The research is focused on integrative physiological responses to hypoxia, exercise, training, and environmental challenges such as immersion and cold exposure. Of particular interest has been to study aspects related to the cardiovascular and respiratory responses to apnea. Voluntary apnea is a prerequisite for performing breath-hold diving, which is both a sport and a means for collecting food for many populations around the globe. Involuntary apnea occurs with drowning or choking, but also in conditions such as sleep apnea and sudden infant death syndrome. We also study the spleen in relation to its function as a dynamic blood reservoir and the spleen's potential importance in blood pressure regulation. With a frequent use of breath-hold divers as volunteer subjects came an interest in understanding the techniques these divers use to enhance their performances, and the risks that may be associated with breath-hold diving, risks related to pulmonary, cardiac muscle, and brain damage.