Comparative plethysmography; evidence for a hydrostatic effect on foot blood flow

Summary Blood flow in the right foot of 11 subjects was measured simultaneously by a strain gauge placed around the mid metatarsal circumference of the foot and a water displacement plethysmograph in which the foot was resting. A close linear correlation (r=0.88) between the results of the two methods existed over a wide range of blood flows. It was apparent however that blood flow at the mid metatarsal region of the foot was only about 30% of the total foot blood flow measured by the plethysmograph. The likely cause of this finding is the varying proportion of bone to soft tissue along the length of the foot. It was observed that the strain gauge estimates of blood flow increased two to three fold when the plethysmograph was emptied, an effect that was abolished by refilling the plethysmograph. These changes were highly statistically significant (P<0.01) in all ten subjects in whom this comparison was made. The application of progressively increasing hydrostatic pressure in a further 4 subjects demonstrated that the reduction in blood flow was proportional to the pressure applied. Explanations for this effect based upon small temperature and pressure changes altering strain gauge performance are excluded. Three mechanisms are proposed, based upon an increase in venous leakage, a reduction in arterial inflow and the consequence of increased capillary filling occurring as a result of hydrostatic pressure within the plethysmograph.     

Early effects of abrupt reduction of local pressure on the forearm and its circulation

1. The pressure at the surface of a segment of forearm enclosed in a plethysmograph was abruptly reduced from atmospheric to -20 to -120 mm Hg.2. Forearm circumference (equivalent to the volume of a small segment of forearm (V(f))) was measured with a strain gauge. Pressure was measured in the plethysmograph (P(p)), in veins exposed (P(ve)) and not exposed (P(vne)) to suction, in the brachial artery not exposed to suction (P(bane)) and in forearm tissue (P(t)).3. Reduction of P(p) caused increase of V(f). This was not due to gas evolution, since bubbles would not be liberated at the pressures employed. Nor was increase of V(f) due to venous backflow since P(ve) fell, but P(vne) did not, even with upper arm circulation occluded or when P(vne) was raised by venous occlusion prior to reduction of P(p).4. Reduction of P(p) temporarily arrested venous outflow since P(ve) < P(vne) < P(bane) for 30 sec. With reduction of P(p) 30 sec after occlusion of the upper-arm circulation, P(ve) < P(vne) for > 1 min, indicating that arterial inflow was then minimal.5. Increase of V(f), following reduction of P(p), was therefore due to inflow of arterial blood, of soft tissue or interstitial fluid. Interstitial fluid could flow from regions external to the plethysmograph, or enter as the result of filtration across capillaries. Occlusion of the upper arm circulation was not expected to interfere with motion of forearm soft tissue or the intratissue flow of interstitial fluid. It appears that capillary filtration is small compared with observed blood flow. Therefore subtraction of V(foccl) measured at intervals after reduction of P(p) (upper arm circulation occluded) from V(f) similarly obtained (but upper arm circulation free) appeared to give change of forearm volume due to inflow of arterial blood (DeltaV(b)). V(b), the volume inflow rate of arterial blood during suction, was then obtained.6. Resting forearm flow was 1.8 ml./min/100 ml. in seven normal subjects (average mean arterial blood pressure 86 mm Hg). With P(p) = -90 mm Hg, V(b) was 10.2 ml./min/100 ml. Suction therefore reduced vascular resistance, measured as (P(bane)-P(ve)) /V(b).     

Early changes in the forearm circulation following transient increase of local external pressure

1. The pressure at the surface of a segment of forearm enclosed in a plethysmograph was abruptly raised from atmospheric level to +40 mm Hg, held at the new level for 4 sec, and abruptly dropped to atmospheric level.

2. Forearm circumference (V_f) equivalent to the volume of a small segment of forearm, was monitored with a mercury-in-rubber strain gauge. Pressure was measured in the cylinder (P_p) in veins exposed to external compression (P_{v, e}), and in the radial artery exposed to compression (P_ra).

3. Forearm blood flow was measured by venous occlusion plethysmography before, and after, release of external compression. There was, on average, over the 3rd and 4th second after release of pressure, a 2·4-fold increase of inflow, as compared with resting level.

