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Pulmonology > 03: Respiratory Physiology > Flashcards

03: Respiratory Physiology Flashcards

1
Q

FIO2

A

Fractional concentration of oxygen in inspired gas (21%).

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2
Q

Hypercapnia

A

Too much CO2 in blood; increases cerebral blood flow/intracranial pressure; causes tremor, confusion, coma; causes acidemia (low blood pH)

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3
Q

Calculation of a partial pressure.

A

Pgas = Fgas x Ptotal

Use to calculate partial pressure of oxygen in air at sea level.

Caution: Must also accont for water vapor pressure!

PiO2 = (Patm - PH2O) x FiO2

Where PH2O = 47 mmHg

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4
Q

Muscles of inspiration

A

Diaphragm, external intercostals, accessory muscles (scalenes & SCMs)

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5
Q

Muscles of expiration

A

Passive during quiet breathing, but active during exercise or times of stress (abdominal wall musculature, internal intercostals)

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6
Q

Transpulmonary pressure

A

The pressure expanding the lung.

Ptp = Palv - Pip

Where Ptp is transpulmonary pressure, Palv is alveolar pressure, and Pip is intrapleural pressure.

At rest, Ptp = +5cm H2O

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7
Q

Pleural pressure

A

Pressure within the pleural cavity.

Normally -5 cm H2O, due to chest wall elastic recoil (outward) = lung elastic recoil (inward).

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8
Q

RR

A

Respiratory rate.

10-16 per minute.

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9
Q

VT

A

Tidal volume

Gas inspired in a single breath.

~0.5 liters.

Composed of gas delivered to dead space and to alveolar space: VT = VD + VA (500mL = 150mL + 350 mL).

Use to determine V.A (alveolar ventilation):

VT x RR = (VD x RR) + (VA x RR)

V.E = V.D + V.A
(6 L/min = 1.8 L/min + 4.2 L/min)

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10
Q

VE

A

Minute ventilation

Volume of gas expired per minute.

~6-7 liters/minute.

VE = RR x VT

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11
Q

Hyperpnea

A

Increased tidal volume

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12
Q

Dead space

A

Anatomic dead space: conducting zone; does not participate in gas exchange; normal; 1ml per lb of body weight.

Physiologic dead space: ADS + diseased areas of lung; areas not participating in gas exchange.

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13
Q

Alveolar ventilation

A
  • Eliminates CO2 from alveoli (too much = hypercapnia); hypercapnia causes:
    • ↑cerebral blood flow, intracranial pressure
    • tremor, confusion, coma
    • acidemia
  • Delivers O2 to alveoli (not enough = hypoxemia); hypoxemia causes:
    • tissue hypoxia
    • inhibition of cellular aerobic respiration
    • death
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14
Q

What factors control breathing?

A
  • Peripheral chemoreceptors (O2, CO2, H+ [via CN IX, X])
    • Located in carotid and aortic bodies
  • Central chemoreceptors (H+)
    • Indirect response to CO2 stimulation
    • CO2 readily passes through BBB, joins with H2O to form H+ and HCO3-
    • Strongest influence on minute-to-minute control of breathing!
    • Note: If arterial PCO2 > 100 mmHg, can actually cause decrease in respiratory drive (especially if acute); due to metabolic depression of all CNS functions: CO2 narcosis
  • Inspiratory inhibition reflex (Hering-Breuer reflex)​
    • ​Mechanoreceptors in airway smooth muscle
    • Deep inspiration (distension stimulus) triggers decreased breathing rate
  • Irritant receptors​
    • Inhaled irritants stimulate receptors in airway epithelium
    • Causes tachypnea, bronchoconstriction
  • J (juxtacapillary) receptors
    • Located in alveolar walls
    • Pulmonary edema, other long processes activate receptors
    • Cause ↑ respiratory drive
  • Joint & muscle receptors
    • ↑ respiratory drive in anticipation of exercise

All activate the inspiratory center, which stimulates the phrenic nerve (which controls the diaphragm).

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15
Q

V.CO2

A

Rate of transfer of CO2from pulmonary circulation to alveolus.

