Assessing the severity of aortic valve stenosis by spectral analysis of cardiac murmurs (spectral vibrocardiography). Part I: Technical aspects

Assessing the severity of aortic stenosis remains an important clinical problem. The turbulent pressure fluctuations generated by the confined jet down-stream of the stenotic valve produce vibrations in the aortic wall. These vibrations are transmitted through the chest to the skin surface, where they can be measured as systolic ejection murmurs. The purpose of the present study was to find the relationship between the severity of aortic valve stenosis and the frequency content of the precordial systolic murmurs, and to evaluate the transthoracic attenuation of murmurs and its variation from patient to patient. Twenty-four patients with clinical signs of aortic stenosis underwent cardiac catheterization to measure the peak transvalvular pressure difference. The mean energy density spectrum of the measured systolic precordial murmurs was calculated and the murmur energy ratio between 100-500 Hz and 20-500 Hz was correlated to the transvalvular pressure difference. The inter-individual variability of the transthoracic attenuation was evaluated by calculating the transthoracic transfer function from simultaneous measurements of precordial vibrations at the second right intercostal space and intravascular recordings of high frequency pressure fluctuations in the ascending aorta. The transvalvular pressure difference and the square root of the murmur energy ratio correlated well (r = 0.81, SEE = 27 mmHg). In the frequency range from 10-500 Hz the transthoracic transfer function could be modelled by a low-pass filter function with a low frequency attenuation of 36 +/- 7.7 dB (mean +/- SD), a corner frequency of 26 +/- 12 Hz and an attenuation slope of -29 +/- 7.9 dB/decade. Spectral analysis of systolic murmurs might be an attractive non-invasive addition to the array of techniques already in use for assessing the severity of aortic stenosis. It is a simple and cost effective technique, and requires less skill and time for data analysis than conventional methods.

Three dimensional visualisation of velocity profiles in the normal porcine pulmonary trunk

OBJECTIVE

The aim was to obtain detailed data of velocity profile development in the porcine pulmonary trunk.

METHODS

Hot film anemometry was used for point blood velocity measurements in the entire cross sectional area one diameter downstream of the normal porcine pulmonary valve. Computerised three dimensional visualisations of the spatial and temporal development of blood velocity profiles were made. Measurement series were conducted under spontaneous and stressed haemodynamic conditions in 16 pigs with a body weight of approximately 90 kg.

RESULTS

The velocity profiles revealed consistent temporal and spatial development characteristics. In the systolic acceleration phase the profile was flat, but during peak systole an initially counterclockwise rotation was seen; subsequently the profile turned clockwise and ultimately counterclockwise to become flat during early and late systolic deceleration phases.

CONCLUSIONS

These skewed, rotating velocity profiles are in conflict with the generally accepted assumption that the velocity profile in the pulmonary trunk is flat. The rotating skewness of the velocity profile in the porcine pulmonary trunk has not been described before. The reason for the rotating velocity profile is obscure.

Lowered threshold for ventricular fibrillation in amiodarone-treated pigs undergoing cardiopulmonary bypass and cardioplegic arrest with St. Thomas' cardioplegic solution

The antiarrhythmic agent amiodarone has been suspected of causing reduced cardiac performance after extracorporeal circulation and cardioplegic arrest in patients. This has recently been confirmed in an experimental model where pigs were exposed to cardiopulmonary bypass and cold cardioplegic arrest with Bretschneider's solution. Due to the high concentration of the cardio-depressant agent procain in Bretschneider's solution, it could be speculated whether it is the combination of amiodarone and this solution that may be potentially deleterious, rather than amiodarone alone. To investigate this, adult pigs (75 +/- 2 kg at surgery) were treated with amiodarone for 30 +/- 2 days (1400 mg/day: n = 8, untreated controls: n = 4, blind experiment), followed by exposure to cardiopulmonary bypass with universal cooling to 28 degrees C and topical cold cardioplegic arrest with St. Thomas' solution for 60 min. Apart from 1 g of calcium (Ca2+) at the end of bypass, no inotropic drugs were administered. Cardiac reserve was tested by right ventricular pacing (200 beats/min until death or up to 30 min). The two groups did not differ concerning preload or afterload, heart rate, cardiac output, left ventricular pressure, arterial pressure or rate of change in left ventricular relaxation (-dP/dt) before or after bypass was terminated, while the rate of change in left ventricular contraction (+dP/dt) was lower in the amiodarone-treated pigs. The time on bypass, before stable hemodynamics had recovered, was prolonged in amiodarone-treated animals, 46 +/- 4 min versus 31 +/- 3 min in the controls (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial fibrillation and flutter after coronary artery bypass surgery: epidemiology, risk factors and preventive trials

