Baroreceptor-heart rate reflex sensitivity enhancement after urinary bladder distention in essential hypertensives

Our objective was to determine if urinary bladder distention modifies the s ensitivity of the baroreceptor-heart rate reflex in hypertensive and contro l subjects. The baroreceptor-heart rate reflex sensitivity was measured in 15 male patients (mean age 37 +/- 8 years) with mild untreated hypertension (mean 163 +/- 8/ 95 +/- 12 mmHg) and 17 age- and sex-matched control subje cts before and after urinary bladder distention. Bladder filling was perfor med infusing saline heated to 37 degrees C via a urinary catheter; the volu me infused in each patient corresponded to that which caused the urge to vo id without reaching the pain threshold. The baroreceptor-heart rate reflex sensitivity was determined correlating the variations of the systolic press ure and of the peak blood flow velocity in the common carotid artery with t he variations of the ECG RR' interval of the following heart beat, both dur ing spontaneous and phenylephrine-induced fluctuations of the haemodynamic variables. After bladder distention the diastolic pressure of the hypertens ive subjects increased significantly (95 +/- 12 vs. 100 +/- 12 mmHg; P < 0. 02), whereas the heart rate decreased (RR = 873 +/- 70 vs. 926 +/- 80 ms; P < 0.005). These parameters were unchanged in the normotensive subjects (84 +/- 9 vs. 83 +/- 8 mmHg and 914 +/- 158 vs. 913 +/- 140 ms, respectively). The baroreceptor-heart rate reflex sensitivity, measured on the basis of s pontaneous pressure and carotid blood flow velocity fluctuations in relatio nship to RR changes, decreased in the normotensive subjects after bladder d istention (10.7 +/- 4.6 vs. 9.4 +/- 2.7 ms/mmHg; P < 0.05 and 423 +/- 99 vs . 356 +/- 102 ms/kHz; P < 0.01, respectively), whereas it increased in the hypertensive patients (6.9 +/- 3.6 vs. 8.3 +/- 2.8 ms/mmHg; P < 0.03, and 3 32 +/- 86 vs. 381 +/- 97 ms/kHz; P < 0.03 respectively). After bladder dist ention and phenylephrine administration the baroreceptor-heart rate reflex sensitivity, measured by the correlation between systolic pressure and RR i nterval, increased only in the hypertensive group (10.2 +/- 5.4 vs. 15.2 +/ - 7.7 ms/mmHg; P < 0.005). In conclusion urinary bladder distention provoke s in hypertensives but not normotensive controls a brisk parasympathetic re sponse of the component of the baroreceptor-heart rate reflex which control s heart rate.