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1. Using Negative Pressure Breathing to Enhance Nitrogen Elimination and its Effect on Specific Cardiovascular ParametersMelina Bowdwin*, David Pendergast, Ed.D.Center for Research and Education in Special Environments, Department of Physiology and Biophysics, University at Buffalo Results: Analysisof Variance Methods/Materials Abstract Facilitating nitrogen (N2) elimination is important to astronauts and divers in decreasing the risk for decompression sickness. Cardiac Output (CO) plays a major role in N2 elimination. Recent studies confirmed that head-down tilt and water immersion both increase CO. We hypothesized that Negative Pressure Breathing (NPB) will cause an increase in CO while sitting erect. Also, that continuous NPB (-10 or -15 cmH2O) will be more effective than intermitted NPB. A comparison between 21% oxygen in Argon (normoxic) and a 100% oxygen gas mixture was also made. Male subjects (n = 8) were tested inside of a tent that has 0% nitrogen. CO, heart rate (HR), and blood pressure (BP) were measured by a finapres device every 10 minutes over 2 hours. CO steadily increased as a function of time at -15 cmH2O breathing 100% oxygen. The increase in CO was not significantly different from the normoxic -15 cmH2O intermittent and -10 cmH2O continuous conditions. CO also increased significantly with the -15 cmH2O continuous condition. CO increased by the same amount in the -15 cmH2O intermittent, -10 and -15 cmH2O continuous conditions. Increases in CO were a result of increased stroke volume. HR was constant as a function of time, but increased significantly breathing the normoxic mixture (-10 cmH2O) and 100% oxygen (-15 cmH2O). BP did not increase in any condition. These data demonstrate that negative pressure breathing in the sitting erect position significantly increased CO, and should increase N2 elimination. Experimental Setup Data Analysis Data were analyzed by ANOVA for repeated measures, P ≤ 0.05. NPB conditions were compared to the control condition. Cardiac Output: • 100% Oxygen: NPB intermitted and continuous were shown to be statistically significantly different from the control. • Normoxic: NPB continuous was significantly different from the control, NPB intermitted was not. Stroke Volume: • NPB intermitted and continuous showed to be statistically significantly different from the control for 100% O2 and normoxic gas mixtures. Rebreathing bags Figure 2: Subject sits in N2-free tent, monitor records HR, BP and CO, subject rebreathes from collection bags.Bags are switched every 10 min. for 120 min. Figure 1: Schematic overview of the experimental setup. Conclusions • The major finding is that NPB significantly increased CO. • The increased CO was due to increased SV, as HR was unaffected. • Blood pressure was close to the control conditions; the increase in cardiac output was offset by vasodilatation of blood vessels causing lower vascular resistance. • It was reasonable to hypothesize that NPB would enhance N2 elimination, increasing the safety of astronauts and divers. Figure 3: Subject on finapres equipment Figure 5: CO, HR, and BP records on monitor Figure 4:Finometer measures CO Background Results: Cardiac Output, Heart Rate, and Stroke Volume • Facilitating nitrogen (N2) elimination is important to astronauts and divers in decreasing the risk for decompression sickness. • Cardiac output (CO = stroke volume (SV) times heart rate (HR)) plays a major role in N2 elimination. • CO can be increased by water immersion and head-down tilt of the subject. • N2 elimination has also been shown to be affected by breathing a 100% O2 or normoxic (21% O2 in argon) gas mixture. • The purpose of this study is to increase CO is through negative pressure breathing (NPB) over a range of -10 to -15 cmH2O. References 1. Balldin, U.I and C.E. Lundgren, Effects of immersion with the head above water on tissue nitrogen elimination in man.  Aerosp Med, 1972. 43(10): p. 1101-8. 2. Curry, T., Lundgren, C.E.G.  Negative pressure breathing enhances nitrogen elimination. Aviation, Space and Environmental Medicine. 74(10); 1034-1039, 2003. 3. John J. Bodkin,1, Timothy B. Curry,  Claes E. G. Lundgren. Negative pressure oxygen breathing and head-down tilt increase nitrogen elimination. Undersea and Hyperbaric Medicine, 2006; 33(6) 455-462. Figure 6: CO increased during O2 breathing by 8% in the -15 cmH2O intermitted (I) and continuous (C) as well as -10 cmH2O continuous. Figure 7: CO also increased under normoxicNPB conditions (9% in -15 intermitted and -10 continuous cmH2O, and 6% in -15 cmH2O continuous). Specific Objectives/Hypotheses Acknowledgements • NPB will increase cardiac output (CO) in the erect position. • Intermitted and continuous NPB will increase CO using both -10 and -15 cmH2O NPB. • Continuous NPB will increase CO using both -10 and -15 cmH2O NPB more than intermitted NPB. The authors wish to thank the subjects for their participation, and Michael Fletcher and Lukas Eckhardt for their technical assistance. Study was funded by a grant from the Naval Sea System Command and the Naval Experimental Diving Unit, Panama City, Florida. • Figure 8: These graphs show stroke volume as a function of the experimental conditions.The increase in stroke volume, above the control, primarily caused the increase in cardiac output.