Changes in thenar eminence tissue oxygen saturation measured using near-infrared spectroscopy suggest ischaemic preconditioning in a repeated arterial occlusion forearm ischaemia model

Introduction

Ischaemic preconditioning (IP) describes the process whereby a tissue exposed to brief sublethal periods of ischaemia becomes protected from longer lethal episodes of ischaemia. One mechanism by which skeletal muscle may effect protection from ischaemic insult is to reduce the resting rate of oxygen consumption (VO₂) following a preconditioning stimulus. Tissue oxygen saturation (StO₂) reflects the dynamic balance between oxygen supply and utilisation. We hypothesised that using near-infrared spectroscopy to measure thenar eminence StO₂ repeated arterial occlusion of the upper arm would induce an IP effect.

Methods

The study was approved by the UCL Research Ethics Committee and written consent was obtained from 20 healthy volunteers. StO₂ was measured using the InSpectra Tissue Spectrometer (Model 325; Hutchinson Technology Inc., USA). The tissue spectrometer probe was attached to the left thenar eminence and a blood pressure cuff was placed around the left upper arm. The repeated arterial occlusion forearm ischaemia model (RAOFIM) consisted of resting measurements and then a cycle of four cuff inflations (200 mmHg, 3 min) and four deflations (5 min). Finally the cuff was inflated for 3 minutes on the right upper arm while the StO₂ was measured from the right thenar eminence. Paired t tests were used to compare rates of oxygen desaturation; P < 0.05 was considered statistically significant.

Results

There was a fall in thenar eminence StO₂ during all arterial occlusions. The rate of decline of StO₂ was significantly reduced during the fourth inflation (0.160%/s) as compared with the first in the left arm (0.213%/s), P < 0.001. There was an increase in the rate of StO₂ decline in the right arm (0.268%/s) when compared with the first left occlusion (P < 0.001).

Conclusion

The data from this pilot study demonstrate that, following preconditioning using a RAOFIM, the rate of oxygen desaturation in resting skeletal muscle during subsequent arterial occlusion manoeuvres is reduced. This could be explained by a fall in resting muscle VO₂ as a result of the preceding short ischaemic stimuli and therefore represents evidence of IP in skeletal muscle. These data do not provide evidence to support a remote IP effect in the contralateral arm.