Chapter 2- The respiratory system Flashcards
What is minute ventilation?
Vmin is the volume of air breathed per minute
What determines ventilation?
The Tidal volume (VT) and the respiratory frequency
Vmin= VT x frequency
What is another name for the conducting airways?
Anatomical dead space
True/False: There is no gas exchange in the conducting airways (dead space)
True
What can increase mechanical dead space during anesthesia?
An excessively long endotracheal tube or a large face mask
What provides the energy during inhalation?
The respiratory muscles
What provides the energy during exhalation?
The elastic force stored in the stretched lung and thorax
Inhalation is ____ while exhalation is ____ process
An active process; a passive process
What happens with the intraabdominal pressure during diaphragm contraction?
The intraabdominal pressure increases
Why can the diaphragm function be altered during recumbency?
Because the abdominal viscera is stretching the diaphragm beyond optimal length
What do the external intercostal muscles do?
Move the ribs outward and forward
What do the sternohyoid and sternocephalic muscles do during strenuous breathing?
They move the sternum rostrally
What do the abdominal and internal intercostal muscles do?
Expiratory muscles
How does contraction of the internal intercostal muscles decrease the size of the thorax?
Moves the ribs caudally and downward
Define functional residual capacity (FRC)?
Is the residual volume of air after expiration
What is the FRC in horses?
45mL/kg
What happens during inhalation with the pleural pressure (numbers also)?
It decreases from -5 cm H2O to -10 cm H2O
Why are higher pressures needed to ventilate the horse during respiratory disease?
Because the disease can change resistance and elasticity and increase the work of breathing
What is pressure-volume hysteresis?
Is the difference between the pressure that takes to re-inflate the lungs and the pressure that is needed to maintain a certain pressure during deflation
Why is the hysteresis higher during anesthesia?
Because FRC decreases and airways might close, increasing the pressure needed to re-inflate
What is surfactant?
Is a combination of lipids and proteins that facilitate surfactant recruitment to the alveolar surface
What does surfactant do?
Reduces surface tension on the alveolar lining fluid
Who produces surfactant?
Type II alveolar cells
How does a conscious animal reactivate surfactant?
By sighing and expanding alveolar surface several times per hour
What can reduce the activation of surfactant?
- Anesthesia
- Chest pain
The nasal cavity, pharynx, and larynx provide ____ of the frictional resistance to breathing
50-70%
The trachea, bronchi and bronchioles provide the remaining ____ of the resistance divided in this way
30-50% divided in trachea 40%, bronchi 40% and bronchioles 20%
What produces the lung sounds perceived with the sthetoscope?
High velocity, turbulent airflow in trachea and bronchi
What effect does the parasympathetic (vagal) stimulation have in the airways, specially which structure?
It narrows it, specially bronchi
True/False: Intrapulmonary smooth muscle has a high concentration of sympathetic innervation
False
How does relaxation of the smooth muscles happen in the airways?
Activation of Alpha-2-adrenoceptors by epinephrine released from the adrenal medulla
What is the effect of volatile anesthetics in the airways, why?
Bronchodilation by relaxing airway smooth muscle
How do inhalant anesthetics, IV anesthetics, and benzodiazepines decrease airway smooth muscle tone?
By reducing Ca influx through voltage-dependent Ca channels
Why does dynamic compression happen?
When pressure surrounding the airway is higher than pressure within the airway
Why is contraction of the abductor muscles necessary to avoid collapse in nares, pharynx, and larynx during inhalation?
Because pressure within airways is subatmospheric and is surrounded by atmospheric pressure
Why are heavily sedated or anesthetized horses more prone to collapse of the nares, pharynx or larynx?
Because anesthesia reduces the tone of the abductor muscles
When can intrathoracic dynamic collapse happen?
When the intrapleural pressure exceeds the intraluminal pressure (obstructive lung disease)
True/False: High pressures are needed to reopen closed airways in the lung of an anesthetized horse.
True
What does a decrease in FRC lead to, why?
Hypoxemia, presumably due airway closure that leads to uneven distribution of ventilation and V/Q inequalities
True/False: Pulmonary circulation has low vascular resistance
True
Where is blood flow distributed preferentially in an anesthetized horse, independently from the recumbency?
To the caudal-most portion of the caudal lobe of the lung
Why horses anesthetized with halothane, enflurane and isoflurane are less effective at redistributing blood flow to better oxygenated regions of the lung?
Because a dose-dependent decrease of the Hypoxic pulmonary vasoconstrictor phenomenon
Why do PPV and PEEP decrease CO?
By decreasing venous return due to increased intrathoracic pressure
True/False: Air has 21% oxygen everywhere, the partial pressure changes with altitude
True
Mixing of gases and exchange of O2 with CO2 occurs by ____
Diffusion
What can affect the rate of diffusion? (4)
- The area available for diffusion
- Thickness of the air-blood area
- Physical properties of the gas
- Driving pressure gradient between alveolus and capillary blood
Why does blood progressively rises its oxygen partial pressure (Driving pressure gradient)?
Alveolar PO2 = avg 100 mmHg
Venous PO2 = ~40 mmHg
Driving pressure gradient 60 mmHg causes rapid diffusion of O2 into the capillary
What does Hb do during the oxygen diffusion?
It helps maintain the pressure gradient
How long does it take for equilibration to happen?
0.25 seconds
What can increase the driving pressure gradient?
Increasing the amount of oxygen that the horse is breathing (During anesthesia can be 100%)
CO2 is ____ times more diffusible than O2 because of its higher solubility
20 times
What is V/Q match, why is it important?
Is the matching of ventilation to blood flow, is the most important determinant of gas exchange
What happens with V/Q in regions that receive reduced amount of ventilation, but continue to receive blood flow?
Those regions will have a low V/Q having a high CO2 content
What happens with V/Q in areas of atelectasis (right-to-left shunt)?
That V/Q =0
What happens with the blood in the areas of atelectasis?
Shunted blood does not participate of gas exchange
What can happen when blood that did not participate on the gas exchange mixes with oxygenated blood?
It will cause hypoxemia
What determines the magnitude of hypoxemia during right-to-left shunt?
The size of the shunt blood flow
What can cause an elevated V/Q match?
Decreased pulmonary flow
What does the Bohr equation calculate?
The amount of wasted ventilation (VD/VT)
VD/VT=(PaCO2-PECO2)/PaCO2
V/Q relationships and consequences (TABLE)
True/False: Gas exchange impairments result from blood flow to regions of the lung that are not ventilated rather than blood flow to regions served by intermittently closed airways
True
How can Right-to-Left shunts be reduced?
By selective mechanical ventilation
True/False: Gas exchange problems are more common when dissociative anesthetics are used during field anesthesia
False, hypoventilation does not occur
What can the presence of pure oxygen (100%) cause in the alveoli?
Right-to-left shunting due to absorption atelectasis
Why is PACO2 rarely affected by diffusion abnormalities, V/Q mismatch or right-to-left shunts?
Because hypoxemia stimulates ventilation
Each molecule in the hemoglobin can bind to ____ molecules of oxygen reversibly
4 molecules of oxygen
When leaving the lungs, Hb is saturated to ____, mixed venous blood is ____ saturated with oxygen when P)2 is 40 mm Hg.
95%; 75%
A left shift in the Hb-oxygen dissociation curve will make release of oxygen into tissues ____
Slower
