Blood Flow and Metabolism Flashcards
For flow to be the same on both the right and left sides of the heart, what do you need?
Pressure & resistance are much lower in the pulmonary circulation
The entire blood supply moves through the lungs every minute.
In the right ventricle, systolic contraction produces a pressure of __mmHg.
In diastole, the RV pressure is ___ mmHg.
Systole: 25 mmHg
Diastole: 0 mmHg (for filling)
What are the systolic and diastolic pressures of the main pulmonary artery?
What’s the mean pressure of the pulmonary artery?
Systolic: 25 mmHg
Diastolic: 8 mmHg
(not 0 bc of the closure of the pulm valve and the elastic distention of pulmonary vessels)
–> Mean: 15 mmHg, with pulsatile flow
Crossing the alveoli causes a pressure drop.
What is pulmonary venous pressure?
What’s the flow like?
8mmHg
No longer pulsatile
Blood returns to the left atrium with a pressure of ~5mmHg
LV contraction produces __ mmHg of pressure
Diastole produces ___ mmHg of pressure
Systole: 120 mmHg
Diastole: 80 mmHg
(not 0 like during filling bc of closure of mitral valve and elastic distension of aorta nd systemic muscular arteries
Mean arterial pressure: 100 mmHg
Pressure in large veins returning to right heart is ___ mmHg
Right atrial filling pressure is ___ mmHg
Pressure in large veins returning to right heart is 10 mmHg
Right atrial filling pressure is 2 mmHg
Alveolar vs extra-alveolar vessels during an inspiration
-
Alveolar capillary vessels are compressed if alveolar pressure exceeds capillary pressure
- Like stretching a tube, the diameter gets smaller
- Extra-alveolar vessels (of the lung parenchyma) expand with lung parenchyma during a breath (when the thoracic cavity expands)
As the thoracic cavity expands during inhalation,
intrathoracic pressure becomes more ___ and __ blood is brought into the thoracic cavity.
Intrathoracic pressure becomes more negative and more blood is brought into the thoracic cavity.
This includes both pulmonary and cardiac blood flow (preload) –> normal fluctuations in blood pressure w each breath
In mechanical ventilation, air is pushed into the lung.
What does this do to intrathoracic pressure and blood pressure?
Increases intrathoracic pressure (more positive)
–> decreases venous return to the heart during inspiration, thus decreasing blood pressure
Given that V = IR, where voltage is like pressure and I is like blood flow,
What is pulmonary vascular resistance?
Sine pressure drop across the pulmonary vascular bed is ~10 and normal cardiac output is 6L/min,
normal pulmonary vascular resistance is 10/6 = 1.7mmHg min/L
What pressures does the pulmonary artery catheter / Swan-Ganz catheter measure?
- Pressure entering the lung
- Pulmonary artery pressure
-
Pressure leaving the lung / Pulmonary artery occlusion pressure / “Wedge pressure” / Left ventricular filling pressure
- Tip of the catheter (distal to the inflated balloon occluding blood flow) can measure the pressure in pulmonary veins
If the wedge pressure / left ventricular filling pressure is greater than __ mmHg, pulmonary edema can occur
18
Describe the distribution of blood flow in the lung
Blood enters the lung from a single pulmonary artery on each side.
Because of gravity, flow is greater in the lowest portion of the lung and decreases linearly as you go up
Alveolar pressure (PA)
characteristics
- = atmospheric pressure
- Slightly negative when you inhale, slightly positive when you exhale
- Does not change much from the top to the bottom of the lung
Pulmonary arterial pressure (Pa)
- Changes significantly as we go from the top to the bottom of the lung
- Always greater than the pulmonary venous pressure
Pulmonary venous pressure (Pv)
characteristics
- Changes significantly from the top to the bottom of the lung
- Lower than the pulmonary arterial pressure
- The difference between the arterial and venous blood pressure within the lung is always the same
West’s Zone 1
- Alveolar pressure (fixed) is greater than both arterial and venous pressure
- No blood flow
- Usually only occurs if
- arterial pressure is severely reduced (e.g. hemorrhage)
- or alveolar pressure is raised (e.g. positive pressure ventilation)
- Any zone 1 in health is usually used up during exercise or stress when pulmonary arterial pressure rises above alveolar atmospheric pressure.
