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Biomedical subjects

D A Mary

Publications and source records attributed to D A Mary.

At least 19 recordsLinked to original sources
PubMed1992

Indices for detection of changes in cardiorespiratory fitness during exercise training in man.

A decrease in the elevation of the linear relation of heart rate on oxygen consumption (HR/VO2) throughout submaximal exercise testing has previously been used in individuals as an index of improvement in cardiorespiratory fitness after a moderate intensity training programme. In the present investigation, changes in HR/VO2 elevation and its variability were quantified and compared with those of other similar indices. These comprised changes in the level of oxygen consumption or heart rate attained at respiratory exchange ratio (R) of unity (VO2/R=1 or HR/R=1. In a first trial in six healthy volunteers, the decrease in HR/VO2 elevation caused by 16 weeks of training significantly exceeded measurement variability, and was associated with increases and decreases respectively in VO2/R=1 and HR/R=1. In a second trial in eight healthy volunteers, the three indices were obtained at four stages during the course of the 16 weeks of training, to grade the improvement in fitness. There were progressive changes in the three indices, the magnitude of which was greatest in the case of the HR/VO2 index. The findings make it possible quantitatively to obtain a graded measure of improvement in fitness during exercise training as indicated by the magnitude of decreases in HR/VO2 elevation.

Adult↗
PubMed1992

Haemodynamic effects of distension of the descending colon in anaesthetized dogs.

1. This study was undertaken to determine whether distension of the descending colon in anaesthetized dogs reflexly affects the heart rate, arterial blood pressure or the left ventricular inotropic state. 2. Experiments were performed on twenty-six dogs, which were anaesthetized with sodium pentobarbitone and artificially ventilated. A segment of the distal descending colon was isolated and was distended with warm Ringer solution at a steady intraluminal pressure. 3. In each animal, distension of the colon caused an increase in heart rate and aortic blood pressure. The response of an increase in heart rate was augmented by preventing changes in aortic blood pressure, and was graded in seven dogs by step increments in the distending pressure. In the same animals, distension of the colon always caused a small increase in left ventricular (dP/dt)max at constant heart rate and aortic blood pressure. 4. In four of the twenty-six dogs, cutting the pelvic nerves did not abolish the observed responses to the distension. In seven of the twenty-six dogs, which included the four animals with sectioned pelvic nerves, cutting the hypogastric nerves completely abolished all the observed responses. 5. In thirteen of the twenty-six dogs, propranolol or bretylium tosylate completely abolished the reflex increases in heart rate and left ventricular (dP/dt)max, and phentolamine or bretylium tosylate abolished the reflex increase in aortic blood pressure. 6. These results showed that distension of the colon reflexly increased the heart rate, arterial blood pressure and left ventricular inotropic state. These reflex responses were mediated by sympathetic effects and their afferent limb involved the hypogastric nerves.

Animals↗
PubMed1992

Efferent limb of the coronary vasoconstrictor reflex elicited by distension of the descending colon in anesthetized dogs.

Distension of the descending colon elicits reflex coronary vasoconstriction. To study the efferent branch of this reflex, experiments were performed on 5 dogs anesthetized with pentobarbitone. A pouch was formed from the distal 15 cm of the descending colon and distended at constant pressure (54 +/- 8.9 mmHg) with warm Ringer solution from a pressurized bottle. During distensions of the colon, arterial blood pressure and heart rate were kept constant by the withdrawal of blood and pacing of the heart, respectively. Experiments were performed before and after intravenous bretylium tosylate (10 mg/kg), a compound which prevents the outflow of catecholamines from the sympathetic postganglionic neurons. Before chemical sympathectomy, colon distension at constant heart rate and blood pressure caused a decrease in mean coronary blood flow by 7 +/- 3.3% (mean +/- SD, p less than 0.0005). This response was abolished after the administration of bretylium (-0.07 +/- 0.95%, p greater than 0.40). We conclude that the efferent branch of the reflex coronary vasoconstriction elicited by colon distension is through sympathetic nerves.

