Lecture 2: Mechanics Of Respiration Flashcards
What are the 4 goals of the respiratory system?
- Distribute air and blood flow for gas exchange
- Provide oxygen to cells in body tissues
- Remove carbon dioxide from body
- Maintain constant homeostasis for metabolic needs
What are the four functional events of respiration?
- Mechanics of pulmonary ventilation
- Diffusion of O2 and CO2 between alveoli and blood
- Transport of O2 and CO2 to and from tissues
- Regulation of ventilation and respiration
What is EXTERNAL respiration?
- Mechanics of breathing
- Movement of gases into and out of body
- Gas transfer from lungs to tissues of body
- Maintain body cellular homeostasis
What is INTERNAL respiration?
- Intracellular oxygen metabolism
- Cellular transformation
- Krebs cycle—aerobic ATP generation
- Mitochondria and O2 utilization
What is the main purpose of ventilation?
To maintain an optimal composition of alveolar gas
Alveolar gas acts as a ___ ___ ___ between the ___ and ___.
- stabilizing buffer compartment
- between the environment and pulmonary capillary blood
How does alveolar gas act as a stabilizing buffer compartment? (3 things)
- Oxygen is constantly removed from alveolar gas by blood
- Carbon dioxide continuously added to alveoli from blood
- O2 replenished and CO2 removed by process of ventilation, by simple diffusion
What provides the stable alveolar environment?
The two ventilation phases—inspiration and expiration
Breathing is the act of ___
Creating inflow and outflow of air between the atmosphere and the lung alveoli
How much does the lung weigh?
- 1.5% of body weight
- 1 kg in 70 kg adult
Alveolar tissue is ___ of lung weight
60%
Alveoli have ___
Very large surface area—40x the external body surface area
___ diffusion pathway for gases
Short
What does the short diffusion pathway for gases permit?
Permits rapid and efficient gas exchange into blood—only 1.5 micrometers between the air and alveolar capillary RBC (very thin layer)
What is the blood volume in the lung?
500 mL (10% of total blood volume)
Respiratory muscles generate ___ to inflate and deflate the lungs
Force
What are two things that impede ventilation?
Tissue elastance and resistance
What are two other factors that alter lung volumes?
- Distribution of air movement within the lung, resistance within the airway
- Overcoming surface tension within alveoli
Air flow requires ___
A pressure gradient
Air flows from ___ to ___ pressures
High to low
During inspiration, alveolar pressure is ___
Sub-atmospheric, allowing air flow into the lungs
During expiration, alveolar pressure is ___
Higher than atmospheric pressure, allowing airflow out of the lungs
What generates changes in alveolar pressure?
Changes in pleural pressure
Inspiration is the ___ phase of the breathing cycle
ACTIVE phase
What nerves transmit motor stimulation to the diaphragm?
Phrenic nerve—C3, 4, 5
What nerves send signals to the external intercostal muscles?
Intercostal nerves T1-T11
Describe what happens during inhalation (4 main things)
- Thoracic cavity expands to lower pressure (to sub-atmospheric) in pleural space surrounding the lungs
- Pressure in alveolar ducts/alveoli decreases
- Fresh air flows through conducting airways into terminal air spaces until pressures are equalized
- Lungs expand passively as pleural pressure falls
The act of inhaling is ___
Negative-pressure ventilation
What is the most important muscle of inspiration?
Diaphragm
The diaphragm is responsible for ___ of inspiratory effort
75%
What is the diaphragm?
Thin, dome-shaped muscle attached to the lower ribs, xiphoid process, lumbar vertebra
What is the diaphragm innervated by?
Phrenic nerve—C3, 4, 5
During contraction of diaphragm—abdominal contents are forced ___
Downward and forward, causing an increase in vertical dimension of chest cavity
During contraction of diaphragm—rib margins are ___
Lifted and moved outward, causing increase in the transverse diameter of the thorax
How much does the diaphragm move down during normal inspiration?
1 cm
How much does the diaphragm move down during forced inspiration?
10 cm
What happens to the diaphragm when paralyzed?
- Paradoxical movement
- Upward movement with inspiratory drop of intrathoracic pressure
- Occurs when the diaphragm muscle is denervated (paralyzed)
What is transdiaphragmatic pressure?
