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The
problem of the effect of radiation upon the cardiac functions of man and
animals has been reflected in local and foreign publications. In the majority
of cases the cardiac functions have been rated with the consideration of
external irradiation of the whole body or in the region of the heart primarily
in experimental conditions. In particular, single time exposure of experimental
animals (dogs, rabbits, rats) to a dose of 15 Gy and more produces degenerative
and necrotic modifications of the myocardium (A.P. Amvrosjev et al., 1989)
accompanied by the evolution of exhudative pericarditis (Schultz-Hector,
1992) leading to hemodynamic disorders in the form of minute and impact
volume reduction, expansion of the diastolic volume of the left ventricle
(Schultz-Hector et al., 1992). It has been observed that the functioning
of the cardiovascular system is upset by general irradiation with 60Co
gamma quanta of rats due to the exhaustion of the activating effect of
the median brain blue spot (V.A. Fedorovich, 1991) and suppression of the
modulating effect of the rear nuclei of the brain seam (V.A. Sjusukin,
A.I. Ledeneva, 1991)].
The
detected restructuring of the neurohormonal control governs the suppression
of adaptation capabilities of the blood circulation system and may stimulate
the evolution of prepathological conditions (L.M. Lobanok, 1991).
External
exposure of the organism, including the heart, causes suppression of the
contractile activity of myofibrils, reduction of the volume rate of coronary
circulation (M.A. Tatarinchik, A.E. Kirienkov, 1991).
Functional
modifications of the cardiovascular system can possibly be attributed to
the damage of blood vessels, specifically arterioles (A.G. Zakharov et
al., 1992), or capillaries (Darcourt et al., 1992), variation of the volume
of catecholamines and electrolytes in vessel walls (S .A. Litvinov, 1992).
Using
isolated rat heart preparations it has been demonstrated that external
gamma irradiation with a dose 6 Gy suppresses the contractility of the
myocardium and alters the chronotropic relations: the relationship between
the frequency-force and the potentiating effect in the atria at the interval
of rest increases, while the potentiating effect in the ventricles reduces.
Modification of the chronotropic relationships may be due to the alteration
of the calcium transport in the heart cells (V.V. Shilov, L.M. Lobanok,
1991).
After
a single exposure to X-ray and neutron irradiation in doses 0.4 and 1.0
Gy the rabbits would not manifest any significant disorder of the functional
condition of the cardiovascular system, yet pronounced responses to pharmacological
preparations have been registered (G.P. Katsnelson, 1991). It is possibly
due to the modification of the structural and functional density, the affinity
to the "beta" agonist and sensitivity to the sulfohydril reagent (N.V.
Gerasimovich, 1991).
The
results of the experimental research accomplished by E.F. Konoplya et al.
(1996) allow to conclude that acute gamma-irradiation with doses 0.25;
0.5 and
1.0 Gy upsets the calcium transport system of the sarcoplasmatic reticulum
of the muscular tissue. The activity of Ca2+ATP at doses 0.25 and 0.5 Gy
increases, while it is strongly suppressed at a dose 1.0 Gy.
It is assumed that the appearance of peroxide groupings in fatty acidic chains of phospholipids under the effect of ionizing radiation alters the structure of the membranes of the sarcoplasmatic reticulum, their penetrability by various substances and the activity of membrane-bound enzymes, specifically Ca2+ATP.
These
results are corroborated by the data obtained while screening the population
affected by the Chernobyl radiation. In particular, 95.5% of the children
and adolescents have manifested disorders of the functional condition of
blood circulation in the form of upset rhythm of the cardiac activity,
conduction, metabolic and restorative processes in the myocardium, suppressed
tolerance of physical exercise, elevated arterial pressure.
These
disorders of the functional condition of the cardiovascular system are
most pronounced among the children aged between 6 and 10 years assumed
healthy before (V.N. Novikova, 1991).
I.S.
Tsybulskaya et al. [143] indicate also that 74.4% of the children during
their first year of life in the areas where the soil is contaminated with
radiation within 5-20 Ci/km2 manifest pronounced electrocardiographic
modifications: intricate rhythm disorders, alteration of the teeth of the
ventricular repolarization.
Domination
of the syndrome of premature repolarization of ventricles and elevated
arterial pressure are typical for these groups of children (A.N. Arinchik,
G.L. Nalivajko, 1991).
