The ratio of the 30th to the 15th cardiac cycle duration on an electrocardiogram (30:15 ratio) immediately after active standing from the supine position has been used as one of the markers of baroreflex function. A ratio of ≤1.0 has been suggested to indicate baroreflex dysfunction. Blood pressure (BP) changes were measured and the 30:15 ratio was calculated after standing and during 45-degree passive head-up tilt from the supine position in 10 nondiabetic men (mean age ± SE 70.1 ± 1.05 years, and BP <150/90 mm Hg). After tilt the decrease in systolic BP (from 132 ± 4.8 to 117 ± 6.3 mm Hg; p < 0.001) appeared to be larger than that after standing (from 132 ± 4.6 to 123 ± 5.8 mm Hg; p < 0.01), whereas the 30:15 ratios were 0.965 ± 0.006 and 0.970 ± 0.014, respectively, which suggested baroreflex dysfunction. Although the mean of the 2 ratios did not differ, the variance appeared to be less during tilting than after standing. Thus, the 45-degree passive head-up tilt appeared to be a better and more uniform inducer of orthostatic stress than active standing. Therefore, 45-degree head-up tilt was used in a group of 10 nondiabetic male patients (aged 70 ± 1.46 years) with isolated systolic hypertension (systolic BP >160 mm Hg, diastolic BP of <90 mm Hg) to assess their baroreflex function. Upon tilting, their systolic BP decreased from 190 ± 5.5 to 179 ± 5.8 mm Hg (p < 0.05) and their 30:15 ratio was 0.985 ± 0.011. The ratio had no correlation with systolic BP in either group. Patients were then treated with oral hydrochlorothiazide 50 mg/ day. After 1 month of therapy, systolic BP decreased from 190 ± 5.5 to 173 ± 9.3 mm Hg, and this decrease was maintained at 1 year (167 ± 7.7 mm Hg); the 30:15 ratios were 0.977 ± 0.01 and 0.995 ± 0.01, respectively, comparable to the pretreatment value. Thus, the depressed baroreflex function (30:15 ratio ≤1) in nondiabetic elderly patients seemed to be a phenomenon of advance dage rather than related to systolic hypertension, and long-term thiazide diuretic therapy did not affect this autonomic mechanism in these patients.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine