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Razmerje med aktivnostjo simpatika in parasimpatika pri testu z nagibno mizo
Avtor: Melita T. Kermavnar
Mentor: prof. dr. sci. Anton Grad, dr, med.
Somentor: asist. mag. Bernard Meglic, dr. Med
Uvod. Nevrokardiogena sinkopa je najpogostejša oblika prehodne izgube zavesti, ki nastane zaradi neustreznega proženja Bezold-Jarischovega refleksa. Vzrok je najpogosteje pokoncni položaj telesa. S tehniko spektralne analize variabilnosti srcnega ritma so dokazali, da je tik pred sinkopo aktivnost simpatika mocno povecana, ob sinkopi pa pride do paradoksne inhibicije simpatika, kar privede do vazodilatacije in bradikardije, ter posledicne izgube zavesti. Ugotoviti smo želeli, ali se pri testu z nagibno mizo odzivi avtonomnega živcevja med preiskovanci z in brez nevrokardiogene sinkope razlikujejo, in ce so te razlike pri testiranju z nitroglicerinom vecje.
Preiskovanci in metode. Primerjali smo skupino 30 preiskovancev, testiranih z nitroglicerinom (ntg+) in skupino 30 preiskovancev, testiranih brez nitroglicerina (ntg-). V vsaki skupini smo pri polovici preiskovancev s testom izzvali sinkopo (sin+), pri drugi polovici pa ne (sin-). S spektralno analizo variabilnosti srcnega ritma smo izracunali kolicnik MF/HF, ki predstavlja ravnovesje med simpatikom in parasimpatikom, ter srednjo srcno frekvenco. Rezultate znotraj skupine smo primerjali s testom t za parne vzorce, med skupinami pa s Studentovim testom t. Za statisticno pomembno razliko smo upoštevali vrednost p ? 0,05.
Rezultati. V vseh skupinah, razen v skupini ntg-/sin-, se vrednosti MF/HF in sprememba srednje srcne frekvence statisticno pomembno povecajo po dvigu preiskovanca iz ležecega položaja na nagibni kot 60°. Za spremembo kolicnika MF/HF velja: p < 0,001 (ntg+/sin+), p < 0,005 (ntg+/sin-), p < 0,05 (ntg-/sin+), NS (ntg-/sin-); za spremembo srednje srcne frekvence pa: p < 0,001 za vse skupine. Statisticno pomembno povecanje smo našli tudi med ležecim položajem in dodatkom nitroglicerina za spremembo MF/HF (skupina ntg+/sin+: p < 0,01, skupina ntg+/sin-: p < 0,001) in spremembo srednje srcne frekvence (za obe skupini velja, da je p < 0,001). Med skupinami nismo našli pomembnih razlik (za vse skupine velja p > 0,05).
Zakljucek. S spektralno analizo variabilnosti srcnega ritma med testom z nagibno mizo smo dokazali, da je zacetni odziv na ortostatski stres enak pri preiskovancih z in brez nevrokardiogene sinkope. Z dvigom preiskovanca na nagibni kot 60° se ravnovesje med simpatikom in parasimpatikom spremeni v prid prvega, poviša se tudi srcna frekvenca. Po dodatku nitroglicerina se spremembe še povecajo. Nitroglicerin poviša tonus simpatika pri vseh preiskovancih, vendar ne obstajajo statisticno pomembne razlike med skupinami.
[Abstract / English version]
The balance between sympathetic and parasympathetic activity in head-up tilt table test
Author: Melita T. Kermavnar
Mentor: prof. dr. sci. Anton Grad, dr, med.
Co-mentor: asist. mag. Bernard Meglic, dr. Med
Introduction. Neurocardiogenic syncope is the most frequent transitional loss of consciousness, which is caused by inappropriate triggering of Bezold-Jarisch reflex. The triggering agent is most commonly the upright posture. With the help of spectral analysis technicque, the researcers demonstrated, that there is a large increase in sympathetic activity just before syncope, but at the point of syncope a paradox inhibiton of this activity occurs with consequent vasodilatation and bradycardia, which result in loss of consciousness. In our study we wanted to find out whether the autonomic nervous system differences exist between patients and controls in response to head-up tilt table testing, and whether these differences are larger in tilt table test with nitroglycerine.
Subjects and methods. We compared a group of 30 subjects, who recieved nitroglycerine during the test (ntg+), to a group of 30 subjects who were tested without nitroglycerine (ntg-). In half of patients of each group syncope occured during the test (sin+) and in the other half it did not (sin-). With spectral analysis of heart rate variability we determined the LF/HF ratio which represents the balance between sympathetic and parasympathetic nervous systems. In addition we measured the mean heart rate in different phases of the test. The results were compared with t test for dependant samples for changes within each group and with Student t test for comparisson between groups. Statistically signifficant difference was p < 0,05.
Results. We found a signifficant difference in MF/HF ratio and heart rate between supine and tilt position in all groups except group ntg-/sin-. The results for MF/HF were: p < 0,001 (ntg+/sin+), p < 0,005 (ntg+/sin-), p < 0,05 (ntg-/sin+), NS (ntg-/sin-); the results for heart rate variability were: p < 0,001 for all groups. Signifficant differences existed between supine position and addition of nitroglycerine (MF/HF: ntg+/sin+: p < 0,01, ntg+/sin-: p < 0,001; heart rate: p < 0,001 for both groups). There were no statistically signifficant differences in changes of these parameters between the groups.
Conclusion. Spectral analysis of heart rate variability showed that the initial response to orthostatic stress is identical in subjects with and without neurocardiogenic syncope. The change of position from supine to tilt angle 60° changes the balance between sympathetic and parasympathetic system towards the former and heart rate increases. With the addition of nitroglycerine these changes increase. Nitroglycerine increases the sympathetic tone in all subjects with no signifficant differences between the groups.