Effect of arterial oxygen tension on cerebral blood flow at different levels of arterial PCO2

The ability of the pulmonary circulation of the fetal lamb to respond to a rise in oxygen tension was studied from 94 to 146 days of gestation. The unanesthetized ewe breathed room air at normal atmospheric pressure, followed by 100% oxygen at three atmospheres absolute pressure in a hyperbaric chamber. In eleven near-term lambs (132 to 146 days of gestation), fetal arterial oxygen tension (PaO2) increased from 25 +/- 1 to 55 +/- 6 Torr (mean +/- SE), which increased the proportion of right ventricular output distributed to the fetal lungs from 8 +/- 1 to 59 +/- 5%. In five very immature lambs (94 to 101 days of gestation), fetal PaO2 increased from 27 +/- 1 to 174 +/- 70 Torr, but the proportion of right ventricular output distributed to the lung did not change, 8 +/- 1 to 9 +/- 1%. In five of the near-term lambs, pulmonary blood flow was measured. It increased from 34 +/- 3 to 298 +/- 35 ml.kg fetal wt-1.min-1, an 8.8-fold increase. We conclude that the pulmonary circulation of the fetal lamb does not respond to an increase in oxygen tension before 101 days of gestation; however, near term an increase in oxygen tension alone can induce the entire increase in pulmonary blood flow that normally occurs after the onset of breathing at birth.

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On the Relation between the Chorda Tympani Nerve Response, Arterial Oxygen Tension and Blood Flow in the Tongue of the Rat

Acta Physiologica Scandinavica ◽

10.1111/j.1748-1716.1971.tb04989.x ◽

1971 ◽

Vol 82 (4) ◽

pp. 453-459 ◽

Cited By ~ 14

Author(s):

Göran Hellekant

Keyword(s):

Blood Flow ◽

Oxygen Tension ◽

Arterial Oxygen Tension ◽

Arterial Oxygen ◽

Chorda Tympani ◽

Chorda Tympani Nerve ◽

Nerve Response

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Cerebral blood flow in birds: effect of hypoxia

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1978.234.3.h230 ◽

1978 ◽

Vol 234 (3) ◽

pp. H230-H234 ◽

Cited By ~ 2

Author(s):

B. Grubb ◽

J. M. Colacino ◽

K. Schmidt-Nielsen

Keyword(s):

Blood Flow ◽

Cerebral Blood Flow ◽

Arterial Oxygen Tension ◽

Arterial Oxygen ◽

Two Component ◽

Flow Through ◽

Oxygen Tensions ◽

Xenon 133 ◽

Arterial Po2 ◽

Increased Blood Flow

The effect of hypoxia on cerebral blood flow in ducks was investigated by the rate at which arterially injected xenon-133 was cleared from the duck's brain. A two-component clearance curve resulted, which we have attributed to flow through the grey and white matter. Decreasing the arterial oxygen tension (PaO2) to 75 mmHg had no effect on cerebral blood flow. However, decreasing the PaO2 below 75 mmHg significantly increased blood flow to the fast-clearing compartment. The greatest increase in blood flow was seen when the arterial PO2 was below 50 mmHg. At an arterial PO2 of 30 mmHg, the cerebral blood flow to the fast-clearing compartment was increased more than 600% above the normoxic level. The magnitude of this increase is much greater in the duck than has been reported for mammals at roughly equivalent arterial oxygen tensions. The ability of avian cerebral blood flow to increase at moderate levels of hypoxia, plus the magnitude of the increase, may play a role in the exceptional tolerance of birds to hypoxia.

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