Relationship between muscle stress and intramuscular pressure during dynamic muscle contractions

Intramuscular pressure (IMP) has been used to estimate muscle stress indirectly. However, the ability of this technique to estimate muscle stress under dynamic conditions is poorly characterized. Therefore, the purpose of this study was to determine the extent to which IMP is a valid surrogate for muscle stress during dynamic contractions. IMP and muscle stress were compared under steady-state isotonic conditions and during complex dynamic length changes. During concentric contractions the shape of the IMP–velocity curve mimicked the basic shape of the force–velocity curve but with much higher variability. For eccentric contractions, a precipitous drop in IMP was observed despite increased muscle stress. The dissociation between muscle stress and IMP during dynamic contractions was partially explained by sensor movement. When the muscle was not moving, IMP explained 89% ± 5% of the variance in muscle force. However, when transducer movement occurred the linear relationship between IMP and stress was no longer observed. These findings demonstrate the difficulty in interpreting IMP under dynamic conditions when sensor movement occurs. They also illustrate the need to control transducer movement if muscle stress is to be inferred from IMP measurements such as might be desired during clinical gait testing. Muscle Nerve, 2007Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56124/1/20828_ftp.pd

Return to sport activity after anterior cruciate ligament reconstruction in skeletally immature athletes with manual drilling original all inside reconstruction at 8 years follow-up

Objective: Anterior cruciate ligament (ACL) tears are common injuries in adolescent athletes, especially in those who bear high stress on their knees due to shearing forces. The goal of the surgical procedures in skeletally immature patients is to restore joint stability avoiding the adverse effects on the growth process. The aim of this study was to verify the return of the skeletally immature professional athletes to sports in the long-term, following ACL reconstruction with the original all-inside technique and with manual drilling. Methods: This study included 24 athletes (14 boys, 10 girls; mean age: 13.15 years, range: 9e14 years) who had radiographic evidence of open physes, were less than 14 years of age at the time of surgery and those with a minimum follow-up of eight years. All patients completed a questionnaire, the IKDC subjective knee evaluation form, and Tegner Activity Scale. Biomechanical outcomes of the KT-1000 arthrometer, gait analysis, and stabilometric and isokinetic results were also evaluated. A plain radiograph of both lower limbs was taken to obtain a precise measurement of the limb length and mechanical axis angles. Results: The patients returned to sport activities in a mean time of 6.43 months. No rerupture or resurgery due to growth abnormalities was observed. The mean difference in length between the operated and contralateral legs was 0.4 (range: 0.2 to 0.7) cm. The mean side-to-side difference measured with the KT-1000 arthrometer was 5.2 (range: 3.5 to 7) mm in the preoperative and 0.8 (range: 0 to 2.5) mm in the postoperative measurements. Conclusion: In conclusion, the original all-inside technique with manual drilling with a half tunnel and short graft seems to be a very effective technique for the surgical management of ACL injuries in pediatric/ adolescent athletes. A good rate of return to sports at pre-injury levels or higher, high patient satisfaction and a decent motor and proprioceptive function is possible as shown by our analysis. Level of evidence: Level IV, Therapeutic study

Molecular and functional characterization of the endothelial ATP-sensitive potassium channel

British Heart Foundation Grant RG/15/15/31742 and was facilitated by the National Institute for Health Research Biomedical Research Centre at Barts

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017

Adenosine receptor subtypes and vasodilatation in rat skeletal muscle during systemic hypoxia: a role for A1 receptors

In anaesthetized rats we tested responses evoked by systemic hypoxia (breathing 8% O2 for 5 min) and adenosine (i.a. infusion for 5 min) before and after administration of a selective adenosine A1 receptor antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine), or a selective adenosine A2A receptor antagonist ZM 241385. Arterial blood pressure, (ABP), heart rate (HR), femoral blood flow (FBF) and femoral vascular conductance (FVC: FBF/ABP) were recorded together with the K+ concentration in arterial blood ([K+]a) and in venous blood of hindlimb muscle ([K+]v) before and at the 5th minute of hypoxia or agonist infusion.In 12 rats, DPCPX reversed the fall in ABP and HR and the increase in FVC evoked by the selective A1 agonist CCPA (2-chloro-N6-cyclopentyladenosine; i.a. infusion for 5 min). DPCPX also reduced both the increase in FVC induced by hypoxia and that induced by adenosine; the control responses to these stimuli were comparable in magnitude and both were reduced by ∼50%.In 11 rats, ZM 241385 reversed the fall in ABP and increase in FVC evoked by the selective A2A agonist CGS 21680 (2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethylcarboxamidoadenosine hydrochloride; i.a. infusion for 5 min). ZM 241385 also reduced the increase in FVC induced by adenosine by ∼50%, but had no effect on the increase in FVC induced by hypoxia.In these same studies, before administration of DPCPX, or ZM 241385, hypoxia had no effect on the venous-arterial difference for K+ ([K+]v-a), whereas after administration of either antagonist, hypoxia significantly reduced [K+]v-a suggesting an increase in hypoxia-induced K+ uptake, or a reduction in K+ efflux.These results indicate that both A1 and A2A receptors are present in hindlimb muscle and can mediate vasodilatation and that A1 and A2A receptors contribute equally to dilatation induced by infused adenosine. However, they suggest that endogenous adenosine released during systemic hypoxia induces dilatation only by acting on A1 receptors. Given previous evidence that adenosine can stimulate receptors on skeletal muscle fibres that are coupled to ATP-sensitive K+ (KATP) channels so promoting K+ efflux, our results allow the proposal that KATP channels may be coupled to both A1 and to A2A receptors and may be stimulated to open by adenosine released during hypoxia, but indicate that, during systemic hypoxia, K+ efflux caused by either receptor subtype makes a very minor contribution to the muscle vasodilatation