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Biomedical subjects

M J Purves

Publications and source records attributed to M J Purves.

64 records · Page 4Linked to original sources
PubMed1967

Observations on carotid body chemoreceptor activity and cervical sympathetic discharge in the cat.

1. Parallel recordings have been made of the cervical sympathetic and carotid body chemoreceptor activity in the anaesthetized cat.2. The sympathetic activity remains remarkably constant while the chemoreceptor activity is varied by changes in the blood gas tensions of relatively short duration.3. Changes in intrathoracic pressure by obstruction to the airway or thoracic compression were associated with changes in the activity of both nerves.4. It is likely that, under normal conditions, the sympathetic nervous activity provides a stable vasomotor tone within the carotid body.

Action Potentials↗
PubMed1967

Factors affecting the cat carotid chemoreceptor and cervical sympathetic activity with special reference to passive hind-limb movements.

1. Recordings have been made of the activity in carotid body chemoreceptor afferent fibres and in the cervical sympathetic of the cat during passive movement of the hind limbs.2. The chemoreceptor activity increases immediately the limbs are moved and is maintained at a raised level with preservation of the chemoreceptor rhythm fluctuations throughout. In some cases, the increase persists for a time after the movements are stopped.3. This early change does not occur if the cervical sympathetic on the same side as the carotid body from which recordings are made is cut, nor does it occur if the femoral and sciatic nerves are cut.4. The carotid artery oxygen tension (P(a, O2)) increases early; in the majority of experiments, there was no significant change in end-tidal P(CO2) although the minute volume of ventilation (V) increased by about 20% of control with passive movement of the hind limbs.5. Passive movement of the hind limbs also causes an immediate rise in cervical sympathetic activity which is sustained, and which is abolished if the femoral and sciatic nerves are cut.6. Electrical stimulation of the cervical sympathetic causes an increase in chemoreceptor afferent discharge.7. Bilateral cervical sympathectomy causes the respiratory lag to increase from approximately 1 sec to some 20 sec and, when passive movements cease, the fall in V is more sluggish than control.8. These results are discussed in the light of the controversy regarding humoral and neurogenic causes for the increase in respiration in exercise.

Animals↗
PubMed1967

Carotid body chemoreceptor activity in the new-born lamb.

1. Tidal volume, carotid artery oxygen tension (P(a,O2)) and blood pressure and chemoreceptor activity in the sinus nerve have been continuously measured and recorded in nine lambs anaesthetized with pentobarbitone sodium, and varying in age from some minutes after birth to 5 days after birth.2. Inhalation of 100% oxygen caused, after a delay of 3-4 sec, a rise in P(a,O2), a fall in minute ventilation (V) and chemoreceptor activity. The respiratory response was abolished after section of both sinus nerves.3. Inhalation of 10% oxygen in nitrogen caused a fall in carotid P(a,O2), a rise in respiration and in chemoreceptor activity. The respiratory response was abolished after both sinus nerves had been cut.4. Minute ventilation, carotid P(a,O2) and chemoreceptor activity increased on breathing 5% CO(2) in air. Section of both sinus nerves did not affect the maximum increase in ventilation but the lag of the respiratory response approximately doubled while respiration increased more slowly.5. From these results, it was calculated that the chemoreceptors had a latency of 0.25-0.5 sec and the time constant of the rate of change of chemoreceptor activity was 10-15 sec.6. The chemoreceptors responded to changes in P(a,O2) of +/-5-10 mm Hg.7. Comparison of these results with those reported in adult animals suggest that the peripheral chemoreceptors are fully mature at birth, that their response does not differ with the age of the lamb and that the carotid body chemoreceptors are concerned both in the mediation of the hypoxic drive to ventilation and in the respiratory response to inhaled CO(2).

Action Potentials↗
PubMed1966

Respiratory and circulatory effects of breathing 100 per cent oxygen in the new-born lamb before and after denervation of the carotid chemoreceptors.

