Systolic time intervals during +Gz acceleration

Area of Science:

• Cardiovascular Physiology
• Aerospace Medicine
• Biomedical Engineering

Background:

• High Gz acceleration significantly impacts cardiovascular function.
• Noninvasive monitoring of cardiovascular responses during Gz exposure is crucial for safety and performance.
• Systolic time intervals (STI) offer a potential noninvasive method to assess cardiac function.

Purpose of the Study:

• To investigate the feasibility of using STI to noninvasively estimate transient cardiovascular function changes during +Gz acceleration.
• To analyze the effects of varying +Gz levels on STI parameters.
• To assess the recovery patterns of cardiovascular function after Gz exposure.

Main Methods:

• Systolic time intervals (STI) were recorded in 8 healthy male volunteers.
• Measurements were taken before, during, and after 30-second exposures to +3 Gz, +5 Gz, and +7 Gz.
• Cardiovascular variables including heart rate (HR), left ventricular ejection time (LVETc), and pre-ejection period (PEPc) were analyzed.
• Estimated stroke volume (SV) and cardiac output (CO) were derived from STI.

Main Results:

• Heart rate (HR) and all measured STI parameters increased proportionally with increasing +Gz levels.
• Changes in STI, including PEPc and PEP/LVET, persisted into the early recovery period at higher Gz levels.
• HR and STI returned to baseline levels within 60 seconds of recovery.
• Estimated cardiac output (CO) generally increased as stroke volume (SV) decreased during acceleration.
• CO remained slightly below baseline during recovery due to persistently low estimated SV.

Conclusions:

• Systolic time intervals (STI) provide a feasible noninvasive method for assessing cardiovascular adjustments during +Gz acceleration.
• STI can track transient changes in cardiac function, including HR, LVETc, and PEPc, under simulated high-G conditions.
• The study validates the use of STI for monitoring cardiovascular responses in aerospace and related fields.