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Altered Ventilation and Diffusion
Respiratory Structures
Rate and volume of ventilation is regulated by:
1. Functioning respiratory control center (RCC): responds to chemical messages in the
body. Composed of neurons in the pons/medulla. It sends impulses to diaphragm,
muscles to contract/relax. (Constriction= Para, Dilation = Symp)
2. Lung receptors: Located in the epithelium/smooth muscle airways.
3. Chemoreceptors: detect gas exchange needs based on PaO2, PaCo2, pH levels.
Central chemoreceptors: near RCC, respond to pH changes in the CSF. Detects CO2
levels in the blood. (↑ CO2 = ↑ ventilation to expel CO2)
Peripheral chemorecepotrs: sensitive to O2 levels, located in aorta/carotid arteries.
( ↓ O2 = ↑ ventilation)
Alveolar type 1: provide structure and air
exchange
Alveolar type 2: lubricant that coats the
inner portion of the alveolus, promotes
easy expansion, repels fluid accumulation
** inflation would be impossible w/out it
Ventilation: Process of moving air in/out of lungs
• Involves both acquiring oxygen (inspiration) and removing carbon dioxide (expiration)
from the blood
• Neuronal impulses are directed by lung receptors, which map the current state of
breathing and lung function
• Uses the intercostal muscles, diaphragm, and sternocleidomastoid muscles
Inspiration
• Breathing in to acquire oxygen
• Unidirectional from high pressure to low pressure.
• Chest cavity size changes to alter the pressure gradient
• Neuronal stimulation/movement moves diaphragm down and out (reduces pressure inside
lungs to pull air in)
Expiration
• Removing carbon dioxide out of the body through the lungs
• The diaphragm and external intercostal muscles relax
• Lungs compress and increase the pressure inside the airways
• Chest wall moves in and diaphragm moves upwards.
• Inside pressure is more than atm pressure (so air moves OUT)
Measurement of Ventilation
1. Tidal volume (TV): the amount of air exhaled after passive inspiration (air in and out at
rest) ** 500 mL
2. Vital capacity (VC): max amount of air in/out of lungs with forced inhale/exhale
3. Forced capacity (FVC): amount exhaled during forced exhale
4. Forced expiratory volume in 1 second (FEV1): amount exhaled from lungs in 1 sec
5. Residual volume (RV): volume of air left in lungs after maximal expiration
6. Total lung capacity: total air in lungs when they are maximally expanded (VC+ RV)
Diffusion: Process of moving/exchanging O2/Co2 through membranes
• Oxygen and carbon dioxide are exchanged at alveolar capillary junctions
• Two major process occur:
• Oxygen is trying to get to all the cells
• Carbon dioxide is trying to escape the body through the lungs
• Effectiveness depends on: Pressure (Co2, O2 in blood), Solubility (Co2 more soluble),
and Membranes (thickness/SA)
Partial Pressure
• The collision of oxygen and carbon dioxide creates pressure
• PaO2
• PaCO2
Perfusion: Process of supplying oxygenated blood to lungs and organ systems via blood vessels
Respiration: Process in which cells in the body use O2 to make energy
Oxygen Diffusion and Transport
• Oxyhemoglobin (HbO2): As PaCO2 ↑ oxygen dissociates from the plasma and connects
with hemoglobin molecules on RBC’s. Based on attraction to iron. When it is attached to
hemoglobin, it is not available to the cell.
• Oxygen Saturation (SaO2): Attraction of hemoglobin continutes until the hemoglobin
molecules are completely saturated. It is NOT affected by blood volume.
• Once saturation occurs, oxygen continues to diffuse and dissolve in the plasma, until the
partial pressures in arteries = that in the alveoli
Carbon Dioxide Diffusion and Transport
• Dissolved in the plasma (10%)
• Bound to hemoglobin (20%)
• Diffused into the red blood cell as bicarbonate (70%): converted to either carbonic
acid, bicarbonate ions (which helps regulate pH)
Diffusing Capacity
• The measurement of carbon monoxide, oxygen, or nitric oxide transfer from inspired gas
to pulmonary capillary blood and is reflective of the volume of a gas that diffuses through
the alveolar capillary membrane each minute.
