Regional alveolar gas composition and lung function in sheep

doi:10.1016/0034-5687(79)90073-2

Respiration Physiology

Volume 37, Issue 3, August 1979, Pages 239-254

Respiration Physiolo...

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Abstract

The influence of regional alveolar oxygen and carbon dioxide tensions on the distribution of lung blood flow and gas exchange was studied in unanaesthetised sheep. Right apical lobe (RAL) hypoxia, induced by administering nitrogen or nitrogen/oxygen mixtures to the lobe, stimulated a prompt, graded and well sustained reduction in lobar blood flow. Maximum hypoxia was accompanied by an approximate 65% reduction in perfusion, a significant fall in RAL carbon dioxide tension and output, a reversal of lobar oxygen flux and an average 13 Torr fall in arterial oxygen tension. The reduction in perfusion and gas exchange persisted in the face of elevated systemic oxygen tensions produced by giving pure oxygen instead of air to the remainder of the lung (RL). Mild RAL hypercapnia potentiated the hypoxia-induced change in perfusion and gas exchange. During lobar hypoxia RL blood flow and gas exchange increased to maintain total pulmonary gas exchange at an essentially constant level. RAL hyperoxia did not significantly alter the distribution of perfusion or gas exchange.

References (21)

E.H. Bergofsky
Mechanisms underlying vasomotor regulation of regional pulmonary blood flow in normal and disease states
Am. J. Med.
(1974)
A. Hemingway et al.
Respiration of sheep at thermoneutral temperature
Respir. Physiol.
(1966)
P. Howard et al.
Factors causing and reversing vasoconstriction in unventilated lung
Respir. Physiol.
(1975)
M. Arborelius
⁸⁵Kr in the study of pulmonary circulation during bronchospirometry
Scand. J. Clin. Lab. Invest.
(1965)
G.R. Barer et al.
Stimulus-response curves for the pulmonary vascular bed to hypoxia and hypercapnia
J. Physiol. (London)
(1970)
J.L. Benumof et al.
Cyclic hypoxic pulmonary vasoconstriction induced by concomitant carbon dioxide changes
J. Appl. Physiol.
(1976)
A.W.T. Edwards
Regional pulmonary function by lobar spirometry in unanaesthetized sheep
J. Appl. Physiol.
(1966)
L.E. Farhi
Ventilation-perfusion relationship and its role in alveolar gas exchange
A.P. Fishman
Respiratory gases in the regulation of the pulmonary circulation
Physiol. Rev.
(1961)
A.P. Fishman
Hypoxia on the pulmonary circulation. How and where it acts
Circ. Res.
(1976)

There are more references available in the full text version of this article.

Cited by (9)

Local pulmonary blood flow: control and gas exchange
1993, Respiration Physiology
We studied the local response of the pulmonary vasculature to combiend changes in alveolar O_o₂ and P_co₂ in the right apical lobe (RAL) of six conscious sheep. That lobe inspired an O₂CO₂N₂ mixture adjusted to produce one of 12 alveolar gas compositions: end-tidal P_co₂ (Pet_co₂) of 40, 50, and 60 Torr, each coupled with end-tidal P_o₂ (Pet_o₂) of 100, 75, 50, and 25 Torr. In addition, at each of the four Pet_o₂, the inspired CO₂ was set to O and Pet_co₂ was allowed to vary as RAL perfusion changed. The remainder of the lung, which served as control (CL) inspired air. Fraction of the total pulmonary blood flow going to the RAL (%Q̇ral) was ontained by comparing the methane elimination from the RAL to that of the whole lung, and expressed as a percentage of that fraction at $Pet_{co_{2}} = 40, Pet_{o_{2}} = 100$ . Cardiac output, pulmonary vascular pressures, and CL gas tensions were unaffected or only mimimally affected by changes in RAL gas composition. A drop in P_o₂ from 100 to 50 Torr decreased local blood flow by 60% in normocapnia and by 66% at a P_co₂ of 60. At all levels of oxygenation, an increase in P_co₂ from 40 to 60 reduced Q̇ral by nearly 50%. With these stimulus-response data, we developed a model of gas exchange, which takes into account the effects of test segment size on blood flow diversion. This model predicts that: (1) when the ventilation to one compartment of a two compartment lung is progressively decreased, Pa_o₂ remains above 60 Torr for up to 60% reductions in alveolar ventilation, irrespective of compartment size; (2) the decrease in Pa_o₂ that occurs at altitude is accompanied by a drop in Pa_co₂ that limits the decrease in conductance and minimizes the pulmonary hypertension; and (3) as we stand, local blood flow control by the alveolar gas tensions halves the alveolar arterial P_o₂ and P_co₂ differences imposed by gravity.
Pulmonary hypoxic vasoconstriction: How strong? how fast?
1992, Respiration Physiology
We have developed a minimally invasive technique for studying regional blood flow in conscious sheep, bypassing the complications of open-chest surgery, flow probes and tracer infusion. We quantitate regional perfusion continuously on the basis of regional clearance of methane (methane is produced in the sheep rumen, enters the circulation and is eliminated nearly completely (>95%) in the lung). Tracheal intubation with a dual-lumen catheter isolates the gas exchange of the right apical lobe (RAL; <15% of the lung) from that of the remainder of the lung, which serves as a control (CL). We measure RAL and CL methane elimination by entraining expirates in constant flows, sampled continuously for methane. Results obtained with this technique and from regional oxygen uptake are in excellent agreement. We have found that hypoxic vasoconstriction is far more potent and stable during eucapnic hypoxia than during hypocapnic hypoxia. The time course of the vasoconstriction suggests that many of the data in the literature may have been obtained prior to steady state.
Quantitative significance of hypoxic vasoconstriction in the ferret lung
1981, Respiration Physiology
Stimulus-response curves for the pulmonary vascular bed to alveolar hypoxia have been measured in ferrets under conditions of perfusion either at constant pressure or at constant flow in vivo or in isolated lungs. In all circumstances the relationship between alveolar oxygen tension and the fall in blood flow or rise in pulmonary artery pressure was sigmoid although there were important differences between the in vivo and in vitro preparations. The significance of these observations in constant pressure and constant flow preparations in relation to pulmonary hypertension and ventilation/perfusion regulation is discussed.
Pulmonary hemodynamics responses to hypoxia and/or CO<inf>2</inf> inhalation during moderate exercise in humans
2018, Pflugers Archiv European Journal of Physiology
Hypoxic pulmonary vasoconstriction
2012, Physiological Reviews
Restoration of cardiopulmonary function with 21% versus 100% oxygen after hypoxaemia in newborn pigs
2005, Archives of Disease in Childhood: Fetal and Neonatal Edition

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^☆: This work was supported by a grant from the Medical Research Council of New Zealand.

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Regional alveolar gas composition and lung function in sheep☆

Abstract

Am. J. Med.

Respir. Physiol.

Respir. Physiol.

85Kr in the study of pulmonary circulation during bronchospirometry

Scand. J. Clin. Lab. Invest.

Stimulus-response curves for the pulmonary vascular bed to hypoxia and hypercapnia

J. Physiol. (London)

Cyclic hypoxic pulmonary vasoconstriction induced by concomitant carbon dioxide changes

J. Appl. Physiol.

Regional pulmonary function by lobar spirometry in unanaesthetized sheep

J. Appl. Physiol.

Ventilation-perfusion relationship and its role in alveolar gas exchange

Respiratory gases in the regulation of the pulmonary circulation

Physiol. Rev.

Hypoxia on the pulmonary circulation. How and where it acts

Circ. Res.

⁸⁵Kr in the study of pulmonary circulation during bronchospirometry