The amount of blood emitted by the ventricle of the heart in the arteries per minute is an important indicator of the functional state of the cardiovascular system (CAS) and is called minute volume blood test (IOC). It is the same for both ventricles and alone is 4.5–5 l.
An important characteristic of the pumping function of the heart is stroke volume, also called systolic volume or systolic surge. Impact volume – The amount of blood released by the ventricle of the heart into the arterial system in one systole. (If we divide the IOC by heart rate per minute, we obtain the systolic volume (CO) of the blood flow.) With a heart rate of 75 beats per minute, it is 65–70 ml, and during operation it increases to 125 ml. In athletes at rest, it is 100 ml, while working increases to 180 ml. The definition of IOC and CO is widely used in the clinic.
Emission fraction (EF) – percentage ratio of stroke volume of the heart to the end-diastolic volume of the ventricle. EF at rest in a healthy person is 50-75%, and during physical exertion it can reach 80%.
The volume of blood in the cavity of the ventricle, which it occupies in front of its systole, is of course a diastolic volume (120–130 ml).
Course systolic volume (CSR) is the amount of blood remaining in the ventricle immediately after systole. At rest, it is less than 50% of BWW, or 50-60 ml. Part of this blood volume is reserve volume.
The reserve volume is realized with an increase in CO under load. Normally, it is 15–20% of the end-diastolic.
The volume of blood in the cavities of the heart, remaining with the full realization of the reserve volume, at the maximum systole is the residual volume. CO and IOC values are non-constant. With muscular activity, the IOC increases to 30–38 l due to an increase in heart contractions and an increase in the SOC.
A number of indicators are used to assess cardiac muscle contractility. These include: ejection fraction, the rate of expulsion of blood in the phase of rapid filling, the rate of increase in pressure in the ventricle during the voltage period (measured during ventricular sensing) /
Blood expulsion rate changed by the Doppler method with ultrasound of the heart.
Rate of pressure increase in the cavities is considered the ventricles is considered one of the most reliable indicators of myocardial contractility. For the left ventricle, the value of this indicator is normally 2000-2500 mmHg / s.
A decrease in the ejection fraction below 50%, a decrease in the rate of expulsion of blood, a rate of pressure increase indicate a decrease in myocardial contractility and the possibility of development of insufficiency of the pumping function of the heart.
The magnitude of the IOC divided by the surface area of the body in m 2 is defined as the cardiac index (l / min / m 2).
SI = MOK / S (l / min × m 2)
It is an indicator of the pumping function of the heart. Normally, the cardiac index is 3-4 l / min × m 2.
IOC, WOC and SI are united by the general concept cardiac output.
If IOC and blood pressure is known in the aorta (or pulmonary artery), it is possible to determine the external work of the heart.
Р – heart work in min. In kilograms (kg / m).
IOC – minute blood volume (L).
BP – pressure in meters of water column.
During physical rest, the external work of the heart is 70–110 J, during work it increases to 800 J, for each ventricle separately.
Thus, the work of the heart is determined by 2 factors:
1. The amount of blood flowing to it.
2. The resistance of blood vessels in the expulsion of blood in the arteries (aorta and pulmonary artery). When the heart is unable, with a given vascular resistance, to pump all the blood into the arteries, heart failure occurs.
There are 3 options for heart failure:
1. Insufficiency from overload, when excessive demands are made on the heart with a normal contractile ability in case of defects, hypertension.
2. Heart failure with myocardial damage: infections, intoxication, avitaminosis, impaired coronary circulation. This reduces the contractile function of the heart.
3. A mixed form of failure – with rheumatism, dystrophic changes in the myocardium, etc.
The whole complex of manifestations of the heart activity is registered using various physiological methods – cardiographies: ECG, electromyography, ballistocardiography, dynamocardiography, apical cardiography, ultrasound cardiography, etc.
