Heart Rate Variability and Plasma Norepinephrine Concentration in Diabetic Dogs at Rest

Cardiac autonomic neuropathy in dogs with diabetes mellitus (DM) were evaluated using time-and frequency-domain parameters of heart rate variability (HRV) as well as the plasma norepinephrine (NE) concentration compared with control healthy non-diabetic dogs. Dogs were divided into 2 groups according to frequency of insulin adjustment, their fasting plasma glucose and plasma fructosamine concentrations: group 1, the control healthy non-DM group (n = 13), group 2, diabetic group (n = 22). The diabetic group was further divided into 2 subgroups, the well-controlled DM (n = 11) and the poorly-controlled DM (n = 11). None of these dogs had heart failure or received any drug that affected HRV or autonomic nervous system. The blood pressures were recorded along with the measurements of complete blood count, blood gas analysis, biochemical profiles and plasma NE concentrations. For HRV, the electrocardiogram (ECG) was recorded continuously for at least 30 minutes at rest. The results showed that the concentrations of fasting blood glucose and serum fructosamine were significantly higher in both DM subgroups compared with control group (p < 0.001). The time-domain parameters, NNA and SDANN in poorly-controlled DM were significantly lower than control group (601.9+28.5 vs 697.4+31.9 ms and 22.40+5.53 vs 50.96+10.74 ms, respectively) ( p < 0.05) while heart rate was significantly higher than control and well-controlled DM (102.7+6.6 vs 88.1+3.9 and 85.7+3.7 bpm, respectively) (p < 0.05). In poorly-controlled DM, the NNA, SDNN, SDNN index and pNN50% were also significantly lower when compared with well-controlled DM (601.9+28.5 vs 711.5+27.1 ms, 118.9 +12.3 vs 178.1+19.0 ms, 115.4+12.2 vs 174.5+18.7 ms and 46.73+6.96 vs 68.23+5.25 ms, respectively) (p < 0.05). The frequency-domain parameters, HF and total power in poorly-controlled DM were significantly lower (7,670+1,829 vs 20,503+6,030 ms2 and 14,694+2591 vs 32,097+7,148 ms2,respectively) (p < 0.05) while the LF/HF was higher (0.54+0.15 vs 0.21+0.04) (p < 0.05) when compared with well-controlled DM. In poorly-controlled DM, systolic, diastolic and mean arterial blood pressures were significantly higher while plasma NE concentrations were significantly lower than control group (210.4+36.7 vs 478.9+74.3 pg/ml) (p <0.05). However, in well-controlled DM group, no significant change was found among all parameters when compared with control group. The plasma NE concentrations had negative correlation with plasma fructosamine concentrations (p < 0.05, r = -0.359). It is concluded that the cardiac autonomic neuropathy occurred only in poorly-controlled DM dogs. The sympathetic activity in this group was suppressed as shown by decrease in both plasma NE concentration and LF component resulting in higher arterial blood pressure and heart rate.