Copyright © 2005 Undersea and Hyperbaric Medical Society, Inc. UHM 2005, Vol. 32, No. 2 – Age and HBO 2 on vagal tone Effect of age and repeated hyperbaric oxygen treatments on vagal tone. V.E. LUND 1 , E. KENTALA 1 , H. SCHEININ 2 , K. LERTOLA 3 , J. KLOSSNER 1 , K. AITASALO 4 , K. SARIOLA-HEINONEN 1 , J. JALONEN 1 1 Dept. of Anesthesiology and Intensive Care, Turku University Hospital, 2 Turku PET Centre and Department of Pharmacology and Clinical Pharmacology, University of Turku, 3 Dept. of Statistics, University of Turku, 4 Dept. of Oto-Rhino-Laryngology, Turku University Hospital, Turku, Finland Lund VE, Kentala K, Scheinin H, Lertola K, Klossner J, Aitasalo K, Sariola-Heinonen K, Salonen J. Effect of age and repeated hyperbaric oxygen treatments on vagal tone. Undersea Hyperb Med 2005; 32(2):111-120. Objectives: To evaluate the influence of repeated hyperbaric oxygen (HBO 2 ) exposures and age on vagal response to hyperbaric oxygenation, and to evaluate the timing of changes in vagal activity during the treatments. Study design: Open, controlled, non-randomized study. Methods: Heart rate variability of 23 patients with chronic osteomyelitis or radionecrosis of the jaw or reconstructive surgery of the facial region was studied during repeated treatments. During each treatment, the patients were exposed to HBO 2 at 2.5 ATA and heart rate variability was measured using power spectral analysis before compression, three times at 2.5 ATA and during and after decompression. The patients were grouped according to age (Cut-off point 50 years). Statistical analysis was carried out using analysis of variance for repeated measurements. Results: Repeated exposures did not change vagal response to hyperbaric oxygenation. Vagal activity measured by HF power increased significantly in both age groups during the HBO 2 exposures but there were no significant difference between the groups in the response. However, the level of HF power was significantly higher in the subjects under 50 years old. Significant differences between consecutive measurements were related to pressure changes. Conclusions: Repeated therapeutic HBO 2 exposures are not causing permanent changes in vagal control of the heart. Vagal responsiveness to hyperbaric hyperoxia is preserved in advanced age. INTRODUCTION The reason for increased parasympathetic activity during hyperbaric exposure is increased partial pressure of oxygen (1,2). Hyperbaric oxygen (HBO 2 ) treatment decreases heart rate and increases peripheral vascular resistance with redistribution of regional blood flow to central circulation (3-5). Arterioles have been found to constrict in the environment of increased dissolved oxygen content in vitro (6). Hyperbaric oxygen has been shown to form peroxynitrite (ONOO- ) from superoxide (•O2-) and nitric oxide (NO) This reaction decreases bioavailability of NO for vasodilatation (7). However, increased endothelin-1 concentrations have been detected during hyperoxia in healthy volunteers, suggesting that endothelin- induced vasoconstriction may also be involved (8). Increased peripheral vascular resistance increases blood pressure and activates baroreflex, which could be one of the main factors that increase parasympathetic tone during single exposure to hyperbaric hyperoxia. The increase in parasympathetic tone during hyperoxia has been detected by increased high frequency power of heart rate variability (HRV) (1,2). In hyperbaric medicine, HBO 2 treatments are usually given in series, depending on the indication. Repeated hyperbaric exposures have been found to decrease lung function in man (9,10) 111