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.

Atrial receptors in the cat

Action potentials were recorded from slips of the cervical vagi in anaesthetized cats. Single functional units with atrial patterns of discharge (type A, B and Intermediate) were first obtained and then attempts were made to alter (i.e. convert) their patterns of discharge. Finally the points of origin of their action potentials were located. The investigations were done in five stages. 2. In the first series, thirty unselected units were investigated in thirty cats. Twenty-five of these were located in the endocardium of vein-atrial system and consisted of two type A, fifteen type B and eight Intermediate type units. The remaining five units were located elsewhere in the chest Conversion of the pattern of discharge was achieved in sixteen of the twenty-five atrial units. Both atrial type A units were converted. 3. In the second series, eight type A units were selectively studied in twelve cats. Five were located in the atrial endocardium and all were converted. Of the other three units which were located at other sites in the chest, one could not be converted. 4. In the third series, four type A units which could not be converted were selectively studied in twenty cats. All were located outside the atria. 5. In the fourth series, three type B units which could not be converted were selectively studied in six cats. These units were located in the pulmonary veins and in the lateral walls of the atria. 6. In the fifth series, fifty-five units were investigated in three anaesthetized spontaneously breathing cats. The proportion of the types of units were similar to that obtained in the artificially respired cats (first series). 7. The present study has shown that atrial receptors with a type A pattern of discharge are relatively rare in the cat and that conversion of the patterns of discharge is a common phenomenon. Evidence is presented which suggests that there is one basic type of atrial receptor whose pattern of discharge is determined by their precise location in the vein-atrial system.

Method for continuous measurement of carbon dioxide output

An open-circut flow-through technique for the continous measurement of carbon dioxide output in man has been described. A stream of room air is drawn past the subject who respires freely from it. The difference in the concentration of carbon dioxide between room air from which the subject inspires and the expired gas/room air mixture is measured and expressed as a voltage. This voltage is amplified by a factor proportional to the rate of flow of room air to yield a continous measurement of carbon dioxide output. This technique has no systematic error and a random error (95% tolerance limits) of +/-3.4, +/-1.7, and +/-1.4% at mean carbon dioxide outputs of 254, 846, and 1,906 ml/min, respectively.

Effect of environmental temperatures on oxygen consumption in infants with congenital disease of the heart

The effect of changes in environmental temperature on the oxygen consumption in babies with congenital disease of the heart has been studied and it has been shown that an inverse relation exists between those two variables. The significance of these findings on the practice of calculating systemic and pulmonary blood flow from predicted values of oxygen consumption is discussed.

Gradation of the reflex response from atrial receptors

1. In anaesthetized dogs, distension of balloons so as to stimulate atrial receptors resulted in a reflex increase in heart rate. 2. Successive distensions of one, two and three balloons positioned in the left upper and middle pulmonary vein-atrial junctions and in the left atrial appendage resulted in a progressive increase in the magnitude of this response. 3. It is concluded that the magnitude of the increase in heart rate is related to the extent of receptor area stimulated.

Atrial receptors and heart rate: the efferent pathway

1. Stimulation of left atrial receptors by distension of the junctions between the pulmonary veins and the left atrium is known to cause a reflex increase in heart rate. It was suggested that the efferent path of this reflex was solely in the sympathetic nerves to the heart but more recently the existence of a vagal efferent component has been postulated by Albrook, Bennion & Ledsome (1972). 3. The junctions between the pulmonary veins and the levt atrium were distended before and after the administration of I.C.I. 66082 and bretylium tosylate. The response of an increase in heart rate was significantly decreased after the administration of I.C.I. 66082 (5 mg/kg) and abolished after the administration of bretylium tosylate (10 mg/kg). 3. It is concluded that the efferent pathway of the reflex is solely in the sympathetic nerves to the heart.

The assessment of acid-base disturbance in man by the use of carbon dioxide titration curves

1. Carbon dioxide titration curves were determined in vivo in dog and man at various degrees of acute non-respiratory acidaemia and alkalaemia. 2. The slope of the CO2 titration curve (delta log Pco2/delta pH) was found to increase with the severity of the acute non-respiratory alkalaemia the slope (delta log Pco2/delta pH) tended towards unity. 3. A simple scheme based on the CO2 titration curves determined in vivo has been proposed for the assessment of acute acid-base disturbances in man. 4. Carbon dioxide titration curves were also determined in vivo in patients with chronic respiratory and non-respiratory acidaemia and it was found that these curves were not significantly different from those obtained in states of acute acid-base disturbances. It is therefore suggested that the scheme described in this paper is applicable to all acid-base disturbances.

Effect of destruction of the posterior pituitary on the diuresis from left atrial receptors

1. In anaesthetized dogs, stimulation of atrial receptors after destruction of the pituitary gland results in a diuresis. This response was not abolished by the administration of bretylium tosylate and was also observed in a surgically denervated kidney. 2. The diuresis is qualitatively similar to that observed in anaesthetized dogs with intact pituitary glands. 3. It is concluded that the diuresis which results from stimulation of the left atrial receptors is mediated by a blood-borne agent which is not the antidiuretic hormone.

