|MadSci Network: Anatomy|
On average, how much air pressure can be generated by human lungs? Or restated, how hard can one blow?
This is a very interesting question. In considering the answer, it is best to look at the medical and physiology literature for some definitions.
In medicine, there are many pulmonary function tests. The neural output from the respiratory center located on the surface of the medulla controls alveolar ventilation. Also required is an effective musculoskeletal system generating an appropriate transpulmonary pressure. If the resultant inspiration is transmitted through structurally sound, unobstructed airways, then alveolar ventilation is proportional to the metabolic rate and respiratory quotient: VCO2/VO2 and arterial blood gas tensions are maintained within a very narrow range.
Static Lung Volumes
Forced vital capacity (FVC) is the maximum volume of air that can be forcibly expired after a full inspiration. This simple test is still one of the most valuable measurements of pulmonary function.
Functional residual capacity (FRC) is the volume of air in the lungs at the end of a normal expiration. Decreased lung elasticity will lead to increased FRC (such as with emphysema).
Dynamic Lung Volumes
FEV1 is the volume of expired air during the first second of FVC (see above) and normally comprises more than 75% of the vital capacity.
Maximal voluntary ventilation (MVV) is determined by having the patient hyperventilate maximally for 12 seconds; the amount of gas expired during that interval is expressed in L/min. The MVV generally parallels the FEV1 and can be used as a test for consistency in either test.
Maximal inspiratory and expiratory pressures reflect the strength of the respiratory muscles. They are measured by having the patient forcibly inspire from RV (residual volume) and expire from TLC (total lung capacity) through a closed mouthpiece attached to a pressure gauge. Maximal pressures are characteristically low in neuromuscular disorders (such as myasthenia gravis and Guillain Barre syndrome).
In the exercise physiology literature, there is much discussion around the effect exercise has on lung volume at the end of expiration. First, lung volume decreases with progressive exercise (in other words, the chest wall muscles are better trained to blow off more volume). The abdominal and diaphragmatic influence provides passive recoil for the ensuing inspiration. Second, tidal volume (the flow in and out) increases with exercise. Third, pleural pressure development during expiration approaches flow limit pressures near EELV (end expiratory lung volume). Fourth, on inspiration, peak pleural pressure reaches only 50% of the estimated capacity for pressure generation as determined by lung volume and flow rate for which peak pressure was obtained.
Pleural pressure is usually measured in cm of H2O and flow is L/s (liters per second). In a young subject, pleural pressure tends to peak at about 16 cm H2O and a flow of about 4+L/s. As we age, those numbers can change to about 8 cm H2O and 2 L/s.
Since there are some many factors that could influence these figures, positively or negatively, it is difficult to state that these are norms. But this indirectly and directly answers the question posed.
Roland J. Perreault, MA, PT, ATC, MTC Rebound Physical Therapy & Sports Rehabilitation Associates, P.C. 27 Depot Street Watertown, CT 06795 ReboundPT@aol.com
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