TISSUE PRESSURE (INTRACUTANEOUS, SUBCUTANEOUS, AND INTRAMUSCULAR) AS RELATED TO VENOUS PRESSURE, CAPILLARY FILTRATION, AND OTHER FACTORS

Calf muscle pump pressure-flow cycle during ambulation

OBJECTIVE

Calf muscle pump (CMP) failure contributes to the severity and progression of chronic venous disease. Attempts to improve CMP function through resistance exercise have failed to improve chronic venous disease severity or quality of life, partially because the selection of the type of exercise was based on the assumption that the CMP ejects blood from the intramuscular venous sinuses (VSs), which has never been tested in humans. In the present study, we investigated the real-time changes in the pressure and size of the VS during the entire gait cycle of ambulation.

METHODS

We studied 12 lower extremities of nine healthy volunteers at rest and while walking on a treadmill at three different speeds (60, 90, and 120 steps/min). The changes in the VS cross-sectional area (CSA) and pressure were measured. Myography of the gastrocnemius muscle (GCM) and anterior tibial muscle (ATM) was used to register muscle activity. The relationship between the phases of the gait cycle and the measured parameters was analyzed using video records of all experiments.

RESULTS

The observed timing of events was consistent among all limbs studied. At rest, with the participants standing still, the VS pressure and CSA was 70.3 ± 4.2 mm Hg and 23.3 ± 14.6 mm2, respectively. During ambulation, at the first half of the stance, the GCM and ATM eccentrically contract, and the pressure is low (17 ± 8 mm Hg, 20 ± 12 mm Hg, and 29 ± 13 mm Hg at 1, 1.5, and 2 Hz, respectively), and the VS is collapsed. When the heel starts rising (the second half of the stance), the GCM concentrically contracts, the pressure increases, reaching its maximum value (143 ± 37, 134 ± 46, and 128 ± 41 mm Hg), and the VS opens, reaching its maximal size (1.8 ± 1.4 and 2.3 ± 2.2 mm2 at 1 and 1.5 Hz, respectively), followed by collapse of the VS. During the swing phase, the GCM relaxes, and the ATM concentrically contracts, resulting in a rapid decrease in pressure (2.6 ± 4.7, 1.1 ± 6.2, and -4.7 ± 3.2 mm Hg). The VS CSA remained negligible.

CONCLUSIONS

The GCM concentric contraction was associated with a simultaneous increase in VS pressure and CSA. GCM relaxation with ATM concentric contraction coincided with a decrease in VS pressure to negative values. The VSs do not fill but remain empty during the swing phase of ambulation, acting, not as a reservoir, but as a conduit, transferring blood from the network of intramuscular veins to the axial deep veins.

A pH-regulated drug delivery dermal patch for targeting infected regions in chronic wounds

This work presents a low-cost, passive, flexible, polymeric pump for topical drug delivery which uses wound pH as a trigger for localized drug release. Its operation relies on a pH-responsive hydrogel actuator which swells when exposed to the alkaline pH of an infected wound. The pump enables slow release (<0.1 μL min-1) of aqueous anti-bacterial solution for up to 4 hours and sustains against up to 8 kPa of backpressure. Featuring a scalable layer-by-layer fabrication technique to expand the pump into a 2 × 2 array, the device can dispense 50 μl onto a 160 mm2 dermal coverage within 4 hours. Robustness tests show that when integrated within a medical adhesive, the device can be worn around the forearm and can withstand various daily activities (non-intensive) for up to 12 hours. In vitro experiments demonstrate a 58 times decrease of live P. aeruginosa after 24 hours of the pump assisted antibiotics treatment.

Evaluation of mesotherapy as a transdermal drug delivery tool

BACKGROUND

There has been no research about the exact mechanism of transdermal drug delivery during mesotherapy.

OBJECTIVE

We aimed to evaluate whether the commercial mesogun can be an appropriate technique for a transdermal drug delivery.

MATERIALS AND METHODS

We injected blue ink into the polyurethane foam or pig skin with three types of mesotherapy using a commercial mesogun, or local made intradermal injector, or a manual injection of syringe. To assess the internal pressure of the cylinder and drug delivery time, we designed the evaluation setup using a needle tip pressure transducer.

