ABSTRACT
The objective of the present study was to investigate the possibility of measuring lung tissue oxygen pressure (PtO2) distributions at the microvascular level, and also if a change in the lung tissue oxygenation could be detected during hypoventilation (50% reduction in ventilatory settings). Experiments were carried out on eight mechanically ventilated ketamine-anaesthetised pigs. A thoracotomy was performed through the third right intercostal space. PtO2 measurements were made using a Clark-type multiwire microelectrode placed onto the pleural surface of the middle lobe. PtO2 was measured during normoventilation, hypoventilation (3 minutes) (reduction of respiratory volume/minute and frequency by SO%), and a second period of normoventilation. Baseline PtO2 was 5.8 (range 4.4 to 10.3) kPa and decreased to 2.9 (range 1.6 to 4.2) kPa during hypoventilation, associated with some PtO2 values close to zero. The PtO2 increased to 5.4 (range 3.4 to 8.4) kPa during the second normoventilatory period, some values still close to zero. This study demonstrates that lung tissue PO, registrations can be made in a suitable animal (pig) model, and that hypoventilation induced an almost reversible decrease in lung tissue oxygen pressure distributions. In addition, no microscopically visible tissue damage was inflicted by the electrode on the underlying lung surface.
Although the lung is mostly referred to as a respiratory organ it also exhibits a variety of metabolic functions, e.g. uptake, storage and/or synthesis and metabolism of compounds as different as biogenic amines, prostaglandins and angiotensin I. In spite of this vast metabolic capacity and the respiratory role of the lung, the oxygenation of lung tissue itself has been less studied, vide infra.
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