Blood circulation system. Heart physiology (cardiac activity phases, heart tones, electrocardiogram). 


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Blood circulation system. Heart physiology (cardiac activity phases, heart tones, electrocardiogram).



Blood circulation system provides continuous blood movement through vessels. As it is well-known, it consists of 2 main parts – heart and vessels. Heart work beginning is atriums systole. Right atrium contracts before left atrium on 0,01 sec because main pacemaker is in right atrium. Excitement spreading through heart begins from it. This phase duration is 0,1 sec. During atrium systole pressures in atriums are increased: in right – to 5-8 mm, in left – till 8-15 mm mercury col. Blood moves to atriums and it is accompanied by atrio-ventricular foramens closage. Ventricles systole takes place simultaneousely (atriums are relaxed in that time). Ventricles systole duration is about 0,3 sec. Ventricles systole begins with asynchronic contraction phase. It lasts about 0,05 sec and is the process of excitement spreading and contraction through myocardium. Pressure in ventricles is practically constant. While further contraction when pressure in ventricles increases to the size sufficient to atrio-ventricular valves closage but insufficient to semilunar valves opening, isometric contraction phase occurs. Its duration is up to 0,03 sec. Sometimes these phases are united in one and are called by tension phase (0,05-0,08 sec). In this phase pressure in right ventricle increases up to 30-60 mm merc.col., in left one – up to 150-200 mm merc.col. Tension is increased (valves are closed) and muscular fiber length doesn’t change in course of asynchronic contraction. In the end of tension phase pressure provides semilunar valves opening and ventricle systole next phase is begun – of fast blood expulsion. In course of this phase which lasts from 0,05 to 0,12 sec, pressure reaches its maximal ziphras. Later pressure reduces up to 20-30 and 130-140 mm merc. col. in corresponding ventricles and this moment of their work is called slow blood expulsion. This ventricle systole phase duration is from 0,13 to 0,20 sec. Pressure is sharply reduced with its ending. Pressure is decreased rather slower in magistral arteries that provides later clapping of semilunar valves and prevent blood regurgitation. But it occurs in the moment when ventricle muscle begins its relaxation and their dyastole takes place. Space time from ventricles relaxation beginning to semilunar valves closage is first dyastole phaseprotodyastolic. Next dyastole phase – tension reducing or isometric relaxation takes place. It is expressed at closed valves and lasts approximately 0,05-0,08 sec from the moment when pressure in atriums is higher than in ventricles (206 mm.merc.col.) that leads to atrio-ventricular valves opening after which blood comes in ventricle. First, it occurs quickly (for 0,05 sec) – ventricles fast filling with blood phase and then slowly (for 0,25 sec) - ventricles slow filling with blood phase. Uniterrupted blood coming from magistral veins both in atriums and in ventricles takes place at the beginning of this phase. And, finally, last phase of ventricles dyastole is their filling due to atriums systole (0,1 sec). If to sum ventricles systole and dyastole time than we will receive time corresponding to complete cardiac cycle which is 0,8 sec in adults. In course of heart work there is such moment when both atriums and ventricles together (simultaneousely) are in dyastole state. This heart work period is called heart pause the duration of which is 0,4 sec.

In course of systole heart pumps in blood circulation up to 70-100 ml of blood. This blood volume is known as systolic volume (SV). If SV multiply on heart contraction freaquency (HFC) we will receive minute volume (MV) of heart work the size of which is about 4,0-5,0 l.

Heart tones. These are sound phenomena by which heart work is accompanied by. Different heart structures fluctuations (of valves, muscles, vessel wall) are on the basis of their occurence. As any fluctuations, tones are characterized by intensivity (altitude), freaquency and duration. There are 2 clinical methods of their assessment: auscultation (hearing by sthethoscope) and graphical one – phonocardiography.

I-st tone – systolic – is lower and more prolonged, it occurs in atrio-ventricular valves region simultaneousely with ventricle systole beginning. Duration: 0,08-0,25 sec, freaquency – 15-150 Gz. Optimal place for auscultation: heart apex. Its reasons:

· atrio-ventricular valves closage and tension;

· heart cavity walls fluctuation in course of systole;

· ventricles musculature contraction.

