What happens to Human Lungsduring Breath-Hold Diving? - Abstract
The underwater environment is characterized by an increase of the hydrostatic pressure surrounding the body who is immersed. Each 10 meters under the sea-surface the hydrostatic pressure increases by one atmosphere. It turns that this increase can elicit some physiological and/or pathological response in terms of respiratory and subsequently cardiac homeostasis which needs to be known. Centralization of blood volume from periphery of the body, reduction of lung volumes, abnormal lung mechanics, gas exchange disorders, changes in pulmonary vascular resistances, ventilation and perfusion mismatch, sensory disorders and mental status are some of them. The entities of these reactions depend on the depth that is reached, the period of immersion, how diving is performed, if this is done in breath holding or whether it is performed by use of breathing gas mixtures with special apparatuses. Other contributing factors may include hemodynamic changes due to the water immersion, cold exposure, wearing weat suits, exertion with elevated cardiac output.
Objectives of this review is to outline relevant features derived from papers dealing mainly with the mechanisms responsible for the respiratory modifications during underwater apnea especially for the dramatic effects above the integrity of the alveolar capillary membrane. This effort has been donein order to stress much more the concept that a thorough evaluation of the pulmonary function is mandatory whenever subjects wish to perform the breath-holding apnea or where they have to get a recreational diving licence.
In order thus to get this purpose,most relevant publications, appeared in these last ten years on breath-hold divingactivities, have been reviewed and their results have been pointed out.
One of the main results of these works outlinesthe fact that the health of recreational divers may be endangered by high extracorporeal ambient pressures with its many cardio-pulmonary effects.During breath-holding diving apnea, the reduction of static lung volumes seems at the same time associated with a peripheral vasoconstriction (maximum in the muscle and skin organs) and derived consequent redistribution of the blood volume at the thoracic level (“blood shift”) and, in particular, from the areas of the lung bases to the middle and apical regions. The redistribution of ventilation and blood flow inside the lungs may be responsible for the significant increase observed in the diffusion of carbon monoxide along the alveolar capillary membranewithin the first two minutes from an apnea dive, followed by a progressive reduction in the following minutes lower than baseline values. The increase in the diffusion of the CO within the first minutes may suggest persistence of the “blood shift” (effect of increasing the pulmonary capillary blood volume). Another intriguing aspect of the health status during apnea is the fact that pulmonary gas exchange may be deteriorated in the course of repeated diving as result of the occurrence of interstial edema at the level of the alveolar-capillary membrane.
From these evaluations it turns out that there is a need to have a more accurate evaluation of the lung function, especially when people are going to apply for getting the licence for recreational activities related to breath-holding dive.
It could be hypothezised that the evaluation of diffusion capacity along the alveolar capillary membranemay be be added to the respiratory work-upduring the procedures to declare a person fit to breath-hold diving.