UDC

612.171:796.015

DOI

10.37482/2687-1491-Z131

Authors

Lev I. Irzhak* ORCID: https://orcid.org/0000-0003-3459-7848
Nadezhda G. Russkikh* ORCID: https://orcid.org/0000-0003-4413-8258
Aleksandra N. Parshukova* ORCID: https://orcid.org/0000-0001-7297-3395

*Syktyvkar State University named after Pitirim Sorokin (Syktyvkar, Komi Republic, Russian Federation)

Corresponding author: Lev Irzhak, address: prosp. Oktyabr’skiy 55, Syktyvkar, 167000, Respublika Komi, Russian Federation; e-mail: irzhak31@mail.ru

Abstract

The purpose of this article was to study the mechanism of reduction in stroke volume after intense physical activity (the Astrand effect). Materials and methods. The research involved 23 apparently healthy male students of Syktyvkar State University named after Pitirim Sorokin (age: 19 ± 1 years, body weight: 75 ± 13 kg, height: 177 ± 7 cm, body mass index: 24 ± 4 kg/m2). The physical load consisted of the Stange test (voluntary inspiratory breath-holding) and the Martinet test (squats to failure) performed simultaneously. The parameters of intracardiac haemodynamics were assessed using electrocardiography and ultrasonography. Results. We established that at rest, about 80 cm3 of blood passes through the mitral valve and the aortic valve in a cardiac cycle lasting on average about 0.30 s. Under physical load, the total blood flow volume through the mitral valve is reduced by 8 %, while through the aortic valve, by 15 %. The decrease in stroke volume under physical load, accompanied by an increase in heart rate, is due to a reduction in the TP segment of the electrocardiogram (diastole). The free blood flow (during diastole) from the left atrium through the mitral valve stops and the forced flow (during systole) starts, coinciding in time with the PQ interval (left atrial systole) on the electrocardiogram. Changes in the subjects’ parameters associated with the flow dynamics through the mitral valve and further through the aortic valve, as well as the processes in the TP segment (diastole) indicate that it is the shortened diastole during exercise that serves as the main link in the mechanism of all subsequent rearrangements of intracardiac haemodynamics. This study contributes to the understanding of the mechanism of the Astrand effect. Moreover, it demonstrated the dependence of the diastolic function of the ventricles on the volume of free blood flow (during diastole) through the mitral valve during the contraction of the TP segment according to the electrocardiographic data.

Keywords

mitral valve, aortic valve, stroke volume, cardiac output, ECG intervals and segments, intense physical load, heart ultrasound, electrical properties of the myocardium

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