The diagnostic method for the clinic is the electrical registration of the movement of the contour of the heart shadow on the screen of the x-ray apparatus. A photocell connected to an oscilloscope is applied to the screen at the edges of the contour of the heart. When the heart moves, the photocell illumination changes. This is recorded by the oscilloscope in the form of a curve of contraction and relaxation of the heart. This technique is called electromyography.
Apical cardiogram is recorded by any system that catches small local movements. The sensor is strengthened in the 5 intercostal space above the place of the cardiac impulse. It characterizes all phases of the cardiac cycle. But it is not always possible to register all phases: a heart impulse is projected differently, some of the force is applied to the ribs. The recording of different people and one person may differ, affects the degree of development of the fat layer, etc.
The clinic also uses research methods based on the use of ultrasound – ultrasound cardiography.
Ultrasonic vibrations at a frequency of 500 kHz and higher penetrate deeply through the tissues being formed by ultrasound emitters attached to the surface of the chest. Ultrasound is reflected from tissues of different density – from the outer and inner surface of the heart, from the vessels, from the valves. The time to reach the reflected ultrasound to the pickup device is determined.
If the reflecting surface moves, then the return time of the ultrasonic vibrations changes. This method can be used to register changes in the configuration of the structures of the heart during its activity in the form of curves recorded from the screen of an electron-beam tube. These techniques are called non-invasive.
Invasive techniques include:
Catheterization of the cavities of the heart. An elastic catheter probe is inserted into the central end of the opened brachial vein and pushed to the heart (in its right half). A probe is inserted into the aorta or the left ventricle through the brachial artery.
Ultrasound scan – The ultrasound source is inserted into the heart using a catheter.
Angiography is a study of the movements of the heart in the field of X-rays, etc.
Mechanical and sound manifestations of cardiac activity. Heart sounds, their genesis. Polycardiography. Comparison in time of periods and phases of the ECG and FCG cardiac cycle and mechanical manifestations of cardiac activity.
Heart push. With diastole, the heart takes the form of an ellipsoid. When systole it takes the form of a ball, its longitudinal diameter decreases, the transverse increases. The top of the systole rises and presses against the anterior chest wall. In 5th intercostal space, a cardiac impulse occurs, which can be registered (apical cardiography). The expulsion of blood from the ventricles and its movement through the vessels due to reactive recoil causes oscillations of the whole body. Registration of these oscillations is called ballistocardiography. The work of the heart is also accompanied by sound phenomena.
Heart sounds. When listening to the heart, two tones are determined: the first is systolic, the second is diastolic.
Ø Systolic tone is low, broaching (0.12 s). Several overlapping components are involved in its genesis:
1. Component of the mitral valve closure.
2. Closure of the tricuspid valve.
3. The pulmonary tone of the expulsion of blood.
4. Aortic expulsion of blood.
The characteristic of the I tone is determined by the tension of the flap valves, the tension of the tendon filaments, papillary muscles, and the walls of the ventricular myocardium.
The components of the expulsion of blood occur when the tension of the walls of the great vessels. I tone is well heard in the 5th left intercostal space. When pathology in the genesis of the first tone are involved:
1. The aortic valve opening component.
2. Opening the pulmonary valve.
3. The tone of stretching of the pulmonary artery.
4. Tone of stretching the aorta.
Gain I tone can be when:
1. Hyperdinamia: physical exertion, emotions.
2. In violation of the temporal relationship between atrial and ventricular systole.
3. With poor filling of the left ventricle (especially with mitral stenosis, when the valves do not fully open). The third variant of the amplification of the I tone has a significant diagnostic value.
The weakening of the I tone is possible with mitral valve insufficiency, when the leaflets are not tightly closed, with the defeat of the myocardium, etc.
Ø II tone – diastolic (high, short 0.08 s). Occurs when the voltage closed semilunar valves. On a sphygmogram, its equivalent is incisur. The tone is higher, the higher the pressure in the aorta and pulmonary artery. Well listened to the 2-intercostal space to the right and left of the sternum. It increases with sclerosis of the ascending aorta, pulmonary artery. The sound of the I and II tones of the heart most closely conveys the combination of sounds when pronouncing the phrase “LAB-DAB.”
