Interval hypoxic training improves autonomic cardiovascular and respiratory control in patients with mild chronic obstructive pulmonary disease - Haider et al. (2009)
Key Points
Autonomic dysfunction in present, even in mild COPD
Three weeks of intermittent hypoxia training (IHT) improves autonomic function, reduces respiration rate, and improves heart rate variability
IHT improves chemoreflex response in COPD patients
The Breathing Diabetic Summary
As I read this paper, I noticed some eerie similarities between COPD and diabetes. For example, COPD patients have reduced baroreflex sensitivity (BRS), reduced heart rate variability (HRV), increased activation of the sympathetic nervous system, and reduced chemoreflexes. We have covered several papers related to these issues and diabetes. What’s more, we have also seen that slow breathing positively impacts all of these problems. However, this study takes a different approach to these issues: intermittent hypoxic training (IHT).
IHT has many benefits when applied safely (see review paper here). Similar to slow breathing, IHT has been shown to improve chemoreflexes and reduce sympathetic activity. These effects would act to restore cardiovascular, autonomic, and respiratory control. Therefore, the goal of this study was to examine if IHT could improve cardio-autonomic balance in COPD patients.
The study had 18 patients with mild COPD and 14 age-matched controls. Although this is a rather small sample size, this was a double-blind placebo-controlled study, something that is rare in the field of breath science. Nine COPD patients were randomly assigned to the IHT group and 9 to the placebo group. The IHT group performed training sessions 5 days/week for 3 weeks (15 sessions total). Each session consisted of 3-5 hypoxic periods lasting 3-5 min. Hypoxia was achieved by inhaling air with 12-15% oxygen (well within the therapeutic range). Between each hypoxic set, they would breathe normal air for 3 mins. The participants were seated throughout the whole procedure. The placebo group performed the same protocol, but inhaled normal air the whole time. Finally, both groups performed rebreathing tests to examine hypoxic and hypercapnic breathing drive, an indicator of chemoreflex status.
At baseline, the BRS and HRV of the COPD patients were significantly lower than the healthy controls. After 3 weeks of IHT, these patterns reversed. The BRS and HRV of the COPD patients increased significantly, to levels almost as high as the healthy controls. The placebo group actually showed slight worsening of these measures, although the changes were not significant.
IHT also increased hypercapnic ventilatory drive in the COPD patients. Typically, I talk about increasing our tolerance to CO2, which would reduce our hypercapnic ventilatory drive. However, in COPD, hypercapnia can be dangerous. Therefore, the goal is to increase their hypercapnic drive back to normal levels. IHT accomplished this. Lastly, IHT also reduced their resting breathing rate from ~14.4 breaths/min down to 13.1 breaths/min.
In slow breathing studies, we typically see improvements during and right after the slow breathing exercise. However, here we are seeing that IHT resets cardio-autonomic balance toward normal so that even when you’re not performing a “breathing exercise” your scores of cardio-autonomic control are improved. That is, IHT resets the baseline to almost normal levels.
Overall, this paper showed that IHT has the ability to improve BRS, improve HRV, reduced breathing rate, and improve chemoreflex response in COPD patients. Thus, IHT potentially could be used as a non-pharmacological treatment option in COPD (or perhaps any disease associated with autonomic dysfunction). For us, this study highlights the therapeutic benefits of Principle 3 for improving our overall health as diabetics.
Abstract from Paper
OBJECTIVES: Chronic obstructive pulmonary disease (COPD) is associated with cardiac autonomic nervous system dysregulation. This study evaluates the effects of interval hypoxic training on cardiovascular and respiratory control in patients with mild COPD.
METHODS: In 18 eucapnic normoxic mild COPD patients (age 51.7 +/- 2.4 years, mean +/- SEM), randomly assigned to either training or placebo group, and 14 age-matched healthy controls (47.7 +/- 2.8 years), we monitored end-tidal carbon dioxide, airway flow, arterial oxygen saturation, electrocardiogram, and continuous noninvasive blood pressure at rest, during progressive hypercapnic hyperoxia and isocapnic hypoxia to compare baroreflex sensitivity to hypoxia and hypercapnia before and after 3 weeks of hypoxic training. In double-blind fashion, both groups received 15 sessions of passive intermittent hypoxia (training group) or normoxia (placebo group). For the hypoxia group, each session consisted of three to five hypoxic (15-12% oxygen) periods (3-5 min) with 3-min normoxic intervals. The placebo group inhaled normoxic air.
RESULTS: Before training, COPD patients showed depressed baroreflex sensitivity, as compared with healthy individuals, without evident chemoreflex abnormalities. After training, in contrast to placebo group, the training group showed increased (P < 0.05) baroreflex sensitivity up to normal levels and selectively increased hypercapnic ventilatory response (P < 0.05), without changes in hypoxic ventilatory response.
CONCLUSION: Eucapnic normoxic mild COPD patients already showed signs of cardiovascular autonomic abnormalities at baseline, which normalized with hypoxic training. If confirmed in more severe patients, interval hypoxic training may be a therapeutic strategy to rebalance early autonomic dysfunction in COPD patients.
Journal Reference:
Haider T, Casucci G, Linser T, et al. Interval hypoxic training improves autonomic cardiovascular and respiratory control in patients with mild chronic obstructive pulmonary disease. J Hypertens. 2009;27(8):1648-1654. DOI:10.1097/HJH.0b013e32832c0018.