Atrial fibrillation and atrial flutter are common arrhythmias after coronary artery bypass grafting. Although the consequences of the arrhythmia are generally not life-threatening, it constitutes a major clinical problem often requiring conversion to sinus rhythm. Atrial fibrillation or flutter can result in hypotension, heart failure, pneumonia, and stroke. This article reviews the literature on epidemiology, electrophysiology, risk factors, and preventive trials. The major conclusions are: (1) In patients undergoing coronary artery bypass surgery, the incidence of postoperative atrial fibrillation or flutter is 20-30%, the peak incidence being on the second or third postoperative day. (2) The strongest independent preoperative predictor for atrial fibrillation or flutter is the patients' age. (3) Intra-atrial conduction delay recorded pre and peroperatively may predict development of atrial fibrillation. (4) Peroperative inducibility of atrial fibrillation by pacing the right atrium may identify patients at risk for postoperative atrial fibrillation. (5) Development of postoperative atrial fibrillation or flutter has not been associated with peroperative or postoperative events. (6) The specificity and sensitivity of age and other possible relevant factors for prediction of atrial fibrillation or flutter after coronary artery bypass grafting is low. (7) No effective prophylactic regimen has yet been established.

Reduced cardiac reserve in amiodarone-treated pigs after cardiopulmonary bypass and cardioplegic arrest

An animal model was designed for blinded study to elucidate whether cardiac pump failure after heart surgery in amiodarone-treated patients is due to interference between the drug and the surgical procedures. Seventeen adult pigs were treated with amiodarone for 30 days (study animals, 1,400 mg/day, n = 9; untreated control animals, n = 8) followed by exposure to cardiopulmonary bypass and topical cold cardioplegic arrest (Bretschneiders solution) for 60 min. Apart from 1 g of calcium, no inotropic agents were administered. Cardiac reserve was tested by ventricular pacing (200 beats/min for 30 min or until exhaustion). No difference in hemodynamic status was observed between the treated and the untreated group before pacing. Pacing duration in the amiodarone-treated pigs was 10 +/- 3 versus 22 +/- 4 min in control pigs (p less than 0.05). Only one amiodarone-treated pig survived 30 min of pacing compared with five control pigs (11% vs. 63%, p less than 0.05). The following variables differed significantly in the two groups during pacing: cardiac output, left ventricular pressure, arterial pressure and peak positive and negative first derivative of left ventricular pressure (dP/dt). Most marked were the changes in peak positive dP/dt, indicating a compromised systolic function. The two groups did not differ in preload or afterload at any time during the experiments.

Two-dimensional color-mapping of turbulent shear stress distribution downstream of two aortic bioprosthetic valves in vitro

Since artificial heart valve related complications such as thrombus formation, hemolysis and calcification are considered related to flow disturbances caused by the inserted valve, a thorough hemodynamic characterization of heart valve prostheses is essential. In a pulsatile flow model, fluid velocities were measured one diameter downstream of a Hancock Porcine (HAPO) and a Ionescu-Shiley Pericardial Standard (ISPS) aortic valve. Hot-film anemometry (HFA) was used for velocity measurements at 41 points in the cross-sectional area of the ascending aorta. Three-dimensional visualization of the velocity profiles, at 100 different instants during one mean pump cycle, was performed. Turbulence analysis was performed as a function of time by calculating the axial turbulence energy within 50 ms overlapping time windows during the systole. The turbulent shear stresses were estimated by using the correlation equation between Reynolds normal stress and turbulent (Reynolds) shear stress. The turbulent shear stress distribution was visualized by two-dimensional color-mapping at different instants during one mean pump cycle. Based on the velocity profiles and the turbulent shear stress distribution, a relative blood damage index (RBDI) was calculated. It has the feature of combining the magnitude and exposure time of the estimated shear stresses in one index, covering the entire cross-sectional area. The HAPO valve showed a skewed jet-type velocity profile with the highest velocities towards the left posterior aortic wall. The ISPS valve revealed a more parabolic-shaped velocity profile during systole. The turbulent shear stresses were highest in areas of high or rapidly changing velocity gradients. For the HAPO valve the maximum estimated turbulent shear stress was 194 N m-2 and for the ISPS valve 154 Nm-2. The RBDI was the same for the two valves. The turbulent shear stresses had magnitudes and exposure times that might cause endothelial damage and sublethal or lethal damage to blood corpuscules. The RBDI makes comparison between different heart valves easier and may prove important when making correlation with clinical observations.

