Abnormal ventilatory responses to hypoxia in Type 2 diabetes

Aims: The incidence of Type 2 diabetes is increasing, along with its associated micro- and macrovascular disease manifestations. Previous studies indicate that patients with Type 2 diabetes exhibit abnormal cardiopulmonary reflex responses to various stimuli, although the impact of hypoxia, a common physiological stimulus, on ventilatory responses has not previously been studied in humans with Type 2 diabetes. Methods: Minute ventilation (V̇_E) breathing pattern responses (total breath time, T _TOT; expiratory time, T_E; inspiratory time, T_I; inspiratory duty cycle, T_I/T_TOT) were measured during 5 min each of normoxia and isocapnic hypoxia (arterial O₂ saturation -85%) in eight subjects with Type 2 diabetes and seven age- and body mass index-matched healthy subjects. Results: During normoxia, V̇_E was similar in control and diabetic subjects (6.4 ± 1.2, 6.4 ± 1.1 l/min, respectively). In response to hypoxia, V̇_E significantly increased in both groups (to 17.0 ± 5.0 and 9.5 ± 2.0 l/min, respectively, P < 0.05), but the magnitude of increase in V̇_E. was significantly less in diabetic than in control subjects (P < 0.05). In addition, the breathing pattern response to hypoxia differed between groups in terms of T_I/T_TOT and T_TOT (P < 0.05), with control subjects significantly decreasing T_TOT and T_E (P < 0.05) while diabetic subjects tended to increase both. Conclusions: Relative to matched control subjects, Type 2 diabetic subjects exhibit blunted V̇_E responses to acute isocapnic hypoxia, suggesting that this group of diabetic subjects possesses a chemoreflex ill-equipped to respond homeostatically to hypoxic challenge.