Itt írjon a(z) HeartRateVariability-ról/ről

Introduction

As stated by (Almeida-Santos MA, et al), Heart rate variability (HRV) is a parameter that measures time variations of sinus rhythm, reflecting regulatory effects of the nervous system and humoral factors on the sinoatrial node (Almeida-Santos MA, et al). Measuring HRV is a dependable way to evaluate differences in the autonomic nervous system (Peng RC, Yan WR et al). When we discuss heart rate variability, we must include the standard deviation of normal-to-normal RR intervals (SDNN) and also the root mean square of successive differences (RMSSD). The (SDNN) describes both the sympathetic and vagal activity, while the (RMSSD) describes mostly the sympathetic activity (Yi HT, Hsieh YC et al). There are numerous methods of measuring heart rate variability. One of the most common methods is using electrocardiography (ECG). 24 hour ECG recordings are completed when the test subject goes about their regular life. These recordings are very useful for analysing the risk of pathological problems and for assessing autonomic dysfunction.

Effects of disease on heart rate variability

The effects that a disease may have on heart rate variability, or the irregularities of heart rate variability which informs us of an underlining physiological problem has been demonstrated by many different experiments and has proved useful in aiding diagnoses and treatment of diseases. Two diseases that affect heart rate variability are: Gastric Cancer (GC), and Diabetes mellitus (type one). (Michael Kessler and Javdat Karimov).Gastric Cancer is a frequent type of gastrointestinal cancer that has an extremely high mortality rate among common cancers (Park JY, von Karsa L et al). The study investigated changes of SDNN and RMSSD on patients with Gastric Cancer in order to scrutinize the predicting role of HRV in relation to the disease. The result of the experiment demonstrated that as the gastric cancer developed, the SDNN and the RMSSD decreased (Songjie Hu, Jie Lou et al). This decrease in HRV has been noted with patients that have mid to late stage tumours, this is a result of damage to the autonomic nerves (Walsh D, Nelson KA et al). Clinical Investigations have proven that the HRV can be used as an insight of the extremity of different types of cancers (De Couck M, Gidron Y). The study analysed, measured different tumour sites and stages. It was discovered that in Gastric Cancer patients, there was a relationship between tumour size and HRV, although when the tumour reached above 2 centimetres, the decrease in HRV was inhibited. The experiment also discovered that the deterioration of the vagal nerves had a direct effect on the spread of the tumour in gastric cancer patients. In conclusion, patients with gastric cancer have a decreased heart rate variability in comparison to the healthy control patients. Diabetes Mellitus (DM) type one is a disease that causes the degradation of Beta cells, leading to an insulin deficiency which in turn decreases glucose uptake (World Health Organization, Sociedade Brasileira de Diabetes). Investigations on heart rate variability and type one DM is scarce in comparison to type two DM. Diabetes mellitus (DM) may be accompanied by autonomic nervous system (ANS) dysfunction. Measuring heart rate variability may detect this ANS dysfunction (Malpas SC, Maling TJ,Boulton AJ, Vinik AI et al). Using heart rate variability measurements, it has been noted that patients with diabetes mellitus type one have decreased heart rate variability and also a parasympathetic decrease along with an increase in sympathetic activity in comparison to healthy patients (Guzik P, Piskorski J et al, Javorka M, Javorková J et al, Chessa M, Butera G,Kardelen F, Akçurin G et al). Measuring heart rate variability has been shown to prove useful in prognostics and diagnostics by recognising autonomic changes and changes in cardiac rhythm (Khandoker AH, Jelinek HF et al, Pivatelli FC, Santos MA et al). Bearing this in mind, the study investigated aimed to demonstrate that heart rate variability indices have a predictive role in type one diabetic patients by identifying autonomic and cardiac rhythm changes (Anne Kastelianne França da Silva et al). The study concluded that patients with type one Diabetes Mellitus had irregular HRV, in comparison to the healthy control patients. These changes in HRV are suggestive of an irregular autonomic nervous system which can lead to an increased mortality rate (Schmid H). As an overall review, this study’s findings indicate that the use of HRV indices can be an inexpensive and easy tool to detect diabetes mellitus type one, and to allow clinical assessments of ANS dysfunction, which may be able to decrease mortality rate in patients with type one Diabetes mellitus (Zochodne DW)

