EVALUATION OF MUSCLE CONTRACTION Relationship between load and contraction velocity of skeletal muscle EVALUATION OF CONTRACTION IN SKELETAL MUSCLE Velocityofcontraction load mmax Vmax (m +a)v = (mmax- m) b Hill equation corresponds to the maximal cycling rate of the cross-bridges constants Physiological factors affecting relationship between load and contraction velocity of skeletal muscle 1) Initial length of muscle (sarcomeres) contraction from resting length Velocityofcontraction load mmaxmmax contraction of shortened or stretched muscle Vmax 2) Number of active sarcomeres Velocityofcontraction load mmaxmmax trained muscle mmax untrained muscle Vmax trained muscle untrained muscle Isometricforce[%] sarcomere length [m] 3) Type of muscle fibres predominance of fast twitch fibres Velocityofcontraction load mmax predominance of slow twitch fibres Vmax slow twitch muscle fibres aerobic metabolisms, slow rate of contraction, can be active long time before they fatigue fast twitch muscle fibers anaerobic metabolismus, high rate of contraction, fatigue quickly Note: Depending on the intensity of muscle contraction only certain types of muscle fibbers are activated. s = 0.07 m Vmean = Exploration of dependence of contraction velocity on skeletal muscle load t = ? s t Index (dP/dt)max Normal values: 1300-1900 mmHg/s SV Assessment: by means of cardiac catheterization 1 Index (dP/dt)max represents maximum velocity of left ventricle pressure rise (dP/dt)mean dP dt dP/dt Note.: this index may be affected by the Frank-Starling mechanism (e.g. at hypertension when end-diastolic volume is increased)! EVALUATION OF CARDIAC MUSCLE CONTRACTILITY Use: mainly for research purposes (difficult and expensive invasive method) Index [(dP/dt)/P]max Assessment: by means of cardiac catheterization 2 Index [(dP/dt)/P]max represents maximum velocity of cardiac muscle contraction [(dP/dt)/P]max (dP/dt)/P control hypertension effect of Frank - Starling mechanism P8 mmHg 70 mmHg Note.: this index may be affected by high end-diastolic pressure in left ventricle! Use: mainly for research purposes (difficult and expensive invasive method) Index Vmax Assessment: by means of cardiac catheterization 3 Index Vmax represents velocity of cardiac muscle contraction at zero pressure (dP/dt)/P P0 70 Vmax extrapolation 15 Note.: This index may be affected by inaccurate extrapolation! ! 8 [mmHg] (dP/dt)/P P0 70 Vmax extrapolation 158 [mmHg] control control Use: mainly for research purposes (difficult and expensive invasive method) Index Emax Assessment: by means of cardiac catheterization 5 Index Emax represents slope of the line determined from end-systolic values of P-V diagrams Note.: most exact method for evaluation of cardiac muscle contractility independent on preload and afterload of left ventricle! P V30 ml 100 ml Emax= Pes Ves 70 110 [mmHg] [ml] aorta closed by a balloon contr. normal Emax smaller Emax lower contractility Pes Ves Ves Pes - end-systolic pressure Ves - end-systolic volume 4 Use: mainly for research purposes (difficult and expensive invasive method) Ejection fraction (EF) EF = SV EDV SV – stroke volume EDV – end-diastolic volume Normal values: SV  70 ml, EDV  100 ml, EF = 50 - 70% SV EDV EF increases under sympathetic stimulation and with increasing inotropic state EF lower than 40 % indicates decreased contractility of cardiac muscle (systolic dysfunction) Assessment: by means of magnetic resonance or echocardiography 5 Use.: Assessment of EF is a non-invasive method commonly used in clinical practice to estimate left ventricular contractility and systolic performance! clinic Velocity of circumferential fiber shortening (Vcf) Cd – length of inner circumferential left ventricle fibre in diastole Cs – length of inner circumferential left ventricle fibre in systole tef – duration of ejection fraction Normal value: 1.09  0.12 circ  s-1 Cd Assessment: by means of echocardiography 6 Cs clinic Use.: Assessment of Vcf is a non-invasive method commonly used in clinical practice to estimate left ventricular contractility! Vcf = (Cd-Cs) Cd  tef