the terminus (end) of the bronchial tree where primary gas exchange occurs in the lung.


main branches of airways connecting the trachea to the bronchioles in the lung.


airways connecting the bronchi to the alveoli.

Dry powder inhaler (DPI)

a device used to deliver medication to the lungs using a dry powder without an aerosol propellant.


a component of red blood cells that transports oxygen from lungs to cells and tissues throughout the body.


a portion of the respiratory tract connecting the pharynx to the trachea. It contains the vocal cords, which vibrate and allow a person to vocalize. The larynx is also referred to as the voice box.


the two organs (left and right) located in the chest that take in oxygen from the air by inhalation and distribute it to the bloodstream for use by the body, while removing carbon dioxide waste from the body by exhalation.

Metered dose inhaler (MDI)

a device used to deliver medication to the lungs using an aerosol propellant.


a device used to deliver medication to the lungs using a fine mist that requires a compressor (mechanical device) and nebulizer cup.


the portion of the respiratory tract connecting the larynx and trachea. The pharynx is also referred to as the throat and is part of both the respiratory and gastrointestinal tracts.


a tube-like device that connects to the mouthpiece of an MDI allowing more medication to reach the lungs.


a breathing test used to diagnose and monitor lung disease. It measures pulmonary function, with results reported as pulmonary function tests (PFTs).

Thoracic diaphragm

the primary muscle involved in respiration. It sits below the base of the lungs and separates the chest from the abdomen.


the portion of the respiratory tract connecting the larynx to the bronchi. The trachea is also referred to as the windpipe.


After completing this chapter, you should be able to

  1. Identify components of the upper and lower respiratory systems.

  2. Recall the basic physiology of the respiratory system.

  3. Describe the process of respiratory gas exchange between oxygen and carbon dioxide and explain its importance.

  4. Recognize the different pulmonary function tests used to evaluate respiratory function.

  5. Describe the proper technique for administration of medications via respiratory routes.

Oxygen is essential to sustain life; it is needed by all cells throughout the body to perform normal metabolic functions. Carbon dioxide is a waste byproduct of cellular metabolism and must be removed from the body. The primary function of the respiratory system is breathing—the inhalation of oxygen and the exhalation of carbon dioxide, with an exchange of gases (oxygen and carbon dioxide) between the air and blood. Oxygen is transported into the lungs through passageways via inhaled air and, once in the lungs, passively diffuses (moves) into the blood. Once in the blood, it is transported to cells and tissues throughout the body. Carbon dioxide is then released from those cells, where it moves into the blood to be carried to the lungs where it is exhaled. This process is dependent upon the epithelial cells that line the respiratory system; these cells are thin and moist to enable gas exchange between the blood and the air in the lungs.

The respiration process involves the entire respiratory system, including the upper and lower respiratory tracts. These tracts are essentially a network of tubes and passageways that allow air to travel to the lungs. The passageways are lined with the mucus-secreting goblet cells and hair-like cilia that protect the respiratory system from any foreign bodies. The mucus traps foreign bodies, which in turn allows the cilia to sweep the foreign body up out of the respiratory system to be expelled.

Respiratory Anatomy and Physiology

Upper Respiratory System

The primary function of the upper respiratory system is to deliver air through passageways to the lungs. The upper respiratory system involves primarily the head and neck region, including the nose, pharynx, and larynx (Figure 18-1).

FIGURE 18-1.
FIGURE 18-1.

Anatomy of the respiratory system.

