Biomechanics of ocular pneumoplethysmography

A mathematical analysis of ocular pneumoplethysmography is presented, based on the physiological, anatomical, and biomechanical properties of the eye. Ocular pneumoplethysmography is a clinical procedure involving elevation of intraocular pressure, by application of a suction cup to the sclera, to a level that exceeds ophthalmic artery systolic pressure. As decay in intraocular pressure is allowed, return of retinal artery pulsations indicates ophthalmic artery systolic pressure. We obtain a quantitative relationship between increase in intraocular pressure and applied vacuum, and compare the theoretical predictions with experiments on rabbits in which a variable descending vacuum was applied to bilateral scleral eyecups. The bilateral intraocular pressures were simultaneously recorded from cannulae in the respective vitreous bodies, and the pressures at which return of ocular pulsations were observed were correlated with the scleral vacuums. Regression lines were calculated for three serial determinations in each animal, with two groups of animals distinguished by the inner diameter of the eyecups used. The theoretical results indicate that the relationship between intraocular pressure increase and applied vacuum is independent of Young's modulus, and depends primarily on the ratio of the diameter of the vacuum cup to the diameter of the eye.

Evaluation of sympathetic control of digital blood flow

A noninvasive strain-gauge method of measuring blood flow in the digit was used to assess the influence of the sympathetic system in the digit. The sympathetic system was stimulated by the sudden application of ice to the neck, thus avoiding in the hand local reflexes and responses to cold. Seventeen normal subjects responded in similar fashion. Maximum flow reduction ranged from 26% to 92%, with a mean of 61%. This method should be useful diagnostically and for research when sympathetic reactivity, in contrast to basal sympathetic tone, needs to be determined.

Age and gender effects on nasal respiratory function in normal subjects

One hundred and ninety-seven normal individuals between the ages of 5 and 73 years were evaluated to determine nasal resistance, nasal cross-sectional area, and respiratory mode during quiet breathing. Subjects were categorized into three age groups. Nasal resistance and respiratory mode were directly determined using posterior rhinomanometry and the SNORT technique, respectively. Nasal cross-sectional area was estimated using the hydrokinetic equation. Results indicated significant effects of age on all variables; significant gender differences were found for respiratory mode. Weak correlations were found between respiratory mode and nasal resistance. The results are presented as normative data on nasorespiratory characteristics to facilitate diagnostic and treatment decisions relative to individuals with normal morphology as well as to patients with craniofacial anomalies. A fundamental issue of both clinical and theoretical importance arising from the study pertains to the definitions of normality and impairment.

A reassessment of mercury in silastic strain gauge plethysmography for microvascular permeability assessment in man

1. We have used non-invasive mercury in a silastic strain gauge system to assess the effect of pressure step size, on the time course of the rapid volume response (RVR) to occlusion pressure. We also obtained values for hydraulic conductance (Kf), isovolumetric venous pressure (Pvi) and venous pressure (Pv) in thirty-five studies on the legs of twenty-three supine control subjects. 2. The initial rapid volume response to small (9.53 +/- 0.45 mmHg, mean +/- S.E.M.) stepped increases in venous pressure, the rapid volume response, could be described by a single exponential of time constant 15.54 +/- 1.14 s. 3. Increasing the size of the pressure step, to 49.8 +/- 1.1 mmHg, gave a larger value for the RVR time constant (mean 77.3 +/- 11.6 s). 4. We propose that the pressure-dependent difference in the duration of the rapid volume response, in these two situations, might be due to a vascular smooth muscle-based mechanism, e.g. the veni-arteriolar reflex. 5. The mean (+/- S.E.M.) values for Kf, Pvi and Pv were 4.27 +/- 0.18 (units, ml min-1 (100 g)-1 mmHg-1 x 10(-3), 21.50 +/- 0.81 (units, mmHg) and 9.11 +/- 0.94 (units, mmHg), respectively. 6. During simultaneous assessment of these parameters in arms and legs, it was found that they did not differ significantly from one another. 7. We propose that the mercury strain gauge system offers a useful, non-invasive means of studying the mechanisms governing fluid filtration in human limbs.

