Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location.
anatomical dead space. In pulmonary physiology, the area in the trachea, bronchi, and air passages containing air that does not reach the alveoli during inspiration and is not involved in gas exchange. This is termed dead space because the air does not reach the alveoli and is not involved in gas exchange. Normal anatomical dead space is 2.2 ml/kg or 1 ml/lb.
Dr. Stern responded: Dead space in lung. Dead space is a term used to describe an area of the lung where gas exchange cannot occur - it does not mean dead lung tissue. Everyone has dead space and it is comprised mainly of your airways. It is measured as a percentage. Dead space is affected by many variables including the size of the breath we inhale.