Environmental physiology

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We study the effects of gravity and ambient pressure in humans.

Our research group uses changes in the physical environment as tools to investigate physiological and pathophysiological processes in humans. Our research facilities include pressure chambers for altitude and diving simulations, a water tank for immersion studies, and a human centrifuge for high-gravity exposure. 

Experiments in weightlessness are performed during space flight under the coordination of the European Space Agency, ESA. 

Effects of gravity on pulmonary function

The distributions of ventilation and perfusion in the lungs have been studied at zero gravity during space flight and at increased gravity in a human centrifuge. Recent findings based on the exchange of inert gas mixtures suggest that gravity-related factors are less important than previously thought for the distribution of ventilation, and that only inter-regional but not intraregional inhomogeneity of lung perfusion is gravity-dependent.

A better understanding of the effects of gravity on pulmonary function has important implications for intensive care patients. We have studied the topographical distributions of ventilation and perfusion during increased gravity in supine and prone position in humans in order to develop a model for ventilation/perfusion mismatch in severe pulmonary insufficiency.

Cardiovascular effects of space flight or long-term bedrest

The cardiovascular effects of long-term absence of gravity in the head-to-foot direction has been studied in healthy humans, either in astronauts during and after space flight or in volunteers during and after long-term bedrest. Time courses for the development of and recovery from cardiovascular deconditioning have been determined. Recent findings suggest that blood pressure control during dynamic and isometric exercise is impaired after long-term absence of gravity in the head-to-foot direction.

New diagnostic and therapeutic methods for patients with lung embolism

Divers are at risk of the formation of gas bubbles in the tissues and in the blood during decompression. So are astronauts and aviators when exposed to extreme altitude. We have shown that venous gas emboli - gas bubbles that are usually filtered by the lungs without causing decompression sickness - changes the nitric oxide excretion from the lungs. Similar changes take place in experimental lung embolism which suggests new diagnostic and therapeutic methods for patients with lung embolism.

Group members

Dag LinnarssonProfessor, senior
Lars KarlssonAssistant professor
Roger KölegårdAssociated
Tryggve HemmingssonAssociated


Airway nitric oxide in microgravity (1)

Studies of signs of airway inflammation after subchronic dust inhalation in weightlessness where dust never settles.

Airway nitric oxide in microgravity (2)

Detection of venous gas emboli after decompression during space walks using exhaled nitric oxide as an indicator. Parallel ground-based studies include human experiments in our altitude chamber, and animal experiments where lung embolism is induced with gas and solid elements.

Hypergravity as a model of Acute Respiratory Distress Syndrome

Prone and supine humans are studied during up to 5 times normal gravity. Mechanisms of arterial desaturation are studied using Single-Photon Emission Tomography and interference with pulmonary hypoxic vasoconstriction.

Efficiency of dynamic leg exercise in hypergravity

The internal cost of leg motion is studied and effects of leg mass (inertia) is separated from those of leg weight (gravity).


Our research group has unique research facilities that may be used by other researchers at Karolinska Institutet, or by other universities or organisations: 

Pressure chambers

  • 8 m3 hyperbaric chamber, for experiments in a high-pressure environment
  • Maximum pressure of 16 bar corresponding to a simulated water depth of 150 metres
  • Temperature control system with a very high capacity to compensate for pressure-induced changes in chamber temperature
  • 25 m3 hypobaric chamber for altitude experiments.

Both chambers have multiple hull penetrations for power and gas supply, gas analysis and signal transmission.

Human centrifuge

  • 7.2 meter radius human centrifuge, for high-gravity experiments
  • The centrifuge gondola can accommodate one subject and a total "payload" mass of 300 kg
  • Up to 9 times normal gravity (9 g) with humans and 15 g with equipment only
  • Platform designed for animal experiments on the opposite centrifuge arm
  • 50 slip-rings for signal transmission from the gondola or platform
  • 10 slip-rings for power transmission.

Routine monitoring of subjects includes audiovisual communication, electrocardiogram and peripheral vision. Additional physiological monitoring equipment includes invasive or non-invasive blood pressure, respiratory gas analysis and remote-controlled syringes for blood sampling or infusions.

Microgravity (weightlessness)

Access to this unique environment is obtained through the European Space Agency. Experiments requiring long-term microgravity are performed on the International Space Station and experiment requiring only transient microgravity are performed during parabolic flight in an aircraft.

Financial support


Lung diffusing capacity for nitric oxide at lowered and raised ambient pressures.
Linnarsson D, Hemmingsson T, Frostell C, Van Muylem A, Kerckx Y, Gustafsson L
Respir Physiol Neurobiol 2013 Dec;189(3):552-7

Toxicity of lunar dust
Linnarsson D, Carpenter J, Fubini B, Gerde P, Karlsson LL, Loftus DJ, Prisk GK, Staufer U, Tranfield EM, van Westrenen W
Planetary and Space Science 74(1):57-71, 2012

Effects of ambient pressure on pulmonary nitric oxide.
Hemmingsson T, Linnarsson D, Frostell C, Van Muylem A, Kerckx Y, Gustafsson L
J. Appl. Physiol. 2012 Feb;112(4):580-6

No protective role for hypoxic pulmonary vasoconstriction in severe hypergravity-induced arterial hypoxemia.
Karlsson L, Rohdin M, Nekludov M, Ax M, Petersson J
Eur. J. Appl. Physiol. 2011 Sep;111(9):2099-104

Microgravity decreases and hypergravity increases exhaled nitric oxide.
Karlsson L, Kerckx Y, Gustafsson L, Hemmingsson T, Linnarsson D
J. Appl. Physiol. 2009 Nov;107(5):1431-7

Venous gas emboli and exhaled nitric oxide with simulated and actual extravehicular activity.
Karlsson L, Blogg S, Lindholm P, Gennser M, Hemmingsson T, Linnarsson D
Respir Physiol Neurobiol 2009 Oct;169 Suppl 1():S59-62

Paradoxical redistribution of pulmonary blood flow in prone and supine humans exposed to hypergravity.
Petersson J, Rohdin M, Sánchez-Crespo A, Nyrén S, Jacobsson H, Larsson S, et al
J. Appl. Physiol. 2006 Jan;100(1):240-8

Residual heterogeneity of intra- and interregional pulmonary perfusion in short-term microgravity.
Montmerle S, Sundblad P, Linnarsson D
J. Appl. Physiol. 2005 Jun;98(6):2268-77

Long-term bed rest-induced reductions in stroke volume during rest and exercise: cardiac dysfunction vs. volume depletion.
Spaak J, Montmerle S, Sundblad P, Linnarsson D
J. Appl. Physiol. 2005 Feb;98(2):648-54

Protective effect of prone posture against hypergravity-induced arterial hypoxaemia in humans.
Rohdin M, Petersson J, Mure M, Glenny R, Lindahl S, Linnarsson D
J. Physiol. (Lond.) 2003 Apr;548(Pt 2):585-91

Contact us

Assistant professor

Lars Karlsson

Phone: 08-524 868 90
Organizational unit: Karlsson Lars group - Environmental Physiology
E-mail: Lars.Karlsson@ki.se