4. By the 15th second after release of compression, forearm blood flow had returned to its previous resting level.

5. The increase in blood flow after compression appears to be due to active reduction in vascular resistance, for refilling of the arteries and arterioles would be completed before the increased flow was recorded; venous backflow can be excluded, and the pressure difference for flow (arterial minus venous) is virtually unchanged.

     

Noninvasive imaging of human skin hemodynamics using a digital red-green-blue camera

In order to visualize human skin hemodynamics, we investigated a method that is specifically developed for the visualization of concentrations of oxygenated blood, deoxygenated blood, and melanin in skin tissue from digital RGB color images. Images of total blood concentration and oxygen saturation can also be reconstructed from the results of oxygenated and deoxygenated blood. Experiments using tissue-like agar gel phantoms demonstrated the ability of the developed method to quantitatively visualize the transition from an oxygenated blood to a deoxygenated blood in dermis. In vivo imaging of the chromophore concentrations and tissue oxygen saturation in the skin of the human hand are performed for 14 subjects during upper limb occlusion at 50 and 250 mm Hg. The response of the total blood concentration in the skin acquired by this method and forearm volume changes obtained from the conventional strain-gauge plethysmograph were comparable during the upper arm occlusion at pressures of both 50 and 250 mm Hg. The results presented in the present paper indicate the possibility of visualizing the hemodynamics of subsurface skin tissue.     

Effect of chronic sympathetic denervation upon the transcapillary filtration rate induced by venous stasis

The effect of venous pressure elevation upon capillary filtration rate in the limb was studied in 6 chronically sympathectomized patients. Five healthy subjects served as controls. Volume changes of the forearm or calf were recorded by a strain-gauge plethysmograph. Relative blod flow in subcutaneous and muscle tissue during venous stasis was measured by the local ¹³³Xe washout technique. In the denervated limbs there was a linear relationship between net capillary filtration rate and venous pressure elevation. In the controls a non-linear relationship was seen as venous pressure elevation of 40 mmHg only caused an increase in net filtration rate of about 66% of that expected from a linear relationship. In the denervated limbs blood flow in muscle and subcutaneous tissue remained constant during venous pressure elevation of more than 30 mmHg whereas in the non-denervated limbs blood flow decreased by about 50% in both tissues. The results suggest that a local sympathetic veno-arteriolar (axon) reflex plays a dominant role for the reduced increase in net capillary filtration rate during large increases in venous pressure. The local axon reflex may therefore act as an edema protecting factor.     

Forearm vasodilatation following release of venous congestion

1. The volume rate of forearm blood flow was measured with a mercury-in-rubber strain gauge, or with a water-filled plethysmograph, from 1 sec after termination of a 2-3 min period of venous congestion.2. When congesting pressure had been less than 18 mm Hg, average post-congestion flow (five subjects) was constant during approx. 10 sec and not significantly different from resting flow.3. When congesting pressure had been 30 mm Hg, average post-congestion flow (eight subjects) was 26% higher than resting, during 3-4 sec after release of congestion, but rose to 273% of resting during 4-6 sec after release of congestion.4. In other studies forearm vascular resistance had been found normal or increased during such venous congestion, and theoretical studies here indicated that passive mechanical factors could not account for the delayed occurrence of high post-congestion flow.5. It appears, therefore, that the forearm vascular bed dilates actively shortly after release of substantial venous congestion. It would seem more likely that a myogenic mechanism, rather than a metabolic one, is responsible.     

Automated strain-gauge plethysmograph

An automatic 2-channel strain-gauge plethysmograph, based on an absolute resistance measurement technique, will be described in the paper. This device is compact, easy to use, provides inherent self-calibration for any gauge and any length of that gauge, automatically performs the measured cycle, and generates annotated graphical printouts of the measurement data, along with the results which it computes from that data.     

Forearm blood flow measurements using computerized R-wave triggered strain-gauge venous occlusion plethysmography: unilateral vs. bilateral measurements.