RESULT

All types of injectors induced adequate penetration of blue ink into the polyurethane foam without backflow. In the pig skin, blue ink leaked out rapidly with the backward movement of the needle in the commercial mesogun in contrast to the local made injector or the manual injection of syringe. When the time for backward movement of the syringe approaches 1000 ms, the cylinder pressure of the syringe is saturated at around 25 mmHg which can be translated into the dermal pressure of the pig skin.

CONCLUSION

There should be sufficient time between the insertion and withdrawal of the needle of injector for the adequate transdermal drug delivery and it must be considered for mesotherapy.

Porcine model to evaluate local tissue tolerability associated with subcutaneous delivery of protein

INTRODUCTION

The conversion from intravenous (IV) to subcutaneous (SC) delivery of biotherapeutics has increased in recent years. Some of the reasons for this shift in route of delivery are due to patient convenience, reduced adverse systemic effects, lack of a need for vascular access, and reduced cost of patient care, which ultimately lead to improved patient quality of life. One caveat to SC delivery is the limited volumes that can be administered at a single site and the associated local tolerability. To characterize factors that affect subcutaneous delivery of large volumes of therapeutic proteins, a porcine model was developed. Model endpoints included measurement of interstitial pressure, assessment of local skin visco-elasticity, and the qualitative assessment of local infusion sites.

METHODS

Immunoglobulin G (IgG) was subcutaneously infused into the abdominal region of Yucatan miniature swine. Changes in interstitial pressure were measured, using an in-line pressure transducer, during and after infusions. Additionally, pre- and post-infusion changes in local skin visco-elasticity were measured using a Cutometer®. Lastly, infusion sites were assessed for post-infusion local skin reactions such as erythema and swelling. Similar assessments were made following SC IgG delivery with the permeation enhancer recombinant human hyaluronidase PH20 (rHuPH20).

RESULTS

Subcutaneous infusions of IgG, in the presence of rHuPH20, significantly reduced average interstitial pressures by 55% during the infusion period and by 67% during the post-infusion period, compared to the control. Infusions in the presence of rHuPH20 also maintained better local skin elasticity as seen by a 42% increase in local skin pliability compared to the control. Finally, infusions with rHuPH20 resulted in an 80% reduction in swelling area compared to the control.

DISCUSSION

A large animal model was developed that incorporates both quantitative and qualitative assessment methods to aid in understanding SC delivery of proteins.

Polymeric microdevices for transdermal and subcutaneous drug delivery

Low cost manufacturing of polymeric microdevices for transdermal and subcutaneous drug delivery is slated to have a major impact on next generation devices for administration of biopharmaceuticals and other emerging new formulations. These devices range in complexity from simple microneedle arrays to more complicated systems incorporating micropumps, micro-reservoirs, on-board sensors, and electronic intelligence. In this paper, we review devices currently in the market and those in the earlier stages of research and development. We also present two examples of the research in our laboratory towards using phase change liquids in polymeric structures to create disposable micropumps and the development of an elastomeric reservoir for MEMS-based transdermal drug delivery systems.

Thermal injury to the hand: review of the literature

This paper is a comprehensive review of hand burn injuries. The different classifications of thermal burns, out- and inpatient care, indications for escharotomies as well as surgical management, skin substitutes, and paediatric hand burns are thoroughly reviewed.

Influence of tissue pressure on central venous pressure/peripheral venous pressure correlation: An experimental report

BACKGROUND

Peripheral venous pressure (PVP) has been shown to correlate with central venous pressure (CVP) in a number of reports. Few studies, however, have explored the relationship between tissue pressure (TP) and PVP/CVP correlation.

METHODS

PVP and CVP were simultaneously recorded in a bench-top model of the venous circulation of the upper limb and in a single human volunteer after undergoing graded manipulation of tissue pressure surrounding the intervening venous conduit. Measures of correlation were determined below and above a point wherein absolute CVP exceeded TP.

RESULTS

Greater correlation was observed between PVP and CVP when CVP exceeded TP in both models. Linear regression slope was 0.975 (95% CI: 0.959-0.990); r (2) 0.998 above tissue pressure 10 cmH2O vs. 0.393 (95% CI: 0.360-0.426); and r (2) 0.972 below 10 cmH2O at a flow rate of 2000 mL/h in the in vitro model. Linear regression slope was 0.839 (95% CI: 0.754-0.925); r (2) 0.933 above tissue pressure 10 mmHg vs. slope 0.238 (95% CI: -0.052-0.528); and r (2) 0.276 in the en vivo model.

CONCLUSION

PVP more accurately reflects CVP when absolute CVP values exceed tissue pressure.

