PhD defense by Lonnie Petersen

The aim of this thesis was to investigate gravitational blood volume distribution and effects on regional pressure, especially intracranial pressure. Graded head-up and down tilt was used to manipulate the magnitude and direction of the hydrostatic gradients (study I and study III). However, the only way to abolish hydrostatic gradients altogether is by weightlessness. Therefore weightlessness is a unique research-tool because it provides a control-situation for the effects of gravity and this was used by study II and study IV.

The thesis was based on the following publications:

1. Petersen LG, Carlsen JF, Nielsen MB, Damgaard M, Secher NH. The hydrostatic pressure indifference point underestimates or- thostatic redistribution of blood in humans. J Appl Physiol. 116: 730–735, 2014.
2. Petersen LG, Damgaard M, Petersen JCG, Norsk P. Mechanisms of increase in cardiac output during acute weightlessness in hu- mans. J Appl Physiol. 111: 407–411, 2011.
3. Petersen LG, Petersen JCG, Andresen M, Secher NH, Juhler M. Postural influence on intracranial and cerebral perfusion pres- sure in ambulatory neurosurgical patients. Am J Physiol Regul Integr Comp Physiol. 310: r100–104, 2016.
4. Lawley JS, Petersen LG, Howden EJ, Sarma S, Cornwell WK, Zhang R, Whitworth LA, Williams M, Levine BD. Effect of grav- ity on the intracranial pressure: Implications for visual impairment in space. Unpublished, manuscript in preparation.

Supervisor and reviewers

The primary thesis supervisor was:

Professor Niels H. Secher
Department of Anaesthesia,
The Copenhagen Muscle Research Centre,
Rigshospitalet, University of Copenhagen, DK

The thesis reviewers were:

• (Chairperson) Professor Christian Aalkjær
  Department of Biomedical Sciences,
  University of Copenhagen, DK
• Professor Tobias Wang
  Department of Bioscience,
  Aarhus University, DK
• Professor Richard Hughson
  Department of Kinesiology,
  Faculty of Applied Health Sciences,
  University of Waterloo, Canada