Hypertension, Resistant to Conventional Therapy Clinical Trial
Official title:
Peripheral Chemoreflex/Arterial Baroreflex Interaction in Patients With Electrical Carotid Sinus Stimulation
Peripheral chemoreceptors and baroreceptors are located in close proximity in the carotid artery wall at the level of the carotid bifurcation. Baroreceptor stimulation lowers sympathetic activity and blood pressure. In contrast, chemoreceptor stimulation raises sympathetic activity and blood pressure. Thus, beneficial effects of electrical carotid sinus stimulation on blood pressure could be diminished by chemoreceptor overactivity and/or concomitant chemoreceptor activation through the device. Therefore, our study will assess baroreflex/chemoreflex interactions in patients with resistant hypertension equipped with carotid sinus stimulators. The study will inform us of potential additional anti-hypertensive benefits of simultaneous chemoreceptor denervation during electrode placement. Furthermore, the results may provide information about suitable electrode design to spare co-activation of peripheral chemoreceptors. Taken together, the study will help develop strategies for improving responder rate and efficacy of carotid sinus stimulators in patients with resistant hypertension.
Patients with implanted devices for electrical baroreflex stimulation are recruited according
to inclusion and exclusion criteria until good quality recordings have been obtained in 10
out of maximally 15 patients. After obtaining written informed consent patients will be
investigated in the laboratory on one day. In up to 20% of the patients we may fail to find
an appropriate nerve recording position. In these cases we will ask the patient to repeat the
experiment.
Patients will be investigated in the post-absorptive state after emptying their bladder.
During instrumentation and measurements they will rest in supine position. We will fix chest
electrodes for ECG and impedance cardiography. A peripheral venous catheter will be
introduced for later dopamine infusion. Cuffs will be used at the upper arm and the finger in
order to monitor blood pressure and to allow for pulse-contour analysis. Finally, we will
search for a suitable nerve recording position in the peroneal nerve for recordings of muscle
sympathetic nerve activity (MSNA, postganglionic vasoconstrictor sympathetic drive). All
bioelectric signals will be recorded continuously for the duration of the experiments.
After the preparations baseline recordings will be performed. Subsequently, the electrical
baroreflex stimulator is switched OFF and ON repeatedly (toggling) under normoxic conditions.
Every OFF and ON state will last for 4 minutes. Oscillometric blood-pressure readings are
taken every two minutes so as to acquire two readings per stimulation period. Toggling under
normoxia is meant to ensure that the patient is a responder at the experimental day and to
rule out that the blood pressure rises are too high off stimulation (safety concern).
Afterwards, the breathing gas will be changed in order to have the patient inhale a hypoxic
or hyperoxic mixture in a blinded manner. After reaching a stable ventilatory and autonomic
state, stimulator toggling and blood-pressure measurements will be repeated. The same
procedures will take place after establishing the opposite oxygenation state. Stimulation
will be ON in between the oxygen states implying that the first switches will be OFF switches
with all oxygenation conditions. Afterwards, the last oxygenation state will be maintained
and additional low-dose dopamine infusion will be applied. Again, the electrical baroreflex
stimulator will be switched off and on repeatedly and blood-pressure readings are taken.
During the last two stimulator toggling states of each oxygenation level, venous blood
samples are drawn for hormone measurements and inert gas rebreathing will take place for
cardiac output determination. Finally, the correct positioning of the microneurography
electrode is checked again.
The duration of such an experiment depends on the time needed to find the sympathetic nerve
bundles before the measurements and during the experiment, in case the recording position
gets lost. However, experiments will rarely exceed 5 hours in total.
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