Systolic early relaxation phenomenon (SERP)
Category
An angiographic phenomenon not well explained up to now.
In two papers in this site it is explained how our attention was attracted upon the observation the heart accelerates two masses of blood, and consequently its action should be described using dynamics laws instead of static variables (pressure/volume diagram). This description of cardiac cycle allowed us to understand cardiac relaxation, unsatisfactorily explained up to now, since myocardium has only agonistic musculature. As a corollary, we are now able to explain Systolic Early Relaxation Phenomenon (SERP), a distension of a focal portion of ventricular myocardium in early systole, when cardiac muscle starts contraction.
The explanation requires the use of the variable "time", ignored in pressure/volume diagram, but of capital importance in coupling cardiac electrical/mechanical phenomena.
Electrical systole. Stimuli activating cardiac contraction reach ventricular myocardium along specialized fibers conducting at speed of about 4 m/sec, and Purkinje fibers scatter impulses so that cardiac contraction occurs in coordinated way. Rapid complex (QRS) of electrocardiogram (ECG) represents electrical systole: it lasts 0.10 - 0.12 sec. and consists in an instant flux of sodium ions into muscular fibers reversing their trans-membrane polarity: from -90 mV to about +10 mV. This phenomenon causes the liberation of calcium ions which in contact with actin and myosin filaments give rise to fibers shortening. Electrical re-polarization (ECG T wave) follows S-T segment, and its function is to take out calcium ions from myofilaments and to restore trans-membrane potential of -90 mV. The complete course of ventricular electrical phenomena (depolarization and re-polarization i.e. QTc time interval) last 0.25 to 0.40 sec according to heart rate (HR).
Mechanical contraction follows electrical systole by 0.04 sec and lasts 0.28 - 0.22 sec according to heart rate (it shortens while HR increases). When pressure in the left ventricle exceeds pressure in the aorta, semi-lunar valve opens and a cylindrical blood mass is pushed into the aorta.
Fig 1. See text for explanatin.
All striated muscles have antagonistic ones which lengthen after contraction. All but myocardium, therefore its relaxation musts depend from different forces. In fact, during ejection, ascending aorta accumulates resilient energy due to heart recoil (dynamics 3rd principle). As cardiac apex is fixed to the diaphragm, the elastic recall of the aorta pulls back the heart in longitudinal sense after ejection. Atrial blood plus ventricular residual volume, both drawn down during ejection, form a unique mass of blood exerting a lateral push over walls of re-ascending ventricle (dynamics 1st principle). Therefore myocardium relaxation is a dynamic phenomenon. This is the critical point, because elastic recall follows immediately aortic valve closure, at the end of ECG T wave (fig. 1). If for any reason (generally insufficient blood supplying), in a restricted area of myocardium calcium ions are removed after the elastic recall, myocardial fibers of that area can't be lengthened by described dynamic mechanisms (aortic recall - rapid filling). Afterwards (diastasis period) there are no forces able to lengthen these fibers. When ventricular pressure starts rising in following systole, fibers remained shortened become lengthened by an internal force, generating the phenomenon named SERP.
Recent Posts
The discovery of a withholding lost mail ignites a controversy
18/05/2016
An angiographic phenomenon not well explained up to now.
27/08/2016
The heart is a very efficient hydrodynamic pump
11/03/2016
I commenti
Cheap goods 09/15/2016
I like what you guys tend to be up too. Such clever work and coverage! Keep up the very good works guys I've incorporated you guys to my personal blogroll.
Cheap goods 09/15/2016
Wynn documented revenue before last number of quartersit could possibly preserve stagnating, or maybe counterpicking.
Cheap goods 09/25/2016
Hi Dear, are you in fact visiting this website daily, if so then you will definitely take fastidious knowledge.
Cheap goods 09/25/2016
Pretty portion of content. I just stumbled upon your web site and in accession capital to assert that I acquire actually enjoyed account your blog posts. Any way I will be subscribing in your augment or even I fulfillment you access constantly quickly.