Air is inhaled through the nose, where it is warmed and moistened within the nasal cavity. The nose also functions as a filter to remove dust particles from the air to protect the lungs from foreign bodies. The nasal cavity empties into the pharynx, the passageway that connects the nose and mouth, commonly referred to as the throat. The pharynx is a component of both the respiratory and digestive systems as it delivers both air to the lungs and food to the stomach. It has three distinct regions: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is the uppermost portion (encompassing the upper part of the throat) that is connected to the nasal cavity. The oropharynx is the portion of the pharynx directly below that extends between the soft palate and base of the tongue; it contains the tonsils. The oral cavity empties into the oropharynx. The laryngopharynx lies directly below the oropharynx; it connects to both the larynx (respiratory system) and the esophagus (digestive system), and carries both air and food. The epiglottis is a small piece of cartilage that acts as a tiny “lid” to cover the larynx when food and drink are being swallowed, directing them to the esophagus. In the absence of solids and liquids, it remains open, allowing air to be delivered to the larynx. The larynx (also called the voice box) is located directly below the laryngopharynx and leads into the trachea of the lower respiratory system.

Lower Respiratory System

The lower respiratory system encompasses primarily the chest area of the body and includes the trachea, lungs, and thoracic diaphragm. The primary function of the lower respiratory system is the absorption of oxygen and removal of carbon dioxide from the body. The trachea (commonly referred to as the windpipe) is the final passageway leading to the lungs. It is a flexible tube that is approximately 1 inch in diameter that branches into the left and right primary bronchi that enter the left and right lung, respectively. The bronchi are slightly smaller than the trachea, and they continue to branch into smaller and smaller passageways called the secondary bronchi and the bronchioles (see Figure 18-1).

Thoracic Diaphragm

The thoracic diaphragm is the primary muscle involved in respiration. It is a thin, dome-shaped muscle that extends across the body just below the lungs, separating the chest and abdominal cavities; it contracts during inhalation and relaxes during exhalation. As the diaphragm contracts and flattens it allows more room for the lungs to fully expand, causing a negative lung pressure and subsequent suction that further draws air into the lungs. Exhalation occurs due to the relaxation of the diaphragm combined with elastic recoil of the lungs. This process causes the lungs to decrease back to their original size and increases lung pressure to help draw air out of the lungs.

Bronchial Tree

The trachea branches off into two separate passageways called the primary left and right bronchi at a point called the carina. The carina is the ridge of cartilage between the two bronchi and contains sensitive nerves. When triggered by a foreign body, it produces a strong coughing reflex that helps to expel the material before it can enter the lungs. The primary left bronchus enters the left lung and supplies it with air, while the primary right bronchus enters the right lung and supplies it with air. The primary right bronchus has a slightly larger diameter, when compared to the primary left bronchus, and enters the lung at a slightly more vertical position. The increased diameter and position of the primary right bronchus make it more accessible to foreign bodies, and, thus, more susceptible to infections. The primary left and right bronchi (plural form of bronchus) continue to branch progressively into smaller bronchi (known as the secondary and tertiary bronchi) and finally to the smallest tubes, the terminal bronchioles. The branching of the bronchus is commonly referred to as the bronchial tree, because the structure resembles the branching of a tree. The bronchioles are the smallest passageways within the respiratory system. The terminal bronchioles deliver air to the alveolar ducts, which lead to the alveoli.

The alveoli are the primary site of gas exchange within the lungs. Alveoli are small, sac-like structures located at the end of the bronchial trees, further giving the appearance of a tree. The alveoli resemble a bunch of grapes in appearance. Their structure and shape dramatically increase the available surface area in the lungs, resulting in increased gas exchange to oxygenate the body. The alveoli have very thin walls and are connected to an intricate system of blood vessels that allow oxygen to enter the blood stream and carbon dioxide to leave.


The lungs are located inside the thoracic cavity, above the diaphragm and within the protective barrier of the rib cage. Each lung is contained within a separate membranous sac known as a pleural cavity and are separated by the mediastinum. Each pleural cavity is lined with a double layer of a single cell membrane called the pleura. The pleural membranes secrete a small amount of pleural fluid that fills the gap between the two membranes, providing a moist, slippery environment, which allows the two layers to slide against one another during breathing. The pleural space has a slightly decreased air pressure, creating a mild suction that prevents the lungs from collapsing. The lungs are divided into lobes. The right lung has three lobes: upper, middle, and lower; while the left lung only has two lobes: upper and lower.


