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PubMedDate not supplied

Effectiveness of atrial pacing in Macaca mulatta as a function of pacing pulse intensity: modification by atropine and propranolol.

The functional relationship between heart rate, under atrial pacing, and the intensity of pacing pulses, was determined for intensities ranging from well below the complete heart rate capture threshold to suprathreshold intensities. A separate capture-intensity function was determined for each of the pacing frequencies 180, 240, 300 and 360 pulses per min, and then used to evaluate the effects of propranolol hydrochloride and atropine sulfate on atrial pacing. Propranolol resulted in an increase in the amount of current (mA) required to achieve a given degree of cardiac capture, whereas atropine resulted in a decrease. These shifts in the capture-intensity functions along the intensity axis were possibly caused by drug antagonism of beta-adrenergic and cholinergic receptors, respectively, although the effects might also have been due to modifications of the electrical responsivity of the cardiac muscle, independently of the neural blockade.

Animals↗
PubMed1978

Ultrastructural alterations of atrial myocardium induced by adriamycin in chronically treated animals.

The clinical use of adriamycin (AM) is limited by a possible dose-dependent myocardiopathy. Severe lesions of ventricular myocardium widely described by electron microscopy have been correlated to irreversible congestive heart failure. On the other hand, the atrial contractile elements which differ from the ventricular ones because of the presence of the so-called specific granules have rarely been considered. In the work described in this paper, adriamycin was injected into rabbits and mice according to schedules of chronic toxicity. At the end of the treatment the atrial myocells presented diffuse ultrastructural lesions of mitochondria, sarcoplasmic reticulum and myofibrillar bundles. These alterations might be caused by the ribonucleoprotein synthesis inhibition, by a direct drug toxicity or by an energetic crisis due to early mitochondrial lesions. Besides, adriamycin produces a decrease of the specific atrial granules that play a hypothetic role in the metabolism of myocardial cells. However, lack of information about the contents and the exact function of atrial granules does not allow us to conclude that their decrease in treated animals has a pathogenetic significance in myocardiopathy induced by adriamycin.

Animals↗
PubMed1979

Blood flow in pulmonary veins: I. Studies in dog and man.

The pattern of blood flow in the large extra parenchymal pulmonary veins is pulsatile in both dog and man. This pulsatility is dominated by the changes in left atrial pressure taking place throughout the cardiac cycle. No pulsatile component of low in the large pulmonary veins could be attributed to forward transmission of a flow pulse conducted from the lung capillaries. The findings suggest that there must be a region of considerable compliance in the pulmonary venous system which can absorb pulsations from the lung capillaries and eliminate their transmission to the left atrium.

Animals↗
PubMed1977

Detector electrode introduced by mediastinoscopy for atrial triggered cardiac pacing. A follow-up of electrode function in 82 patients.

An atrial detector electrode was introduced by mediastinoscopy in 82 patients requiring permanent cardiac pacing. There were no complications. An adequate P wave was recorded in 80 patients. During the following week, the P wave became ineffective in 5 patients; angina occurred in 2 and atrial arrhythmias in 2. Atrially triggered ventricular pacing established in 73 patients and was followed in 71 patients for a period of 1 to 113 months. In 17 cases, it had to be terminated because of an ineffective or unstable P wave,in 6 cases because of atrial arrhythmias, and in 4 cases because of advanced age and recurrent infections. The method is technically simple and place little stress on the patient.

Adult↗
PubMed1979

Fine structure of cells and their histologic organization within internodal pathways of the heart: clinical and electrocardiographic implications.

The fine structure of the normal internodal pathways was studied in 1 human and 2 canine hearts and correlated with histologic observations on more than 100 human and 10 canine hearts. From the electron microscopic studies six different kinds of myocardial cells were classified from two locations: the Eustachian ridge (posterior internodal pathway) and the Bachmann bundle (anterior internodal pathway). Five of the six kinds of cells (working myocardial cells, Purkinje-like cells, either broad or slender transitional cells and P cells, all previously described) were present in both locations. A sixth cell, pleomorphic and dark in appearance, with a special intertwined relation to P cells, is newly designated as an ameboid cell. It was found solely in the Eustachian ridge. In the same area a rare direct contact between a nerve and a myocardial cell was observed. The importance of these different kinds of cells, their respective cell connections, and their topographic locations inside the internodal pathways are discussed relative to certain functions such as rapid conduction and subsidiary pacemaking. The possible influence of these factors on clinical electrocardiographic changes is considered.

