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Biomedical subjects

B A Cross

Publications and source records attributed to B A Cross.

At least 37 records · Page 2Linked to original sources
PubMed1980

Effects of intrapulmonary CO2 and airway pressure on phrenic activity and pulmonary stretch receptor discharge in dogs.

Intrapulmonary CO2 and stretch sensitivity were studied in anesthetized, thoracotomized dogs in which both lungs were independently ventilated. The left pulmonary artery was occluded so that changes in left (Test) lung CO2 did not alter systemic arterial PCO2. Adequate gas exchange was maintained in the right lung, which was vagally denervated. In one series of experiments, neural activity in the C5 root of the phrenic nerve was integrated to assess ventilatory drive at various levels of Test lung CO2 and airway pressure both during cyclic ventilation and static lung inflation. In a second series, single unit activity in vagal afferents from pulmonary stretch receptors (PSR) was recorded. Both phrenic activity and PSR discharge were strongly affected by changes in airway pressure but not by changes in Test lung CO2 between 2 and 7%. However, when test lung CO2 was decreased below 2%, phrenic activity decreased and PSR activity increased. These changes were invariably accompanied by an increase in peak airway pressure during cyclic ventilation suggesting that lung mechanics had been altered. The results indicate that, in this preparation, the effects of lung stretch on ventilatory drive spans a wide range whereas intrapulmonary CO2 exerts an effect only at very low levels. It appears that the reflex effects of both stimuli can be accounted by an effect on PSR activity.

Afferent Pathways↗
PubMed1980

The role of vagal afferent information during inspiration in determining phrenic motoneurone output.

Dogs were anaesthetised, paralysed and artifically ventilated using ramp inflations triggered by the onset of the 'integrated' phrenic signal. VT was initially adjusted to maintain a constant PaCO2 and the duration of inflation (TI(resp)) was adjusted to match the phrenic TI. With these control values of VT and TI(resp) a variety of experimental manoeuvres were performed to alter the pattern of volume information delivered during inspiration. These manoeuvres included: (1) alterations in VT while maintaining a constant TI(resp); (2) alterations in TI(resp) alone, with and without obstruction to expiration; (3) delays in the onset of inflation with and without a simultaneous reduction in TI(resp) and (4) the imposition of two inflations, each with the same reduced TI(resp) within the same inspiration. The results suggest that the pattern of vagally-mediated volume information during inspiration determines both the shape and the duration of phrenic motoneurone output. The importance of volume at inspiratory 'offswitch' as the sole determinant of TI is therefore denied. The rate of inflation was not found to contribute to the responses obtained.

Afferent Pathways↗
PubMed1980

Effect of the suckling stimulus on secretion of prolactin and luteinizing hormone in conscious and anaesthetized rats.

Luteinizing hormone and prolactin were measured in plasma samples taken from conscious and anaesthetized, lactating, suckled rats after overnight separation from their litters except for one pup. In the conscious rats, there was a marked fall in plasma LH concentration (P < 0.05), and a large increase in that of prolactin (P < 0.01) within 30 min of returning the pups to the mothers. When the mothers were anaesthetized with urethane and then suckled by their litters, there was no significant change in plasma LH values, but prolactin values rose significantly (P < 0.05) after 2.5 h of suckling. However, suckling caused no significant change in plasma concentrations of LH or prolactin when the milk-ejection frequency was doubled (P < 0.001) by administering xylazine to urethane-anaesthetized mothers. It was concluded that the conscious lactating rat, separated from her litter overnight, is a very sensitive model for studying the neural events controlling LH and prolactin secretion during suckling. Anaesthesia by urethane blocks this sensitized response, but the blockade is not associated with interference in the milk-ejection reflex.

Anesthesia, General↗
PubMed1979

Dependence of phrenic motoneurone output on the oscillatory component of arterial blood gas composition.

