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With the popularization of pulse wave signals by the spread of wearable watch devices incorporating photoplethysmography (PPG) sensors, many studies are reporting the accuracy of pulse rate variability (PRV) as a surrogate of heart rate variability (HRV). However, the authors are concerned about their research paradigm based on the assumption that PRV is a biomarker that reflects the same biological properties as HRV. Because PPG pulse wave and ECG R wave both reflect the periodic beating of the heart, pulse rate and heart rate should be equal, but it does not guarantee that the respective variabilities are also the same. The process from ECG R wave to PPG pulse wave involves several transformation steps of physical properties, such as those of electromechanical coupling and conversions from force to volume, volume to pressure, pressure impulse to wave, pressure wave to volume, and volume to light intensity. In fact, there is concreate evidence that shows discrepancy between PRV and HRV, such as that demonstrating the presence of PRV in the absence of HRV, differences in PRV with measurement sites, and differing effects of body posture and exercise between them. Our observations in adult patients with an implanted cardiac pacemaker also indicate that fluctuations in R-R intervals, pulse transit time, and pulse intervals are modulated differently by autonomic functions, respiration, and other factors. The authors suggest that it is more appropriate to recognize PRV as a different biomarker than HRV. Although HRV is a major determinant of PRV, PRV is caused by many other sources of variability, which could contain useful biomedical information that is neither error nor noise.

High prevalence of deep vein thrombosis (DVT) in disaster shelters has been reported in the aftermath of earthquakes in Japan. Calf DVT was examined using sonography in the shelters after the Great East Japan earthquake on March 11, 2011. By the end of July 2011, 701 out of 8,630 evacuees suspected with calf DVT, judged by inspections or medical interviews, were examined in 32 shelters, and 190 evacuees were confirmed to have calf DVT. The prevalence of DVT was 2.20%, which was 200 times higher than the usual incidence in Japan. The DVT prevalence seemed to decrease with time. By the end of May, a significantly higher prevalence of DVT was found in tsunami-flooded shelters (109 of 3,871 evacuees; 2.82%) than in non-flooded shelters (53 of 3,155 evacuees; 1.68%). After June, its prevalence was still higher (18/541; 3.33%) in tsunami-flooded shelters than in non-flooded shelters (10/1063; 0.94%). The cause of the high prevalence of DVT was supposed to be dehydration due to the delay in supplying drinking water, vomiting, and diarrhea experienced by the evacuees because of a shortage of clean water to wash their hands. Dehydration was especially noticed in women because they restricted themselves of water intake to avoid using unsanitary toilet facilities. Moreover, crowded shelters restricted the mobility of elderly people, which would exacerbate the prevalence of DVT. Those deteriorated and crowded shelters were observed in tsunami-flooded areas. Therefore, long-term shelters should not be set up in flooded areas after tsunami.

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