Left atrial receptors and the antidiuretic hormone

1. Stimulation of left atrial receptors by distending balloons located at the junction between the pulmonary veins and the left atrium and in the body of the left atrium resulted in a diuresis in anaesthetized dogs.2. In the same dogs the diuresis was not consistently associated with a reduction in the antidiuretic activity of plasma as compared with that during the initial control period. The antidiuretic activity of dog plasma was assayed in water-loaded rats anaesthetized with ethanol.3. Intravenous injections of vasopressin suppressed a water diuresis in water-loaded dogs anaesthetized with chloralose. The changes in antidiuretic activity of dog plasma which resulted from these injections were reliably detected by the bio-assay in the rat.4. It is concluded that the diuretic response to the stimulation of left atrial receptors is not accompanied by a reduction in the plasma antidiuretic hormone level.

Effect of stimulating right atrial receptors on urine flow in the dog

1. Complex unencapsulated nerve endings (right atrial receptors) have previously been found in the endocardium of the right atrial appendage and the junction between the superior vena cava and the right atrium.2. Distension of balloons located in the right atrial appendage and at the junction between the superior vena cava and the right atrium resulted in an increase in urine flow. This diuresis was accompanied by a small increase in the excretion of sodium.3. Cooling the right cervical vagus caused a reduction in the response to distension of the right atrial appendage.4. It is concluded that stimulation of right atrial receptors by the distension of balloons located in the right atrial appendage and at the junction between the right atrium and the superior vena cava results in a reflex increase in urine flow.

Oxygen consumption in children with congenital diseases of the heart

1. An open-circuit method for the measurement of oxygen consumption in children which is suitable for use during cardiac catheterization has been described.

2. Since it has been previously shown that there is no systematic error in this method, the accuracy of the method is described by the random error (i.e. reproducibility). The reproducibility of the method has been determined by the repeated measurement of oxygen consumption in children with congenital diseases of the heart under specified ‘standard’ conditions.

3. A simple method of predicting the oxygen consumption in these children was devised by subjecting the data to a multivariate regression analysis.

4. It is concluded that the accuracy of these predictions, although considerably better than that in the published literature, is not good enough to merit its use in the routine haemodynamic assessment.

The effect of distending the atrial appendages on urine flow in the dog

1. Distension of the atrial appendages resulted in a diuresis, an increase in the rate of Na(+) excretion and an increase in heart rate.2. Both the urinary and heart rate responses to distension of the appendages were either abolished or much reduced by crushing the bases of the appendages.3. The diuresis in response to distension of the atrial appendages is similar to that previously described in response to distension of the pulmonary vein-atrial junctions by Ledsome & Linden (1968).4. It is concluded that stimulation of nerve endings within the atrial appendages results in a reflex increase in urine flow and heart rate.

The effect of stretching the superior vena caval-right atrial junction on right atrial receptors in the dog

1. Action potentials were recorded from fibres in the right cervical vagus, the receptor endings of which were localized to the endocardial surface of the superior vena caval-right atrial junction.2. Stretching the junction between the superior vena cava and the right atrium without obstructing venous return caused an increase in the discharge of these fibres. This increase in impulse frequency was similar to that caused by small changes in mean right atrial pressure (range 0-13.5 cm H(2)O).3. This evidence supports the earlier suggestion that stimulation of the right atrial receptors by stretching the superior vena caval-right atrial junction causes a reflex increase in heart rate.

The CO 2 titration curve of mixed venous blood

1. Simultaneous CO2 titration curves of arterial and mixed venous blood were determined in both dog and man in vivo.

2. The slopes of the CO2 titration curves of mixed venous blood were significantly less than those of the corresponding arterial curves.

3. The non-respiratory pH values of the CO2 titration curves of mixed venous blood were significantly greater than those of the corresponding arterial curves.

4. The theoretical explanations of these differences have been discussed.

The effect on heart rate of distending the atrial appendages in the dog

1. Stretching the atrial appendages in anaesthetized dogs caused an increase in heart rate. This response was unrelated to changes in arterial blood pressure and left and right atrial pressures.2. The increase in heart rate was a reflex response; the afferent path was in the vagi and the efferent solely in the sympathetic nerves.3. The receptors involved in this reflex have been localized to the atrial appendages but there is no conclusive evidence as to their nature.

A new method for assessing states of acute acidaemia in man

1. CO2 titration curves in vivo were determined at various degrees of acute non-respiratory acidaemia in man.

2. The slope of the CO2 titration curve was found to increase as the severity of the acute non-respiratory acidaemia increased.

3. A simple scheme based on the CO2 titration curves in vivo has been proposed for the assessment of acute acidaemia in man.

A reflex increase in heart rate from distension of the junction between the superior vena cava and the right atrium

1. Localized distension of the junction between the superior vena cava and the right atrium without obstructing venous return caused an increase in heart rate.2. This increase in heart rate was a reflex response; the afferent path was in the vagi and the efferent solely in the sympathetic nerves.3. The receptors most likely to be stimulated by the distension of the junction between the superior vena cava and the right atrium are the right atrial receptors located on the endocardial surface of the intrapericardial portion of the superior vena caval-right atrial junction.