The human forearm is a well established model to study local vascular reactivity in humans in vivo, using strain-gauge venous occlusion plethysmography to measure blood flow and changes in blood flow in the forearm. To reduce the intra-individual variability of the forearm blood flow (FBF), it has been advocated that simultaneous measurements of contralateral forearm blood flow is obligatory. Therefore, the use of the calculated forearm ratio (FR) is recommended instead of using the actual FBF. In the present study we compared the intra-individual variability of forearm blood flow measurements and the forearm ratio, by using computerized R-wave triggered strain-gauge venous occlusion plethysmography, to test if bilateral expression of measurements is better than unilateral. Results were obtained in eight volunteers. Intra-arterial infused sodium nitroprusside induced a dose dependent increase in forearm blood flow and a dose dependent increase in the calculated forearm ratio. Intra-arterial infused norepinephrine induced a dose dependent decrease in forearm blood flow and a dose dependent decrease in the calculated forearm ratio. The differences between the variation coefficients of the forearm blood flow measurements and the calculated forearm ratio were different. These results support our hypothesis that by using a computerized, R-wave triggered system for unilateral forearm blood flow measurement is a more reliable outcome than the calculated forearm ratio derived from bilateral measurements.     

Contribution of different sized vessels in the extremities to the arterial pulse waveform as recorded by electrical impedance and volume plethysmography

The plethysmographic signal (either volume or electrical impedance) obtained from a limb segment has contributions due to volume change contributions from the arteries, veins and smaller blood vessels. The electrical impedance plethysmograph signal contains, in addition, contributions due to blood resistivity changes in all these vessels. Uncertainty exists as to the relative contributions of different vessels. We have modelled the leg circulation in detail, with more than 80 simultaneous differential equations, to determine the pressure and flow in different sized vessels and hence their contribution to the impedance and volume plethysmograph signals.     

Validity and reproducibility of electrical impedance tomography for measurement of calf blood flow in healthy subjects

The Sheffield electrical impedance tomography; (EIT) system produces images of changes in the distribution of resistivity within tissue. The paper reports on the application of electrical impedance tomography in monitoring volume changes in the limb during venous occlusion. The aim of the study is to assess the feasibility, reproducibility and validity of calf blood flow measurements by EIT. In 14 healthy volunteers calf blood flow is compared, as determined in a calf segment by strain-gauge plethysmography (SGP), with the impedence changes measured by EIT during rest and post-ischaemic hyperaemia. The measurements are repeated to assess reproducibility. The reproducibility for the EIT, assessed from the repeated measurements and expressed as a reproducibility coefficient, is 0.88 during rest and 0.89 during hyperaemia. The reproducibility coefficient for SGP data is 0.83 at rest and 0.67 during hyperaemia. Flow measurements, assessed by means of two methods, correlate well at rest (r=0.89), but only moderately during hyperaemia (r=0.51). The correlation coefficient for the pooled flow measurements is 0.98. It is concluded that EIT is a valid and reliable method for assessing blood flow in the limb. Possible applications of EIT in localising fluid changes are discussed.     

Cardiac and forearm plethysmographic responses to high intensity auditory stimulation

This paper reports an investigation of forearm blood flow and cardiac responses to high intensity auditory stimulation. Blood was assessed in terms of forearm girth (FG) using a strain gauge, and since this technique had not been used previously, a preliminary study was conducted to validate the measure. In Experiment 1 (N = 24), subjects performed either a fast- or slow-paced mental arithmetic task. The data indicated that the strain gauge technique differentiated periods of rest from arithmetic stress and produced results comparable with those obtained using limb volume plethysmography. In Experiment 2 (N = 24), subjects received eight presentations of either a 60 dB or a 110 dB white noise stimulus at randomly ordered intervals of 35, 40, 45 and 50 sec; stimulus rise time was 50 msec and the duration 1 sec. Both groups displayed short-latency (i.e. within 10 beats poststimulus) cardiac accelerative responses which habituated over trials. In addition, the 110dB group displayed a long-latency (19.9 sec) accelerative response of approximately 25 beats per min and this was accompanied by an increase in FG. These responses occurred only following the first stimulus presentation, and analysis of the EKG T-wave amplitude suggested that the cardiac response was mediated sympathetically. These results are discussed in terms of conceptions of the startle and defence responses in man and the fight/flight reaction in animals.     