Vagotonia
with asympathycotonic reactivity has been revealed among 36 out of 102
examined children aged 11-15 years living in the area with the 134Cs,
137Cs soil
contamination 0.4-10 Ci/km2. The children in this group have
manifested disorders of the lipid metabolism
in the form of hypocholesterinemia, hypolipidemia, hypophosphatemia ({.V.
Kvashnina et al., 1992). V.V. Nedvestkaya and S.A. Ljalikov (1994) also
indicate modifications of the vegetative regulation evolving among the
children aged 6-17 years in the contaminated areas of Belarus
which are more pronounced among girls than among boys. These modifications
are characterized by the suppression of the tone of the sympathetic compartment
of the nervous system, a tendency towards hyporeactivity and stress of
the compensatory mechanisms of the parasympathetic compartment. Correlation
analysis has revealed a close relationship between vegetovascular dystonia
appearing among the children evacuated from the heavily contaminated areas,
and thyroid hyperplasia, psychic disorders, disorders of digestive organs
(A.U. Lagutin, V.M. Sidelnikov, 1992).
Children
from the affected areas manifest modifications of the responses of the
cardiovascular system to catecholamines (L.S. Valeva et al., 1993).
Arterial
hypotonia detected among 34.3% of boys and 30.2% of girls in the Gomel
and Moguilev regions reflects disorders of the vegetative regulation of
cardiac functions (A.V. Sikorenskii, G.E. Vagel, 1992). Modifications of
cardiac functions are registered among adults exposed to external irradiation,
in addition to children.
It
has been demonstrated that men aged 20-40 years who were involved in the
cleaning-up operations in 1986-1988 after the disaster manifest disorders
of neurohumoral regulation of the cardiac tone and myocardium contractility
(S.S. Korytko, 1991). The incidence of cardiac ischemias and arterial hypertensions
among liquidators of the Chernobyl aftermath is validly higher than among
individuals in the control group in Moscow (V.M. Shamarin, et al., 1996).
Disabled individuals with cardiac ischemias living in the contaminated
areas have more frequent and stable cardiac rhythm disorders than individuals
with similar pathologies living in "clean" areas (N.T. Arinchina, V.K.
Milkamanovich, 1992).
Dysfunction
of the vegetative nervous system in the form of secondary domination of
the stray nerve tone as bradicardias and ectopic precardiac rhythm has
been observed among male liquidators and evacuated individuals (G.P. Karaseva,
1991).
Evolution
of arterial hypertension is one of the manifestations of the above condition
(N.S. Zanozdra, E.G. Kuchinskaja, 1991). In particular, borderline hypertension
has been detected among individuals in the contaminated areas 1.5 times
more frequently than in the "clean" areas (I.I. Goncharik, 1992).
Thus,
stable neurovegetative disorders in the form of the neurocirculatory dystonic
syndrome among the individuals affected by radioisotopes indicate the involvement
of hormonal and humoral mechanisms in the induction of functional pathology,
including that of the cardiovascular system (A.M. Kovalenko, 1991). Yet,
for evaluating the consequences of the Chernobyl disaster it is more essential
to determine the effect of internal irradiation from incorporated radioisotopes
upon the condition of vital systems, including the cardiovascular system.
In
particular, when incorporated 131I creates
absorbed doses in the thyroid after 1-12 months at a level 94.6-94.7 Gy,
the responses of the myocardium to the stimulation of aipha-adrenergic
receptors is attenuated, while the responses of the coronary passage to
such stimulation are intensified (A.E. Kirienko et al., 1992). Incorporation
of 131I
and 137Cs by rats induces modifications of the heart pace-maker
activity, the functional condition of the coronary vascular passage, electric
and contractile activity of cardiomyocytes and flat muscle vascular cells
(A.E. Kirienko et al., 1990).
Examinations
of the children living in the contaminated areas (Gomel - 1-5 Ci/km2)
have revealed high frequency of disorders of cardiac activity - 72.3%,
primarily due to the disorders of conduction of the cardiac impulse in
the form of incomplete blockades of the His right stem bundle, upset redox
processes and vegetovascular dystonias, together with a close relation
between the doses of endogenously incorporated radioisotopes and electrocardiographic
disorders. Though the average accumulated dose in the organisms of children
in these two groups did not have any valid difference and amounted to 30.32
+- 0.66 Bq/kg in the test and 29.74 +- 0.67 in the control (p >0.1), the
Gomel children have manifested a more pronounced and statistically valid
direct proportionality between the accumulated dose and ECO modifications,
valid differences between the subgroups of 11-25.9 Bq/kg and 37.0-74.0
Bq/kg (Fig. 6).
