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Biomedical subjects

J A Bernards

Publications and source records attributed to J A Bernards.

At least 19 recordsLinked to original sources
PubMed1978

Effects of pulmonary gas embolism on circulation and respiration in the dog. V. Effect of changing breathing gas composition on pulmonary gas embolization.

It was found in previous investigations that during venous gas infusion at low rates (1--5 ml/min-1) circulatory and respiratory variables reached a constant level after about 10--15 min. The present study demonstrates that this steady state can be disturbed by changing the composition of the breathing gas mixture. Alteration from air to 21% O2 in helium rapidly increased the embolic effects up to a maximum within 1.5--2 min; in the next 5--8 min the circulatory and respiratory variables returned to their previous levels during air breathing. Reverse effects occurred when changing from 21% O2 in helium to air. Similar phenomena were seen after switching from air to pure oxygen and from 21% O2 helium to pure oxygen. However, the extent of the circulatory and respiratory changes differed depending on the composition of the respective alternating breathing gas mixtures and on the initial embolic level as determined by infusion rate and kind of infusion gas. Gas movements between intravascular bubbles and alveolar space might be responsible for these changes.

Animals↗
PubMed1978

Effects of pulmonary gas emoblism on circulation and respiration in the dog. VI. Influence of body position on the effects of pulmonary gas embolism.

In the present study the influence of body position on the effects of venous gas infusion was examined. The body position of anesthetized dogs ventilated artifically varied between supine, right-side-down and left-side-down position. Without venous gas infusion the change of body position hardly affected pulmonary arterial pressure (Pap) and alveolar CO2 fractional concentration (FACO2). However, during venous gas infusion a change of body position immediately elicited a rapid increase Pap and a decrease in FACO2 completed within a few seconds. Thereafter both variables gradually returned to their initial levels as before the change of body position. The extent of change in Pap and FACO2 due to alteration of body position depended on the initial embolic level (determined by the rate of infusion and the nature of the gas used) and on the change of body position.

Animals↗
PubMed1977

Effects of pulmonary gas embolism on circulation and respiration in the dog. III. Excretion of venous gas bubbles by the lung.

Intravenous injection of gas (10-60 ml) causes acute pulmonary embolism, which disappears completely within 10-20 min. Intravenous infusion of gas (1-5 ml min-1) can be continued for a long time. During these infusions a steady state is reached in which pulmonary arterial pressure is increased and cardiac output remains unaltered. This indicates that the degree of embolization has reached a constant level despite the continuous gas infusion. These findings can be explained by a gradual disappearance of the bubbles from the pulmonary circulation. The purpose of this study was to measure the possible excretion of gas from the intravascular gas bubbles into the alveolar air after venous administration. Neon was used as a test gas since its fractional concentration in ambient air is low (0.00018) and it can be detected by gas chromatography with sufficient accuracy. It could be demonstrated that after injection neon was present in the expiration gas. During the steady state of infusion the rate of excretion in the expiration gas appeared to be equal to the rate of infusion. Changes in the pulmonary arterial pressure curve were reflected in the neon wash-out curve. It may be concluded that during pulmonary gas embolism the administered gas is excreted into the alveolar air and that the excretion rate largely depends on the increased pulmonary arterial pressure due to the obstructing bubbles themselves.

Animals↗
PubMed1977

Effects of pulmonary gas embolism on circulation and respiration in the dog. I. Effects on circulation.

Mongrel dogs weighing 15-25 kg and anesthetized with thiopental-gamma-hydroxybutyric acid were used to investigate the effects of pulmonary gas embolism on pulmonary arterial pressure (Pap), systemic arterial pressure (Pa) and cardiac output (Q). Pulmonary gas embolism was produced either by venous injecton or by venous infusion. The most marked effect of pulmonary gas embolism on circulation was an increase in Pap which returned to the original level after stopping the gas administration. 1. After gas injection Pap rose to a maximum within 30--60 s. The extent of this rise in Pap showed a positive correlation with the volume of the injected gas. The kind of gas (oxygen, helium, neon, nitrogen, air), however, did not influence the extent of the rise in Pap, but did influence the time of return of Pap to the original level. Carbon dioxide showed an exceptional behavior in that it had almost no effect on Pap at all. P a hardly changed with the volume of the gas injections (20--60 ml injected within 1 s); Q was not measured after gas injection (the direct Fick method is not usable in this situation). 2. Gas infusion caused a slow rise of Pap, its steepness and extent depending on the rate of infusion and on the physical properties of the infused gas. When the right ventricle was able to maintain its output, a constant level of Pap was reached after 10--15 min. In this circulatory steady state Pap appeared to be a measure of the degree of embolization. However, this relationship no longer held when the right ventricle failed as evidenced by a fall in Pap, Pa and Q. It may be concluded that pulmonary gas embolism produces a transient partial obstruction in the pulmonary circulation and that the performance of the right ventricle determines the maximum degree of embolization compatible with a sufficient circulation.

