PO2 Distribution in Resting Muscle and Pulmonary Gas Exchange in Patients with Cirrhosis

Heinrich, R.; Schomerus, H.; Fleckenstein, W.; Grauer, W.; Huber, Armin; Weiß, Ch.

doi:10.1007/978-3-642-71226-5_9

Cited by 1 publication

(1 citation statement)

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“…Whether the retina is similar to any other, possibly more heterogeneous, tissues is less clear. Some microelectrode studies in skeletal muscle show low P%'s (e.g., Heinrich et al, 1985). Mean P%'s in the range of 15-25 mmHg have also been found in the cerebrum of guinea pig (e.g., LUbbers, 1977) and rat (Feng et al, 1988), but only rarely in cat (Gronczewski and Leniger-Follert, 1984), where the mean is instead generally >30 mmHg (Leniger-Follert, 1985) and there are few values < 10 mmHg.…”

Section: Inner Retinal Pomentioning

confidence: 98%

Oxygen distribution and consumption in the cat retina during normoxia and hypoxemia.

Linsenmeier

Braun

1992

The Journal of General Physiology

221

226

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Oxygen tension (Po2) was measured with microelectrodes within the retina of anesthetized cats during normoxia and hypoxemia (i.e., systemic hypoxia), and photoreceptor oxygen consumption was determined by fitting Po~ measurements to a model of steady-state oxygen diffusion and consumption. Choroidal Po 2 fell linearly during hypoxemia, about 0.64 mmHg/mmHg decrease in arterial Po~ (Pao~). The choroidal circulation provided ~91% of the photoreceptors" oxygen supply under dark-adapted conditions during both normoxia and hypoxemia. In light adaptation the choroid supplied all of the oxygen during normoxia, but at Pao~'s <60 mmHg the retinal circulation supplied ~ 10% of the oxygen. In the dark-adapted retina the decrease in choroidal Po2 caused a large decrease in photoreceptor oxygen consumption, from ~ 5.1 ml OJ 100 g.min during normoxia to 2.6 ml Off 100 g'min at a P,o 2 of 50 mmHg. When the retina was adapted to a rod saturating background, normoxic oxygen consumption was ~ 33% of the darkadapted value, and hypoxemia caused almost no change in oxygen consumption. This difference in metabolic effects ofhypoxemia in light and dark explains why the standing potential of the eye and retinal extracellular potassium concentration were previously found to be more affected by hypoxemia in darkness. Frequency histograms of intraretinal Po~ were used to characterize the oxygenation of the vascularized inner half of the retina, where the oxygen distribution is heterogeneous and simple diffusion models cannot be used. Inner retinal Po~ during normoxia was relatively low: 18 -12 mmHg (mean and SD; n = 8,328 values from 36 profiles) in dark adaptation, and significantly lower, 13 -+ 6 mmHg (n --4,349 values from 19 profiles) in light adaptation. Even in the dark-adapted retina, 30% of the values were < 10 mmHg. The mean Po~ in the inner (i.e., proximal) half of the retina was well regulated during hypoxemia. In dark adaptation it was significantly reduced only at Pao2's < 45 mmHg, and it was reduced less at these P~o~'s in light adaptation.

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