Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA006

Poster Communications

Investigation of the osmopressor response in young healthy adults

M. Carew1

1. Pharmacy, Kingston University, Woking, Surrey, United Kingdom.

  • Figure 1. Effect of water ingestion (500 ml over 5 minutes) on systolic blood pressure, diastolic pressure, and heart rate in young healthy adults tested in the seated position. Controls had no drink. Mean (SEM), n=37. *p<0.05 by ANOVA.

Introduction The osmopressor response was reported in 1999 in patients with orthostatic hypotension secondary to autonomic nervous failure. Ingestion of 480 ml water increased systolic blood pressure by 33-37 mm Hg and diastolic blood pressure by 14 mm Hg (1, 2). However, the nature and size of the osmopressor response in healthy people is unclear (3, 4, 5). The aim of this study was to determine if water ingestion increased blood pressure in young healthy volunteers. Methods Thirty-seven young undergraduates (median age 22 years, range 20-25; 13 male: 24 female) were enrolled on the study. All subjects self-declared as healthy and not on medication. Institutional ethics approval for the study was granted. Subjects sat at a table in a well-lit, air-conditioned room (22-24 oC) for 80 minutes. Blood pressure was measured using automated brachial cuff monitors every 5 minutes. After 20 minutes subjects ingested 500 ml water within five minutes, or otherwise received no drink. Test runs were performed on three separate occasions for each subject. Data was analysed by two-way ANOVA with Dunnett's post-hoc tests and correction for multiple testing (Graph Pad Prism). Mean values of parameters at 25-80 minutes were compared to the control mean at 20 minutes. Differences in means with p <0.05 were considered significant. A sub-group of 13 subjects also ingested 300 ml orange juice to compare with any effects of water. Results Systolic blood pressure was increased transiently 10 minutes after onset of water ingestion: 20 minutes (baseline) = 109.2 (1.7) mmHg (mean, SEM, n=37); 30 minutes = 112.6 (1.7) mmHg (p<0.05). Diastolic blood pressure was also increased at this time point: 78.4 (1.4) mmHg at 30 minutes compared to baseline: 73 (1.1) mmHg (p<0.05). The major response to water ingestion was a long-lasting decrease in heart rate (Figure 1). Heart rate decreased from a baseline of 79.8 (1.4 bpm) to 76.2 (1.4) bpm at 30 minutes (p<0.05), with a maximum decrease of nearly 6 bpm at 40 minutes: 73.8 (1.3) bpm (p<0.05). The decrease in HR lasted until 65 minutes (45 minutes post water ingestion). Heart rate naturally decreased in the sitting position with no drink and was significantly different to baseline after 70-80 minutes. Ingestion of 300 ml orange juice had no sustained effects on any parameter. Conclusion The major response to water ingestion in these young healthy volunteers was a long lasting negative chronotropic response or bradycardia. A transient increase in systolic and diastolic blood pressure was recorded 10 minutes after onset of water ingestion but was not sustained. The bradycardia may be as a result of the baroreceptor reflex and/or increased vagal drive to the heart. Further research into the mechanism and utility of the response is planned.

Where applicable, experiments conform with Society ethical requirements