Resp. Mechanics (3) Flashcards
What are the 3 goals that need to be met in order for effective gas exchange?
1) to provide large, microscopically thin interface between air and blood for gas exchange
2) to deliver air and blood evenly over the interface as efficiently as possible
3) to keep the interface clean and dry
ribs role in respiration
- physical expandability of the rib cage provides the condition for air movement
- ribs, with its tendency to spring outward (compliance), sustains a negative pressure around the lungs
Diaphragms role in respiration
- MAIN MUSCLE OF INSPIRATION
- Generates a negative pressure
- DIAPHRAGM has LITTLE role in expiration
- diaphragm paralysis or subdiaphragmatic ascess cause significant decrease in inspiration
- in these situations accessory muscles have to be employed for effective quiet breathing
Intercostal muscles role in Inspiration
- External and internal intercostal muscles connect neighboring ribs, but oriented 90 degrees at eachother (provide opposing effects)
- contraction of external intercostals RAISES RIB CAGE (allowing inspiration)
- Contraction of Internal intercostals muscles LOWERS RIB CAGE, facilitating EXPIRATION
- *contraction of intercostals during INSPIRATION is a sign of DYSPNEA
scaleni and sternocleidomastoids role in INSPIRATION
Raises the first and second ribs, contributing to INSPIRATION
- NOT USED during normal quiet breathing
- visible contraction of these muscles signifies DYSPNEA
describe muscles of EXPIRATION
- Abdominal wall muscle contraction forces the diaphragm UPWARD, causing expiration
- NORMAL: expiration is more of a passive process - relaxation of diaphragm in addition to intrinsic recoil of lung tissue cause relaxation
- ABSENCE of abdominal muscles or abdominal muscle pain may cause limited FORCED EXPIRATION
Describe breathing sequence during INSPIRATION
1) brain –> nerves –> inspiratory muscles
4) Thoracic volume INCREASES as the chest wall expands
5) Intrapleural pressure becomes more negative
6) Alveolar transmural presure gradient INCREASES
7) alveoli expand; increases alveolar elastic recoil
8) alveolar pressure falls below atmospheric pressure as the alveolar volume increases, thus establishing a pressure gradient for airflow
9) air flows into the alveoli until alveolar pressure equilibrates with Atmospheric pressure
describe breathing sequence during EXPIRATION
1) brain ceases inspiratory command –> inspiratory muscles relax
2) Thoracic volume decreases, causing intrapleural pressure to become LESS NEGATIVE and DECREASING alveolar transmural pressure gradient
3) decreased alveolar transmural pressure gradient allows INCREASED alveolar elastic recoil to return to pre-inspiratory volume
4) decreased alveolar volume increases alveolar pressure above atmospheric pressure, thus establishing a pressure gradient for AIRFLOW
5) air FLOWS OUT of the alveoli until alveolar pressure equalibriates with ATM
Passive vs active expiration
- under normal conditions, expiration is passive
- expiration is ACTIVE in pathological states that require efforts to expel air, SUCH AS ASTHMA, BRONCHITIS, or CHRONIC OBSTRUCTIVE pulmonary disease
LUNG COMPLIANCE
- lung compliance is the extent to which the lungs will expand for each unit increase in transpulonary pressure
- -> reflects LUNG DISTENSIBILITY
- expressed by slope between two points on pressure-volume curve (during expiration limb)
What are the determinants o flung compliance
- elastic forces of lung tissue (elastin and collagen)
- Elastic forces of surface tension
HYSTERESIS b/w inspiration and expiration pressure-volume relationship - differences in inspiration and expiration limbs of pressure volume loop due to SURFACE TENSION
describe SULFACTANT
- synthesized by Type II epithelial cells
- secreted into alveolar spaces
- DECREASES SURFACE TENSION of alveolar aqueous surface
- prevent atelectasis following expiration during breathing
- main component = lecithin
Describe the use of Lecithin/sphingomyelin ratio in clinical setting
- lecithin/sphingomyelin ratio in amniotic fluid is a measure of FETAL LUNG MATURITY
- fetal lungs produce primarily sphingomyelin
- during 3rd trimester, type II pneumocytes convert glycogen to lecithin
- Indivates risk of RESPIRATORY DISTRESS SYNDROME (RDS)
Define Infantile respiratory distress syndrome
- newborns with ineffective lecithin or premature newborns are at high risk of respiratory distress upon delivery
- use of L/S ratio to measure the maturity of fetal lungs
- TREATMENT = corticoid, positive end expiratory pressure (PEEP) ventilation
Emphysema
INCREASED LUNG COMPLIEANCE
- loss of elastic fibers in the lungs
- lungs compliance increases
- steeper slope of pressure-volume curve
- HIGHER FRC
- breathes at higher lung volumes
- BARREL-SHAPED CHEST
