Regional myocardial perfusion and performance

The function of the heart is to pump blood from the veins into the arteries in response to the need of the tissues for oxygen and substrates. During its action the heart itself needs these nutrients. Factors that mainly determine the myocardial oxygen demand are (fig.0.1): heart rate, myocardial contractile performance (contractility) and ventricular wall tension. The oxygen supply is delivered by the coronary perfusion. Under normal conditions of coronary perfusion an equilibrium between the demand and the supply is present and adaptation is possible during a wide range of circumstances where myocardial oxygen demand is increased. A limitation of the coronary inflow, due to a coronary stenosis, quickly leads to an oxygen deficit. Even at slight flow reductions a redistribution of blood flow from the endocardium to the epicardium leads to endocardial malfunction. Therefore, the distribution of the blood flow within the myocardium is also a determinant of myocardial oxygen supply (fig.0.1). Acute myocardial ischaemia leads within seconds to an impaired segmental contractile function. When the ischaemic area constitutes a considerable fraction of the left ventricular muscle mass, a decrease in overall contractile function, cardiac output and arterial blood pressure occurs. Furthermore, the cardiac electro-physiological stability is disturbed, which frequently leads to arrhythmias of various severities including ventricular fibrillation. The pharmacological treatment of ischaemia is directed to restore the myocardial oxygen demand and supply relationship, either by decreasing the demand or by increasing the supply, whereas antiarrhythmic therapy is used to stabilize the haemodynamic condition and to reduce the risk of fatal arrhythmias. Enhancement of the oxygen supply can theoretically be realized by augmentation of perfusion pressure or perfusion time, while another approach is to lower the coronary vascular resistance or to augment the blood flow through interarterial collateral channels. The reduction of myocardial oxygen demand is carried out by reducing heart rate, myocardial contractility or intramyocardial wall tension. The present thesis, where an attempt is made to gain insight into the transmural distribution of the myocardial blood flow and its relationship with segmental function, has been broadly subdivided into four part

Ground reaction forces of elite dressage horses in collected trot and 1 passage

In this study, sagittal plane ground reaction forces (GRFs) in ridden elite dressage horses performing ‘collected trot’ and in ‘passage’ over ground were determined. In-ground force plates captured GRF data from four Dutch Warmblood and four Lusitano horses ridden by their trainers. At least three stance phases were analysed for forelimbs and hind limbs per horse. The variables extracted were vertical and longitudinal (braking, propulsive) force maxima, their times of occurrence and the respective impulses for forelimbs and hind limbs. Lusitanos had lower vertical impulses than Dutch warmbloods in collected trot. Across all horses, passage had larger vertical impulses than collected trot in the forelimbs and hind limbs. Propulsive impulse increased in the hind limbs in passage. Prolonged stance durations in passage contributed to higher vertical impulses that are needed to increase the vertical excursions of the centre of mas

Mechanical Properties of the Tendinous Equine Interosseus Muscle are Affected by in Vivo Transducer Implantation

Liquid metal strain gauges (LMSGs) were implanted in the tendinous interosseous muscle, also called suspensory ligament (SL), in the forelimbs of 6 ponies in order to quantify in vivo strains and forces. Kinematics and ground reaction forces were recorded simultaneously with LMSG signals at the walk and the trot prior to implantation, and 3 and 4 days thereafter. The ponies were euthanised and tensile and failure tests were performed on the instrumented tendons and on the tendons of the contra lateral limb, which were instrumented post mortem. The origo–insertional (OI) strain of the SL was computed from pre- and post-operative kinematics, using a 2D geometrical model. The LMSG-recorded peak strain of the SL was 5.4±0.9% at the walk and 9.1±1.3% at the trot. Failure occurred at 15.4±2.1% (mean±S.D.). The LMSG strain was higher than the simultaneously recorded OI strain 0.5±0.7% strain at the walk and 2.2±1.1% strain at the trot. Post-operative OI strains were only slightly higher than pre-operative values. Failure strains of in vivo instrumented SLs were 2.0±1.2% strain higher, and failure forces were slightly lower, than those of the contra lateral SLs that were instrumented post mortem. SL strains appeared to be considerably higher than those found in earlier acute experiments. Differences between in vivo LMSG and OI strains, supported by lower failure strains comparing in vivo and post mortem instrumented SLs, revealed that local changes in tendon mechanical properties occurred within 3 to 4 days after transducer implantation. Therefore, measurements of normal physiological tendon strains should be performed as soon as possible after transducer implantation

Kunststof breekboom

De Nederlandse Hippische Sportbond heeft in maart 1998 een commissie ingesteld met als taak het ontwikkelen, testen en implementeren van alternatieve materialen of constructies voor hindernisbouw in de militarysport

Ground Reaction Forces: The Sine Qua Non of Legged Locomotion

Legged locomotion results from the feet pressing against the ground to generate ground reaction forces (GRFs) that are responsible for moving the body. By changing limb coordination patterns and muscle forces, the GRFs are adjusted to allow the horse to move in different gaits, speeds, and directions with appropriate balance and self-carriage. This article describes the typical GRF patterns in each gait, the adaptations that produce turning, and the GRF patterns used to unload the painful limb when the horse is lame. The intent is to provide information that is of practical interest and value to equine scientists rather than being a comprehensive review of the topic. [Abstract copyright: Copyright © 2019 Elsevier Inc. All rights reserved.

Comparing subjective and objective evaluation of show jumping competition and warm-up arena surfaces

The development of safety and quality standards for equestrian surfaces needs to be based on objective, repeatable measurements which allow comparisons between surfaces. These measurements should incorporate the assessment of surface performance by riders. This study provides data from objective and subjective assessment of functional properties of high-level show jumping competition and warm-up arenas. Twenty-five arenas in nine international show jumping events were evaluated by mechanical insitu testing with a surface tester, rider assessments using visual analogue scales (198 riders provided 749 arena evaluations), descriptions of arena constructions and by laboratory tests of surface material. Mixed models were used to present subjective evaluation of rider perception of the functional properties for each arena while controlling for rider and event. The association between objective and subjective assessments were also explored creating mixed models, controlling for rider and event. Mechanical measurements of impact firmness, and to a lesser extent cushioning and grip, had a significant positive association with the riders’ perception. Responsiveness as assessed by the Orono biomechanical surface tester (OBST) was negatively associated with the riders’ perceptions, which suggests riders and the OBST had different concepts of this functional property and that further developments of the OBST might be necessary. Objectively measured uniformity showed no useful association with riders’ perception. Even though arena assessments were made by top level riders, a substantial inter-rider variation was demonstrated