Physiology Lecture 3: Lung Dynamics Flashcards
6 respiratory muscles
- Diaphragm
- Inspiratory intercostal muscles
- External intercostals
- Parasternal intercostals
- Accessory muscles
- Scalenes
- Sternocleidomastoids
- Trapezius
What drives normal expiration (i.e. not during exercise)
Passive elastic recoil pressure of the lung
Expiratory muscles (i.e. during exericse) (5)
- Abdominal muscles
- Rectus abdominis
- Transverse abdominis
- Internal obliques
- External obliques
- Thoracic muscles
- Internal intercostal muscles
Number of generations in the airway structure
23
2 zones of the airways
Conducting zone
Respiratory zone
How many generations does the conducting zone contain?
First 16
Typical tidal volume at rest
500 mL
Approximate increase in tidal volume with exercise
3 L or more
3 types of lung compartment ventilation
VE = minute ventilation
VA = Alveolar ventilation
VD = Dead Space ventilation
Definition of minute ventilation
Total volume of fresh gas drawn into the lungs each minute
Equation for minute ventilation
VE = f x VT
where:
- f = respiratory rate
- VT = tidal volume
normal respiratory rate
12 - 20 breaths/minute
Approx vol of anatomical dead space
150 mL
Requirement for gas exchange in terms of VT and VD
VT > VD
Define physiological dead space
Anatomic dead space + non-functional alveoli
Define anatomic dead space ventilation
The volume of fresh gas reaching the anatomic dead space each minute
Define alveolar ventilation
The volume of fresh gas reaching the respiratory zone each minute
Equation for alveolar ventilation
V(dot)A = f x (VT - VD)
Where VD = dead space bolume (NOT ventilation)
2 equations for minute ventilation
VE = VA + VD
VD = VE - VA
Typical PAO2
100 mm Hg
Typical PACO2
40 mm Hg
Typical PiO2
149 mm Hg
Typical PiCO2
0 mm Hg
What determines PACO2
The ratio os CO2 production and alveolar ventilation
PACO2 α VCO2/VA
How is PCO2 kept within tight limits in the body?
Minute ventilation is adjusted by ensuring adequate alveolar ventilation
Define hypoventilation
Alveolar ventilation too low
2 consequences of hypoventilation
- Increased PCO2
- Respiratory acidosis (-> increase H+ in the blood)
Define hyperventilation
Alveolar ventilation too high
2 consequences of hyperventilation
- Decreased PCO2
- Respiratory alkalosis (-> decreased H+ in the blood)
Difference in intrapleural pressure according to gravity
Less negative at the bottom compared to the apex
Difference in resting volume and expansion according to gravity
Bottom of the lugn has a smaller resting volume and expands better during inspiration
Differnece in ventilation according to gravity
Greatest in lower zones and least in upper zones
Regional differences in Compliance
Larger at bottom than at top
Upright regional alveolar size at TLC
Upright regional alveolar size at FRC
Upright regional alveolar size at RV
Effect of astham and increased COPD
Increased resistance
Effect of lung fibrosis
Decreased compliance
Effect of kyphoscoliosis
Deformed chest wall
Effect of diseases that change the mechanicla properties of the lung
Increase respiratory workload = harder to breathe
Define respiratory failure
When the respiratory system is unable to keep up and cannot accomplish its job of exchanging O2 and CO2 because of inadequate ventilation
Type I respiratory failure
Decrease PaCO2
(Blood/perfusion problem)
Type II respiratory failure
Increase PaCO2
(Ventilatory problem)
Where do the bronchial veins drain into? What effect does this have?
Into the pulmonary veins, which drain into the left atrium, so de-oxygenated blood mixes with oxygenated blood = small “shunt”
Effect of hyperpnea
Airway surface cools and dries from evaporation of fluid
Why do the resistances of the systemic and pulmonary circuits differ?
- Systemic blood flow actively directs to various organs = may require high pressure
- Lung rarely directs blood to any one region = arterial pressure just high enough to lift blood to the top of the lung
Equation for resistance
Define resistance
The impedance t oflow (the energy cost for flow)
Define pulmonary vascular resistance (PVR)
Energy cost for flow in the pulmonary vasculature from the pulmonary artery to the left atrium
Equation for PVR
What determines PVR
Cardiac output flowing through the pulmonary arteries, capillaries and veins
What does pulmonary vascular diameter depend on?
Transmural pressure across the arterial or capillary wall
2 mechanisms that explain why PVR is lower at higher flow
- Vascular distension (increase diamter or open vessels)
- Vascular recruitment (open previously closed vessels)
Effect of lung volume on alveolar vessles
Get smaller with increasing lung volume
Effect of lung volume on extra-alveolar vessels
Get larger with increasing lung volume
Effect of alveolar volume on spetal capillaries
Increased alveolar volume = stretched and narrowed septal capillaries
Effect of alveolar pressure on septal capillaries
Increased alveolar pressure = compressed septal capillaries
West Zone I characteristics
- PA > Pa > Pv
- Vessels are compressed = no flow
- At the top of the lung when upright
West Zone II characteristics
- Pa > PA > Pv
- PA = downstream pressure
- ‘Vascular waterfall condition”
- Flow depends on the difference between Pa and PA
West Zone III characteristics
- Pa > Pv > PA
- Flow depends on arterio-venous pressure difference
Clinical setting for zone I
increased PA (i.e. on a mechanical ventilator)
Clinicla setting for Zone II
Increase Pa or decreased PA
Clinical setting for Zone III
Increased Pv, especially in cardiac dysfunction (i.e. crackles)
Effect of hypoxia on pulmonary vessels
Hypoxic pulmonary vasoconstriction (accentuated by low pH)
Note that systemic vessels vasodilate under these circumstances
Effect of nitric oxide on pulmonary vessels
Pulmonary vasodilation (smooth muscle relaxation)
