Effects of a single bout of interval hypoxia on cardiorespiratory control in patients with type 1 diabetes

Abstract

Hypoxemia is common in diabetes, and reflex responses to hypoxia are blunted. These abnormalities could lead to cardiovascular/renal complications. Interval hypoxia (IH) (5-6 short periods of hypoxia each day over 1-3 weeks) was successfully used to improve the adaptation to hypoxia in patients with chronic obstructive pulmonary disease. We tested whether IH over 1 day could initiate a long-lasting response potentially leading to better adaptation to hypoxia. In 15 patients with type 1 diabetes, we measured hypoxic and hypercapnic ventilatory responses (HCVRs), ventilatory recruitment threshold (VRT-CO2), baroreflex sensitivity (BRS), blood pressure, and blood lactate before and after 0, 3, and 6 h of a 1-h single bout of IH. All measurements were repeated on a placebo day (single-blind protocol, randomized sequence). After IH (immediately and after 3 h), hypoxic and HCVR increased, whereas the VRT-CO2 dropped. No such changes were observed on the placebo day. Systolic and diastolic blood pressure increased, whereas blood lactate decreased after IH. Despite exposure to hypoxia, BRS remained unchanged. Repeated exposures to hypoxia over 1 day induced an initial adaptation to hypoxia, with improvement in respiratory reflexes. Prolonging the exposure to IH (>2 weeks) in type 1 diabetic patients will be a matter for further studies.

FIG. 1.

Diagram of the study protocol, comprising measurements at t1, t2, t3, and t4. The intervention consisted of either 1) 6-min breathing of 13% oxygen mixture five times, each separated by 6-min recovery (IH) or 2) placebo exposure (breathing room air with 21% FiO₂ for 1 h) in a single blind protocol. A standardized meal was given to the patients after t2 on both days. IH and placebo days were spaced at least 7 days apart.

FIG. 2.

Outline of the VRT-CO₂ that illustrates the point at which the ventilation started to increase during the progressive HCVR. VRT-CO₂ was identified by interpolating the ventilation/CO₂-et plot using a fourth-order polynomial function. VE L/min, minute ventilation (liters/minute).

FIG. 3.

Plot shows changes in HCVR (top panel), VRT-CO₂ (middle panel), and HVR (bottom panel) immediately after one single hour of IH or placebo exposure (n = 14). *Significant differences (P < 0.05, paired t test) from t1 to t2. Thick lines show mean values ± SEM.

FIG. 4.

Blood glucose changes over daytime on hypoxia day and placebo day. Measurements were performed at t1, t2, t3, and t4 after the hypoxic or placebo exposure (n = 15). Standardized meal was taken after t2 on both days (see indication). Blood glucose levels were compared with t1 of the same day. Data are presented as means ± SEM.