Habitual coffee and tea drinkers experienced increases in blood pressure after consuming low to moderate doses of caffeine; these increases were larger upright than in the supine posture

Caffeine users have been encouraged to consume caffeine regularly to maintain their caffeine tolerance and so avoid caffeine’s acute pressor effects. In controlled conditions complete caffeine tolerance to intervention doses of 250 mg develops rapidly following several days of caffeine ingestion, nevertheless, complete tolerance is not evident for lower intervention doses. Similarly complete caffeine tolerance to 250 mg intervention doses has been demonstrated in habitual coffee and tea drinkers’ but for lower intervention doses complete tolerance is not evident. This study investigated a group of habitual caffeine users following their self-determined consumption pattern involving two to six servings daily. Cardiovascular responses following the ingestion of low to moderate amounts caffeine (67, 133 and 200 mg) were compared with placebo in a double-blind, randomised design without caffeine abstinence. Pre-intervention and post-intervention (30 and 60 min) 90 s continuous cardiovascular recordings were obtained with the Finometer in both the supine and upright postures. Participants were 12 healthy habitual coffee and tea drinkers (10 female, mean age 36). Doses of 67 and 133 mg increased systolic pressure in both postures while in the upright posture diastolic pressure and aortic impedance increased while arterial compliance decreased. These vascular changes were larger upright than supine for 133 mg caffeine. Additionally 67 mg caffeine increased dp/dt and indexed peripheral resistance in the upright posture. For 200 mg caffeine there was complete caffeine tolerance. Cardiovascular responses to caffeine appear to be associated with the size of the intervention dose. Habitual tea and coffee drinking does not generate complete tolerance to caffeine as has been previously suggested. Both the type and the extent of caffeine induced cardiovascular changes were influenced by posture.

The Finometer can function as a standalone instrument in blood pressure variability studies and does not require support equipment to determine breathing frequency

Objective: The Finometer (FMS, Finapres Measurement Systems, Amsterdam) records the beat-to-beat finger pulse contour and has been recommended for research studies assessing shortterm changes of blood pressure and its variability. Variability measured in the frequency domain using spectral analysis requires that the impact of breathing be restricted to high frequency spectra (> 0.15 Hz) so data from participants needs to be excluded when the breathing impact occurs in the low frequency spectra (0.04 - 0.15 Hz). This study tested whether breathing frequency can be estimated from standard Finometer recordings using either stroke volume oscillation frequency or spectral stroke volume variability maximum scores. Methods: 22 healthy volunteers were tested for 270s in the supine and upright positions. Finometer recorded the finger pulse contour and a respiratory transducer recorded breathing. Stoke volume oscillation frequency was calculated manually while the stroke volume spectral maximums were obtained using the software Cardiovascular Parameter Analysis (Nevrokard Kiauta, Izola, Slovenia). These estimates were compared to the breathing frequency using the Bland-Altman procedures. Results: Stroke volume oscillation frequency estimated breathing frequency to <±10% 95% levels of agreement in both supine (-7.7 to 7.0%) and upright (-6.7 to 5.4%) postures. Stroke volume variability maximum scores did not accurately estimate breathing frequency. Conclusions: Breathing frequency can be accurately derived from standard Finometer recordings using stroke volume oscillations for healthy individuals in both supine and upright postures. The Finometer can function as a standalone instrument in blood pressure variability studies and does not require support equipment to determine breathing frequency.