Using the oscilloscope, you can register heart tones in the form of curves. This technique is called phonocardiography. On the curves recorded in this way, weaker III and IV tones are noted.
For a more reliable analysis of the tones and noises of the heart, PCG are always recorded simultaneously with the ECG. Occurrence of the I tone in a healthy person is always recorded at the beginning of ventricular systole (stress period, end of the asynchronous contraction phase), and its full registration coincides with the recording of the ventricular QRS complex on an ECG. The onset of tone II under normal conditions coincides with the onset of diastole of the ventricles, delaying by 0.02-0.04 s by the end of the T wave on the ECG. The third tone is formed by oscillations of the walls of the ventricles with rapid filling them with blood during the diastole phase of the same name. IV tone is formed when the additional filling of the ventricles during atrial systole. If III and IV are heard, in most cases this indicates the presence of cardiac pathology.
Listen to heart sounds with a phonendoscope (stethoscope) or put your ear to your chest.
At incomplete closing of valves, owing to the turbulent movement of blood, cordial noise appear. Their identification has important diagnostic value.
3. Regulation of cardiac activity
Adaptation of the heart to the changing needs of the body is carried out using regulatory mechanisms:
Ø Myogenic autoregulation.
Ø Nerve regulation mechanism.
Ø Humoral regulation mechanism.
Myogenic autoregulation. The mechanisms of myogenic autoregulation are determined by the properties of the muscle fibers of the heart. There are intracellular regulation. In each cardiomyocyte there are mechanisms of regulation of protein synthesis. With an increase in the load on the heart, there is an increase in the synthesis of myocardial contractile proteins and structures that ensure their activity. At the same time, physiological hypertrophy of the myocardium occurs (for example, in athletes).
Intercellular regulation. Associated with the function of the nexus. Here the impulses are transferred from one cardiomyocyte to another, the transport of substances, the interaction of myofibrils. A part of the self-regulation mechanisms is associated with reactions arising from a change in the initial length of the myocardial fibers — heterometric regulation and reactions unrelated to a change in the initial length of the myocardial fibers — homeometric regulation.
The concept of heterometric regulation was formulated by Frank and Starling. It was found that the more the ventricles stretch during diastole (up to a certain limit), the stronger their reduction to the next systole. Increased filling of the heart with blood, caused by an increase in its inflow, or a decrease in the release of blood into the vessels, leads to a stretching of the myocardial fibers and an increase in the force of contractions. An increase in blood flow to the ventricles is called load volume or preload
Homeometric regulation includes effects associated with changes in pressure in the aorta (the Anrep effect) and changes in the rhythm of heart contractions (the effect or Bowditch ladder). The effect of Anrep – the force of contraction of the myocardium of the ventricle increases in proportion to the increase in resistance in the aorta. Such an increase in resistance to blood expulsion has been called pressure loads or afterload. The effect of Anrep is that an increase in aortic pressure leads to a decrease in systolic surge and an increase in residual blood volume in the ventricle. The incoming new blood volume leads to stretching of the fibers, heterometric regulation is activated, which leads to increased contraction of the left ventricle. The heart is freed from excess residual blood. Establishes the equality of venous flow and cardiac output. At the same time, throwing out the same volume of blood against the increased resistance in the aorta, as with a smaller pressure in the aorta, performs increased work. With a constant rate of contraction, the power of each systole increases. Hetero and homeometric regulation (both mechanisms) are interrelated. The effect of Bowdich is that as the heart rate increases, the strength of the contractions increases. If the frog’s isolated, stopped heart is subjected to rhythmic stimulation, with increasing frequency, the amplitude of contractions for each subsequent stimulus gradually increases. The increase in the force of contractions for each subsequent stimulus (up to a certain value) was called the “phenomenon” (ladder) of Bowdich. With frequent impulses, calcium ions do not have time to be removed from sarcoplasm, which creates conditions for a more intense interaction between actin and myosin filaments.