CO2 diffuses freely between blood and alveolus; highly soluble in tissues and not limited by properties of lung.

V.CO2 dependent on amount of CO2 delivered to alveolus (alveolar perfusion); depends on CO2 production and cardiac output (both constant at rest).

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16
Q

PACO2

A

Alveolar PCO2

Determined by 1) CO2 transer from blood to alveolus (V.CO2) and 2) CO2 elimination via expiration (V.A).

Can rearrange equation to measure alveolar ventilation.

Since CO2 diffuses freely between blood and alveolus, PACO2 = PaCO2.

17
Q

Clinical assessment of alveolar ventilation.

A
  • Normal PaCO2 = 37-42mmHg
  • PaCO2 < 37mmHg
    • Hypocapnia
    • 2/2 alveloar hyperventilation
  • PaCO2 > 42mmHg
    • Hypercapnia
    • 2/2 alveolar hypoventilation
18
Q

Causes of alveolar hyperventilation

A

Due to increased respiratory drive

  • Hypoxemia
  • Acidemia
  • Stimulation of lung receptors
  • Drugs (ASA, progestins)
  • Pain
  • Anxiety
  • Fever
  • Pregnancy
  • Exercise
  • Hypercapnia
19
Q

Causes of alveolar hypoventilation

A

Decreased respiratory drive and/or effort

  • Drugs (benzodiazepines)
  • Brain injury (trauma, stroke, ↑intracranial pressure)
  • CO2 narcosis: PCO2 >100mmHg causes metabolic depression
  • Sleep
  • Breath-holding

Neuromuscular problem

  • Failed NM transmission (spinal cord, peripheral nerve)
  • Muscle weakness

Muscle fatigue due to increased load

  • Abnormal mechanics
  • ↑dead space
20
Q

Work of breathing

A
  • Energy expended during ventilation
  • Causes of ↑WOB
    • ↑respiratory drive
    • abn. respiratory system mechanics
    • ↑dead space
  • Signs of ↑WOB
    • accessory muscle use
    • tachypnea
    • nasal flaring
    • paradoxical breathing
  • Consequences of ↑WOB
    • respiratory muscle fatigue
    • cannot continue indefinitely
    • fatigue –> alveolar hypoventilation
21
Q

Dead space

A
  • Ventilated space that does not participate in gas exchange
  • Sources
    • External conducting airways (e.g., snorkel, ventilator tubing)
    • Created from alveolar space
      • ↑dead space, ↓alveolar space
  • Results in ↑minute ventilation –> ↑WOB –> fatigue
22
Q

Factors ↑ventilatory load

A
  • ↑respiratory drive
  • dead space
  • tight airways
  • stiff lungs
23
Q

Factors ↓ventilatory capacity

A
  • Muscular fatigue
  • Neuromuscular disease
  • CNS depression
24
Q

Acute vs. chronic alveolar hypoventilation

A
  • Acute: minutes to hours
    • Renal compensation limited
    • pH < 7.3
    • Acute hypercapneic respiratory failure
  • ​Chronic: days or longer
    • Renal compensation nearly complete
    • pH nears 7.4
25
Q

Ventilator settings

A
  • Flow rate during inspiration
  • FiO2
  • Tidal volume
  • Respiratory rate
26
Q

Problems with positive pressure ventilation

A
  • Cardiovascular
    • ↓venous return –> HoTN/↓CO
  • Lung mechanics
    • Ventilator-induced lung injury
      • High volume & pressure
      • High FiO2
    • Barotrauma (pneumothorax)
    • Gas-trapping –> auto-PEEP
  • Gas exchange & dead space ventilation
    • ↑dead space ventilation
    • ↑R-L shunt
27
Q

Non-invasive positive pressure ventilation (NIPPV)

A
  • Pressure control; “bilevel” ventilation
  • Set inspiratory pressure “IPAP” and expiratory pressure “EPAP”
  • Contraindications
    • Cardiac arrest
    • Apnea (respiratory arrest)
    • Severely altered mental status
    • Facial injury/deformity/surgery
    • High risk for aspiration

Pulmonology (16 decks)

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