When the effect of abdominal pressure on the chest wall mechanics is transmitted across the diaphragm
In supine position, abdominal pressure equals ___
Atmospheric pressure (when respiratory muscles are relaxed)
What happens to the diaphragm when abdominal pressure is increased?
The diaphragm is pushed cephalad (towards the head) into the thoracic cavity, decreasing functional residual capacity (FRC)
FRC is reduced by…
Increased intra-abdominal pressure situations
Examples: pregnancy, obesity, bowel obstruction, laparoscopic surgery, ascites, abdominal mass, hepatomegaly, trendelenburg position, valsalva maneuver
What are 3 positions that can decrease abdominal pressure and allow easier lung ventilation?
- Upright
- Reverse trendelenburg
- Prone position
What do the external intercostal muscles connect to?
Adjacent ribs
EIM are responsible for ___ of inspiratory effort
25%—diaphragm is responsible for 75%
Where do the nerves that innervate the intercostal muscles (intercostal nerves) originate?
Motor neurons to the EIM originate in the respiratory centers of the brainstem and travel down the spinal cord
Where do the intercostal nerves originate?
T1-T11
-The nerves pass under each rib along with the intercostal veins and arteries
Contraction of the EIM pulls the ribs ___
Upward and forward—ribs move outward in “bucket-handle” fashion
What happens to the diameters of the thorax when the EIMs contract?
Thorax diameters increase in both lateral and anteroposterior directions
What nerves innervate the EIMs?
Intercostal nerves
What happens with paralysis of the EIMs?
Inspiration is not seriously altered because the diaphragm is so effective
-Sensation of inhalation is decreased (i.e.: may see this in pregnant women under spinal anesthesia)
What do the accessory muscles of inspiration do?
They assist with forced inspiration during periods of stress or exercise
Scalene muscle
- Attaches cervical spine to apical rib
- Elevates the first two ribs during forced inspiration
Sternocleidomastoid muscle
- Attaches base of the skull (mastoid process) to top of sternum and clavicle medically
- Raises the sternum during forced inspiration
What are two accessory muscles of inspiration?
- Scalene muscle
- Sternocleidomastoid muscle
Expiration is the ___ phase of the breathing cycle
PASSIVE phase
During expiration—chest muscles and diaphragm ___
Relax
During expiration—pleural and alveolar pressures…
Rise
During expiration, gas flows ___
Passively out of the lung
Expiration is active during ___ and ___
Hyperventilation and exercise
What does active expiration require?
Abdominal and internal intercostal muscle contraction
What are 3 different muscles of active expiration?
- Rectus abdominis
- Abdominal oblique muscles
- Internal intercostal muscles
Rectus abdominis/abdominal oblique muscles (function)
- Contraction raises intra-abdominal pressure to move diaphragm upward
- Intra-thoracic pressure raises and forces air out from lung
How do the internal intercostal muscles assist with active expiration?
- Pull the ribs downward and inward
- Decrease thoracic volume
- Stiffen intercostal spaces to prevent outward bulging during straining
The muscles of active expiration also contract forcefully during ___, ___, and ___
- coughing
- vomiting
- defecation
What is transpulmonary pressure?
-The pressure difference between the alveolar pressure and pleural pressure on the outside of the lungs
What happens to the alveoli when the pleural pressure attempts to pull outward?
Alveoli tend to collapse together
What is recoil pressure?
The elastic forces which tend to collapse the lung during respiration
What are two parts of the pleural membrane?
- Visceral pleura
- Parietal pleura
What is visceral pleura?
A thin serosal membrane that envelopes the lobes of the lungs (surrounds the lungs)
What is parietal pleura?
Lines the inner surface of the chest wall, lateral mediastinum, and most of the diaphragm
The pleura space is enclosed by a ___
Continuous membrane
The two pleural membranes (visceral and parietal)…
- slide against each other
- are difficult to separate apart
What are the two pleural membranes separated by?
Separated by a thin layer of serous fluid
-A large amount would be a pleural effusion, as seen in CHF, CA, infection
What is the pleura sac?
-Contains both pleural membranes and a small amount of fluid inbetween them (serous fluid)
What does pleural fluid do?
- Functions as a lubricant between the membranes, prevents frictional irritation
- Causes the visceral and parietal pleura to adhere together, maintains surface tension
- Lymphatic drainage maintains constant suction on pleura (-5cm H2O)
What is pleural pressure?
