Cold According to one study on 10 healthy people, when the body adjusts to cold temperatures, your fight-or-flight (sympathetic) system declines and your rest-and-digest (parasympathetic) system increases, which is mediated by the vagus nerve.
Although the effects of cold showers on vagus nerve tone haven’t been studied, many people advocate for this traditional cooling method.
When we think about it, all showers were cold showers before the advent of water-heating techniques.
Vagal maneuvers are ways to treat a fast heart rate of more than 100 beats per minute that starts in the upper chambers of your heart, the atria. Doctors call this type of heartbeat supraventricular tachycardia, or SVT.
SVT happens when electrical signals in your heart’s atria get out of sync. This interferes with signals from the sinoatrial (SA) node, your heart’s natural pacemaker. Early beats in the atria speed up your heart rate.
time-domain interbeat interval (IBI) - time period between successive heartbeats
time-domain indices – quantifications of the variability in interbeat interval measurements by discrete time buckets
values may be expressed in original units or as the natural logarithm (Ln) of original units to achieve a more normal distribution
time buckets short-term (ST) – about 5 minutes
ultra-short-term (UST) – under 5 minutes
ST and UST values are NOT interchangeable with 24h values