Lung volumes<unk>  <unk>  is the volume of air present in the lungs at the end of passive expiration. At<unk> , the opposing elastic recoil forces of the lungs and chest wall are in equilibrium and there is no exertion by the diaphragm or other respiratory muscles.<unk>  is the sum of expiratory reserve volume (ERV) and<unk>  volume (RV) and measures approximately 2500 mL in a 70 kg, average-sized male (or approximately 30ml/kg). It cannot be estimated through spirometry, since it includes the<unk>  volume. In order to measure RV precisely, one would need to perform a test such as nitrogen washout, helium dilution or body plethysmography. A lowered or elevated<unk>  is often an indication of some form of respiratory disease. For instance, in emphysema,<unk>  is increased, because the lungs are more compliant and the equilibrium between the inward recoil of the lungs and outward recoil of the chest wall is disturbed. As such, patients with emphysema often have noticeably broader chests due to the relatively unopposed outward recoil of the chest wall. Total lung capacity also increases, largely as a result of increased<unk> . In healthy humans,<unk>  changes with body posture. Obese patients will have a lower<unk>  in the supine position due to the added tissue weight opposing the outward recoil of the chest wall. Positioning plays a significant role in altering<unk> . It is highest when in an upright position and decreases as one moves from upright to supine/prone or Trendelenburg position. The greatest decrease in<unk>  occurs when going from 60° to totally supine at 0°. There is no significant change in<unk>  as position changes from 0° to Trendelenburg of up to −30°. However, beyond −30°, the drop in<unk>  is considerable. The helium dilution technique and pulmonary plethysmograph are two common ways of measuring the<unk>  of the lungs. The predicted value of<unk>  was measured for large populations and published in several references.<unk>  was found to vary by a patient's age, height, and sex.<unk>  is directly proportional to height and indirectly proportional with obesity. It is reduced in the setting of obesity primarily due to a reduction in chest wall compliance.
Functional residual capacity
Vital capacity
Lung compliance
Peak expiratory flow
Peak inspiratory pressure
Ventilatory threshold
Diffusing capacity
FEV1/FVC ratio