Animals↗
PubMed1991

The effect of distension of the urinary bladder on coronary blood flow in anesthetized dogs.

To determine whether distension of the urinary bladder reflexly affects coronary blood flow, experiments were performed in eleven dogs anaesthetized with sodium pentobarbitone. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution at a steady intravesical pressure. Arterial blood pressure was prevented from changing by a pressurized reservoir of warm Ringer solution connected to the femoral arteries. Coronary blood flow was measured with an electromagnetic flowmeter positioned around the origin of the left circumflex coronary artery. When the reflex increase in heart rate was prevented by atrial pacing in seven dogs, distension of the urinary bladder always caused a decrease in mean coronary blood flow. Similar results were obtained in all eleven dogs after administration of propranolol. The decrease in mean coronary blood flow was significantly reduced by atropine or bilateral cervical vagotomy, and was abolished by bretylium tosylate. The results showed that distension of the urinary bladder reflexly decreased mean coronary blood flow, a response involving efferent cardiac vagal and sympathetic pathways.

Animals↗
PubMed1991

The efferent mechanisms of reflex hemodynamic responses to distension of the descending colon in anesthetized dogs.

We have recently shown that distension of the descending colon in anesthetized dogs causes reflex increases in heart rate, aortic blood pressure and the maximal rate of rise of left ventricular pressure, involving afferent pathways in the hypogastric nerves. In this study we have examined the efferent mechanisms involved in those responses. The descending colon was distended using Ringer solution at constant pressure in 13 anesthetized dogs. As previously shown, distension of the colon caused an increase in aortic blood pressure, heart rate and the maximal rate of rise of left ventricular pressure. The increase in the aortic blood pressure was abolished by either bretylium tosylate or phentolamine. Propranolol or bretylium tosylate abolished the increases in heart rate when changes in the aortic blood pressure were prevented, and abolished the increases in the maximal rate of rise of left ventricular pressure when the increases in heart rate were also prevented. These results indicate that the reflex increases in heart rate, arterial blood pressure and the maximal rate of rise of left ventricular pressure involved efferent sympathetic pathways.

Animals↗
PubMed1990

The relationship between left atrial pressure and atrial receptor discharge in dogs and cats with different body weights.

The diuretic response to distension of a large balloon in the left atrium and the increase in discharge of atrial receptors for a given increment in left atrial pressure have been found to be greater in dogs with a high blood volume than in dogs with a low blood volume. To determine whether atrial size may influence atrial receptor discharge, a group of cats and two groups of dogs with different body weights were examined under anaesthesia with alpha-chloralose. The relationship between atrial receptor discharge and left atrial pressure was determined in twenty-six fibres from seven cats, thirty-seven fibres from eight small dogs weighing less than 15 kg and twenty-five fibres from five large dogs weighing more than 25 kg. The slope of the relationship between the increase in atrial receptor activity and increments in left atrial pressure was shown to be significantly greater in the large dogs than in the small dogs, and the slopes in dogs were greater than in cats. The size of the atria was greater in larger dogs than small, and both those groups had atria larger than those of the cats. These findings indicate that the response of an increase in atrial receptor discharge to the same increment in left atrial pressure was greater in large animals than small and that this difference is possibly due to the different atrial size.

Animals↗
PubMed1990

The effect of distension of the urinary bladder on left ventricular inotropic state in anesthetized dogs.

To decide whether distension of the urinary bladder reflexly affects the left ventricular inotropic state, experiments were performed in eight dogs anesthetized with pentobarbitone. After cannulation of both ureters the urinary bladder was repeatedly distended through a urethral catheter with warm Ringer solution at a steady intravesical pressure. The maximal rate of rise of left ventricular pressure (dP/dtmax) obtained at constant heart rate and cardiovascular pressures was used to assess changes in left ventricular inotropic state. Arterial blood pressure was prevented from changing by a pressurized reservoir containing warm Ringer solution and connected to the femoral arteries. Following prevention of the reflex increase in heart rate by atrial pacing, distension of the urinary bladder always increased the maximal rate of rise of left ventricular pressure in the eight dogs. There were no significant changes in left ventricular systolic or end-diastolic pressures. The increase in maximal rate of rise of left ventricular pressure was abolished following the administration of propranolol. The results indicate that a reflex increase in left ventricular inotropic state occurred in response to distension of the urinary bladder. This reflex response involved beta-adrenergic stimulation.

