text: Obtaining measurements of various chemicals in the human body is desirable in a variety of situations. In particular, the measurement of oxygen (O2) in the body can be an important indication of whether the body is properly receiving and processing oxygen, and thus can be indicative of disease or trauma, among other things. Such information can be of use in a variety of environments, including for example in an operating room or in an ambulance, in physical-fitness or exercise environments, as well as in high-altitude environments or underwater environments (e.g., as experienced by mountain climbers, miners, and divers employing scuba gear).
  In the hospital setting, various tests exist for measuring a patient's oxygen levels. One conventional test involves measuring the oxygen saturation of hemoglobin in the patient's bloodstream by way of a pulse oxymeter. While conveniently small and portable, this device is limited insofar as the data it provides cannot be used to determine whether a patient is hyperventilating or underventilating. Additionally, this device is not particularly helpful in some situations such as high-altitude situations, because changes in oxygen levels in a person's bloodstream can vary nonlinearly in relation to oxygen levels that are occurring in the person's lungs (due to a nonlinear dissociation curve), such that measurements of the oxygen levels in the person's bloodstream may not provide a clear or accurate indication of the oxygen levels in the person's lungs.
  Pulse oxymeter tests are not the only type of test that currently exists that can be employed to determine oxygen levels in a patient. Direct measurements of oxygen gas levels and/or other gas levels deep within a person's lungs (e.g., within the alveoli of the lungs) also can be a useful measure of oxygenation of the lung and thus be useful in assessing one of the links in the chain of oxygen delivery to body tissues. However, although the usefulness of measuring gas levels deep within a person's lungs— or “alveolar gas” levels—has been recognized for decades, conventional techniques for testing such alveolar gas levels are slow in operation and difficult to use.
  In particular, conventional devices used to measure alveolar gas levels, such as those employed in some anesthetic machines, are undesirable insofar as those devices typically are large, cumbersome and not portable. Consequently, such devices are not easily employed in environments outside a given hospital operating room or pulmonary function laboratory. Further, although there do exist some conventional devices for measuring gas levels in lungs that are portable, these devices are incapable of distinguishing the alveolar gases existing deep within a patient's lungs from other “mixed gases” that emanate from the bronchial passages of the patient, as well as distinguishing the alveolar gases from the outside atmosphere.
  For example, specifically in the context of physical-fitness/exercise, a portable oxygen consumption measuring device has been developed that can be carried on a person's back, namely, the Jaeger Oxycon Mobile by VIASYS Healthcare GmbH of Hoechberg, Germany. This device is not intended to measure alveolar gas but instead is intended to measure the mixed gases emanating from the bronchial passages of the patient, which typically have significantly different levels of oxygen, carbon dioxide, and other gases than exist within the alveoli. Also for example, while breathalyzer devices have been developed for sensing alcohol on the breath of drunk drivers, these devices again are incapable of localizing alveolar gases from the mixed gases of the bronchial passages and, in any event, cannot measure alveolar oxygen and carbon dioxide gas levels.
  In view of the value of information regarding alveolar gas levels, and in view of the inadequacies of conventional techniques for determining such gas levels within the human body, it therefore would be advantageous if a new, portable/mobile (possibly hand-held) device for measuring alveolar gas levels such as oxygen and/or carbon dioxide levels (among others) could be developed. In particular, it would be advantageous if such a new, portable device could be utilized by a patient alone or with a technician/physician to quickly measure such alveolar gas levels.
  Additionally, it would be advantageous if such a new device could be easily operated such that substantially accurate data concerning the concentration(s) of alveolar gas(es) of interest could be obtained. More particularly, it would be advantageous if the data obtained using the device was substantially accurate notwithstanding the existence of mixed gases within the bronchial passages of a subject's lungs, and notwithstanding differences between the characteristics of the air of the atmosphere relative to the alveolar gases. It further would be advantageous if this new device was robust, self-contained, light in weight, and inexpensive to manufacture.