THE PRESSURE AND INTERSTITIAL RESISTANCE PREVAILING IN THE NORMAL AND EDEMATOUS SKIN OF ANIMALS AND MAN

Means have been described for the study of pressure conditions in normal and pathological skin of living human beings and mice. The true pressure in normal skin cannot be measured directly by any of the means hitherto described, because there is insufficient free fluid to make manometric determinations. However, for practical purposes, the intracutaneous pressure has been approximately estimated by introducing into skin exceedingly small amounts of a relatively unabsorbable fluid, a mixture of Locke's solution and a vital dye, and then finding the least pressure required to overcome the resistance of the skin to the passage of this fluid through it at the lowest rate measurable with accuracy by the apparatus at hand. In the present paper measurements of this pressure have been termed the interstitial resistance. In normal skin the interstitial pressure, as estimated by measurements of the interstitial resistance, is low, slightly less, on the average, than 1.7 cm. of water in the skin of the mouse, and less than 3.1 cm. of water in human skin. It remains unchanged in states of active hyperemia. In edematous skin the interstitial pressure can be directly measured by determination of the edema fluid pressure. It has been compared with determinations of the interstitial resistance and found to be only 0.5 cm. of water lower in both the mouse and man. Under the conditions of our experiments, in skin rendered slowly edematous by the introduction of irritant chemicals or their topical application, little rise in pressure took place. On the other hand, in rapidly forming edema of the skin the edema fluid pressure and the intradermal interstitial resistance rose and became great enough to hinder materially the further escape of fluid from the blood vessels. The edema fluid pressure rose in proportion to the rapidity with which the edema formed. When a rapidly formed edema subsided, the edema fluid pressure and interstitial resistance fell, but if inflammation and induration followed later, the interstitial resistance became high again. As these conditions subsided the interstitial resistance fell, at times to normal levels, even in the presence of edema. In mouse skin injured by squeezing according to a standard procedure, with result in pronounced edema, the intradermal interstitial resistance rose within a few hours to levels of 10 to 15 cm. of water. In those instances in which the injury progressed to induration, the interstitial resistance rose to such high levels that it seemed impossible that fluid could continue to escape from the capillaries. Such a state of affairs may be of great importance in determining whether necrosis follows trauma.

THE EFFECTS OF VENOUS OBSTRUCTION UPON INTERSTITIAL PRESSURE IN ANIMAL AND HUMAN SKIN

The changes of intracutaneous pressure in the limbs of mice and human beings have been followed during and after periods of venous obstruction with almost unhindered arterial flow. During the first 30 minutes of obstruction the interstitial pressure in the tense skin of the lower legs of mice, a pressure which is slightly higher than that in the loose skin of the ears, backs, and thighs (21), rose from 2.6 to 4.6 cm. of water to about 32 cm., thereafter remaining constant. It would appear that the escape of fluid from the capillaries is checked at this pressure. In the skin of the arm and leg of man the interstitial pressure rose from 2.5–3.7 cm. of water to 15.0–23.0, within 15 to 27 minutes after venous obstruction had been produced, mounting no higher during the period of observation. When venous obstruction had existed for about 20 minutes or more the subjects sometimes experienced sensations of relief from congestion as if some tissue adjustment or the opening of some venous by-pass in the marrow had occurred, preventing a further rise of pressure. However this may be, the pressures still appeared to be great enough to prevent further escape of fluid from the capillaries, at least for the time being.

Skeletal muscle pump versus respiratory muscle pump: modulation of venous return from the locomotor limb in humans

The vast majority of quantitative data examining the effects of breathing on venous return have been derived from anaesthetized or reduced animal preparations, making an extrapolation to an upright exercising human problematic due to the lack of a hydrostatic column and an absence of muscular contraction. Thus, this study is the first to quantitatively examine the effects of different breathing mechanics on venous return from the locomotor limbs both at rest and during calf contraction exercise in the semirecumbent human. When subjects inspired using predominantly their ribcage/accessory inspiratory muscles at rest (change in gastric pressure (DeltaP(GA)) = <2 cmH(2)O, change in oesophageal pressure (DeltaP(ES)) = approximately -6 cmH(2)O; inspiratory time/total breath time (T(I)/T(TOT)) = 0.5), a slight facilitation of femoral venous return was observed during inspiration (65% of all flow occurred during inspiration), with a slight reduction in femoral venous return during the ensuing expiratory phase of the breath. However, when subjects inspired using a predominantly diaphragmatic breath at rest (DeltaP(GA) = > 5 cmH(2)O, DeltaP(ES) = approximately -6 cmH(2)O; T(I)/T(TOT) = 0.5), femoral venous return was markedly impeded (net retrograde flow of 11%) and significantly lower than that observed during ribcage breathing conditions (P < 0.01). During the ensuing expiratory phase of a diaphragmatic breath, there was a large resurgence of femoral venous blood flow. The pattern of modulation during ribcage and diaphragmatic breathing persisted during both mild (peak calf force = 7 kg) and moderate (peak calf force = 11 kg) levels of calf contraction. Despite the significant within-breath modulation of femoral venous return by breathing, net blood flow in the steady state was not altered by the breathing pattern followed by the subjects. Though popliteal blood flow appeared to be modulated by respiration at rest, this pattern was absent during mild calf contraction where popliteal outflow was phasic with the concentric phase of calf contraction. We conclude that respiratory muscle pressure production is the predominant factor modulating venous return from the locomotor limb both at rest and during calf contraction even when the veins of the lower limb are distended due to the presence of a physiologic hydrostatic column.

The intrarenal pressure; its relation to age, weight, blood pressure, and sex

1. The intrarenal pressure of dogs anesthetized with pentobarbital averages 26 mm. Hg, and ranges from 10 to 58 mm.; that of decerebrate dogs is 25 mm., and that of unanesthetized dogs with explanted kidneys is 25 mm. Tests of a few cats and rabbits indicate that their intrarenal pressure has about the same magnitude. 2. There is a slight positive correlation between intrarenal pressure and both body weight and kidney weight, but intrarenal pressure is not related to sex, blood pressure, or age.

A method for rapid measurement of intrarenal and other tissue pressures

A rapid method for measuring tissue pressures has been designed. A pressure of 250 mm. Hg is imposed on a manometer. Then the system is allowed to discharge into a needle cannula inserted in the tissue. The manometer forces out fluid (about 10 c.mm.) until the pressure within it is the same as that within the tissue. Records of the pressure changes are made. Each observation takes about a minute. The method gives results that are closely comparable with other reports of tissue pressures. With this method, the pressure in the following organs of dogs was found to be: kidney, 26 mm. Hg, cerebral cortex, 0 to 5 mm., muscle, 1 to 10 mm., spleen, S to 16 mm., subcutaneous tissue, 0 to 3 mm., and liver –2 to 14 mm. The reliability of the method was tested on the kidneys of decerebrate dogs. Measurements were found to be the same within narrow limits over a period of an hour; they were the same when taken simultaneously in different regions of the same kidney or in opposite kidneys. They were independent of the volume of fluid forced into the tissue. Similar pressures were observed with 1 or 5 or 10 holes bored in the shaft of the cannulating needle. The intrarenal pressure was also measured by inserting a needle cannula into the tissue and then allowing the pressure to reach equilibrium passively with a manometer. This method gave similar results. The intrarenal pressure has now found to be the same when measured by three different technics.

Diagnosis and treatment of varicose veins: a review

Varicose veins are superficial vessels that are abnormally twisted, lengthened, or dilated and are usually caused by inefficient or defective valves within the vein. They represent a medical condition accompanied by symptoms deserving treatment. Varicose veins are a manifestation of venous disease that may precede later severe complications. Varicosities cause cutaneous disease in addition to complications specific to the venous system. This article reviews the epidemiology, adverse sequelae, anatomy, pathophysiology, evaluation, and treatment of varicose veins.

The tilting cardiovascular response in orthostatic syncope

159 patients with a previous discharge diagnosis of recurrent vasodepressor syncope associated with prolonged standing or other circumstance known to trigger the condition were examined in order to isolate the orthostatic form. 72 patients with a history of at least two episodes of loss of consciousness after standing still for at least 10' were selected for testing by head-up tilt. Those who showed signs or symptoms during the test were tested a further twice, the third time after atropine administration. This process resulted in the diagnosis of orthostatic vasodepressor syncope in 28 patients who presented both 1) a positive test associated with hypotension and bradycardia and 2) bradycardia-free hypotention on repetition of the test with atropine.

