Key result
Caffeine increases the standing heart rate max/min ratio to ~1.8 vs. 1.6 with placebo.
Why the study?
Caffeine is a widely consumed stimulant, yet its effects on autonomic cardiovascular function during autonomic reflex tests are not fully understood.
Does a single 200 mg oral dose of caffeine alter autonomic cardiovascular responses (heart rate, blood pressure, and peripheral resistance) during standard autonomic reflex tests (active standing, Valsalva manoeuvre, and sustained handgrip) in healthy young adults?
RCT (n=14)
Single-blind
Randomized counterbalanced crossover design
No
Does a single 200 mg oral dose of caffeine alter autonomic cardiovascular responses (heart rate, blood pressure, and peripheral resistance) during standard autonomic reflex tests (active standing, Valsalva manoeuvre, and sustained handgrip) in healthy young adults?
A single 200 mg dose of caffeine significantly alters heart rate, systolic blood pressure, and peripheral resistance responses across standard autonomic reflex tests, underscoring the necessity of controlling for caffeine intake prior to clinical autonomic testing.
Answers are grounded in this paper and cite their sources.
Clinicians should control caffeine intake before autonomic testing; extends evidence of acute effects on cardiovascular reflexes to healthy young adults.
Caffeine is a widely consumed stimulant, yet its effects on autonomic cardiovascular function are not fully understood. This study investigated the effects of 200 mg of caffeine during three autonomic reflex tests. Fourteen healthy individuals (11 females, 3 males; 19.7 ± 0.7 years) completed two counterbalanced sessions—caffeine and placebo—in a randomized crossover design. Participants performed an active standing test, Valsalva manoeuvre, and a submaximal handgrip test (30% of maximum for 2 min) while heart rate, systolic blood pressure, diastolic blood pressure, and peripheral resistance were monitored via a Finapres Nova. Data were analyzed using repeated‐measures analyses of variance and dependent t ‐tests ( α = 0.05). Caffeine significantly increased the heart rate maximum/minimum ratio during both the standing test (1.8 ± 0.2 vs. 1.6 ± 0.2) and the Valsalva manoeuvre (2.1 ± 0.6 vs. 1.7 ± 0.3). During the Valsalva manoeuvre, caffeine elevated baseline systolic blood pressure (141.9 ± 15.7 vs. 129.3 ± 13.9 mmHg), enhanced the post‐strain decline in systolic blood pressure (−26.2 ± 13.9 vs. −14.0 ± 13.5 mmHg), and enlarged the subsequent systolic blood pressure overshoot (37.4 ± 21.4 vs. 25.3 ± 7.9 mmHg). Caffeine also increased both the baseline peripheral resistance and decline in resistance following Valsalva strain release. Finally, caffeine significantly enhanced the peripheral resistance during the handgrip test (0.3 ± 0.3 vs. 0.1 ± 0.1 mmHg.s/mL). These findings indicate that caffeine meaningfully alters autonomic reflex test results, which underscores the importance of controlling for intake before testing occurs.
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Lamp et al. (2026) conducted an RCT in Healthy individuals undergoing autonomic reflex testing (n=14). Caffeine vs. Placebo (4-5 ounces of unsweetened 100% cranberry juice without caffeine) was evaluated on Heart rate maximum/minimum ratio (HRmax/HRmin) during the active standing test (Cohen's d -1.40, p=<0.001). Caffeine increased the heart rate max/min ratio during standing and Valsalva compared to placebo.
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