Three-dimensional visualization of velocity profiles in the porcine abdominal aortic trifurcation

To study the local distribution of blood velocities in the abdominal aorta and trifurcation, hot-film anemometry was used for point blood velocity measurements in the entire cross-sectional area in the abdominal aorta and abdominal aortic trifurcation in pigs weighing 90 kg. The geometry was visualized by use of a casting procedure. General hemodynamic and geometric parameters in the abdominal aorta were comparable to values found in humans. The porcine trifurcation differed somewhat from the human bifurcation. The velocity measurements in the abdominal aorta showed consistently skewed velocity profiles with the highest velocities at the anterior vessel wall. No signs of developed turbulence were found. Velocity measurements in the external iliac vessels showed high velocities at the flow divider, and low velocities with signs of retrograde flow during part of diastole at the lateral vessel wall.

Nonpharmacologic treatment of supraventricular and ventricular tachyarrhythmias. A review of 249 consecutive patients

Incapacitating or life-threatening tachyarrhythmias were treated nonpharmacologically in 249 patients from 1982 to 1991. Among 92 patients surgically treated for supraventricular tachycardia the cure rate was 93% and the complication rate 12%. Radiofrequency catheter ablation gave an equal cure rate in 51 patients, but with no major complications or mortality. Direct-current catheter ablation of the His bundle was successful in 96% of 27 patients with drug-refractory atrial fibrillation or other supraventricular tachyarrhythmias. Among 64 patients undergoing surgery for ventricular tachycardia/ventricular fibrillation, the perioperative mortality was 9%, estimated 5-year survival 69% and estimated 5-year freedom from the preoperative arrhythmias 72%. Of 18 patients treated with implantable cardioverter defibrillator, three (18%) died of heart failure during follow-up. Nonpharmacologic treatment of tachyarrhythmias is concluded to be effective and often definitively curative. The safety-risk ratio is improving as new treatment modalities are developed.

Quantitation of the turbulent stress distribution downstream of normal, diseased and artificial aortic valves in humans

Damage to blood corpuscles seems to be related to the magnitude and exposure time of the turbulent shear stresses (TSS). According to in vitro studies the critical TSS level for lethal erythrocyte and thrombocyte damage is 150-400 N/m2, for exposure times within physiological ranges. To study the distribution of TSS in the human ascending aorta, a hot-film anemometer needle probe was used to register blood velocities at 41 evenly distributed measuring points in the cross-sectional area 5-6 cm downstream of the aortic annulus. Measurements were made in the ascending aorta after normal aortic valves (prior to coronary bypass surgery), after stenotic aortic valves, and after implantation of either St. Jude Medical or Starr Edwards Silastic Ball valves. Three-dimensional visualization of velocity profiles were performed and Reynolds normal stresses (RNS) were calculated within 50-ms overlapping time windows in systole. By coordinating the mean RNS for each time window and for all 41 measuring points, 2-dimensional color-coded mapping of the RNS distribution was made. Based on the velocity profiles and the RNS distribution a relative blood damage index (RBDI) was calculated to incorporate the magnitude and exposure time for RNS in the entire cross-sectional area into one parameter. Turbulent shear stresses were estimated by using a previously determined correlation equation between RNS and TSS. After normal aortic valves, RNS was below 4 N/m2.(ABSTRACT TRUNCATED AT 250 WORDS)

Velocity field studies at surgically imposed arterial stenoses on the abdominal aorta in pigs

In order to describe velocity profiles and the size of deterministic and non-deterministic velocity disturbances at arterial stenoses, symmetrical and asymmetrical stenoses with intended area reductions of 50% ('moderate') and 85% ('severe') were applied on the abdominal aorta in six pigs. Blood velocities were registered by hot-film anemometry in 21 measuring points distributed across the vessel cross-sectional area in one pre-stenotic and three post-stenotic positions. Signal analysis included ensemble averaging, the high-pass filtering technique, and three-dimensional visualization. None of the stenoses affected the pre-stenotic velocity field. Downstream moderate stenoses flow separation and vortex formation were present. Moderate asymmetric stenoses induced turbulence in the post-stenotic velocity field. Immediately downstream of severe stenoses a prominent post-stenotic jet was present. Farther downstream, a multitude of coherent vortices and turbulence dominated the flow field. The transverse distribution of turbulence intensity paralleled with the peak systolic velocity profile, whereas transverse profiles of the relative turbulence intensity (turbulence intensity/mean velocity) revealed peak values in flow field locations with high velocity gradients. Velocity parameters for symmetric and asymmetric severe stenoses were highly comparable. However, the exact degree of stenosis was significantly higher for symmetrical (85%) than for asymmetrical (76%) stenoses. Therefore, recalling that stenosis severity strongly influences the development of velocity disturbances, this indicates that asymmetry of a stenosis is a predictor for blood velocity disturbances.

