Most clinical offices rely on automated oscillometric devices to measure blood pressure (BP), but the accuracy of this technique versus auscultatory determination using a mercury manometer is controversial. To assess the accuracy of automated oscillometric readings, BP was measured from the same site and cuff, in 337 consecutive patients seen in a routine cardiology office, using a simultaneous connection to an automated oscillometric and a mercury manometer technique. The mean systolic BP (133 ± 20 mm Hg) and diastolic BP (72 ± 11 mm Hg) were significantly greater using the mercury manometer than the automated oscillometric technique (systolic 131 ± 18 and diastolic 70 ± 12 mm Hg, p <0.0001). Discrepancies (almost always lower oscillometric and greater mercury manometer) in systolic BP were seen in 22% of all patients. Discrepancies in diastolic BP were seen in 20% of all patients. The mean of the discrepancy between the 2 techniques was 1.95 ± 5 mm Hg (range 1 to 26) for systolic BP and 1.3 ± 4 mm Hg (range 1 to 25) for diastolic BP. The discrepancies were greater in patients >65 years. In conclusion, the mercury manometer technique resulted in consistently greater BP values than oscillometric devices. These findings have important clinical implications, including the concept that patients whose BP appears to be under control using the oscillometric technique might not be at their goal BP and might have been undertreated.
To measure patients’ blood pressure (BP), most clinical offices, hospitals, and home monitoring devices rely on automated oscillometric technology. In contrast, many clinical trials that have tested antihypertensive agents have relied on auscultatory assessment with a mercury manometer. However, the mercury products are being phased out, although some controversy exists regarding the accuracy of the automated oscillometric devices compared to the standard auscultatory mercury technique of measuring BP. The present study compared the accuracy of machine (automated oscillometric device) readings and auscultatory/mercury measurements when the 2 types of BP readings were analyzed simultaneously for the same patient, during the same heart beats, within a clinical cardiology office.
Methods
To assess the agreement of BP measurements using 2 techniques, the BP was measured from the same site and same cuff, simultaneously, in 337 consecutive patients during a routine clinic visit with their cardiologist. All BP measurements were performed with a Y connector from an appropriate size cuff (Welch Allyn, Skaneateles Falls, New York) and stethoscope placed over the brachial artery, connected to both an automatic oscillometric BP device (BioZ, Cardio Dynamics, Bothel, Washington) and a mercury manometer (Pymah, Somerville, New Jersey). All BP readings using the same oscillometric and mercury manometer devices were obtained by a senior cardiologist (SHW). The patients rested for about 3 minutes in a seated position before the BP measurements were taken in the right arm. Both the arm and monitors were at heart level, and deflation of the cuff occurred at approximately 2 mm Hg/s. The systolic BP by auscultation was defined as the appearance of Korotkoff sounds on slow deflation; diastolic BP was defined as the disappearance of the Korotkoff sounds with further deflation. The data were also categorized by the number of patients exhibiting a discrepancy of <5 mm Hg between the 2 BP measurement techniques (both systolic and diastolic), the number of patients with discrepancies of 5 to <10 mm Hg; 10 to <15 mm Hg; 15 to <20 mm Hg; and ≥20 mm Hg. The data were also analyzed for subgroups of patients, including age ≥65 years and <65 years. An additional assessment was performed for those with and without a known diagnosis or risk factors, including the clinical diagnosis of hypertension, diabetes, coronary artery disease, peripheral vascular disease, chronic renal disease, and dyslipidemia. Paired t tests were used to determine the significance of the BP discrepancies within the same patients using the auscultatory/mercury manometer versus the automatic oscillometric technique. A p value of <0.05 was considered statistically significant.
Results
BP measurements were available for 337 consecutive patients (mean ± SD age 70.0 ± 13.4 years, range 22 to 98). The mean systolic BP was significantly greater using the auscultation/mercury (133 ± 20 mm Hg) than the automatic oscillometric (131 ± 18 mm Hg) technique (p <0.0001). The mean diastolic BP was significantly greater using the auscultation/mercury technique (72 ± 11 mm Hg) than the automatic oscillometric technique (70 ± 12 mm Hg, p <0.0001). Discrepancies (almost always lower for the automatic oscillometric and greater for the auscultation/mercury technique) in systolic BP were observed in 22% of all patients. For systolic BP, a discrepancy of <5 mm Hg was observed in 4% of patients; 5 to <10 mm Hg in 5% of patients; 10 to <15 mm Hg in 7% of patients; 15 to <20 mm Hg in 4% of patients, and ≥20 mm Hg in 2% of patients. Discrepancies in diastolic BP were seen in 20% of all patients (again the BP reading was almost always greater using the auscultation/mercury technique and lower using the automatic oscillometric technique). A discrepancy of <5 mm Hg in diastolic BP was seen in 7% of patients; 5 to <10 mm Hg in 5% of patients, 10 to <15 mm Hg in 6% of patients; 15 to <20 mm Hg in 1% of patients, and ≥20 mm Hg in 1% of patients. The mean discrepancy between the 2 techniques was 1.95 ± 5 mm Hg (range 1 to 26) for systolic BP and 1.3 ± 4 mm Hg (range 1 to 25) for diastolic BP.
Table 1 lists the mean BP results for all patients and the subgroups. A discrepancy between the 2 techniques was observed in both women and men. Of the patients <65 years old, 10.4% demonstrated a discrepancy in the BP measurements between the 2 techniques; in patients ≥65 years old, 28.6% demonstrated a discrepancy. Those with risk factors or cardiovascular diagnoses were more likely to exhibit BP discrepancies.
| Characteristic | Auscultatory BP (mm Hg) (n = 337) | Oscillometric BP (mm Hg) (n = 337) | P Value | |
|---|---|---|---|---|
| Systolic BP | Diastolic BP | |||
| All patients | 133.2/71.6 | 131.3/70.3 | <0.0001 | <0.0001 |
| Gender | ||||
| Women | 137.0/71.2 | 134.7/69.5 | <0.0001 | 0.0001 |
| Men | 130.0/71.9 | 128.3/71.0 | <0.0001 | 0.0002 |
| Age (years) | ||||
| <65 | 128.1/76.0 | 127.5/75.8 | 0.094 | 0.18 |
| ≥65 | 135.6/69.6 | 133.0/67.8 | <0.0001 | <0.0001 |
| Diagnosis ⁎ | ||||
| 0 | 128.1/72.9 | 126.6/71.8 | 0.065 | 0.17 |
| ≥1 | 133.7/71.5 | 131.7/70.2 | <0.0001 | <0.0001 |
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