Normal Respiratory Function and Assessment

Normal Respiratory Function and the Nursing Role

• Overview of Respiratory Function: The respiratory system is responsible for replenishing the body's oxygen ($O_2$) supply and eliminating waste in the form of carbon dioxide ($CO_2$).

• Nursing Assessment and Observations: During the assessment of respiratory function, nurses perform several critical tasks:

  • Determining the effectiveness of the patient's breathing through observation.

  • Gathering subjective information directly from the patient.

  • Auscultating (listening to) breath sounds using a stethoscope.

  • Interpreting laboratory test results.

  • Identifying risk factors that contribute to respiratory impairment.

• Nursing Responsibilities by Practice Area:

  • School Nursing: Conducting education regarding the hazards of smoking.

  • Surgical Nursing: Instructing patients on deep-breathing techniques to prevent postoperative complications.

  • Community Nursing: Screening for tuberculosis and teaching prevention strategies.

  • Critical and Long-Term Care: Managing sophisticated life-supporting ventilator systems and positioning debilitated patients to improve breathing.

Anatomy of the Respiratory System

• The Airways: Air passes through a series of tubes collectively known as the airways before reaching the site of gas exchange.

• Upper Respiratory Tract: Consists of the mouth, nose, and pharynx.

  • Nasopharynx: The structure that connects the mouth and nose, allowing air to travel into the lower portions of the pharynx.

• Lower Respiratory Tract: Located within the thoracic cavity, it includes the trachea, lobar bronchi, segmental bronchi, and the lungs.

  • Bronchial Tree: The bronchi branch into smaller bronchioles, which connect the larger conducting airways to the lung parenchyma.

• Lung Parenchyma and Alveoli: The gas-exchanging portion of the lung.

  • Alveoli: Millions of tiny, thin-walled epithelial air sacs.

  • Capillary Network: A well-developed network in contact with the alveoli where oxygen crosses the epithelium into the blood for transport to the heart and tissues.

• Muscles of Breathing: Lung movement is passive; they stretch and recoil based on muscular movement.

  • Diaphragm: The primary muscle that separates the chest from the abdominal cavity.

  • Intercostal Muscles: Muscles located between the ribs that facilitate breathing.

Physiological Processes of Ventilation

• Ventilation Defined: The physical process of moving air into and out of the lungs to facilitate gas exchange, resulting from volume and pressure changes in the chest cavity.

• Inspiration (Active Process):

  • The diaphragm and external intercostal muscles contract.

  • The thoracic volume enlarges, which decreases the intrathoracic pressure.

  • The expanding chest wall pulls the lungs outward, causing pressure within the airways to drop.

  • When airway pressure falls below atmospheric pressure, air rushes into the lungs.

• Exhalation (Passive Process):

  • The diaphragm and intercostal muscles relax.

  • The thorax returns to its smaller resting size.

  • Pressure in the chest increases, forcing air out of the lungs.

• Airway Resistance:

  • Large Airways: Held open by cartilage to ensure free air flow.

  • Bronchioles: Composed primarily of smooth muscle. Because there are millions of them, they have a large collective diameter, offering little resistance to breathing.

Mechanisms of Gas Diffusion and Transport

• Gas Diffusion: The process where molecules move from an area of higher concentration/pressure to an area of lower concentration/pressure.

• Partial Pressure Notation:

  • P: Indicates pressure.

  • A (Uppercase): Indicates the alveoli (e.g., $PAO_2$, $PACO_2$).

  • a (Lowercase): Indicates arterial blood (e.g., $PaO_2$, $PaCO_2$).

  • v (Lowercase): Indicates venous blood (e.g., $PvO_2$).

  • No Letter: If the letter is omitted (e.g., $PO_2$), the location is assumed to be arterial.

• Diffusion in the Lungs:

  • $PAO_2$ is high due to constant replenishment by breathing; $PO_2$ in pulmonary capillary blood is lower, so oxygen diffuses into the blood.

  • $CO_2$ is rich in pulmonary artery blood and low in the alveoli ($PACO_2$), so it diffuses into the alveolar space.

• Oxygen Transport:

  • 3%: Physically dissolved in the plasma.

  • 97%: Attached to hemoglobin molecules on red blood cells.

  • Hemoglobin carries oxygen in its molecular form (rather than as an ion), which is necessary for tissue metabolism.

• Carbon Dioxide Transport:

  • Transported in a dissolved state ($PaCO_2$).

  • Can combine with amino acids.

