Predictions from a mathematical model of decompression compared to Doppler scores.

This paper describes an attempt to calibrate a mathematical model that predicts the extent of bubble formation in both the tissue and blood of subjects experiencing decompression from a hyperbaric exposure. The model combines an inert gas dynamics model for uptake and elimination of inert anesthetic gases with a simple model of bubble dynamics in perfused tissues. The calibration has been carried out using the model prediction for volume of free gas (bubbles) as microl/ml in central venous blood and relating this to Doppler scores recorded at the end of hyperbaric exposures.

Venous gas embolism in chamber attendants after hyperbaric exposure.

An initial occupational survey (OS) was initiated to investigate the prevalence of venous gas embolism (VGE) in chamber attendants assisting hyperbaric oxygen (HBO2) treatments. Nine female subjects were exposed for three consecutive days to the routine hospital procedure of compressed air exposure to 240 kPa for approximately 115 min with 12 min of terminal oxygen (O2) breathing. VGE was monitored with ultrasound Doppler in 15 min intervals for 2h after the first and third exposure.

Effect of oxygen tension and rate of pressure reduction during decompression on central gas bubbles.

Reduction in ascent speed and an increase in the O2 tension in the inspired air have been used to reduce the risk for decompression sickness. It has previously been reported that decompression speed and O2 partial pressure are linearly related for human decompressions from saturation hyperbaric exposures. The constant of proportionality K (K = rate/partial pressure of inspired O2) indicates the incidence of decompression sickness.

Inspiratory flow limitation in divers.

Inspiratory dyspnea becomes an important factor in reducing a diver's ability to carry out physical work at depths in excess of 300 m. It is possible that dynamic compression of the trachea occurs when the intratracheal pressure drops below environmental pressure, thereby causing transient reduction in inspiratory flow. Vocal cords form an orifice of variable diameter, and orifice flow is predicted to occur at flow rates as low as 22 liter/min when gas density is 5 kg/m3 or more.

A computer program to calculate mean skin temperature from measurements available from field trials.

Attempts to estimate mean skin temperature for subjects during prolonged experiments in field conditions are often made difficult because probes become disconnected or cease to function. There are several equations which allow estimation of mean skin temperature from a reduced number of functioning probes. The Fortran program described chooses the appropriate equation, calculates the mean skin temperature using whichever readings are available from the six selected sites and calculates mean body temperature using also rectal temperature.

An artificial circulation for the study of thrombolysis. The influence of flow rate and pressure on thrombolysis and a comparison between urokinase and tissue activator as thrombolytic agents.

The construction of an artificial circulation for the study of thrombolysis allowing variation in fluid pressure and flow rate is described. The lysis of 125I-fibrin was not influenced by variation in pressure between 10 and 30 cm H2O, but was significantly faster at a flow rate of 25 ml/min than at 40 ml/min or 10 ml/min. At equivalent concentrations as assessed on fibrin plates tissue activator induced greater thrombolysis than urokinase.

Environmental and body temperatures of 52 divers in hyperbaric heliox.

Rectal and skin temperatures were recorded over periods as long as 24 h on 52 divers at depths as great as 300 m. Chamber temperature and body temperatures are correlated with depth, and the correlation between chamber temperature and mean skin temperature is evaluated. To ensure thermal balance daytime chamber temperatures must change with depth in meters according to the relationship Tch = 28.