Anatomy & Physiology

Anatomy & Physiology Study Guide respiratory minute volume . The respiratory rate at rest averages 12 breaths per minute, and the tidal volume at rest averages around 500 mL per breath. Only a small proportion of the air in the lungs is exchanged during a single quiet respiratory cycle; the tidal volume can be increased by inhaling more vigorously and exhaling more completely. Adult females, on average, have smaller bodies and thus smaller lung volumes than do males. As a result, there are sex-related differences in respiratory volumes and capacities. Pulmonary volumes include the following: • The resting tidal volume is the amount of air moved into or out of the lungs during a single respiratory cycle under resting conditions. The resting tidal volume averages about 500 mL in both males and females. • The expiratory reserve volume (ERV) is the amount of air that can be voluntarily expelled after a regular, quiet respiratory cycle. For example, with the maximum use of accessory muscles, males on average can expel an additional 1000 mL of air and females 700 mL. • The residual volume is the amount of air that remains in the lungs even after a maximal exhalation—typically about 1200 mL in males and 1100 mL in females. If lungs were allowed to collapse then the minimal volume (a component of the residual volume) would range from 30 to 120 mL, but unlike other volumes, it cannot be measured in a healthy person. • The fluid bond between the lungs and the chest wall prevents the recoil of the elastic fibers which is what makes the minimal volume different from the residual volume. Some air remains in the lungs, even at minimal volume, because the surfactant coating the alveolar surfaces prevents their collapse. • The inspiratory reserve volume (IRV) is the amount of air that you can take in over and above the tidal volume. On average, the lungs of males are larger than those of females, and as a result, the inspiratory reserve volume of males average 3300 mL, compared with 1900 mL in females. Calculate respiratory capacities by adding the values of various volumes. Examples include the following: • The inspiratory capacity is the amount of air that you can draw into your lungs after you have completed a quiet respiratory cycle. The sum of the tidal volume and the inspiratory reserve volume is the inspiratory capacity. • The functional residual capacity (FRC) is the amount of air remaining in your lungs after you have completed a quiet respiratory cycle. After you have completed a quiet respiratory cycle the amount of air that remains in your lungs is referred to as functional residual capacity (FRC). FRC is equal to the expiratory reserve volume plus the residual volume.

©2018

Achieve Page 305

of 368