Diminished Alveolar Microvascular Reserves in Type 2 Diabetes Reflect Systemic Microangiopathy

Abstract

OBJECTIVE—Alveolar microvascular function is moderately impaired in type 1 diabetes, as manifested by restriction of lung volume and diffusing capacity (DLCO). We examined whether similar impairment develops in type 2 diabetes and defined the physiologic sources of impairment as well as the relationships to glycemia and systemic microangiopathy.RESEARCH DESIGN AND METHODS—A cross-sectional study was conducted at a university-affiliated diabetes treatment center and outpatient diabetes clinic, involving 69 nonsmoking type 2 diabetic patients without overt cardiopulmonary disease. Lung volume, pulmonary blood flow (Q̇), DLCO, membrane diffusing capacity (measured from nitric oxide uptake [DLNO]), and pulmonary capillary blood volume (VC) were determined at rest and exercise for comparison with those in 45 healthy nonsmokers as well as with normal reference values.RESULTS—In type 2 diabetic patients, peak levels of oxygen uptake, Q̇ and DLCO, DLNO, and VC at exercise were 10–25% lower compared with those in control subjects. In nonobese patients (BMI <30 kg/m2), reductions in DLCO, DLNO, and VC were fully explained by the lower lung volume and peak Q̇, but these factors did not fully explain the impairment in obese patients (BMI >30 kg/m2). The slope of the increase in VC with respect to Q̇ was reduced ∼20% in patients regardless of BMI, consistent with impaired alveolar-capillary recruitment. Functional impairment was directly related to A1C level, retinopathy, neuropathy, and microalbuminuria in a sex-specific manner.CONCLUSIONS—Alveolar microvascular reserves are reduced in type 2 diabetes, reflecting restriction of lung volume, alveolar perfusion, and capillary recruitment. This reduction correlates with glycemic control and extrapulmonary microangiopathy and is aggravated by obesity.