Pulmonary function tests in type 2 diabetes mellitus and their association with glycemic status and insulin resistance

Type 2 diabetes mellitus (T2DM) is associated with long-term complications in different organs, and this is attributable to macrovascular and microvascular changes as reported by Fowler. Pulmonary complications, however, have been poorly characterised.

The present study was a case–control study done at SRN Hospital, Prayagraj to correlate the pulmonary functions with glycemic status and insulin resistance in 100 patients with diabetes (cases) and compare these parameters in patients without diabetes (controls). Baseline values of fasting plasma glucose (FPG), prandial plasma glucose (PPG) and glycated hemoglobin (A1C) were significantly increased in cases as compared with controls.

Forced expiratory volume (FEV1) (78.71% compared with 88.15%) and forced vital capacity (FVC) (67.48% compared with 96.58%) were both decreased in cases compared with controls but as decline in FVC was more compared with FEV1; their ratio, FEV1/FVC (121.70 as compared to 90.19), was increased in cases. FVC decreased with increase in A1C values (96.2%, 84.2%, 71.2% for A1C values 5.7%, 5.7–6.4% and > 6.4% respectively). FVC was also decreased for greater values of Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (98.2% for HOMA-IR < 2.5 and 74.6% for HOMA-IR > 2.5). The ratio of FEV1/FVC was more with higher values of A1C (103.3 for A1C > 2.5 and 91.1 for A1C < 2.5). FVC also decreased with increasing values of FPG (97.4%, 91.1% and 71.2% for FPG values of < 100 mg%, 100–125 mg% and ≥ 126 mg%).

A total of 65% of patients had abnormal pulmonary function tests with predominance of restrictive pattern. This restrictive decline is significantly associated with increasing dysglycemia and insulin resistance. However, it is unrelated to levels of low-density lipoprotein (LDL) and duration of T2DM.