Animals↗
PubMed1977

Effects of pulmonary gas embolism on circulation and respiration in the dog. II. Effects on respiration.

In mongrel dogs weighing 15--25 kg and anesthetized with thiopental-gamma-hydroxybutyric acid the effects of venous gas infusion and injection on several respiratory variables were investigated. During spontaneous respiration pulmonary gas embolism caused an increase of the ventilatory minute volume depending on the degree of embolization. The contribution of breathing frequency and tidal volume to the increase of ventilatory minute volume varied from one animal to the other. During constant artificial ventilation pulmonary gas embolism impaired the pulmonary gas exchange depending on the degree of embolization. How far a steady-state phase in gas exchange can be reached during continuous venous gas infusion depended on the adaptation of the circulation. At severe degrees of embolization circulation as well as gas exchange became deficient. Increasing artificial ventilation during pulmonary gas embolism improved the wash-out of carbon dioxide, but hardly affected the uptake of oxygen. The most important origin of the disturbed gas exchange in pulmonary gas embolism seemed to be an increased inequality of the ventilation-perfusion ratio distribution.

Animals↗
PubMed1977

Capnostat and oxystat. Electronic devices to automatically maintain the end-tidal PCO2 and PO2 of a subject connected to a closed respiratory circuit at adjustable levels.

In respiratory physiology it is often desirable to maintain the end-tidal PCO2 and PO2 at adjustable levels independent of each other, e.g., when taking steady-state CO2 or O2 response curves, or when studying the ventilatory effects of exercise or drugs at constant levels of PCO2 and PO2. Based on the closed respiratory circuit described by Folgering et al. (1974), a new version was designed. The main new features of this version are that end-tidal PO2 instead of inspiratory PO2 can be kept constant, and that the correcting activity of both controllers (capnostat and oxystat) is proportional to the magnitude of the difference between the actual and the adjusted end-tidal PCO2 or PO2. An optic as well as an acoustic alarm is provided and will be switched on whenever no end-tidal PO2 is detected for an adjustable time.

Carbon Dioxide↗
PubMed1976

The role of the fusimotor system with respect to the contribution of the diaphragm and the intercostal muscles to the respiratory tidal volume.

The efferent electrical activity in the phrenic nerve can be quantified in such a way that it gives a good correlation to tidal volume. After administration of the drug benzoctamine this relationship changes: more phrenic nerve activity is needed for the same tidal volume. No changes were found in the neuro-muscular transmission from the phrenic nerve to the diaphragm. There was no alteration in dynamic compliance of the lungs or in airway resistance. The afferent phrenic nerve activity from proprioceptors in the diaphragm did not change. It seems unlikely that respiratory neurons in the brainstem were affected since the sensitivity of the respiratory system to CO2 did not change. It is known that the tonic fusimotoneuron activity is suppressed at a supraspinal level by benzoctamine. Since intercostal muscles have muscle spindles and the diaphragm hardly has any, the intercostal muscle activity will be affected more than diaphragmatic activity by benzoctamine. This could actually be shown by quantifying the electromyogram of inspiratory external intercostal muscles. The tidal volume regulation is controlled by the vagal feedback loop. In order to reach a certain tidal volume after administration of benzoctamine, the contribution of the diaphragm has to increase because the activity of the intercostal muscles is diminished.

Animals↗
PubMed1975

Ventilation estimated from efferent phrenic nerve activity in the paralysed cat.

The purpose of this study is to develop a reliable method for obtaining information about "spontaneous respiration" in paralysed cats. Therefore action potentials from one of the phrenic nerves are recorded. In a spontaneously breathing animal, a CO2 rebreathing experiment is performed in order to obtain a relationship between phrenic nerve activity and tidal volume. This phrenic nerve activity is corrected for the noise measured during expiration and quantified proportional to the square root of the mean impulse rate of the whole nerve bundle. Thus, high correlation coefficients (0.95 or more) between phrenic nerve activity and tidal volume can be obtained. After paralysing the cat this relationship can be used to estimate "spontaneous tidal volume" from the phrenic nerve activity. It appears to be necessary to perform unilateral phrenicotomy on the nerve from which recordings are taken, because there is a condiserable amount of afferent signals in the phrenic nerve which is dependent on the stroke volume of the respirator, on the alveolar PCO2 and somewhat on the alveolar PO2. It is concluded that after vagotomy and phrenicotomy and if suitably quantified, the electrical activity in the phrenic nerve gives accurate information on "spontaneous ventilation" in a paralysed cat.

Action Potentials↗