1. The hypothesis that respiratory oscillations of arterial blood gas composition influence ventilation has been examined. 2. Phrenic motoneurone output recorded in the C5 root of the left phrenic nerve and the respiratory oscillations of arterial pH in the right common carotid artery were measured in vagotomized anaesthetized dogs which had been paralysed and artificially ventilated. 3. The effect of a change in tidal volume for one or two breaths on phrenic motoneurone output was measured with the inspiratory pump set at a constant frequency similar to, and in phase with, the animal's own respiratory frequency. A reduction of tidal volume to zero or an increase by 30% led to a corresponding change of mean carotid artery pH level. The changes of carotid artery pH resulted in a change of phrenic motoneurone output, predominantly of expiratory time (Te) but to a lesser extent of inspiratory time (T1) and also peak amplitude of 'integrated' phrenic motoneurone output (Phr). Denervation of the carotid bifurcation blocked this response. 4. The onset of movement of the inspiratory pump was triggered by the onset of phrenic motoneurone output. When a time delay was interposed between them, the phase relationship between respiratory oscillations of arterial pH and phrenic motoneurone output altered. The dominant effect was to alter Te; smaller and less consistent changes of Phr and T1 were observed. 5. When the inspiratory pump was maintained at a constant frequency but independent of and slightly different from the animal's own respiratory frequency (as judged by phrenic motoneurone output), the phase relationship between phrenic motoneurone output and the respiratory oscillations of pH changed breath by breath over a sequence of 100-200 breaths, without change of the mean level of arterial blood gas composition. Te varied by up to 30% about its mean value depending on the phase relationship. Ti and Phr were also dependent on the phase relationship but varied to a lesser extent. The changes were comparable to the results obtained in paragraph 4. 6. It was concluded that phrenic motoneurone output is dependent in part on its relationship to the respiratory oscillations of arterial blood gas composition. 7. Information concerning a transient ventilatory disturbance is stored in the arterial blood in the form of an altered pattern of the respiratory oscillations of blood gas composition; this in turn can change breathing by an effect on the carotid bodies.

Action Potentials↗
PubMed1978

Discovery and application: lessons from animal research.

The cumbersome administrative machinery for agricultural research set up following the Rothschild Report is criticised and the view challenged that mission-oriented research is quicker, cheaper and more useful than problem-oriented research. Examples are give from two areas of biological study, corpus luteum physiology and cell membranes, to illustrate the rapid application of basic discoveries to livestock health and production.

Agriculture↗
PubMed1976

Animal, vegetable or cerebral: brains in agricultural production.

Recent developments in brain research seem to have passed unnoticed in veterinary and agricultural circles. Yet they have transformed views on the subject and, Dr Cross argues, made study of the brain mandatory for future advance in animal health and production.

Agriculture↗
PubMed1976

The effect of anaesthesia of the airway in dog and man: a study of respiratory reflexes, sensations and lung mechanics.

1. The effect of breathing an anaesthetic aerosol of 5% bupivacaine hydrochloride has been assessed in dog and man. 2. In the dog, the cough reflex was abolished and the Hering-Breuer inflation reflex severely impaired or abolished; breathing became slower and deeper; no pathological changes were found in the lungs of these dogs. 3. In man, no untoward effects resulted from a 10 min period of aerosol inhalation; there were no systematic effects on airway resistance or lung volumes and the cough reflex in response to either tactile or chemical (citric acid aerosol) stimulation was invariably abolished. The Hering-Breuer inflation reflex was impaired, but this was not associated with any change in resting ventilation. The Ve/CO2 response was enhanced after aerosol anaesthesia; subjects felt an exaggerated dyspnoea. The aerosol anaesthesia abolished the afferent pathway of a reflexly elicited bronchoconstriction in one subject. There was no effect on the ability to hold the breath, or on the quality of the associated sensation. 4. Control aerosols of sodium chloride solution or phosphate buffer produced no effects. Control experiments with intravenous infusions of bupivacaine proved that none of the effects could have been produced by systemic effects of the absorbed anaesthetic. 5. Plasma concentrations of bupivacaine in man did not exceed a recognized toxic level. The experiments demonstrate a safe reversible anaesthesia of the airways in man lasting for a period of 10-20 min.

Aerosols↗
PubMed1975

The effect of varying tidal volume on the associated phrenic motoneurone output:studies of vagal and chemical feedback.

Two groups of dogs were anaesthetised, paralysed and artificially ventilated using a respirator driven by the phrenic motoneurone output, electrically processed to resemble transpulmonary pressure. In one group, blood gases were maintained constant with closed-chest cardiopulmonary bypass; the second group were studied without "bypass". Therefore it was possible to determine the relative contributions of vagal and chemial feedback to the effect of altering the depth of an inspiration on the associated phrenic motoneurone output. Mono-exponential regressions between change of respirator gain and changes in both inspiratory time and peak amplitude of the processed phrenic signal were found for all dogs. The rate of rise of the processed phrenic signal usually changed in the direction of the change in respirator gain, suggesting the presence of vagal positive feedback during eupnoeic breathing. After vagotomy, all responses were absent in the "bypass" group and small in the "non-bypass" group. These experiments quantitate the role of pulmonary vagal afferent discharge, in phase with inspiration, in the regulation of phrenic motoneurone output in a closed-loop situation.

Animals↗
PubMed1975

Endocrine neurons.

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Action Potentials↗