Intracardial peripheral reflexes are closed in the intramural (intraorganic) myocardial ganglia. This system includes:
1. Afferent neurons form mechanoreceptors on myocytes and caronal vessels.
2. Inserted neurons.
3. Efferent neurons. Innervate the myocardium and coronary vessels. These links form intracardiac reflex arcs. These include reflexes
1. With low blood pressure in the cavities:
an increase in right atrial sprain increases contractions of the left ventricle to make room for flowing blood and relieve the system
2. With high blood pressure in the aorta mouth:
the overflow of the heart chambers with blood reduces the force of contractions, the blood is released less and it is deposited in the venous part of the system
These reflexes are formed in ontogenesis early before the appearance of central reflex regulation.
Extracardiac nervous regulation. The highest level of adaptation of the cardiovascular system, which is carried out with the participation of centers located in the brain and spinal cord, as well as the activity of the autonomic nervous system.
Influence of the vagus nerve. From the nucleus of the vagus nerve, located in the medulla oblongata, the axons in the composition of the right and left nerve trunks, approach the heart and form synapses on the motor neurons of the intramural ganglia. Fibers of the right vagus nerve are distributed mainly in the right atrium: they innervate the myocardium, coronary vessels, the SA node. Fibers of the left innervate mainly AV node, affect the conduction of excitation. Research Weber brothers (1845) found an inhibitory effect of these nerves on the activity of the heart.
Upon irritation of the peripheral end of the cut vagus nerve, the following changes were identified:
1. The negative chronotropic effect (slowing the rhythm of contractions).
2. Negative inotropic effect – reducing the amplitude of contractions.
3. A negative bathmotropic effect – a decrease in myocardial excitability.
4. Negative dromotropic effect – reducing the rate of excitation in cardiomyocytes.
Irritation of the vagus nerve can cause a complete cessation of cardiac activity, there comes a complete blockade of the excitation in the AV-node. However, with continued irritation, the heart again restores contractions, and the heart escapes from the influence of the vagus nerve.
Influences of the sympathetic nerve. The first neurons of the sympathetic nerves are located in the lateral horns of the 5 upper segments of the thoracic spinal cord. The second neurons from the cervical and upper thoracic sympathetic nodes go mainly to the ventricular myocardium and the conducting system. The impact of their heart explored
1. Positive chronotropic effect (increased heart rate).
2. Positive inotropic effect (increase in the amplitude of contractions).
3. Positive bathmotropic effect (increased excitability of the myocardium).
4. Positive dromotropic effect (increase in the rate of excitation).
With simultaneous stimulation of the sympathetic and vagus nerves, the effect of the vagus predominates. Despite the opposite effects of the sympathetic and vagus nerves, they are functional synergists. Depending on the degree of filling the heart and coronary vessels with blood, the vagus nerve may have the opposite effect,
Transmission of arousal from the endings of the sympathetic nerve to the heart is carried out with the help of a mediator noradrenaline. It collapses more slowly and lasts longer. In the endings of the vagus nerve acetylcholine is formed. It is rapidly destroyed by AH-esterase, therefore it has only a local effect. When both nerves (both sympathetic and wandering) are cut, a higher rhythm of the AV node is observed. Consequently, his own rhythm is much higher than under the influence of the nervous system.
The nerve centers of the medulla oblongata, from which the vagus nerves flow to the heart, are in a state of constant central tone. From them to the heart comes constant braking effects. When you cut both vagus nerves, there is an increase in heart contractions. The following factors affect the tone of the nuclei of the vagus nerve: an increase in the blood levels of adrenaline, Ca 2+ ions, and CO2. Breathing affects: when you inhale, the nucleus of the vagus nerve decreases, when you exhale, the tone increases and heart activity slows down (respiratory arrhythmia).
Regulation of cardiac activity is carried out by the hypothalamus, the limbic system, the cerebral cortex.
An important role in the regulation of the heart is played by the receptors of the vascular system, which form vascular reflexogenic zones.
