A method to assess heart rate variability in neonate rats: validation in normotensive and hypertensive animals.

Several studies have focused on the heart rate variability (HRV) of murine species, while studies discussing HRV in murine neonates and infants remain scarce, since recording hemodynamic signals through invasive methods in small animals has been found to be quite challenging. Thus, this study aimed at describing and validating a novel method to assess HRV in newborn rats. An electrocardiogram (ECG) system was used to determine RR intervals in awake newborns and evaluate HRV in normotensive (Wistar) and hypertensive (SHR) neonate rats. After birth, ECG was recorded in the awake newborns, and they were allowed to rest on a heated surface, restricted only by the weight of the adhesive ECG electrodes. The electrodes were cut and adapted to provide more comfort to the animal, and gently placed on the newborn's skin. RR intervals were recorded over a 30-min period using an ECG system together with LabChart software (4 KHz). Three sequences of 5 min each from the ECG recording period were analyzed in time and frequency domains, using CardioSeries software. ECG data resulted in a clearly interpretable signal that was used to generate an RR interval sequence through time for the analysis of HRV. SHR neonates presented increased cardiac sympathovagal balance compared to Wistar neonates (low frequency/high frequency: 3.85±0.71 vs 0.90±0.09). In conclusion, the ECG setup here described may be used to record RR intervals to assess HRV in neonate rats, thus detecting early impairment of HRV in hypertensive newborns.

A method to assess heart rate variability in neonate rats: validation in normotensive and hypertensive animals

Several studies have focused on the heart rate variability (HRV) of murine species, while studies discussing HRV in murine neonates and infants remain scarce, since recording hemodynamic signals through invasive methods in small animals has been found to be quite challenging. Thus, this study aimed at describing and validating a novel method to assess HRV in newborn rats. An electrocardiogram (ECG) system was used to determine RR intervals in awake newborns and evaluate HRV in normotensive (Wistar) and hypertensive (SHR) neonate rats. After birth, ECG was recorded in the awake newborns, and they were allowed to rest on a heated surface, restricted only by the weight of the adhesive ECG electrodes. The electrodes were cut and adapted to provide more comfort to the animal, and gently placed on the newborn's skin. RR intervals were recorded over a 30-min period using an ECG system together with LabChart software (4 KHz). Three sequences of 5 min each from the ECG recording period were analyzed in time and frequency domains, using CardioSeries software. ECG data resulted in a clearly interpretable signal that was used to generate an RR interval sequence through time for the analysis of HRV. SHR neonates presented increased cardiac sympathovagal balance compared to Wistar neonates (low frequency/high frequency: 3.85±0.71 vs 0.90±0.09). In conclusion, the ECG setup here described may be used to record RR intervals to assess HRV in neonate rats, thus detecting early impairment of HRV in hypertensive newborns.

Standardization of resistance exercise training: effects in diabetic ovariectomized rats.

This study was carried out with a 3-fold aim: 1) to standardize a maximal load test (MLT) on ladders for prescription of resistance exercise training (RET) in rats, 2) to prescribe moderate-intensity RET based on this MLT and 3) to test the effect of this RET in diabetic ovariectomized rats. Female Wistar rats were divided into control (C), diabetic ovariectomized sedentary (DOS) and trained (DOT) groups. The MLT was standardized with increased load applied to the rat tail for each climb, and blood lactate was measured to identify lactate threshold in C rats. MLT was applied in the 1st, 4th and 8th week of the protocol. After 8 weeks of RET, the arterial pressure was directly recorded. DOS group reduced performance in MLT, body weight, left ventricular, plantar and soleus muscles mass (vs. C). DOT rats showed an improvement in MLT associated with plantar muscle mass increased (vs. C and DOS), with attenuation of hypotension and bradycardia (vs. DOS). In conclusion, the results provide a useful method for determining the maximal load and applying RET in rats. Moreover, this study showed that moderate intensity RET improves hemodynamic status in diabetic ovariectomized rats, thereby reinforcing the role of RET in diabetes management.