PubMed Health⌕ Search

Biomedical subjects

R L Coon

Publications and source records attributed to R L Coon.

54 records · Page 3Linked to original sources
PubMed1980

Cardiac, aortic, pericardial, and pulmonary receptors in the dog.

Afferent nerve activity from left and right atrial, left and right ventricular, interventricular septal, papillary muscle, pericardial, aortic and pulmonary vascular receptors was recorded from the left T3 white ramus communicans and the innominate, dorsal, recurrent, ventromedial, craniovagal and caudovagal cardiac nerves in alpha-chloralose-anesthetized dogs. The receptors were localized and the nature of the stimuli required to excite these receptors was also determined. Some ventricular receptors were excited during maximal contraction of the myocardium. Other ventricular and aortic receptors were stimulated by elevation of intracardiac or aortic pressure. The pericardial, atrial, and papillary muscle receptors were excited by stretching the surrounding tissue. The discharge patterns of these receptors were not always synchronous with the events of the cardiac cycle. The stimuli required to excite each type of receptor (ventricular, atrial, etc.) and their resultant discharge patterns were not identical for all of the receptors. Excitation of cardiac receptors with sympathetic afferents resulted in 1--2 spikes per cardiac cycle, whereas receptors with vagal afferents resulted in bursts of spikes per cardiac cycle.

Action Potentials↗
PubMed1979

Breathing frequency responses to pulmonary CO2 in an isolated lobe of the canine lung.

Recent studies have indicated that the breathing frequency responses to inspired CO2 in part result from changes in pulmonary stretch receptor activity. Pulmonary CO2 may alter frequency by direct inhibition of stretch receptor discharge, or secondarily, by changes in airway mechanics. The vascularly isolated left lower lobe (LLL) of the canine lung was used to determine the effect of hypocapnic airway constriction on the pulmonary CO2 reflex. The upper and middle lobes of the left lung were removed and the right vagus nerve sectioned. Blood was recirculated through the LLL. Diaphragm electromyogram was used as an index of respiratory center activity and to trigger ventilation of the left lower lobe. Lobar hypocapnia increased peak airway pressure and reduced respiratory rate. However, infusion of isoproterenol or the use of a mechanical overflow system to block the airway pressure response prevented the frequency changes associated with CO2. Although both the direct and mechanical effects of CO2 on stretch receptors may contribute to the reflex, in the LLL preparation the mechanical effects predominate.

Airway Resistance↗
PubMed1978

Systemic arterial blood pH servocontrol of mechanical ventilation.

Servocontrol of mechanical ventilation using systemic arterial blood pH, measured by a dual-function pH/PCO2 intra-arterial sensor, as the controlled variable uas carried out in 30 dogs anesthetized with pentobarbital, 30 mg/kg. The control loop consisted of the animal, an intra-arterial dual-function pH/PCO2 sensor and sensor amplifier, a controller, and a Siemans-Elema 900 servoventilator. The system responded appropriately to changes in set-point pH from 7.30 to 7.50, as well as to infusions of lactic acid, which, with the control loop open, decreased systemic arterial blood pH 0.1 TO 0.2 PH units. Long-term (16 hr) ventilation of one dog with the systemic arterial blood pH servocontrol ventilator was shown to be feasible.

Acid-Base Equilibrium↗
PubMed1978

Halothane, tracheal compliance and upper-airway mechanoreceptors.

This study was designed to define the effects of halothane on the compliance of the trachea. An isolated in-situ tracheal preparation was studied in 14 mongrel dogs anesthetized with pentobarbital. Compliance of the closed tracheal segment was measured with continuous intraluminal pressure recordings during repeated injections of known volumes of air: Slow-adapting neural activity observed in paratracheal branches of the recurrent laryngeal nerve accurately reflected pressure in the tracheal segment. Halothane at 0.5--4.0 per cent concentrations caused a significant (P less than 0.001) average 10 per cent increase in the compliance of the trachea. Stimulation of the efferent vagus caused a significant (P less than 0.001) average 8 per cent decrease in compliance of the trachea. After exposure to halothane, vagal stimulation still caused a significant decrease in compliance of the trachea.

Airway Resistance↗
PubMed1978

Respiratory inhibition with sympathetic afferent stimulation in the canine and primate.

