Heart Rate Affected by Nocturnal Hypoglycemia in Type 1's

For adults with type 1 diabetes there is a marked decrease in the low-frequency component of heart rate variability during spontaneous nocturnal hypoglycemia, according to a study.

Minna L. Koivikko, M.D., from the University of Oulu in Finland, and colleagues conducted a study involving 37 adults with type 1 diabetes who underwent continuous glucose monitoring via a subcutaneous sensor as well as recording of R-R interval or electrocardiogram for three nights. During periods of hypoglycemia (glucose 3.9 mmol/L) of equal duration at the same time of night, heart rate variability was analyzed.

The researchers found that hypoglycemic and control episodes lasted a mean of 71 minutes, and heart rate or the high-frequency component of heart rate power spectrum did not change significantly during hypoglycemia. There was a significant decrease in the low-frequency component of heart rate variability seen with hypoglycemia. There was a significant positive association between the decline in the glucose concentration and the decrease of the low-frequency component of heart rate variability (r = 0.48; P = 0.04). During controlled sympathetic activation, the decrease in the low-frequency component of heart rate variability was closely related to an increase in muscle sympathetic nerve action recorded in 10 subjects.

"Spontaneous nocturnal hypoglycemia in patients with type 1 diabetes results in a reduction of the low-frequency component of heart rate, which is best explained by excessive sympathetic activation without a concomitant withdrawal of vagal outflow," the authors write.

Published online before print May 18, 2012, doi: 10.2337/dc11-2120 Diabetes Care May 18, 2012