Compare/contrast West’s zones 2 & 3
-
Zone 2:
- Pa > PA > Pv
- Blood flow is determined by the difference between arterial and alveolar pressures –> blood flow increases as you go down because arterial pressure increases
-
Zone 3:
- Pa > Pv > PA
- Blood flow is determined by the difference between Pa & Pv, which is more constant
- Flow rate is more constant than it was in zone 2
When there is an area of the lung that’s becoming hypoxic, blood that flows through it without being oxygenated is called
shunt
Hypoxic pulmonary vasoconstriction (HPV) - what is it and what could happen if the entire lung becomes hypoxic?
Blood vessels leading to hypoxic alveoli constrict to decrease the amt of blood shunted through the lung.
If the whole lung is hypoxic, the entire lung could vasoconstrict and develop pulmonary hypertension.
Also important in constricting pulmonary blood flow in utero and opening pulmonary blood flow after the first breath of life.
Describe the water balance in lung tissues
- Increased bp (e.g. heart failure) in pulmonary capillaries increases hydrostatic pressure –> cause fluid to leak out
- Oncotic pressure of blood-borne molecules like albumin, sodium, glucose, etc suck the water back in
What happens to water that leaks out of pulmonary capiillaries
interstitial space > lymphatic vessels > hilum > mediastinum > thoracic duct > venous criculation
Interstitial edema
Excessive fluid build up in the interstitial space; presents with Kerley B lines on radiography
Pulmonary edema
So much fluid builds up in the interstitial space that it seeps into the alveolar space, impairing as exchange
Non-respiratory functions of the lung
Blood reservoir: it can recruit and distend blood vessels to accommodate increases in CO during exercise, stress, and disease
Blood filter: clots, wBCs, and other foreign particles are filtered out of the blood by the lungs before they return to the heart; this is also how many cancers metastasize once they’re blood born
Angiotensin-converting enzyme
- Converts angiotesnin I to II
- Inactivates bradykinin in the blood
- Without ACE, you can get a cough
The lung inactivates ___ and ___
Pulmonary mast cells contain ____
Inactivates & stores serotonin
Inactivates prostaglandins E1, E2, and F2a
Pulmonary mast cells contain heparin, which alters the clotting mechanism under certain conditions
Synthetic functions of the lung
- Making mucopolysaccharides that form the anti-bacterial surface of bronchial mucus
- Abnormal mucopolysaccharides cause cystic fibrosis
- Secreting IgA that binds and inactivates inhaled infectious oragnisms
- Deficient IgA is an immune deficiency
- Producing collagen and elastin for the lung
- Increased breakdown of collagen & elastin causes emphysema
Transmural pressure
Pressure difference between inside and outside of capillaries
If pulmonary blood flow increases, what happens to pulmonary vascular resistnace? why?
It decreases because there is recruitment and distention of pulmonary alveolar capillaries
What is the effect of lung volume on PVR?
- Low lung volume: resistance is high because extra-alveolar vessels are compressed
- High lung volume: resistance is high because alveolar capillaries are stretched
- Resistance is least at normal breathing volumes (FRC)
Factors that increase pulmonary vascular resistance (contracts smooth muscle)
Serotonin
Histamine
Norepinephrine
Endothelin
Hypoxia
Factors that decrease pulmonary vascular resistance (relaxes smooth muscle)
Acetylcholine
Phosphodiesterase inhibitors
Calcium channel blockers
Prostacycline (PGI2)
Fick’s principle
Oxygen consumption =
Cardiac output multiplied by the drop in O2 content from arterial to mixed venous blood
Hypoxemia causes vasoconstriction ONLY in the ___ bed
pulmonary bed
Compare the flow in systemic vs pulmonary circulation
The flow is the same, but the mean pressure difference is 10x higher in systemic circulation than it is in pulmonary circulation.
What impact would acutely increasing pulmonary venous pressure have on pulmonary vascular resistance?
It will reduce resistance by recruiting & distending the capillaries
A patient with severe pnemonia is placed on mechanical ventilation, but his hypoxemia worsens. he has a pH of 7.47 and an arterial pO2 of 55mmHg. Why did an echocardiogram show normal LV function and LA size but significantly increased systolic pulmonary artery pressure?
- decreased arterial pO2
- increased blood pH
- decreased sympathetic activity
- decreased alveolar pO2
Hypoxic pulmonary vasoconstriction due to decreased alveolar pO2.
