Background Zusanli (ST36) is one of the most commonly used acupoints in acupuncture and has shown good therapeutic effects on cardiovascular and other systemic diseases. However, the autonomic nervous system modulation pattern of deep needling at ST36 still lacks objective quantitative evidence.

Objective To observe the effects of deep needling (near the blood vessel) at Zusanli on heart rate variability (HRV), blood pressure variability (BPV), cardiac output (CO), and baroreflex sensitivity (BRS) in healthy subjects, thereby elucidating the regulatory effect of acupuncture on cardiovascular autonomic nerves and providing objective evidence for the acupuncture theory of "regulating Qi and blood".

Methods This study was a single-blind, two-arm, parallel-group randomized controlled trial. Healthy volunteers were recruited at Chinese PLA General Hospital from October to December 2025 and randomly divided into a deep needling group and a superficial needling group. ST36 was used in both groups. In the deep needling group, a filiform needle was inserted perpendicularly about 30 mm under ultrasound guidance to reach the branches of the anterior tibial artery, followed by lifting-thrusting manipulation for 150 seconds before withdrawal. In the superficial needling group, the needle was inserted about 10 mm without reaching the blood vessel and without any manipulation. Electrocardiogram and continuous blood pressure signals were simultaneously collected for 5 minutes at five time points: before needling (T1), during needling (T2), immediately after needling (T3), 30 min (T4) and 120 min (T5) after needling. HRV, BPV, and CO were analyzed, and BRS was analyzed using transfer function analysis.

Results A total of 68 subjects were enrolled, including 34 in the deep needling group (15 males, 19 females, mean age 26.2 ± 3.2 years) and 34 in the superficial needling group (16 males, 18 females, mean age 25.5 +/-3.3 years). There were no statistically significant differences in baseline characteristics between the two groups (P > 0.05). For the primary endpoint, the deep needling group demonstrated significantly increased systolic blood pressure coefficient of variation (SBP-CV) and systolic blood pressure standard deviation (SBP-SD) at T2 compared with T1 (both P < 0.01), while the superficial needling group showed no significant changes at any time points relative to T1 (all P > 0.05); between-group comparison indicated that SBP-CV and SBP-SD at T2 were significantly higher in the deep needling group than in the superficial needling group (SBP-CV: 0.057 +/- 0.021 vs 0.042 +/- 0.011; SBP-SD: 6.5 +/-2.6 mmHg vs 4.9 +/-1.4 mmHg, both P < 0.01). For secondary endpoints, (1) HRV: the deep needling group showed significantly higher natural logarithm of the root mean square of successive RR interval differences (lnRMSSD) at T2, T3, and T4 compared with T1 (all P < 0.01), while no significant difference was found between T5 and T1 (P > 0.05); the superficial needling group exhibited no significant differences in lnRMSSD at any time points relative to T1 (all P > 0.05), and between-group comparison revealed that, after adjusting for baseline T1, lnRMSSD at T2 was significantly higher in the deep needling group than in the superficial needling group (adjusted mean difference = 0.22, 95% CI: 0.08 to 0.36, P < 0.01). (2) BRS: the deep needling group had significantly elevated BRS gain at T3 compared with T1 (P < 0.05), whereas the superficial needling group exhibited no significant differences across any time points relative to T1 (all P > 0.05); between-group comparison demonstrated that BRS gain at T3 was significantly higher in the deep needling group than in the superficial needling group (10.66 6.81, 17.76 ms/mmHg vs 8.37 7.03, 10.50 ms/mmHg, P < 0.05). (3) CO: no significant interaction effect was observed (P > 0.05), although a significant time effect was present (P < 0.05), with post hoc pairwise comparisons showing that CO at T2, T3, and T4 was significantly lower than at T1 (P < 0.05).

Conclusion Deep needling at Zusanli regulates autonomic nerves for both the heart and blood vessels. For blood vessels, it mainly manifests a sympathetic effect; for the heart, it mainly manifests a parasympathetic effect. This study may provide a preliminary clinical reference for the treatment of cardiovascular diseases such as sinus tachycardia, cardiac neurosis, and orthostatic hypotension.