46 & 47: Respiratory Muscles & Breathing Cycle Flashcards
Muscles of Inspiration
Scalene
Sternomastoid
External Intercostals
Diaphragm contracts
Muscles of Expiration
Rectus Abdominis
Internal Intercostals
Obliques
Transversus Abdominis
Diaphragm relaxes
Bucket Handle
muscles pull ribcage downwards and inwards, increasing IP pressure, squeezing air out of lungs
Diaphragm
main muscle responsible for driving ventilation during tidal breathing
contraction and shortening pull it flatter
increase the volume inside the thoracic cavity
Pleural Membrane
visceral pleural:
is physically attached to the lung surface
parietal pleural:
membrane is attached to the wall of the thorax and diaphragm
Pressure Equation
Force/Area
increasing area (volume) decreases pressure
Combined Gas Laws
P1V1/T1 = P2V2/T2
increase temperature = increase in volume
Boyle’s Law
P1V1 = P2V2
closed system: pressure falls as volume expands
open system: airflow inward until pressure inside = P(ATM)
Intrapleural pressure (PIP)
pressure inside pleural space
Alveolar pressure (PA)
pressure inside alveolus
Transmural pressure (PTM)
any pressure gradient across a wall
Transpulmonary pressure (PTP)
lung elastic recoil pressure
transmural pressure across the alveolar wall (PA-PIP)
Pressure Changes during Breathing
Pleural pressure falls (from -5 to -8)
Transpulmonary pressure gradient increases
(PTP = PA – PIP)
alveolar expansion
Alveolar pressure falls (from 0 to -1)
How long does inspiration take?
2 seconds
How long does expiration take?
3 seconds
longer than inspiration b/c of increased airway resistance, pressure gradient larger
Lung Compliance
Pressure Volume Relationship
C = ΔV(l)/ ΔP(tp)
C = 1/E
Hysteresis
the pressure/volume relationship differs depending on inflation or deflation
What forces are needed to overcome in lung compliance?
Airway resistance
Frictional forces
Inertia of air + tissues
Elasticity of lung
What happens if lungs are filled with saline so there is no surface tension?
hysteresis is not apparent
Surface Tension
Intermolecular forces of attraction
Molecules at surface are only attracted from below and with each other
the surface of liquid acts as an elastic sheet
Force per unit length/ energy per unit area
LaPlace’s Law
P = (n)T / r
T surface tension, r radius
↑ radius ↓P
↓ radius ↑P
Surface Tension and Alveoli
Small alveoli develop a large pressure
Large alveoli develop a smaller pressure
air from smaller to larger alveoli
small alveoli collapse and large alveoli to fill
Surfactant
lipoprotein rich in phospholipid
secreted by type II cells
reduces surface tension by increasing lung compliance
alveoli shrink, surfactant conc. increases, surface tension decreases
Surfactant Constituents
90% Phospholipids:(phosphatidylcholine; DPPC)
10% Proteins:
SPA, SPB, SPC, SPD
Surfactant and Surface Area
Smaller surface area, surfactant closely packed, surface tension is less
Larger surface area, surfactant spread out, surface tension is more
Lung High Compliance
Walls of lung thinner
Higher surfactant
Large volume change; lung inflates easily and has little elastic recoil
air trapped inside must use extra force to get it out
Emphysema
COPD
Lung Low Compliance
Walls of lung thicker
lung inflates with difficulty due to large elastic recoil
Low surfactant, labored breathing
Pulmonary fibrosis
Respiratory distress syndrome
FRC
Functional Residual Capacity
Volume of the lung at rest between breaths
lung volume at which the inwardly directed lung recoil is exactly
balanced by the outwardly directed chest wall recoil
the volume of the lung when there is no active muscle input