There are two types of respiration: internal and external. Internal respiration occurs within cells when oxygen is utilized to make energy and the waste byproduct, carbon dioxide, is formed. Carbon dioxide is then released from cells into the bloodstream to return to the lungs for removal from the body. External respiration occurs when carbon dioxide is exchanged for oxygen in the lungs. The cycle is continuous; oxygen is distributed throughout the body to be utilized for cellular metabolism and the carbon dioxide is then removed from the body.

Measures of Pulmonary Function

Pulmonary function tests (PFTs) or lung function tests are used to assess how efficiently the lungs are able to exchange oxygen and carbon dioxide to oxygenate the body. The term “pulmonary function test” refers to several different assessments that attempt to evaluate lung function. PFTs include blood gas measurements, oxygen saturation, and spirometry. The normal values for PFTs vary among patients as they are based on factors such as height, weight, sex, and ethnicity. It is important to establish baseline PFTs (levels taken at the start of therapy) for each patient. In common respiratory disorders, PFTs are often done at specified intervals to monitor for any changes in their baseline levels indicating a change in lung function. PFTs are used to identify or diagnose a decline in lung function, but they are also used to help classify the type of lung function decline, assess effectiveness of lung treatments, and monitor for adverse lung side effects.1 PFTs provide information on airflow limitations, lung volumes, and gas exchange.

Arterial blood gas measurements (ABGs) determine how well the body is able to exchange gas based on evaluation of the amount of oxygen and carbon dioxide that is in the blood. Oxygen (PaO2) and carbon dioxide (PaCO2) are reported as partial pressures in mm Hg (the same unit of measurement used for blood pressure). If the lungs are working at a normal capacity, it is expected that the arterial oxygen level would be much higher than the carbon dioxide as the arterial system should be primarily carrying oxygen to the body.

Because the lungs, along with the kidneys, function to regulate the body’s acid-base balance (see Chapter 13), changes in blood pH may also indicate respiratory issues. A lower than normal pH (< 7.4), caused by an inability to exhale carbon dioxide efficiently, is termed respiratory acidosis.

Oxygen saturation (O2 sat) is not only a measurement of how much oxygen is in the blood, but also considers the hemoglobin capacity to carry the oxygen. It is expressed as a ratio of the oxygen that is actually bound to hemoglobin versus the amount of oxygen that could be bound to hemoglobin at a specified pressure (to distinguish the difference between respiratory issues and anemia).

Spirometry is a noninvasive examination and only requires the patient to breath in and out through a mouthpiece that is attached to a spirometer. A spirometer is an instrument that measures the amount of air that the patient breathes in and out at specific intervals. The validity of the spirometry results are directly dependent on patient cooperation during the testing process, correct equipment calibration, and experienced test administrators. For spirometry measurements and their definitions, see Table 18-1.

TABLE 18-1.

Spirometry Measurementa

Spirometry Value

What Is Measured


Tidal volume

Volume of air inhaled and exhaled during normal breathing

Vital capacity

Maximum volume of air exhaled after maximum inhalation

Residual volume

Amount of residual air in lungs after maximum exhalation

Total lung capacity (TLC)

Vital capacity plus residual volume

Forced vital capacity (FVC)

Amount of air exhaled with force after maximum inhalation

Forced expiratory volume (FEV)

Maximum amount of air exhaled forcefully after maximum inhalation in one breath

This is often measured at second intervals: FEV1, FEV2, FEV3

FEV1/FVC is calculated and determines the ability to move air through the lungs


Normal values vary depending on factors such as height, weight, gender, age, and ethnicity.

