Comparative analysis of the blood circulation of the index finger and second toe in middle-aged people in the dynamics of a pharmacological test with nitroglycerin
The main aspect of the application of the nitroglycerin test is the differential diagnosis of functional and morphological changes in the elasticity and tone of the walls of blood vessels of various diameters.
Nitroglycerin is a non-selective vasodilator. At the same time, it is not clear how much the vasodilating effect of nitroglycerin depends on the initial tone of the blood vessels. It is also unclear how different the effect of the drug on the blood circulation of the fingers of the upper and lower extremities, taking into account the fact that in the same subject, the tone of the arteries and arterioles of the upper extremities can be significantly higher than the tone of similar vessels in the foot region.
This study presents the results of the analysis of photoplethysmograms of the vascular regions of the index finger and second toe of practically healthy middle-aged individuals in the dynamics of the drug test with nitroglycerin. Photoplethysmograms of both vascular regions were recorded synchronously with spirograms. Photoplethysmograms were used to calculate parameters characterizing the pulse blood filling of large arteries, the tone of small arteries and arterioles. For these indicators, a variational-statistical and spectral analysis was carried out.
In the initial state, the pulse blood filling and the tone of small arteries and arterioles of the index finger region were significantly higher than those of the second toe. The dominant harmonic in the tone spectrum of small arteries in both regions was the respiratory harmonic.
In the vascular region of the index finger, the amplitude of the respiratory harmonic in the tone spectrum of small arteries increased significantly at the 2-7th minute of the nitroglycerin test and gradually decreased by the 15-20th minute of the test. In the vascular region of the second toe, the amplitude of the respiratory harmonic, on the contrary, significantly decreased, gradually increasing by the 15-20th minute of the pharmacological test.
Thus, if the initial tone of the resistance arteries is high, vasodilation contributes to an increase in the amplitude of the respiratory harmonic, and if the initial tone is low, then pronounced vasodilation of the resistance arteries contributes to a decrease in the amplitude of the respiratory harmonic in the spectrum of the tone of the resistance arteries.
Based on the results of the spectral analysis of PPG parameters characterizing the tone of the resistance arteries, it can be concluded that nitroglycerin reduces the effectiveness of local, myogenic mechanisms of blood circulation regulation, mainly in conditions of initial hypotension of the vascular wall. Apparently, this is due to the fact that nitroglycerin causes a pronounced relaxation of the smooth muscle elements of the wall of resistive vessels, which initially have a low tone. As a result, the effectiveness of the indirect venous-arterial influence of the suction action of the chest cavity during the respiratory cycle on the arterial blood flow is weakened or eliminated.
Igor B. Isupov
Volgograd State Medical University
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