Transcutaneous auricular vagus nerve stimulation augments postprandial inhibition of ghrelin

Figures

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  FIGURE 1. First protocol: Subjects reported to the laboratory after an average of 3.0 ± 0.5 h of fasting. The first blood sample was obtained after a 30‐min baseline ECG and blood pressure (BP) recording. Then taVNS or sham‐taVNS (randomized order, at least 1 week apart) was performed for 30 min during which the ECG and BP recordings were continued. This was followed by another 30 min of ECG and BP recording before the second blood sample was obtained. Second protocol: Subjects reported to the laboratory after an average of 6.6 ± 0.8 h of fasting. The first blood sample was obtained after a 30‐min baseline ECG and BP recording. Following ingestion of a high‐calorie beverage, taVNS or sham‐taVNS (randomized order, at least 1 week apart) was performed for 30 min during which the ECG and BP recordings were continued. Then the second blood sample was obtained

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  FIGURE 2. Effects of sham‐taVNS and taVNS on concentrations of blood glucose (top left), plasma glucagon (top right), plasma insulin (bottom left), and plasma C‐peptide (bottom right) were measured in the first protocol without caloric intake. Concentrations before (white columns) and after (grey columns) the taVNS or sham‐taVNS interventions are shown. Data are presented as box‐whisker plots (median, upper/lower quartile, upper/lower extreme). *: p < 0.05 before versus after intervention (paired t‐test)

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  FIGURE 3. Effects of sham‐taVNS and taVNS on concentrations of blood glucose (top left), plasma glucagon (top right), plasma insulin (bottom left), and plasma C‐peptide (bottom right) in response to ingestion of a high‐calorie beverage (second protocol). Concentrations before (white columns) and after (grey columns) the taVNS or sham‐taVNS interventions are shown. Data are presented as box‐whisker plots (median, upper/lower quartile, upper/lower extreme). *: p < 0.05 before versus after intervention (paired t‐test)

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  FIGURE 4. Effects of sham‐taVNS (left) and taVNS (right) on plasma ghrelin concentration in response to ingestion of a high‐calorie beverage (second protocol). Data obtained before and after taVNS or sham‐taVNS are shown for individual study participants (grey circles, n = 9) and as box‐whisker plots (median, upper/lower quartile, upper/lower extreme). *: p < 0.05 after versus before taVNS (paired t‐test)

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  FIGURE 5. Effect of sham‐taVNS (white bars) and taVNS (grey bars) on heart rate (HR), time‐domain heart rate variability (HRV) parameters standard deviation of NN intervals (SDNN) and root mean square of successive RR interval differences (RMSSD), and frequency‐domain HRV parameters low‐frequency spectral power (LF), high‐frequency spectral power (HF), and LF to HF ratio. The left column shows HR and HRV parameters obtained in the first protocol (n = 15) and the right column shows HR and HRV parameters obtained in response to a high‐calorie beverage (second protocol, n = 10). Baseline data were obtained during the recording that preceded the taVNS or sham‐taVNS intervention. Intervention data were obtained during the application of taVNS or sham‐taVNS. Recovery data were only recorded in the first protocol and were obtained following the taVNS or sham‐taVNS intervention as illustrated in Figure 1. Data are presented as box‐whisker plots (median, upper/lower quartile, upper/lower extreme). *: p < 0.05 versus baseline (1‐way ANOVA with post‐hoc Scheffé test in protocol 1; paired t‐test in protocol 2). #: p < 0.05 baseline values of second protocol versus baseline values of first protocol…

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  FIGURE 6. Effects of sham‐taVNS (white bars) and taVNS (grey bars) on baroreceptor‐heart rate reflex sensitivity (BRS) in the first protocol (left) and in response to a high‐calorie beverage (second protocol, right). No significant differences from baseline values were observed during the taVNS or sham‐taVNS interventions (both protocols) or during the recovery recording following the interventions (first protocol only). Data are presented as box‐whisker plots (median, upper/lower quartile, upper/lower extreme)