The cerebral hyperperfusion syndrome: diagnostic value of ocular pneumoplethysmography

PURPOSE

There were two purposes to our study. The first was to characterize the ocular hyperperfusion associated with carotid endarterectomy. The second was to relate ocular hyperperfusion to the clinical presentation of cerebral hyperperfusion syndrome.

METHODS

This was a retrospective chart review of 2331 patients who underwent carotid endarterectomy at our institution between June 1978 and May 1991.

RESULTS

Twelve of these carotid endarterectomies were associated with ocular hyperperfusion on the side of operation. Clinical evidence of cerebral hyperperfusion syndrome was observed in five of these 12 procedures. In these five patients there were two associated fatal intracerebral hemorrhages and one permanent coma. In the latter three patients the contralateral internal carotid arteries were totally occluded.

CONCLUSION

Ocular hyperperfusion, as documented with ocular pneumoplethysmography, is useful in alerting the physician to the potential for development of the cerebral hyperperfusion syndrome.

[The noninvasive quantitative evaluation of the acute hemodynamic effects of sublingual and transdermal nitroglycerin in man]

BACKGROUND

Organic nitrates are complex vasodilators: the hemodynamic action of these drugs is different in the venous and arterial resistance and capacitance beds. The aim of our study was to obtain a quantitative, noninvasive evaluation of the acute effects of sublingual and transdermal (td) nitroglycerin (NTG).

METHODS

Twenty-one pts (mean age 49 years) underwent strain-gauge plethysmography and digital photoplethysmography under control conditions, 5 min after sublingual NTG (0.4 mg), 1 hour thereafter and 2 hours after NTG td (10 mg patch). Forearm venous capacitance (CV, ml.100 ml-1) and arteriolar resistance (RA, mmHg.ml-1.100 ml.min) and the b/a ratio of arterial pulse wave (%) were measured.

RESULTS

After sublingual NTG, CV increased (+24%, p < 0.01) and b/a was reduced (-35%, p < 0.01), while heart rate and RA increased (+9% and +36% respectively, both p < 0.01). Two hours after NTG td, CV increase was not statistically significant (+11%, p = 0.056), b/a was reduced (-31%, p < 0.01), heart rate and RA did not change.

CONCLUSIONS

The combined use of plethysmography and digital photoplethysmography is suitable for the evaluation of vasoactive drugs such as nitrates, which have a complex profile of action on arterial and venous beds. By this method we have shown that NTG td 10 mg dilates venous beds to a low extent; this approach will be utilized in future studies aimed at elucidating dose-response and regimen effect of these drugs.

Assessment of the human splanchnic venous volume-pressure relation using radionuclide plethysmography. Effect of nitroglycerin

BACKGROUND

No method exists to assess human splanchnic venous function, the most important region in terms of vascular capacity.

METHODS AND RESULTS

We studied 25 stable patients without heart failure or hypertension to develop a method to assess the splanchnic venous volume-pressure (V-P) relation and to determine the effect of nitroglycerin (GTN). We used blood pool scintigraphy to assess changes in regional splanchnic vascular volume (SVV) and low levels of continuous positive airway pressure (CPAP) to passively alter venous pressure and thus, SVV. We postulated that the relation between SVV and the CPAP used would reflect the capacitance of the splanchnic venous bed and that changes in the position of this relation would provide a relative measurement of any change in capacitance. In 12 patients (group 1), the splanchnic vascular V-P curves were recorded before and 2, 9, and 20 minutes after 0.6 mg sublingual GTN; in eight patients (group 2), recordings were made at similar times before and after sublingual administration of placebo; in five patients (group 3), the hemodynamic effects of CPAP were assessed by means of right and left cardiac catheterization. Right atrial and femoral venous pressures increased (p < 0.001) and cardiac output fell (p < 0.05) during CPAP. There was an apparently linear relation between CPAP and SVV (r = 0.74-0.98); SVV increased an average of 7.4 +/- 2.2% (p < 0.001) by 12 cm H2O CPAP: The splanchnic vascular V-P curves were reproducible with minimal variability in SVV (+/- 2%, p > 0.2) in group 2. After administration of GTN, the splanchnic vascular V-P curve shifted away from the pressure axis in a parallel fashion by an average of 9.4 +/- 5.4% (p < 0.001).

