Diabetes worsens pulmonary diffusion in heart failure, and insulin counteracts this effect

Chronic heart failure (CHF) (hydrostatic stress) and diabetes (basal laminae thickening) share the potentiality of damaging the alveolar-capillary membrane. We investigated 15 control subjects and 3 groups of 15 patients each having type 2 diabetes (Group 1), CHF (Group 2), and diabetes and CHF (Group 3), to probe whether addition of diabetes worsens lung diffusion in CHF and whether insulin counteracts this effect. Compared with control subjects, carbon monoxide diffusing capacity (DLCO) and diffusing capacity of the alveolar-capillary membrane at rest were increasingly depressed from Group 1 through Group 3. DLCO was lower than predicted in 11 patients each in Groups 1 and 2 and in all patients in Group 3. Regular insulin (10 IU) was ineffective in CHF alone, whereas it improved DLCO and diffusing capacity of the alveolar-capillary membrane in diabetes; changes, however, were significantly greater in the patients with both diabetes and CHF (+17.6%, +27.3%) than in those with diabetes alone (+9.2%, +13.1%). Insulin did not affect lung spirometry, volumes, and hemodynamics. Thus, gas transfer is depressed in a number of patients with diabetes or CHF; comorbidity increases the frequency and extent of this disorder. Insulin facilitates diffusion in diabetes, through an influence on alveolar-capillary conductance, and its efficacy is greater in comorbidity; diabetes is more disturbing in patients with CHF and produces a synergistic rather than a simple additive effect.