Week 2 Mechanics Of Respiration Flashcards
What are the goals of respiration?
- distribute air and blood flow for gas exchange
- provide oxygen to cells in body tissues
- remove CO2 from body
- maintain constant homeostasis for metabolic needs
What are the functions of respiration?
Respiration is divided into four functional events:
- Mechanics of pulmonary ventilation
- Diffusion of O2 and COS2 between alveoli and blood
- Transport O2 and CO2 to and from tissues
- Regulation of ventilation and respiration
What is external respiration?
- mechanics of breathing
- the movement of gases into and out of body
- gas transfer from lungs to tissues of body
- maintain body and 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
The lungs make up what percentage of body weight?
1.5%
What is the alveolar surface area?
- 40x the external body surface
- 70m2 internal surface area
What is the benefit of short diffusion pathways for gases?
- Permits rapid and efficient gas exchange into blood
- 1.5um between air and alveolar capillary into blood
- blood volume in lung - 500mL (10% of total blood volume)
What are the factors required to alter lung volumes?
- respiratory muscles generate force to inflate and deflate lungs
- tissue elastance and resistance impedes ventilation
- distribution of air movement within the lung, resistance within the airway
- overcoming surface tension within alveoli
How does air flow during breathing cycle?
It moves from higher to lower pressure.
During inspiration, alveolar pressure is sub-atmospheric, allowing airflow into lungs
Higher pressure in alveoli during expiration than atmosphere allows airflow out of lung
Changes in alveolar pressure are generated by changes in pleural pressure
What is the active phase of breathing cycle?
Inspiration
what nerve transmits motor stimulation to diaphragm?
Phrenic nerve: Cervical segments 3, 4, 5
The diaphragm does what percentage of the work of breathing?
75%
The external intercostal muscles does what percentage of the work of breathing?
25%
The act of spontaneous inhalation is what type of ventilation?
Negative pressure ventilation
What happens during contraction of diaphragm?
- abdominal contents forced downward and forward
- rib margins are lifted and moved outward
- diaphragm moves down 1cm during normal inspiration
- during forced inspiration diaphragm can move down 10cm
What is transdiaphragmatic pressure?
Effect of abdominal pressure on chest wall mechanics is transmitted across the diaphragm
What happens when increasing abdominal pressure pushed diaphragm cephalad into thoracic cavity?
FRC decreases
What are examples of things that would increase intra-abdominal pressure and reduce FRC?
Pregnancy Obesity Bowel obstruction Laparoscopic surgery Ascites Abdominal mass Hepatomegaly Trendelenburg position Valsalva maneuver
What positions decrease abdominal pressure and allow easier lung ventilation?
Upright
Reverse trendelenberg
Prone
What happens if there is paralysis of external intercostal muscles?
Does not seriously alter inspiration bc diaphragm is so effective
Sensation of inhalation is decreased
When are accessory muscles used during inspiration?
During periods of stress or exercise
What are accessory muscles for respiration?
- scalene muscle
- elevate the first 2 ribs during forced inspiration
- sternocleidomastoid muscle
- raise the sternum during forced inspiration
What is the passive phase of the breathing cycle
Exhalation/expiration
What are the muscles of active expiration?
- reclusive abdominus/abdominal oblique muscles
- contraction raises intra-abdominal pressure to move diaphragm upward. Intra thoracic pressure raises and forces air out from lung
Internal interconstals muscles
- assist in expiration by pulling ribs downward and inward - decrease thoracic volume
*these muscles contract forcefully during coughing, vomiting and defecatioin
What is transpulmonary pressure?
- the pressure difference between the alveolar pressure and pleural pressure on outside of lungs
- the alveoli tend to collapse together while the pleural pressure attempts to pull outward
- the elastic forces tend to collapse the lung during respiration is recoil pressure
What are the partsof the pleural membrane?
- visceral pleura: this serosal membrane that envelope the lobes of the lung
- parietal pleura: lines the inner surface of the chest wall, lateral mediastinum, and most of diaphragm
What separates the pleural membranes?
A thin layer of serous fluid
*a large amount would be a pleural effusion as seen in CHF, CA, infection
What is the function of pleural fluid?
- functions as a lubricant between the membranes
- causes visceral and parietal pleura to adhere together, maintains surface tension
- lymphatic drainage maintains constant suction on pleura (-5cmH2O)
What is pleural pressure?
- the pressure of the fluid in the space between the lung pleura and chest wall
- always negative
- holds the lungs open at rest
- if becomes positive, the lung will collapse:pneumothorax, hemothorax, chylothorax (lymph)
What is normal pleural pressure?
- at rest: -5cmH2O
- during inspiration becomes more negative: -7.5cmH2O, allowing for negative pressure respiration
What is vital capacity?
The greatest volume of breath that can be expelled from the lungs after taking the deepest possible breath
VC = IRV + TV + ERV
What is inspiration capacity?
The total amount of air that can be drawn into the lungs after normal expiration
IC = TV + IRV
What is inspiration reserve volume?
