Question 4(p.2)

Discuss the factors affecting pulmonary vascular resistance.

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College Answer

A good answer to this question required a discussion that focused on the following key
Recruitment and distension of pulmonary capillaries. Helps limit pulmonary vascular
resistance as pressure and flow increase.
Lung volume. Lung inflation is thought to have a dual effect, expanding large vessels
by traction while compressing smaller vessels and resistance is dependent upon lung volume,
being lowest at approx FRC.
Gravity. Perfusion is distributed down a vertical gradient in the lung, reflecting the
balance between intra-alveolar pressure and the distending vascular pressure. (West’s Zones)
Oxygen. Hypoxia causes pulmonary vasoconstriction. Diverts blood away from
hypoxic regions of the lung.
Hypercapnia and acidosis vasoconstriction
Autonomic innervation. Alpha -adrenergic stimulation - vasoconstrictor,
Beta-adrenergic stimulation - vasodilatation, Parasympathetic stimulation - Vasodilatation
Local mediators. Vasoconstrictors (Serotonin, histamine, endothelins) and
Vasodilators (NO, prostacyclin, isoprenaline)
The majority of these points could be efficiently explained through the use of graphs/figures,
all of which are commonly found in the majority of physiology books that include respiratory
physiology. Those candidates who failed to do so were also those who scored fewer points
with this question.
Syllabus - B1i2b
Reference – Respiratory Physiology, the Essentials, West 5th Ed Chp4 p33-44


The factors which affect pulmonary vascular resistance are:

  • Pulmonary blood flow:
    • Increased blood flow results in decreased pulmonary vascular resistance in order for pulmonary arterial pressure to remain stable
    • This is due to: 
      • Distension of pulmonary capillaries (mainly), and
      • Recruitment of previously collapsed or narrowed capillaries
  • Lung volume:
    • Relationship between lung volume and PVR is "U"-shaped
    • Pulmonary vascular resistance is lowest at FRC
    • At low lung volumes, it increases due to the compression of larger vessels
    • At high lung volumes, it increases due to the compression of small vessels
  • Hypoxic pulmonary vasoconstriction
    • A biphasic process (rapid immediate vasoconstriction over minutes, then a gradual increase in resistance over hours)
    • Mainly due to the constriction of small distal pulmonary arteries
    • HPV is attenuated by:
      • Sepsis and pneumonia
      • hypothermia
      • iron infusion
  • Metabolic and endocrine factors:
    • Catecholamines, arachidonic acid metabolites (eg. thromboxane A2) and histamine increase PVR
    • Hypercapnia and (independently) acidaemia also increase pVR
    • Alkalaemia decreases PVR and suppresses hypoxic pulmonary vasoconstriction
    • Hypothermia increases PVR and suppresses hypoxic pulmonary vasoconstriction
  • Autonomic nervous system:
    • αreceptors: vasoconstriction
    • β2 receptors: vasodilation
    • Muscarinic M3 receptors: vasodilation
  • Blood viscosity
    • PVR increases with increasing haematocrit
  • Drug effects:
    • Pulmonary vasoconstrictors: Adrenaline, noradrenaline and adenosine
    • Pulmonary vasodilators: Nitric oxide, milrinone, levosimendan, sildenafil, vasopressin, bosantan / ambrisantan, prostacycline and its analogs, calcium channel blockers and ACE-inhibitors.


West, J. B., and C. T. Dollery. "Distribution of blood flow and the pressure-flow relations of the whole lung." Journal of Applied Physiology 20.2 (1965): 175-183.

Sobin, Sidney S., et al. "Elasticity of the pulmonary alveolar microvascular sheet in the cat." Circulation Research 30.4 (1972): 440-450.

Johnson Jr, R. L., and C. C. Hsia. "Functional recruitment of pulmonary capillaries." Journal of Applied Physiology 76.4 (1994): 1405-1407.

Hanson, WENDY L., et al. "Site of recruitment in the pulmonary microcirculation." Journal of Applied Physiology 66.5 (1989): 2079-2083.

Conhaim, R. L., and B. A. Harms. "Perfusion of alveolar septa in isolated rat lungs in zone 1." Journal of Applied Physiology 75.2 (1993): 704-711.

Konig, M. F., JOHN M. Lucocq, and EWALD R. Weibel. "Demonstration of pulmonary vascular perfusion by electron and light microscopy." Journal of applied physiology 75.4 (1993): 1877-1883.

Carlin, J. I., et al. "Recruitment of lung diffusing capacity with exercise before and after pneumonectomy in dogs." Journal of applied physiology 70.1 (1991): 135-142.

Godbey, PATRICIA S., et al. "Effect of capillary pressure and lung distension on capillary recruitment." Journal of Applied Physiology 79.4 (1995): 1142-1147.

SIMMONS, DANIEL H., et al. "Relation between lung volume and pulmonary vascular resistance." Circulation Research 9.2 (1961): 465-471.

Thomas JR, Lewis J., Zora J. Griffo, and Albert Roos. "Effect of negative-pressure inflation of the lung on pulmonary vascular resistance." Journal of applied physiology 16.3 (1961): 451-456.

Permutt, S. "Howell JB, Proctor DF, Riley RL." Effect of lung inflation on static pressure-volume characteristics of pulmonary vessels. J Appl Physiol 16 (1961): 64-70.

