The effect of increasing the intraluminal pressure in the right heart on the activity of isolated perfused dog hearts and the effect of increasing the intraluminal pressure on the activity of isolated right atria of dogs, rabbits, guinea pigs and albino rats have been studied. It has been observed that there is a direct relationship between the magnitude of intraluminal right atrial pressure and the inotropic and chronotropic responses of the whole heart and right atrium up to certain critical pressures (5–15 mm Hg). Some modifications in this behavior of the hearts due to repeated changes in the intraluminal pressure have also been described. It has been suggested that stretch of the cardiac tissue due to increased intraluminal pressure may cause alterations in membrane metabolism at the pacemaker.
As the appropriate usage (59.65%) of blood components was low in the present study, regular auditing of transfusion practices from time to time is indicated. This not only helps guide their judicious use but also serves to evaluate and decrease their inappropriate usage.
Intravenous infusions on intact dog hearts both in closed- and open-chest experiments indicate that a rise in the intra-atrial pressure is accompanied by either a positive, a negative or a no chronotropic effect, irrespective of the integrity of vagi. Positive chronotropic effects of similar intensity were also obtained even after bilateral vagotomy, topical application of cocaine or parenteral administration of atropine, tetraethylammonium or hexamethonium compounds. Moreover, the rise in the intra-atrial pressure or the degree of visible distention of the right atrium was not necessarily associated with a parallel rise in the heart rate. Thus, the infusion acceleration response obtained with some infusions only, fails to fulfill the requirements of a reflex action. There is, therefore, no justification for labeling it as a "reflex" effect, as advocated by Bainbridge. The chronotropic effects of the infusions seem to be due to stretch-induced alterations in impulse generation as a result of changes in the intra-atrial pressure and possibly depend upon the initial conditions at the pacemaker.
Mechanical stretch is a fundamental biological stimulus for pacemaker activity. Stretch-sensitiveness enables the heart to autoregulate its rate in relation to venous return. Phylogenetically the importance of this primitive mechanism has been diminished by the emergence of neurohumoral influences which permit a quicker and more effective adaptation of cardiac performance. Nevertheless, the intrinsic autoregulatory mechanism is capable of independent operation and may support extrinsic neurohumoral influences under various conditions.
The influence of stretch due to increased intraluminal pressure on the formation and conduction of electrical impulse was studied electrocardiographically in 12 isolated sinoauricular chambers of frog hearts perfused with frogs' Ringer. The impulse frequency was found to be directly proportional to the degree of intraluminal perfusion pressure up to a certain critical head of pressure (2–6 cm Ringer), beyond which the impulse frequency declined. At higher pressures the electrogram showed a diminished amplitude of the action potential and broadening and notching of sinus waves and auricular complexes. The duration and conduction velocity of electrical impulse was increased.
Background: The ABO and Rhesus (Rh) blood group systems are the most important of the various blood group systems known so far in human beings. The distribution of blood groups varies in various parts of the world and also in different parts of the country. Method: This study was conducted to determine the distribution of ABO and Rh blood groups in females comprising pregnant females coming for antenatal visits as well as females coming for blood donation and thus representing general female population and distribution of blood groups in males coming for blood donation, representing general male population and to show if there was any sex wise variation in blood group distribution. A retrospective study was conducted at the department of Pathology (Blood bank and Gynaecology laboratory), VMMC and Safdarjung hospital, New Delhi from January 2017 to March 2017 consisting of 2832 females (2810 pregnant females and 22 female donors). During this period total number of male donors both voluntary and replacement were 7567. To ensure proper comparison equal numbers of males (2832) were included in the study. First 2832 male donors were taken for the study. The blood samples were obtained in EDTA vacutainers by venepuncture and blood group antigens were determined by commercially available monoclonal antisera by electromagnetic technology. Both ABO and Rh status was tested. Results: The blood group B was the commonest in both males and females followed by O, A, AB group. Conclusion: The commonest blood group in males and females in New Delhi and nearby areas was B group.
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