CONCLUSIONS

We have developed a reproducible noninvasive technique that may be used to assess human splanchnic venous V-P relations. We have demonstrated for the first time in humans that GTN exerts its dilatory effect by increasing the unstressed splanchnic venous volume.

A rational approach to detection of significant reflux with duplex Doppler scanning and air plethysmography

PURPOSE

Several techniques are currently available for the detection of venous reflux. We have attempted to determine the relative value and accuracy of available techniques to develop a logical strategy of investigation in reflux venous insufficiency.

METHODS

The morphologic distribution of venous incompetence (erect duplex and descending venography); the results of ambulatory venous pressure measurement, venous refilling time, the Valsalva test, and air-plethysmography (venous refilling index, VFI); and the clinical severity were described in 118 consecutive limbs. In an attempt to validate the tests, results were correlated with the clinical severity classification (class 0, n = 34; class 1, n = 42; class 2, n = 11; class 3, n = 31) and with a standardized quantification of reflux (multisegment score) as seen on standing duplex Doppler scanning with rapid deflation cuffs.

RESULTS

Twenty-nine percent of limbs with severe venous disease (class 2/3) had pure deep insufficiency, only 6% had pure superficial disease, and the remainder had a combination. A history of previous thrombosis and the presence of posterior tibial vein incompetence were markedly common with ulcer disease (84% and 42%, respectively). The duplex Doppler multisegment score correlated strongly with clinical severity classification (r = 0.97). The venous refilling time and VFI had the highest sensitivity in identifying severe venous disease (class 2/3), and the ambulatory venous pressure had excellent specificity.

CONCLUSIONS

For noninvasive determination of reflux, the combination of VFI and duplex scanning not only localized reflux but also separated severe clinical vein disease from mild, with high sensitivity and specificity. Air plethysmography may also provide valuable information regarding calf muscle pump and outflow obstruction.

Noninvasive tests in venous insufficiency

Chronic venous insufficiency (CVI) is the result of outflow obstruction, reflux or a combination of both. Noninvasive tests detect an quantify obstruction and reflux if present and define the anatomic localisation of the abnormality. In evaluating CVI noninvasive tests combine physiologic and imaging techniques. These tests are widely available, simple, quick and cost-effective and therefore they are the methods of choice for initial objective evaluation. Different tests provide answers to different questions. The optimum clinically useful information can be now obtained using only three instruments: pocket Doppler, duplex or color duplex scanner and air plethysmography. The value of ambulatory venous pressure, photoplethysmography and light reflection reography, air plethysmography, duplex and color duplex scanning to assess reflux and the value of tests to assess out-flow obstruction are presented. Pooled data collected from large studies are also presented for reference. Qualitative and quantitative assessment of CVI are useful both for clinical assessment and to evaluate the effect of treatments.

Pulse volume recording

Noninvasive studies, in general, and pulse volume recordings (PVRs), in particular, play important roles in diagnosis, planning, and monitoring of therapy for vascular disorders of the upper extremity. Essentially, PVR is a useful screening tool to show whether hemodynamically significant vascular disease has produced alterations of digital flow patterns. PVR also has a role in differentiating between vasospastic and vaso-occlusive disease, in evaluating cold sensitivity, in monitoring medical and surgical treatments, and as a research tool. This method also has its limitations, which must be appreciated, to place the true role of this very useful noninvasive modality in proper perspective.