Placebo-controlled, double-blind study of the effect of verapamil in intermittent claudication

The clinical effect of verapamil was tested in 24 patients with intermittent claudication in a randomized, placebo-controlled, double-blind, crossover study. Slow-release verapamil or placebo was given for two periods of three weeks. The walking distance, systemic blood pressure, and ankle-brachial blood pressure index were measured. Furthermore, a possible change in peripheral vascular tone was provoked by hyperventilation. The walking distance rose after both verapamil (40%) and placebo (31%) (p less than 0.01 for both) but tended to increase only after verapamil (7%) as compared with placebo. Blood pressure fell equally after both verapamil and placebo (p less than 0.05 for both). Verapamil did not influence the ankle-branchial blood pressure index. No signs of vasoactivity in the lower extremities were seen after hyperventilation. Although the greatest individual improvements in walking distance were seen after verapamil administration, it was not possible to predict positive responders among the patients.

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro

Measuring turbulent shear stresses is of major importance in artificial heart valve evaluation. Bi- and unidirectional fluid velocity measurements enable calculation of Reynolds shear stress [formula: see text] and Reynolds normal stress [formula: see text]. tau is important due to the relation to hemolysis and thrombus formation, but sigma is the only obtainable parameter in vivo. Therefore, determination of a correlation factor between tau and sigma is pertinent. In a pulsatile flow model, laser Doppler (LDA) and hot-film (HFA) anemometry were used for simultaneous bi- and unidirectional fluid velocity measurements downstream of a Hall Kaster and a Hancock Porcine aortic valve. Velocities were registered in two flow field locations and at four cardiac outputs. The velocity signals were subjected to analog signal processing prior to digital turbulence analysis, as a basis for calculation of tau and sigma. A correlation factor of 0.5 with a correlation coefficient of 0.97 was found between the maximum Reynolds shear stress and Reynolds normal stress, implying [formula: see text]. In vitro estimation of turbulent shear stresses downstream of artificial aortic valves, based on the axial velocity component alone, seems possible.

Turbulent stresses downstream of porcine and pericardial aortic valves implanted in pigs

Because late valve-related complications such as hemolysis and thromboembolic events are considered related to flow disturbances caused by the inserted valve, velocity fields downstream of aortic valve prostheses were studied in pigs. Acute hemodynamic evaluation of size 25-mm porcine and pericardial aortic valve prostheses 1 diameter downstream of the valve ring was performed using dynamic three-dimensional visualization of velocity profiles and spatial distribution of turbulence. Point blood velocity signals obtained with a 1-mm hot-film anemometer needle probe were used to compute Reynolds normal stresses (RNS) by calculation of the turbulent velocity energy of the axial velocity component in the systole. The porcine valves caused a skewed velocity and turbulence profile revealing mean spatial systolic RNS at 70 nm-2 +/- 35 nm-2 (+/- SD). The spatial maximum RNS was 275 +/- 139 nm-2. Corresponding values for the pericardial valves were 20 +/- 11 nm-2 and 72 +/- 46 nm-2. The pericardial valves revealed plug-shaped velocity profiles and turbulent profiles with slightly higher RNS values at the stent posts. From a hemodynamic point of view, these acute studies indicate superiority of the pericardial valves compared to the porcine valves. The turbulent stresses found in this study are of a magnitude that may cause blood corpuscular and endothelial damage.

