PULMONARY DYSFUNCTION IN TYPE-1 DIABETES IN RELATION TO METABOLIC LONG-TERM CONTROL AND TO INCIPIENT DIABETIC NEPHROPATHY

The available data on pulmonary function in type 1 diabetes are still conflicting. Recently, restrictive alterations of pulmonary function w ere demonstrated in type 1 diabetic patients with end-stage renal fail ure (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 diabete s and the relationship of pulmonary function tests to incipient diabet ic nephropathy and metabolic long-term control were analyzed. Pulmonar y function tests were performed in longstanding type 1 diabetic patien ts (n = 39) with normal serum creatinine levels (< 1.3 mg/dl) and the results compared with those of healthy controls (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 pul monary function tests (performed by standardized spirometry and whole- body plethysmography) as compared with controls (C) in diabetic patien ts with microalbuminuria (M) and in diabetic patients with normoalbumi nuria (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 (FEV (1); % predicted: M 81.2, p < 0.002; N 88.8, p < 0.02; C 93.8), and di ffusing 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 ai rway resistance (kPa/l/s: M 0.22, p < 0.03; N 0.2, p = NS; C 0.18). Th e differences in TLC (% predicted) between diabetic patients with norm o- and microalbuminuria were significant (p < 0.04). Further a close r elation of pulmonary function tests to metabolic long-term control (me an values of repeated HbA(1c) measurements) was observed: TLC (% predi cted: 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 FEV(1) (% predicted: M r = -0.50 , p < 0.03; N r = -0.62, p < 0.003). In conclusion: pulmonary dysfunct ion in long-standing type I diabetic patients is more pronounced in pa tients with increased AER. Typical features of restrictive pulmonary d efects, namely a reduction of TLC (% predicted) plus DLCO (% predicted ) were observed predominantly in patients with incipient diabetic neph ropathy. The clear correlation of pulmonary function tests with HbA(1c ) measurements stresses the importance of optimal metabolic long-term control in type 1 diabetes.