Lung Mechanics Under Stress

Question 1

Types of Stridor

Answer 1

• Inspiratory Stridor: generally occurs in the extrathoracic region
• Expiratory Stridor: generally occurs in the intrathoracic region
• Can specify stridor based on where we think it might be happening in the respiratory tract:
  
  • Supraglottic, Subglottic, intrathoracic
  • Supraglottic and subglottic are both extrathoracic

Question 2

Causes of Chronic Cough

Answer 2

• Upper Airway Cough Syndrome (AKA: Post-nasal drip)
• Asthma
• Gastroesophageal Reflux Disease (GERD)
• Chronic bronchitis
• ACE Inhibitor induced cough

Question 3

cholinergic parasympathetic stimulus to bronchial smooth muscle

Answer 3

stimulation leads to contraction and increased glandular mucus secretion; acetylcholine stimulates muscarinic receptors leading to muscle contraction; acetylcholine is a promoter of bronchial smooth muscle contraction

Question 4

Causes of Glottic/Subglottic Stridor

Answer 4

• Croup – An upper airway infection that blocks breathing and has a distinctive barking cough.
• Anaphylaxis
• Foreign Body
• Tracheitis
• Tracheomalacia
• Vocal Cord Paralysis
• Subglottic Stenosis

Question 5

Causes of Supraglottic Stridor

Answer 5

• Anaphylaxis
• Epiglottitis
• Retropharyngeal Abscess
• Laryngomalacia
• Congenital malformations
• Tumor of the oral cavity
• Tonsillar enlargement

Question 6

Causes of increased airway resistance

Answer 6

• Airway inflammation
• Smooth muscle contraction (bronchoconstriction)
• Mucus production
• Excess tissue
• Foreign body or masses

Question 7

Examples of Bronchoconstrictors

Answer 7

• Acetylcholine
• α-agonists
• Inhaled irritants (smoke, dust)
• Histamine
• Leukotrienes
• Serotonin
• Endothelin
• ↓ PCO2 in small airways

Question 8

Diseases Associated with Airway Obstruction

Answer 8

• Obstructive Lung Disease: Asthma, COPD, Cystic Fibrosis (will be covered next week)
• Wheezing
• Stridor
• Cough

Question 9

adrenergic sympathetic stimulus to bronchial smooth muscle

Answer 9

stimulation leads to relaxation and inhibition of glandular secretion; notably have beta-2 receptors: G-protein coupled transmembrane protein that results in production in cAMP leading to smooth muscle relaxation; could use beta-2 agonist to stimulate opening of airways

Question 10

Wheezing: Presentation, Etiology, Causes

Answer 10

• Continuous adventitial lung sounds, typically high pitched with whistling quality
• Etiology: fluttering of airway walls and fluid together induced by critical flow velocity
• Can occur throughout the respiratory cycle (both during inspiration and expiration)
• Causes
  
  • Allergies § Anaphylaxis § Asthma § Bronchiectasis § Bronchiolitis § Bronchitis § COPD § Epiglottitis § Foreign body aspiration § Gastroesophageal reflux § Congestive Heart Failure § Lung Cancer § Medications (aspirin) § Pneumonia § Obesity § Smoking § Vocal Cord Dysfunction

Question 11

Evaluating and Treating Chronic Cough

Answer 11

• Identifying likely cause with history and physical
• Bronchoprovocation studies such as methacholine challenge could identify asthma
• pH probe studies can identify GERD
• Sequential treatment for three most common causes – see what works to help with diagnosis (upper airway cough syndrome, asthma, GERD)

Question 12

Define the dead space fraction.*

Answer 12

• Portion of the lung that is not participating in gas exchange
• Dead Space Fraction: VD / VT
• Normal ratio is 1:3 or 0.30
• About a third of our tidal volume is composed of some sort of dead space
• Can be elevated in states of stress or pathology
• Typically is low in the normal individual but can be significant in states of stress or pathology

Question 13

Examples of Bronchodilators

Answer 13

• β2-agonists: Albuterol
• Anti-cholinergic: Ipratropium
• Nitric oxide
• ↑ PCO2 in small airways
• ↓ PO2 in small airways

Question 14

Dynamic compression of the airways

Answer 14

results when intrapleural pressure equals or exceeds alveolar pressure, which causes dynamic collapsing of the lung airways. It is termed dynamic given the transpulmonary pressure (alveolar pressure − intrapleural pressure) varies based on factors including lung volume, compliance, resistance, existing pathologies, etc

Question 15

Summarize the factors affecting airway resistance and how it is distributed along the tracheobroncial tree

Answer 15

• Resistance is inversely proportional to the radius of the tube
• Initial resistance met in the upper airway: nose, nasal turbinates, and pharynx (35-50% of all resistance)
• Along the tracheobronchial tree, highest resistance is encountered in the large to medium sized bronchi
• Airway resistance is inversely proportional to lung volume

Question 16

Describe the clinical indications for exercise testing in evaluating lung function*

Answer 16

Cardiopulmonary Exercise Test

• Evaluation of Exercise Intolerance Evaluation of Unexplained Dyspnea
• Evaluation of patients with Cardiovascular or Pulmonary Disease
• Preoperative Evaluation
• Lung resection: lung cancer or LVRS
• Heart or Lung Transplantation
• Evaluation of Disability or Impairment

Question 17

Stridor: presentation, etiology

Answer 17

• High-pitched monophonic sound best heard over the anterior neck
• Etiology: oscillation of the narrowed airway, notably the major larger airways
• Requires prompt evaluation due to concern of maintenance of airway patency

Question 18

Causes of Intrathoracic Stridor

Answer 18

• Tracheitis or Bronchitis
• Foreign Body
• Anaphylaxis
• Tracheobronchomalacia
• Tracheal stenosis
• Bronchogenic tumor

Question 19

Classification of Cough

Answer 19

• Acute: <3 weeks
• Subacute: 3 – 8 weeks
• Chronic: > 8 weeks

Question 20

Explain why the dead space fraction changes with exercise in health and disease*

Answer 20

Healthy

• Anatomic Dead Space increases slightly in inspiration due to airway distention at high lung volumes
• VD / VT actually decreases due to ↑ in VT
• Alveolar Dead Space decreases due to increased cardiac output in response to exercise
• Physiologic Dead Space therefore decreases in Exercise

Disease (heart or lung)

• the VD / VT ratio will be elevated
• Congestive Heart Failure
  
  • Cardiac output is diminished and cannot increase the levels needed in exercise
  • This leads to portions of the lung with inadequate blood flow and are not participating in gas exchange (↑ VD)
• Pulmonary Disease (COPD, ILD, PH) ILD = interstitial lung disease, PH = pulmonary hypertension
  
  • Already issues with ventilation and are unable to increase tidal volume enough in exercise (↑ VD/VT)

Question 21

*List the variables that determine resistance to flow through a tube, write the mathematical formula relating them, and name the variable that normally plays the most influential role in varying resistance to flow.

Answer 21

• Resistance is dependent on the flow type; higher flow leads to turbulence
  
  • Smaller airways: laminar flow
  • Larger airways: turbulent and transitional flow
• Flow through a tube is determined by Poiseuille’s Law
  
  • Change in pressure = VxR (V is airflow and R is resistance)
  • R = 8nl/(pi)r^4
  • Resistance is inversely proportional to the radius of the tube
• Resistance = Pressure difference (cm H20) / Flow (L/min)