Accelerated plethysmogram in nursing home residents

To investigate the peripheral blood circulation, 24 young volunteers, 28 nursing home residents with cerebrovascular diseases (CVD) and 42 residents without them were studied for accelerated plethysmogram (APG). Both residents were rated by the modified Stockton geriatric rating scale (modified SGRS) which have four aspects of impairments; physical disability, socially irritating behavior, communication failure and apathy. As to the waveform patterns of APG, the majority of the young volunteers and both the residents showed patterns B and G, respectively. Coefficient of APG (Co-APG) of the former was significantly larger than that of the latter. In the residents without CVD, Co-APG was significantly negatively correlated with physical disability and apathy of the modified SGRS. But, Co-APG did not correlate with the modified SGRS in the residents with CVD.

Physiologic similarities between extremities with varicose veins and with chronic venous insufficiency utilizing air plethysmography

Air plethysmography (APG) was used to measure maximal venous outflow rate (MVO), a test for proximal venous obstruction; venous volume; venous filling index, an estimate of valvular incompetence; ejection fraction (EF), a test of calf-muscle pump efficiency; and residual volume fraction (RVF), an estimate of ambulatory venous pressure. MVO was lower in patients with chronic venous insufficiency (CVI) than in those with varicose veins (VV), but the difference was small (p = 0.06). RVF was significantly greater in extremities with CVI when compared with those with VV (p less than 0.01). However, the degree of abnormality in venous volume, venous filling index, and EF was similar in CVI and VV extremities. In summary, although RVF tends to be higher in extremities with CVI when compared with those with VV, there is tremendous overlap between VV and CVI for each of the hemodynamic variables measured by APG. Therefore, the pathophysiology of CVI is likely to involve not only hemodynamic abnormalities but also other factors that have not yet been clearly identified.

Passive partitioning of respiratory volumes and time constants in ventilated patients

If the thoracoabdominal partitioning of volumes in the mechanical respiratory apparatus was constant, one transducer of indirect spirometry should be sufficient to measure volume variations. To verify this hypothesis we used respiratory inductive plethysmography (RIP) in 16 paralysed patients, of whom eight had normal lungs and 8 had not, to measure: 1) the thoracoabdominal partitioning of volumes (400-1,200 ml) insufflated from either a syringe (Syr) or a ventilator (Vent); and 2) thoracic (Tho) and abdominal (Abd) time constants (T0.368) on spontaneous deflation to barometric pressure. In eleven additional subjects with normal lungs we measured only the time constants. 1) Correlation coefficients of the calibration lines were in all but one subject > 0.98. In all patients the error of volume was < +/- 10% when either one of two coils alone was used to assess volumes with no difference between the two coils; 2) Partitioning varied little with volumes (4 +/- 2%), but widely between subjects, with no group average significant difference between Syr and Vent; 3) T0.368 were identical for Tho and Abd except in one patient; 4) Partitioning and T0.368 were volume size independent. We conclude that, to measure volume variations and time constants in ventilated, paralysed patients, the use of either a thoracic or abdominal single coil RIP is justified. We also provide the normal range for time constant in 19 subjects (0.73 +/- 0.29 s).

Photoplethysmography: a valuable noninvasive tool in the assessment of venous dysfunction?

We have investigated the photoplethysmography findings in 152 patients admitted to the Middlesex Hospital Vascular Laboratory with suspected lower limb venous disease, and we compared the results obtained with patient grouping using clinical criteria and the presence of reflux on color duplex scanning. All photoplethysmography traces were normalized with use of computer software to enable direct comparison between the traces. The parameters investigated were the 95% and 50% refilling times and the initial gradient of the refilling curve. Receiver operating characteristic curves were constructed to determine which parameter was the most useful predictor of disease and to identify which value within each observation gave the greatest sensitivity and specificity. We found a large overlap between interquartile values for all three parameters, with limbs grouped both clinically and by duplex scanning, making differentiation between normal and abnormal limbs difficult on the basis of photoplethysmography traces alone. We found that a 95% refilling time of less than 15 seconds indicated venous dysfunction with the greatest sensitivity and specificity and suggest that this value is most useful. Photoplethysmography readings are reproducible, noninvasive, and correlate well with the presence of clinical disease, and photoplethysmography remains useful in the assessment of venous dysfunction.

