Local intravascular pressure habituation in relation to G-induced arm pain.
BACKGROUND
During high +Gz loads, pilots may experience arm pain. It is commonly assumed that such pain is caused by distension of blood vessels and that vascular distensibility adapts to the prevailing transmural pressure. The aim was to investigate whether vascular pressure habituation (PH) is as efficient in alleviating G-induced arm pain as using counterpressure/support garments.


METHODS
In Series I, 7 subjects underwent a 5-wk PH regimen, consisting of 15 40-min sessions, during which intravascular pressures in one arm were elevated by 65-105 mmHg. Before and after PH, arm pain was determined during incremental +Gz-exposures in a centrifuge. In Series II, the effect on G-induced arm pain of wearing protective garments around the lower part of the upper arm was investigated in 10 subjects in 4 conditions: 1) counterpressure; 2) rigid support; 3) sham support; and 4) no support (control). Pain was rated using a 10-point graded scale.


RESULTS
PH reduced arm pain at 7.5 G from [median (range)] 4 (2-9) to 2 (0-5) in the pressure-habituated arm. The sham support did not affect pain compared to in the control condition (5.2; 3.0-10.0), whereas pain was reduced by both the rigid support (3.7; 1.0-8.0) and the counterpressure (2.5; 0.0-5.5). PH was as efficient in alleviating pain as the counterpressure and more efficient than the rigid support.


CONCLUSIONS
The results support the notion that G-induced arm pain is caused by vascular overdistension. Repeated moderate elevations of local intravascular pressure reduce G-induced arm pain, presumably because such PH reduces vascular distensibility.
Department of Environmental Physiology, School of Technology and Health, Royal Institute of Technology, Solna, Sweden. ola.eiken@sth.kth.se
Ola
O
Eiken
Igor B
IB
Mekjavic
Roger
R
Kölegård
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000337:Aerospace Medicine; D000704:Analysis of Variance; D001132:Arm / Q000098:blood supply*; D001808:Blood Vessels / Q000502:physiology*; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D010146:Pain / Q000209:etiology* / Q000503:physiopathology*; D011312:Pressure; D011481:Protective Clothing; D018709:Statistics, Nonparametric