Heart rate variability (HRV) is also called heart rate variability.
The heart regulates blood pressure through small fluctuations in pulse rate. The better the heart can regulate blood pressure by small extensions or reductions in the time between two beats, the better the blood pressure is optimally balanced. This balancing ability of the heart is measured as HRV.
1. Heart rate variability (HRV)¶
It has been established that the adaptability of the heart to small fluctuations in blood pressure, measured as heart rate variability, is a highly significant marker of stress. The higher the heart rate variability (HRV), the lower the stress level. Many thousands of years ago, Chinese physicians already knew that patients whose hearts beat like clockwork in an absolutely uniform rhythm, i.e. have a very low to non-existent HRV, are seriously ill.
HRV is the standard measurement tool for the activity of the parasympathetic nervous system, which is part of the autonomic nervous system.
ADHD shows decreased heart rate variability (HRV), indicating decreased stress regulation capacity of the autonomic (vegetative) nervous system.
At the same time, the sympathetic nervous system (here: the cardiac-linked sympathetic index 0V%) is overactivated in ADHD. Together with reduced cardiac-linked parasympathetic activity and HRV, this represents a non-invasive marker for prefrontal hypoactivity and ADHD.
Heart rate variability can be measured by several parameters.
1.1. RMSSD¶
rMSSD: Root Mean Square of successive differences between inter-beat intervals
- No differences between ADHD sufferers and non-sufferers, even when tested separately by gender, age, or ADHD subtype. One small study found decreased rMSSD scores.
- Low values correlate with
- Fears
- Oppositional behaviors
- Social problems
1.2. HFA¶
The HFA is the absolute high frequency power.
HFA maps parasympathetic (= vagal) tone.
- Regarding HFA, the results are unclear in relation to ADHD.
One large study found no differences between ADHD sufferers and non-sufferers, even when tested separately by gender, age, or ADHD subtype.. One small study found decreased HFA scores. Another study found increased scores in boys with Inattention and Oppositional Defiant Disorder (ODD).
- Low values correlate with
- Fears
- Oppositional behaviors
- Social problems
1.3. HF¶
In one study, the normalized high frequency band of heart rate variability was labeled HF and described as representative of the parasympathetic nervous system. This study found a 20% reduction in HF in boys with ADHD compared to unaffected boys.
1.4. LFA¶
The LFA is the absolute low frequency power.
LFA maps both sympathetic and parasympathetic tone, but in practice represents sympathetic tone.
- Low values correlate in boys with
- Inattention
- Hyperactivity/impulsivity
- Oppositional Deficit Disorder (ODD)
1.5. LF / HF ratio¶
LF / HF: ratio of low frequency power to high frequency power
LF / HF ratio means sympathovagilance. An increase / high values of LF / HF ratio means sympathetic dominance, a decrease / low values of LF / HF ratio means parasympathetic dominance.
- In ADHD, the LF / HF ratio is higher in both resting and sustained attention states, especially in male children
- Low values correlate in boys with
- Inattention
- Hyperactivity/impulsivity
- Oppositional Deficit Disorder (ODD)
- Higher LF / HF ratio during sustained attention correlates with poorer attentional performance in ADHD sufferers and nonafflicted individuals
1.6. SD¶
SD: Square of the interval differences
- A small study found reduced SD levels in ADHD-affected children
1.7. TP¶
TP: Total power of HRV
- A small study found reduced TP levels in ADHD-affected children
In children, Emotional Dysregulation is associated with heart rate variability.
2. HRV measurement through sports tracker¶
HRV can now be measured and evaluated by a simple sports watch (fitness tracker).
2.1. Garmin vivosmart 3 / vivosmart 4¶
The Garmin vivosmart 3 or its successor vivosmart 4 (beware, there are some other models that sound similar but do not have stress measurement) is a standard sports watch that measures the usual data such as heart rate, calories burned, sleep, exercise, etc. The Garmin vivosmart 3 is also a fitness tracker. However, as a feature rarely found in such fitness tracker sports watches, this one also measures heart rate variability and provides a granular picture of HRV progression throughout the day for this purpose. Evaluations are available long-term via the Garmin app. The cost of this device ranges from €80 to €140. However, the device only shows an overall HRV value, which is also not specified in more detail.
According to this assessment, the evaluations are nevertheless meaningful enough to be able to perform an analysis of influencing parameters on HRV. For example, it is clearly recognizable when sleep has not entered the recovery range, e.g. due to alcohol consumption.
The clear daily evaluation allows a rough biofeedback use. It becomes comprehensible which stressors influence the HRV value. The development of the HRV value reveals, for example, whether sleep allows sufficient recovery or whether certain situations lead to particular stress loads. For example, smoking directly worsens the HRV value.
Long-term measurement over weeks or months provides insights into which circumstances reduce stress levels and which increase them.
For example, under suitable circumstances, the effects of food intolerances can be detected in the HRV level. In a patient known to us, the stress level is significantly increased for about 2 days after consumption of an intolerant food.
2.2. Apple Watch¶
The Apple Watch does offer HRV measurement, but it is far less detailed than that of the Garmin vivosmart 3 / 4. In addition, we are not aware of an app that displays the values in a meaningful way. According to this review, the Apple Watch is not particularly useful even for non-medical analyses.
2.3. Polar H10 chest strap with V800 sports watch¶
A more accurate option that can also be used for medical analyses (although not approved as a medical device for this purpose) is the measurement of heartbeats using a chest strap. A combination of an H10 chest strap and a V800 tracking watch (both from Polar), which together cost about €300 (as of May 2018), allow raw heartbeat data to be read out over 24 hours. The results can then be analyzed by companies such as Autonom Health. A single evaluation there costs €50 as of May 2018 and allows analysis of the parasympathetic nervous system and (slightly limited) the sympathetic nervous system. Concrete evaluation analyses are provided that are understandable for the person concerned.
To date, no evaluations or data analyses related to ADHD are available.
3. HRV influence by medication¶
Methylphenidate improves heart rate variability and autonomic nervous system control in ADHD sufferers.
A compilation of the influence of drugs on heart rate variability can be found at www.hrv24.de, whereby the data on methylphenidate contradict each other. As a result, methylphenidate is likely to increase (improve) HVR, although the value of non-affected persons is not reached.
