Gender and age differences in transthoracic bioimpedance

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Medical Diagnostics

Background:

• Thoracic impedance (Z0) is a baseline measurement influenced by thoracic structure, varying with sex and age.
• The peak rate of change in thoracic impedance ((dZ/dt)max) reflects ascending aortic blood flow.
• Z0 is a denominator variable in Sramek's formula for stroke volume calculation.

Purpose of the Study:

• To investigate if age- and sex-related variations in basal thoracic impedance (Z0) impact bioimpedance measurements of stroke volume.
• To determine the relationship between Z0, (dZ/dt)max, and stroke index across different age and sex groups.

Main Methods:

• Transthoracic bioimpedance cardiography was used to measure Z0, (dZ/dt)max, and stroke volume index (SI).
• 111 healthy subjects (55 males, 56 females) aged 20-69 years were studied, divided into age decades.
• Comparisons were made between sexes and across age groups.

Main Results:

• Females generally exhibited higher Z0 and (dZ/dt)max than males, except in the oldest age groups.
• No significant sex difference was found in stroke index (SI).
• The opposing roles of Z0 and (dZ/dt)max in Sramek's formula may mitigate the impact of their variations on SI.

Conclusions:

• Age- and sex-related variations in basal thoracic impedance (Z0) and peak aortic flow ((dZ/dt)max) do not significantly alter bioimpedance-derived stroke volume index (SI).
• The interplay between Z0 and (dZ/dt)max in Sramek's formula likely maintains the robustness of SI measurements despite demographic differences.