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

Abstract

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.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Participant recruitment flowchart.

Fig 2. Tidal volume in supine position pre and post ingestion of caffeine.

* = outlier; § = significant difference between pre and post (p

Fig 3. Differences in tidal volume (supine position) from pre to post ingestion between placebo and caffeine trial.

° = outlier; * = extreme outlier; § = significant difference between the change from pre to post caffeine compared to placebo ingestion (p

Fig 4

Changes in plasma epinephrine (a), norepinephrine (b) and caffeine (c) concentrations from pre to post ingestion of the supplement illustrated for all three groups. Dashed line represents placebo trail, bold line represents caffeine trial; ●, ○ = able-bodied, ■, □ = paraplegic and ▲, Δ = tetraplegic group.