Animals↗
PubMed1989

The effect of distension of the urinary bladder on activity in efferent vagal fibres in anaesthetized dogs.

Experiments were performed in anaesthetized dogs to find out whether the response of decreases in vagus nerve activity to distension of the urinary bladder is affected by changes in carotid sinus pressure. The carotid sinuses were vascularly isolated and perfused with blood at constant flow. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution. In eight dogs, all eleven efferent vagus fibres which responded to changes in carotid sinus pressure also responded to distension of the urinary bladder by a decrease in activity. This response of a decrease in activity was obtained at all levels of carotid sinus pressure between 8.4 and 30 kPa, and was greater at high than at low carotid sinus pressure. In the same vagus fibres, a relation was shown between progressive decreases in activity and either increases in intravesical pressure up to 8.7 kPa or reductions in carotid sinus pressure between 9 and 30 kPa. The decreases in activity were greater at high than at low carotid sinus pressure. These findings have shown that the inhibition of vagus nerve activity caused by bladder distension was affected by the level of carotid sinus pressure.

Animals↗
PubMed1989

Efferent limb of the atrial receptor reflex decrease in plasma renin activity in anaesthetized dogs.

The efferent limb of the reflex response of a decrease in plasma renin activity in response to stimulation of atrial receptors was examined in two groups of experiments in anaesthetized dogs. The atrial receptors were discretely stimulated by distension of small balloons in the left pulmonary vein-atrial junction and in the atrial appendage. In the first group, in which the responses of tachycardia and natriuresis were blocked, the diuretic response was accompanied by decreases in plasma renin activity. This decrease was abolished in the second group by renal denervation. The results have shown that the efferent limb of the response of a decrease in plasma renin activity involved the renal nerves.

Animals↗
PubMed1989

The effect of stimulation of left atrial receptors on coronary blood flow in anaesthetized dogs.

1. To determine whether stimulation of atrial receptors reflexly affects coronary blood flow, experiments were performed in seven dogs anaesthetized with alpha-chloralose. The left upper and middle pulmonary vein-atrial junctions and atrial appendage were stretched by distension of small balloons. Coronary blood flow was measured using an electromagnetic flowmeter positioned around the origin of the left anterior descending or circumflex coronary artery. 2. Following prevention of the reflex increase in heart rate by atrial pacing or propranolol, distension of the small balloons was shown to result in a decrease in mean coronary blood flow. 3. Cooling of the cervical vagosympathetic nerve trunks to 9 degrees C abolished the response of a decrease in mean coronary blood flow to distension of the balloons. 4. The response of a decrease in mean coronary blood flow was abolished by bretylium tosylate. 5. It was shown that a decrease in mean coronary blood flow occurred in response to stimulation of left atrial receptors, and that this decrease was reflex in nature. This reflex response is likely to involve atrial receptors discharging into afferent myelinated vagal fibres, and the efferent limb involves cardiac sympathetic pathways.

Animals↗
PubMed1989

The effect of distension of the urinary bladder on activity in efferent renal fibres in anaesthetized dogs.

1. To test whether distension of the urinary bladder causes a consistent change in activity in efferent renal nerve fibres, bladder distension was performed in anaesthetized dogs. The carotid sinuses were vascularly isolated and perfused with blood at constant flow. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution at a steady intravesical pressure. 2. In a first series of experiments all twenty-six renal nerve fibres in eleven dogs which responded to changes in carotid sinus pressure and changes in the nature of the blood perfusing the carotid sinuses also responded to distension of the bladder. 3. In a second series of experiments, graded bladder distension over a range of pressure of 0-9.2 kPa led to a graded increase in activity in thirteen efferent renal fibres in six dogs. The magnitude of the renal nerve response was greater at low than at high carotid sinus pressure. Over a range of carotid sinus pressure of 9-30 kPa, the greatest renal nerve activity was obtained at the lower end of this range in the presence of bladder distension. 4. Thus distension of the urinary bladder resulted in the response of a consistent increase in efferent renal nerve activity, which could be graded according to intravesical pressure. The magnitude of the responses to bladder distension was affected by carotid sinus pressure.

