About the PhD thesis

Recently, there has been increased focus on the amount of oxygen administrated to critically ill patients, as too little or too much can have side effects. Gas exchange happens in the ventilated parts of the lungs. If by some means, parts of the lungs are not ventilated hypoxic pulmo-nary vasoconstriction (HPV) occurs in those regions. This response can be beneficial for the patient in certain situations, but it will often have negative effect in form of increased pulmonary vascular resistance (PVR). The regulation of PVR is assumed to take place in the pulmo-nary artery, as we know it from the systemic circulation. This is however still debated and there are references suggesting the regulation hap-pening in the pulmonary veins. Knowing the site of regulation is im-portant in order to treat the hypoxia most efficiently.

The general aim of this thesis was to elucidate which effect oxygen, in varying concentration, has on the lung physiology and lung pathophysi-ology as well as on the lung parenchyma. This was done with experi-mental studies, using pigs as models for humans.

In study 1, pigs were exposed to 100% oxygen for five hours, using apneic oxygenation technique with one uninterrupted inspiration, while CO2 was removed with an arterio-venous ECMO.
Study 2 was an essential method study in which PVR was measured using SG catheter and the results compared to measurements made with a flow probe placed around the pulmonary artery.
In study 3, PVR was measured using the flow probe around the pulmo-nary artery while using veno-venous ECMO to oxygenate and deoxy-genate the blood in the vena cava and the pulmonary artery. At the same time, the animals were ventilated with either extreme high FiO2 or extreme low FiO2.

The work of this thesis has led to improved knowledge about the mo-lecular effect of short duration of hyperoxia on the lung tissue. A new experimental set-up for intervention in oxygen supply has been intro-duced and it demonstrated that the regulation of PVR happens on the venous side of the pulmonary circulation.