Inhibition of phrenic efferent nerve activity, diaphragm electromyogram (EMG), and external intercostal EMG was observed in halothane- and pentobarbital-anesthetized mongrel dogs and pentobarbital-anesthetized monkeys with stimulation of sympathetic afferents. The central end of the transected ventral limb of the left ansa subclavia, the sympathetic chain, or individual white rami were stimulated while simultaneously recording phrenic efferent nerve activity, diaphragm EMG, or the external intercostal EMG. Averaged phrenic efferent bursts or MEG were used to trigger an electronic respirator. In all of the dogs and monkeys, electrical stimulation of sympathetic afferent pathways resulted in inhibition of phrenic efferent nerve activity, diaphragm EMG, or external intercostal EMG. Although the exact origin of these fibers was not determined, the conduction velocities of these afferents were 4-7 m/s, which places them in the Adelta fiber-type range. The importance of these afferents in the regulation of respiration in the awake animal remains unknown.

Adrenergic Fibers↗
PubMed1976

Cardiac responses to stimulation of thoracic afferents in the primate and canine.

Excitatory cardiovascular responses to electrically stimulated upper thoracic sympathetic afferent nerves were observed in halothane-anesthetized mongrel dogs and monkeys. The central end of the transected ventral limb of the left ansa subclavia was stimulated before and after several types of denervation. Significant increases in right and left ventricular maximum systolic pressures, systolic and diastolic systemic blood pressures, and aortic flow were observed. The carotid sinuses were denervated bilaterally and stimulation of the ansa was repeated. The cardiovascular responses to stimulation of the ventral ansa after carotid sinus denervation were greater in magnitude than those observed prior to denervation. This carotid sinus modulation of cardiovascular responses was observed in dogs and monkeys. Cardiovascular responses to stimulation of the ventral ansa after bilateral vagotomy were significantly less than the responses observed after carotid sinus denervation prior to vagotomy. However, the responses after vagotomy were statistically identical to responses obtained while stimulating the ventral ansa when the carotid sinuses and vagi remained intact.

Afferent Pathways↗
PubMed1976

Evaluation of a dual-function pH and PCO2 in vivo sensor.

A newly developed, dual-function pH and PCO2 sensor was evaluated in this study. The sensors were placed in the femoral arteries of dogs anesthetized with sodium pentobarbital. Comparisons were made between systemic arterial pH and PCO2 measured using the sensor and those measured from blood samples drawn at 15-min intervals over a 7-h period using a bench instrument. The mean pH of the bench instrument measurements was 7.43. The mean difference of the sensor measurements from the bench instrument measurements for 207 comparisons was 0.0003 pH +/- 0.061 SD. The mean PCO2 of the bench instrument measurements was 40 mmHg. The mean difference of the sensor measurements from those of the bench instrument for 212 comparisons was -1.43 mmHg +/- 5.17 SD. The sensors performed equally well in the presence of metabolic or respiratory acidosis and alkalosis. The dual-function sensors evaluated in this study are useful for trend monitoring of pH and PCO2 over at least a 7-h period without recalibration. With improvement in the consistency of sensor construction, these sensors will be reliable in vivo sensing devices for blood pH and PCO2 and thus valuable research and clinical instruments.

Animals↗
PubMed1975

Hypocapnic bronchoconstriction and inhalation anesthetics.

The effects of halothane, enflurane, and methoxyflurane on hypocapnic bronchoconstriction (increased airway resistance and decreased compliance of the lung) were studied in vivo in the isolated left lower lobe of the canine lung. Hypocapnic bronchoconstriction, induced by altering the concentration of CO2 in gas ventilating the lobe, was repeated in the presence and absence of various concentrations of anesthetic gases (halothane: 0.5, 1.0, and 3.0 per cent; enflurane: 1.0, 3.0, and 5.0 per cent; methoxyflurane: 0.25, 0.50, and 1.0 per cent). In the higher concentrations, all three drugs blocked the bronchoconstrictor effect produced when the inspired CO2 was decreased from 5 to 0 per cent. In lower concentrations, halothane was the most effective blocking drug. Propranolol did not affect the ability of the three anesthetics to block hypocapnic bronchoconstriction, nor did the beta-receptor blocking drug sotalol affect the blocking effects of halothane. The ability of these anesthetics to block hypocapnic bronchoconstriction probably is mediated not through an adrenergic mechanism but by one that is nonspecific. (Key words: Lung, bronchoconstriction; Carbon dioxide, hypocarbia; Anesthetics, volatile, halothane; Anesthetics, volatile, enflurane; Anesthetics, volatile, methoxyflurane.)

Adrenergic beta-Antagonists↗
PubMed1975

Sympathetic afferent nerve activity of right heart origin.

