DOI: 10.12731/wsd-2014-10-14 UDC 612.16/.17+612.27
alterations of both rhythmic relations concerning pre-and postexercise of the heart and ecg r-r intervals under the conditions of severe normobaric hypoxia
Radchenko A.S., Borisenko N.S., Kalinichenko A.N., Rodionova Y. Y., Korolev Y.N., Golubev V.N.
It is known that severe hypoxia causes relaxation of the smooth muscle rigid walls of the arteries and thus regulates the vascular lumen s well as local blood flow. However, it is unclear, in these conditions, the way rhythmic interaction ofpre- and postexercise of the heart as well as its pumping characteristics alter. The purpose of research is to study rhythmic relations of the end diastolic pressure (EDP) of the left ventricle, specific peripheral vascular resistance (SPVR), cardio intervals (R-R) concerning the respiration rate and alterations of their absolute values due to adaptation to hypoxia.
9 men (aged 18,5 ± 0,6y.o.; weight 70,94 ± 5,93 kg, height 178,1 ± 4,4 cm) were exposed to intermittent hypoxia (IH) for 6 weeks in a day (FjO2 = 0,11). 5 min of hypoxia + 5 min of normoxia (6 times an hour). Hypoxic tests (HT1 and HT2) were carried out before and after a series of IH took place, which consisted of exposure to same continuous 15 min GH. While HT1 and HT2 were being carried out the following indications were registered: oxygen saturation of arterial hemoglobin (SpO2%); indices of central hemodynamics - tetrapolar rheography; ECG in I-III leads. The data were taken in consideration that were recorded at 13-15 min HT. Variability of EDP, SPVR, ECG R-R were estimated by spectral, coherent and phase analysis on respiratory rate.
When comparing HT2 to HT1 the average SpO2 increased significantly -82.7% and 92.1%, respectively (P<0,05). Having been affected by HT1 and HT2 MOS increased significantly when compared to rest condition (6,1 ± 1,39 L./min and 6,42 ± 1,44 L./min; 5,34 ± 1,01 L./min and 5,74 ± 1,21 L./ min, respectively) (P<0,05), while, having been affected by HT2, MOS was significantly lower both at rest and during the test itself when compared with HT1 (P<0,05). SPVR decreased significantly (27,39 ± 5,45 s.u. and 25,62 ± 4,96 s.u.; 30,59 ± 6,34 s.u. and 27,93 ± 5,77s.u., respectively) (P<0,05). It is shown thatfluctuations in EDP at HT2 (rest - test) were significantly more ahead of time (phase) than SPVR and R-R fluctuations in respiratory rate compared to HT1 (with 1.19 ± 0,64 and 1,99 to ± 0,63; 1.65 ± 1,28 and 2,22 to ± 0,87, respectively) (P<0,05).
To sum it up, severe hypoxia increases the MOS with both the adapted and unadapted test subjects. At rest, MOS is significantly lower with the adapted than the unadapted individuals. Fluctuations of EDP are far ahead of time (phase) than SPVR and R-R intervals fluctuations at breathing frequency of the individuals adapted to hypoxia by lowering the tonus of blood vessel smooth muscle walls.
Keywords: hypoxia; adaptation; transfer function; baroreflex.
изменение ритмических взаимоотношений пред- и постнагрузки сердца и r-r интервалов экг жесткой нормобарической гипоксии
Радченко А.С., Борисенко Н.С., Калиниченко А.Н., Родионова Ю., Королев Ю.Н., Голубев В.Н.
Известно, что жесткая гипоксия вызывает расслабление гладко-мышечной стенки артерий и этим регулирует просвет сосудов и регионарный кровоток. Однако неясно как в этих условиях изменяется
ритмическое взаимодействие пред- и постнагрузки сердца и его насосные характеристики. Цель исследования - изучение ритмических взаимоотношений конечного диастолического давления (КДД) левого желудочка, удельного периферического сопротивления сосудов (УПС), кардиоинтервалов (Я-Я) на частоте дыхания и изменения их абсолютных значений в результате адаптации к гипоксии.
9 мужчин (возраст 18,5 ± 0,6 лет; масса тела 70,94 ± 5,93 кг; рост 178,1 ± 4,4 см) 6 недель через день подвергались воздействию интервальной гипоксии (ИГ) (Я^'О = 0,11). 5 мин гипоксии + 5 мин нормоксии (6 раз в 1 час). До и после серии воздействий ИГ проводились гипокси-ческие тестирования (ГТ1 и ГТ2), которые состояли из воздействия такой-же непрерывной 15 мин ЖГ. При ГТ1 и ГТ2 регистрировались: сатурация артериального гемоглобина кислородом (Бр02%); индексы центральной гемодинамики - тетраполярная реография; ЭКГ в 1-Ш ст. отведениях. В расчет брались данные, зарегистрированные на 1315 мин ГТ. Вариабельность КДД, УПС, Я-Я интервалов ЭКГ оценивались посредством спектрального, когерентного и фазового анализа на частоте дыхания.
