Respiratory Flashcards
What are the cut-offs for pulmonary arterial (PA) systolic and mean pressures that define pulmonary hypertension (PH)?
PA systolic > 30mmHg, PA mean >20mmHg
List the 5 disease classes which can lead to pulmonary hypertension.
ACVIM consensus
Group 1 (pulmonary arterial hypertension) – primary diseases of the vasculature. E.g. idiopathic, familial, drugs/toxins, congenital heart disease (systemic-to-pulmonary shunts), HWD, veno-occlusive disease, persistent PH of newborns.
Group 2 (pulmonary venous hypertension) – left-sided heart disease & chronic increases in LA pressure. Valvular or myocardial dz. MOST COMMON in dogs.
Group 3 (PH associated with lung diseases or hypoxemia) – obstructive pulmonary disease, interstitial lung disease, alveolar hypoventilation, sleep apnea, chronic exposure to high altitude, developmental abnormalities.
Group 4 (PH associated with chronic thrombotic or embolic) – obstruction of proximal or distal PAs, non-thrombotic embolism (HWD or other parasites, neoplasia, foreign material – catheter or coil)
Group 5 (systemic & other disorders) – compression of pulmonary vessels, lymphadenopathy, neoplasia, fibrosing mediastinitis, granulomatous disease, others (histiocytosis, sarcoidosis, lymphangiomatosis)
Bronchial collapse occurs most commonly in which regions?
L cranial & R middle bronchi
Bronchial collapse occurs most commonly in which regions?
L cranial & R middle bronchi
Thoracic radiographs most sensitive for the diagnosis of airway collapse in which regions of the lungs?
Sn for the detection of bronchoscopically identified collapse was highest for radiography at the trachea, left lobar bronchi & right middle bronchus. But relatively low Sp.
What clinical sign can epiglottic entrapment of the soft palate cause?
Reverse sneezing
How to calculate estimated systolic PA pressure from echo?
Measure TRV max
Modified Bernoulli equation:
Pressure gradient (aka estimated systolic PAP) = 4 x (TRVmax)^2 in mmHg
ACVIM consensus panel’s definition (cut-offs) for pulmonary hypertension in dogs?
TR PG cut-off of >46 mmHg (TRVmax >3.4 m/s)
Defined as moderate PH historically
Specific treatment for PH targets which 3 pathways?
ACVIM consensus.
NO, endothelin & prostacyclin pathways
These mediate pulmonary arterial/arteriolar vasoconstriction (secondary to endothelial injury).
What is a rare disease to be suspected if a dog with pulmonary hypertension develops pulmonary oedema after sildanefil treatment? How does this occur?
ACVIM consensus
Pulmonary veno-occlusive disease or pulmonary capillary hemangiomatosis.
Also caution when administering PDE5-i in dogs with LHD & congenital shunts.
Reactive” or “responsive” pulmonary arteries (or arterioles) have an unpredictable response to tx. Increased right sided CO, acutely increases pulmonary VR to the LA»_space; subsequently increase LA & thus pulmonary venous and capillary pressures»_space; pulmonary oedema.
What anti-neoplastic drug may be considered as an adjunct treatment for refractory PH in dogs & MOA? What evidence is there to support its efficacy?
ACVIM consensus
TKIs (e.g. toceranib, imatinib) - cause PA vasodilation by inhibiting action of PDGF (by inhibiting phosphorylation of PDGF-receptor TK). Used in people, little data in dogs, but imatinib reduced PAP in dogs with PH 2’ to LHD in 1 study.
Define the 2 kinds of gas transfer, and list examples of gases under these classifications.
Diffusion limited: gas transfer is limited by the diffusion properties of the blood gas barrier. E.g. CO (binds with high affinity to Hb, pp doesn’t change in blood)
Perfusion limited: gas transfer limited by capillary blood flow. E.g. NO, CO2 (diffusion stops when capillary & alveolar P equilibrate). NB CO2 has 20x solubility in blood vs O2.
O2 is in between. Normally perfusion limited; when blood-gas barrier thickened > becomes diffusion limited.
(T/F) Hypoxic pulmonary vasoconstriction occurs as a local response secondary to changes in arterial PO2.