Blushing as a function of audience size

Almost no experimental analysis of blushing has been done since Darwin's observations in 1872. Forty-eight college women watched a videotape intended to elicit blushing, and a videotape not intended to elicit blushing, but elicit physiological responses. A subject was alone, or with one or four persons present. Blushing, which was measured directly with a photoplethysmograph probe on the cheek, was greater during the blushing than nonblushing stimulation. Blushing increased as audience size increased from one to four, but not from zero to one. Audience size and kind of stimulation interacted statistically. Similar results were obtained with ear coloration, cheek temperature, and skin conductance responses, although confidence levels were lower. Cheek coloration and temperature were significantly correlated during nonblushing stimulation, and the zero and one audience conditions, but not during the four audience condition, when blushing was greatest. These results may be placed within the context of emotional effects of audience size generally, including stuttering and speech disturbance, disruption of learning, and self-reported tension.

Evaluation of respiratory inductive plethysmography in the measurement of breathing pattern and PEEP-induced changes in lung volume

STUDY OBJECTIVE

To assess the accuracy of the respiratory inductive plethysmography in the measurement of PEEP-induced changes in end-expiratory lung volume during mechanical ventilation and its accuracy and stability in the measurement of ventilation during controlled mechanical ventilation and spontaneous breathing.

DESIGN

An open comparison between two methods using a criterion standard. Either a pneumotachometer (mechanically ventilated patients) or a spirometer (spontaneously breathing subjects) was used as the reference method.

SETTING

Tertiary care center; a multidisciplinary intensive care unit and a metabolic research unit.

PATIENTS

Six mechanically ventilated, paralyzed postoperative open heart surgery patients, six spontaneously breathing COPD patients, and eight healthy volunteers.

INTERVENTIONS

Stepwise increases and reductions of PEEP from zero to 12 cm H2O during controlled mechanical ventilation; repeated validation of the calibration of the respiratory inductive plethysmography (RIP) in both mechanically ventilated and spontaneously breathing subjects.

MEASUREMENTS AND RESULTS

The baseline drift of the RIP in vitro was 10 ml/150 min and in a ventilated model it was 20 ml/150 min. In mechanically ventilated patients, the mean error of the calibration after 150 min was within +/- 5 percent. Change in end-expiratory lung volume (EELV) during the stepwise increase of PEEP up to 12 cm H2O was 849 +/- 136 ml with the RIP and 809 +/- 125 ml with the pneumotachometer (PT), and during the stepwise reduction of PEEP it was 845 +/- 124 ml and 922 +/- 122, respectively (not significant [NS]. The mean difference between methods in the measurement of change in EELV was -6.6 +/- 3.5 percent during increasing and 6.6 +/- 6.7 percent during decreasing PEEP (NS). Both in mechanically ventilated and spontaneously breathing subjects, the difference between methods was significant for VT and VT/TI. The difference in VT was -2.2 +/- 0.2 percent during mechanical ventilation, -1.1 +/- 0.5 percent in spontaneously breathing COPD patients, and 2.9 +/- 0.4 percent in healthy volunteers (NS between groups).

CONCLUSIONS

The RIP is sufficiently accurate for the measurement of PEEP-induced changes in EELV during controlled mechanical ventilation. The accuracy of tidal volume measurement is similar during mechanical ventilation and spontaneous breathing. The calibration of the RIP is stable enough for bedside monitoring of changes in lung volumes.

