Skin blood pressure in the forehead in patients with internal carotid lesions

Cerebral venous steal equation for intracranial segmental perfusion pressure predicts and quantifies reversible intracranial to extracranial flow diversion

Cerebral perfusion is determined by segmental perfusion pressure for the intracranial compartment (SPP), which is lower than cerebral perfusion pressure (CPP) because of extracranial stenosis. We used the Thevenin model of Starling resistors to represent the intra-extra-cranial compartments, with outflow pressures ICP and Pe, to express SPP = Pd–ICP = FFR*CPP–Ge(1 − FFR)(ICP–Pe). Here Pd is intracranial inflow pressure in the circle of Willis, ICP—intracranial pressure; FFR = Pd/Pa is fractional flow reserve (Pd scaled to the systemic pressure Pa), Ge—relative extracranial conductance. The second term (cerebral venous steal) decreases SPP when FFR < 1 and ICP > Pe. We verified the SPP equation in a bench of fluid flow through the collapsible tubes. We estimated Pd, measuring pressure in the intra-extracranial collateral (supraorbital artery) in a volunteer. To manipulate extracranial outflow pressure Pe, we inflated the infraorbital cuff, which led to the Pd increase and directional Doppler flow signal reversal in the supraorbital artery. SPP equation accounts for the hemodynamic effect of inflow stenosis and intra-extracranial flow diversion, and is a more precise perfusion pressure target than CPP for the intracranial compartment. Manipulation of intra-extracranial pressure gradient ICP–Pe can augment intracranial inflow pressure (Pd) and reverse intra-extracranial steal.

Skin perfusion pressure measured with a photo sensor in an air-filled plastic balloon: validity and reproducibility on the lower leg in normal subjects and patients suspected of obliterative arterial disease

An inflatable small plastic bag including a photo sensor was constructed for measurement of skin perfusion pressure avoiding the rim of the photo sensor over bony and tendineous surfaces of the tibia below the knee, at the ankle, and on the dorsal forefoot. Compression was obtained using a conical blood pressure cuff with continuous decrease from suprasystolic arm pressure. The validity of skin perfusion pressure with the new device was compared to that of isotope washout below the knee in normal subjects and in patients with an ischemic forefoot with acceptable agreement. The method had a high reproducibility within and between days in normal subjects. Compared to systolic arterial pressure measured using a strain gauge with a cuff on the ankle in normal subjects and patients with intermittent claudication the new device showed blood pressure in the skin closer to the diastolic pressure. The new pressure device thus had acceptable validity and reproducibility for estimation of the skin perfusion pressure and can be used on bony and tendineous sites on the lower limb in regions where critical wound healing is frequent, e.g. ankle and forefoot.

Skin perfusion pressure on the legs measured as the external pressure required for skin reddening after blanching: a photo-electric technique compared to isotope washout

The skin perfusion on the calf was measured photo-electrically and by isotope washout technique using external counter pressure by a blood pressure cuff. By the photocell the skin blanching threshold external pressure (BTEP) was recorded on histamine flared red skin. By isotope washout technique the skin blood flow cessation external pressure (FCEP) was recorded using intra-dermal [131I-]-antipyrine mixed with histamine in estimating the skin blood flow. The external pressure was measured with an airfilled plastic cushion connected to a mercury manometer. Over a wide range of pressures as obtained from twenty patients with occlusive arterial disease of the legs, five normal subjects and eleven patients treated for arterial hypertension the values of the two different methods were highly significantly correlated (r = 0.97, P < 0.001). On average the BTEP was equal to the FCEP: 83.9 mmHg (range 18-187) compared to 80.8 mmHg (range 18-158) (P > 0.1). A normal material was obtained from twenty-four subjects measured on the thigh, calf and ankle; the average gradients between the auscultatory brachial mean blood pressure and the BTEP were: thigh 10.7 mmHg (SD 12.7); calf 4.0 mmHg (SD 12.1); ankle 5.1 mmHg (SD 8.7). As compared to the intra-arterial blood pressure the BTEP was found to lie close to the mean blood pressure in normal subjects as well as in hypertensive subjects. The present data indicate that the skin perfusion pressure on the legs can be measured by the rapid photo-electric technique. The clinical application and sources of error are discussed.

Ophthalmodynamography and ophthalmodynamometry in neurological practice

Inventarisation of atraumatic methods of analysing the circulation in the carotid region shows that they generally can be classified as physiological or anatomical. Physiological methods focus on blood circulation time or on the pulsating changes in blood pressure, blood velocity, blood vessel diameter and cerebral volume. In this study the reliability of two pressure-dependent methods, namely ophthalmodynamography and ophthalmodynamometry, for the detection of haemodynamically significant carotid stenosis is established. Correct results were found in 78--82% of cases. Ophthalmodynamography, and the advantage of combining this method with ophthalmodynamometry, are more extensively investigated. Although in recent years attention has been focussed on the study of the blood velocity pulsations with the Doppler technique, maximal diagnostic efficacy can be expected from a combination of pressure and flow wave studies. A way to compare all the information contained in the curves can be found in the technique of Fourier analysis. The results obtained by Fourier analysis of the ophthalmodynamographic curves are presented.