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.

Plethysmographic findings in normal subjects using a capacitance mode

A new strain-gauge plethysmographic system, Phlebotest, was evaluated in 19 normal subjects, yielding 38 lower limbs for study. A capacitance mode was used which allowed both the left and right calves to reach their maximal volume expansion before releasing the cuff pressure (60 mmHg in this study). Parameters such as the maximum volume change (V sec), the outflow rate during the first second after deflation (F 1.0), the expelled volume in four seconds (EV 4.0) and the surface area over the curve during the first four seconds after deflation (IND) were automatically calculated and their side differences between the left and right legs were determined respectively. There was a good linear correlation between EV 4.0 and V sec (r = 0.9274, p less than 0.0005) and the EV 4.0/V sec ratio was calculated. In contrast to the previous reports, between three consecutive determinations there were no significant differences in the measurements of these parameters, and V sec consistently kept an identical mean value. These results suggest that using this new system only one determination of calf expansion is required. The reason might be that, in addition to some technical improvements, the computer-controlled capacitance function can secure the optimal venous filling in every determination.

Exercise strain-gauge venous plethysmography: evaluation of a "new" device for assessing lower limb venous incompetence

Plethysmography can be used to detect and assess venous incompetence in the lower extremities. The authors recently evaluated a new device designed for this purpose that uses strain gauges to determine changes in lower extremity circumference occurring with (and immediately after) exercise. The device plots a curve of volume against time for each limb and automatically calculates key values such as the volume of blood expelled from the lower limb veins during exercise and the time required for the veins to refill following exercise. The apparatus was incorporated into their noninvasive vascular laboratory and used (along with other standard tests) to study patients referred for suspected venous incompetence. They observed the following: (1) A shortened postexercise refilling time accurately identified limbs with venous incompetence. (2) The clinical severity of venous incompetence was inversely related to the refilling time. (3) Exercise-induced changes in lower extremity volume correlated well with simultaneously determined changes in venous pressure. (4) Valvular incompetence could be localized to the deep or superficial veins based upon the improvement in refilling times seen following placement of elastic tourniquets around the lower limb. (5) The type of exercise performed (knee bends while the patient was standing versus ankle reflexes while sitting) had little effect on results. The authors conclude that exercise venous plethysmography is a useful noninvasive tool for assessing lower limb venous incompetence.

Antepartum assessment of the maternal peripheral venous system with light reflection rheology

The noninvasive detection of deep venous thrombosis (DVT) in pregnancy is a significant problem. The Hemodynamics AV-1000 uses light reflection rheology in superficial capillaries to detect DVT but has not been evaluated adequately in pregnancy. Four hundred one pregnant women in the second and third trimesters were studied with the AV-1000; none had symptoms of DVT or thrombophlebitis, and all had uncomplicated pregnancy outcomes. AV-1000 reflection curves were related to maternal age, gestational age, weight gain, Quetelet index and device sensitivity settings. No statistically significant differences in test outcomes were found for any variable. The high incidence of abnormal (25%) and inadequate (19%) tracings, coupled with an overall specificity of 45%, suggests that the system would not be useful in distinguishing patients with DVT from normal ones and could lead to excessive follow-up testing.

Diagnostic value of automatically interpreted oculopneumoplethysmography

The diagnostic value of the Gee-oculopneumoplethysmography test for the detection of hemodynamically significant carotid artery obstructions has frequently been questioned due to the rather low agreement with arteriography. The kappa-corrected diagnostic accuracy of this test has been reported to be in the range between 0.54 and 0.68. These values indicate a "fair to good" agreement with arteriography. One of the causes for this rather low agreement is the variability in the interpretation of oculopneumoplethysmography recordings. Automatic analysis of oculopneumoplethysmography recordings might minimize the risks of misinterpretation and might improve the clinical significance of the Gee-oculopneumoplethysmography test. By assessing the signals of a conventional Gee-oculopneumoplethysmography apparatus in a personal computer, this automatic analysis has been realized. In a clinical study (population of 85 patients) the diagnostic value of automatic analysis of oculopneumoplethysmography recordings has been evaluated. The automatically interpreted Gee-oculopneumoplethysmography test had a kappa-corrected diagnostic accuracy of 0.71 on a "per side" base and of 0.76 on a "per patient" base.

