A Modified Method of Quantifying the Carotid Baroreceptor-Heart Rate Reflex in Man: The Effect of Age and Blood Pressure

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Abstract
Carotid baroreceptor-heart rate sensitivity has been measured non-invasively by a modified neck-chamber method that utilizes all cardiac intervals recorded in 6 min during 84 respiratory cycles. In a replication study in 10 subjects the mean baroreflex sensitivity was 5.52 ms/mm Hg and the mean (SD) difference between determinations was 0.70 (0.74) ms/mmHg. Baroreflex sensitivity was measured in 48 untreated subjects of mean age 43 (range 20-71) years with blood pressures ranging from 104 to 202 mmHg (13.9 to 26.9 kPa) systolic and 52 to 120 mmHg (6.9 to 16.0 kPa) diastolic [average 142/87 mmHg (18.9/11.6 kPa)]. Both systolic and diastolic pressures correlated with age (r = 0.53, P < 0.001 and r = 0.44, P < 0.01). Baroreflex sensitivity determined throughout respiration was log-normally distributed and a median value of 2.24 ms/mmHg, which declined with age (r = -0.63, P < 0.001). After allowing for the effects of age, baroreflex sensitivity throughout respiration was not independently related to either systolic or diastolic blood pressure.