Measured every 10 seconds, heart rate variability (HRV) ratio reflects the variability between your heart beats.

Your resting pulse rate is an overall average of the number of beats per minute pumped by your heart; however, the beats may not come at the same cadence throughout that minute. The Ava bracelet measures your pulse rate via optical feedback. The underlying sensor technology is called photopletysmography.

HRV ratio captures how much the pattern of beats changes: does your heart beat close to every second, with little variation or does it fluctuate a lot, beating more rapidly for a few seconds then slow down again?

Your in-app Health Data shows you your daily HRV ratio, one measure of HRV and defined as low frequency divided by high frequency power. In addition to contextual factors like sleep deprivation, recent exercise, and pre-existing medical conditions, HRV can vary depending on menstrual cycle phase. Ava’s clinical trials have demonstrated HRV ratio increases after menses and drops after ovulation, providing another potential biophysical clue about your menstrual cycle phase.