What is the most important muscle of inspiration?
What muscles are involved in Inspiration and Expiration?
Inspiration: DIAPHRAGM!, external intercostal muscles (pulls on ribs to open), and accessory muscles (scaline muscle: raises first two ribs; sternomastoid muscle: raises the sternum)
Expiration: abdominal muscles! i.e. rectus abdominus, internal and external obliques, transverse abdominus: pushes diaphragm upward to exhale
As we breath in what two things to happen so volume can fill our lungs?
- 1. Diaphragm moves down
- 2. Ribs spread out
True or False: It is possible for the diaphragm and ribs to be out of sync with each other.
TRUE. It's called asynchronous movement.
What is lung compliance?
The change in lung volume per unit change in the transpulmonary gradient
[ie. pressure between alveolus and intrapleural space]
What is the typical, normal value for lung compliance?
Name some things that REDUCE lung compliance.
-BIGGEST CAUSE OF DECREASED COMPLIANCE!: DISEASE (ie. pulmonary fibrosis)
- -pulmonary venous congestion
- -restriction of chest expansion (chest strapping: similar physio in low ventilation anesthesia)
- -high expanding pressures
- -alveolar edema
- -if lung remains unventilated for a long amount of time
Name some things that INCREASE lung compliance.
- -Emphysema: dt loss of elastin & collagen- why patients are barrel chested
- -normal aging
- -asthma attack
- -filling sue's cats lungs with saline
True or False. Lung volume is greater at any point in exhalation that in inhalation.
True. Lung are more compliant and more open on exhalation! This is called hysteresis!
What is the reason for the compliance difference in expiration and inspiration?
What cells release surfactant?
Alveolar Type 2 Cells
-release during high inflation volumes and during endocrine system stimulation (fight/flight)
True of False. Ability to produce surfactant occurs late in fetal maturation.
True. If suspect pre-term birth: give mom steroids at 35-36 weeks... more effective than giving baby synthetic surfactant
True of False. Surfactant is a phospholipid.
Describe the two characteristics of each end of a surfactant phospholipid.
Hydrophilic- repels water from entering the alveoli
Lipophilic- repels lipids *gas is a lipid* to keep gas from escaping alveoli
Surfactant increases/decreases surface tension of the alveoli.
What three main functions does surfactant serve in the alveoli?
1. Lowers surface tension
2. Promotes stability of the alveoli
3. Helps keep the alveoli dry
Describe the term interdependence as it relates to alveoli.
Interdependence simply means that alveoli are more stable because they support each other.
What negative consequences would there be if you had no or little surfactant?
- -decreased compliance
- -pulmonary edema
- -very stiff lungs
- -severe hyoxemia
Describe the regional differences in ventilation and the importance of surfactant in preventing collapse.
Apex: large expanding pressure, big resting volume, small change in volume on inspiration
Base: small resting volume (relatively compressed at resting state), better ventilated than apex...without surfactant the alveoli in the based of the lung would collapse!
Name some causes for DECREASED compliance of the chest wall.
- -ossification of ribs and costal cartilages (stiff, unmoving ribs)
- -obesity or abdominal distention (pregos, ascites)
- -pathological skin conditions (burn victims, scarring of skin over chest)
True or False: When lung and chest wall are at equilibrium this is also FRC.
The intrapleural space must be above/below atmospheric pressure to maintain a normal lung and chest wall relationship.
If intrapleural pressure equals atmospheric pressure, a pneumthorax occurs!
What two problems do we need to overcome when breathing? (Think airway resistance)
- 1. Elastic Resistance: results from numerous causes of impedance to inflation of the lung
- (ex. pulmonary fibrosis, obese)
- 2. Non-elastic Resistance [AKA: Air Flow Resistance]: caused by frictional resistance to air flow and thoracic tissue deformation
- (ex. asthma, obstructive disease)
Name the three ways gas can flow.
- 1. Laminar flow
- 2. Turbulent flow
- 3. Transitional flow
In laminar flow, _______ is only aspect of the gas that is important.
Viscosity is the only factor that can be changed or manipulated.
True or False. In laminar flow, the gas flow rate is directly proportional to the pressure gradient along the tube.
What was the idea behind the laminar flow OR's?
Flow was stream-lined and all air was put through a HEPA filter: idea was to create a "more sterile" environment- but was never really proven.
In turbulent flow, ___________ is the most important aspect of the gas.
Can effect the work of breathing by having patient breathe in less dense gas (ex. helium)
What are the properties of transitional flow?
Properties fall in between laminar and turbulent flow.
