Bronchial response to breathing dry gas at 3.7 MPa ambient pressure

Saturation diving; physiology and pathophysiology

In saturation diving, divers stay under pressure until most of their tissues are saturated with breathing gas. Divers spend a long time in isolation exposed to increased partial pressure of oxygen, potentially toxic gases, bacteria, and bubble formation during decompression combined with shift work and long periods of relative inactivity. Hyperoxia may lead to the production of reactive oxygen species (ROS) that interact with cell structures, causing damage to proteins, lipids, and nucleic acid. Vascular gas-bubble formation and hyperoxia may lead to dysfunction of the endothelium. The antioxidant status of the diver is an important mechanism in the protection against injury and is influenced both by diet and genetic factors. The factors mentioned above may lead to production of heat shock proteins (HSP) that also may have a negative effect on endothelial function. On the other hand, there is a great deal of evidence that HSPs may also have a "conditioning" effect, thus protecting against injury. As people age, their ability to produce antioxidants decreases. We do not currently know the capacity for antioxidant defense, but it is reasonable to assume that it has a limit. Many studies have linked ROS to disease states such as cancer, insulin resistance, diabetes mellitus, cardiovascular diseases, and atherosclerosis as well as to old age. However, ROS are also involved in a number of protective mechanisms, for instance immune defense, antibacterial action, vascular tone, and signal transduction. Low-grade oxidative stress can increase antioxidant production. While under pressure, divers change depth frequently. After such changes and at the end of the dive, divers must follow procedures to decompress safely. Decompression sickness (DCS) used to be one of the major causes of injury in saturation diving. Improved decompression procedures have significantly reduced the number of reported incidents; however, data indicate considerable underreporting of injuries. Furthermore, divers who are required to return to the surface quickly are under higher risk of serious injury as no adequate decompression procedures for such situations are available. Decompression also leads to the production of endothelial microparticles that may reduce endothelial function. As good endothelial function is a documented indicator of health that can be influenced by regular exercise, regular physical exercise is recommended for saturation divers. Nowadays, saturation diving is a reasonably safe and well controlled method for working under water. Until now, no long-term impact on health due to diving has been documented. However, we still have limited knowledge about the pathophysiologic mechanisms involved. In particular we know little about the effect of long exposure to hyperoxia and microparticles on the endothelium.

Ultrasonic evidence of acute interstitial lung edema after SCUBA diving is resolved within 2-3h

Recently, an increase in extravascular lung water (EVLW) accumulation with diminished left ventricular contractility within 60 min after SCUBA diving was reported. We have observed previously that diving was associated with reduced diffusing lung capacity for carbon monoxide (DLCO) and arterial oxygen pressure for up to 60-80 min postdive. Here we investigated whether increased EVLW persists 2-3h after successive deep dives in a group of seven male divers. The echocardiographic indices of pulmonary water accumulation (ultrasound lung comets (ULC)) and left ventricular function, respiratory functional measurements and arterial oxygen saturation (SaO(2)) were assessed 2-3h post diving, while venous gas bubbles (VGB) and the blood levels of NT-proBNP and proANP were analyzed 40 min after surfacing. Spirometry values, flow-volume, DLCO, SaO(2) and ULC were unchanged after each dive, except for significant increase in ULC after the second dive. Left ventricular function was reduced, while NT-proBNP and proANP levels were significantly elevated after majority of dives, suggesting a cardiac strain.

Breathing at Depth: Physiologic and Clinical Aspects of Diving while Breathing Compressed Gas

When diving, human beings are exposed to hazards that are unique to the hyperbaric underwater environment and the physical behavior of gases at higher ambient pressure. Hypercapnia, hyperoxia, carbon monoxide intoxication, inert gas (predominantly nitrogen) narcosis, and decompression illness all may lead to impaired consciousness, with a high risk of drowning in this non-respirable environment. Proper physiologic function and adaptation of the respiratory system are of the utmost importance to minimize the risks associated with compressed gas diving. This article provides an introduction to the diving techniques, the physics, and the pertinent human physiology and pathophysiology associated with this extreme environment. The causes of the major medical problems encountered in diving are described, with an emphasis on the underlying respiratory physiology.

Effects on pulmonary function of daily exposure to dry or humidified hyperbaric oxygen

The purpose of this study was to examine the effects of breathing dry or humidified hyperbaric oxygen on pulmonary function. Pulmonary function tests were performed before and after each of 10 hyperbaric oxygen exposures at 2.5 atmospheres absolute (ATA) for 95 min in a group of 13 patients treated daily by hyperbaric oxygen for problem wounds. Patients breathed dry oxygen during five successive sessions and humidified oxygen during the remaining five. No differences were found between forced vital capacities (FVC) and maximal expiratory flows before and after hyperbaric oxygen exposure while breathing dry or humidified oxygen. Significant differences were found for the changes in the percentage of FVC expired in 1 s (FEV1%) and mean forced mid-expiratory flow rate during the middle half of the FVC (FEF25-75%) on day 1 alone: decrements of 1.42 and 2.96%, respectively, under dry oxygen, vs. increments of 3.93 and 34.4%, respectively, for humidified oxygen. Day-to-day decrements in the percent changes in FEV1% and FEF25-75% were observed while breathing humidified hyperbaric oxygen. These results demonstrate that repeated daily exposure to humidified hyperbaric oxygen abolishes the initial beneficial effect of humidification on peripheral airways flow characteristics.