respiratory ii Flashcards
Common values for atmospheric pressure, transpulmonary pressure, intrapleural pressure, and intrapulmonary pressure
0
4
-4
0
Pressure relationships
If Pip= Ppul or Patm —> lungs collapse
Ppul - Pip = transpulmonary pressure
- keeps airway open
- greater transpulmonary pressure –> larger lungs
Pulmonary ventilation
inspiration and expiration
mechanical processes that depend on volume changes in thoracic cavity
- volume changes –> pressure changes
- pressure changes –> gases flow to equalize pressure
Boyle’s law
relationship bt pressure and volume of gas
-gases fill container; if container size reduced, increased pressure
Pressure varies inversely with volume
P1V1 = P2V2
Inspiration
Active process
- inspiratory muscles (diaphragm and external intercostals) contract
- thoracic volume increases –> intrapulmonary pressure drops to -1 mm Hg
- lungs stretched and intrapulmonary volume increases
- air flow into lungs, down its pressure gradient, until Ppul = Patm
Forced inspiration
Vigorous exercise, COPD –> accessory muscles (scalenes, sternocleidomastoid, pectoralis minor) –> further increase thoracic cage size
Expiration
Quiet expiration normally passive
- inspiratory muscles relax
- thoracic cavity volume decreases
- elastic lungs recoil and intrapulmonary volume decreases –> pressure increases (Ppul rises to +1 mm Hg)
- Air flow out of lungs down its pressure gradient until Ppul = 0
Forced expiration is active and uses abdominal (oblique and transvers) and internal intercostal muscles
Changes in intrapulmonary and Intrapleural pressure while taking a breath –> also volume of breath
Ppul decreases as lung volume increases and vice versa
Pip decreases as chest wall expands and returns to normal (still negative) during exhalation
During each breath, the pressure gradients move 0.5 L of air into and out of the lungs
3 Physical factors influencing pulmonary ventilation
These influence the ease of air passage and the amount of energy required for ventilation:
- airway resistance
- alveolar surface tension
- lung compliance
Airway resistance: equation
- Friction = major nonelastic source of resistance to gas flow –> occurs in airways
- Relationship between flow, pressure, and resistance is F = dP/R
dP = pressure gradient bt atmosphere and alveoli (2 mm Hg or less during normal quiet breathing)
Gas flow changes inversely with resistance
Airway resistance: resistance
Resistance usually insignificant
- large airway diameters in first part of conducting zone
- progressive branching of airways as get smaller, increasing total cross-sectional area
- resistance greatest in medium-sized bronchi
Reisstance disappears at terminal bronchioles where diffusion drives gas movement
Homeostatic imbalance
-as airway resistance rises, breathing movements become more strenuous
Severe constriction or obstruction of bronchioles
- can prevent life-sustaining ventilation
- can occur during acute asthma attacks or acute allergic reactions; stops ventilation
Epinephrine dilates bronchioles, reducing air resistance
Alveolar surface tension: def of surface tension
Surface tension
- attracts liquid molecules to one another at gas-liquid interface
- resists any force that tends to increase surface area of liquid
- water has high surface tension; coats alveolar walls –> reduces them to smallest size
Alveolar surface tension: surfactant
detergent-like lipid and protein complex produced by type II alveolar cells
- reduces surface tension of alveolar fluid and discourages alveolar collapse
- insufficient quantity in premature infants causes infant respiratory ditress syndrome –> alveoli collapse after each breath
Lung Compliance
- measure of change in lung volume that occurs with given change in transpulmonary pressure
- higher lung compliance –> easier to expand lungs
Normally high due to
- distensibility of lung tissue
- surfactant which decreases alveolar surface tension
Diminished by
- nonelastic scar tissue replacing lung tissue (fibrosis)
- reduced production of surfactant
- decreased flexibility of thoracic cage
