The effect of hyperbaric oxygen breathing on the visual field in glaucoma.

Following the hypothesis that chronic ischemia is the main cause of functional deficiency in glaucoma, a double blind clinical experiment was carried out to study the effect of hyperbaric oxygenation in 51 glaucoma subjects, of which 31 were in the experimental group and 20 in the control group. In the experimental group there was a significant improvement of visual fields (p < 0.05), whereas there was no change in the subjects in the control group. Hyperbaric oxygen did not have any influence on intraocular pressure. The achieved visual field improvements remained stable for 3 months (p < 0.05), except for I3 and I4 isopters of the left eye and I4 isopter of the right eye, while they were considerably reduced after 6 months (p > 0.05).

Effect of a single air dive on pulmonary diffusing capacity in professional divers.

The aim of this study was to determine whether venous gas embolism after a single air dive, evaluated using precordial Doppler monitoring, was associated with alterations in spirometry, lung volumes, arterial blood gases, or pulmonary diffusing capacity for carbon monoxide (DLCO). Postdive time course monitoring of pulmonary function was undertaken in 10 professional divers exposed to absolute air pressure of 5.5 bar for 25 min in a dry walk-in chamber. The US Navy decompression table was followed. Venous bubbles were detected by precordial Doppler monitoring. Two types of decompression were used: air and 100% O2 applied for 21 min during decompression stops. Spirometry, flow-volume, and body plethysmography parameters were unchanged after the dive with air decompression (AD) as well as with O2 decompression (OD). A significant reduction in arterial PO2, on average 20 Torr, was found after the dive with AD. DLCO was decreased in all divers 20, 40, 60, and 80 min after diving with AD (P < 0.001), whereas it was not significantly decreased after diving with OD. Maximal DLCO decrease of approximately 15% occurred 20 min postdive. In AD diving, maximum bubble grade for each individual vs. maximum DLCO reduction correlated significantly (r = 0.85, P = 0.002), as well as DLCO vs. arterial PO2 (r = 0.64, P = 0.017). In conclusion, a reduction in pulmonary diffusing capacity is observed in parallel with the appearance of venous bubbles detected by precordial Doppler. We suggest that bubbles cause pulmonary microembolization, triggering a complex sequence of events that remains to be resolved. Measuring DLCO complements Doppler bubble detection in postdiving assessment of pulmonary function.

Suppression of rat tumor colonies in the lung by oxygen at high pressure is a local effect.

The effect of hyperbaric oxygen (HBO) on the growth of anaplastic carcinoma colonies in rat lungs after intravenous tumor cell injection was studied. From the first day after tumor cell injection, the rats were exposed to HBO for 16-21 days, 90 min per day. Oxygen at a pressure of 300 kPa (3.0 ATA) significantly decreased the number of lung tumor colonies and increased the survival of tumor-bearing rats, whereas the application of oxygen at a pressure of 100 kPa had no effect. An oxygen-nitrogen normoxic mixture balanced with nitrogen to 300 kPa (3.0 ATA) did not affect the number of colonies, suggesting that the effect was specific for oxygen and not for the increased pressure itself. A 6-day application of oxygen at a 300 kPa pressure suppressed the growth of lung tumor colonies when applied on days 1-6 and 7-12 after intravenous tumor cell injection, but had no effect when applied on days 13-18. In contrast to dramatic effects of HBO on the development of artificial lung metastases, the oxygen at the same 300 kPa pressure had no effect on the growth of tumor cells injected in the hind foot. Thus it appears that the suppression of lung tumor colonies by HBO was due to local oxygen effects in the lungs.