Pulmonary Circulation: Week 7 Flashcards
What two structures do the right pulmonary veins pass behind?
- right atrium
2. superior vena cava
What structure do the left pulmonary veins pass in front of?
descending thoracic aorta
Primary site of gas exchange
pulmonary capillaries
What is the normal pulmonary artery pressure?
15mmHg/8mmHg
Blood pressure varies with the height of the lung. What is the pressure at the apex? What is the pressure at the base?
12mmHg; 36mmHg
What percentage of pulmonary vascular resistance is at the level of the capillaries?
35-45%
What does low pre-capillary resistance lead to? What happens in pulmonary arterial hypertension?
pulsatile motion in the microvascular bed; this motion is lost in severe pulmonary arterial hypertension
What is the transit time across the microcirculation?
0.5-1 sec
Equation for pulmonary vascular resistance. How does pulmonary vascular resistance compare to systemic vascular resistance?
PPA - PPV / Pulmonary Blood Flow
About 1/10th of systemic vascular resistance, because there are no arterioles to regulate blood flow.
As pressure in the left atrium increases, pulmonary vascular resistance will no longer decrease as a result of increasing PPA. Why?
The vascular bed is fully distended.
Capillaries are near atmospheric pressure (alveolar pressure). How?
Because of surfactant
Pressure decreases further when lung expands, causing radial traction. What two things occur?
- Pulls open vessels
2. Reduces pressure
Pulmonary vascular resistance can be decreased by three mechanisms. What are they?
- Recruitment (opening of previously closed capillaries
- Distension (increase caliber of already open capillaries
- Expansion of lung volume
What does pulmonary artery wedge pressure measure? What are the normal values?
Measures static fluid pressure in the pulmonary circuit. Reflects left atrial pressure and estimates total body fluid balance. Normal values range from 8-12mmHg.
Describe the general pattern of blood flow from base to apex in the lung.
From base to apex, there is a decrease in flow.
Discuss the relationships of alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure at the apex of the lungs (zone 1).
Alveolar pressure > pulmonary arterial pressure > pulmonary venous pressure
Discuss the relationships of alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure at the base of the lungs (zone 3).
Pulmonary arterial pressure>pulmonary venous pressure>alveolar pressure
Discuss the relationships of alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure at the midsection of the lungs (zone 2)
Pa > PA > Pv
In the supine position, what happens to apical blood flow? What happens to basal blood flow?
Apical blood flow increases; basal blood flow stays the same
What happens to apical blood flow during exercise? What happens to basal blood flow?
Apical blood flow increases; basal blood flow increases
What is the main reason for regional blood flow differences?
Hydrostatic pressure
In zone 1 of the lungs, the apex is ventilated but not perfused. This is referred to as?
Dead space ventilation
What occurs during dead space ventilation?
Capillaries are flattened due to increased alveolar pressure
What determines blood flow in zone 2?
Blood flow determined by difference between Palveolar and Parterial. This is called the waterfall effect.
What determines blood flow in zone 3?
Blood flow determined by usual arterial - venous pressure
Physiological phenomenon in which pulmonary arteries constrict in the presence of hypoxia (low oxygen levels) without hypercapnia (high carbon dioxide levels), redirecting blood flow to alveoli with a higher oxygen content
Hypoxic vasoconstriction
At what level of PO2 is hypoxic vasoconstriction most responsive?
PO2 alveolar less than 70mmHg
What happens at high altitude? What happens to pressure in the pulmonary arteries?
Generalized vasoconstriction; increased pressure in pulmonary arteries
Factors that inhibit hypoxic vasoconstriction
CO Increased pulmonary vascular resistance Acidosis/alkalosis Ca+ channel blockers Inhaled anesthetics
Where does fluid leaking from capillaries go?
To the interstitium of alveolar walls via perivascular and peribronchial lymph nodes. May cause interstitial edema.
What happens when the capacity of the lymphatics is exceeded?
Alveolar edema. Fluid pours into alveoli and interferes with gas exchange.
Increased intracranial pressure leading to increased pulmonary capillary pressure
Neurogenic pulmonary edema
Accumulation of proteinaceous fluid in the alveoli due to a number of causes
Adult respiratory distress syndrome
Causes of ARDS
- severe trauma
- sepsis
- pancreatitis
- aspiration pneumonia
- community-acquired pneumonia
Treatment for ARDS
low tidal volume ventilation
Variant of ARDS
Occurs with massive blood product transfusion, most commonly fresh frozen plasma
Transfusion related acute lung injury (TRALI)
What’s the proposed mechanism for TRALI?
Mechanism thought to be development of anti-granulocyte antibodies which then attack the recipient’s granulocytes, and initiate an inflammatory response in the pulmonary capillaries
2 other functions of pulmonary circulation
- reservoir for blood
2. filtration
One metabolic function of the lungs includes the activation of what?
Angiotensin I to Angiotensin II
One metabolic function of the lungs includes the inactivation of what?
Bradykinin, serotonin, prostaglandins, norepi, arachidonic acid
The lung converts arachidonic acid to what two things?
- leukotrienes (via lipoxygenase)
2. prostaglandins (via COX)
What two things do all prostaglandins cause?
- platelet aggregation
2. bronchoconstriction in asthma
What does prostaglandin E2 do?
Relaxes patent ductus arteriosus in fetus
