Impaired circadian modulation of sympathovagal activity in diabetes: A possible explanation for altered temporal onset of cardiovascular disease - Bernardi et al. (1992)

Key Points

  • Diabetics have a higher sympathetic tone during the nighttime hours than controls

  • The increased sympathetic tone during both day and night highlights the importance of Principle 1 and Principle 2

The Breathing Diabetic Summary

This study is extremely important for diabetics.  And, although it is not related to breathing, it has huge implications for how we breathe, especially before bed.

People generally show a day-night (circadian) rhythm of autonomic activity: during the morning and daytime, their sympathetic nervous system is predominant, while at night parasympathetic activity increases.  This makes sense because we want to be alert during the morning and daytime, and then relax and recover at night.  This study wanted to investigate how this diurnal autonomic activity looks for diabetics with and without autonomic problems.

The study used 34 type-1 diabetics and 20 type-2 diabetics; thus, these results are relevant to all diabetics.

The most important finding of this paper was that diabetics had less of a day/night difference in autonomic activity and generally showed a lower parasympathetic tone at night.  Therefore, the circadian rhythm mentioned earlier was out of balance and the sympathetic nervous system predominated during both day and night.  Perhaps unsurprisingly, this abnormality was larger in diabetics with autonomic dysfunction.  However, the trend was present in all diabetics regardless of autonomic status.

What does this mean for us as diabetics?  Even if we have no signs of autonomic dysfunction, we might still be suffering from a disrupted circadian sympathovagal balance.  This might help explain why diabetics suffer from higher rates of obstructive sleep apnea and, as this study points out, why diabetics suffer heart attacks at “abnormal” times compared to the general population.

Overall, these results support using Principle 1 before bedtime to increase our parasympathetic tone, and then to use Principle 2 to slow our breathing and maintain the increase in parasympathetic activity all night.

Abstract from Paper

Background. Diabetic subjects have a high incidence of cardiovascular accidents, with an altered circadian distribution. Abnormalities in the circadian rhythm of autonomic tone may be responsible for this altered temporal onset of cardiovascular disease.

Methods and Results. To assess circadian changes of sympathovagal balance in diabetes, we performed 24-hour power spectral analysis of RR interval fluctuations in 54 diabetic subjects (age, 44+2 years) with either normal autonomic function or mild to severe autonomic neuropathy and in 54 age-matched control subjects. The power in the low-frequency (LF, 0.03-0.15 Hz) and high-frequency (HF, 0.18-0.40 Hz) bands was considered an index of relative sympathetic and vagal activity, respectively. Diabetic subjects with autonomic abnormalities showed a reduction in LF compared with control subjects (5.95±0.12 In-msec2 versus 6.73+0.11, p<0.001) and an even greater reduction in LF, particularly during the night and the first hours after awakening (5.11+0.18 In-msec2 versus 6.52±0.14, p<0.001). Day-night rhythm in sympathovagal balance was reduced or absent in diabetic subjects compared with control subjects.

Conclsions. Diabetic subjects with or without signs of autonomic neuropathy have a decreased vagal activity (and hence a relatively higher sympathetic activity) during night hours and at the same time of the day, during which a higher frequency of cardiovascular accidents has been reported. These observations may provide insight into the increased cardiac risk of diabetic patients, particularly if autonomic neuropathy is present.

Journal Reference:

Luciano Bernardi, MD; Luigi Ricordi, MD; Pierangelo Lazzari, MD; Pierluigi Soldai, MD; Alessandro Calciati, MD; Maria Rosa Ferrari, MD; Ignazio Vandea, MD; Giorgio Finardi, MD; and Pietro Fratino, MD, (1992) Impaired Circadian Modulation of Sympathovagal Activity in Diabetes A Possible Explanation for Altered Temporal Onset of Cardiovascular Disease, Circulation, 86 (5), 1443 – 1452.