When does turbulent flow occur, and what are the characteristics of it?
Turbulent flow occurs at high flow rates, particularly in branching or irregular tubes, and results in the disorderly flow of gas
Describe the three types of flow and where they are found in the airway.
- Turbulent flow: trachea
- Transitional flow: most of the airway
- Laminar flow: alveoli
What is the Reynolds number?
The Reynolds number is a way to predict the nature of gas flow
What is the equation for the Reynolds number?
and which factor has the most effect on whether flow is turbulent or laminar?
Linear velocity makes the most different for turbulent or laminar flow (because its the only part of the process we can effect/manipulate)
Where is airway resistance the highest?
Airway resistance is highest in medium sized bronchi and lowest in small airways
How do we calculate airway resistance?
Airway Resistance =
Name and describe the four grades of airway resistance.
Grade One: Slight Resistance: pt. can indefinitely sustain normal alveolar function
Grade Two: Moderate Resistance: there is an increased work of breathing to maintain alveolar ventilation
Grade Three: Severe Resistance: pt. is unable to preserve normal alveolar ventilation
Grade Four: Respiratory Obstructive: completely airway obstruction, incompatible with life if not rectified right away (ex. pt. biting on ETT)
If a child with epiglottitis is crying and hyperventilating, what is our goal as practitioners to improve the status of the airway?
As the child is crying, the velocity of the airway is increased... which is INCREASING airway resistance... THATS BAD!
Our goal is to stop the crying, calm the baby in order to keep airway resistance low by decreasing the velocity of the air coming into it !
Name some causes of increased airway resistance.
- 1. material within the lumen of the airway (ex. mucous plug in the ETT)
- 2. thickening or contraction of the wall of the passage (bronchospasm, mucosal swelling, secretions)
- 3. intraluminar obstruction of the lower respiratory tract (tumor, edema fluid)
- 4. MOST IMPORTANT: DISEASES!! (asthma)
During inhalation, the lungs create a __________ pressure.
Elastic recoil increases and intrapleural pressure decreases [-5 to -8]
Breathing normally: negative pressure
Mechanical ventilation: _____________
Process of inhalation is kickstarted by:
a decrease in alveolar pressure [-1]
Resistance is highest at ________ lung volumes.
- -Airway collapse occurs more readily because the airways are smaller
- -Airway of 3L has much higher resistance than airway of 6L
- -Alveoli at base of the lungs are much more prone to collapse at low lung volumes (atelectasis)
Resistance is lowest at _______lung volumes.
- -Resistance decreases and gas trapping is prevent at high lung volumes
- -We can increase lung volume by increasing PEEP, BiPAP, CPAP to decrease airway resistance
- -Alveoli less likely to collapse at high lung volumes
Why do COPD patients compensate with pursed lip breathing?
They exhale slower to keep their lung volume high in order to prevent airway collapse
What is closing capacity?
The lung volume at which dependent airways close
Closing capacity increases with:
- (a) lung disease
- (b) normal aging
True or False: the relationship between FRC and closing capacity determines airway patency.
True or False: In clinical practice, we expect more airway closure when pt is in a supine position.
True or False: Rate of exhalation depends on airway compression.
When airway pressure is less than intrapleural pressure, what happens?
Name some factors that can increase the predisposition to airway collapse.
- 1. loss of recoil: pressure inside the airways is lower, airway collapse occurs- ie elderly
- 2. narrow airway: increases air flow resistance
What are the four pathways of muscular control of airway diameter?
- 1. Neural Pathways- important efferent release of acetylcholine (c. smooth mm contraction)
- 2. Humoral control- bronchial smooth mm has Beta receptors (mechanism by which beta agonists/albuterol works to increase airway diameter)
- 3. Direct physical and Chemical Effects- bronchoconstriction caused by cold airway, gastric acid in airway, endotracheal tube
- 4. Local Cellular Mechanisms- mast cell degranulation, histamine release (narrows airway in bronchoconstriction)
Work of breathing over comes what 2 main sources of impedance?
- 1. ELASTIC RESISTANCE
- 2. AIR FLOW RESISTANCE
What patients have increased elastic resistance?
If we were ventilating them, where is their work of breathing least?
Pulmonary Fibrosis patients! Stiff lungs!
Work of breathing least at low tidal volumes and increased respiratory rates
What patients have increased air flow resistance?
If we were ventilating them, where is their work of breathing least?
Work of breathing least at high tidal volume and low respiratory rates
How can you calculate the work of breathing?
What is a normal value for efficient percent in work of breathing?