Diaphragm: The Relationship between Blood Supply Regulation and Characteristics of the Contractile Function
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Diaphragm: The Relationship between Blood Supply Regulation and Characteristics of the Contractile Function A. A. Borzykha,*, O. L. Vinogradovaa,b, and O. S. Tarasovaa,c a Institute
for Biomedical Problems, Russian Academy of Sciences, Moscow, 123007 Russia of Basic Medicine, Moscow State University, Moscow, 119991 Russia c Faculty of Biology, Moscow State University, Moscow, 119234 Russia *e-mail: [email protected]
b Faculty
Received March 22, 2020; revised May 5, 2020; accepted May 17, 2020
Abstract—The diaphragm is a unique skeletal muscle; it is active throughout the lifetime and, therefore, differs from locomotor muscles in the properties of muscle fibers and the mechanisms of blood supply control. The aim of this review was to survey the structural characteristics of diaphragm muscle tissue, which provide its integral contractile properties; to compare the activity of vascular tone control mechanisms in the diaphragm and locomotor muscles; and to explore their relationship with the regulation of contractile function. The diaphragm differs from the majority of skeletal muscles by a high content of both slow fatigue-resistant muscle fibers of type I and fast fibers of type IIb, which provides endurance and high force-velocity characteristics of the diaphragm. The muscle fibers in the diaphragm are smaller, and the density of capillarization is much higher than in locomotor muscles. Arteries and arterioles that regulate blood supply to the diaphragm capillary bed combine the properties of arteries from muscles composed mainly of oxidative or mainly of glycolytic fibers. Such variety provides blood flow in the diaphragm adequate to its functional load with various patterns of activity. The mechanisms of vasoregulation in the diaphragm can qualitatively differ in the proximal and distal parts of the vascular bed. The functional properties of the proximal arteries can in part be explained by their proximity to the aorta and their small length. The contractile characteristics and blood supply of the diaphragm in various conditions should be considered when conducting respiratory muscle training in sports and rehabilitation medicine. Keywords: myosin heavy chain isoforms, metabolic types of muscle fibers, respiratory muscles, resistance arteries, exercise hyperemia, sympathetic nervous system, nitric oxide DOI: 10.3103/S0096392520020029
vated during a functional load. For example, lung ventilation increases approximately three times in small mammals, such as rats [3], and 10–20 times in humans during intense physical exertion [4]. It should be noted that a many-fold increase in the respiratory rate and respiratory volume in humans at maximum load is not accompanied by a change in the relative duration of the inspiratory phase (like quiet breathing, the inspiratory phase is approximately half the respiratory cycle [5]), which makes high demands on the rate of diaphragm contraction and relaxation. Finally, the diaphragm can develop strong short-term contractions, which is especially important for the implem
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