A modified method of quantifying the carotid baroreceptor-heart rate reflex in man: the effect of age and blood pressure.

1. 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. 2. In a replication study in 10 subjects the mean baroreflex sensitivity was 5.52 ms/mmHg and the mean (SD) difference between determinations was 0.70 (0.74) ms/mmHg. 3. 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 less than 0.001 and r = 0.44, P less than 0.01). 4. Baroreflex sensitivity determined throughout respiration was log-normally distributed with a median value of 2.24 ms/mmHg, which declined with age (r = -0.63, P less than 0.001). 5. After allowing for the effects of age, baroreflex sensitivity throughout respiration was not independently related to either systolic or diastolic blood pressure.