The most significant: aortic, sino-carotid zone, the zone of the pulmonary artery, the heart itself. The mechano- and chemoreceptors involved in these zones are involved in stimulating or slowing down the heart’s activity, which leads to an increase or decrease in blood pressure. Allocate:
Internal system reflexes:
Holtz reflex, Ashner-Danini reflex, reflexes from the capsule of the liver and biliary tract, reflex from the ventral surface of the medulla oblongata, pain reflexes, respiratory-cardiac reflexes, conditioned reflexes
Excitation from the receptors of the mouths of the hollow veins leads to an increase and increase in heart rate, which is associated with a decrease in the tone of the vagus nerve, and an increase in the tone of the sympathetic – Bainbridge reflex.
Goering reflex – irritation of the aorta baroreceptors and the carotid sinus causes a decrease in heart rate due to an increase in the tone of the centers of the vagus. Under natural conditions, these reflexes are caused by an increase in blood pressure in the carotid artery and aorta.
Reflex Parina – an increase in blood pressure in the vessels of the pulmonary circle also leads to bradycardia, hypotension, dilation of the spleen vessels. Stagnation of blood in the lungs is eliminated.
The Holtz reflex is one of the classic vagal reflex. With mechanical effects on the stomach or intestines of a frog, cardiac arrest is observed (the influence of the vagus nerve). In humans, this is observed when hitting the front abdominal wall.
The eye-heart reflex Danini-Ashner. When pressing on the eyeballs, the contractions of the heart decrease by 10–20 per minute (the influence of the vagus nerve).
Increasing and strengthening of the contractions of the heart is observed in pain, muscular work, and emotions.
The involvement of the cortex in the regulation of the heart proves the method of conditioned reflexes. If you repeatedly combine the conditioned stimulus (sound) with pressure on the eyeballs, which leads to a contraction of the heart, then after a while only the conditioned stimulus (sound) will cause the same reaction – the conditioned eye-heart reflex of Danini-Ashner.
In case of neurosis, disturbances may also appear in the cardiovascular system, which are fixed in accordance with the type of pathological conditioned reflexes. Signals from the proprioceptors of the muscles are of great importance in the regulation of the activity of the heart. With muscular loads, impulses from them exert inhibitory effects on the centers of the vagus, which leads to an increase in heart contractions. Heart rate can change under the influence of excitation from thermoreceptors. An increase in body temperature or the environment causes an increase in contractions. Cooling the body when entering into cold water, while bathing leads to a contraction of contractions.
Humoral regulation. It is carried out by hormones and ions of the extracellular fluid. Stimulate: catecholamines (adrenaline and norepinephrine), increase the strength and rhythm of contractions. Adrenaline interacts with beta receptors, adenylate cyclase is activated, cyclic AMP is formed, inactive phosphorylase is converted into active, glycogen is split, glucose is formed, and as a result of these processes, energy is released. Adrenaline increases membrane permeability for Ca 2+, which is involved in cardiomyocyte contraction. The same effect on the reduction of glucagon, corticosteroids – (aldosterone), angiotensin, serotonin, thyroxin. Ca 2+ increases the excitability and conductivity of the myocardium.
Acetylcholine, hypoxemia, hypercapnia, acidosis, K +, HCO -, and H + ions inhibit cardiac activity.
Electrolytes are of great importance for the normal functioning of the heart. The concentration of K + and Ca 2+ ions affects the automatization and contractile properties of the heart. An excess of K + causes a decrease in rhythm, contraction forces, a decrease in excitability and conductivity. Washing the isolated heart of animals with a concentrated K + solution leads to relaxation of the myocardium and cardiac arrest in diastole.
Ca 2+ ions increase the rhythm, increase the strength of heart contractions, excitability, and conductivity. An excess of Ca 2+ leads to cardiac arrest in systole. Deficiency – weakens contractions of the heart.
Date Added: 2014-12-15; views: 102 | Copyright infringement