Impaired Ventilation
• A problem of blocking airflow in and out of the lungs
• Two major mechanisms implicated:
• Compression or narrowing of the airways
(↑ airway resistance, leading to difficulties with airway clearance, ie. Edema,
exudates or inflammation)
• Disruption of the neuronal transmissions needed to stimulate the mechanics
of the airways
(ignores messages sent by chemoreceptors/lung receptors, ie. Drug overdose)
Impaired Ventilation-Perfusion Matching
• Two possible scenarios:
• Lung are ventilated, but not perfused
• Lung is perfused, but not ventilated
• Impaired ventilation: inadequate o2 comes from lungs even though the blood flow is
ready and able to carry oz.
• Impaired perfusion: the blood flow to the lungs is restricted in one or more areas.
Oxygen might be coming in, but have no blood flow to carry it to the body.
Altered Ventilation and Perfusion
Impaired Diffusion
• Restricted transfer of oxygen or carbon dioxide across the alveolar capillary junction
• Dependent upon:
• solubility and partial pressure of the gas: partial pressure is increased when
molecules are packed in a space, temp increases, when barometric pressure
increases. Decreased oxygen pp can occur in o2 deprevation, hypothermia. CO2
increases with metabolism increase/ exercise.
• surface area and thickness of the membrane
The Effects of Impaired Ventilation and Diffusion
1. Hypoxemia: is decreased oxygen in the arterial blood leading to a decrease in the PaO2.
(caused by o2 deprivation, hypoventilation)
2. Hypoxia: When cells are deprived of adequate oxygen. (widespread hypoxemia)
3. Hypercapnia: a state of ↑CO2 in the blood (CO2 is more easily diffused, so it only really
happens when there is severe alveolar hypoventilation followed by hypoxia).
General Manifestations of Impaired Ventilation and Diffusion
• Local manifestations: usually due to inflammatory processes
• Cough (common, protective), mucus, hemoptysis
• Dyspnea (feeling of SOB), orthopnea (the physical need to sit in an
upright/standing position)
• Adventitious lung sounds (altered) (ie. Wheezing= constricted airway)
• Use of accessory muscles (retractions= the pulling in of accessory muscles to
promote more effective inspiration)
• Chest pain (can originate in the visceral/pleural/airway/chest wall. Pleural pain
increases with deep inspiration and often described as sharp/stabbing pain)
• Barrel chest: due to chronic dilation and distention of the alveoli (i.e
emphysema)
• Systemic manifestations: due to hypoxemia/ hypercapnia
• Fever, malaise, leukocytosis
• ↑ plasma proteins
• Dusky/cyanotic mucus membrane color
• Changes in arterial blood gases
• Mental status changes
• Finger clubbing (painless enlargement/flattening of tips of fingers/toes, caused
by chronic hypoxia)
Laboratory and Diagnostic Tests
• History and physical examination
• Visualization (bronchoscopy, x-ray, CT, MRI, nuclear medicine, etc.)
• Pulmonary function tests
• Pulse oximetry
• Laboratory studies
Treating Impaired Ventilation and Diffusion
• Remove obstruction and restore physical integrity of airways, lung tissues
• Decrease inflammation and mucus; treat infection
• Supplemental oxygen
• Mechanical ventilation
Pneumonia
Pathophysiology:
• Acute infectious process on ventilation/diffusion (caused by miccrorganism, community
acquired: strep/staph/influenza; nosocomial: pseudo/staph)
• Respiratory droplet spread
• Causes inflammation of the lungs
• Occurs commonly in the bronchioles, interstitial lung tissue and/or the alveoli
• Products of inflammation accumulate and cause consolidation (products of inflammation
accumulate as a solid mass)
• 3 stages: 1. Recent infection shows rapid filling of alveolar capillaries with purulent
fluid, 2. Red hepatization: fills with fibrinous exudates, appear as dry red lung tissue,
3. Gray hepatization: WBC’s pack into alveoli as RBC’s degenerate. Pneumococcal
bacteria release toxins that contribute to cell death (forming yellow exudates which are
absorbed and resolution begins).
