Search PubMed⌕ Search

Biomedical subjects

T N James

Publications and source records attributed to T N James.

At least 109 records · Page 6Linked to original sources
PubMed1982

The direct negative chronotropic action of prazosin on the canine sinus node.

The direct and indirect chronotropic effects of prazosin were studied in 22 anesthetized dogs using the technique of selective perfusion of the sinus node. Concentrations of 1, 10, 50 and 100 micrograms/ml of prazosin produced cumulative, dose-related reductions in mean sinus rat of 4 +/- 2; 10 +/- 6; 15 +/- 9 and 27 +/- 15 beats/min, respectively (P less than .0001). Intranodal prazosin did not significantly alter the positive chronotropic sinus node response to norepinephrine (0.05 and 0.1 micrograms/ml) administered via the same route. Sinus rate increases during stimulus frequency response curves after right stellate stimulation were not influenced by prior administration of prazosin. Sinus bradycardia elicited by submaximal vagal stimulation also was not affected by intranodal prazosin.l In six reserpinized dogs, methoxamine (10 and 25 micrograms/ml) injected into the sinus node artery caused a sinus rate increase of 10 4/- 2 and 14 +/- 3 beats/min (P less than .001). Intranodal prazosin (50 micrograms/ml) prevented this effect. Taken together, these results indicate that prazosin exerts a direct negative chronotropic action on the canine sinus node and that this effect is at least in part mediated through interference with alpha-1 receptors located in or near the sinus node. Prazosin has little or no effect on the presynaptic alpha-2 receptors nor does it interfere with the cholinergic mechanism in the sinus node.

Animals↗
PubMed1981

Renal function during reflexly activated catecholamine flow through an adrenorenal rete.

Reflex vasoconstriction that occurs in the kidney of the dog can be the result of either of two mechanisms. The first is by activation of the renal sympathetic nerves and the second by reflex activation of catecholamine flow through an adrenorenal rete. Both reflex mechanisms can be activated by transient hypotension caused by experimentally induced atrial fibrillation in the sodium-replete pentobarbital-anesthetized dog. This study was undertaken to measure and compare the magnitude of changes in renal function that occur when these reflex mechanisms are activated and to evaluate the possible role of intrarenal angiotensin II in these two reflex effects. Reflex activation of catecholamine flow through an adrenorenal rete in intact or denervated kidneys produced a 26 +/- 3% decrease in renal plasma flow, a 23 +/- 4% decrease in glomerular filtration rate, a 58 +/- 7% decrease in urinary sodium excretion, and a 4 +/- 1% increase in filtration fraction, but no change in the fractional distribution of intrarenal blood flow. Changes of a similar direction and magnitude were seen in the same animals during reflex activation of the renal sympathetic nerves in the kidneys with intact or ligated adrenorenal rete. The same studies were performed after the intrarenal action of angiotensin II was blocked with [Sar1,Ala8]angiotensin II and similar responses were seen. Both of these reflexes appear to be important mechanisms by which the kidney can maintain vascular volume, and neither depends on intrarenal angiotensin II activity.

Adrenal Medulla↗
PubMed1981

Atrial excitability and conduction during rapid atrial pacing.

Using temporary atrial wire electrodes placed at selected atrial sites, rapid atrial pacing at rates of up to 368 beats/min was used to study atrial excitability and conduction in seven patients who underwent open heart surgery. The threshold for atrial pacing was found to be an exponential function of pacing rate (r = 0.55, p less than 0.01), increasing threefold when the fastest pacing rates were compared with the slowest pacing rates (p less than 0.005). Atrial conduction times (measured from pacing to recording sites), prolonged during rapid atrial pacing both for studies conducted before institution of cardiopulmonary bypass (p less than 0.005) and for those done 7 days postoperatively (p less than 0.05). However, prolongation of conduction times always depended on achievement of a critically rapid pacing rate. During rapid atrial pacing, we observed a high incidence of alternans of the atrial electrogram (17 of 42 studies). Thus, human atrial excitability, conduction and electrogram morphology are not constant during pacing at rapid rates. Rather, at rapid pacing rates, there is depression of atrial excitability, prolongation of atrial conduction times and alternation in electrogram morphology. These findings have clinical relevance and theoretical implications for the understanding and treatment of rapid atrial rhythms.

