In the circles that decry mask "totalitarianism" and its dangers, much has been made about a 2008 Turkish study of Beder et al.:
Repeated measures, longitudinal and prospective observational study was performed on 53 surgeons using a pulse oximeter pre and postoperatively.
Our study revealed a decrease in the oxygen saturation of arterial pulsations (SpO2) and a slight increase in pulse rates compared to preoperative values in all surgeon groups. The decrease was more prominent in the surgeons aged over 35.
Considering our findings, pulse rates of the surgeon's increase and SpO2 decrease after the first hour. This early change in SpO2 may be either due to the facial mask or the operational stress. Since a very small decrease in saturation at this level, reflects a large decrease in PaO2, our findings may have a clinical value for the health workers and the surgeons.
This study has been one of the linchpins of a narrative review by a group of 8 German doctors (published alas in a journal that also publishes anti-vaxxer studies like linking ADHD to vaccines) which aims to prove that masks not only don't work in the general public (they have a full page in their review on that) but are also are potentially dangerous.
Somewhat amusingly, the same journal published another study (from Canada) that proves the contrary at least in a young healthy people, even on cycling stress to exhaustion, in a cross-over RCT:
Wearing face masks is recommended for the prevention of contracting or exposing others to cardiorespiratory infections, such as COVID-19. Controversy exists on whether wearing face masks during vigorous exercise affects performance. We used a randomized, counterbalanced cross-over design to evaluate the effects of wearing a surgical mask, a cloth mask, or no mask in 14 participants (7 men and 7 women; 28.2 ± 8.7 y) during a cycle ergometry test to exhaustion. Arterial oxygen saturation (pulse oximetry) and tissue oxygenation index (indicator of hemoglobin saturation/desaturation) at vastus lateralis (near-infrared spectroscopy) were assessed throughout the exercise tests. Wearing face masks had no effect on performance (time to exhaustion (mean ± SD): no mask 622 ± 141 s, surgical mask 657 ± 158 s, cloth mask 637 ± 153 s (p = 0.20); peak power: no mask 234 ± 56 W, surgical mask 241 ± 57 W, cloth mask 241 ± 51 W (p = 0.49)). When expressed relative to peak exercise performance, no differences were evident between wearing or not wearing a mask for arterial oxygen saturation, tissue oxygenation index, rating of perceived exertion, or heart rate at any time during the exercise tests. Wearing a face mask during vigorous exercise had no discernable detrimental effect on blood or muscle oxygenation, and exercise performance in young, healthy participants (ClinicalTrials.gov, NCT04557605).
There are also some media reports, e.g. on BBC, of doctors wearing several masks while using a SpO2 meter showing no O2 decreases, albeit only in a short time span (and the doctor demonstrating that looked fairly young). A similar video has been posed by UC San Diego; it took 7 layered masks to register a 1% change in SpO2; again the subject looked fairly young though.
So, are there some meta-analyses of such O2 measurements while wearing masks studies, as opposed to narrative reviews? And any such with moderator analyses, e.g. are there consistently replicated settings in which wearing a mask does decrease O2, e.g. older people?
