Autonomic, Cardiovascular and Respiratory Responses to Hyperglycemic Stimulus in Healthy Subjects

In ten healthy subjects we assessed the effects of hyperglycemia, provoked by the ingestion of 75 g of glucose on: R-R intervals (RR), systolic pressure (SP), diastolic pressure (DP), respiratory frequency (RF) and tidal volume (VT) 5-min time series; the time course of their low-frequency (LFRR, LFSP, LFDP), high-frequency (HFRR, HFDP, HFRes) powers and their central frequencies (cfLFDP, cfHFRR, cfHFDP), computed by a time-frequency distribution; baroreflex (BRS) and respiratory sinus arrhythmia sensitivities (RSAS), obtained by alpha index and their coherences (cBRS and cRSAS) by cross time-frequency analysis. In relation to control, in hyperglycemia (peak of 143±12 mg/100 ml, p<0.001) 1-min epoch mean values of: LFRR, LFDP, HFRR, HFRes, BRS, cBRS, RR, DP and VT decreased (p<0.03); cfLFDP, cfHFRR, RSAS, cRSAS and RF increased (p<0.04); and LFSP and SP were similar. Our findings outline an integrative dynamic response to hyperglycemia characterized by: vagal activity inhibition associated to RR shortening; sympathetic outflow inhibition associated to reduced DP, which, via baroreflex with reduced sensitivity and input-output coupling degree, reinforces the vagal reduction; and respiratory activity modification associated to VT decrease, RF increase and improved respiratory modulation of cardiovascular function.