Surgical repair of ruptured aortic sinus of Valsalva aneurysm

Surgical repair of ruptured aortic sinus of Valsalva aneurysm was performed on six patients. The NYHA functional class was I in one case, II in three and III in two cases. All aneurysms had ruptured into the right atrium. Three originated from the right, and three from the non-coronary aortic sinus of Valsalva. The preoperative shunt was 55-200% (mean 118%) of the peripheral cardiac output. At aneurysmal repair, closure of secundum-type atrial septal defect was performed in one case and insertion of a St Jude Medical aortic valve in another. There were no perioperative deaths. Five patients were asymptomatic in the follow-up period (5 months-17 years). One patient died of cardiomyopathy 11 years postoperatively. The long-term results after surgical repair of ruptured aortic sinus of Valsalva aneurysm thus were good, and early operation is recommended in order to avoid congestive heart failure.

Curative surgical treatment of atrioventricular junctional re-entrant tachycardia by perinodal dissection

The medical treatment of an atrioventricular junctional (AV-nodal) re-entrant tachycardia (AVJRT) is often ineffective due to failure of response or significant side effects. Recently, reports of curative surgical procedures using either dissection or cryocoagulation in the AV node area with preservation of normal AV conduction, have been published with excellent short term results in small series. The present paper describes our experience of surgical treatment using the dissection method in five patients. In all patients, AVJRT with short retrograde conduction intervals was diagnosed during the pre- and intraoperative electrophysiological studies. The earliest site of atrial activation during tachycardia was seen close to the triangle of Koch, antero-medially to the AV node. Elective open heart surgery was performed and after cold cardioplegic arrest, the right atrial endocardium was incised and the perinodal atrium carefully disconnected from the AV node. After surgery, a tachycardia could not be induced in any of the patients. In a follow-up period of 14-29 months, all patients have been free of symptoms without antiarrhythmic drugs. Early electrophysiological evaluation of patients with supraventricular tachycardia is advocated and in patients with medically refractory AVJRT, surgery is recommended.

Three-dimensional visualization of velocity profiles in the ascending aorta in humans. A comparative study among normal aortic valves, St. Jude Medical and Starr-Edwards Silastic Ball valves

Blood velocities were recorded intraoperatively in the ascending aorta approximately 6 cm downstream of the aortic annulus in eight patients with normal aortic valves (prior to coronary bypass surgery) and in seven patients after implantation of a St. Jude Medical valve (4) or Starr-Edwards Silastic Ball valve (3) in the aortic position by means of constant temperature hot-film anemometry. The velocities were measured during 5-15 heart cycles at 41 predetermined measurement points almost evenly distributed in the cross sectional area. Velocity profiles were visualized three-dimensionally at 100 time intervals during one mean heart cycle. The standard deviation of velocities was correspondingly three-dimensionally visualized. For the patients with normal aortic valves the velocity profiles were generally flat but skew, with the highest velocity closer to the left vessel wall at the start of systole. During systole the skewness turned counter-clockwise with the highest velocities closer to the posterior, right and finally anterior vessel wall at the end of systole. In patients with an artificial heart valve in the aortic position the design of the valve was reflected on the contour of the profiles. The findings correspond well with model studies.

Analysis of velocity in the ascending aorta in humans. A comparative study among normal aortic valves, St. Jude Medical and Starr-Edwards Silastic Ball valves

To analyze velocity spectral energy distribution in humans, blood velocities were recorded by means of hot-film anemometry at 41 predetermined measurement points in the cross-sectional area of the ascending aorta approximately 6 cm downstream of the aortic valves. Measurements were made in 8 patients with normal aortic valves, in 4 after insertion of a St. Jude Medical (SJM) aortic valve and in 3 after insertion of a Starr-Edwards Silastic Ball (SSB) aortic valve. Data analysis based on Fast Fourier Transform demonstrated that turbulence energy was lower in patients with normal aortic valves than in patients after insertion of an artificial valve in the aortic position and probably more pronounced after SSB valves than after SJM valves. The spatial distribution of the turbulence energy above 100 Hz was more irregular than corresponding laminar velocities previously presented. The VER100 (Velocity Energy Ratio at 100 Hz, i.e. the velocity energy above 100 Hz divided by the total velocity energy) proved useful for evaluating differences in flow disturbances downstream of different aortic valves. The mean VER100 in the three categories of patients were respectively 0.3, 1.4, and 2.1%.

