Pulmonary Circulation Flashcards
1
Q
differences between pulmonary and systemic circulation
A
- pulmonary circulation is the only vascular bed to receive the entire CO
- ischemic damage is rare because of multiple supplies:
- pulmonary circulation
- bronchial circulation
- alveolar gas oxygen supply
- minimal basal tone in pulmonary vessels
- passive distension with increased pressure or flow without significant autoregulation
- hypoxic vasoconstriction in lung
- change in pulmonary resistance has same affect as increase in vascular resistance for left ventricle
- pulmonary endothelium synthesizes NO and prostaglandins
2
Q
pulm circulation and pressures
A
- smaller than systemic-lesser
- blood pressures are lower because PVR is 10x lower than TPR
- afterload of right ventricle is less than afterload of left ventricle, so right heart does less stroke work than left heart
3
Q
anatomic and physiologic shunts
A
- bronchial circulation is a normal anatomic shunt
- left to left shunt
- 1-2% of CO
- bronchial circulation starts at base of aorta, perfuses large airways, vessels, nerves, then drains into bronchial veins and pulmonary vein and left atrium
- responsible for slight drop from Pend cap of 100 to Pa02 95
- accounts for slight difference in right and left ventricle output
4
Q
lymphatic system
A
- vessels that drain excess fluid from the interstitial space and return it to the circulation via caudal mediastinal lymph node and the thoracic duct
- valves that are regulated by intrinsic propulsion, mechanical pumping during breathing and SNS
- intrinsic pumping can generate up to 20 mmHg if flow is occluded
5
Q
physiological shunt
A
sum of normal anatomic shunts plus any pathological intrapulmonary right to left shunt that occurs when airways are blocked
6
Q
pathological right to left shunts
A
-result in hypoxemia without much hypercapnea
7
Q
features of pulmonary vessels
A
- pulmonary arteries and veins are both thin walled and highly distensible
- gradation of muscularity from muscular to partially muscular to non muscular with no distinct arterioles
- capillaries surrounded by alveolar air, so external pressure is alveolar pressure, which oscillates during breathing
- changes in lung volume during breathing affect pulmonary vascular resistance
- vessels are gas exchanging if they are less than 1 mm in diameter
- alveolar and extra-alveolar vessels have different mechanical properties and are affected differently by changes in lung volume but do not differ anatomically
8
Q
pulmonary blood pressure
A
- low and dissipated gradually along vasculature
- mean Ppa > 20 is pulmonary hypertension
- mean Ppa > 25 gives pulmonary edema, resulting in a diffusion problem
- measured with cardiac catheter 100 cm long and 1 mm diameter inserted through skin in peripheral vein
- advanced to pulmonary artery and inflated to occlude flow
- wedge pressure used as estimate as LA pressure
- not capillary pressure-its pulmonary wedge pressure
- tells you about pre load for left ventricle
- mean pulmonary artery pressure is 12 for systolic and 5 for diastolic
- low resistance means low windkessel effect
9
Q
pulmonary vascular resistance
A
- PVR = (PpA-PLA)/CO
- difference in pulm artery pressure and LA pressure over CO
- Ppa measured with other catheter
- 10x less than TPR
- work of right ventricle is 10x less
- right heart failure only problem in extreme obstructed pulmonary circulation
- diastolic pressure n pulmonary artery nearly equal to left atrial pressure
- need to measure carefully
- subject supine and middle of ant/post axis
10
Q
changes in PVR
A
- mostly passive
- pulm blood volume is 200-300 ml and can increase 2-3x during exercise but vessels are so compliant that pressure doesn’t increase much
- pressure is inversely proportional to radius and resistance
- decreases as pressure increases
- in body, resistance increases as compensation to increased pressure
11
Q
inflation
A
- alveolar blood vessels are stretched and become narrower as the capillaries increase in length