A critical review of the theory of the mercury strain-gauge plethysmograph

A short introductory treatment of the basic theory of the mercury strain-gauge plethysmograph is presented. Some physiological aspects of this type of plethysmography are then discussed which, among other things, illuminate the difficulty in discriminating between skin-flow and muscular flow. A detailed calculation of the elastic influences follows and shows that one cannot generally expect a cancellation of these influences when comparing measurements with the calibration. This part illuminates further the difficulties in discriminating between skin-flow and muscular flow. As a result, such discrimination should be regarded as dubious. Some other sources of error are also discussed briefly. Two proposals for a new design are given. Finally, the Appendix shows the values of the gauge stretch which will give cancellation of the elastic errors in a simple model. The actual values cannot be used in practice but they indicate that the amount of stretch is quite critical.     

Comparison of forearm plethysmographic methods with brachial artery pulsed Doppler flowmetry in man

Blood flow in the forearm was evaluated using simultaneous measurements of pulsed Doppler flowmetry and strain-gauge plethysmography in 32 normal subjects and 91 patients with sustained essential hypertension. The two determinations of blood flow were strongly correlated (r = 0.58). Measurements with strain-gauge plethysmography reflected changes in blood flow velocity but were poorly correlated with changes in arterial diameter as measured by pulsed Doppler flowmetry. The latter method permits evaluation of instantaneous variations in blood flow velocity and detection of active modifications of arterial diameter.     

A plethysmograph for the measurement of digital blood flow

Venous occlusion plethysmography using a water-filled plethysmograph is an accurate and reliable method for the measurement of limb flow which has been used for many years. The technique has been adapted to produce a plethysmograph for the measurement of digital blood flow. The device is small, light, cheap, simple to use, and can be calibrated directly with the digit 'in situ'. It is especially suitable for the assessment of digital blood flow, since flow through a large portion of the whole digit is measured and the local temperature of the digit is accurately controlled.     

Electric impedance cuff for the indirect measurement of blood pressure and volume elastic modulus in human limb and finger arteries

A new plethysmograph, the electric impedance cuff, was designed for the indirect measurement of blood pressure, volume elastic modulus E_v and compliance C_a in human limb arteries. This comprises a compression chamber filled with electrolyte solution and a tetrapolar electric impedance plethysmograph whose electrodes are placed inside the chamber; the former for controlling transmural arterial pressure P_t, and the latter for detecting total limb volume V_o, mean arterial volume and its variation ΔV_a. Systolic and mean arterial pressure in the upper arms, forearms and fingers were measured by detecting pulsatile impedance variation during the gradual (3–5 mm Hg per heart beat) increase (or decrease) in chamber pressure by the volume oscillometric technique. Diastolic and pulse pressure ΔP were calculated from these pressure values. Compliance C_a=ΔV/ΔP and volume elastic modulus were recorded at various P_t levels, controlled by the compression pressure. Although this is a kind of impedance plethysmograph, the volume change in a limb segment can be detected by this method without passing electric current through the limb.     

Blood flow in skin, subcutaneous adipose tissue and skeletal muscle in the forearm of normal man during an oral glucose load

Blood flow to the forearm, and the subcutaneous tissue and skin in the forearm were measured by strain gauge plethysmography, 133Xe-elimination and Laser Doppler flowmetry during an oral glucose load (I g glucose kg-1 lean body mass) and during control conditions. The forearm blood flow remained constant during both experiments. Glucose induced a two-fold vasodilatation in subcutaneous tissue. In skin, glucose induced a relative vasodilatation and later a relative vasoconstriction compared with control experiments. When estimated from forearm blood flow and subcutaneous and skin blood flows, muscle blood flow decreased about 20-30% during both experiments. Proximal nervous blockade did not abolish the glucose-induced vasodilatation in subcutaneous tissue. In the glucose experiment, arterial glucose concentration increased to 7.8 +/- 1.17 mmol l-1 30 min after the load was given and then decreased to 4.5 +/- 0.34 mmol l-1 at the end of the experiment. In the control experiments glucose concentration was constant. Arterial noradrenaline concentration increased significantly from 1.0 +/- 0.13 to about 1.5 +/- 0.3 nmol l-1 120 min after glucose and remained at this level during the experiment. Similarly adrenaline increased from 0.16 +/- 0.11 to about 0.4 +/- 0.16 nmol l-1 180 min after glucose. It is hypothesized that the vasodilating effect of glucose in subcutaneous tissue is secondary to metabolic events connected to glucose uptake and energy deposition in adipose tissue.     

