Acupuncture and heart rate variability: A systematic review

This systematic review examined 12 randomized clinical trials that investigated the effects of acupuncture on heart rate variability (HRV), an objective measure of autonomic nervous system activity. HRV is a sensitive indicator of how the nervous system controls the heart, reflecting the balance between sympathetic and parasympathetic activity. The study sought to determine whether acupuncture could modulate these autonomic functions in a specific and measurable way. The 354 participants included in the analyzed trials consisted primarily of healthy individuals, in addition to some patients with mild depression, anxiety disorders, and migraine.

The trials tested different conditions, including normal resting states, mental stress situations, fatigue from prolonged driving, and caffeine consumption. The methodology varied across trials, with some using traditional manual acupuncture and others employing electroacupuncture. The most commonly used points included PC-6 (Neiguan), HT-7 (Shenmen), LI-4 (Hegu), and ST-36 (Zusanli), chosen based on traditional Chinese medicine theory or on previous studies. As a control, sham acupuncture was used, consisting primarily of superficial needling at nonspecific points.

Of the 12 trials analyzed, only five found significant differences between true acupuncture and sham acupuncture. Two trials showed changes in HRV in patients with specific clinical conditions: one in people with mild depression or anxiety, in which acupuncture reduced the LF/HF ratio at 5 minutes after the third treatment, and another in patients with migraine, in which there was a reduction in high-frequency (HF) power. One trial demonstrated effects in healthy individuals subjected to fatigue from prolonged driving, and another showed benefits in individuals under mental stress. A fifth trial found specific effects related to the Sishencong points in healthy individuals.

The meta-analysis of trials in healthy individuals revealed no significant differences between true acupuncture and sham for any of the HRV parameters analyzed. For high-frequency power, the p-value was 0.53; for low-frequency power, p = 0.48; and for the LF/HF ratio, p = 0.87. These results suggest that, in the healthy population, there is no evidence of specific effects of acupuncture on HRV. The methodological quality of the trials presented important limitations.

Only five trials adequately described randomization methods, and none reported details on allocation concealment. Only three trials implemented double-blinding, while the rest used only patient blinding. Most trials had small samples, increasing the risk of type II errors. In addition, only one trial controlled for respiratory rate, an important confounder in HRV analysis.

The clinical implications of these findings are significant. Although acupuncture is widely used to treat various conditions presumed to involve autonomic nervous system imbalances, this review does not provide robust evidence that acupuncture has specific measurable effects on cardiac autonomic control. This does not necessarily mean that acupuncture is ineffective, but rather that its mechanisms of action may be different from what is traditionally proposed, or that current methods of HRV measurement may not be sensitive enough to detect subtle changes. The authors also raise the possibility that sham acupuncture may have its own physiological effects, which would complicate the interpretation of results.

Needling, regardless of location, can induce physiological responses that influence the autonomic nervous system, making it difficult to distinguish between specific and nonspecific effects of acupuncture.