Dr. K. Ažukaitis Explained How Important the Elasticity of Blood Vessels in Children Is and Why It Is Difficult to Measure It
Why do children’s blood vessels lose elasticity, and what are the difficulties in correctly measuring vascular stiffness in children? We interviewed Dr Karolis Ažukaitis, VU Faculty of Medicine Vice-Dean for Research and Innovation, a paediatric nephrologist, to find out more about this.
Cardiovascular damage: an area of interest for the paediatric nephrologist
As a paediatric nephrologist, Dr Ažukaitis pays particular attention to the quality of his research: “This is a narrow field and at the same time a very broad one. My main area of interest is early cardiovascular damage. My work in this field started when I started working on a study at the University of Heidelberg. It looked at children with chronic kidney disease and their early cardiovascular damage. Although these children, when young, do not have serious cardiovascular problems or serious diseases, the cardiovascular disease becomes the dominant cause of death when they reach the age of 30 to 40 years. It seems to me that the whole of paediatrics is now moving towards the fact that we are not only concerned with treating the disease, but also with ensuring that the patient lives as long and as healthy a life as possible. Or in other words, to avoid premature biological ageing and to prevent the processes that start in childhood and will lead to illnesses 20-30 years later.”
The study was carried out in Finland on children from childhood into adulthood. The results showed that elevated blood pressure in childhood has a direct correlation with cardiac abnormalities at the age of 40. “While childhood hypertension was once a rare event, mostly associated with comorbidities – in the kidney, and endocrinological – we now have an epidemic of obesity and hypertension not only in the adult population but also in children. So, my research has turned to cardiovascular damage in early childhood, both in children with arterial hypertension and in children with chronic kidney disease”, he said.
The researcher noted that he does not have the luxury of following his patients until they reach age 40, but he is interested in understanding as much as possible about the patient in childhood: “You can observe the child to see how effective the treatment is if there are small structural changes in the heart – if the ventricle is thickening, if the geometry of the heart is changing, or if there are subtle disturbances in the relaxation of the heart that you can measure. It is also possible to assess the health of the blood vessels, and this has become my major interest. In particular, I can assess whether a child’s atherosclerosis is progressing faster than it should according to normal physiological development, by assessing whether the blood vessels are stiffer than they should be for their age”.
How is arterial stiffness measured?
The question, “How to measure arterial stiffness in children?” is almost a fundamental problem, because it is quite difficult to achieve. According to Dr Ažukaitis, he relies on methods that are used in the adult population, but the changes that occur in children’s arteries are particularly subtle. “This means that if I want to measure them, I have to pay attention to whether I am really getting a number that indicates the stiffness of the arteries, and what is the tolerance of that measuring device. If the error rate in the data is high, then I will no longer be able to detect a subtle change that differs from their peers.”
There are many methodological problems with these studies. First of all, there are many devices available to measure arterial stiffness, but not all of them are suitable for children. “A few years ago, we did a review of these devices, and their validity in the paediatric population, and we saw how differently people use them – how differently they interpret the data. These reasons may be responsible for the fact that many of the methods used in the research misjudge arterial stiffness and sometimes the results do not reflect it accurately at all,” he noted.
According to the researcher, his study with colleagues from the European Childhood Hypertension Network (HyperChildNET) found that arterial stiffness in children depends almost entirely on blood pressure. This prompted the question of whether their measurements of arterial stiffness were indirectly measuring blood pressure. “This is a very difficult question to answer. We know what tests would need to be done to answer it, but they would be unethical, with too much risk of intervention. So, at the moment, we are still measuring pulse wave velocity – how fast the pulse wave travels through the large blood vessels. This can be measured very simply by using a special device to record when the pulse occurs in the neck and when it occurs, for example, in the leg. The distance between the two is then measured, which roughly reflects the course of the aorta, and the faster the pulse travels from the neck to the leg, the stiffer the aorta is.”
In concluding the interview, Dr Ažukaitis pointed out that as children grow up, their height changes every year. It is therefore important to compare the data with the normal values for children of the same age, height and gender. Another challenge is that each machine that measures arterial stiffness, measures a slightly different amount, so each machine needs the same data. Moreover, there can be large errors. “Imagine the number of risks in this process if, instead of measuring arterial stiffness, I were to measure something we sometimes call ‘milk fat’. We do these tests on children where body changes are extremely subtle, the child is growing up, everything is changing all the time, so minimal mistakes, especially if they are made at the first, second, or third stage of the test, will lead to your test results being completely meaningless. With poor quality baseline data, we will never get a reliable result.”