yogabook / movement physiology / Heart rate variability HRV
Heart rate variability / HRV
The measured resting heart rate, or rather the measured heart rate, is usually determined over a time interval, i.e. averaged. Physiologically, however, the heart does not beat completely evenly at rest, but slightly irregularly. This was already known to the Chinese physician Wang Shu-ho (180 – 270 a.d.), who predicted that death would occur within three days if the heart beat was completely regular. The small fluctuations in the range of a tenth of a second are due to the influence of the sympathetic nervous system (noradrenaline-mediated) and parasympathetic nervous system (acetylcholine-mediated), because of which even small mental/emotional processes cause fluctuations in the heart rate. At rest and under low stress, vagal control predominates. The better the heart is adapted to high physical stress, the higher the vagal resting tone. This is reflected in a lower resting heart rate and a higher HRV. Apart from this, breathing has a clear influence on the heart rate: during inhalation, the pulse speeds up a little, while exhalation slows it down again. This sympathetic-mediated phenomenon is known as respiratory (sinus) arrhythmia. It is all the more pronounced the deeper and more strained the inhalation is. The breathing cycles are usually in the range of 2 – 7 seconds. The high-frequency fluctuations are almost exclusively mediated via the vagus nerve, while slower fluctuations, corresponding to 0.04 to 0.15 Hz, i.e. of the order of around 10 s, are mostly vagal and sympathetic. Respiratory arrhythmia falls into the so-called HF (high frequency) range of 0.15 to 0.4 Hz.
Both phenomena are included in the heart rate variability HRV. This measures the distance between two neighboring R-waves in the ECG, also known as the RR interval or (to avoid confusion with blood pressure) the NN interval. Chronic stress, for example, causes a permanent sympathetic tone with a permanent pulse increase and (largely uninfluenced by the parasympathetic nervous system) a stabilization of the rhythm with a weakening or even elimination of HRV. Much research has been done on HRV in recent decades, so that today it can be used for risk prediction, performance objectification and in stress medicine and psychophysiology. Some factors such as age, heart attacks, cardiovascular pathologies or chronic stress damage the fast-conducting myelinated vagus nerve, which is the main factor in HRV, so that it is chronically reduced. If the disturbances are temporary and only last for a few months, the vagus nerve can recover, which then manifests itself in daytime sleepiness. If the stress lasts for years, the vagus nerve is no longer able to recover and the night-time recovery phases also deteriorate. The HRV measurement can be used to recognize the extent of damage to the vagus nerve and possibly predict burnout as the next stage. HRV is one of the few objective parameters besides low DHEA, noradrenaline/adrenaline rate of burnout. If the parasympathetic nervous system has collapsed, the sympathetic nervous system can also collapse as a result. Poor HRV can be considered a predictor of cardiovascular mortality. Factors that influence HRV positively oder negatively include:
Alcohol short-term and chronic: –
Breathing in terms of respiratory sinus arrhythmia RSA
Sporting activity: during activity: – after recovery: +
Gender: parasympathetic activity is usually higher in women than in men
Cardiovascular diseases, heart failure: –
arterial hypertension and prehypertensive blood pressures: –
if myocardial infarction has occurred, existing CHD or angina pectoris: –
sepsis: –
Kidney disease: –
Metabolic diseases: –
Smoking: –
Heat –
Night shifts: –
Pollutants: –
Medication: –
Cold -/+ Adaptation to cold usually only after 60 days,
Increased body fat –
Noise –
Age: HRV is highest in young adulthood and then drops non-linearly
Anxiety disorders, PTSD, depression –
Inhalation and passive smoking –
Shift work with night shifts –
Diabetes mellitus and metabolic syndrome –
Stress –
HRV follows a circadian rhythm: it reaches a maximum during sleep and falls with the sympathetic tone of the day.
In order to use the heart rate variability in a meaningful way, it can be specified as a scalar value (measured value) for a specific period of time or in real time over a specified time interval as a moving average. The most important evaluation of the R-R intervals (in the sense of the ECG, in general: the heart contractions) included in the HRV is the RMSSD (Root Mean Square of Successive Differences), i.e. the square root of the sum of the squares of the RR-differences. As HRV decreases with age, it is often given for age groups, for example as follows (Lj: HRV interval) in a Californian study:
10 – 19: 25 ± 9
20 – 29: 43 ± 9
30 – 39: 35 ± 11
40 – 49: 31 ± 11
50 – 59: 25 ± 9
60 – 69: 22 ± 6
70 – 79: 22 ± 7
80 – 99: 21 ± 6
This study clearly shows how HRV decreases with age from adolescence onwards.