Venous haemodynamics--a consideration of macro- and microvascular effects

In health, valves in the deep veins function unidirectionally permitting blood flow towards the heart. This function is often degraded following deep vein thrombosis leading to venous hypertension and disturbed haemodynamics in the legs of the patient. Hypertension, in turn, promotes venous ulceration through a series of degenerative pathological steps. Traditional methods of treatment include leg elevation and compression using elasticated garments or bandaging. These techniques manage the problem with varying success but do not cure it. Recent advances in surgical research suggest that novel techniques are being developed for treating valve incompetence. In these circumstances, vascular scientists should be examining methods of addressing both the macro- and the microcirculation so that changes in these consequent to venous hypertension may be measured. This review examines existing methods of measuring the macrocirculation as well as the potential techniques to study effects of venous haemodynamics in the microcirculation.

Calf blood flow and posture: Doppler ultrasound measurements during and after exercise

To investigate the joint effects of body posture and calf muscle pump, the calf blood flow of eight healthy volunteers was measured with pulsed Doppler equipment during and after 3 min of rhythmic exercise on a calf ergometer in the supine, sitting, and standing postures. Muscle contractions seriously impeded calf blood flow. Consequently, blood flow occurred mainly between contractions and reached a plateau that lasted at least the final 100 s of each exercise series. After exercise the blood flow decreased much faster in the sitting and standing postures than in the supine posture. There was no difference in blood flow between various postures during the same submaximal exercise. However, subjects in the standing posture were able to perform exercise with a higher load than in the supine posture, and blood flow in the standing posture could become twice as high as in the supine posture. We conclude that calf blood flow is regulated according to needs; available perfusion pressure determined maximal blood flow and exercise; and compared with the supine posture, the standing posture and calf muscle pump increase the perfusion pressure.

The feasibility of spectrophotometric measurements of arterial oxygen saturation from the fetal scalp utilizing noninvasive skin-reflectance pulse oximetry

In in-vivo animal experiments, the authors evaluated the feasibility of measuring arterial oxyhemoglobin saturation (SaO2) noninvasively during simulated delivery conditions with a skin-reflectance pulse oximeter sensor attached to the fetal scalp. The optical reflectance sensor consisted of three pairs of red and infrared light-emitting diodes and a concentric array of six identical photodiodes. Two prototype sensor assemblies, incorporating different means of attachment to the scalp, were evaluated. Each sensor was interfaced to a commercial Datascope ACCUSTAT transmittance pulse oximeter, adapted to perform as a reflectance pulse oximeter. This method, once successfully developed, could potentially be used in combination with other fetal monitoring techniques to elucidate the role of noninvasive pulse oximetry in reducing fetal morbidity and mortality.

Critical analysis of methods for assessing regional blood flow and their reliability in clinical medicine

The advantages and inadequacies of the currently available techniques to measure regional blood flow in the lower limbs are being reviewed. Thermodilution technique and local 133xenon washout technique have the advantage of allowing determination of blood flow during exercise, while venous occlusion plethysmography and pulsed-Doppler duplex ultrasonography only allow determination of blood flow at rest. Overall, measurements of lower limb blood flow are not highly reproducible by any technique, and the variability in measurements of regional blood flow should lead to careful interpretation of derived parameters such as vascular conductance and resistance. Determination of vascular input impedance by Fourier analysis of pressure data, recorded with high fidelity catheter, and flow velocity measurements obtained transcutaneously by Doppler ultrasonography, may offer a more accurate quantitative analysis of the characteristics of the lower limb vascular system.

Ambulatory strain-gauge plethysmography and blood volume scintimetry for quantitative assessment of venous insufficiency

In the present study, a strain-guage plethysmographic method (ASGP) is compared to an isotope plethysmographic method (ABVS), in order to evaluate how an externally recorded volume change corresponds to blood displacement within the leg during exercise. The coefficient of correlation for RT (venous return time) was 0.67 (P less than 0.001) and for EV (expelled volume) it was 0.61 (P less than 0.001). The RT values were similar by the two methods both in healthy controls and in patients with Chronic Venous Insufficiency (CVI). The corresponding EV values showed the same pattern in controls and patients but the values differed substantially. By ASGP the value was approximately 2 ml per 100 ml tissue compared to 33 ml per 100 ml blood by the ABVS method. Both methods could clearly distinguish normal controls from patients with chronic deep venous insufficiency, but ABVS could only make this distinction when the ankle area of measurement was applied.