以前臂内侧皮神经及营养血管为蒂的前臂内侧皮瓣的应用解剖

目的　为带前臂内侧皮神经及其营养血管筋膜皮瓣提供形态学基础。方法　在 32侧成人上肢标本上 ,观测前臂内侧皮神经营养血管及其周围皮肤的血供情况。结果　前臂内侧皮神经近侧的血供来源于尺侧返动脉混合肌皮支 ,起始处外径为 0 .8mm ,穿出深筋膜前长度为 1.1cm ;中部主要来自尺动脉近中段和远中段的粗大皮支 ,起始处外径均为 0 .7mm ,穿出深筋膜前长度均为 1.0cm ;远侧有尺动脉腕上皮支 ,起始处外径为 0 .9mm ,穿出深筋膜前长度均为 1.0cm ;远侧有尺动脉腕上皮支 ,起始处外径为 0 .9mm ,穿出深筋膜前长为 2 .6cm。其神经旁血管网与神经皮穿支及神经内血管广泛吻合组成了皮神经血管轴。结论　可设计成带前臂内侧皮神经及营养血管为蒂筋膜上瓣 ,顺行或逆行转位修复邻近部位的软组织缺损。     

Comparison of plethysmographic methods with pulsed D?ppler blood flowmetry.

Hand blood flow was measured at rest, with local warming, and with local cooling. Three methods were simultaneously used: water plethysmography (WP), mercury-in-rubber strain gauge plethysmography (SG), and pulsed D?ppler flowmetry (D). Of these, water plethysmography is the most sensitive and accurate; strain gauge plethysmography is simpler but less accurate; and pulsed D?ppler flowmetry precisely measures instantaneous arterial blood flow without venous occlusion.     

Forearm vasoreactivity in type 1diabetic subjects.

This study compared forearm vasoreactivity in 15 Type I diabetic subjects with 15 healthy controls. The groups were matched for age, exercise capacity, and the absence of other cardiovascular risk factors. Vasoreactivity was measured using strain gauge plethysmography, at rest, after arterial occlusion (OCC), and following OCC coupled with handgrip exercise (ROCC). Forearm blood flows were significantly elevated between conditions 2.58 +/- 0.37ml/100mltissue at rest to 26.80 +/- 6.56 after OCC and 32.80 +/- 8.26ml/100mltissue following ROCC in Type I diabetic subjects. There were no differences in forearm blood flow between groups for any of the conditions. These data indicate the degree of forearm blood flow is directly related to the intensity of the vasodilatory stimulus. However, our study did not reveal evidence of impaired vasodilatory capacity in Type I diabetic subjects compared to controls in the absence of other risk factors.     

以前臂内侧皮神经及营养血管为蒂筋膜皮瓣的应用解剖

目的:为带前臂内侧皮神经及其营养血管筋膜皮瓣提供形态学基础。方法:在32侧成人上肢标本上,观测前臂内侧皮神经营养血管及其周围皮肤的供血情况。结果:前臂内侧皮神经近侧的血供来源于尺侧返动脉混合肌皮支,起始处外径为0.8mm,穿出筋膜前长度为1.1cm;中段主要来自尺动脉近中段和远中段的粗大皮支,起始处外径均为0.7mm,穿出深筋膜前长度均为1.0cm;远侧有尺动脉腕上皮支,起始处外径为0.9mm,穿出深筋膜前长为2.6cm。其神经旁血管网与神经皮(穿)支及神经内血管广泛吻合组成了皮神经血管轴。结论:可设计成带前臂内侧皮神经及营养血管为蒂筋膜皮瓣,顺行或逆行转位修复邻近部位的软组织缺损。