- extra-alveolar blood vessels expand due to the more negative intrapleural pressure increasing their transmural pressure
- vessels near alveoli are exposed to those pressures, others influenced by intrapleural
- interstitial pressure around large vessels becomes more negative when the lung inflates
12
Q
optimum volume
A
- lung has optimum volume that minimizes PVR
- alveolar and extra-alveolar vessels are in series, so their resistances are additive
- PVR is at minimum at FRC
- lung volume changes during breathing and affects resistance
- U shaped relationship
- increases as transpulmonary pressure increases or decreases
- at very low, kinked, increased resistance
- U shape is sum of two curves for alveolar and extra alveolar vessels
- corner vessels-in alveolar septum but at junctional corners of alveoli-expand during inflation and lower resistance-extra-alveolar and never close during inflation
13
Q
normal breathing
A
- alveolar pressure fluctuates between pos and neg 2
- caps remain open
- mechanical ventilation-alveolar pressure positive-greater tendency for caps to collapse and increase their resistance
- causes Ppa to rise increases the afterload of the right ventricle
- ventilated at low pressure settings
- healthy heart responds to this by augmenting CO
14
Q
active factors affecting pulmonary vascular resistance
A
- vasodilators:
- prostacyclin, histamine, calcium channel blockers, NO
- vasoconstrictors:
- hypoxic vasoconstriction shunts blood to better ventilated region of the lung
- increased PCO2, low pH
- norepi
- thromboxane
- angiotensin II
- serotonin, ATP
- neural influence plays minimal role in regulating PVR
- pathological conditions remodel and increase PVR-hypertension, asthma, ARDS, COPD, high altitude, PE, veno occlusive disease, tumors
15
Q
hypoxic pulmonary vasoconstriction
A
- regional level
- shunts blood to better ventilated regions of lung
16
Q
gravity
A
- makes blood flow greatest at base of lung
- passive distension
- 6x greater
- pressure increases in capillaries gradually from top to bottom due to hydrostatic pressure from intrapleural fluid
- top is Ppa-10, bottom is Ppa+10
- caps at base have high transmural pressure and are wide open, resistance to blood flow lower, so flow increases
17
Q
three zone model
A
- top, middle bottom
- top PA >Pa>Pv-not usually in healthy lung
- middle Pa>PA>Pv alveolar in middle, flow depends on alveolar pressure
- hydrostatic pressure increases and intravascular pressure exceed alveolar pressure, opening of caps with increase in flow, partial collapse on low pressure side but flow stays
- determined by differences between Ppa and Palv
- waterfall flow- comes from before the falls
- bottom Pa>Pv>PA-flow increases due to gravity and passive distension
18
Q
pulmonary edema causes
A
- increased capillary permeability
- increased cap hydrostatic pressure
- decreased interstitial hydrostatic pressure
- decreased colloid osmotic pressure
- insufficient pulmonary lymphatic drainage
- unknown
19
Q
clinical problems
A
- adult resp distress syndrome
- oxygen toxicity
- inhaled/circulating toxins
- increased left atrial pressure resulting from L ven infarction or mitral stenosis
- overadmission of IV fluids
- too rapid evacuation of pneumothorax
- protein starvation
- dilution of blood proteins by IV
- renal problems resulting in urinary protein loss
- tumors
- interstitial fibrosing diseases
- high altitude
- head energy
- drug overdose
20
Q
right to left shunt
A
-causes hypoxemia
-Qs/Qt= (CcO2-CsO2)/(CcO2-CvO2)
-difference in cap/shunt over difference in cap veins
-obtained from oxygen dissociation curve
-if Qs=0, no shunt
-if Qs=Qt, no oxygenation
if Qs=1/2 Qt, half oxygenation
21
Q
shunts
A
- give more hypoxemia than hypercapnea
- these patients will not respond to O2 because you will just send it into the shunt
- small drop in oxygen makes large drop in partial pressure
- small drop in carbon dioxide makes small drop in partial pressure