Clinical Manifestations: Oxygen diffusion is impaired, hypoxia, metabolic acidosis,
dehydration
• Sudden onset of fever
• Chills
• Cough
• Sputum production
• Fatigue
• Loss of appetite
• Dyspnea (SOB)
• Tachypnea (rapid breathing)
• Tachycardia
• Pleuritic pain
• Crackles in lungs
Diagnostic Criteria:
• History and physical examination
• Complete blood cell count (↑WBC’s)
• Chest X-ray
• Thoracic CT scan (to see areas of consolidation)
• Examine sputum: pneumococcal= bloody/rust color, pseudomonas = green, anaerobic=
foul smelling
Treatment:
• Restore optimal ventilation and diffusion
• Identify pathogen and target with appropriate pharmacologic treatment (with C&S, and
gram stain)
• Supplemental oxygen
COPD
• Refers to all chronic obstructive lung problems: Emphysema, Chronic Bronchitis and Asthma
• Usually used to denote E+ CB
• Inflammatory processes in both bronchi/ bronchioles
• Progressive, unremitting diseases
Emphysema
Pathophysiology:
• Irreversible enlargement of the air spaces beyond terminal bronchioles
• destruction of the alveolar walls
• obstruction of airflow
• Chronic smoking most often implicated
• Loss of elastic recoil in alveoli leads to airflow obstruction
• Vascular changes: The inner lining of arteries/arterioles become thicker and fibrotic
Clinical Manifestations:
• Persistent cough
• Dyspnea
• Wheezing
• Barrel chest
• Pursed lip breathing
Diagnostic Criteria:
• History and physical examination
• Pulmonary function tests (↓ AAT)
• Chest x-ray (signs of hyperinflation)
• Hypoxemia (early)/ Hypercapnia (later stages)
• FEV1 is most common test, 6+ seconds is bad
Treatment:
• Maintain optimal lung function in order to allow the individual to perform the desired
activities of daily life
• Smoking cessation
• Pharmacologic therapy (bronchodilators, steroids)
• Lung volume reduction or transplant
Smoking: impairs alveolar function:
1. Inhalation of smoke triggers an inflammatory response
2. Neutrophils/ macrophages are activated and retain in lung tissue
3. They release proteolytic enzymes (proteinases/elastases), that destroy components
of ECM (i.e. elastin)
4. The elasticity of the lung is significantly reduced leading to inability of the alveoli
to recoil and release CO2 into atm.
** Elasticity is key! If the alveoli wall collapses, air gets trapped (which decreases O2 intake and
CO2 release). Hyperinflation results, which makes them get further stretched and continue to
lose elasticity. CO2 retained and pH is reduced.
