CONTRIBUTION OF ENDOTHELIAL FUNCTION TO THE RADIAL
ARTERIAL PRESSURE WAVEFORM. CS. Hayward, CM. Webb and P. Collins. Department of Cardiac Medicine, Imperial
College, London SW3 6LY, United Kingdom. Endothelial function is typically defined
in discrete arterial beds such as the brachial or coronary systems. The peripheral arterial pressure waveform is
determined by a number of factors including reflection of the pressure wave
ejected from the heart. We hypothesised
that endothelial function contributes to the pressure waveform under resting
conditions by affecting "global" wave reflection. We used applanation tonometry to non‑invasively record
radial arterial pressure waveform responses to intravenous N‑monomethyl‑L‑arginine
(L‑NMMA, 2-3mg/kg over 5 mins) then sublingual glyceryl trinitrate (GTN,
200mcg) in 10 healthy males aged 29±2 years (mean±SEM). Eight subjects also received Substance P
(SubsP, 5pmol/kg over 5 mins) before NMMA.
Subjects were studied supine, fasting.
Brachial DP (Dinamap), heart rate (HR), and tonometry (Sphygmocor)
recordings were taken every 5 mins.
There was no significant effect of NMMA on systolic or mean BP. SubsP induced a facial flush in all subjects
and decreased systolic and mean BP (119±2.4 vs 113±2.9 and 84±2 vs 78±2mmHg,
p<0.02 for both). GTN decreased mean
BP only. Peripheral augmentation index
(AIx), an index of wave reflection, increased significantly following NMMA
(49.7±4.3 vs 56.1±4.5%, p<0.05) and fell markedly following GTN (49.7±4.3 vs
31.2±2.6%, p<0.01). The secondary
wave shoulder disappeared after SubsP, precluding calculation of AIx. HR fell slightly post NMMA and increased
following GTN, though changes were not significant after Bonferroni
correction. SubsP increased HR
significantly from baseline (73±4 vs 62±1bpm, P<0.01). Derived central systolic BP did not change
in response to NMMA or GTN but decreased significantly following SubsP. In conclusion, we found that endothelial
function contributes significantly to the peripheral arterial pressure waveform. Agents such as GTN affect the pressure
waveform independently of the endothelium.
