The effects of mechanical ventilation on heart rate variability and complexity in mice

Abstract

In a variety of diseases, altered respiratory modulation is often as an early sign of autonomic dysfunc-tion. Therefore, understanding and evaluating the effects of mechanical ventilation on the autonomic nervous system is vital. The effects of mechanical ventilation on autonomic balance have been assessed by heart rate variability (HRV) using frequency domain and non-linear analysis including fractal complexity and entropy analysis in anesthetized mice. BALB/c mice (n=48) were divided into two groups: Spontaneous breathing and mechanical ventilation. The electrocardiograms were recorded. Four different types of analysis were employed: i. frequency domain analysis, ii. Poincare plots, iii. Detrended Fluctuation Analysis (DFA) and iv. Entropy analysis. An unpaired t-test was used for statistical analysis. In a ventilated group, very low frequency (VLF) and low frequency (LF) parameters were not changed, whereas the high frequency parameter was decreased compared to spontaneous breathing mice. DFA alpha 1 was significantly increased due to mechanical ventilation but DFA alpha 2 was unchanged. In Poincare plots analysis, standard deviation 2 (SD2) / standard deviation 1 (SD1) ratio was increased, however, SD1 and SD2 were not significantly affected. Also, Approximate Entropy and Sample Entropy remained unchanged. HF parameter, DFA alpha 1, and SD2/SD1 were affected by mechanical ventilation. Decreased HF and increased DFA alpha 1, further support the notion that HRV is dominated by respiratory sinus arrhythmia at high frequencies, this may be due to decreased vagal tone caused by me-chanical ventilation. This novel results of HRV analysis are important considering increased usage of HRV techniques day by day in animal models and other medical practices.