Inhalation as a Route of Administration

Inhalation is the preferred method of medication administration for the treatment of most pulmonary conditions. The major benefit of treating pulmonary conditions with an inhaled medication is that the medication is rapidly deposited and absorbed for action directly where it is needed, providing faster symptom relief. The specificity of inhaled medication for the lungs also decreases the likelihood of systemic (body-wide) adverse effects. Inhaled medications must have a particle size small enough to enter the lungs, and the exact particle size of the medication largely determines where in the bronchial tree the medication will be absorbed; the smaller the particle size, the farther down the bronchial tree the medication will reach. There are several types of devices used to administer inhaled medications, including the metered-dose inhaler (MDI), dry powder inhaler (DPI), and nebulizer.


Patients should be instructed to clean the spacer once a week in warm water, with one drop of liquid dish soap added to the sink, then rinse the mouthpiece only and allow it to air dry in a vertical position.

The MDI and DPI inhalers are effective pulmonary medication delivery devices when used properly. Each inhaler has specific instructions for use to assure that the correct amount of medication reaches the lungs. Improper inhaler technique can result in the medication either being lost in the process or swallowed (and delivered to the gastrointestinal tract instead of the respiratory system). Patients need thorough instruction on the proper use of inhalers and should be periodically asked to demonstrate to a healthcare professional how they are using their inhalers, to ensure that an improper technique is quickly corrected. Patients using inhalers should be directed to report any symptoms of mouth or throat soreness or hoarseness as this can be a sign of improper technique. Patients should wash their hands prior to using any inhaled delivery device.

To achieve the greatest benefit from MDI inhalers, patients must coordinate inhaler release with their inhaled breath. This can be a particularly difficult task for pediatric and elderly patients; however, most people can benefit from using a spacer. A spacer is a tube-like device that can be attached to the mouthpiece of an MDI to help ensure that the medication is adequately inhaled into the lungs. It includes a new mouthpiece for the patient and can help to ensure inhalation of the medication for absorption into the lungs rather than swallowing it and having it absorbed through the gut. The spacer provides a holding chamber for the medication, allowing the patient additional time to fully inhale the medication. When a spacer is attached, the MDI should still be used exactly as discussed below, including the priming instructions.

The MDIs contain a propellant that helps expel the medication when the canister is depressed. It is important that the patient knows to remove the cap from the inhaler and then shake it prior to each dose. The inhaler should be primed by pressing the canister, wasting one puff prior to the first use of a new inhaler or when the inhaler has not been used recently. (Each inhaler package includes specific instructions for priming.) The inhaler should be held in an upright position while the patient either places the inhaler directly in or 1–2 inches in front of the mouth. The patient should be instructed to exhale completely, then the canister should be pressed at the same time that the patient starts to breathe in slowly and deeply through the mouth. The patient should continue to breathe in slowly for 3–5 seconds and then to hold the breath for 10 seconds or for as long as comfortably possible. This provides the medication time to reach the lungs. The patient should repeat puffs if directed by the physician, but should wait approximately 30 seconds between puffs to ensure optimal absorption of the second puff.


It is important that the patient understands that the canister should be pressed only once for each puff.

It may be difficult for pediatric or elderly patients using an MDI to get the proper dosage of medication as it requires the patient to coordinate breathing with the release of medication. All patients using an inhaled corticosteroid should be reminded to rinse their mouths after each use to prevent irritation or possible infection. The MDI must be cleaned once a week by removing the canister and rinsing the plastic container with warm water and allowing it to air dry.


Many MDIs and DPIs are packaged in a sealed pouch, and the expiration dating on the package refers to the product in the unopened pouch. Once the seal is broken and the inhaler removed, the medication may be stable for a much shorter time. Most DPIs, for instance, have instructions to discard them 30 days after the pouch is opened; MDIs in pouches are generally said to be good for 12 months. Technicians should call patients’ attention to the manufacturers’ instructions to reduce the danger of using subpotent expired inhalers.


Inhalation instructions may vary among MDI brands and should be consulted for the recommended use of that particular product.

