Sphygmo Cor is a validated system that uses applanation tonometry to noninvasively translate a radial pressure waveform taken at the wrist to an aortic pressure waveform. Based on some of our previous data, we expected a change in the energy drink arm of 10 ms and no change in the caffeine control arm.
To detect a between‐group difference of 10 ms and assuming an SD of 14 ms (2‐sided α=5% and 80% power), we would need 18 participants for the study.
The dose was based on the observation that cardiovascular adverse effects typically occur with high consumption of energy drink/caffeine.5 The amount of energy drink participants were asked to consume (2 cans totaling 320 mg caffeine) correlates to the average daily caffeine consumption (300 mg) of the US population.12 Further, nearly 15% of military personnel consume 3 cans a day in the deployed setting, which may predispose them to a higher risk threshold.5, 13 After a minimum 6‐day washout period, participants proceeded to consume the alternate study drink.
Participants were required to fast for 12 hours, and abstain from any caffeinated products 48 hours prior to each study day and throughout the 24‐hour follow‐up period.
Participants were excluded if they had a current or previous diagnosis of abnormal heart rhythm, a BP 140/90 mm Hg, any comorbid medical conditions, history of substance abuse, renal or hepatic dysfunction, concurrent use of drugs or over‐the‐counter products that may interact with study drinks or affect ECG or BP parameters (excluding oral contraceptives), or were pregnant or lactating.
This was a randomized, double‐blind, caffeine‐controlled, crossover study in healthy adults.
Twelve men and 6 women (n=18) were included, of which 11 identified as white, 3 as Asian, 2 as Hispanic, 1 as black, and 1 undisclosed.
Average age, height, and weight were 26.7±4.0 years, 171.9±12.2 cm, and 74.4±15.0 kg, respectively.
There was no evidence of a statistically significant difference in the baseline‐adjusted HR 2 hours after energy drink consumption when compared with caffeine (3.39±11.04 versus −0.61±9.13, respectively; A significant difference in baseline‐adjusted p SBP (Figure 3) was evident 6 hours after energy drink consumption when compared with the caffeine arm (4.72±4.67 mm Hg versus 0.83±6.09 mm Hg, respectively; Adverse effects were experienced by 15 participants during the energy drink arm and by 13 participants during the caffeine control arm (Table 2).
The time‐matched changes from baseline were compared between the energy drink and control arms using the Wilcoxon signed rank test.
All data were reported as mean±SD unless otherwise stated.
Peripheral BP measurements were obtained in duplicate after a 5‐minute rest using a standard automated vital signs monitor (Masimo SET Vital Sign Monitor; Welch Allyn; Skaneateles Falls, NY).
Central BP measurements were obtained using the Sphygmo Cor PWA system (At Cor Medical Pty Ltd, West Ryde, Australia).