Action Potentials↗
PubMed1989

The effect of stimulation of the atrial receptors on plasma cortisol level in the dog.

1. Experiments were performed in dogs anaesthetized with alpha-chloralose to determine whether stimulation of atrial receptors reflexly results in a consistent change in plasma cortisol levels. Either a large balloon in the lumen of the left atrium or small balloons positioned at the upper and middle pulmonary vein-atrial junctions and atrial appendage were distended. Plasma samples obtained from these dogs during control periods and during periods of stimulation were assayed for plasma cortisol level. 2. Initially, stimulation of left atrial receptors by either large or small balloon distension was shown consistently to cause the responses of an increase in urine flow and a decrease in plasma cortisol level. The responses were greater during stimulation using the large balloon than the small balloons. 3. The afferent limb of the responses was shown to involve the vagal nerves. Cooling of the cervical vagosympathetic nerve trunks to 9 degrees C abolished the responses to balloon distension of an increase in urine flow and decrease in the level of plasma cortisol. 4. The efferent limb of the cortisol response was shown to require the pituitary gland. Hypophysectomy abolished the response of a decrease in plasma cortisol level, but not the diuretic response. 5. It was shown that stimulation of left atrial receptors causes a reflex decrease in plasma cortisol level, the afferent limb of which involved vagal nerves and the efferent limb of which depended on the pituitary gland.

Afferent Pathways↗
PubMed1986

The effect of indoramin on exercise performance in mild hypertension.

The alpha 1-adrenoceptor antagonist indoramin is proposed to reduce arterial blood pressure without a concomitantly significant increase in heart rate (HR). The present study involves assessment of the effect of alpha 1-adrenoceptor antagonism in patients with mild hypertension on the HR/oxygen consumption (Vo2) relationship, which has previously been shown to indicate improvement in cardiorespiratory fitness following exercise training. A total of 16 patients with a systolic blood pressure of 140-200 mm Hg and diastolic blood pressure of 95-110 mm Hg were examined. A double-blind, placebo-controlled study design was utilized. Following initial observations, the patients were randomized into one group (a) of seven patients who were given a placebo, indoramin, and finally placebo, and a second group (b) of nine patients who were given the two agents in the reverse order, i.e., indoramin, placebo, indoramin; each intervention lasted for 2 weeks and indoramin was given in a dose of 75 mg/day. Indoramin caused a reduction in the elevation of the computed regression line relating HR to Vo2 (a shift to the right), such that at the same HR a greater Vo2 was attained in 11 of the 16 patients in comparison with the baseline exercise test. Pooled results showed a shift of the HR/Vo2 regression line to the right when indoramin was compared with baseline (p less than 0.05) or placebo. In the same patients, indoramin caused a decrease in arterial blood pressure during exercise relative to baseline or placebo periods, and a decrease in the HR during exercise relative to baseline period, but not when compared with placebo periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Trials as Topic↗
PubMed1979

Diagnostic value of routine exercise testing in hospital patients with angina pectoris.

A group of patients with angina pectoris were investigated prospectively using a simple and well-recognised exercise test protocol, and S-T segment displacements during exercise were correlated with the results of coronary arteriography. Definitive exercise results in 100 patients correlated well with findings on coronary angiograms: 69 out of 70 patients with positive exercise test results had significant coronary disease on angiography, while 23 out of 30 with negative exercise test results had no significant coronary disease. In six patients a period of physical training changed indeterminate initial tests to definitive ones after the training. These results show that the use of a widely available exercise test and a light physical training programme, with rigid adherence to the protocol, can reduce the overall demand on coronary arteriography.

Adult↗