Six mongrel dogs anesthetized with sodium pentobarbital and paralyzed with gallamine triethiodide were studied on total cardiopulmonary bypass. This study verified the existence of right heart mechanoreceptors whose afferent nerves traverse the upper thoracic white rami communicantes. these mechanoreceptors were studied by observing changes in average maximum, and total nerve spike frequency when right atrial and right ventricular systolic and diastolic pressures were altered by means of intracardiac balloons. Receptors that responded to volume and pressure changes were found in both the right atrium and right ventricle. Nerve activity in these afferents increased with increasing right atrial and right ventricular pressures. These mechanoreceptors were more responsive in the upper physiological ranges of right heart pressures. In most nerve fibers studied, maximum activity occurred during both right atrial and right ventricular diastole.

Animals↗
PubMed1975

Pulmonary afferent activity recorded from sympathetic nerves.

This study in mongrel dogs, anesthetized with sodium pentobarbital, verified the existence of pulmonary receptors whose afferents traverse the right and left upper thoracic white rami communicantes. These receptors responded to lung inflation as well as pinching of the lung parenchyma and were nonadapting in nature. In some fibers, increases in afferent activity were also observed when the pulmonary artery and veins were mechanically stimulated by probing. Conduction velocities of these afferents were measured in single-fiber preparations and were of the Adelta fiber type.

Animals↗
PubMed1975

Local control of pulmonary resistance and lung compliance in the canine lung.

Local control of pulmonary resistance and lung compliance was studied in the in situ left lower lobe of the canine lung. Recirculation of blood through the lobe while the Pco2 of the ventilatory gas was varied resulted in an increase in resistance and a decrease in compliance only when the pulmonary venous pH was greater than 7.42. Alternating sodium bicarbonate and lactic acid infusion while alveolar Pco2 was maintained below 5 mmHg demonstrated the dependence of the hypocapnic response on the acid-base status of the blood perfusing the respiratory airways. The increase in resistance and decrease in compliance observed at a pulmonary venous pH of 7.64 was comparable to that observed after lobar pulmonary artery occlusion. Varying degrees of hypoxia did not significantly affect bronchomotor tone, nor was the bronchoconstriction following lobar pulmonary artery occlusion affected by the hypoxia. Vagal stimulation superimposed on a stepwise increase in pulmonary venous pH from 7.32 to 7.62 resulted in an increase in resistance which paralleled the increase in resistance when pulmonary venous pH alone was increased. Compliance was not significantly affected by vagal stimulation at any level of pulmonary venous pH.

Airway Resistance↗
PubMedDate not supplied

Tracheal afferent nerves.

The individual fibers of the inferior laryngeal nerve and anastomosing branch of the superior laryngeal nerve arising from the upper five to six tracheal rings were studied. In 30 mongrel dogs using simple and multifiber nerve preparations, afferent nerve activity was studied both in the intact trachea and in an isolated segment of trachea with artificial stimuli of graded pressure and flow. The adaptation rate, threshold, spontaneous firing frequency, maximum firing frequency, and rate of change in afferent discharge were recorded. Subsequently, these fibers were electrically stimulated to determine what reflex effects could be produced. Afferent nerve activity recorded from the upper trachea was found to be sensitive to tracheal pressure changes of 0.5 to 12 mm Hg. Nerve activity paralleled the frequency of pressure changes. Electrical stimulation of these fibers demonstrated reflex bradycardia, bradypnea and alteration of blood pressure. These data and that of other investigators indicate that upper airway mechano-receptors may be significant, not only in the initiation of upper airway protective reflexes, but also in the regulation of normal respiration.

Afferent Pathways↗
PubMedDate not supplied

Accessory muscle activity and respiration.

The relationship between the accessory muscle activity (sternohyoid and sternothyroid) and respiration was studied in canines. These animals do not have an omohyoid muscle such as found in primates. Therefore, chair-trained monkeys that have all three accessory muscles were used in a portion of the study. Findings in canines supported those previously reported. The sternothyroid muscle fired spontaneously with the onset of inspiration, but there was no similar activity in the sternohyoid. The activity of both muscles was observed after sectioning the recurrent laryngeal nerves and inducing hypoxia and hypercarbia. The severely hypoxic animals produced some negligible activity in the sternohyoid muscle. The data obtained from the chair-trained monkeys showed no consistent accessory muscle activity during normal respiration with recordings taken immediately after electrode placement, at 24 hours, and one week later. Respiratory activity was consistent in the omohyoid and sternothyroid but not in the sternohyoid muscle when partial airway obstruction and hypoxia were induced.

Airway Obstruction↗