Observe the movement of your stomach …

Normal ventilation is an automatic, seemingly effortless inspiratory expansion and expiratory contraction of the chest cage. This act of normal breathing has a relatively constant rate and inspiratory volume that together constitute normal respiratory rhythm. The accessory muscles of inspiration (sternocleidomastoid and scalenes) and expiration (abdominal) are not normally used in the resting state. Abnormalities may occur in rate, rhythm, and in the effort of breathing.

Technique

The establishment of the tidal volume and pattern of respiration in normal individuals is a complicated process. Recognizing alterations in these factors is an important early clue of disease recognition. While frequently it is nonspecific, in many instances it can lead directly to a diagnosis. Careful observation of the respiratory rate and pattern is a crucial part of the physical examination.

Simple inspection of the respiratory cycle, observing rate, rhythm, inspiratory volume, and effort of breathing, is all that is necessary. The rate is noted by observing the frequency of the inspiratory phase, since this phase is active and easy to count. Record the number of breaths per minute; this is the respiratory rate. While observing the rate, note the inspiratory expansion of the chest cage. This expansion should be the same during each cycle.

Normally, the accessory muscles of inspiration and expiration are not used. Their use should be observed and, if found, recorded as "use of accessory muscles on inspiration" and "expiration is active with abdominal muscle contraction."

Basic Science

The respiratory system's major functions are to provide an adequate oxygen (O₂) supply to meet the energy production requirements of the body and maintain a suitable acid-base status by removing carbon dioxide (CO₂) from the body. This is accomplished by moving varying volumes of air into and out of the lungs. Ventilation, the process of air movement into the lungs, is a carefully controlled modality with a wide range of response that enables the markers of gas exchange adequacy (Pao2, Paco2, and pH) to be kept within a relatively small physiologic range.