In animals with lungs, physiological respiration involves respiratory cycles of inhaled and exhaled breaths. Tidal volume is the amount of air inhaled or exhaled normally at rest. Pentane is a component of exhaled breath for some individuals. NO was first detected in exhaled breath samples in 1991. Inflammation in the lungs can be estimated by the level of exhaled nitric oxide. Cardiopulmonary exercise testing involves measurement of exhaled oxygen and carbon dioxide during exercise. The maximum volume of breath that can be exhaled is called the vital capacity. EBC has potential uses in combination with exhaled breath analysis. Sidestream tobacco smoke, or exhaled mainstream smoke, is particularly harmful. VC is the maximum amount of air that can be exhaled after a maximum inhalation. They are generally produced by the modification of an airstream exhaled from the lungs. The ratio is determined by comparing exhaled gases to room air. The material used in the rebreather to remove exhaled carbon dioxide was sodium hydroxide. Capnometry, which provides exhaled CO levels, may help guide breathing. To estimate energy expenditure from the exhaled gases, several algorithms were developed.