Difference in blood pressure between arms might reflect peripheral vascular disease

Editor—I believe that McAlister and Straus underestimate the frequency and significance of a blood pressure difference between the arms.¹ They quote 6% from the paper by Harrison et al, but this group reported a difference in 10/131 (that is, 7.6%) normotensive subjects for systolic or diastolic differences, 44/310 hypertensive patients (14%) for a systolic difference, and 31/310 hypertensive patients (10%) for a diastolic difference.²

I have reviewed the English language literature and identified 11 studies with comparable data on at least 100 subjects. These studies (table) reported prevalences ranging from 12% to 18.4% for a systolic difference ⩾20 mm Hg and 13% to 33.7% for a diastolic difference ⩾10 mm Hg in selected populations. No publications were identified from primary care.

I have been prospectively gathering pairs of readings from hypertensive patients. To date I have collected 435 pairs of recordings from 205 patients. The mean absolute systolic difference is ⩾10 mm Hg in 64 (31%) patients and ⩾20 mm Hg in eight (4%). The mean absolute diastolic difference is ⩾10 mm Hg in 27 (13%) patients. These data suggest that identification of any difference in blood pressure between arms is a vital part of the assessment of hypertensive patients if their diagnosis is to be accurate and their response to treatment reliably monitored.

The causes of a pressure difference between arms are unclear. Harrison et al found fewer differences with intra-arterial measurements than with indirect techniques, suggesting that variations in the measurement techniques or the soft tissues may play a part.² For some patients the difference is vascular in origin. This may be due to characteristics of flow in a normal arterial tree,³ but I suggest that vascular disease may also cause a difference. One study found an increased prevalence of differences in patients with coronary heart disease or peripheral vascular disease,⁴ and another showed that 83% of vascular surgical patients with differences had angiographic evidence of innominate or subclavian artery stenosis on the side of the lower pressure.⁵

The importance of a difference is already recognised between the arm and the leg, as measured by the ankle-brachial pressure index, which is reduced in the presence of asymptomatic peripheral vascular disease; a reduced index is associated with increased mortality. Why should the pathology, and prognostic implications, not be the same with differences between arms?

Until more work is done, hypertensive patients with a reproducible difference in blood pressure between arms should be investigated and managed intensively, on the assumption that they have asymptomatic peripheral vascular disease.

Table.

Summary of previous studies searched

Population	Method of assessment	Sample size	Systolic pressure	Diastolic pressure	Year	Reference
General medical practice	Not stated	125	12% >20 mm Hg	13% >10 mm Hg	1930	Kay and Gardneri
Not stated	Not stated	516	Differences >20 mm Hg systolic or 10 mm Hg diastolic in 60% of cases		1935	Southbyii
Normotensive patients	Simultaneous measurement	700	12.1% >20 mm Hg	14.3% >10 mm Hg	1943	Amsterdam and Amsterdamiii
Hypertensive patients		230	60.5% >20 mm Hg	31.6% >10 mm Hg
Hypertensive patients	Not stated	125	18.4% ⩾20 mm Hg		1944	Israeliv
Not stated	Not stated	755	13.6% systolic ⩾20 mm Hg	33.7% diastolic ⩾10 mm Hg	1951	Ruegerv
Selected volunteers	Simultaneous direct intra-arterial	53	No significant differences detected		1960	Harrison et alvi
Normotensive patients	Sequential indirect	55	34.5% ⩾20 mm Hg	14.5% ⩾10 mm Hg	1982	Kristensen and Kornerupvii
Normotensive inpatients	Sequential random zero	23	26.1% ⩾20 mm Hg	43.5% ⩾10 mm Hg
Hypertensive outpatients	Sequential random zero	57	15.8% ⩾20 mm Hg	73.1% ⩾10 mm Hg
Hypertensive outpatients	Sequential indirect	62	12.9% ⩾20 mm Hg	25.8% ⩾10 mm Hg
Hypertensive patients	Simultaneous random zero	91	Dismissed differences >20 mm Hg as erroneous; found no apparent mean differences >10 mm Hg systolic or diastolic. Concluded that no bias is introduced by making measurements in different arms		1985	Gould et alviii
Patients with peripheral vascular disease	Sequential automated recording (Dinamap)	58	21% ⩾20 mm Hg		1991	Frank et alix
Patients with coronary heart disease		38	3% ⩾20 mm Hg
Controls		38	13% ⩾10 mm Hg
Elderly inpatients and outpatients	Simultaneous automated	40	10% >10 mm Hg		1993	Fotherby et alx
Young inpatients and outpatients		40	None
Ambulant patients >5 years old attending university hospital emergency department	Single sequential automated indirect (right then left arm)	300	13.3% >20 mm Hg	28% >10 mm Hg	1996	Singer and Hollanderxi
	Single simultaneous automated indirect	310	11.6% >20 mm Hg	20.6% >10 mm Hg

ⁱKay WE, Gardner KD. Comparative blood pressures in the two arms. California Western Medicine 1930;33:578-9. 

ⁱⁱSouthby R. Some clinical observations on blood pressure and their practical application, with special reference to variation of blood pressure readings in the two arms. Med J Australia 1935;2:569-80. (Quoted from Amsterdam and Amsterdam, reference iii.) 

ⁱⁱⁱAmsterdam B, Amsterdam AL. Disparity in blood pressures in both arms in normals and hypertensives and its clinical significance. N Y State J Med 1943;43:2294-2300. 

^ivIsrael E. Differences in blood pressure in both arms. Acta Med Orientalia 1944;3:86. (Quoted from Harrison et al, reference vi.) 

^vRueger MJ. Blood pressure variations in 2 arms. Ann Intern Med 1951;35:1023. (Quoted from Harrison et al, reference vi.) 

^viHarrison EG, Roth GM, Hines EA. Bilateral indirect and direct arterial pressures. Circulation 1960;22:419-36. 

^viiKristensen BO, Kornerup HJ. Which arm to measure the blood pressure? Acta Med Scand 1982;670(suppl):69-73. 

^viiiGould BA, Hornung RS, Kieso HA, Altman DG, Raferty EB. Is the blood pressure the same in both arms? Clin Cardiol 1985;8:423-6. 

^ixFrank SM, Norris EJ, Christopherson R, Beattie C. Right and left arm blood pressure discrepancies in vascular surgery patients. Anesthesiology 1991;75:457-63. 

^xFotherby MD, Panayiotou B, Potter JF. Age-related differences in simultaneous interarm blood pressure measurements. Postgrad Med J 1993;69:194-6. 

^xiSinger AJ and Hollander JE. Blood pressure: assessment of interarm differences. Arch Intern Med 1996;156:2005-8.