Chronic Bronchitis
Pathophysiology:
• Persistent, productive cough lasting three months or greater, for two or more consecutive
years
• Result of changes in bronchi/bronchioles:
1. Chronic inflammation and edema of the airways
2. Hyperplasia of the bronchial mucous glands and smooth muscles
3. Destruction of cilia
4. Squamous cell metaplasia
5. Bronchial wall thickening and development of fibrosis
Clinical Manifestations:
• Cough
• Purulent sputum
• Dyspnea
• Adventitious lung sounds
• Hypoxemia, hypercapnia and cyanosis (more common than emphysema, b/c excess
mucous/obstructed ventilation)
Diagnostic Criteria:
• History and physical examination (recurrent upper/lower resp infections)
• Arterial blood gases
• Pulmonary function tests
• Pulse oximetry
• Sputum analysis
Treatment:
• Smoking cessation
• Pulmonary rehabilitation
• Pharmacologic therapy
• Supplemental oxygen
Asthma
Pathophysiology:
• Intermittent or persistent airway obstruction due to:
1. Bronchial hyperresponsiveness (IgE mediators cause edema, bronchoconstriction,
release histamine, prostaglandins, leukotrienes, forms mucous in airways)
2. Chronic inflammation
3. Bronchoconstriction
4. Excess mucous production
Clinical Manifestations:
• Wheezing and tachypnea, use of accessory muscles
• Dyspnea and coughing
• Chest tightness
• Excessive sputum production
• Anxiety
• Hyperventilation can lead to respiratory alkalosis
Diagnostic Criteria:
• History and physical examination
• Evidence of respiratory distress
• Pulsus paradoxus: exaggerated decrease in systolic BP during inspiration
• Wheezing
• Prolong expiratory phase
• Atopic dermatitis: eczema, hypersensitivity reactions on skin.
• Pulmonary function tests
• Laboratory studies
• Chest x-ray
Treatment:
1. Monitor lung function
2. Control environmental triggers
3. Pharmacologic therapy
4. Patient and family education; action plan
Cystic Fibrosis
Pathophysiology:
• Autosomal recessive disorder of electrolyte and water transport affecting certain
epithelial cells (respiratory, digestive, and reproductive lining)
• Mutation of the CF gene (both parents have to have it); inability of epithelial cells to
conduct Cl; and therefore transport water across mucosal surfaces leads to thick
secretions and obstructions in the resp tract
• Associated with mucus plugging, inflammation, and infection in the lungs; also affects
other body systems
• Respiratory failure is most common cause of death
Clinical Manifestations:
1. Reproductive: Men get infertile (clogs vas deferens), but the women get altered menses
2. Respiratory: respiratory infections, chronic cough, sputum, vomiting, tachypnea,
wheezing, crackles, chest pain, respiratory distress, cyanosis, barrel chest, recurrent
sinusitis, nasal polyps
3. Gastrointestinal: ↓Cl secretions, get large, greasy BM’s. Get inflammation/scars which
increase bowel obstructions, poor fat absorption, weight loss
Diagnostic Criteria:
• History and physical examination
• Sweat test (Since there are problems with the Cl channels, get salty deposits on the skin)
• Genetic testing
• Chest x-ray (see how much secretions)
• Sputum analysis
Treatment:
• Respiratory
• Chest physiotherapy (press on back)
• Pharmacologic treatment (aerosol to thin secretions)
• Lung transplant (extensive scarring/cysts on the lungs)
• Gastrointestinal
• Optimal nutrition
• Pancreatic enzymes
Mucous plugging: (result of)
1. Greater mucus production
2. Airway dehydration, due to thickened mucus caused by impaired cl secretion, excess Na absorption, decreased
water
3. Adherence of mucus to epithelium with impaired cilia
Acute Respiratory Distress Syndrome: ARDS
Pathophysiology: Sepsis is most common cause
• Lung injury to respiratory distress within 24-48 hours
• Severe acute inflammation and pulmonary edema without evidence of fluid overload or
impaired cardiac function
• pulm edema, damages alveolar capillary junction, damage to type II cells, increased
protein, disruption of surfactant = atelectasis, alveolar collapse)
• Mortality rate 30%-40% from multi-system organ failure in those untreated
Clinical Manifestations:
• Tachypnea
• Dyspnea
• Retractions
• Crackles due to fluid accumulation
• Restlessness, anxiety
Diagnostic Criteria:
• History and physical examination (lung injury)
• Arterial blood gases: depict hypoxemia/hypercapnia resp. alkylosis
• Laboratory studies (blood cultures to detect sepsis)
• Imaging studies
Treatment
• Remove causative factors
• Administration of 100% oxygen
• Mechanical ventilation