Acute Effects of Caffeine on Heart Rate Variability, Blood Pressure and Tidal Volume in Paraplegic and Tetraplegic Compared to Able-Bodied Individuals: A Randomized, Blinded Trial.

Caffeine increases sympathetic nerve activity in healthy individuals. Such modulation of nervous system activity can be tracked by assessing the heart rate variability. This study aimed to investigate the influence of caffeine on time- and frequency-domain heart rate variability parameters, blood pressure and tidal volume in paraplegic and tetraplegic compared to able-bodied participants. Heart rate variability was measured in supine and sitting position pre and post ingestion of either placebo or 6 mg caffeine in 12 able-bodied, 9 paraplegic and 7 tetraplegic participants in a placebo-controlled, randomized and double-blind study design. Metronomic breathing was applied (0.25 Hz) and tidal volume was recorded during heart rate variability assessment. Blood pressure, plasma caffeine and epinephrine concentrations were analyzed pre and post ingestion. Most parameters of heart rate variability did not significantly change post caffeine ingestion compared to placebo. Tidal volume significantly increased post caffeine ingestion in able-bodied (p = 0.021) and paraplegic (p = 0.036) but not in tetraplegic participants (p = 0.34). Systolic and diastolic blood pressure increased significantly post caffeine in able-bodied (systolic: p = 0.003; diastolic: p = 0.021) and tetraplegic (systolic: p = 0.043; diastolic: p = 0.042) but not in paraplegic participants (systolic: p = 0.09; diastolic: p = 0.33). Plasma caffeine concentrations were significantly increased post caffeine ingestion in all three groups of participants (p<0.05). Plasma epinephrine concentrations increased significantly in able-bodied (p = 0.002) and paraplegic (p = 0.032) but not in tetraplegic participants (p = 0.63). The influence of caffeine on the autonomic nervous system seems to depend on the level of lesion and the extent of the impairment. Therefore, tetraplegic participants may be less influenced by caffeine ingestion. TRIAL REGISTRATION: ClinicalTrials.gov NCT02083328.

Ergogenic Effects of Caffeine Consumption in a 3-min All-Out Arm Crank Test in Paraplegic and Tetraplegic Compared With Able-Bodied Individuals.

The aim of our study was to investigate the effect of caffeine supplementation on 3-min all-out arm crank exercise performance in paraplegic (P) and tetraplegic (T) compared with able-bodied (AB) participants. A placebo-controlled, randomized, crossover, and double-blind study design was chosen to investigate the differences between caffeine (CAF) and placebo (PLC). In total, 34 healthy, trained participants were tested. Seventeen were AB (median [minimum; maximum] VO2peak: 33.9 mL/min/kg [23.6; 57.6]), 10 were P (VO2peak: 34.4 mL/min/kg [19.5; 48.8]), and 7 were T (VO2peak: 13.6 mL/min/kg [8.6; 16.3]). All participants performed two 3-min all-out tests on an arm crank ergometer following the ingestion of either PLC or CAF. Power output parameters, plasma caffeine (PC), epinephrine (EPI), and norepinephrine (NOR) concentrations were assessed. CAF significantly increased average power over the first 30 s (p = .028) and 60 s (p = .005) in P, but not in T (p = .61; p = .87) nor in AB (p = .25; p = .44). Peak power was increased in the CAF trial in AB (+46 W) as well as in P (+21 W) but was not significantly different from PLC (AB: p = .10; P: p = .17). PC significantly increased in all groups (AB: p = .002; P: p = .005; T: p = .018) whereas EPI showed a significant increase only in AB (p = .002) and in P (p = .018). NOR increased significantly in AB (p = .018) but did not increase in the other groups. Caffeine seems to enhance short-duration exercise performance in P. In contrast, T showed a high interindividual variability and overall no ergogenic effect was detected in this group.