Controlling the inspiration/expiration ratio benefits the deceleration capacity index of heart rate in assessing the sympatho-vagal balance

Deceleration capacity (DC) of heart rate is a novel index for evaluating the activity of the autonomic nervous system (ANS). We examined whether controlling the inspiration/expiration (I/E) ratio benefits the DC analysis based on a model-generated RR interval (RRI) database. A cardiovascular system model was adopted to simulate RRI time series. The model allows analyzing the role of sympathetic and vagal activities in the ANS. The respiratory pattern can be controlled in the model. Three hundred RRI time series with random sympathetic and vagal activities were simulated. According to the ratio between the sympathetic and vagal activities (S/V ratio), these subjects were categorized into a case group (S/V>1) and a control group (S/V<;1). DC was computed for each subject. The performance of DC in distinguishing the two groups was examined by the receiver operating characteristic (ROC) analysis. The respiratory period is set to 6 s. The I/E ratio was controlled as 1:2, 1:1 and 2:1, respectively, and the performances of DC under different I/E ratios were compared. The numbers of subjects in the case group and the control group are 139 and 161. With the I/E ratio as 1:2, 1:1, and 2:1, the mean area under the ROC curves (A UCs) of DC are 0.64, 0.74 and 0.75. DCs obtained with the I/E ratio of 1:1 and 2:1 have significantly larger AUCs than that obtained under the normal physiological I/E ratio of 1:2 (p<;0.05). Controlling the I/E ratio above the normal physiological level renders a better ability of DC in assessing the sympatho-vagal balance.