Animals↗
PubMed1977

Atrial receptors in the dog and rabbit.

1. Action potentials were recorded from slips of the cervical vagi in anaesthetized dogs and rabbits. Single functional units with atrial patterns of discharge (Paintal Type A, B and intermediate) were obtained and then attempts were made to alter (i.e. convert) their patterns of discharge. Finally the points of origin of these action potentials were located.2. Thirty unselected units were investigated in thirty dogs. Twenty-seven of these were located in the endocardium of the vein-atrial system and the ratio of the type A, type B and intermediate type receptors was 1:16:10; three units were located elsewhere in the chest. Conversion of the pattern of discharge was achieved in twenty of the twenty-seven units; conversion was achieved in the single type A unit.3. In a second series of experiments in dogs, eight Paintal Type A units were selectively studied in fifteen animals. Four of these were located in the endocardium and all were converted. The remaining four were located outside the endocardium and conversion could not be achieved in two of these. Thus in the entire investigation, the ;type A' units which could not be converted were all located at sites other than the atrial endocardium.4. In the corresponding unselected study in the rabbit, eleven units were studied in eleven animals. Nine of these units were located in the atrial endocardium and the ratio of the type A, type B and intermediate type receptors was 2:1:6. Conversion was achieved in both type A units, the sole type B unit and two of the intermediate units. One of the two units found outside the atrial endocardium was a ;type A' unit and could not be converted.5. The present investigation has shown that the atrial receptors with a Paintal Type A pattern of discharge are relatively rare in both dogs and rabbits. Conversion of the pattern of discharge is a relatively common phenomenon. Evidence for the proposition that there is one basic type of atrial receptor whose pattern of discharge is determined by its precise location in the vein-atrial system is discussed.

Action Potentials↗
PubMed1976

Electrophysiologic effects of atropine on human sinus node and atrium.

Electrophysiologic studies were conducted in 17 patients without apparent sinus node disease before and after intravenous administration of 1 to 2 mg of atropine. Mean values in milliseconds (+/- standard error of the mean) before and after administration of atropine were as follows: sinus cycle length 846 +/- 26.4 versus 647 +/- 20.0 (P less than 0.001); sinus nodal recovery time 1,029 +/- 37 versus 774 +/- 36 (P less than 0.001); mean calculated sinoatrial (S-A) conduction time 103 +/- 5.7 versus 58 +/- 3.9 (P less than 0.001); mean P-A interval 34 +/- 1.5 msec versus 31 +/- 1.5 (P less than 0.05); mean atrial effective and functional refractory periods during sinus rhythm 285 +/- 11.3 versus 238 +/- 7.9 and 331 +/0 11.6 versus 280 +/- 8.6, respectively (P less than 0.001 for both); mean atrial effective and functional refractory periods measured at equivalent driven cycle length 239 +/- 7.7 versus 213 +/- 7.4 and 277 +/- 11.4 versus 245 +/- 9.5, respectively (P less than 0.001 for both). In conclusion, atropine shortened sinus cycle length, sinus nodal recovery time and calculated S-A conduction time. The shortening of atrial refractory periods with atropine implies that vagotonia prolongs atrial refractoriness in man.

Adult↗
PubMed1975

[On the mechanism of valve plane (author's transl)].

A detailed description of the functional sequence and mechanism of the valve plane movements is given as an extension of the studies on the functional morphology of cardiac movements. The valve plane mechanism is driven in the small, rapidly beating heart by the contraction of the external and internal spiral fibres of the myocardium which decreases the width of the chamber. The atrium is enlarged during systole by the descent of the valvular ring towards the apex. The auricular apendices must act as a compensation reservoir giving the atrial wall the necessary freedom of movement within the pericardial dome. Under these working conditions (hypovolaemia, decreased venous return pathophysiological consequences are discernible as subendocardial bleeding secondary to increased sliding movement of the inner layer of the myocardium against the middle layer. Chamber dilation as a consequence of endocardial fibrosis is explained as a result of progressive rigidity of endo-epicardial fixation. These structural changes progressively impair the systolic-diastolic changes in wall thickness.

Animals↗
PubMed1979

In vivo haemodynamic evaluation of the Hall-Kaster central flow prosthetic heart valve.

The first in vivo haemodynamic observations of the recently developed Hall-Kaster central flow prosthetic heart valve are reported. Haemodynamic evaluation of valve function was performed both in acute and chronic experiments following implantation of the Hall-Kaster prosthesis in the mitral position in dogs. These studies showed a low transvalvular pressure gradient, an effective opening angle of about 70 degrees and good diastolic flow through both the large and small orifices of the prosthesis. A slow rotational movement was depicted by the disc during opening and closure.