The
children with the above accumulated doses but living in Grodno did not
manifest any valid differences in the frequency of registered ECG modifications.
This
fact in the main group is basically due to the disorders of intraventricular
conduction in the form of incomplete blockades of the His right stem bundle
(Fig. 7).
When
children accumulate significantly higher doses of radioisotopes 89.93 +- 3.65 Bq/kg
on the average (Vetka) the ECG-registerable effects have been detected
among 86.8% with the disorders of the intracardiac conduction amounting
to 53.95% (G.S. Bandazhevskaya, 1996).
Examinations of the students of the Gomel Medical Institute have yielded similar results (Yu.I. Bandazhevsky, et al., 1996).
Thus,
investigation of the electrophysiological processes in the cardiac muscle
among children in the areas with higher levels of radioactive contamination
has revealed a number of modifications of electrocardiographic activity
with the frequency being a function of the internally accumulated dose.
Damage
of the myocardium structure is accompanied by the intensified activity
of AST in the blood serum (Fig. 8).
Experimental studies of
laboratory animals (the Vistar line rats) evidence the effect of endogenously
incorporated radioisotopes upon the myocardium.
The
experimental animals were kept during ten days on a diet of oats containing
radioactive elements in the concentration exceeding the control level 10
times (137Cs concentration
was 445.7 Bq/kg, 90Sr - 15.5 Bq/kg). This diet would
bring the 137Cs concentration in the organisms of the
animals in the test group to 63.35
+/- 3.58 Bq/kg
versus 5.43 +/- 0.87 Bq/kg in the control group (p < 0.001).
In
this way the animals would accumulate radioisotopes within a
relatively short period of time, 137Cs in
particular. A direct proportionality between the accumulated 137Cs dose
and the concentration of this element in the
16
Analysis
of the results has indicated that the myocardium tissue acquires the maximum
concentration of this radioactive element.
Significant
concentrations of 137Cs
have been registered among the residents of Gomel and the Gomel Region
(Yu.I. Bandazhevsky, A. M. Perepletchikov, 1996). It
is manifested by the suppressed activity of the most essential enzymes,
such as alkaline phosphatase and creatin phosphokinase (Fig. 9). Considering
that creatinin phosphokinase is a key enzyme of the energy metabolism in
the cardiac muscle governing reactions between macroergic phosphate and
creatinin, its suppressed activity leads to substantial disorders of the
functions of cardiomyocytes.
Disorders
of energy processes in the heart modify its contractile apparatus, vis.
myofibrils in the form of contractions or their declustering and lysis
in various degrees of expression (L.M. Nepomnjashchikh, 1966).
Modification
of the polarization behavior of cardiomyocytes in the form of expanding
A-discs is a morphological criterion of this pathology (Fig. 9-10). The
obtained data explain origination of disorders of cardiac conduction, including
the cardiac rhythm, induced by incorporated radioisotopes.
Examinations
of the biopsied material have manifested that contracted cardiomyocytes
with ultrastructural modifications and disorders of the structures of insert
discs and atrophic cardiomyocytes and cells with signs of apoptopic degeneration
typical for this condition prevail in the arhythmogenic portions of the
heart, unlike the nonarhythmogenic zones (Bakerija et al., 1995).
Thus,
it has been experimentally demonstrated that incorporation of radioisotopes
by laboratory animals with food (primarily
137Cs) damages the myocardium cells producing relevant structural
and functional modifications. Clinical and experimental studies have revealed
a significant sensitivity of the myocardium cells of a growing organism
to incorporated radioisotopes. A whole combination of modifications evolves
evidencing a direct injury of the cardiac muscle, organs and systems controlling
its functions. The role of pathological processes evolving in the cardiac
nervous apparatus should be taken into consideration by all means.
Hence,
the problem of reducing doses of internal accumulation of radioisotopes
comes into foreground, including application of sorption preparations (Yu.I.
Bandazhevsky et al., 1994), requiring to project treatment actions for
improving metabolic processes in the myocardium.
Analysis
of the arterial pressure among children with different incorporated doses
has revealed a dose-dependent effect. As the dose increases the number
children with hypertension goes up. Totally 41.6% of the children in the
areas contaminated with 137Cs in excess of 15 Ci/km manifested
arterial hypertension (A.I. Kienja, N.M. Ermolitskii, 1997).
