Quantitative electrocardiography during extended space flight: the second manned Skylab mission

Area of Science:

• Cardiovascular Physiology
• Space Medicine
• Biomedical Engineering

Background:

• Spaceflight poses unique challenges to cardiovascular health.
• Understanding cardiac electrical property changes is crucial for astronaut well-being.
• Previous studies have indicated potential alterations in heart function during space missions.

Purpose of the Study:

• To evaluate the impact of spaceflight on the cardiac electrical properties of astronauts.
• To analyze changes in vectorcardiograms (VCG) during and after a long-duration space mission.
• To correlate observed cardiac changes with physiological factors like exercise and fluid shifts.

Main Methods:

• Utilized the Frank lead system for vectorcardiogram (VCG) recordings.
• Collected data at rest, during various exercise intensities, and post-exercise.
• Analyzed 47 in-flight tests, comparing them to pre- and post-flight baseline data.

Main Results:

• Observed a statistically significant increase in QRS maximum vector magnitude in all astronauts.
• Noted a significant increase in resting PR interval across the crew.
• Exercise heart rates remained consistent in-flight but increased post-flight; no major vector direction changes occurred.

Conclusions:

• Increased QRS magnitude may mimic athletic conditioning, potentially due to fluid shifts or exercise.
• Prolonged resting PR interval suggests altered autonomic tone (increased vagal, decreased sympathetic activity).
• Cardiac electrical properties are demonstrably affected by spaceflight, necessitating continued monitoring and research.