Study of the osmopressor response in human volunteers with and without hypertension

The osmopressor response refers to the increase in blood pressure and associated change in heart rate that occurs in some people after ingestion of water (1). The response does not occur after drinking other liquids or beverages. It is therefore an intriguing physiological response dependent upon the low osmolality of water. The mechanism of action is not fully understood but probably involves sympathetic activation at the level of the spinal cord. Vasoconstriction of the peripheral and splanchnic vasculature may support an increase in blood pressure (2).

In patients with autonomic nervous system failure, the simple act of trying to stand up from lying down is a difficult challenge. The normal mechanism that supports blood pressure and blood flow to the head and brain upon standing (baroreceptor reflex) does not work properly. Patients feel weak, dizzy and may faint as they attempt the change in posture (orthostasis). In other words, these patients have poor orthostatic tolerance. Drinking water improves orthostatic tolerance in these patients (1). The osmopressor response is therefore of importance in this patient group, who are advised to drink water before getting out of bed in the morning, or if feeling faint.

Healthy participants also show a type of osmopressor response (3). Drinking 500 ml water decreases heart rate (bradycardia, decrease of bpm for 30-40 minutes) in young healthy volunteers with less of a direct effect on blood pressure. These findings have been replicated in a student population at Kingston University. The effect of water ingestion in patients with hypertension is relatively unexplored.

The initial aims of the project are to:

1) Develop and validate an experimental protocol for use with the participant populations.

2) Determine the effect of water ingestion on systolic and diastolic blood pressure, heart rate and other cardiodynamic parameters.

3) Determine the relevance of the hydration status of volunteers on the size and nature of the osmopressor response.

4) Determine the activity of the autonomic nervous system and other key parameters during and after water ingestion.

The project will involve experimental work conducted in and out of the laboratory. The research will be conducted by a multi-disciplinary team across the Department of Pharmacy, and the Department of Sports Science in the Faculty of Science Engineering & Computing at Kingston University, as well as at partner institutions. A wide range of techniques in physiology and biochemistry will be employed. The exact programme of work will be established between the candidate and supervisory team.

Candidates should have a first or upper second class honours in an area relevant to the proposed research. This includes areas such as human physiology, biochemistry, pharmacology, and sports science. You will have excellent practical laboratory skills and excellent interpersonal skills for working with healthy volunteers and patients. In all cases a master’s degree or equivalent qualification or other evidence of research skills and experience is preferred but not essential.