False. True as local response, but determined by alveolar PO2 (occurs regardless of PaO2 value)
(T/F) Hypoxic pulmonary vasoconstriction occurs as a local response secondary to changes in arterial PO2.
False. True as local response, but determined by alveolar PO2 (occurs regardless of PaO2 value). Marked vasoconstriction when PAO2 <70mmHg.
Which of the following causes of hypoxemia result in an increased A-a gradient?
- V/Q mismatch
- Diffusion limitation
- Shunt
- Hypoventilation
All except hypoventilation (A-a gradient is normal i.e. PaO2 = PAO2 +/- 10mmHg)
(Causes of hypoventilation = airway obstruction, decreased ventilatory muscle function e.g. GA, CNS disease, polyneuro/myopathy, NMJ dz, fatigue), chest wall/pleural space dz, COPD
One of the main regulators of ventilation involves the effect of PaCO2 on……
CSF pH (CO2 diffuses across BBB > H+ + HCO3-, where H+ is a potent stimulator of central chemoreceptors in the chemosensitive area in the medulla > inspiration)
NB: CO2 is the most potent (indirect) stimulator of CSF pH (not H+ directly)
Increased PaCO2 –> cerebral vasodilation –> increased ICP
What % of dogs with laryngeal paralysis are diagnosed with hypothyroidism? Does thyroxine supplementation help to improve clinical signs of lar par?
30% (but no direct association proven).
No.
What treatments are available for treatment of nasopharyngeal stenosis in dogs/cats? Recurrence and complication rates?
Berent VCNA review
1. Balloon dilation + topical mitomycin C 0.1% OR triamcinolone submucosal inj:
- Cats - 50% success (typically thinner, patent, caudal NP). Dogs - 30% with single dilation, 40% with up to 3 procedures.
2. Metallic stent placement (covered vs uncovered)
3. Temporary silicone tubing after stenosis dilation.
Complications
Stenosis recurrence - >70% (esp with BD alone)
Tissue ingrowth - most common, esp in balloon dilation cases (60-70%), least in covered metallic stent cases (0%)
Oronasal fistula - middle NP stenosis, related to stent mvt
Cats overall better success (87%) vs dogs (60%) - can be imperforate
Define hypoxemia and list the 5 causes of it?
PaO2 <80mmHg (severe <60mmHg).
Low FiO2, global hypoventilation, R-L shunt, diffusion impairment, V/Q mismatch (most common)
What drug can cause neutrophilic-eosinophilic lower airway disease in cats?
KBr
What is a normal A-a gradient?
Equations to calculate A-a gradient?
PAO2 = 150 - PaCO2 / 0.8
A-a gradient = PAO2 - PaO2
Normal <10, >15-20 = abnormal –> diffusion impairment.
(NB brachys have higher A-a gradient)
(Assume Patm = 760mmHg, a water vapor of 47mmHg, FiO2 0.21) R (respiratory quotient) = 0.8
What are the 3 complications of oxygen therapy?
- O2 toxicity: prolonged exposure to high O2 concentrations (e.g. 100% O2 for >12hrs). Toxic effects are due to the formation of O2-derived free radical species, which induce endothelial and epithelial cell damage, increase endothelial permeability, and ultimately cause inflammation and alveolar damage.
- Absorption atelectasis: high concentrations of O2 being delivered to the alveoli result in a washout of the nitrogen support skeleton, resulting in alveolar collapse.
- Hypoventilation: O2 replaces CO2 as the main respiratory stimulus in patients with COPD/brachys. O2 supp can decrease respiratory drive & result in significant hypoventilation.
What are the adverse effects of using albuterol chronically in asthmatic cats?
Inhalant albuterol is a racemic mixture consisting of the R-enantiomer (possesses bronchodilatory properties) & S-enantiomer (promotes bronchospasm and inflammation). With chronic/repeated use, S-enantiomer preferentially accumulates in the lung because of slower metabolism/clearance, enhancing bronchoconstrictive and proinflammatory effects.
What is a distinguishing feature between feline asthma & chronic bronchitis which can be demonstrated using barometric whole body plethysmography (BWBP)?
Airway hyperresponsiveness (bronchoconstriction) is more prominent with feline asthma at lower bronchoprovocant doses.