Cardiac Pacing, Artificial↗
PubMed1981

Virus-like particles associated with intracardiac ganglionitis in 2 cases of sudden unexpected death.

Two previously healthy young individuals died suddenly and unexpectedly, and in both of them there was ganglionitis in the heart, especially near the sinus node. Electron microscopic examination demonstrated virus-like particles in the vicinity of the ganglionitis of both hearts. Viral cardioneuropathy may play a role in the pathogenesis of sudden unexpected deaths and deserves further investigation.

Adolescent↗
PubMed1981

[Wolff-Parkinson-White syndrome and longitudinal dissociation of the atrioventricular node. Anatomical and electrophysiological correlates].

A 58 year old man who died of metastatic carcinoma had undergone electrophysiological investigation 4 years previously for a Wolff-Parkinson-White syndrome (Rosenbaum Type A, Frank and Boineau Type IV) associated with supraventricular tachycardia (SVT) at 180/mn, atrial fibrillation and flutter and slow junctional (or low atrial) rhythm at 70-80/mn. Atrial extrasystoles or appropriate atrial stimulation not only induced and terminated the SVT but also the junctional rhythm and allowed passage from one arrhythmia to another. These studies showed the presence of a left lateral Kent bundle responsible for orthodromic SVT with retrograde conduction through the accessory pathway, and suggested that the junctional rhythm might be due to longitudinal dissociation of the AV node. Autopsy findings confirmed the presence of the left posterolateral Kent bundle in an almost horizontal position, parallel to the mitral annulus (it might therefore have escaped eventual surgical section) and the longitudinal dissociation of the AV node.

Atrioventricular Node↗
PubMed1981

Effects of selectively produced changes in cardiac rhythm or conduction upon flow in the superior vena cava.

The effects of changes in cardiac rhythm or conduction on the rate of volume flow in the superior vena cava (SVC) were studied in 25 dogs anesthetized with sodium pentobarbital. Slowing of sinus rate from 145 +/- 16 to 114 +/- 12 beats/min was achieved by selective perfusion of Ringer's solution into the sinus node artery. During sinus slowing there was a continuous change in the systolic-diastolic flow ratio measured in the SVC. At control sinus rate (net), total forward flow as 6.3 ml/beat with a systolic volume of 6.5 ml and a diastolic volume of -0.2 ml. At the slowest bradycardia, total forward flow had increased by 25%. Since there was no significant change in the systolic volume, the entire 25% increase in forward flow occurred during ventricular diastole. During atrioventricular (AV) block (second-degree or complete), achieved by selective perfusion of eserine into the AV node artery, unimpaired acceleration of flow was readily demonstrable in the SVC even in the absence of ventricular contraction. Thus systolic ventricular suction (vis a fronte) has little or no effect on right atrial filling. During high-degree AV block, the normal atrial contraction readily opened the tricuspid valve, and when both atrium and ventricle were filled to or near maximum capacity, atrial contraction was consistently vigorous enough to propel blood into the pulmonary artery. Given appropriate hemodynamic circumstances, these results confirm the remarkable effectiveness of right atrial contractile performance.

Animals↗
PubMed1980

Sudden death while driving. Role of sinus perinodal degeneration and cardiac neural degeneration and ganglionitis.

A young business executive was seen to slump over his steering wheel while driving, after which the automobile veered and turned over. Quickly taken unconscious to a nearby emergency room, he was pronounced dead on arrival. Because there was insufficient physical injury found to account for his death, and because atrial fibrillation had been detected for the first time on a routine physical examination 3 months previously, special examination of the cardiac conduction system was performed. A fibroma was present on the right side of the central fibrous body above the His bundle, similar to several fibromas on the mitral valve. Small foci of neuritis were present in the ventricular myocardium and the atrioventricular node. More extensive neural degeneration and ganglionitis were found near the sinus node, which also exhibited an encircling perinodal fibrosis. Ways in which these abnormalities could have caused a fatal electrical instability of the heart are discussed. Careful examination of the cardiac conduction system is warranted in other fatal automobile accidents under similar circumstances.

Accidents, Traffic↗
PubMed1980

Reflex heart block. Baroreflex, chemoreflex and bronchopulmonary reflex causes.

