cough Flashcards
the amount of gas dissolved in blood will depend on what 2 factors?
1) solubility of that gas in blood around alveolus - CONSTANT
2) pressure of that gas in the alveolar air - VARIABLE
what are the 2 reasons for why PO2 in alveoli (100mmHg) differs from atmospheric PO2 (160mmHg)
1) atmospheric P becomes saturated with water vapour (diluted by 47mmHg)
2) because of dead space, not all air is fresh with every breath
what is the partial pressure gradients of O2 and CO2 across pulmonary capillaries? - drive gas exchange
O2:
- 60mmHg (alveoli 100 > blood 40)
CO2:
- 6mmHg (blood 46 > alveoli 40)
how do we achieve changes in gas pressure from alveoli >pulmonary capillaries >systemic arterial blood
varying pulmonary ventilation by controlling the rate and depth of breathing
VE = TV x RF
(typically 500mL x 12/min = 6000mL/min at rest. can achieve 100mL/min during exercise)
what are the key elements of the respiratory control system?
sensors: receptors (chemoreceptors in aortic and carotid bodies and medulla - triggered by arterial CO2)
central controller: (pons and medulla in midbrain)
effectors: respiratory muscles
where is the major rhythm generator
medulla
how does the pre-Botzinger complex drive inspiration?
fires signals to the dorsal respiratory group (fundamental in initiating inhalation) that then fires in bursts, leading to contraction of respiratory muscles. when firing stops you get passive expiration
what happens in active expiration during hyperventilation?
increased firing of the dorsal neurones cause the excitation of ventral respiratory group which is normally inactive. Expiratory muscles (internal ICs and abdominal) produce forceful expiration
the basic rhythm set by the pre-Botzinger complex can be modified by what 2 opposing neurons in the pons?
1) pneumotaxic centre - controls the rate and pattern of breathing by terminating inspiration
2) apneustic centre - controls the intensity of breathing by prolonging inspiration. promotes inhalation by constant stimulation of DRG
what would happen without the pneumotaxic centre?
prolong inspiratory gasps with brief expiration = apneusis
describe how voluntary control of respiration (for speaking, singing, whistling) can be achieved
input to medullary control centre from cerebral cortex, bypassing resp.centres. signals sent directly to motor neurones in spinal cord that supply the resp. muscles.
will be overridden by rep.centres if hypo/hyper ventilate to extremes
what are the 4 reflex modifications of breathing (input into medullary control centres)?
1) Hering-Breuer reflex: pulmonary stretch receptors inhibit inspiration
2) irritant receptors: initiate reflex bronchial and laryngeal constriction, mucus production
3) Juxta-capillary receptors: respond to vol of fluid inducing changes in resp. rhythm
4) receptors in upper airways initiating cough and sneezes
what nerve stimulates the cough reflex? and what is the cough reflex?
vagus n.
- up to 2.5L air rapidly inspired
- epiglottis and vocal cords close, trapping air in lungs
- abs contract, push up against diaphragm. expiratory accessory muscles contract
- pressure in lungs increases
- epiglottis and vocal cords open suddenly, releasing air at 75-100 mph
- force is enough to collapse bronchi and trachea, air ejected through narrow slits
- irritant ejected
what chemical is the most important driver in regulating quiet ventilation?
PCO2
what is the most likely virus to cause rhinitis?
rhinovirus
or coronovirus
what percentage of tonsillitis is viral? and what is the most common bacterial cause?
50-80%
streptococcus group A (GABHS)
is pharyngitis (sore throat) usually a viral or bacterial infection?
viral. common respiratory viruses = adenovirus, coronavirus, enterovirus and rhinovirus
what is the viral and bacterial cause of otitis media (and mastoiditis)?
viral - RSV and rhinovirus
bacteria = streptococcus pneumoniae and haemophilus influenza
what URTI are you likely to get diarrhoea and vomiting ?
Otitis media
why would you get sinusitis secondary to viral URTI?
occurs as a secondary bacterial infection to common cold (which is usually viral). muscosal swelling prevents muco-ciliary clearance of initial infection. bacterial causes = S.pneumoniae, H.influenza, S,milleri
how does croup present and what is the viral aetiology?
stridor, seal like cough, sternal/intercostal recession (possible lethargy, agitation), preceded by fever and coryza. symptoms worse at night. peaks at 2/6months to 6years.
caused by parainfluenza virus
how does epiglottitis present and what is the viral aetiology?
rapid onset fever, sore throat, inability to control secretions, classic tripod positioning, difficulty breathing and irritability
caused by haemophilus influenza type b
compare croup and epiglottitis
croup vs epiglottitis:
- onset over days vs hours
- preceding coryza vs no coryza
- severe barking cough vs silence
- able to drink vs not able
- no drooling vs uncontrollable
- unwell looking vs toxic, very ill!!
- fever <38.5 vs >38.5
- harsh and rasping stridor vs soft and whispering
- hoarse voice vs muffled