The maximal amount of additional air that can be drawn into lungs by determined effort after normal inspiration
What is expiratory reserve volume?
The additional amount of air that can be expired from the lungs by determined effort after normal expiration
What is tidal volume?
The lung volume representing normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied
What is total lung capacity?
The volume of air contained in the lungs at the end of maximal inspiration
TLC = IRV + TV + ERV + RV
What is functional residual capacity?
The volume of air present in the lungs at the end of passive expiration
FRC = ERV + RV
What spirometry values cannot be measured?
-residual volume
Thus functional residual capacity and total lung capacity cannot be determined using spirometer alone
What is lung compliance?
It’s a measure of the distensiblity of the lungs
Compliance = change in lung/change in lung pressure
How do lung volumes change related to transpulmonary pressure?
In the presence of increased airway resistance or decreased lung compliance, an increased transpulmonary pressure is required to produce a given tidal volume and thus the work of breathing is increased
What creates the elastic forces of the lungs?
- elastic lung tissue
- elastin and collagen fibers of lung parenchyma
- natural state of these fibers is contracted coils
- recoil force assists to deflate lungs
- surface air-fluid interface
- 2/3 of total elastic force of lung
- surfactant in the alveoli fluid reduces surface tension, keep alveoli from collapsing
Does surfactant work better when molecules are closer together or farther apart?
Closer together
What are the functions of surfactant?
- lowers surface tension of alveoli and lung
- reduces work of breathing
- increases compliance of lung
- promotes stability of alveoli
- surfactant reduces forces causing atelectasis
- prevents transduction of fluid into alveoli
- decreases fluid from getting pulled in
What is minute ventilation or total ventilation?
Minute ventilation = Vt x frequency
Total volume of air conducted into lungs per minute
What is alveolar ventilation?
- volume of fresh air entering alveoli each minute (70% of total ventilation or minute ventilation)
- anatomical dead space and its portion of tidal volume (30%) affect amount of gas exchanged in alveoli
What is wasted ventilation?
The concept of physiologic dead space (Vpd) describes a deviation from ideal ventilation relative to blood flow
-for example: PE, air emboli, fat emboli
What is closing volume?
Volume of the lung at which small airways close. If CV > FRC then small airways collapse during normal TVs leading to atelectasis and hypoxemia
What are features of laminar flow?
- is parallel streams of flow
- velocity in center of airway is twice as fast than at edges of tube
What is Poiseuille’ Law
Describes resistance to flow through a tube
- pressure increases proportional to flow rate and gas viscosity - smaller airway radius and longer distances increase flow resistance
*huge increase in resistance by narrowing radius
What is Ohm’s Law?
P = F x R
P: pressure
F: flow
R: resistance
At what flow rate does turbulent flow occur?
Higher flow rates
What increases turbulent flow?
- density
- velocity
- airway resistance
What is the chief site of airway resistance?
Major resistance is at the medium-sized bronchi
What factors determine airway resistance?
Lung volume
-as lung volume is reduced - airway resistance increases
Bronchial smooth muscle
- contraction of airways increases resistance
Density and viscosity of inspired gas
- increased resistance to flow the elevated gas density - changes in density rather than viscosity have more influence on resistance
What helps to provide a stable alveolar environment?
The 2 ventilation phases
-inhalation and exhalation
- oxygen ins constantly removed from alveolar gas by blood
- CO2 continuously added to alveoli from blood
What nerve innervates the external intercostal muscles?
Intercostal nerves T 1-11
Originate from the ventral rami of T1-11
What happens to movement of the diaphragm when paralyzed?
*paradoxical movement of diaphragm
- upward movement with inspiratory drop of intrathoracic pressure
- occurs when the diaphragm muscle is denervated
What is abdominal pressure compared to atmospheric pressure in supine position when respiratory muscles are relaxed?
Abdominal pressure is equal to atmospheric pressure
When is exhalation active?
During hyperventilation and exercise
What is spirometry?
Measure the volumes of respriration
What is a Flow-Volume Loop?
A graph of the rate of airflow as a function of lung volume during a complete respiratory cycle consisting of a forced inspiration followed by a forced exhalation.
- used in assessing pulmonary function.
- Inspiration on bottom, expiration on top, looks like an upside down ice cream cone
What reduces lung compliance?
- Higher or lower lung volumes
- higher expansion pressures
- venous congestion
- alveolar edema
- atelectasis and fibrosis
What increases lung compliance?
- age
- emphysema secondary to alterations of elastic fibers
What is a compliance diagram?
Lung volume changes related to transpulmonary pressure
What is hysteresis?
Different curve for inhalation and exhalation, different lung volumes for each
What can be used to determine the work of breathing?
Oxygen conusumption
What is the chemical name of surfactant?
DPPC-Dipalmitoyl phosphatidyl choline
What is the Bernoulli effect?
When you breath through a pipe with various sizes, the flow is fastest through the narrowest portion. This can cause lower pressures at that point and airways to collapse
