Intra-abdominal pressure effects on porcine thoracic compliance in weightlessness: implications for physiologic tolerance of laparoscopic surgery in space.
OBJECTIVE
Laparoscopic surgery (LS) is envisioned as an option for spaceflight, but requires intra-abdominal hypertension (IAH) to create the surgical domain. Prolonged weightlessness induces physiologic deconditioning that questions the ability of ill or injured astronauts to tolerate IAH. On earth, IAH results in marked ventilatory embarrassment. As there has been no previous study of physiologic changes related to LS in weightlessness, we studied anesthetized pigs in parabolic flight.


METHODS
Parabolic flight research laboratory.


METHODS
Five anesthetized Yorkshire pigs.


METHODS
Subjects were transported from an animal care facility and secured aboard an aircraft capable of generating hypergravity and weightlessness. Mechanical ventilation was performed using pressure control and positive end-expiratory pressure at 15 and 2 cm H2O, respectively; rate 12 breaths/min. Three abdominal conditions were used during LS: insufflation to produce IAH, abdominal wall retraction (AWR), and no abdominal wall manipulation (baseline). During each parabola breath by breath-tidal volumes (Vt) were recorded by a transport ventilator (HT-50 Newport Medical).


RESULTS
Least square means (LS-means) of weight corrected Vt (milliliter per kilogram) by gravity (g) and abdominal condition were determined using a mixed effects model for repeated measures analysis. Increasing gravity (g) consistently reduced Vt (p = 0.0011) as did insufflation (p < 0.0001). In 1g, Vt (LS-mean 13.7, 95% confidence interval [CI]: 12.4-15.0) was relatively unaffected by AWR (LS-mean 12.8, 95% CI: 11.5-14.00), but markedly decreased by IAH (LS-mean 10.00, 95% CI: 8.9-11.1), an effect accentuated in hypergravity (LS-mean 8.1, 95% CI: 6.4-9.8). In weightlessness, Vt reduction during insufflation was near obviated (LS-mean 12.3, 95% CI: 10.6-14.1), and AWR regularly but inconsistently increased the Vt above 1g baseline (LS-mean 13.7, 95% CI: 11.7-15.8).


CONCLUSIONS
Weightlessness protects against thoracic compliance changes that are inherent in IAH during induced pneumoperitoneum in gravity. The technique-related physiologic cost of performing LS in space deconditioned astronauts should be incorporated into design concepts for space surgery systems.
Kirkpatrick
Andrew W
AW
Department of Surgery, Regional Trauma Services, Calgary Heath Region and Foothills Medical Centre, Calgary, Alberta, Canada. Andrew.kirkpatrick@calgaryhealthregion.ca
Keaney
Marilyn
M
Hemmelgarn
Brenda
B
Zhang
Jianguo
J
Ball
Chad G
CG
Groleau
Michelle
M
Tyssen
Michelle
M
Keyte
Jennifer
J
Campbell
Mark R
MR
Kmet
Leanne
L
McBeth
Paul
P
Broderick
Timothy J
TJ
D000005:Abdomen / Q000502:physiology*; D000222:Adaptation, Physiological; D000337:Aerospace Medicine; D000818:Animals; D005118:Extraterrestrial Environment; D005260:Female; D010535:Laparoscopy; D008170:Lung Compliance / Q000502:physiology; D008297:Male; D013552:Swine; D013909:Thorax / Q000502:physiology*; D014893:Weightlessness; D018474:Weightlessness Simulation / Q000379:methods