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 RegistrationClinicalTrials.gov NCT02083328
Highlights
It is already well-known, that a spinal cord injury implies some crucial physiological adaptations due to the injury
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
Our results showed a trend toward a reduction of low frequency (LF)/high frequency (HF) ratio as well, even if this reduction was only significant in paraplegic participants
Summary
It is already well-known, that a spinal cord injury implies some crucial physiological adaptations due to the injury. Such consequences include bone mass, active muscle mass or the inability to use the limbs, and gastrointestinal transition time, bladder, bowel and sexual functions as well as cardiovascular capacity and the activation of the autonomous nervous system [1,2,3,4,5,6]. Heart rate variability (HRV) is a non-invasive measure of markers of cardiac autonomic modulation. It is generally accepted that HF is a marker of cardiac parasympathetic activity [8] and that LF fluctuations of HRV at rest are not related to muscle sympathetic nerve activity [9]. When measured in an orthostatic challenge, it has been shown that LF/HF power ratio and muscle sympathetic nerve activation change in parallel [10, 11], suggesting that this HRV ratio may reflect enhanced adrenergic activity as response to provoked stress
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