the context of traditional assessment tools such as dyspnea indexes and pulmonary function tests.
The results for the six patients are shown in the following table.
PatientInterventionPre/Post Mean ADC (Cm2/sec)Pre/Post FeV1 (Liters)Pre/Post RV/TLCPre/Post 6Minute Walk (Feet)Dyspnea Index Scores1Bil LVRS.48/.48.96/2.1073%/49%1325/1675Improved2Bil LVRS.60/.56.54/1.0480%/57%1350/1650Improved3Bil LVRS.50/.43.54/1.0578%/43%1125/1650Improved4Left BULL.47/.48.88/1.2375%/55%1350/1710Improved5Left BULL.40/.44.99/1.5170%/54%800/995Improved6Left BULL.42/.352.42/2.6756%/39%1800/1500Improved
(LVRS=Lung Volume Reduction Surgery, BULL=Bullectomy)
Surgery for emphysema produced little change in mean ADC, suggesting that peripheral airspace size remains stable after resection of emphysematous lung tissue. Postoperative subjective and physiologic changes were unrelated to an effect of surgery on airspace size as measureable by this techniques. Pre- and postoperative changes in antomical distribution of ADC may correlate more closely with outcome.
Surgical intervention in meticulously selected patients with emphysmea improves dyspnea and physiological parmaters including 6 minute walk distance. Since these improvements are not correlated with a mean change in peripheral airspace size, it may imply that these changes do not reflect a change in the underlying structural abnormality in the lung.
B.A. Lutey, None.