Can aneroid sphygmomanometers be used at altitude?

Assessing agreement of blood pressure-measuring devices in Tibetan areas of China: a systematic review

BACKGROUND

The validity of blood pressure (BP)-measuring tools at very high altitudes is uncertain. Therefore, the objective of this review was to examine the degree of agreement of BP-measuring devices in Tibet.

METHODS

We conducted electronic searches in Medline, Embase, Cinahl, Cochrane Library, Global Health Library and the ISI Web of Science. Randomised and observational studies were considered for inclusion. The methodological characteristics of included studies were assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 criteria. Our primary outcome was the difference in mean BP measurements between the new device and the gold standard.

RESULTS

We identified three eligible studies, out of which two with a total of 162 participants were included. The studies differed in their methodology. One study reported significantly higher systolic blood pressure (SBP) measurement with electronic sphygmomanometer (Omron) compared with mercury sphygmomanometer (mean difference 5.8±4.7 mm Hg; p<0.001), with no significant difference in diastolic blood pressure (DBP) measurement (0.4±3.9 mm Hg; p=0.23). The second study reported mean differences of 1.0±5.9 mm Hg and -3.1±4.6 mm Hg for SBP and DBP, respectively.

CONCLUSION

The limited evidence from published studies suggests that automated (Omron) BP monitors show a high degree of agreement for DBP when compared against mercury sphygmomanometer at high altitudes. However, the degree of such agreement for SBP is not consistent. Few studies assessing the validity of automated BP monitors at high altitudes have been conducted, and they differ in design and methodology. Further research assessing the suitability of BP-measuring instruments at high altitudes is therefore warranted.

Neck length and mean arterial pressure in the sauropod dinosaurs

How blood was able to reach the heads of the long-necked sauropod dinosaurs has long been a matter of debate and several hypotheses have been presented. For example, it has been proposed that sauropods either had exceptionally large hearts, multiple ‘normal’ sized hearts spaced at regular intervals up the neck, held their necks horizontal, or the siphon effect was in operation. By means of an experimental model, we demonstrate that the siphon principle is able to explain how blood was able to adequately perfuse the sauropod brain. The return venous circulation may have been protected from complete collapse by a structure akin to the vertebral venous plexus. We derive an equation relating neck height and mean arterial pressure, which indicates that with a mean arterial pressure similar to the giraffe, the maximum safe vertical distance between heart and head would have been about 12 m. A hypothesis is presented that the maximum neck length in the fossil record is due to the siphon height limit. The equation indicates that to migrate over high ground, sauropods would either have had to significantly increase their mean arterial pressure or keep their necks below a certain height dependent on altitude.

Validation of the Omron HEM-7201 upper arm blood pressure monitor, for self-measurement in a high-altitude environment, according to the European Society of Hypertension International Protocol revision 2010

Few studies have been conducted on blood pressure monitors and their use at high altitude. This study is the first to evaluate the accuracy of an automatic blood pressure monitor in a high-altitude environment following a standard validation protocol. The Omron HEM-7201 upper arm blood pressure monitor was tested for accuracy in Lhasa, Tibet, China (3650 m above sea level) according to the European Society of Hypertension International Protocol revision 2010 (ESH-IP2). Thirty-three participants received 9-10 sequential blood pressure measurements alternating between a mercury sphygmomanometer and the device. The mean device-observer measurement difference was 1.0±5.9 mm Hg for systolic blood pressure (SBP) and -3.1±4.6 mm Hg for diastolic blood pressure (DBP). Of the 99 measurement pairs analyzed, 72, 90 and 97 device readings were within 5, 10 and 15 mm Hg, respectively, of the observer measurements for SBP, and 68, 92 and 99 readings for DBP. The number of participants with at least two out of three measurements within 5 mm Hg was 27 for SBP and 25 for DBP. Three participants had no measurements within 5 mm Hg for either SBP or DBP. As a result, the Omron HEM-7201 passes the ESH-IP2 validation criteria and can therefore be recommended for use in adults in this setting.