Howell, J. B. L., et al. "Effect of inflation of the lung on different parts of pulmonary vascular bed." Journal of Applied Physiology 16.1 (1961): 71-76.

Kovacs, Gabor, et al. "Pulmonary vascular resistances during exercise in normal subjects: a systematic review." European Respiratory Journal 39.2 (2012): 319-328.

Glasser, Steven A., et al. "Pulmonary blood pressure and flow during atelectasis in the dog." Anesthesiology 58.3 (1983): 225-231.

Talbot, Nick P., et al. "Two temporal components within the human pulmonary vascular response to∼ 2 h of isocapnic hypoxia." Journal of applied physiology 98.3 (2005): 1125-1139.

Benumof, Jonathan L. "Mechanism of decreased blood flow to atelectatic lung." Journal of Applied Physiology 46.6 (1979): 1047-1048.

Woodson, R. Donald, David E. Raab, and D. J. Ferguson. "Pulmonary hemodynamics following acute atelectasis." American Journal of Physiology-Legacy Content 205.1 (1963): 53-56.

Lumb, Andrew B., and Peter Slinger. "Hypoxic Pulmonary VasoconstrictionPhysiology and Anesthetic Implications." Anesthesiology: The Journal of the American Society of Anesthesiologists 122.4 (2015): 932-946.

Euler, US V., and Göran Liljestrand. "Observations on the pulmonary arterial blood pressure in the cat." Acta Physiologica Scandinavica 12.4 (1946): 301-320.

Marshall, B. E., C. Marshall, and H. F. Frasch. "Control of the pulmonary circulation." Anesthesia and the Lung 1992. Springer, Dordrecht, 1992. 9-18.

Marshall, B. E., and C. Marshall. "A model for hypoxic constriction of the pulmonary circulation." J Appl Physiol 64 (1988): 68-77.

Tarry, D., and M. Powell. "Hypoxic pulmonary vasoconstriction." Bja Education 17.6 (2017): 208-213.

Duke, Helen N., and Esther M. Killick. "Pulmonary vasomotor responses of isolated perfused cat lungs to anoxia." The Journal of physiology 117.3 (1952): 303.

Staub, Norman C. "Site of hypoxic pulmonary vasoconstriction." Chest 88.4 (1985): 240S-245S.

Sommer, N., et al. "Regulation of hypoxic pulmonary vasoconstriction: basic mechanisms." European Respiratory Journal 32.6 (2008): 1639-1651.

Davis, MICHAEL J., WILLIAM L. Joyner, and JOSEPH P. Gilmore. "Microvascular pressure distribution and responses of pulmonary allografts and cheek pouch arterioles in the hamster to oxygen." Circulation research 49.1 (1981): 125-132.

Nagasaka, Yukio, et al. "Micropuncture measurement of lung microvascular pressure profile during hypoxia in cats." Circulation research 54.1 (1984): 90-95.

Talbot, Nick P., et al. "Two temporal components within the human pulmonary vascular response to∼ 2 h of isocapnic hypoxia." Journal of applied physiology 98.3 (2005): 1125-1139.

Lam, Carolyn SP, et al. "Age-associated increases in pulmonary artery systolic pressure in the general population." Circulation 119.20 (2009): 2663.

Farrar, J. F., Jeanette Blomfield, and R. D. K. Reye. "The structure and composition of the maturing pulmonary circulation." The Journal of pathology and bacteriology 90.1 (1965): 83-96.

McCORMACK, DAVID G., and N. A. Paterson. "Loss of hypoxic pulmonary vasoconstriction in chronic pneumonia is not mediated by nitric oxide." American Journal of Physiology-Heart and Circulatory Physiology 265.5 (1993): H1523-H1528.

Hyman, A. L., and PHILIP J. Kadowitz. "Effects of alveolar and perfusion hypoxia and hypercapnia on pulmonary vascular resistance in the lamb." American Journal of Physiology-Legacy Content 228.2 (1975): 397-403.

Kiely, David G., Robert I. Cargill, and Brian J. Lipworth. "Effects of hypercapnia on hemodynamic, inotropic, lusitropic, and electrophysiologic indices in humans." Chest 109.5 (1996): 1215-1221.

Rudolph, A. M., and Stanley Yuan. "Response of the pulmonary vasculature to hypoxia and H+ ion concentration changes." The Journal of clinical investigation 45.3 (1966): 399-411.

Presberg, K. W., et al. "Distribution of pulmonary vascular resistance during lactic acid infusion in dogs." Journal of Applied Physiology 68.4 (1990): 1328-1336.

Loeppky, J. A., et al. "Effects of acid-base status on acute hypoxic pulmonary vasoconstriction and gas exchange." Journal of Applied Physiology 72.5 (1992): 1787-1797.

Zayek, M. M., et al. "Induced moderate hypothermia markedly exacerbates pulmonary hypertension and dysoxia in a neonatal piglet model of elevated pulmonary vascular resistance." Critical Care. Vol. 4. No. 1. BioMed Central, 2000.

Kummer, Wolfgang. "Pulmonary vascular innervation and its role in responses to hypoxia: size matters!." Proceedings of the American Thoracic Society 8.6 (2011): 471-476.

Hoffman, Julien IE. "Pulmonary vascular resistance and viscosity: the forgotten factor." Pediatric cardiology 32.5 (2011): 557.