When is expiration passive

This happens due to elastic properties of the lungs, as well as the internal intercostal muscles that lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. Expiration can be either voluntary or involuntary in order to serve different purposes for the body. These two types of expiration are controlled by different centers within the body.

Voluntary expiration is actively controlled. It is generally defined by holding air in the lungs and releasing it at a fixed rate, which enables control over when and how much air to exhale. Involuntary expiration is not under conscious control, and is an important component for metabolic function. Examples include breathing during sleep or meditation. Changes in breathing patterns may also occur for metabolic reasons, such as through increased breathing rate in people with acidosis from negative feedback.

It is the process of air flowing into the lungs during inspiration inhalation and out of the lungs during expiration exhalation. Air flows because of pressure differences between the atmosphere and the gases inside the lungs. Air, like other gases, flows from a region with higher pressure to a region with lower pressure. Muscular breathing movements and recoil of elastic tissues create the changes in pressure that result in ventilation. Pulmonary ventilation involves three different pressures:.

It will be obvious when the sternomastoid and trapezius muscles are in action. Expiration passive or active Observe and feel the abdominal muscles to see whether they are contracting during expiration. If they do, the patient is using active muscle contraction to expire. Note whether he is using pursed lip breathing. Negative pleural pressure Increase in negative pleural pressure can be recognized by intercostal and supraclavicular space retractions and downward pull of the trachea during inspiration.

Number of breaths Count the number of breaths when the patient is unaware that you are counting his breaths. If the patient is conscious,he will develop tachypnoea. Don't count the respiratory rate until patient has settled down and is in his or her basal state.

Normal respiratory rate is breathes per minute. The air in the lungs now has a larger space to fill and so its pressure falls. This produces a partial vacuum, which sucks air into the lungs by bulk flow. Air continues to move into the lungs until the intrapulmonary pressure is the same as atmospheric pressure.

During forced inspiration, the accessory muscles in the neck may also be used to elevate the sternum and first two ribs Fig 1.

This, combined with the maximal contraction of the inspiratory muscles, leads to the generation of a much more negative intrapleural pressure for example, cmH2O and more rapid airflow McGeown, Normally about ml 1 pint of air is moved in and out per breath - this is known as the tidal volume.

In healthy people quiet expiration or exhalation is passive and relies on elastic recoil of the stretched lungs as the inspiratory muscles relax, rather than on muscle contraction. The diaphragm and external intercostal muscles return to their resting position and the volume of the chest cavity and of the lungs decreases. Thus, air is driven out of the lungs by bulk flow, until the atmospheric pressure and pressure within the alveoli are equal. Normally, expiration is effortless but if the respiratory passageways are narrowed by spasm of the bronchioles for example, in asthma or clogged with mucus or fluid for example, in chronic bronchitis or pneumonia , expiration becomes an active process Law and Watson, In forced expiration, when it is necessary to empty the lungs of more air than normal, the abdominal muscles contract and force the diaphragm upwards and contraction of the internal intercostal muscles actively pulls the ribs downwards.

This generates higher air pressures within the lungs and forces the air out more rapidly. Although breathing is simple mechanically, its control is complex.