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Venous Return and Vascular Function
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Alternating contraction and relaxation of limb skeletal muscle squeezes blood out of the veins towards the heart. During contraction, the veins are compressed and blood is expelled from them towards the heart, and when the muscles relax, the veins fill again (one-way flow is ensured by the venous valves). During standing, rhythmic skeletal muscle contractions in the veins of the leg reduce venous pressure and volume. During exercise, the skeletal muscle pump increases the venous return.
The circulatory system
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
The effect of the skeletal muscle pump is essential during exercise. Although there is a mass sympathetic discharge and venous vasoconstriction that enhances VR, this mechanism alone is insufficient to increase VR and, therefore, CO to meet the metabolic demands of strenuous exercise. The skeletal muscle pump mobilizes the blood stored in these tissues and keeps it flowing toward the heart. As the number of muscles involved in the exercise increases, so does the magnitude of the increase in VR and CO.
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
The larger veins in the legs lie close to the skeletal muscle beds and can be compressed with skeletal muscle contraction. This compression pushes the venous blood forward toward the heart (and the valves prevent the backflow when the muscles relax). This is referred to as the skeletal muscle pump, and it is a factor in encouraging venous return. Other factors that aid in venous return include the respiratory suction (the negative pressure created on inspiration) and the diastolic suction (created during isovolumic relaxation); these help create a pressure gradient between the veins and the right atrium.
Risk factors for venous thromboembolism in patients with spinal cord injury: A systematic review and meta-analysis
Published in The Journal of Spinal Cord Medicine, 2023
Bo Wei, Hongjun Zhou, Genlin Liu, Ying Zheng, Ying Zhang, Chunxia Hao, Yiji Wang, Haiqiong Kang, Xiaolei Lu, Yuan Yuan, Qianru Meng
Several studies show that severity of injury and loss of motor function are risk factors for VTE in patients with SCI, 4,5,10,25,47–49 while other reports suggest there is no difference in the incidence of DVT between patients with complete paralysis or incomplete paralysis.50 In one study, the risk of DVT was greater in patients with Frankel A SCI compared to patients with Frankel B, C or D SCI.38 Other studies showed that the risk of thrombosis was increased in patients with AIS Grade A injuries, where complete loss of motor or sensory function in the sacral segments S4–S5 means that the skeletal-muscle pump cannot aid in venous return.33,39 Our search identified no studies reporting on the incidence of DVT in lower AIS grades. The results of our pooled analyses revealed that the risk of VTE in patients with SCI was significantly associated with complete paralysis (OR = 3.69).
Orthostatic intolerance in post-concussion patients
Published in The Physician and Sportsmedicine, 2022
Sara J. Gould, Graham D. Cochrane, Jarvis Johnson, Camden L. Hebson, Mohamed Kazamel
Athletes, in particular (77% of this patient cohort) seem more likely to have false negative orthostatic vital signs testing. Regular exercise leads to favorable cardiovascular and autonomic nervous system alterations, which improve tolerance to orthostatic challenge [20]. Specifically, leg muscle training has been shown to improve venous compliance [21] and can expand blood volume [22]; thus, athletes benefit from an improved ‘skeletal muscle pump’ effect. During orthostatic vital signs measurement, invoking the skeletal muscle pump by not standing completely still or simply tensing muscles improves venous return and cardiac filling and thus, ameliorates the tachycardic response. A HUT test partially neutralizes the effect of skeletal muscle pump by decreasing the need to activate the leg muscles, and thus improves the sensitivity of the test. Even so, reduced sensitivity of HUT in athletes, as compared to nonathletic controls, has been described, highlighting the need to not just rely on testing but also the clinical history and symptom report [20]. The etiology of decreased sensitivity to testing of athletes is a matter of ongoing debate, and beyond the scope of this study, but increased vagal tone, lower systemic vascular resistance, and changes to intrinsic cardiac funny current rate have all been implicated in various reports [20,23,24].
Post-operative delayed ambulation after thymectomy is associated withpre-operative six-minute walk distance
Published in Disability and Rehabilitation, 2018
Kazuhiro Hayashi, Koichi Fukumoto, Kohei Yokoi, Motoki Nagaya, Takayuki Inoue, Satoru Ito, Hiroki Nakajima, Keiko Hattori, Izumi Kadono, Yoshihiro Nishida
It was reported that post-operative delayed ambulation is associated with post-operative orthostatic intolerance symptoms such as nausea, vomiting and dizziness after thoracic surgery [11]. Indeed, our patients with delayed ambulation mostly experienced nausea, vomiting, and dizziness when they tried ambulation after surgery. Orthostatic intolerance is induced by reduced functional exercise capacity, functional deterioration of cardiovascular system, inadequate blood volume and loss of intact physical pumps comprising the skeletal muscle pump [24]. In the present study, post-operative delayed ambulation was associated with pre-operative 6MWD. In contrast, perioperative variables, such as operative time, anaesthesia time, blood loss, intraoperative fluid balance, operative procedure and epidural anaesthesia, were not associated with delayed ambulation. Because the 6MWD reflects the functional exercise capacity, it has been extensively assessed in patients with pulmonary and cardiovascular diseases [25,26] and who underwent surgery [13,17,27]. The present results demonstrated that poor functional exercise capacity leads to post-operative orthostatic intolerance, delayed ambulation and increased post-operative hospital stay in patients undergoing thymectomy, consistent with findings in other diseases. Moreover, it is not known how pre-operative 6MWD affects occurrence of symptoms such as nausea and dizziness which lead to orthostatic intolerance. Therefore, further investigation of the mechanisms is required.