SOLARHEALTH

A variety of medical measures were used in heliobiological studies to assess participant health and their responses to solar changes. One common measure is Heart Rate Variability (HRV) from long-term ECGs. It provides insights into the heart and the Autonomic Nervous System. HRV measures beat-to-beat changes in heart activity and can evaluate also other patterns reflected in heartbeat, including breathing patterns. The HRV method was originally developed to remotely monitor cosmonauts’ health during space flights. It quantified responses of the Autonomic Nervous System (ANS). These responses appeared to occurrdue to changes in geophysical risk factors (Breus, Baevskii, & Chernikova, 2012; Chernouss, Vinogradov, & Vlassova, 2001).

The ANS controls neurons that operate without conscious control. It has two main parts: the sympathetic and parasympathetic nervous systems. The ANS manages essential functions like heart muscle activity, smooth muscles (like those in the gut), and gland functions. The ANS is divided into two sections:

• The sympathetic nervous system speeds up heart rate and raises blood pressure
• The parasympathetic nervous system slows heart rate and increases intestinal and gland activity

The spectral power of heart rate variability (HRV) in the 0.15–0.4 Hz range (high frequency) indicates parasympathetic activity, while the 0.04–0.15 Hz range (low frequency) shows sympathetic influence (Chernouss et al., 2001). In individuals with a sympathetic response, low frequency power is stronger than high frequency power. In contrast, those with a parasympathetic response have stronger high frequency power. The LF/HF ratio changes significantly with age and throughout the day (Qtsuka, Cornélissen, & Halberg, 1997). Therefore, HRV parameters should be measured by minute or hour. Age of participants must be considered. They should also be corrected for circadian rhythm.