The DPIs differ from MDIs because they do not contain a propellant. These inhalers must be activated by either opening the mouthpiece or inserting a power capsule into the unit and then pulling a trigger. Each unit differs and instructions are based on the specific inhaler being used. It is important that the patient does not exhale directly into this inhaler prior to use as this could either waste the medication or decrease the dose delivered. The inhaler should be held level and to the side of the mouth while the patient exhales in preparation to use the inhaler. The DPI requires the patient to inhale quickly and deeply with force as it does not contain a propellant. For maximal benefit, the patient should hold his or her breath for 10 seconds or as long as comfortably possible.

Nebulizers, another type of delivery device, turn liquid medication into a fine mist for inhalation via a mouthpiece or mask. There are several different methods available to reduce the particle size of medications, including compressed air or oxygen, or high frequency vibration to reduce the particle size of medications. They are often used by pediatric and elderly populations as they do not require good coordination for proper medication administration the way MDIs and DPIs do. Each nebulizer unit has specific directions that should be consulted for proper use (Figure 18-2).

FIGURE 18-2.
FIGURE 18-2.

Nebulizer. A nebulizer changes liquid medicine into fine droplets (in aerosol or mist form) that are inhaled through a mouthpiece or mask. A nebulizer may be used instead of a metered dose inhaler (MDI). It is powered by a compressed air machine and plugs into an electrical outlet. Portable nebulizers, powered by an internal battery or cigarette lighter, are available for individuals requiring treatments away from home.

The basic directions for using a nebulizer include placing the device on a level surface and plugging it into an electrical outlet. Tubing is then connected to the device at the air outlet connector. The medication must be placed into the nebulizer by either measuring out the correct amount of medication or utilizing a unit dose vial. The mouthpiece and compressor tubing are then connected to the nebulizer and the compressor is turned on. The patient should be instructed to place the mouthpiece between the teeth, sealing the lips, and take deep breaths until the nebulizer sputters, indicating it is out of medication. The machine should be turned off at this point. The nebulizer tubing is washed after each use in warm soapy water, while the mouthpiece, nebulizer, and other parts should be rinsed in warm water. All parts should be allowed to air dry on a clean towel.


The respiratory system provides the essential oxygen and carbon dioxide gas exchange needed to sustain homeostasis and, ultimately, life. A respiratory system that has been damaged or does not function properly has direct adverse effects on quality of life. Once damage has occurred to the respiratory system, it is commonly irreversible, but further progression is preventable in the majority of cases. Progression can be prevented or slowed through close monitoring with the use of pulmonary function tests (PFTs): arterial blood gas measurements (ABGs), oxygen saturation (O2 sat) measurements, and spirometry. PFTs provide crucial information on progression of the disease and the effects of therapy, including identifying the need for adjustment. Education on the proper administration and storage of inhaled medications is key to successful management of respiratory conditions.


The author wishes to acknowledge and thank Christina Bell, PharmD, and Sandra B. Earle, PharmD, BCPS, authors of this chapter in the first edition of this book.


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  • 2.

    American Thoracic Society. Using your metered dose inhaler. Am J Respir Crit Care Med. 2014;190:56. Accessed April 20, 2021.

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  • Herrier RN, Apgar DA, Boyce RW, Foster SL. Asthma and chronic obstructive pulmonary disease (COPD). In: Patient Assessment in Pharmacy. New York, NY: McGraw-Hill; 2015; chapter 21. Accessed April 20, 2021.

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  • Inhalers. Accessed April 20, 2021.

  • Home Nebulizer. Accessed April 20, 2021.

  • Know How to Use Your Asthma Inhaler. Accessed May 22, 2022.

  • Teaching Kids About Spirometry. Accessed April 20, 2021.

  • Video for DPI Teaching. Accessed April 20, 2021.


  1. Identify the components of the upper and lower respiratory systems and describe the primary function of each.

  2. Describe the importance of respiratory gas exchange.

  3. Explain the process of respiratory gas exchange between oxygen and carbon dioxide.

  4. List the delivery devices available for inhaled medications.

  5. What are pulmonary function tests and why are they important?

  6. What is a spacer and who could benefit from the use of a spacer?