The Role of Aldosterone on Augmented Exercise Pressor Reflex in Hypertension
The overall schema of all experiments are shown in fig 1 (see attached protocol)..
General Methods: BP will be measured with an oscillometric device (Welch Allyn, N.C.).
(1) Microneurography. With the subject supine, we will measure blood pressure, heart rate, and muscle SNA with microelectrodes in the peroneal nerve. The nerve signals are amplified, filtered, rectified and integrated to obtain a mean voltage display of SNA. The criteria for an acceptable recording of muscle SNA has been previously described 15. Sympathetic bursts will be detected by inspection of the filtered and mean voltage neurograms. A deflection on the mean voltage display is counted as a [AND]quot;burst[AND]quot; if it has a minimal signal to noise ratio of 2:1. SNA will recorded at rest in all protocols.
(2) Reflex Interventions: (a) Handgrip exercise . Rhythmic HG (RHG) will be performed in the nondominant arm at 40 beats per minute (50% cycle duty) at 30% and 45% maximal voluntary contraction (MVC), each for 3 minutes. Static HG (SHG) will be performed at 30% MVC for 2 minutes. Ratings of perceived exertion (RPE) will be obtained at the end of each exercise by using a 6- to 20-unit Borg scale. For safety, the study will be terminated if BP during exercise at any time point is 220/105 mmHg or above in accordance with current guidelines 10, 11. (b) Post-Handgrip Exercise Circulatory Arrest (PECA). During the last 5 sec of static HG exercise, a pneumatic cuff on the upper exercising arm will be inflated to 50 mmHg above systolic BP for 2 minutes to activate the metaboreflex. (c) Passive arm cycling. To activate mechanoreflex, the subject[Right Quote]s nondominant hand will be strapped to one of the arm pedal of the arm ergometer while the investigator put their hand on the other pedal to move the arm ergometer at 80 r.p.m. Subjects will be asked to relax their arms during passive arm cycling for 5 minutes. Surface electromyography (EMG) on the bicep muscles (Noraxon, Scottsdale, AZ) will be used to monitor the muscular activity and a biofeedback device to assist the subjects with relaxation of their arm muscles. (d) Arterial baroreflex sensitivity. Arterial baroreflex control of muscle SNA and HR will be assessed during bolus injection of nitroprusside (NTP) and phenylephrine (PE) using the modified Oxford technique 22. For safety reasons, NTP will not be given if BP is =90/60 mmHg and PE will not be given if BP is = 160/100 mmHg immediately prior to administration.
Experiments will be performed on 3 groups of nondiabetic human subjects ages 18 to 80 years of age 1) stage I (140-159/90-99 mmHg) subjects with essential hypertension, 2) stage I hypertensive subjects with primary aldosteronism, and 3) normotensive controls.