Respiratory Physiology Flashcards
Where does anatomic dead space begin and end?
- mouth & nares to terminal bronchioles
- conducting zone (no gas exchange)
Where does gas exchange begin?
- respiratory bronchioles to the alveolar sacs
- respiratory zone (gas exchange takes place)
What is considered part of the transitional zone?
- respiratory bronchioles and alveolar ducts
- serves as an air conduit where some gas exchange takes place
What is transpulmonary pressure?
Alveolar pressure - Intrapleural pressure
What is alveolar pressure?
pressure inside the lungs
What is intrapleural pressure?
pressure outside the lungs
Transpulmonary pressure is always positive or negative?
positive (keeps the airways open)
Intrapleural pressure is always positive or negative?
negative (keeps lungs inflated)
When is the only time that intrapleural pressure becomes positive?
during forced expiration (besides pneumothorax)
What muscles contract during inspiration?
- diaphragm
- external intercostals
What are the accessory muscles of inspiration?
- sternocleidomastoid
- scalene muscles
Expiration is usually passive, but what muscles are used during active exhalation?
- rectus abdominis
- transverse abdominis
- internal and external oblique
“ I let the air out of my TIREs”
`When does exhalation become active?
- when minute ventilation increases
- pts w/ lung disease (COPD)
What is the vital capacity required for an effective cough?
15 mL/kg
How much dead space is in a 70 kg pt?
- 2 mL/kg or 150 mL
Increased dead space widens the PaCO2-EtCO2 gradient and causes?
CO2 retention
How does atropine increase dead space?
- atropine is a bronchodilator, so it increases the volume of the conducting zone
How does positive pressure ventilation increase dead space?
- it increases alveolar pressure, which increases ventilation relative to perfusion (inc dead space)
By what percent does mechanical ventilation increase the Vd/Vt ratio?
50%
What is the most common cause of an increase in Vd/Vt ratio under general anesthesia?
decreased CO
The Bohr Equation can be used to calculate what?
physiologic dead space
What is ventilation and perfusion in L/min and what is the V/Q ratio?
ventilation = 4 perfusion = 5 V/Q = 0.8
What is the most common cause of hypoxemia in the PACU?
- V/Q mismatch (specifically atelectasis)
- treatment: humidified O2 and maneuvers to reopen the airways
CO2 diffuses how many times faster than O2?
20
What happens to combat zone I?
Bronchioles constrict unperfused alveoli
What happens to combat Zone III?
Hypoxic Pulmonary Vasoconstriction
What are 3 normal anatomic shunts?
- Thesbian veins (drain left heart)
- Bronchiolar veins (drain bronchial circulation)
- Pleural veins (drain bronchial circulation)
What dose a respiratory quotient (RQ) >1 and <0.7 indicate?
- RQ >1 = lipogenesis (overfeeding)
- RQ <0.7 = lipolysis (starvation)
What causes of hypoxemia cause a normal A-a gradient?
- hypoxic mixture
- hypoventilation
What causes of hypoxemia cause an increase in A-a gradient?
- diffusion limitation
- V/Q mismatch
- shunt
When breathing room air, what is the normal A-a difference?
<15 mmHg
How do you calculate the estimation of shunt?
Shunt increases 1% for every 20 mmHg
What are ways to measure FRC?
- nitrogen washout
- helium wash in
- body plethsmography
How is closing capacity measured?
- washout of tracer gas (nitrogen or xenon-133)
What is the Bohr Effect?
- CO2 and H+ cause Hgb to release O2
In banked blood does the level of 2,3-DPG increase or decrease?
decrease
What is the P50 of Hgb F?
19
What are drugs that cause a left shift in the CO2 ventilator response curve?
- salicylates
- aminophylline
- doxapram
- norepinephrine
What are some conditions that impair the hypoxic ventilator response?
- carotid endarterectomy (why we don’t do bilat)
- subanesthetic doses of inhaled and IV anesthetics (MAC 0.1)
What are some conditions that do not stimulate the hypoxic ventilatory response?
- anemia
- carbon monoxide poisoning
- even thought the CaO2 is reduced, the PaO2 is usually normal
