Respiratory Disease Clinical Presentation (Corbett) - 11/30/16

Question 1

Hypoxemia vs. Hypoxia

Answer 1

Hypoxemia: Low arterial oxygen tension (PaO₂) in blood

• Reflects free O₂ dissolved in plasma, which react with the measuring electrode
• PaO₂ cannot tell “how much” oxygen is in blood (does not tell you about content)
  
  • O₂ content = (0.003*PaO₂) + (1.35*Hgb) * O₂ saturation

Hypoxia: Low oxygen delivery

Question 2

Cyanosis

Answer 2

• abnormal blue discoloration of the skin and mucous membranes
• caused by inc in deoxygenated hemoglobin level to above 5 g/dL (normal Hgb 13.5-15.0 g/dL).
• Anemic patients:
  
  • do not develop cyanosis until oxygen saturation (SaO2) has fallen to lower levels than for patients with normal hemoglobin levels
• Polycythemic patients:
  
  • develop cyanosis at higher oxygen saturation levels.

Cyanosis can be divided into central and peripheral.

Question 3

How to assess hypoxemia

How is hypoxemia classified?

Answer 3

Pulse oximeter - amt of light received by detector indicates amount of O2 bound to hemoglobin in blood

Question 4

A-a gradient

Answer 4

Alveolar pressure - arterial pressure

Question 5

Hypoxemia (dec. PaO₂)

Answer 5

Question 6

Hypoxia (dec. O₂ delivery to tissue)

Answer 6

Causes:

• Dec. CO
  
  • Inadequate oxygen delivery
• Hypoxemia
  
  • Low arterial oxygen saturation (PaO2)
• Anemia
  
  • Decreased oxygen content (dec. total number of oxygen molecules in blood)
• CO poisoning
  
  • Impaired ability of cells to utilize oxygen

Question 7

Central Cyanosis

Answer 7

• Caused by diseases of heart or lungs, or abnormal hemoglobin
• Seen in the tongue and lips
• Due to desaturation of central arterial blood resulting from cardiac and respiratory disorders associated with shunting of deoxygenated venous blood into the systemic circulation.

Patients who are centrally cyanosed will usually also be peripherally cyanosed.

Question 8

Peripheral Cyanosis

Answer 8

• Caused by decreased local circulation and increased extraction of oxygen in the peripheral tissues.

Isolated peripheral cyanosis occurs in conditions associated with peripheral vasoconstriction and stasis of blood in the extremities, leading to inc. peripheral oxygen extraction - eg, congestive heart failure, circulatory shock, exposure to cold temperatures and abnormalities of the peripheral circulation.

Peripheral cyanosis is most intense in nail beds and may resolve with gentle warming of the extremity. The mucous membranes of the oral cavity are usually spared.

Question 9

Dyspnea vs. Tachypnea

A patient may be observed to be breathing rapidly but may NOT be short of breath… what is an example of this?

Answer 9

Dyspnea = sensation of breathlessness or subjective SOB

Tachypnea = rapid RR > 20 (normal 12-20)

Ex: acidosis

Never assume that a patient with a rapid RR is dyspneic.

Question 10

Step 1:

What are the ventilatory requirements that are received and processed centrally for you to perceive a sense of “breathlessness”?

Answer 10

• Cortex
• CSF Chemoreceptors
  
  • from inc. pCO2
  • active inspiratory center (DRG)
• Carotid bodies (CN IX)
  
  • Severe hypoxemia (O2 < 60 mmHg)
  • If CO2 levels are high in the periphery, carotid bodies more sensitive to oxygen levels
• Chest
  
  • Mechanoreceptors in respiratory muscles
  • Sensory fibers (CN X)
    
    • Stretch
    • Interstitial disease

Question 11

Step 2:

Once info in received, how is it sent?

A ventilator ‘command’ is given.

Answer 11

• Dorsal Respiratory Group
  
  • Inspiratory neurons
    
    • Receives info from chemoreceptors and stretch receptors
    • Sends motor output info to phrenic nerve
• Ventral Respiratory Group
  
  • Inspiratory and expiratory neurons
    
    • Upper airways, intercostals, etc…
• Apneustic Center/Pontine Center
  
  • Limits inspiration

Question 12

Step 3:

“Corollary discharge”

Answer 12

An ascending copy of descending motor activity sent to sensory cortex

If ventilatory demand > supply, there is an imbalance b/w motor drive to breathe (as sensed via corollary discharge) and afferent feedback from mechanoreceptors of respiratory system

Question 13

What stimuli can cause dyspnea in normal subjects? (5)

Answer 13

• Raising CO2
• Breath-holding (w/ and w/o hypercapnia)
• Hypoxia
• Breathing against a resistance load
• Any of these w/ superimposed exercise or in combo

Question 14

Pathophysiologic correlates of diseases causing dyspnea (6)

Answer 14

• Structural or mechanical interfence w/ ventilation
  
  • Obstruction to flow (e.g. emphysema, asthma, chronic bronchitis, upper airway obstruction)
• Restriction to lung or chest wall expansion
  
  • Intrinsic (diseases involving lung parenchyma)
    
    • ARDS
    • CHF
  • Extrinsic (processes not involving lung parenchyma)
    
    • Kyphoscoliosis
    • Obesity
    • Ascites
    • Pregnancy
    • Pleural disease
• Increases in dead space ventilation
  
  • ​Emphysema
  • PE
• Respiratory muscle weakness
• Increases in respiratory drive
  
  • ​Hypoxemia
  • Acidosis
  • Exercise
  • Decreased Hgb or CO
• Psychological disturbances
  
  • ​Anxiety or panic attacks

Question 15

What is the most common symptom of lung disease?

Answer 15

Cough

• Frequently regarded as trivial complaint b/c it is so common
• Normal defense mechanism of the lungs (clears mucus and exessive secretions)
• Persistent cough (3 or more weeks) = need to investigate further

Question 16

Cough is a defense reflex mechanism.

What are the three phases?

Answer 16

1. Inspiratory phase (breathe in)
2. Closure of glottis and diaphragmatic relaxation
3. Rapid contraction fo expiratory muscles
   
   1. Causes rise in intra-abdominal and -pleaural pressures followed by opening of glottis

Question 17

Timing and etiology of cough

Answer 17

Question 18

Hemoptysis

Answer 18

Coughing or spitting of blood derived from lungs or bronchial tubes secondary to pulmonary or bronchial hemorrhage (hematemesis)

Classified according to volume

• Blood-tinged sputum
• Life-threatening amount ( >500 cc/24 H; 100 cc/hr)
  
  • Tends to be bronchial in origin
  • Not a lot in terms of quantity but if any obstruct airway, could be life-threatening in terms of gas exchange

Question 19

What is the most common source of significant hemoptysis?

Answer 19

Bronchiole arteries (90% of bleeding originates from bronchial circulation and its collaterals)

Question 20

Differential diagnosis of hemoptysis in the primary care setting

Source other than lower respiratory tract

Answer 20

Tracheobronchial source = most common

• Bronchitis (acute or chronic)
• Bronchogenic carcinoma, endobronchial metastatic tumor, Kaposi’s sarcoma, bronchial carcinoid
• Bronchiectasis (inflammation of airways; e.g. CF)

Source other than LRT:

• Upper airway (nasopharyngeal) bleeding
• Gastrointestinal bleeding

Question 21

What is the most common cause of hemoptysis in the US?

Answer 21

Infection (60-70% of cases) - causes superficial mucosal inflammation and edema that can lead to rupture of superficial blood vessels

1. Bronchitis (26%)
2. Pneumonia (10%)
3. TB (8%)