module 11 mechanics of breathing Flashcards
4 mechanics of breathing
airway resistance
lung compliance
opposing lung forces (elastic recoil vs chest wall expansion)
work of breathing
lungs and recoil
lungs have natural recoil tendency
chest wall prefers expansion
inspiration
- chest wall muscles contract elevating ribs, diaphragm moves down
expiration: - lung deflates passively d/t recoil and relaxation of diaphragm
lung during heavy breathing (exercise)
elastic forces not strong enough to cause rapid expiration
- abd. muscles contract pushing up
- > compression of lungs
muscles of inspiration
Major:
- intercostal muscles
- diaphragm
- recuts abdominis
accessory: when major are tired - serratus posterior superior
- sternocleidomastoid
- scalenus muscles
- intercostal muscles
airway resistance
resistance = driving pressure/rate of airflow
influence by radius and pattern of gas flow
- resistance inc. as radius dec.
– radius dec. from trachea to terminal bronchioles
pattern of gas flow
turbulent flow
- bronchospasm
laminar
transitional
turbulent flow
nasal cavity -> large bronchi
- inc. friction and resistance
laminar
small airways
smooth flow
transitional flow (mixed)
large airway bifurcations
newborns and resistance
increased until about 5 y/o
lung compliance
compliance = change in volume/ change in pressure
- lung expandability and ease of lung inflation
2 factors
- chest wall expandability
- lung expandability
peds and compliance
increased in neonates and peds < 3.5 yrs
- chest wall flexibility
elderly and compliance
dec compliance
- chest wall rigidity
- dec. motility of ribs
- partial contraction of inspiratory muscles
disease processes affecting compliance
- > stiffer lungs
- pneumonia
- pulmonary edema
- atelectasis
- ARDS
- pulmonary fibrosis
- obesity
- abd. distention
- pregnancy
- kyphosoliosis
- abd. surgery
abnormal inc. in lung compliance w/ loss of elastic recoil
-> WOB d/t inc. effort to exhale
functional components of respiratory system
neurochemical control of ventilation
mechanics of breathing
gas transport
control of pulmonary circulation
neurochemical control
neural control: respiratory center - medulla oblongata - pons Chemoreceptors: - central - peripheral Baroreceptors Proprioceptors Environmental factors
Stimulation to breathe
inc in arterial CO2
respiratory center
efferent nerve impulses form brain -> diaphragm via phrenic nerve -> muscular contraction -> inhalation
medullary center
dorsal respiratory group:
- stimulate inspiratory muscles: intercostal and diaphragm
- ramp signal: generated in increasing fashion. begin slowly and inc. for 2 seconds -> inspiration
abruptly stop for 3 seconds -> expiration
upper pons
pneumotaxic center
- influence rate of respirations
- ends inspiration by inhibiting ramp
lower pons
apneustic center
- pattern of respiration
- provide extra driving force for inspiratory neurons
- > prolonged inspiration
sensory inputs
central chemoreceptors peripheral chemoreceptors Hering-Breuer stretch receptors proprioceptors baroreceptors environmental sensations
central chemoreceptors
change in CO2 and pH
- increase
peripheral chemoreceptors
aortic arch and carotid
sense dec. in arterial O2
hering-breuer reflex
alveolar septa, bronchi, and bronchioles
- inflation of lungs -> vagus nerve stimulation to medulla -> inhibition of inspiration
- affects rate and duration
- primarily seen in neonates at and high tidal vol. (>1500mL)
- prevents overinflation
proprioceptors
muscles and tendons
- body movement -> respiratory rate and depth to maintain O2
baroreceptors
aortic arch and carotid
- sense change in BP
- inc. BP -> dec. respiration
- dec. BP -> inc. respiration
environmental sensations
cold shower pain airway irritation stress smoking infection fever exercise
Distribution of blood flow in lungs
affected by body position and exercise
- upright: blood flow dec. in upper regions of lungs (apices) compared to bases
- supine: blood to posterior is inc. more than anterior
affects of gravity
Perfusion: pulmonary blood flow
pulmonary circulation is a low pressure system and distribution of blood flow is uneven
- zone 1
- zone 2
- zone 3
Zone 1
upper regions of lungs
minimal blood flow
r/t enlarged alveolar sacs -> pressure > capillary pressure -> capillary collapse
- no gas exchange
Zone 2
middle region of lungs
pulmonary artery pressure > pressure in alveoli during systole, but may fall below during diastole
- intermittent perfusion
zone 3
bases of lungs
pulmonary arterial pressure > venous pressure > alveoli pressure
-> capillary vessels distended, dec. vascular resistance
O2 requires high pressure gradient to diffuse
PO2 in alveoli: 104
PO2 in capillaries: 40
affinity of hemoglobin for O2 and shifting of curve
normal curve: normal affinity of hgb for O2
left shift: inc. affinity of hgb for O2
- helps loading of O2 in lungs, decreased release to tissues
right shift: dec. affinity of hgb for O2
- aids in release of O2 to tissues
factors shifting curve to left
increased affinity for O2
- dec. H+, inc. pH
- dec. PCO2
- dec. temp
- hypothyroidism
- carboxyhemoglobin
factors shifting curve to right
decreased affinity for O2
- inc. H+, dec. pH
- inc. PCO2
- inc. temp
- hyperthyroidism
- anemia
- chronic hypoxemia
- high altitude, congenital heart disease
alveoli hypoxic vasoconstriction
alveolar hypoxia -> vasoconstriction r/t no diffusion at that alveoli, body sends blood elsewhere
chronic alveolar hypoxia -> chronic vasoconstriction -> chronic pulmonary HTN
carbon dioxide diffusion and transport
dissolved in plasma (5-10%)
bicarbonate (60-70%)
carbamino compound on hgb (20-30%)
respiratory membrane
what CO2 and O2 pass through for diffusion
- surfactant
- alveolar membrane
- interstitial fluid
- capillary membrane
- plasma
- RBC
O2 concentration in alveoli and partial pressure controlled by
rate of absorption in blood
rate of entry of new O2 into lungs
diffusion capacity impairment
alveolar thickening or capillary membrane
- pneumonia
- pulmonary edema
- interstitial lung disease
dec. surface area - emphysema
inc. physical activity - dec. time of RBC in capillary
factors that determine ability to diffuse
surface area of alveoli and capillaries
integrity of capillary and alveolar membranes
available hemoglobin
solubility of gas
diffusion coefficient of the gas
differences in partial pressure (concentration)
O2 transport mechanisms
dissolved in plasma ( 0.3mL O2/ 100mL blood)
bound to Hgb
- once at area of low O2 partial pressure hgb releases O2
