Differential response of peripheral arterial compliance-related indices to a vasoconstrictive stimulus

Abstract

Peripheral arterial elastic properties are greatly affected by cardiovascular as well as other pathologies, and their assessment can provide useful diagnostic indicators. The photoplethysmographic technique can provide finger blood volume and pressure waveforms non-invasively, which can then be processed statically or beat-to-beat to characterize parameters of the vessel wall mechanics. We employ an occlusion-deflation protocol in 48 healthy volunteers to study peripheral artery compliance-related indices over positive and negative transmural pressure values as well as under the influence of a valid vasoconstrictor (cigarette smoking). We calculate beat-to-beat indices (compliance index CI, distensibility index DI, three viscoelastic model parameters (compliance C, viscosity R and inertia L), pressure-volume loop areas A and damping factor DF as well as symmetrical (C(max)) and asymmetrical (C(A)(max)) static compliance estimates, and their distributions over transmural pressure. All distributions are bell-shaped and centred on negative transmural pressure values. Distribution heights were significantly lower in the smoking group (w.r.t. the non-smoking group) for C, CI, DI and significantly higher in R and DF. The estimated volume signal time lag was also significantly lower in the smoking group. Left and right distribution widths were significantly different in all parameters/groups but DI (both groups), C(A)(max), A (smoking group) and L (non-smoking group), and positions of maxima/minima were significantly altered in C(A)(max), R and DF. C, DF and CI are seen to be most sensitive under this protocol, while C(max) and C(A)(max) are seen to be insensitive. These quantities provide complementary, time- and transmural pressure-dependent information about arterial wall mechanics, and the choice of index should depend on the physiological conditions at hand as well as relevant time resolution and transmural pressure range.

A novel photoplethysmography technique to derive normalized arterial stiffness as a blood pressure independent measure in the finger vascular bed

“…Our exponential model for the P-V function of the finger artery is simple and defined with a clear physical meaning but more sophisticated models may show a stronger fit (Guerrisi et al 2009, Talts et al 2006. However, various models involving the present one are descriptive by nature in any case and have no direct physiological meaning at all since they are not linked by themselves to any characteristic value of the blood vessel wall.…”

Diastolic shock index (DSI) works… and it could be a quite useful tool

“…Vascular tone, defined as the activation degree of vascular smooth muscle cells, provides a measure of vascular regulation in response to external stimuli as hormonal, myogenic, neural and endothelial-derived factors. Nevertheless, direct in vivo assessment of vascular tone during dynamic clinical conditions is not quite evident and it has been typically based on indirect measurements of vascular resistance: blood flow; arterial pressure/volume, pressure/diameter, and compliance/distensibility-pressure relationships [2,3].…”

Using the diastolic shock index to determine when to promptly administer vasopressors in patients with septic shock

“…Classically, a low diastolic arterial pressure (DAP) has been recognized as an indirect sign of vasodilation, although the in vivo assessment of vascular tone (i.e., during dynamic conditions) is not standardized and has been classically based on indirect measurements of vascular resistances. 4 Under normal conditions, the DAP is mainly determined by vascular tone, and it remains nearly identical from the center to the periphery (i.e., from the ascending aorta to the peripheral vessels). 5 In contrast, the systolic arterial pressure (SAP) and consequently the MAP may greatly vary from the aorta to the peripheral vessels as long as peripheral arterial elastance varies.…”

“…A decrease in vascular tone represents one of the leading mechanisms associated with hypotension and tissue hypoperfusion in septic shock [ 3 ], and it is fundamentally characterized by a progressively impaired response from the vascular smooth muscle to endogenous circulating and exogenous vasoconstrictors. Classically, a low diastolic arterial pressure (DAP) has been recognized as an indirect sign of vasodilation, although the in vivo assessment of vascular tone (i.e., during dynamic conditions) is not standardized and has been classically based on indirect measurements of vascular resistances [ 4 ]. Under normal conditions, the DAP is mainly determined by vascular tone, and it remains nearly identical from the center to the periphery (i.e., from the ascending aorta to the peripheral vessels) [ 5 ].…”