При ГТ2 по сравнению с ГТ1 Бр02 в среднем достоверно повысилась - 82,7% и 92,1% соответственно (Р<0,05). При ГТ1 и ГТ2 по сравнению с покоем МОК в среднем достоверно увеличивался (6,1 ± 1,39 л./ мин и 6,42 ± 1,44 л./мин; 5,34 ± 1,01 л./мин и 5,74 ± 1,21 л./мин соответственно) (Р<0,05), при ГТ2 МОК, как в покое, так и при самом тестировании был достоверно ниже по сравнению с ГТ1 (Р<0,05). УПС достоверно уменьшалось (27,39 ± 5,45 у.е. и 25,62 ± 4,96 у.е.; 30,59 ± 6,34 у.е. и 27,93 ± 5,77 у.е. соответственно) (Р<0,05). Показано, что колебания КДД при ГТ2 (покой - тест) достоверно больше опережают по времени (фазе) колебания УПС и Я-Я на частоте дыхания по сравнению с ГТ1 (1,19 с ± 0,64 и 1,99 с ± 0,63; 1,65 с ± 1,28 и 2,22 с ± 0,87 соответственно) (Р<0,05).
В заключение - жесткая гипоксия увеличивает МОК, как у неадаптированных, так и у адаптированных к ИГ одних и тех же ис-
пытуемых. В покое МОК достоверно ниже у адаптированных, чем у неадаптированных лиц. Колебания КДД значительно опережают по времени (фазе) колебания УПС и R-R интервалов на частоте дыхания у адаптированных к гипоксии лиц за счет сниженного тонуса гладко-мышечной стенки сосудов.
Ключевые слова: гипоксия; адаптация; функция передачи; барореф-лекс.
It is known that hypoxia causes relaxation of smooth muscle wall of both the aorta [1] and medium arteries, arterioles and very small arteries [2]. The degree of oxygenation of blood hemoglobin (Hb) modifies blood flow in the microvasculature of the heart [3] and muscle [4,5] according to the oxygen request from the cells, influencing smooth muscle tonus of the vascular wall. Previously, our studies have shown that blood Hb oxygen saturation (SpO2%) significantly increases in a series of impacts on a severe hypoxia tested. This alters the regulation of peripheral vascular resistance [6, 7].
Throughout the last quarter of the 20th century studying the regulation of the heart has been performed by means of the analysis of the transfer function in pairs of functionally linked indices that have the properties of oscillatory processes with beat-to-beat period [8,9]. This approach has been used in quite a few studies to identify the characteristics of the interaction of both the pump and electrical properties of cardiac activity, baroreflex regulation of the heart and blood vessels in the conditions of altering both metabolic reflex and autonomic regulation activity [10, 11, 12, 13, 14].
We suggest changes in SpO2 and associated process of regulations of the vascular lumen due to adaptation to severe normobaric hypoxia might alter the interaction of pre- and postexercise of the heart indicators of the heart and their relations with the R-R intervals, as well as change their absolute values.
Methods
Participants
9 healthy young men participated in the experiment (with a normal ECG). Aged 18,4 ± 1,83 (y.o.), weight 69,7 ± 7,01 (kg), height 176,6 ± 5,12 (cm). All the test subjects were fully informed of the goals, objectives and methods of the study and gave a written informed consent to participate in the experiments according to the protocol approved by the ethics committee of the World Medical Association.
Procedures of normobaric hypoxic influence and hypoxic test and measurement The test subjects were exposed to the effects of interval hypoxic influence (IH) in a day. IH was conducted for 6 weeks and consisted of 20 sessions consisting of 5 minutes of hypoxia (inspired oxygen fraction - FtO2 = 0,1) combined with 5 minutes of breathing atmospheric air, i.e. 6 intervals of severe hypoxia 1 hour and 6 intervals of "rest". The test subject was sitting in a comfortable position. The gas mixture was administered through a hypoxira-tor device mask ("Everest-1", CLIMBI, Moscow). All the test subjects shared the same daily motor activity mode.
Before a series of IH and after the hypoxic tests (HT1 and HT2, respectively) were carried out, which consisted of 15 minutes of continuous breathing a hypoxic mixture same as during the IH (FtO2 = 0,11). When HT was being conduvted the following was continuously recorded: arterial oxyhemoglobin saturation (SpO2%) and heart rate (oxymeter 01C3M, IMA, Samara, Russia); central hemodynamics indicators ("ReoSpektr", Vladimir, Russia) by means of tetrapolar reography [15, 16].
The attachment of the sensors as well as interelectrode distance was the same with the same individual throughout the test periods. Each subject was tested at the same time. Blood pressure was recorded before the test, while at rest, at the 5th and 12th minutes of the HT.
In order to automatically calculate the specific values of specific peripheral vascular resistance (SPVR), end-diastolic pressure (EDP) from a con-
traction to contraction - by the method of N.A. Elizarovoy and others[17], R-R intervals, minute blood volume (MBV), recording of both rheogram and ECG and the last 3 minutes of the hypoxic test were used. Fluctuations in the respiratory movements of the diaphragm were calculated according to the slow fluctuations of the undifferentiated rheogram. Rheogram indicators calculations were conducted automatically using a software system "ReoSpektr" (Vladimir, Russia) after manual correction placement of the cursors on the rheogram. SPVR and EDP calculations are drawn from different parts of the rheowave. The basis of SPVR is the product of maximum amplitude of the differentiated rheogram and duration of the systole, whereas the basis of EDP is the index value of the amplitude of the sy
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