Cuff and Bladder: Overlooked Components of BP Measurement Devices in the Modern Era?

Abstract

Accurate blood pressure (BP) measurement is an essential prerequisite for proper management of hypertension, independently from the technique employed. The use of too narrow or too short bladders may lead to overestimation of BP, a problem often overlooked by many doctors when measuring BP in obese subjects.1 To avoid the consequences of miscuffing, a number of approaches have been used over the years.1,2 Correction formulae have been suggested to adjust measurement errors, a procedure which has the disadvantage of further complicating the BP measurement. Other investigators have proposed the availability of a range of cuffs, so that the user after measuring the arm circumference can choose the appropriate cuff size. However, this requirement is usually neglected in clinical practice. More recently, cuffs containing bladders of varying dimensions have been made available but also these models did not find widespread use because of cuff stiffness, and because of its cost. An adjustable cuff which may encircle all adult arms has been designed by a British Company but there is no sufficient experience to recommend its use.1,2 In the modern era of BP assessment, the different function of the cuff in the different measurement methods should be highlighted. Whereas with traditional auscultatory technique the role of the cuff is to compress the artery under a defined reference pressure, with oscillometric devices the cuff is at the same time the signal sensor. Moreover, depending on the device algorithm, the signal sensing may take place not only during the pressure deflationary phase, but also, or even exclusively, at the inflationary phase and the measurement ends after the systolic pressure is detected. This leads to additional cuff performance requirements in oscillometry compared with Korotkoff. Special attention should be put on the signal transmission characteristics with different bladder materials (for example Latex, PVC, TPU), and on the inflation modality that should not generate noise from sticky bladder walls, friction between bladder and enclosure, or instable or worn out Velcro enclosures. It is therefore important in device validation studies also to document the type, shape and material characteristics of the cuff under investigation. It should be reported whether the cuff has a D-ring typical for self-application cuffs, or no D-ring typical for clinical use when the cuff is applied by another person. Obesity is an emerging problem in developed countries and may result in inaccurate BP measurements. The regular adult cuff size is too short for individuals with an arm circumference of 32 cm or larger and thus overweight and obese patients will often require the use of large-sized cuffs. In patients with morbid obesity, one will encounter very large arm circumferences with short upper arm length. In these patients, measurement with a cuff of the appropriate size is often difficult because the elbow end of a large cuff may extend past the elbow by several centimeters. According to the American Heart Association recommendations, for arm circumferences ranging from 35 to 44cm a bladder measuring 16cm in width should be used.3 For circumferences from 45 to 52cm the bladder width should be 20cm but in subjects with short upper arm length a 16cm wide cuff should be used. Recent results from our laboratory obtained in 349 subjects indicate that these bladders are not suitable for many individuals. According to our data, arm length was <20cm in 22% of the subjects and <16cm in 0.6% of the subjects.4 Thus, a large arm often cannot be correctly cuffed. The practical consequence is that special cuffs that can accommodate a wide range of arm sizes from medium to very large are needed. It should be noted that the present recommendations for cuff size with relation to arm circumference apply to the conventional auscultatory method, whereas much less is known about the relationship between cuff size and performance for oscillometric devices. In the auscultatory BP measurement, a complete artery occlusion is necessary as a prerequisite for the systolic pressure determination. In oscillometry, the reference point is not the artery occlusion, but the oscillometric peak signal which is equivalent to mean BP and is well below the artery occlusion pressure.5 Complete artery occlusion is not critical here because oscillations can be detected also beyond the systolic pressure through the knocking of the pulse at the over inflated bladder wall.5 Modern automatic devices can overcome the problem of miscuffing in obese individuals, thanks to a special software algorithm that can provide accurate BP readings also when coupled to a single cuff of theoretically inappropriate size.6,7 The correct reference pressure in the cuff, in spite of even smaller bladder sizes than traditionally recommended, is reached through a specific cuff design which can provide stable occlusion efficiency over a wide range of arm sizes and in the sof