  • Bicarbonate Buffer System: The most important mechanism. $CO_2$ combines with water and dissociates into bicarbonate ions ($HCO_3^-$), playing a major role in acid-base balance.

Regulation and Control of Ventilation

• Neural Control: Regulated by specialized neurons in the brainstem called respiratory centers, which send rhythmic impulses to respiratory muscles.

• Chemoreceptors:

  • Central Receptors: Located in the medulla.

  • Peripheral Receptors: Located in the aortic arch and carotid arteries.

• Chemical Drivers of Respiration:

  • Carbon Dioxide ($PaCO_2$): The primary driver for the frequency and depth of ventilation. High $PaCO_2$ stimulates deep, rapid breathing; low $PaCO_2$ slows breathing.

  • Oxygen ($PaO_2$) and $pH$: Also stimulate receptors when they decrease, but have less influence than $PaCO_2$.

Protective Defenses of the Respiratory System

• Upper Respiratory Tract Defenses:

  • Conditioning: Warms and humidifies air to keep lower tract mucus fluid.

  • Filtering: Nose hairs and mucus trap dust and irritants.

  • Aspiration Protection: The epiglottis acts as a "trapdoor" to prevent food or foreign matter from entering the lower tract.

• Lower Respiratory Tract Defenses:

  • Mucociliary Escalator: Ciliated cells provide motion to a "mucous blanket" produced by glands, sweeping trapped bacteria and particles upward and out.

  • Alveolar Macrophages: Scavenger white blood cells that engulf bacteria and particles in the alveoli.

• Reflexes:

  • Sneeze: Triggered by nasal irritants to expel material.

  • Cough: A forceful expulsion of air that clears germ-laden mucus and prevents the formation of mucous plugs, keeping airways open for gas exchange.

Characteristics of Normal Breathing Patterns

• General Traits: Smooth, even, regular, and nearly effortless.

• Breathing Rates:

  • Adults and Older Children: $12$ to $20$ breaths per minute.

  • Awake vs. Asleep: Breathing is slightly faster when awake.

• Specific Patterns:

  • Exhalation typically takes twice as long as inhalation.

  • Each breath is usually the same size (excluding sighs or yawns).

  • Effective diaphragmatic breathing is marked by the rise and fall of the abdomen.

• Tidal Volume: The average adult moves about $0.5$ liters ($500\,mL$) of air per breath.

• Exercise Adaptation: Rate and depth increase to provide more $O_2$ and remove excess $CO_2$. Athletes often have slower, deeper resting rates due to respiratory muscle efficiency.

Respiratory Considerations across the Life Span

• Newborns and Infants:

  • Fetal Development: Alveoli develop throughout pregnancy. By week $24$ or $25$, there are enough for effective breathing; another $10$+ weeks are needed for full function.

  • Surfactant: Prevents alveolar collapse; produced late in gestation. Premature infants often need surfactant replacement therapy.

  • Rate: $30$ to $60$ breaths per minute.

  • Periodic Breathing: Occasional pauses of several seconds are normal in the first $3$ months.

  • Apnea: Cessation of breathing for $20$ seconds or longer is abnormal.

• Toddlers and Preschoolers:

  • Rate: By age $3$, rate decreases to $20$ to $30$ breaths per minute.

  • Risk: Increased risk of aspirating foreign objects (e.g., hard candy, small toys).

• Children and Adolescents:

  • Rate: Reaches the adult rate of $12$ to $20$ breaths per minute.

  • Tobacco and Vaping: $90\%$ of smoking adults start by age $18$. In $2022$, $14.1\%$ of high schoolers reported using e-cigarettes (up from $11.7\%$ in $2016$).

  • Nicotine Risks: Stimulates epinephrine, increasing heart rate and blood pressure. E-cigarettes can impair brain development (impulse control, mood) into the early/mid-20s.

  • Poisoning: $50\%$ of e-cigarette poison control calls involve children under age $5$, often from liquid absorption or ingestion.

• Adults and Older Adults:

  • Structural Changes: Thoracic wall becomes rigid; lungs lose elasticity (less stretch).

  • Functional Changes: Decreased ciliary activity, less effective/propulsive cough, and decreased response to hypercapnia.

  • Gas Exchange: Normal $PaO_2$ levels decrease with age.

Cultural Sensitivity in Respiratory Assessment

• Communication Barriers: Diagnosing asthma can be difficult due to translation issues. Some languages lacks direct equivalents for terms like "wheeze," "whistling," "hissing," or "cough."

• Nursing Requirement: Nurses must use astute assessment skills and cultural sensitivity to interpret findings accurately when standardized questionnaire terms are not applicable.