Evaluation of Cardiorespiratory Function During Cardiopulmonary Exercise Testing in Untreated Hypertensive and Healthy Subjects.

Yahui Zhang,Lin Qi,Yanling Liu,Tianjing Zhang,Xinmei Chu,Stephen E Greenwald,Lisheng Xu,Zhihao Jiang,Xingguo Sun

doi:10.3389/fphys.2018.01590

Abstract

Objective: This study aimed to compare differences in cardiorespiratory function between untreated hypertensive subjects (UHS) and healthy subjects (HS) during cardiopulmonary exercise testing (CPET). Additionally, it also aimed to explore the potential mechanisms of different exercise responses in cardiorespiratory function before, during and after CPET.Methods: Thirty subjects (15 UHS and 15 HS) were enrolled. Photoplethysmography (PPG), respiratory signal, and ECG were simultaneously collected while subjects were performing CPET. Fiducial points (a, b, c, d, e) were extracted from the second derivative of the PPG (SDPPG), and the ratios b/a, c/a, d/a, e/a, and (b-c-d-e)/a (named Aging Index, AGI) were calculated as markers of systolic and diastolic function. Additionally, respiratory rate was calculated and analyzed.Results:Before CPET, there were no significant differences in b/a, d/a, and AGI between two groups. However, after CPET, b/a (−0.9 ± 0.19 vs. −1.06 ± 0.19, p-value = 0.03) and AGI (−0.49 ± 0.75 vs. −1.15 ± 0.59, p-value = 0.011) of the UHS group were significantly higher than those of the HS. The d/a (−0.32 ± 0.24 vs. −0.14 ± 0.17, p-value = 0.024), and c/a (−0.33 ± 0.26 vs. −0.07 ± 0.19, p-value = 0.004) were significantly lower in UHS than those in HS. In contrast, before CPET, e/a (0.22 ± 0.11 vs. 0.32 ± 0.09, p-value = 0.007) in UHS was significantly lower than that in HS, while after CPET there was no significant difference between the two groups in this variable. In addition, during CPET, AGI (p-value = 0.003), and respiratory rate (p-value = 0.000) in UHS were significantly higher in comparison with before CPET.Conclusions: Different exercise responses showed the differences of cardiorespiratory function between UHS and HS. These differences not only can highlight the CV risk of UHS, but also can predict the appearance of arterial stiffness in UHS. Additionally, during CPET, significant differences in AGI, autonomic nervous function and respiratory activity assessed by respiratory rate were found between the two groups in comparison with before CPET.

Highlights

Hypertension is the most common cause of, and a major predisposing risk factor for, cardiovascular morbidity and mortality
Continuous and high-quality 20–40 SDPPG indices were extracted from beat to beat PPG and calculated for every subject in each segment
Before cardiopulmonary exercise testing (CPET), e/a (0.22 ± 0.11 vs. 0.32 ± 0.09, p-value = 0.007; Figure 8B) was significantly lower in untreated hypertensive subjects (UHS) than that in HS, while there was no significant difference in this parameter (0.24 ± 0.13 vs. 0.3 ± 0.12, p-value = 0.146) after CPET between two the groups

Summary

Introduction

Hypertension is the most common cause of, and a major predisposing risk factor for, cardiovascular morbidity and mortality. The second derivative of the PPG signal (SDPPG) has been widely used as a simple and reliable measure of pressure augmentation in clinical investigations (Hashimoto et al, 2002) It reflects the ascending aortic systolic pressure wave, and serves as a marker of vascular aging (Takazawa et al, 1998; Hashimoto et al, 2002; Elgendi, 2012). This study aimed to investigate and compare cardiorespiratory function in untreated hypertensive and healthy subjects before, during and after CPET It aimed to better understand the possible causes for the aforementioned lack of consensus based on the measurement and calculation of synchronous multi-physiological signals, including PPG, ECG, and respiratory signal

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