Pulmonary functions in patients with diabetes mellitus

Original Article Address for correspondence: Dr. Muhammad Irfan, The Aga Khan University Hospital, Stadium Road, P.O. Box 3500, Karachi 74800, Pakistan. E-mail: muhammad.irfan@aku.edu Access this article online Quick Response Code: Website:


INTRODUCTION
The association of reduced lung function and diabetes mellitus (DM) has been described for many years. [1]4][5][6][7][8][9][10] Davis et al. [2] suggested that the lung is a target organ in DM and that glycemic exposure is a strong determinant of reduced pulmonary function in type 2 patients.Theoretically, several pathological changes may affect the lungs in patients with DM.Ljubic et al. [11] showed that diabetes could lead to the development of pulmonary complications due to collagen and elastin changes.Another theory suggested acute or chronic pulmonary disease were recruited.Sixtyfour of these subjects had DM and 64 were healthy matched controls.The patients with DM were selected from the outpatient department of AKUH.Healthy matched controls were selected from the Executive Clinic of AKUH.They were non-smokers, non-diabetics, and had no history of any acute or chronic lung disease and they came for their routine check ups.
The detailed history and physical examination was carried out by a specialist physician.All patients having any acute or chronic pulmonary disease, and smokers (defined as smoking of any number of cigarettes) were excluded.Informed consent was taken from all subjects.
The study was approved by Institutional Review Board (IRB) of Aga khan University.

Anthropometric measurements and biochemical profile
Standing height and weight of the patient were measured and body mass index (BMI) was calculated.Fasting and random blood sugars and fasting lipid profile were checked.

Pulmonary function test
Pulmonary functions including forced vital capacity (FVC), forced expired volume in one second (FEV 1 ), FEV 1 /FVC ratio, slow vital capacity (SVC), and peak expiratory flow rate (PEFR) were measured by spirometer MedGraphics Profiler (pulmonary diagnostic system by Medical Graphic Corporation, USA) according to the American Thoracic Society (ATS) criteria. [16]irometry was performed before and 15 min after inhalation of 0.2 mg salbutamol inhaler (Made by GlaxoSmithKline, Pakistan) at room temperature ranged from 19°C to 24°C, with a mean of 22±0.5.The subject breathed in from room air and then exhaled into the spirometer.The wedge opened as air was blown into the spirometer, and a marker moved accordingly along a sheet of paper for 6 seconds.The spirometer was computerized and printed the FEV 1 and FVC values after the forced expiration had been performed.There was no time lag between the onset of forced expiration and the onset of timing for FEV 1 .No extrapolation was performed.Best of three satisfactory readings was taken for the analysis.Highest value for FVC and the highest value for FEV 1 were used in the ratio FEV 1 / FVC.The variables were reported in absolute volume as well as the percent predicted based on the regression equations.

Statistical analysis
Statistical analysis was performed using SPSS version 15.0 for windows (SPSS Inc., Chicago, IL, USA).Patients with diabetes were compared with those without diabetes for all subjects using independent t-test.For the analysis, χ 2 -test and Fisher's exact test were used for categorical variables.Logistic regression was used to examine the patients with diabetes with those without diabetes.

RESULTS
Sixty four patients with DM (37 male) and 64 matched controls (39 male) were selected.The mean age of diabetic patients and matched control were 54.3±9 and 54.0±8 (P<0.87)years, respectively.Demographics and biochemical profile of both groups are presented in Table 1.Diabetic patients have higher blood pressures (P<0.001)than nondiabetics.There was also a significant higher level of triglycerides noted among diabetics (P<0.001).

DISCUSSION
Our study shows decreased pulmonary function impairment in diabetic patients.This association is explained by age, sex, and BMI.Diabetics showed a significant reduction in FVC, FEV1, and SVC, relative to their matched controls.However FEV 1 /FVC was less in diabetics but was statistically nonsignificant.
Meo et al. [3,4] in their studies on Saudi diabetic patients showed significant reduction in FVC, FEV1, and PEF, as compared to their matched controls.They also showed a strong association with a dose-effect response of duration of disease and decreased pulmonary function impairment in their diabetic patients.A study published from the neighboring country India [17] showed a significant reduction in DLco in diabetic patients as compared to the controls but they failed to show any differences among the groups for other pulmonary functions; FVC, FEV1, PEF, and maximal static inspiratory and expiratory pressures.The major limitation in that study was a very small number of patients in each group.
Davis et al. [2] conducted a large community-based study in Western Australia in type 2 diabetic patients and demonstrated that VC, FVC, FEV1, and PEF were decreased in type 2 diabetic patients.They also suggested that the reduced lung volumes and airflow limitation are likely to be chronic complications of type 2 diabetes.
Asanuma [9] also reported that FVC and FEV1 were reduced in Japanese diabetic subjects compared to control subjects.
The pathophysiology for reduced lung functions in diabetics is still not very clear but there have been some reports of histopathological changes in the lungs of diabetic patients, including basal lamina thickening [18] and fibrosis. [19]Impairment in lung function of patients with diabetes are believed to be the consequence of biochemical alterations in the connective tissue constituents of the lung, particularly collagen and elastin, as well as microangiopathy due to the nonenzymatic glycosylation of proteins induced by chronic hyperglycemia. [6,11,20,21]he functional abnormalities ensuing from these changes manifest clinically by way of a reduction in elastic recoil of the lung, lung volumes, and pulmonary capacity for the diffusion of carbon monoxide. [21]The concomitant pulmonary structural impact of these biochemical alterations, described to date, consist of a thickening of the alveolar epithelial basal lamina [22] and a specific type of nodular fibrosis of the lung. [19]Autonomic and phrenic neuropathy causing alterations in bronchial reactivity and respiratory muscle function was also suggested in one study. [23] our study, diabetic patients had significant hypertriglyceridemia as compared to controls.This finding was not observed in other studies.Sinha et al. [17] in their study showed a significant correlation between decreased DLco and cholesterol level.Dyslipidemia might have a contributory role in the pathogenesis of decreased lung functions in diabetic patients.
Our study has several limitations.First, there are less number of patients so we cannot generalize the result in different ethnic groups of Pakistan.Second, we have not checked the DLco in our patients.Several studies showed that DLco is significantly reduced in diabetic patients, even in patients with normal spirometric values.DLco was not done because the cost issues may not be available in most developing country settings.Third, we have not checked the association between the glycemic control and reduced lung function.
In summary, our study also supports the other studies that diabetic patients showed impaired lung function independent of smoking.There was a decrease in FVC, FEV 1 , and SVC as compared to their controls.This reduced lung function is likely to be a chronic complication of diabetes mellitus.Lung functions need to be checked periodically to assess the severity of impairment.There is a need of larger prospective study with long observational course to confirm these observations.

Table 2 : Pulmonary functions test in diabetics and non- diabetics
FVC: Forced vital capacity; FEV 1 : Forced expiratory volume in 1 second; SVC I: Slow vital capacity; MMEF: Maximum mid-expiratory flow