-The pressure of fluid in the space between the lung pleura (visceral) and chest wall pleura (parietal)
Pleural pressure is always ___
Negative
Normally at rest, suction creates a ___ pressure
NEGATIVE pressure at the beginning of inspiration (-5 cm H2O)
What holds the lungs open at rest?
Negative pressure (-5 cm H2O)
Pressure becomes more ___ during inspiration
More negative—moving to -7.5 cm H2O, allowing for negative pressure respiration
What happens if pleural pressure becomes positive?
The lung will collapse—i.e.: pneumothorax, hemothorax, chylothorax
TLC =
IRV + TV + ERV + RV
Total lung capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume + residual volume
VC =
IRV + TV + ERV
Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume
FRC =
ERV + RV
Functional residual capacity = expiratory reserve volume + reserve volume
IC =
TV + IRV
Inspiratory capacity = tidal volume + inspiratory reserve volume
How many pulmonary volumes and capacities are there, and what are they based on?
- 4 volumes, 4 capacities
- Effort dependent
- Values vary based on height, age, sex, and physical training
IRV =
2.5 L
TV =
0.5 L
ERV =
1.5 L
RV =
1 L
IC =
3 L
IC = TV + IRV
VC =
4.5 L
VC = IRV + TV + ERV
FRC =
2.5 L
FRC = ERV + RV
TLC =
5.5 L
TLC = IRV + TV + ERV + RV
What does spirometry NOT measure?
Residual volume (RV)
What can’t be measured using spirometry alone?
Functional residual capacity (FRC) and total lung capacity (TLC)
What are 3 ways we can determine FRC and TLC?
- helium dilution
- nitrogen washout
- body plethysmography
What does compliance measure?
Compliance is a measure of the distensibility of the lungs
Compliance =
Change in lung volume/change in lung pressure
The extent of lung expansion is dependent on an increase in ___
Transpulmonary pressure
What is normal static compliance?
70-100 mL of air/cm of H2O transpulmonary pressure
What can reduce lung compliance?
- Higher or lower lung volumes
- Higher expansion pressures
- Venous congestion
- Alveolar edema
- Atelectasis
- Fibrosis
What increases lung compliance?
-Age and emphysema secondary to alterations of elastic fibers
What are the two fibers in elastic lung tissue?
- Elastin
- Collagen
What is the natural state of the elastin and collagen fibers?
Contracted coils
How does the elastic lung tissue assist to deflate the lungs?
- After the elastic fibers (elastin and collagen) are stretched and elongated, they return to a coiled state, thus generating an elastic force
- The recoil force (the fibers returning to a coiled state) is what deflates the lungs
What comprises 2/3 of the elastic force in the lung?
-The surface air-fluid interface (air entering the lungs + water/surfactant in the lung)
What holds the alveoli open?
-Complex synergy between air and fluid
What does surfactant do?
-Surfactant in the alveoli reduces the surface tension of water and keeps the alveoli from collapsing
How does water tension contribute to the elastic force of the lung?
- Water has a strong attraction to itself, causing high tension—the tension creates an elastic force
- This elastic force caused by water tension attempts to force air out of the alveoli
What is surfactant/what does it do?
- Fatty-acid product of type II pneumocyte (DPPC)
- Surfactant lowers the surface tension of alveolar fluid
What are the ends of the DPPC molecules?
-Hydrophobic and hydrophilic opposing ends
How does DPPC reduce alveolar surface tension?
-DPPC opposes water’s self-attractant elastic force, thus reducing alveolar surface tension
Effect of water on alveoli
Water attracts itself, causing high surface tension in the alveoli; this forces air out of the alveoli
Effect of DPPC on alveoli
DPPC (surfactant) decreases the surface tension of water by breaking up water’s self-attracting forces; this prevents alveolar collapse
What are 3 main functions of surfactant?
- Lowers surface tension of alveoli and lung (increases compliance, reduces work of breathing)
- Promotes stability of alveoli (prevents alveolar collapse)
- Prevents transudation of fluid into alveoli (prevents surface tension forces from drawing fluid into alveoli from capillary)
Total ventilation is AKA
Minute ventilation
Minute ventilation is…
The total volume of air conducted into the lungs per minute
Minute ventilation =
Tidal volume x frequency (number of breaths in one minute)
What is alveolar ventilation?
