Nitric oxide donor drugs cause downward descent of the dicrotic notch (DN) of the digital pulse wave due to attenuation of wave reflection (Imhof et al: Eur.J. Clin Pharmacol. 1980;18:455). Increased shear stress to endothelium causes endothelial nitric oxide synthase to produce nitric oxide. DN was measured during active cycling which increases laminar shear stress, periodic acceleration that increases pulsatile shear stress and passive cycling that should not change shear stress.
DN of photoelectric plethysmographic pulse was measured by dividing (a) pulse amplitude by (b) height of dicrotic notch above end diastolic level. Heart rate (HR) was measured with ECG. 7 men and 5 women performed the following for 3 min with 5 min baseline and recovery times: 1) supine cycling at ∼250 (EX1) and ∼450 Kg-M/min (EX2); 2) supine periodic acceleration (pGz) applied with a motion platform (Non-Invasive Monitoring Systems, North Bay Village, FL); 3) passive cycling at 1 Hz (n=9).
a/b ratios are expressed as peak values during period. *p<.001 Whitney Mann U test for differences between baseline and test. Baseline a/b during EX1 was 2.2 and test 16.9.* Baseline a/b during EX2 was 2.4 and test 42.6.* Baseline a/b during pGz was 2.3 and test 28.0.* In one instance during EX1, 4 instances during EX2, and 3 instances during pGz, DN moved to upstroke of next pulse; here, a/b was assigned a value of 100.CONCLUSIONS: Dicrotic notch position is a simple, sensitive means to demonstrate that nitric oxide is released from laminar or pulsatile shear stress to endothelium.
Since periodic acceleration produces fall of dicrotic notch equivalent to low intensity exercise, it can be utilized to passively achieve the beneficial vasodilator and immunosuppressant effects of exercise through increased release of small quantities of NO from activation of endothelial nitric oxide synthase.
M.A. Sackner, Chairman, Board of Directors, Non-Invasive Monitoring Systems, Inc., shareholder, discussion of product research or unlabeled uses of product.