II-nd tone – dyastolic – is higher and shorter. Its duration is 0,04-0,12 sec, freaquency – 500-1250 Gz. Optimal place for auscultation: second intercostal space on the right and on the left from sternum. Reason: semilunar valves fluctuation. Sometimes these fluctuations are so expressed that tone’s division into two is observed.

III-rd tone – ventricular gallop – is delt with ventricles muscular wall fluctuations at their stretches right after the second tone. It is sometimes called as tone of filling. It is most often auscultated or registrated on phonocardiogram (PCG) in children and sportsmen. One can hear it as a weak, muffled sound, the most comfortable place – on heart apex (when patient is lying) and sternum region (when he is standing).

IV-th tone – atrial gallop – is connected with atriums contraction when they fill actively ventricle with blood. It is auscultated seldom, more often it is registrated on phonocardiogram.

Registration and analysis of electrical potentials occuring in course of heart activity has received the widest spreading in clinical practice.

Electrocardiogram – is a curve, periodically repeated and reflecting heart excitation process spreading in course of time. Separate ECG elements have received their special names: denses, segments, intervals and complexes. Every ECG element reflects excitation process spreading through definite heart regions and has time (in seconds) and high (in mV) characteristics. ECG analysis independently from abduction (lead) is given on the base of denses study (P,Q,R,S,T), intervals (PQ, ST, TP, RR), segments (PQ, ST) and complexes (P – atrial and QRST – ventricular).

As cardiac cycle begins with atriums excitation the first dens on ECG – is dens P. It characterizes atriums excitement. Its ascendent part – of right, descendant - of left one. Its characteristics under norma: duration - from 0,07 to 0,11 sec, altitude - from 0,12 till 0,16 mV. It may be absent in III-rd standard lead (abduction) it may be absent, two-phased or negative. In V1-V2 - it is positive, V3-V4 - it is gradually increased. In one-poled abductions form extremities: aVR – it is negative, in aVL and aVF – positive.

Segment PQ – is a right line section on isoelectric axis from dens P end to dens Q beginning. It characterizes atrio-ventricular lack time and is about 0,04-0,1 sec.

Interval PQ - ECG locus from dens P beginning till dens Q beginning, it characterizes excitement distribution from atriums to ventricles. Its duration is 0,12-0,21 sec.

Dens Q – characterizes interventricular septum and papillar musculature excitement. Under norma its duration is from 0,02 till 0,03 sec, altitude – up to 0,1 mV. It may be absent in the I.

Dens R – characterizes main ventricles musculature excitement. Its altitude is 0,8-0,16 mV, duration – 0,02-0,07 sec. In thoracic abductions V1-V2 it is small, V3-V4 - it is increased, in V5-V6 it is reduced again.

Dens S – describes excitement in distant ventricles locuses. Its altitude reaches up to 0,01 mV and duration – up to 0,02-0,03 sec. It may be absent in I. In V1-V2 it is deep, then it is decreased, in V5-V6 it may be absent.

Segment ST - is a right line section on isoelectric axis from dens S end till dens T beginning and describes the moment when both ventricles are simultaneousely excited. Its duration is from 0,1 till 0,15 sec.

Dens T – describes myocardium repolarization process, it altitude is 0,4-0,8 mV, duration – 0,1-0,25 sec. In I it is always positive, in II - often positive and in III – may be positive, two-phased and negative. In V1-V2 it is negative sometimes, in aVF – negative.

Interval TP – characterizes common heart pause, its duration is 0,4 sec.

Interval R-R – characterizes complete cardiac cycle, its duration is 0,8 sec.

Complex P – atrial.

Complex QRST – ventricular.

As heart excitation begins from its base, than this region is a negative pole, apex region – positive one. Heart electromoving force (EMF) has its size and direction. EMF direction is considered to call heart electrical axis. In the most common cases it is located in parallel to heart anatomical axis (normogram). Direction of one or another dens on ECG reflects an integral vector direction. When vector is directed to heart apex, one can registrate positive (as for electrical axis) denses, if to the heart base - negative. Due to definite heart location in thorax and human body shape, electrical force lines occuring between excited and unexcited heart locus, are distributed unequally on body surface. If heart axis becomes horizontal (lying heart) than such situation is called left-gram, in a case of its vertical localization (hanging heart) – right-gram.

 

Lecture 12.



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