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

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

Onderzoekingen over de aanslag van waterstof door electronen

Proefschrift Utrecht.OPLADEN-RUG0

Accuracy of determining the point of force application with piezoelectric force plates

The accuracy of determining the point of force application with piezoelectric force plates, as specified by the manufacturer, is lower than needed for certain applications. The purpose of this study was to evaluate the accuracy of a commonly used plate (KISTLER type 9287) and to improve it by proposing a correction algorithm. Forces were applied to a wooden board, supported in one corner by a stylus that rested on the force plate. To determine the influence of position and magnitude of the force vector, the stylus was placed on 117 different locations, and calibrated masses were used to exert vertical forces between 0 and 2000 N. To determine the influence of loading rate, dynamic tests were performed in which a subject ran across the board. In static tests at a given stylus position with actual coordinates x (short axis) and y (long axis), it was found that the calculated coordinates x ̂ and y ̂ of the point of force application had virtually constant values at forces above 1000 N. In dynamic tests, oscillations could occur in x ̂ and y ̂ with an amplitude of more than 20 mm. When these were avoided or removed by filtering, static and dynamic tests at a given stylus position showed the same values for x ̂ and y ̂ at forces above 1000 N. Across stylus positions, the errors x ̂-x and y ̂-y (measured at 1600 N) ranged from -20 to +20 mm. The average over 117 points of the absolute errors | x ̂-x| and | y ̂-y| amounted to 3.5 and 6.3 mm, respectively (mean values of three plates). Based upon the observed error distribution, a correction algorithm was selected. After correction, the errors ranged between -10 and +10 mm, and | x ̂-x| and | y ̂-y| were reduced to 1.3 and 1.6 mm, respectively. The algorithm may be applied by other users of the force plate tested here to improve their accuracy in determining the point of force application