ECG gated radionuclide plethysmography--a method for the assessment of pulmonary systolic blood volume increase

During cardiac systole the stroke volume of blood which is ejected from the right ventricle increases the pulmonary blood volume. This systolic pulmonary blood volume increase is measured by using ECG gated chest scintigrams obtained with 99Tcm-labelled red blood cells. The total radiation counts in a region of interest that includes either the right or the left lung increases during systole. On the average, the increase of the total pulmonary systolic radiation was found to be 62% of the systolic radiation decrease in the left ventricle region of interest. The discrepancy between the value of the systolic pulmonary blood volume increase and that of stroke volume is attributed to blood flow from the lungs into the left atrium during the cardiac systole period.

Digital blood flow in cooled and contralateral finger in patients with Raynaud's phenomenon. Comparative measurements between photoelectrical plethysmography and laser Doppler flowmetry

The effects of cooling of a hand on lateral and contralateral digital skin blood flow were investigated in 18 patients with primary or secondary Raynaud's phenomenon. The aim of the study was to compare photoelectrical plethsmography (PhEP) and laser Doppler flowmetry (LDF). PhEP and LDF were used simultaneously for skin blood flow measurements of the third finger of both hands. One hand was cooled in water from 33 degrees to 3 degrees C in steps of 3 degrees C, each step lasting four minutes. It was followed by a recovery period of ten minutes in room air of 24 degrees C. During stepwise cooling from 33 degrees to 9 degrees C the relative PhEP and LDF values, measured on the cooled hand, decreased to 6.2% +/- 3.2% and 10% +/- 12% respectively. The correlation coefficients between LDF and PhEP varied between 0.79 and 0.99. In the contralateral hand the relative PhEP and LDF values decreased to 38% +/- 30.% and 64% +/- 7.9% respectively. The correlation coefficients between LDF and PhEP values were lower on the contralateral hand and ranged from 0.26 to 0.95. By calculating the LDF/PhEP ratios during cooling and recovery, more specific changes in red blood cell velocities during cooling were studied. Increasing LDF/PhEP ratios suggest increasing red blood cell velocities during cooling at 9 degrees C and a difference in the measuring methods. For testing the severity of Raynaud's phenomenon and the effect of treatment the results of both methods show consistent and quite comparable results when measured on the cooled hand. The effect of indirect cooling on the contralateral hand is, however, less consistent.

Plethysmography. A treatise on its evolution, differential methodology and clinical utilization. 1973

Plethysmography is the observation and use of volume changes in physiologic entities. The most influential short-term effect is caused by the pulsatile flow of blood. Attempts to convert these pulsatile volume changes into minimum required blood flow per unit of time have been successful clinically. Plethysmography can be accomplished by encapsulating digits, limbs and entire bodies. Volume changes in the member cause volume changes in the fixed chamber which then influences an observational medium. Plethysmography can also be accomplished with a strain gauge, direct application of electricity to flesh, changing opacity effects on tissue, ultrasound (the Doppler effect) or the piezoelectric method. The piezoelectric plethysmograph was successfully tested on 55 patients.

Reliable measures of behaviorally-evoked cardiovascular reactivity from a PC-based test battery: results from student and community samples

This paper describes efforts to reduce measurement error in the assessment of cardiovascular reactivity by standardizing task requirements and by aggregating data across tasks and testing sessions. Using these methods, reliable measures of reactivity (.80 or greater) were obtained on five different measures of cardiovascular function (heart rate, systolic blood pressure, diastolic blood pressure, stroke volume, pre-ejection period) in samples of college students and community volunteers. Methodological limitations may have hampered previous efforts in this area. Current findings are consistent with a dispositional model of cardiovascular reactivity, and they suggest productive future strategies for obtaining reliable assessments.