The use of magnetic resonance imaging in exertional compartment syndromes

This prospective, double-blind study was carried out to assess the usefulness of magnetic resonance imaging (MRI) as a noninvasive method in the diagnosis of chronic compartment syndrome (CCS). As well, a new radiopharmaceutical known as methoxy isobutyl isonitrile that has been shown to be taken up by muscle in direct proportion to its blood flow was used to illustrate the possible pathophysiology of this syndrome. Twenty patients with a history of chronic leg pain and possible diagnosis of CCS and five normal volunteers had preexercise and postexercise MRI, nuclear medicine imaging, and static and dynamic slit catheter pressure studies. Nine patients had classic symptoms; only five of these nine had abnormal pressure studies. The other 11 patients had an element of pain at rest and had normal pressure studies. The nuclear blood flow studies were normal in all 25 legs tested in this study. Measurement of intrinsic MRI parameters T1 and T2 in the normal legs as well as in those with an atypical history showed a marked elevation with exercise and a gradual return to baseline postexercise that was similar to the pressure curves. In the five patients with a clinical history and elevated pressures, four had abnormal MRI studies with failure of T1 to return to baseline values. Although these results demonstrate the potential of MRI as a tool for noninvasively monitoring muscle status, clinical history and examination remain important in the diagnosis of CCS. This study indicates that the pathophysiology of exertional compartment syndrome does not appear to be related to ischemia.

The effects of body position and exercise on plasma volume dynamics

We examined the plasma volume changes associated with a protocol of either exercise or controlled rest under identical positional and ambient conditions. Nine healthy adult males rode (E) and on another occasion sat quietly (C) on a cycle ergometer for 30 min. Ten minutes of cycle exercise immediately followed the resting C protocol. Ambient temperature was 30 degrees C (rh = 35%) and exercise load was equal to 50% of peak VO2. Venous blood samples were obtained with subjects both in the supine and seated positions prior to all experiments. Additional blood was drawn during minutes 1, 5, 10, and 30 in both experimental conditions. A final sample was taken during C after the 10 min exercise. Moving from the supine to a seated position resulted in an average loss of 162 ml of plasma across all experiments. During the E condition a further reduction in plasma volume (76 ml) occurred by one minute of exercise. Plasma volume stabilized by 5 min of exercise under the E protocol. During the C condition, subsequent fluid loss (98 ml) was not apparent until 10 min after the first seated sample and totalled 176 ml at the end of 30 min of rest. Ten minutes of cycling at the end of the C experiment resulted in a further plasma volume reduction of 137 ml. Plasma protein and albumin contents decreased by 5 min of exercise in E and by 30 min of rest in C. [Na+] and [Cl-] did not change in either condition but a rapid increase in [K+] during exercise indicated an addition of potassium to the vascular volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Lumbar spinal cord responses to limb vein distention

The purpose of this study was to determine if central neural responses were elicited by distention of limb veins, and to compare the pattern of these response to those produced in previous studies using electrical stimulation to excite limb venous afferent fibers. Spinal evoked potentials were measured in response to stretch of the wall of a segment of the femoral-saphenous vein by perfusion-distention or by mechanical stretch. These studies revealed that spinal cord evoked potentials were elicited by these procedures, and that the activated venous afferent fibers coursed through the saphenous nerve and entered the sixth lumber spinal cord segment. The minimum stretches which were required to elicit spinal evoked potentials were produced by perfusion pressures starting at 2-3 mm Hg, or by mechanical stretch of the wall of 5 micron/mm. A vein wall proprioceptor hypothesis is proposed and discussed in the light of these findings. In addition to the cord dorsum evoked potentials, distention or stretch of the vein wall elicited ventral root potentials (excitatory postsynaptic population potentials) which are known to be produced by excitatory inputs to motoneurons. A venous afferent mediated muscle-tonus venopressor mechanism hypothesis is proposed and discussed in the light of these and previous findings.

Reference values for intramuscular pressure in the lower leg in man

Intramuscular pressures in the anterior tibial and superficial posterior compartments of the lower leg were measured by the wick catheter technique in 34 healthy individuals (17 males and 17 females, mean age 42 years). The pressures were measured at rest, during and after exercise and during venous and arterial occlusion. The pressure was 1.1 (range 0.3-3.0) kPa in the anterior tibial and 0.5 (range 0.0-2.0) kPa in the superficial posterior compartment at rest. During exercise the intramuscular pressures rose to 3.5 (range 1.0-8.0) kPa and 0.9 (range 0.1-2.8) kPa respectively. The anterior tibial compartment pressures were lower in females than in males at exercise and lower in older than in younger persons at rest. After exercise the pressures were back to the pre-exercise levels within 5 min. Venous occlusion caused an increase in the pressure which was more marked in the anterior tibial compartment than in the superficial posterior compartment. Arterial occlusion did not cause any dramatic changes in intramuscular pressures, but there was a slight elevation during the period of reactive hyperaemia.

