448 ISSN 1054-660X, Laser Physics, 2007, Vol. 17, No. 4, pp. 448–452. © MAIK “Nauka / Interperiodica” (Russia), 2007. Original Text © Astro, Ltd., 2007. 1. INTRODUCTION Recreational scuba diving exposes individuals to environmental stresses not often encountered in other types of activity. These stresses include increased ambi- ent pressure, raised partial pressure of oxygen, increased resistance to movement, added weight and drag of diving equipment, cold stress, and a higher breathing resistance. In different physiological or pathological stress conditions, a higher quantity of free radicals is generated in our body, also inducing the lipid peroxidation (LP) [1]. The LP process consists in the degradation of cellular membrane phospholipids and leads to the release of low-weight hydrocarbons such as ethane, pentane, and ethylene. We followed up the evo- lution of the ethylene (ET) release by using a laser- based spectroscopic system. Part of the ET produced as a consequence of the LP processes and transported to the lungs by the sanguine flux is eliminated with the breath in very low concentrations (ppb). Adopting a sufficiently sensitive method for measuring ethylene, it is possible to determine the extension of the oxidative stress in a very simple and rapid way by means of a breath test (BT). With this aim, an experiment for detecting any small variation of ET concentration in the breath exhaled by scuba divers during a prolonged record immersion was conducted at the Molecular Spec- troscopy Laboratory in the ENEA Research Centre. The present paper reports a study regarding effects that a prolonged immersion may induce in a human body, performed in the framework of the Abissi 2005 Project. The immersion lasted 10 days at a depth of 6– 8 m (Guinness record established in September 2005 by two Italian divers in the Ponza Sea). The stress condi- tion of the two divers was evaluated by mean of a com- plete set of clinical tests (blood analysis for stress hor- mones monitoring) and psychometric tests performed at Catholic University in Rome, as well as the above- mentioned BT for the physiological stress assessment. The results for each test will be reported and discussed. 2. LASER PHOTOACOUSTIC SPECTROSCOPY Various spectroscopic methods, in particular, back- ground-free techniques, for example Faraday laser magnetic resonance spectroscopy or photoacoustic spectroscopy, can be applied for detecting a wide range of gaseous substances. Infrared absorption spectros- copy is a universal method to achieve the spectral sig- nature of molecules with high resolution and high sen- sitivity [2]. In the last years a higher attention and inter- est were given to the photoacoustic spectroscopy because this is a method that may insure a higher sensi- bility with respect to the conventional spectroscopic techniques. All the spectroscopic methods give qualita- tive and quantitative information by measuring the light absorption in a substance directly or through a side effect. The photoacoustic spectroscopy (PAS) in which we are interested is based on the photoacoustic (PA) effect. The photoacoustic effect, discovered by Alexander Graham Bell, consists in the generation of transient acoustic waves in a gas sample irradiated by light chopped at an audio frequency. In other words, this pro- duces a sound which is detectable by a sensitive micro- phone. The intensity of the sound is proportional to the number of absorbing molecules present in the sample. Consequently, the concentration of the species to be detected can be easily analyzed through a measurement of the electric signal produced by the microphone. The major components of LPAS apparatus are (1) a cell Stress Monitoring in a Guinness 10-Day Scuba Dive A. Puiu a , G. Giubileo a, *, G. Addolorato c , L. Revelli b , G. Gasbarrini c , R. Bellantone b , A. D’Amore b , C. P. Lombardi b , and C. Carrozza d a ENEA, via E. Fermi 45, Frascati (Rome), Italy b Institutes of Endocrine Surgery c Internal Medicine, Catholic University of Rome, Italy d Biochemistry and Clinical Biochemistry, Catholic University of Rome, Italy *e-mail: giubileo@frascati.enea.it Received October 10, 2006 Abstract—Nowadays, there is high demand for sensitive gas sensors both for human and environmental mon- itoring. This paper deals with a high-resolution (0.2 ppb) laser-based photoacoustic spectroscopic system real- ized at ENEA Frascati, Italy, applied for monitoring stress in scuba divers during sustained immersion by ana- lyzing breath samples. Blood tests and psychometric tests for scuba divers were performed at Catholic Univer- sity in Rome. Results will be reported and discussed. PACS numbers: 87.64.Je, 87.14.Cc DOI: 10.1134/S1054660X07040226 BIOPHOTONICS