physiology formative Flashcards
can functional residual capacity be measure with spirometry?
no
FRC = expiratory reserve volume (for big breaths out) + residual volume (whats left of Total lung capacity after biggest breath out)
–> not possible to measure residual volume with spirometry - hence not possible to measure functional residual capactity or total lung capacity)
(40% of total lung capacity)
how is residual volume affected by emphysema
increases ! - due to loss of elastic recoil in emphsema
confirmed diagnosis + classification of COPD
post bronchodilator FEV1/FVC <0.7
mild - FEV1 >=80%
mod - 50-79%
severe - 30-49%
v severe - <30%
what affect does anxiety inducing hyperventilation have on ABG
resp alkalosis
-> wash out of CO2
This results in decreased ionised (free) calcium – more Ca will bind to albumin if pH increases
o Decreased ionised calcium results in nerve excitability + hence numbness + tingling
—-> increased central + autonomic arousal
what affect does low pO2 have on pulonary arterioles?
pulmonary vasoconstriction
(opposite to systemic arterioles)
mechanism involved in causation of SOB in LV heart failure
reduced pulmonary compliance + impaired gas diffusion
-> due to pulmonary oedema
causes on increased lung compliance
- emphysema (Cx COPD) - loss of alveolar walls + assoc elastic tissue
- old age - loss og lung connective tissue
causes of decreased lung compliance
pulmonary fibrosis
pulmonary oedema
pneumonia
absence of surfactant
–> may cause restrictive lung patterns
define lung compliance
change in lung volume per unit change in transmural pressure gradient across lung wall
-> i.e difference between intraalveolar + intrapleural pressure
less compliant lungs -> more work required to produce degree of inflation
when is dynamic airway compression likely to occur in COPD?
active expiration !
Intrapleural pressure
- Falls during inspiration
- Rises during expiration
Dynamic airway compression
- Makes active expiration more difficult in patients with airway obstruction
Rising intrapleural pressure compresses alveolic (pushes air out) + airway (compressing it)
- Good in alveoli – driving pressure
- Undesirable in airway
–> becomes worse if emphysema too (decreased elastic recoil)
why is it important not to give excessive O2 to COPD patients with chronic CO2 retention
May increase V/Q mismatch by diverting blood flow to poorly ventilated alveoli
Increased release of CO2 from oxygenated haemoglobin (Halden Effect)
- COPD patients unable to increase ventilation to match the increase CO2 release
Maintain 88-92%
are patients hyper or hypotensive in during a tension pneumothorax?
hypotensive
- rise in pressure reduces amount of blood returning from body toheart because the blood cannot force its way into the chest back to the heart
-> heart has less blood to pump -> resulting in shock!
pressure changes in a pneumothorax
abolishes transmural pressure gradient - by raising intrathoracis pressure
–> leading to lung collapse
increase in intrapleural pressure - gradual
significance of the sigmoid shape in O2 Hb dissociation curve? flat upper portions vs steep lower
flatter upper - means moderate fall in alveolar pO2 will not much affect oxygen loading
steep lower part - means peripher tissues get a lot of oxygen for a small drop in capillary pO2
which key parameter guides O2 saturation
pO2 guides O2 saturation
(Hb level doesnt make a difference)
(-> but why you short of breath in anaemia then??? -> cos not enough o2 to tissues -> anaerobic resp -> lactic acid)
