Interaction of glucose and standardized massage administration on cardiac reactivity in healthy adults

Hyperglycemia affects cardiac activity at rest, but its effect on cardiac reactivity has not been investigated extensively. While glucose increases hormonal stress responses without changing cardiac stress reactivity, less is known about the interaction of glucose and relaxation interventions on cardiac reactivity. In the present study, we investigated the interaction of glucose administration and a standardized massage intervention on psychophysiological relaxation and sustained attention. Ninety-four participants (age mean = 22.84 years, SD = 2.53 years; 71.28% female) were randomly assigned to consume a drink containing glucose, or pure water before receiving a standardized massage or resting. Directly after the manipulation, they completed the d2 sustained attention test. We repeatedly assessed blood glucose and mood and recorded an electrocardiogram (ECG) and impedance cardiography (ICG) throughout. Root mean square of successive differences (RMSSD) and high-frequency heart rate variability (HF-HRV) were used as a measure of parasympathetic activity, and pre-ejection period (PEP) indexed sympathetic activity. Our preregistered analyses showed that both relaxation interventions increased PNS activity and decreased arousal. Glucose activated the SNS and prevented SNS withdrawal in response to the massage. However, it did not modulate PNS or affective reactivity to the interventions. While cardiac reactivity was not related to sustained attention, higher blood glucose was linked to higher concentration performance and accuracy in explorative analyses. The results provide further support for the autonomic space model demonstrating independence of SNS and PNS regulation depending on the type of manipulation. They may further our understanding of the links between glucose metabolism and autonomic functioning.