1. Methods are described for measuring tidal volume and frequency, end-tidal CO(2), blood pressure and heart rate, and arterial gas tensions in the unanaesthetized new-born lamb.2. The resting values of minute ventilation (V)/kg body wt. and arterial oxygen and carbon dioxide tension, (P(a, o2)) and (P(a, CO2)) were similar to those which have been reported in the new-born baby. There was a direct and significant relation between P(a, o2) and P(a, CO2) and the age of the lamb.3. Thirty-five unanaesthetized lambs aged 40 min to 10 days breathed 100% oxygen; minute ventilation fell by an average of 19% of control, end-tidal CO(2) increased and the ratio of change in tidal volume (DeltaV(T)) to change in pressure (DeltaP) (DeltaV(T)/DeltaP) remained constant. In a proportion of lambs, a small decrease in blood pressure and heart rate was observed. The effect of breathing 100% O(2) on lung compliance was variable.4. These changes in ventilation were virtually abolished after both sinus nerves had been cut.5. The results therefore suggest that a significant hypoxic drive to ventilation exists in the new-born lamb and that this drive is mediated by functioning and mature peripheral chemoreceptors.6. Preliminary evidence suggested that, on 100% O(2), the sensitivity of new-born lambs to inhaled CO(2) was reduced.

Animals↗
PubMed1966

The effects of hypoxia in the new-born lamb before and after denervation of the carotid chemoreceptors.

1. Twenty-seven unanaesthetized new-born lambs, 6 hr-10 days old, responded to two levels of inspired oxygen, 125 and 110 mm Hg (alveolar CO(2) being controlled) with a sustained increase in minute ventilation (V), a small increase in heart rate and a less consistent rise in systemic blood pressure.2. An increase in V was observed when arterial oxygen tension (P(a), (O2)) had fallen by 6-15 mm Hg. There appeared to be no fixed threshold of P(a), (O2) at which ventilation started to increase.3. The increase in ventilation caused by these levels of hypoxia was significantly and directly related to the age of the lamb and to its control alveolar CO(2).4. More severe hypoxia caused a progressive increase in V until P(a), (O2) was about 25 mm Hg when respiration failed. This increase at P(a), (O2) > 25 mm Hg was markedly potentiated when alveolar P(CO2) (P(A), (CO2)) was increased and abolished after bilateral denervation of the carotid chemoreceptors.5. Significant (> 10%) left-to-right shunts were found in ten out of twelve lambs lightly anaesthetized with pentobarbitone sodium, breathing air. Hypoxia diminished the left-to-right pressure gradient largely by its pressor effect on the pulmonary circulation. When inspired O(2) tension (P(I), (O2)) was 70 mm Hg, all seven lambs studied showed a reversal of the pressure gradient and evidence of right-to-left shunts (11-42%) across the ductus arteriosus.6. The implications of these findings have been discussed with reference to previous studies of the new-born response to hypoxia and it is concluded that the peripheral chemoreceptors are fully active at birth and in the new-born period.

Animals↗
PubMed1966

The respiratory response of the new-born lamb to inhaled CO-2 with and without accompanying hypoxia.

1. The respiratory response to inhaled CO(2) was measured in twenty unanaesthetized new-born lambs aged 4 hr-10 days. Measurement of resting arterial pH, P(CO2) and plasma bicarbonate showed a non-respiratory acidosis immediately after birth which was corrected in the first 24-28 hr: thereafter, the acid-base pattern was of a compensated respiratory alkalosis.2. When CO(2) was added to the inspired gases and resting arterial oxygen tension (P(a), (O2)) was controlled, the average increase in minute ventilation (V) was 0.075 l.min(-1).kg(-1).mm Hg, P(a), (CO2) (-1) and duplicate responses in the same lamb differed by 6-22.5%.3. The slope of the V/P(a), (CO2) line (S) varied inversely with P(a), (O2). In one lamb, severe hypoxia (P(a), (O2) = 21 mm Hg) caused a marked depression of the slope.4. Neither the slope S nor the horizontal intercept B of the lines was related to the age of the lamb. B was not related to pH(a) and only slightly affected by acute hypoxia. B was related to arterial [HCO(3) (-)] and values for both were reduced with the acid-base disturbances seen in the first 10 days after birth. Evidence was given which suggested that the response of the new-born lamb to inhaled CO(2) was similar to that of man acclimatized to a P(a), (O2) of 70-75 mm Hg.5. In the lightly anaesthetized lamb, bilateral section of the sinus nerves caused a small reduction in the sensitivity to inhaled 5% CO(2) in air, an increase in the respiratory lag and a reduction in the rate at which V increased.6. It was concluded that, in the new-born lamb, the carotid chemo-receptors are involved in the response to inhaled CO(2) and that hypoxia potentiates this response.

Acidosis↗