The heart rhythm can be divided into the two main phases systole, with tension phase and ejection phase, and diastole, with the relaxation phase. The tension phase is the beginning part of systole, in which the two leaflet valves are closed passively, by the increase in pressure, and also actively, by muscle tension, and the two pocket valves to the aorta and pulmonary artery are initially still closed. With opening of the pocket valves, the tension phase changes to the expulsion phase.
What is the tension phase?
The tense phase is a segment of the cardiac rhythm phases, which can be divided into two main phases, systole and diastole. The tension phase is a segment of the cardiac rhythm phases, which can be divided into the two main phases systole and diastole. Systole is the simultaneous contraction phase of the two chambers (ventricles) of the heart, during which blood is pumped into the aorta (left ventricle) and pulmonary artery (right ventricle). Diastole is the relaxation and at the same time filling phase of the chambers, which coincides with the contraction phase of the atria (atrium). Systole begins with the short tension phase, at the start of which the leaflet valves to the atria close passively due to pressure build-up in the ventricles. The process is actively assisted by muscular tension of the tendon filaments at the edge of the leaflet valves. The leaflet valves that close the aorta (left ventricle) and pulmonary artery (right ventricle) are also still closed during the tension phase. When blood pressure exceeds the diastolic value in the arteries due to contraction of the ventricular muscles (myocardium), the pocket valves open automatically, as they function similar to a check valve. As the pocket valves open, the tense phase transitions to the ejection phase of systole.
Function and purpose
The tense phase marks the transition from diastole, the relaxation and filling phase of the ventricles, to the onset of systole, the tense and ejection phase of the ventricles. During the tightening phase, which lasts only about 50 to 60 milliseconds, the ventricular muscles contract and shorten accordingly. Since all heart valves are closed during this phase, the tightening of the ventricular muscles takes place under isovolumetric conditions, i.e., at constant blood volume in the chambers. This means that the ventricles take on an approximately spherical shape during the tension phase, which facilitates pressure buildup and the subsequent ejection phase. The tense phase is also important for the control of the heart valves. The two leaflet valves, the mitral and tricuspid valves, must close properly so that, as far as possible, no blood that has flowed into the ventricles immediately before is forced back into the atria. The two leaflet valves perform the function of inlet valves for the ventricles. At the same time, the two pocket valves, the pulmonary and the aortic valves, still remain closed to prevent blood from flowing from the arteries back into the ventricles as long as the pressure in the ventricles is lower than the diastolic pressure in the arteries. The two pocket valves act as outlet valves for the ventricles. If the blood pressure in the ventricles exceeds the diastolic blood pressure, the two pocket valves open automatically, allowing blood to be pumped into the main arteries as the ventricular muscles continue to contract. The transition from the tension phase to the ejection phase with opening of the pulmonary and aortic valves enters the unconscious control of the cardiovascular system sensory, via baroreceptors that “measure” blood pressure at specific points in the circulation. The onset of the tense phase coincides with the first heart sound audible with a stethoscope. Typically, it is muffled, i.e., low frequency, and lasts about 140 milliseconds. It results from the tightening of the ventricular muscles and is not due to the closure of the two leaflet valves, as previously thought.
Diseases and complaints
The tense phase of the heart is part of systole and should be viewed in the context of the other phases of the cardiac rhythm, since disturbances or problems with any one of the phases in a closed circuit, such as the circulatory system, inevitably affect the other phases. The tense phase can only function properly if all the components involved are functioning within the normal range.Only when pressure ratios are within the normal range can the heart assume a spherical shape during the tension phase, which serves to support the subsequent ejection phase. In the presence of hypertension (high blood pressure), particularly when diastolic pressure in the arteries is persistently elevated, the myocardium must perform increased work during the tension phase to open the two pocket valves that blood must pass through during the ejection phase. The increased force that the myocardium must exert leads to hypertrophy of the myocardium in the longer term, which has a negative effect on the performance and elasticity of the myocardium. A relatively common dysfunction of the mitral valve, depending on the severity of the insufficiency, leads to the onset of blood return from the left ventricle to the left atrium during the tension phase. This reduces the efficiency of the heartbeat, so that the heart must compensate for the missing power by increasing the frequency and/or blood pressure. In both cases, the heart attempts to compensate for the increased demand on the myocardium by hypertrophy, but this also has the opposite effect. The hypertrophied myocardium becomes inelastic and weaker in overall performance. Insufficiency of the mitral or tricuspid valves may result in the flow resistance, which occurs in the tension phase in closed and tightly holding valves, being too low in one or more leaky valves to allow the myocardium to form an approximate spherical shape. Similar problems may be encountered in the relatively common cardiac arrhythmias, especially atrial fibrillation. The atria fail to contract properly, so that the degree of filling of the ventricles during the tense phase is not equal to normal, and the heart responds by hypertrophying the myocardium.