Animals↗
PubMed1978

The role of cyclic nucleotides and prostaglandins in heart function.

A short review of the role of cyclic nucleotides and prostaglandins (PGs) in normal and pathological functions of the heart is given. Possible interrelationships of these two regulatory systems have been studied by using spontaneously beating rat atria preparations. Addition of noradrenaline (NA) to the incubate (1 . 10(-6) M) caused an increase in amplitude and frequency which was preceded and parallelled by an elevation of the tissue cAMP level. A transient increase in cGMP and PGE values was also seen. Propranolol (5 . 10(-6) M) abolished the increase in amplitude and frequency as well as in cAMP and PGE concentrations. Indomethacin (1 . 10(-5) M) inhibited the formation of PGE. The increase in cGMP was blocked by phenoxybenzamine. Interchange between beta- and alpha-receptors according as the temperature is lowered has been described earlier. Hypothermia (20 degrees C) had a positive inotropic effect on the atria and increased the tissue cAMP concentration. Loading of the atria caused an increase in cAMP without any effects on cGMP or PGs. Slight hypoxia did not change the cAMP or PG levels, but elevated the cGMP values. Arrhythmias induced by hypo- or hyperpotassemia did not modify the biochemical parameters measured. PGF2alpha (1. 10(-5) M) normalized the atrial rhythm and increased the amplitude without changing cyclic nucleotide or PG levels. PGE1 (1 . 10(-4) M) increased the amplitude of normorhythmic atria and the tissue concentration of cAMP. PGE2 was the only PG tested which stimulated the heart adenylate cyclase in vitro. There seems to be close but complicated relationships between cyclic nucleotides and PGs in the heart.

Adenylyl Cyclases↗
PubMed1978

Cardiovascular effects of positive end-expiratory pressure in dogs.

Our purpose was to reexamine the relationship of the fall in cardiac output and blood pressure which occurs during positive end-expiratory pressure (PEEP) to changes in transmural right atrial and left atrial filling pressures. Closed-chest dogs, half with pulmonary edema, were studied during spontaneous breathing and inspiratory positive-pressure breathing (IPPB) with 0-15 cmH2O PEEP. Mean esophageal pressure accurately reflected changes in pericardial pressure and was used to estimate extracardiac pressure. We found that cardiac output fell approximately 50% and blood pressure fell 20% during 15 cmH2OPEEP in spite of well maintained transmural right atrial and left atrial (or pulmonary artery wedge) pressures suggesting a primary or reflex depression of atrial or ventricular function.

Anesthesia↗
PubMed1979

Genesis of the sphygmogram from the kinetocardiogram.

The functional uniformity of the heart and vessels is studied. The idea of the genesis of the carotid sphygmogram from the kinetocardiogram (GS-KCG) was developed on the basis of the analysis of the KCG and carotid-sphygmographic (CSG) pattern obtained in 10 young healthy adults. Two of these examinees were additionally examined under the influence of a s.c. injection of adrenaline (A) and noradrenaline (NA). Two kinds of transducers for the displacement of the chest wall and of the carotid region were used (photoelectric and resonance receiver). They did not touch the skin and were placed in four positions on the thorax; three of them are routine auscultatory positions (ictus, ERB, aorta), one was the carotid artery pulse position. Amplitude and time intervals at rest and under the influence of catecholamines were determined and their interrelationship studied. The amplitudes are more variable than the intervals. The genesis of the waves was studied on the basis of the records in four positions. On this basis, a uniform hypothesis about the genesis of the KCG and CSG waves is derived. From this hypothesis and from the existence of a reflection wave starting at the aorta, the concept of the genesis of the sphygmogram from the kinetocardiogram was developed: the deformation starts at the aorta, is directed to the apex, is there reflected and propagated to the carotid artery. The validity of this concept of the GS-KCG is proved on the basis of experiments with adrenaline and noradrenaline. The quantitative data of peaks and waves from four positions show a stability of the KCG and CSG pattern despite the influence of catecholamines. A comparison is made between the apex cardiogram (ACG) and KCG and determinants of the characteristic pattern of chest movements are given. It was further concluded that the technique of measuring reflection wave velocity (=intracardiac velocity) and pulse wave velocity (=vascular, mixed) can be used as a test for individual reactivity of the cardiovascular system. The wave velocities and the carotid amplitude can help in detecting a disposition towards coronary disease.

Aorta↗