Hyperbaric oxygen and scopolamine.

Scopolamine (Hyoscine), an anticholinergic compound is widely used for the prophylaxis and treatment of motion sickness and might be used with oxygen diving and hyperbaric oxygen therapy. We therefore decided to test the interaction of scopolamine with oxygen at high pressure. Thirty-six rats implanted with cortical EEG electrodes were injected subcutaneously with two doses of scopolamine (0.02 or 0.2 mg.kg-1), or the vehicle (saline), 30 min before exposure to 5 atm abs (0.5 MPa) oxygen. Electroencephalogram and heart rate were monitored continuously. Spectral analysis of the EEG was carried out, and the duration of the latent period before convulsions was determined. No significant difference was found in the duration of the latent period between the control rats receiving vehicle (saline) and rats injected with scopolamine (n = 12 for each group). Changes in background EEG activity and maximal dilation of the pupil were detected at both scopolamine doses. Heart rate significantly decreased at 0.02 mg.kg-1 and increased at the dose of 0.2 mg.kg-1 scopolamine. Our findings indicate that the duration of the latent period preceding hyperoxic seizures is not altered by scopolamine in rats; however, other side effects of the drug regarding visual and cardiovascular symptoms should be considered when scopolamine is used in combination with hyperbaric oxygen.

Ventilatory and occlusion-pressure responses to hypercapnia in divers and non-divers.

Ventilatory (VE/PCO2) and occlusion-pressure (P0.1/PCO2) responses to progressive hypercapnia (rebreathing method of Read (1)) were estimated in 20 normal subjects and 22 scuba divers. Indexes of CO2 sensitivity (slopes of response curves) and absolute response values under strong CO2 drive (PCO2 = 60 mmHg) were significantly lower in the diver group. Individual CO2 sensitivity did not correlate with either diving experience or current diving activity. Positively skewed (log-normal) frequency distribution curves of individual CO2 sensitivities were drawn for the divers and for a larger sample of normal controls (using data from other studies). All divers' values fell in the lower range of non-diver control values and about one-third were below the normal range (mean +/- 2 SD) for CO2 sensitivity. We concluded that our divers did not represent a distinct population different from the normal one but rather a group of normal healthy subjects with either an inherent or acquired relatively low CO2 response. The rebreathing technique is strongly advocated as a tool for investigating divers' CO2 sensitivity and its implications in underwater environments.