Non-invasive Thoracic Electrical Bioimpedance Technique-Derived Hemodynamic Reference Ranges in Chinese Han Adults
Continuous monitoring of hemodynamic status is crucial for detecting early abnormalities in circulation, particularly in critically ill patients. This monitoring aids in the management of such patients by providing real-time data on their cardiovascular function. Over the years, various minimally invasive and non-invasive monitoring systems have been developed to measure functional hemodynamic parameters, which guide treatment planning and improve patient care. Among these, the thoracic electrical bioimpedance (TEB) technique has gained widespread acceptance due to its accuracy and ease of use, especially in post-operative settings like open-heart surgery. However, hemodynamic characteristics can vary significantly among different ethnic groups, and the response to cardiovascular diseases can differ across racial lines. This variability underscores the need for ethnicity-specific hemodynamic reference ranges.
In China, there has been a lack of large-scale, forward-looking research to establish hemodynamic reference ranges for the Chinese Han population. Recognizing this gap, a nationwide study was conducted from July 2012 to September 2017, led by the Ministry of Science and Technology of the People’s Republic of China. The study aimed to establish normal reference ranges for hemodynamic parameters in Chinese Han adults and to evaluate the impact of age and sex on these parameters.
The study was a prospective, cross-sectional cohort investigation organized across six provinces and autonomous regions in China: Heilongjiang, Hebei, Sichuan, Guizhou, Hainan, and Xinjiang Uygur. A total of 1535 Chinese Han adults aged 20 to 79 years were initially enrolled. The inclusion criteria required participants to have normal blood pressure, a normal physical examination, and no history or symptoms of heart diseases. Exclusion criteria included hypertension, stroke, heart failure, coronary artery disease, structural heart disease, abnormal liver or renal function, pregnancy, professional athletes, and alcohol addiction. The study population was divided into six age groups: 20-29, 30-39, 40-49, 50-59, 60-69, and 70-79 years, with approximately 50% men in each group.
The research utilized the BioZ digital non-invasive hemodynamic monitor (CardioDynamics Company, San Diego, CA, USA) across all six provinces. Two trained operators conducted all TEB measurements. Participants were required to rest for 30 minutes before testing and were placed in a supine position. The skin on the neck, chest, and abdomen was cleaned with alcohol and dried. Two pairs of TEB electrodes were placed on the upper abdomen and neck parallel to the spine, while the remaining two pairs were placed at the diaphragm level and the root of the neck. The device recorded electrocardiography signals and processed the TEB data to extract systemic hemodynamic parameters, including blood flow (cardiac output [CO], cardiac index [CI], stroke volume [SV], and stroke index [SI]), contractility and left ventricle performance (left cardiac work [LCW], pre-ejection period [PEP], and left ventricular ejection time [LVET]), and afterload (systemic vascular resistance [SVR], mean arterial pressure [MAP], and thoracic fluid conductivity [TFC]). Demographic data, including height, weight, systolic and diastolic blood pressure, and heart rate, were also collected. The body surface area (BSA) was calculated using the Stevenson formula.
The final cohort included 1478 subjects who met the selection criteria, comprising 769 women and 709 men. The average age was 45.3 ± 12.9 years for women and 44.6 ± 13.2 years for men. The study found that men had higher average values for weight, height, body mass index, BSA, systolic blood pressure (SBP), and diastolic blood pressure (DBP) compared to women. Heart rate did not vary with age in either gender. The highest SBP values were observed in the 70-79 age group for both sexes, while the highest DBP values were found in women aged 50-59 and men aged 40-49.
Hemodynamic parameters were stratified by sex and age. Blood flow values (CO, CI, SV, and SI) were significantly higher in men than in women. These parameters decreased with age in both sexes, except for CI in women, which first decreased and then increased, with the lowest value observed in the 60-69 age group. LCW was higher in men, while PEP and LVET were shorter in men. There were no significant differences in LCW, PEP, and LVET across age groups in either sex. MAP and TFC were higher in men, while SVR was lower in men. MAP and SVR increased with age in both sexes, but TFC did not show a significant trend with age. The lowest TFC value was observed in women aged 50-59.
The TEB technique measures bioimpedance by transmitting small electrical currents through the chest area. Different body tissues have varying levels of electrical conductivity, and changes in impedance recorded by the TEB device reflect the hemodynamic status. The technique has been compared to the gold standard, pulmonary artery thermodilution, and has shown a strong correlation (r = 0.818). The TEB technique is less operator-dependent and has a lower rate of variation, making it a reliable alternative for hemodynamic monitoring. It provides specific parameters reflecting left ventricular contractility, which are not obtainable through pulmonary artery thermodilution, and is particularly useful for detecting worsening left ventricular systolic function and predicting major adverse cardiovascular events and mortality.
The study found that men had better left ventricular contractility performance than women, with no significant differences in LCW, PEP, or LVET across age groups. However, other studies have reported different findings, possibly due to differences in sample size and age distribution. The elasticity and hardness of blood vessels are more affected by aging than the contractility of the heart itself, but further research is needed to understand these phenomena fully.
The TEB technique is also valuable in the hemodynamic monitoring of critically ill patients, helping to guide clinical management and prevent organ failure. In the context of respiratory virus pandemics, TEB-based hemodynamic monitoring can reduce occupational exposure for medical staff and alert physicians to any physical changes in patients.
TFC, another important parameter obtained by the TEB technique, represents the total fluid component in the thorax and is related to body weight, blood circulation state, and myocardial contractility. Some researchers have suggested that TFC could be a potential determinant of ventilatory efficiency in heart failure patients and a substitute for ultrasound in assessing extravascular lung water. However, the study did not find a clear trend in TFC with age, which contrasts with other parameters. Some studies have observed a “U-shaped” pattern of age-related changes in TFC, possibly due to compensatory fluid loss caused by vasoconstriction or the transmission of high left ventricular diastolic pressure to the left atrium and pulmonary circulation.
This study is the largest prospective investigation to establish normal reference ranges for hemodynamic parameters in Chinese Han adults across a wide age range. It also summarized the impact of age and sex on these parameters. However, there are limitations. The medical histories of participants were reviewed at their respective institutions, so the presence of unrecognized cardiovascular diseases, such as sub-clinical coronary artery disease, cannot be ruled out. Additionally, the study was conducted in only six provinces, which may limit the national representativeness of the sample. Data from different geographical regions are also lacking, necessitating further large-scale studies to address these gaps.
doi.org/10.1097/CM9.0000000000001465
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