The volume of fresh air entering the alveoli each minute (70% of total minute ventilation)
Alveolar ventilation is always ___ total (minute) ventilation
Less than
When is an alveolar O2 concentration steady state achieved?
When supply matches demand
What is dead space?
Dead space = ventilated, but not perfused
Dead space is the portion of tidal volume fresh air that…
Does not go directly to the terminal respiratory units; stays in the conducting airways, no gas exchange occurs (~30% of each breath, 150 ccs of tidal volume or 2 ccs/kg)
The conducting airways do not participate in…
Gas exchange
Dead space is approximately how much of ideal body weight?
2 ccs/kg of ideal body weight
Anatomic dead space is different from ___
Physiological dead space (wasted ventilation)
What is physiologic dead space?
- AKA wasted ventilation
- Describes a deviation from ideal ventilation relative to blood flow
Wasted ventilation (physiologic dead space, VPD) includes…
Anatomical dead space + any portion of alveolar ventilation that is not involved in gas exchange (alveolar dead space)
Alveolar dead space is…
Any portion of alveolar ventilation that is not involved in gas exchange (exchange of O2/CO2 with pulmonary blood flow)
Where do we see a V/Q mismatch?
Ventilation/blood flow mismatch is seen where blood flow is blocked (i.e.: d/t clot or emboli)
VT = VA + VD
Tidal volume = alveolar volume + anatomical dead space
VPD = VD + VAD
Wasted ventilation (or physiologic dead space) = anatomical dead space + alveolar dead space
VT = VA + VD + VAD
Tidal volume = alveolar volume + anatomical dead space + alveolar dead space
Is all the gas compressed out of the lungs during exhalation?
- No—small airways in region of respiratory bronchioles collapse
- Gas is trapped in distal alveoli
Dependent (down) regions of the lung are only…
Intermittently ventilated, leading to defective gas exchange (i.e.: patients who are positioned laterally for procedures)
What is closing volume (CV)?
Volume of the lung at which the small airways close
What happens if CV > FRC?
Then the small airways collapse during normal TVs, leading to atelectasis and hypoxemia
Airway closure occurs at ___ in normal young subjects in the lowermost lung regions
Very low lung volumes
Airway closure occurs in normal elderly lungs at ___ volumes and can be present at FRC
Higher
Airway closure frequently develops in ___
Patients with chronic lung disease
Air flow at low flow rates is ___
Laminar
Turbulence occurs at…
Higher flow rates or when there are changes in the air passageway (i.e.: airway branches/diameter/velocity/direction changes)
Laminar flow is…
Parallel streams of flow
Velocity in the center of the airway is ___ than at the edges of the tube
Twice as fast
Poiseuille’s Law
Describes resistance to flow through a tube
Poiseuille’s law—pressure increases proportional to ___ and ___
- flow rate
- gas viscosity
Poiseuille’s Law—___ and ___ increase flow resistance
- smaller airway radius
- longer distances
PL—Higher flow rate = ___ pressure
Higher pressure
PL—Higher viscosity = ___ pressure
Higher pressure
PL—smaller radius = ___ resistance
Greater
PL—longer distance = ___ resistance
Greater
PL—reducing the radius by 16% will ___ the resistance
Double the resistance
PL—reducing the radius by 50% will ___ resistance
Increase resistance 16-fold
Ohm’s Law
Pressure = Flow x Resistance
Resistance = Pressure / Flow
Turbulent flow occurs at ___
Higher flow rates
Increases in what 3 things can cause turbulent flow?
Increases in…
- density
- velocity
- airway resistance
What is the chief site of airway resistance?
The medium-sized bronchi
Very small bronchioles have ___ resistance
Very little
Air velocity in the small bronchioles is ___
Low; diffusion takes over
What are 3 factors that determine airway resistance?
- Lung volume
- Bronchial smooth muscle
- Density and viscosity of inspired gas
As lung volume is reduced, airway resistance ___
Increases
Contraction of bronchial smooth muscle (bronchoconstriction) ___ resistance
Increases
Higher gas density ___ resistance
Increases resistance to flow
Higher viscosity = ___ resistance
Increased
What has more influence on resistance of flow—density or viscosity?
Density
What can we use to determine the work of breathing?
Oxygen consumption measurements
O2 cost of quiet breathing
5% of total resting oxygen consumption
O2 cost of hyperventilation
30% oxygen consumption
O2 cost in obstructive lung disease
High O2 cost limits exercise ability
