Pulmonary Dysfunction in Type 1 Diabetes in Relation to Metabolic Long-Term Control and to Incipient Diabetic Nephropathy

UNLABELLED: The available data on pulmonary function in type 1 diabetes are still conflicting. Recently, restrictive alterations of pulmonary function were demonstrated in type 1 diabetic patients with end-stage renal failure (diabetic nephropathy), whereas patients with kidney failure from other causes had normal pulmonary function test results. In this study, the prevalence and nature of pulmonary dysfunction in type 1 diabetes and the relationship of pulmonary function tests to incipient diabetic nephropathy and metabolic long-term control were analyzed. Pulmonary function tests were performed in long-standing type 1 diabetic patients (n = 39) with normal serum creatinine levels (< 1.3 mg/dl) and the results compared with those of healthy control (n = 44). The patients were divided into those with a normal urinary albumin excretion rate (AER; n = 21, < 30 mg/day) and those with microalbuminuria (n = 18, AER 30-300 mg/day). We found a significant reduction of the following pulmonary function tests (performed by standardized spirometry and wholebody plethysmography) as compared with controls (C) in diabetic patients with microalbuminuria (M) and in diabetic patients with normoalbuminuria (N): total lung capacity (TLC; % predicted: M 89.6, p < 0.004; N 98.5, p = NS; C 101.1), vital capacity (VC; % predicted: M 83.7, p < 0.001; N 90.2, p < 0.03; C 97.3), forced expiratory volume in 1 s (FEV1; % predicted: M 81.2, p < 0.002; N 88.8, p < 0.02; C 93.8), and diffusing capacity of the lung for CO (DLCO; % predicted: M 83.4, p < 0.04; N 92.4, p = NS; C 95.6). We also found a slight increase of the airway resistance (kPa/l/s: M 0.22, p < 0.03; N 0.2, p = NS; C 0.18). The differences in TLC (% predicted) between diabetic patients with normo- and microalbuminuria were significant (p < 0.04). Further a close relation of pulmonary function tests to metabolic long-term control (mean values of repeated HbA1c measurements) was observed: TLC (% predicted: M r= -0.61, p < 0.007, N p = NS), VC (% predicted: M r = -0.57, p < 0.01; N r= -0.59, p < 0.005), and FEV1 (% predicted: M r = -0.50, p < 0.03; N r= -0.62, p < 0.003). IN CONCLUSION: pulmonary dysfunction in long-standing type 1 diabetic patients is more pronounced in patients with increased AER. Typical features of restrictive pulmonary defects, namely a reduction of TLC (% predicted) plus DLCO (% predicted) were observed predominantly in patients with incipient diabetic nephropathy. The clear correlation of pulmonary function tests with HbA1c measurements stresses the importance of optimal metabolic long-term control in type 1 diabetes.