Oxygen Saturation of Dorsiflexor Muscles during Sustained Isometric Contraction

Citation: Paiziev A, Kerimov F (2018) Oxygen Saturation of Dorsiflexor Muscles during Sustained Isometric Contraction. Int J Opt Photonic Eng 3:010 Copyright: © 2018 Paiziev A, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. *Corresponding author: Adkham Paiziev, Uzbekistan State Institute of Physical Culture, Tashkent, Uzbekistan, E-mail: adkhampaiziev@gmail.com Oxygen Saturation of Dorsiflexor Muscles during Sustained Isometric Contraction


Introduction
Sustained isometric contraction (SIC) of skeletal muscles produces intramuscular pressure that restricts muscle blood flow (MBF) and limits O 2 delivery to tissue [1]. MBF plays a key role in regulating the intensity and type of muscle contractions [2]. A limited MBF due to SIC leads to fatigue due lack of O 2 and nutrients. Thus, we have the paradox of rising O 2 demand due to muscle activity and at the same time reduced MBF. To clarify this issue much research has been performed mainly on MBF [3][4][5][6]. But during exercise there are few measurements of MBF by Doppler ultrasound. Although MBF could be measured by fMRI and PET, this is not possible during training [7].
Previous studies indicate that complete occlusion of MBF occurs at 50-60% of maximal voluntary contractions (MVC) during SIC [3,4,6]. MBF was not occluded Abstract Sustained isometric contractions of skeletal muscles produce intramuscular pressures that lead to blood flow restriction. Thus, we have the paradox of rising O 2 demand due to muscle activity and at the same time reduced blood flow. Aim: To assess muscle oxygenation during sustained isometric low (30%), moderate (60%) and submaximal (90% of maximal voluntary contraction (MVC)) contraction of the dorsiflexor muscle. Experiments were conducted on the dominant (right) leg of 8 male students of Uzbekistan State Institute of Physical Culture (age: 19 ± 2 years, weight: 75 ± 6 kg). Tissue oxygen saturation (StO 2 ) was recorded from the tibialis anterior using near-infrared spectroscopy. StO 2 was higher at 30% compared to both 60% and 90% MVC at all time points after the start of the exercise and higher at 60% than 90%. This indicates that the supply of O 2 did not keep up with its consumption. During an arterial occlusion the minimal StO 2 reached 24 ± 1.77%, which is significantly higher than StO 2 during 60% and 90% MVC. After each contraction there was a large and immediate hyperaemic response, whose resaturation rate continuously increased from 30% to 60% to 90% MVC. The StO 2 resaturation rate was positively correlated with the MVC, indicating a vasodilation depending on the intensity of the exercise.
at the level of the conduit artery during any of the contraction intensities [3]. Some studies report insensitivity of MBF to the muscle contraction intensity. Thus, our understanding of the oxygenation of the skeletal muscle in response to different intensities of SIC (low, moderate, submaximal MVC) still remains limited.
Despite advantages of fMRI, PET and Doppler ultrasound only one paper has been partly devoted to measure the hemodynamic response of muscles to SIC [3] by near infrared spectroscopy (NIRS). In the near-infrared spectrum (700-900 nm) light penetrates deeply into the tissue and oxyhemoglobin and deoxyhemoglobin are the strongest absorbers, while myoglobin (Mb) absorbs less. NIRS is an established optical technique to monitor concentration changes of oxyhemoglobin, deoxyhemoglobin, total hemoglobin and tissue oxygen saturation (StO 2 ) in a variety of tissues [8,9]. NIRS instruments are non-invasive, small, and applicable in exercise physiology studies.
period. The performance baseline is the minimum StO 2 value reached during SIC.
Student's t-test was used to compare StO 2 , desaturation rate and resaturation rate at slow, moderate and submaximal MVC. All data were analyzed using the statistical software package "Statistica" for Windows (version 13). Statistical significance was set at 0.05. Figure 1 displays a typical measurement in one subject. PB decreased from low to moderate to submaximal SIC30% MVC (Table 1). Figure 2 compares the StO 2 traces for different intensities of SIC. StO 2 was higher at low compared with both moderate and submaximal MVC (P < 0.05) at all time points after the start of the exercise and higher at moderate than submaximal MVC (p < 0.05). Desaturation rate (De, Table 1) increased from slow (30%) to moderate (60%) to submaximal contractions (p < 0.05). Trends of De as a function of MVC are shown in Figure 2. After each contraction there was a large and immediate hyperemic response (Figure 1). The resaturation rate (Re) of StO 2 after SIC depends on the intensity of the SIC and reflects the integrity and functionality of vascular system. It corresponds to a blood vessel vasodilation in response to the SIC. Re increased from slow to moderate (p < 0.05) but remained similar for moderate to submaximal SIC (Table 1 and Figure 1).

Results
During the arterial occlusion the minimal StO 2 was 52% (Table 1 and Figure 1), which is significantly higher than StO 2 after moderate or submaximal SIC.
The aim was to assess changes in muscle oxygenation during of low, moderate and submaximal SIC of the dorsiflexor muscle.

Methods
The dorsiflexor muscle was selected, because both venous outflow and arterial inflow can be occluded by a proximal cuff. Without blood supply, the muscle metabolism depends on the O 2 in capillaries and muscle cells. Consequently, the oxyhemoglobin and StO 2 decrease, while deoxyhemoglobin increases and total hemoglobin remains constant. After the occlusion a hyperemic response occurs, i.e. a rapid increase in oxyhemoglobin, total hemoglobin and StO 2 , while deoxyhemoglobin is washed-out. From this procedure, we calculated O 2 consumption, reoxygenation rate and the half-recovery times of the signals [10].
The recovery baseline (RB) value is the StO 2 value after stabilisation during the rest period following a test