Background: Although hypothyroidism has an insidious onset and relatively asymptomatic, exertional dyspnea and fatigue can be the presenting complaints.
Objectives: The aim is to assess functional lung impairment in hypothyroid patients both at rest and during exercise.
Methods: A case-control study was carried out on 42 patients with newly diagnosed hypothyroidism and 12 control subjects. Hypothyroidism was diagnosed based on high value of thyroid stimulating hormone (TSH) ≥6 μIU/ml, and low value of free thyroxin (FT4) ≤0.8 ng/dl, both groups had chest X-ray, spirometry, diffusing capacity of the lungs for carbon monoxide (DLCO), arterial blood gases (ABGs) and symptom-limited exercise testing using treadmill.
Results: Both groups were comparable as regard age, sex, and body mass index. Although ABG and spirometry were within normal in both groups, forced vital capacity %, and forced expiratory flow (FEF25-75) % were significantly reduced in the hypothyroid group (P = 0.014, 0.000, respectively), DLCO significantly reduced in hypothyroidism (P = 0.005). As regard exercise testing parameters, maximum oxygen consumption %, minute ventilation, tidal volume, and oxygen pulse were significantly reduced in hypothyroidism (0.005, 0.000, 0.000, and 0.02 respectively). TSH significantly negatively correlated with forced expiratory volume in 1 s %, FEF25-75%, and DLCO while they significantly positively correlated with FT4.
Conclusion: Even with the presence of normal chest X-ray, arterial blood gases, and spirometry in patients with hypothyroidism DLCO and exercise testing parameters can be significantly reduced.
Keywords: Arterial blood gases; exercise; hypothyroidism; resting pulmonary function.