Reflex heart block was studied in 20 dogs anesthetized with sodium pentobarbital and in 5 trained unanesthetized dogs. Three different vagal reflexes were produced: the Marey response during hypertension caused by administering methoxamine, a cardiogenic hypertensive chemoreflex activated by injection of serotonin into the left atrium and the Hering-Breuer reflex observed during normal respiration of unanesthetized dogs. In every dog during any of the three reflexes heart block was consistently observed after the normal slowing response of the sinus node had been selectively eliminated by the direct perfusion of 10 microgram of atropine into the sinus node artery. This was a uniform response despite its being variously produced by a pressor reflex, a chemoreflex or an extracardiac bronchopulmonary reflex. Transient heart block is therefore to be anticipated during reflexes with vagal efferent components if for any reason the sinus node is incapable of slowing suitably. The possible clinical relevance of these experimental observations is discussed.

Animals↗
PubMed1980

Pathogenesis of paroxysmal hypertension developing during and after coronary bypass surgery: a study of hemodynamic and humoral factors.

A prospective study of hypertension first appearing during and after saphenous vein bypass coronary surgery was performed in 28 patients to examine the incidence, hemodynamics and mechanism of this problem. In 15 patients (54 percent) new hypertension developed (mean arterial pressure greater than 107 mm Hg), characterized by increased peripheral vascular resistance and unchanged cardiac output within 1 hour after surgery. These 15 patients had a longer history of angina of greater severity, but also had relatively well preserved ventricular myocardium. Because plasma renin activity was depressed in patients in the hypertensive group, activation of the renin-angiotensin system was not important in the pathogenesis of this postoperative hypertension. The expected decrease in total peripheral resistance at the onset of cardiopulmonary bypass was observed in all patients, but later during bypass the peripheral resistance increased in all patients in association with a rise in plasma epinephrine levels. Patients who had hypertension postoperatively had a greater increase in arterial pressure and total peripheral resistance during cardiopulmonary bypass than did those with normal postoperative blood pressure. An elevation in plasma epinephrine and norepinephrine concentration, suggesting enhanced sympathoadrenal responsiveness to the challenge of cardiopulmonary bypass, was characteristic of the hypertensive group. This evidence of enhanced sympathetic activity during surgery may be a useful predictor of the development of postoperative hypertension.

Blood Pressure↗
PubMed1980

Dilation of coronary artery stenoses after isosorbide dinitrate in man.

The effect of isosorbide dinitrate (ISDN), 5 mg sublingually, on the diameters of coronary artery stenoses (n = 27) was examined in 20 patients. Another 18 patients with angiographically normal coronary arteries received the same amount of ISDN and were used as controls. Prestenotic and stenotic diameters were measured with a vernier calliper having an accuracy of 0.05 mm. The degree of stenosis was expressed as percentage of cross-sectional area reduction. ISDN caused uniform dilatation of every normal epicardial artery; mean increase in diameter was 21 per cent (range: 17 to 26%). In 18 stenoses (28 to 95% obstruction) there was very little change after ISDN. The mean prestenotic diameter increased from 2.82 +/- 0.48 mm to 3.05 +/- 0.43 mm and the mean stenotic diameter from 1.45 +/- 0.49 mm to 1.59 +/- 0.51 mm. However, in the nine other stenoses (35 to 89% obstruction) the mean degree of obstruction decreased significantly from 68 +/- 15.6 per cent to 47 +/- 15.6 per cent after ISDN. This improvement was a result of a significant increase of the mean stenotic diameter from 1.71 +/- 0.47 mm to 2.41 +/- 0.55 mm, whereas the prestenotic diameter showed only an insignificant increase from 3.17 +/- 0.63 mm to 3.31 +/- 0.58 mm after ISDN. In four patients with two obstructions in different coronary branches ISDN dilated one without significantly affecting the other lesion. From the data we conclude that ISDN can dilate some coronary artery stenoses but that this response may vary from one site to another even in the same patient.

Coronary Disease↗
PubMed1980

Changing negative inotropic effect of acetylcholine in maturing canine cardiac muscle.

The effect of maturation on the contractile response to acetylcholine was studied in canine right atrial and right ventricular trabeculae. At any age the only inotropic response observed was negative. The decrease in contractile performance was always significantly greater in the atrial trabecula. Between 3 and 9 mo of age (12 dogs each group) there was a significant increase in the amount of negative inotropic action exerted by identical concentrations of acetylcholine. These data suggest that either the number of muscarinic receptors or the target cell response to acetylcholine increases during maturation.

Acetylcholine↗