Calf blood flow and posture: Doppler ultrasound calibrated by plethysmography

A procedure was developed that enables measurement of rapid variations in calf blood flow during voluntary rhythmic contraction of the calf muscles in supine, sitting, and standing positions. During the exercise, maximum blood velocity is measured by Doppler ultrasound equipment in the popliteal artery. The Doppler signals are calibrated by plethysmography to enable calculation of blood flow during exercise in ml.100 ml-1.min-1. Knowledge of the cross-sectional area of the vessel and the angle of insonation is not required in this procedure. Evaluation of the calibration method with 10 healthy volunteers showed that for each subject a new calibration was necessary after a change in posture; the relationship between the blood flow and the maximum Doppler frequency averaged over one heart cycle was linear for each calibration.

The correlation between three methods of skin perfusion pressure measurement: radionuclide washout, laser Doppler flow, and photoplethysmography

The most accurate measurement of skin perfusion pressure is made with use of radioisotopic clearance techniques. We compared the skin perfusion pressure using radioisotope to the skin perfusion pressure measured simultaneously by placing laser Doppler and photoplethysmography probes within a transparent polyvinylchloride plastic blood pressure cuff in 13 subjects. A new device, which was created for this experiment, consisted of a plastic bladder into which light-emitting probes can be placed, so that the pressure applied to the skin was transmitted by the surface of the bladder, rather than by the surface of a rigid probe. The cuff was inflated to a supra-systolic pressure over the intradermal injection site of technetium Tc 99m, then deflated in 10 mm Hg decrements at 3-minute intervals. The pressures at which radioisotope clearance began, at which microcirculatory flow was detected by laser Doppler, and at which deflection of the photoplethysmography (DC mode) output occurred, were recorded as the skin perfusion pressure. The range of radioisotopic determined skin perfusion pressure was 0 to 100; skin perfusion pressure-laser Doppler was 0 to 100; and skin perfusion pressure-photoplethysmography was 60 to 100, with 7 of 13 limbs demonstrating no clear deflection point and thus an unobtainable skin perfusion pressure-photoplethysmography reading. Linear regression revealed a coefficient of correlation of 0.991 for skin perfusion pressure when the radioisotopic and laser Doppler methods were compared. Our study is not in agreement with previous reports of the successful determination of skin perfusion pressure with use of photoplethysmography. This may be due to differences in our technique when compared with previous reports of skin perfusion pressure-photoplethysmography determination.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of Doppler ultrasound and photoplethysmography in the investigation of venous insufficiency

Non-invasive methods of venous assessment have been developed to improve diagnostic accuracy in the assessment of venous insufficiency. Of these, continuous wave Doppler (CWD) ultrasound and photoplethysmography are the cheapest and most simple to perform. In this study duplex scanning was used to test the accuracy of these two methods. One hundred and thirty-six patients attending the venous outpatient clinic at Middlesex Hospital, London were examined by all three techniques and a diagnosis was reached using each technique. The technicians performing the examinations were unaware of the diagnoses reached by the other methods. Continuous wave Doppler ultrasound was found to be most accurate in the diagnosis of long saphenous incompetence (sensitivity 73%, specificity 85%). Due to the variability of venous anatomy at the popliteal fossa and the 'blindness' of the technique, it was inaccurate in the diagnosis of short saphenous incompetence (sensitivity 33%) and deep vein reflux (sensitivity 48%). Photoplethysmography was found to be most accurate in the diagnosis of deep vein reflux (sensitivity 79%, specificity 70%) but was inaccurate in identification of the site of superficial vein reflux. Inaccuracies may be attributed to the presence of incompetent perforating veins and variation in arterial inflow.