Biomedical subjects
E D Thalmann
Publications and source records attributed to E D Thalmann.
Development of unlimited duration excursion tables and procedures for helium-oxygen saturation diving.
Excursion ascents were performed during a series of experimental helium-oxygen saturation dives ranging between 150 and 1000 fsw to study the limits of multiple and extended duration excursions both deeper and shallower than the saturation depth. The distance a diver can safely ascend without decompression following saturation was found to be a function of depth, increasing from 75 ft at a saturation depth of 225 fsw to 180 ft at 1000 fsw. Initiation of saturation decompression immediately after an excursion was found to be safe. This information is incorporated into new U.S. Navy Unlimited Duration Excursion Tables and Procedures for Saturation Diving.
Chamber-based system for physiological monitoring of submerged exercising subjects.
A system has been designed which allows for measurement of cardiorespiratory parameters in the fully submerged subject performing graded exercise. It consists of a horizontal wet chamber; a waterproofed, electrically braked bicycle ergometer; and a low-resistance "bag-in-a-box" breathing apparatus. Chamber and breathing apparatus design allow for a great deal of flexibility in both positioning of the subject and instrumentation. The 200-liter "bag-in-a-box" configuration provides the subject with humidified gas through 2.5 in. i.d. tubing. A rolling seal spirometer provides the lung counter volume. Provision is made for breath-by-breath gas analysis with a mass spectrometer. Hydrostatic pressure on the diver's thorax relative to chamber pressure can be easily and reproducibly varied over a wide range of positive and negative static lung loads. This system has been used on over 100 man-dives to depths equivalent to 6.5 ATA with oxygen consumptions up to 4.0 liters/min.
Dyspnea in divers at 49.5 ATA: mechanical, not chemical in origin.
Pulmonary function was studied in six divers living in a hyperbaric chamber at a pressure nearly fifty times normal (49.5 atmospheres absolute (ATA), equivalent to 488 m or 1600 ft seawater (fsw)). As expected, ventilatory function was reduced. At 49.5 ATA, maximum voluntary ventilation (MVV) was 45% less than the control value. Instantaneous rates of gas flow during forced expiration were similarly reduced, especially those flow rates measured high in the lung volume. These reductions occurred despite an apparent increase in functional residual capacity (FRC) and the use of transpulmonary pressures considerably greater than those exerted during the same maneuvers at normal (sea-level) pressure. During underwater work at 49.5 ATA, the divers rapidly became exhausted at moderate levels of oxygen consumption (1.9 liters/min), showing severe dyspnea and impending syncope. These symptoms were not due to retention of carbon dioxide, nor to hemodynamic or metabolic causes. Thus, dense gas breathing, like asthma, exemplifies a state in which severe dyspnea may occur with normal or low arterial carbon dioxide and normal oxygen transport. The physiological adjustments the divers employed were similar to those seen in acute asthma, imposing an elastic load in addition to the flow-resistive work of breathing a gas mixture eight times as dense as air. Although men can do moderate work under conditions similar to those of this experiment, they will have only a limited physiological reserve available to meet the possibilities of emergencies or respiratory infections.
Intentional tremor on a helium-oxygen chamber dive to 49.5 ATA.
Tremor is a well-recognized manifestation of the high pressure nervous syndrome (HPNS). As such, its measurement and analysis during deep hyperbaric exposures can be an important index of central nervous system integrity. During the U.S. Navy's experimental chamber dive to a depth equivalent to 1600 fsw (49.5 ATA), objective measures of intentional tremor were obtained at several depths. Six subjects were pressurized in 6 days to 49.5 ATA. After spending 7 days at this pressure, they were decompressed in 19 days to the surface. Measures of intentional tremor were obtained predive and at pressure levels of 13.1, 31.3, 49.5, 40.4, and 31.3 ATA using the Naval Medical Research Institute Mark 3 Mod 1 tremor device. Each subject's microtremor was measured while he produced a force of 50 grams and 500 grams against a finger force transducer. Unlike previous studies of HPNS tremor, special attention was given to amplitude rather than frequency analysis. All subjects displayed a marked increase in tremor that interfered with fine motor performance at depths greater than 1000 fsw. A statistically significant increase in signal frequency was also observed.