Interactions between femoral venous afferents and lumbar spinal reflex pathways

This study reports findings of spinal reflex connections of afferent fibers electrically excited in the wall of the femoral vein. Condition-test experiments, and EMG recordings revealed that the femoral venous afferents have facilitatory connections to flexor and extensor motoneurons of both the proximal and the distal hindlimb muscles. Femoral venous afferent stimulation which produced facilitation, also produced inhibition of the test reflexes following the facilitation. Because the inhibition was enhanced by diazepam injection and because the inhibitory time-course correlated closely to the time-courses of both dorsal root potentials and individual tests of primary afferent depolarization, the inhibition was suggested to be produced by presynaptic inhibition. The potentially significant role of the venous afferent connections in a reflex-elicited skeletal muscle pump or in an increase in intramuscular venous counterpressure is discussed.

Regional tissue fluid pressure in rat calf muscle during sustained contraction or stretch

The tissue fluid equilibration pressure in central and peripheral regions of rat calf muscles has been measured by needles with large smoothed sideholes. Short equilibration periods were normally achieved although saline was not infused. Tissue fluid pressure during rest remained constant at -2 to 0 mmHg. During sustained isometric contraction the average tissue fluid pressure rose almost linearly with increasing force of contraction. The average pressure in the central inner zone of the muscle reached 220 +/- 80 mmHg during maximal force, whereas the average pressure in the outer peripheral zone increased to 85 +/- 56 mmHg, markedly less than in the central zone. Thus, this difference in regional tissue pressure may possibly explain the greater impediment to blood flow in central than in peripheral regions during contraction shown previously by Wisnes & Kirkebø (1976). Although a corresponding regional pressure difference was observed during passive stretch of the muscle, the absolute tissue pressures were much smaller. However, the heterogeneous pattern of muscle fiber directions and relative displacement of various muscle elements during work, may induce shear forces causing focal vessel obstructions that are different during contraction and stretch.

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.

Skin perfusion pressure measured as the external pressure required to stop isotope washout. Methodological considerations and normal values on the legs

The skin perfusion pressure was measured as the external pressure required to stop blood flow, as evidenced by cessation of the washout of an intracutaneous depot of [131I-]antipyrine mixed with histamine. The external pressure on the skin was measured by an 11 x 11 cm slack air-filled plastic cushion connected to a mercury manometer and interposed between the labelled area and a blood pressure cuff. The 'flow cessation external pressure' (FCEP) varied parallel to the intra-arterial femoral mean blood pressure, but was on the average 10.8 mmHg (SD 6.4) lower. FCEP was measured on twenty normal subjects at four different segments of the leg. The average differences between auscultatory brachial mean blood pressure and FCEP were: thigh 12.0 mmHg (SD 7.6); calf 10.4 mmHg (SD 7.4); ankle 12.9 mmHG (SD 10.1); foot 20.2 mmHg (SD 12.1). The SD of the difference between measurements on two different days, performed in forty-four patients with different degrees of occlusive arterial disease, varied between 5.6 and 8.3 mmHg at the different levels. The present data indicate that the skin perfusion pressure on the legs in normal subjects lies approximately 10 mmHg lower than the systemic mean arterial blood pressure.

Muscle Pumping in the Dependent Leg

Since the exercising dependent leg displaces blood toward the heart, against a potential gradient, it must perform useful circulatory work. We studied the peripheral circulation in healthy, sedentary males by measuring calf circumference (using mercury-in-Silastic strain gages), muscle pump ejection velocity (using a transcutaneous Doppler flowmeter), intrathoracic and intra-abdominal pressures (through catheters in the esophagus and rectum) and power of the leg muscle pump (product of blood flow and the upstream-downstream venous pressure difference). Measurements of pressure, flow velocity, and volume changes in the dependent venous beds of healthy young men demonstrated that during running in place, (1) the abdominal contraction necessary to fix the pelvis raised inferior caval pressure and impeded venous outflow from the legs, but that, (2) the leg muscles themselves were capable of effectively pumping blood past this functional obstruction. By doing so, these peripheral pumps contributed more than 30% of the energy required to circulate blood during running.