Metabolism and properties of the myocardium, arterial and venous haemodynamics, blood pressure Romana Šlamberová, M.D. Ph.D. Department of Normal, Pathological and Clinical Physiology

Myocardium - morphology Intercalated disks = the fibers are connected to each other in Z lines –Provide strong union between fibers –Maintain cell-to-cell cohesion – so the pull of one contractile unit is transmitted to the next one –Along the sides of the muscle fibers = „Gap junction“ – provide low-resistant bridges for the spread of excitation = myocardium is functioning as a „syncytium“ Actin, myosin, tropomyosin, troponin Large amount of mitochondrias in tight contact with fibrils

Myocardium – contractil response Contraction – begins just after the start of depolarization and lasts about 1.5 x longer than the action potential Absolute refractory period – cardiac muscle cannot be excited again = therefore tetanus (as in the skeletal muscle) cannot accur Vulnerable period = period at the end of the action potential during which the fibrilation of the heart may accur

Myocardum – correlation length x tension Starling’s law = initial length of the fibers is determined by the degree of diastolic filling of the heart, and the pressure developed in the ventricle is proportionate to the total tension developed The developed tension increases as the diastolic volume increases until it reaches a maximum, then tends to decrease.

Myocardium – metabolism Abundant blood supply, numerous mitochondria, high content of myoglobin (a muscle pigment) as a storage of O 2 Metabolism mostly aerobic, only about 1% anaerobic (during hypoxia possible up to 10% anaerobic, if more – not enough energy for contractions) Utilization of substrates depending on the nutrition – 60% fats (mostly FA), 35% carbohydrates, 5% ketones and AAs

Haemodynamics - arteries Role of arteries in the systemic circulatory system is to transport the blood under the pressure from the left ventricle to separate tissues and organs. Arteries – strong, flexible, elastic wall is responsible for the fast flow of the blood (from lungs – periphery in 10 s = circulatory speed) Arterioles – strong wall consisted mostly by smooth muscles that is adjustable based of the needs of the body

Blood flow in arteries Ascending aorta –During the ejection phase of systole is the speed up to 100 cm/s = turbulent flow –Average speed is only around 20 cm/s –At the beginning of diastole the flow may be even reversed = semilunar valves closure = nárazové proudění aortou Other arteries –Constant continual flow of lower speed

Role of flexibility Systole = transformation of kinetic energy of blood to elastic energy of aorta wall Diastole = transformation of elastic energy of aorta wall to kinetic energy of blood Progression of blood the way of the lowest resistance, i.e. from the heart to the periphery

Blood pressure in arteries Pressure puls = ejection of blood from the left ventricle induces temporary increase of blood pressure in the aorta –Increase of blood pressure is followed by decrease = primary wave –At the beginning of diastole is low increase = dicrotic wave (based of relaxation of ventricle and retrograde blow of blood that closes the aortal valve) –Steady decrease up to the beginning of next ejection phase. Blood pressure never reaches zero level – elasticity of arteries and peripheral resistance

Blood pressure Systolic pressure = the highest value of pressure during the systole –120 mm Hg = 16 kPa Diastolic pressure = the lowest value of pressure during the diastole –80 mm Hg = 12 kPa Puls pressure (pressure amplitude) = difference between the systolic and diastolic pressure (dependent on pulse volume and flexibility of arteries) –50 mm Hg = 6,6 kPa Mean pressure = average value of pressure during the entire heard action (diastole is longer than systole) –90 mm Hg = 12 kPa

Haemodynamics - veins Role of veins in the systemic circulatory system is to transport the blood from separate tissues and organs to the right atrium. Venules and small veins –Blood flow is continual Large veins –Pulsation that is induced by retrograde function of the right atrium = venous pulse (phlebogram from jugular vein) Speed of the blood flow increases from venules to the heart Middle linear speed of the blood flow = cm/s

Phlebogram – Phlebogram – venous pulse a – increase in filling of central veins based of the systole of right atrium c – movement of cuspidal valves in the direction to the atriums at the beginning of isovolumic contraction s – relaxation of atriums and movement of heart basis and cuspidal valves in the direction to the apex at the beginning of ejection of ventricles v – filling of atriums during the isovolumic relaxation y – emptying of atriums during the filling phase

Blood flow in veins Gravity – positive and negative (dependent on location) Muscle pump – skeletal muscles Veins valves – against the retrograde blood flow Respiration – during inspiration the intrathoracal pressure decreases and the blood is sucked into the caval veins and the right atrium Sucking function of the heart – decrease of the pressure in atriums durint the ejection phase of the heart Vein pump – spiral muscle fibers in media Arterial pulse wave – pressure to veins (thanks to valves the flow is also in the direction to the heart)

Blood pressure in veins Depends on gravitation and on flexibility of veins Gravity – Pressure in the head (-10 mmHg) < central blood pressure (0 mmHg) < pressure in legs (90 mmHg) Width of veins – venules (10-15 mmHg), larger veins (5 mmHg) Flexibility of veins – Physiologically affected by sympathetic system – contraction of smooth vein muscles results in lower flexibility and in final in increased blood pressure and blood comeback

Blood pressure Systolic blood pressure depends on: –Systolic blood volume –Elasticity of arterial walls Diastolic blood pressure depends on the resistance of periphery (resistance is induced mostly by arterioles) Normal blood pressure: 120 mmHg (16 kPa) / 80 mmHg (12 kPa) Mean blood pressure: pm = 1/3 ps + 2/3 pd Increased blood pressure: 145 mmHg (19,4 kPa) / 95 mmHg (12,7 kPa) 1 mmHg = 0,133 kPa