#4 Antidepressant effects on HRV

I’ve often wondered if the effects of HRV training were compromised with
patients taking Tricyclic Antidepressants (TCA’s). TCA’s are anticholinergic, thus interfering with the parasympathetic nervous system which uses acetylcholine as its neurotransmitter. TCA’s usually increase resting heart rate, but do they interfere with the ebb and flow of vagal (parasympathetic) tone that gives rise to HRV?

A recent study suggests that TCA’s may interfere with HRV training. Why?

“Reduced cardio-respiratory coupling after treatment with nortriptyline in contrast to S-citalopram.” J Affect Disord. 2010 Jun 8.

Major Depressive Disorder increases cardiac mortality, with decreased HRV estimated to explain 30% of the increased risk. This study measured HRV before and after treatment with an antidepressant-either the TCA nortriptyline or the SSRI s-citalopram.

The results demonstrated decreased HRV and cardio-respiratory coupling, (consistent with interference in parasympathetic regulation) by nortriptyline, but not the SSRI s-citalopram. These results have implications for the treatment of clinical depression in patients who already have a higher risk for cardiovascular disease. That is, use of TCA’s to treat the depression may increase cardiovascular risk relative to use of the SSRI’s via its effect on HRV.

In addition one can speculate that given the decreased cardio-respiratory coupling associated with TCA use, that training with HRV Feedback would be less effective for someone on a TCA. An idea that certainly needs more observation and study.

#3 Fibromyalgia, Baro-receptors and pain

Fibromyalgia is a clinical syndrome characterized by generalized pain, multiple defined tender points, fatigue and non-restorative sleep. The exact nature of its cause remains elusive. There are intriguing clues however.

A recent study of autonomic cardiovascular regulation in Fibromyalgia (Aberrances in Autonomic Cardiovascular Regulation in Fibromyalgia Syndrome and Their Relevance for Clinical Pain Reports-Psychosomatic Medicine 2010 May 13) found abnormalities in Heart Rate Variability and Baro-reflex function.

Specifically there was low power in all HRV bands suggesting reduced Sympathetic and Parasympathetic influence of cardiovascular regulation. In other words, the Autonomic Nervous System (ANS) appears to be "turned down" in Fibromyalgia. And when stressed with an Arithmetic task it didn't "turn on" as much as expected. No wonder it's so hard for patients with Fibromyalgia to "rise to the occasion" and meet the challenges of life, one of the core regulatory systems in the body isn't working well.

Another interesting fact was that there was evidence of reduced baro-receptor sensitivity and function (pressure sensitive receptor which is critical in the regulation of blood pressure and several other functions.. When the baro-receptor is functioning normally it inhibits pain signals traveling from the body up to the brain.) As expected, in Fibromyalgia patients with decreased baro-receptor function, there was a correlation with increased pain, reflecting a loss of the normal pain dampening effect of intact baro-receptor function.

This raises an exciting possibility for clinical intervention. Given that practice with HRV Biofeedback can increase baro-receptor sensitivity (a primary mechanism in treatment of high blood pressure with HRV) perhaps it can reduce pain through this powerful central mechanism. (This same mechanism may help to explain why exercise is helpful in Fibromyalgia since exercise also improves baro receptor function.) I'll try HRV with some of my patients with Fibromyalgia and describe the results in a future post.