A simple technique for measuring arterial blood pressures in conscious human subjects.

A new technique for measuring blood pressure utilizes the subject's ability to sense the onset and cessation of the Korotkoff phenomenon within the artery itself. Of the readings made in this manner with a standard arm cuff 94% were found to agree within +/- 10 mm Hg with readings made with a stethoscope. And 91% of the blood pressures measured by this technique using an infant cuff on the thumb were found to agree within +/- 10 mm Hg with those measured by the same technique with a standard cuff at the brachial artery. Therefore a simple device was designed with which subjects can measure their own systolic and diastolic blood pressure by utilizing a combined syringe and cuff applied to the thumb. There was a mean systolic difference of 4.7 and a mean diastolic difference of 6.1 mm Hg between readings made on 40 subjects with the new instrument and those made with a mercury sphygmomanometer.

Indirect blood pressure measurements: a matter of interpretation.

The indirect measurement of arterial blood pressure is discussed from the standpoint of the intravascular phenomena that occur under the cuff during the production of Korotkoff sounds. The influence of the physical and elastic properties of the vessel wall and blood flow parameters on indirect blood pressure measurement were investigated by using the results of model studies carried out in a properly scaled, simulated mechanical system under controlled conditions. The results of those studies indicate that auscultatory readings may be subject to large errors, depending on the thickness and stiffness of the artery wall. These results are shown to be consistent with comparisons of direct and indirect blood pressures in human subjects in that errors of the order of 30 to 50 mm Hg are not uncommon in the elderly or in patients with advanced arteriosclerosis. The errors discussed here are inherent to the auscultatory technique and are not related to instrument calibration, auditory acuity, or office technique.

Theoretical prediction of a time-at-pressure curve for avoiding pressure sores.

A theoretical development of the pressure versus time curve for the onset of pressure sores is presented which is based upon the use of dimensional analysis. Comparison with available experimental data from humans and from dogs and swine indicate that this approach agrees well with experiment and also shows some promise for predicting the effects of skin elastic modulus and skin blood flow on the allowable pressures which can be safely tolerated by specific individuals.

Skin blood flow changes and tissue deformations produced by cylindrical indentors.

Since skin blood flow as a function of applied pressure depends on many factors, one may find different curves within each group of subjects, making separation of groups difficult. A dimensional analysis has been out which indicates that the percent decrease in skin blood flow associated with external loading is primarily a function of only three variables: the ratios of bone depth and bone diameter to indentor diameter, and percent compression of the tissue overlying the bone. The load itself is found to be unimportant. It is concluded that measurement of bone depth, bone diameter, and tissue deformation are more important than pressure measurements. Measurements of skin displacement and average indentor pressure for four male subjects indicate that tissue stiffness increases with age, regardless of disability, so that higher pressures are required to produce the same displacement in older subjects.

Difficulties in laser Doppler measurement of skin blood flow under applied external pressure.

During the course of a study of skin blood flow under applied external pressure, it became apparent that decreasing blood flow by loading the skin surface reveals problems that are fundamental to the method of laser Doppler flowmetry. These problems have to do with the fact that the laser Doppler is extremely sensitive to red cell motion of any kind, whether associated with the ordered red cell motion of blood flow or the random red cell motion associated with changes in temperature or vessel occlusion. This effect becomes increasingly important whenever blood flow is compromised (a situation of considerable clinical significance), since the random portion of the signal then becomes significant in comparison with the diminished blood flow. Experiments have been conducted in living animals and with stationary drops of blood which clearly show the importance of these effects with regard to the interpretation of laser Doppler signals. Significant laser Doppler flow signals were repeatedly observed after manipulations which could reasonably be expected to reduce blood flow to zero.

The effect of stenosis of bypass grafts on coronary blood flow. A mechanical model study.

A mechanical model of a branched coronary artery with a graft bypassing an 80% stenosis of one branch was used to study the reduction in coronary flow due to stenosis of the bypass graft. Flow Reynolds number and ratio of aortic pressure to dynamic pressure were matched to the living system. Changes in coronary flow were measured for a range of stenoses (0-100%) of bypass grafts with graft-to-coronary-diameter ratios of 4:1, 3:1, 2:1 and 1:1 for conditions that simulated rest and exercise. The results of these studies indicate that: 1) marked stenosis of bypass grafts is needed to decrease coronary flow in the resting state, and even moderate stenosis will decrease flow during exercise when the diameter of the bypass is large relative to the coronary artery; 2) coronary flow is decreased with mild stenosis for bypass grafts of the same diameter as the coronary artery; and 3) a marked decrease in flow due to stenosis of a bypass graft occurs only when the diameter of a stenosis in a graft is less than the diameter of the coronary artery.