Efffect of respiration on Heart Rate Variability

Firstly, the baroreceptors or stretch receptor reflexes sense the changes of arterial pressure and forward the information to the autonomic nervous system. They have an inhibitory effect on the sympathetic output and a stimulating effect on motor neurons of the vagal system. (BERNTSON, G., THOMAS BIGGER et al) These receptors work in phases in a short space of time and under maximal heart rate variability frequency ranges. (Kezdi, P,, & Geller, E) It is the respiratory effect of both the central and peripheral centres that regulates the baroreceptor reflexes. The respiratory centres also regulate the activities of both the spinal sympathetic and vagal motor neurons which vary with each breath. (Eckberg, D. L, et al)Secondly is via the direct connection between the sinoatrial node located in the wall of the right atrium of the heart and the respiratory frequency rhythms of the autonomic nerves.The respiratory frequency rhythms are translated into changes in discharge frequency of the SA node, thus RSA (Respiratory sinus arrhythmia) differs with breathing rate. (BERNTSON, G., THOMAS BIGGERR). SA can be considerably greater during slow breathing than during fast breathing. (Witte, H. and Rother, M)An experiment which proves the connection between respiration and heart rate variability is “The Power Spectrum Analysis of Heart Rate Variability to assess the changes in symapathovagal Balance during graded orthostatic tilt”. (Montano, N., Ruscone, et al). The original hypothesis behind the experiment was that the connection between the sympathetic and vagal regulations of the sinus node in the heart are complementary, i.e increased activity of the sympathetic system, results in the decreased activity of the vagus system. (Schwartz PJ, Pagani M). They followed 22 healthy volunteers and subjected them to passive head tilts at a series of selectively chosen angles: 15°, 30°, 45°, 60°, 90°. These passive head tilts were carried out after a period of rest. They calculated the time and frequency indexes of RR interval variability. ( Montano, N., Ruscone, et al). They measured respiratory activity using a nasal thermistor. The 2 most important oscillatory factors were the High Frequency (HF), which is concurrent with respiration, (Mayer S, Koepchen HP) and Low Frequency (LF) which relates to the slow waves of arterial pressure. ( Malliani A, Pagani M et al, Furlan R, GuzzettiS et al).The respiratory cycle signal was measured once every cardiac cycle in correspondence with the R wave, thus obtaining a repirogram synchronised with a tachogram.They concluded that an upright position is responsible for slight tachycardia (common heart disorder), the neural regulation of SA node in the heart is affected by the sympathetic excitation and vagal withdrawal which accompany an upright position. (Rushmer RF). For further evidence that respiration and heart rate are linked one only needs to consider the effect of smoking on the heart rate variability. In a study conducted in Japan by Junichi Minami, Toshikiko Ishimitsu, Hiroaki Matsuoka, the effect of 1 week smoking cessation on heart variability among other parameters was investigated. The test subjects were habitual male cigarette smokers, smoking more than 10 cigarettes daily (Range 10-80). Their results showed a clear correlation between cigarette smoking and heart variability. They found that not just the daytime HRV but also the nighttime HRV was significantly lower in the non smoking period than the smoking period. The number of total heart beats over a 24 hour period was 10,471 +/ - 188 beats less in the non smoking period. (Minami J, e.) They also recorded the average values of PNN50 ( defined as the mean number of times an hour in which the change in successive normal sinus (NN) intervals exceeds 50 ms 1). (Mietus, J.) This measurement showed that there was also a correlation between smoking cessation and decreased PNN50 over a 24 hour period.However the results also showed that PNN50 was higher during the non- smoking period 15.6+/-2.1% , than during the smoking period 10.0+/-1.6%, indicating that no smoking raised the parasympathetic nerve activity over a 24 hour period. (Minami J, e.)