Velocity fields and turbulent stresses downstream of biological and mechanical aortic valve prostheses implanted in pigs

Since detailed knowledge about velocity fields downstream of heart valve prostheses obtained from in vitro studies has not been followed up by similar detailed studies in vivo a pig model for acute velocity field studies downstream of aortic valve prostheses was established. Two mechanical and two bioprosthetic valves were studied and a dynamic three dimensional visualisation of velocity fields one diameter downstream performed under different haemodynamic conditions in a total of 22 pigs. The Ionescu-Shiley pericardial valve had velocity fields very similar to the normal native porcine aortic valve. The Edwards-Carpentier porcine valve caused a jet type flow, and the valve design of the St Jude Medical and Björk-Shiley Monostrut valves was reflected in the velocity profile. Normalised (mean(SEM] systolic Reynolds normal stresses in the total cross sectional area were: native porcine 15(1.5) Nm-2; St Jude Medical 24(3.4) Nm-2; Björk-Shiley Monostrut 25(1.6) Nm-2; Edwards-Carpentier Supra-annular 51(6.6) Nm-2; Ionescu-Shiley Pericardial 19(2.0) Nm-2. Reynolds normal stresses were higher in areas of rapidly changing or constantly high velocity gradients.

A model for acute haemodynamic studies in the ascending aorta in pigs

Since data on velocity fields in the ascending aorta downstream of normal aortic valves in pigs have not yet been obtained velocity profiles were visualised using a hot film anemometer needle probe before and after total cardiopulmonary bypass and cold cardioplegic arrest. Furthermore, measurements were made during increased heart rate and cardiac output. A dynamic three dimensional visualisation of velocity fields showed a skewed clockwise rotating velocity profile, developing from peak systole and continuing throughout the systolic deceleration phase. This pattern was consistent regardless of the haemodynamic state. Heart rate was increased to 180 beats.min-1 and cardiac output by a maximum of 91%. It is concluded that the pig model is valuable for haemodynamic studies in the ascending aorta before and after cold cardioplegic arrest and that the velocity profiles found in this study are important basic data for velocity field studies downstream of artificial heart valves implanted in the aortic position.

Tetralogy of Fallot associated with anomalous origin of the left coronary artery from the pulmonary artery, pulmonary artery hypoplasia and atrial septal defect. A case report

A 7-year-old girl had tetralogy of Fallot with anomalous origin of the left coronary artery from the pulmonary artery, pulmonary artery hypoplasia and atrial septal defect. The case is presented and diagnostic and surgical implications are discussed.

Three-dimensional visualization of axial velocity profiles downstream of six different mechanical aortic valve prostheses, measured with a hot-film anemometer in a steady state flow model

Hot-film anemometry was used for in vitro steady-state measurements downstream of six mechanical aortic valve prostheses at flow rates 10, 20 and 30 l.min-1. Three-dimensional visualizations of velocity profiles at two downstream levels were made with the valves rotated 0 and 60 degrees in relation to the sinuses of valsalvae. The velocity fields downstream of the disc valves were generally skew with increasing velocity gradients and laminar shear stresses with increasing flow rates. Furthermore, increased skewness of the velocity profiles was noticed when the major orifices of the disc valves were towards the commissure than when approaching a sinus of valsalvae. The velocity profiles downstream of the ball valve were generally flat but with considerably more disturbed flow, consistent with the findings in turbulent flow.

Continuous registration of cardiac output with a new computer system designed for hot-film anemometry: an in vitro study

We have developed and improved a method for the continuous on-line registration of cardiac output. By measuring blood velocity with a hot-film anemometer probe in the pulmonary artery, cardiac output can be estimated by gated systolic integration of the velocity signals. The integrated value for a certain period can be converted to a cardiac output proportional value. A thermistor placed next to the velocity probe enables thermodilution measurement of cardiac output, which serves as in vivo and in situ calibration. In this paper an in vitro study of the method applied to pulsatile flow is presented. A good correlation was found between real flow and both the velocity method and the thermodilution method. Fluid temperature and changing stroke volume and/or pulse frequency had minimal influence on accuracy, whereas altered probe position required recalibration for the velocity method but not for the thermodilution method. The advantages of the velocity method for the measurement of cardiac output are: The continuous on-line monitoring of cardiac output. The need for the injection of only very small volumes of cold saline, as the frequency of thermodilution measurements is reduced.

Verapamil induced increment of oxygen extraction in the arteriosclerotic limb

The acute effect of intravenously administered verapamil (0.08 mg X kg-1 body weight, mean dose 5.1 +/- 0.7 mg) on oxygen exchange and arterial blood flow (measured electromagnetically) of the lower limb was studied during reconstructive arterial surgery in 17 patients with obliterative arterial disease of the lower limbs. Verapamil increased oxygen extraction in the diseased leg by 12% (from a median value of 28.3 to 31.6 ml X litre-1, p less than 0.01) whereas it had no effect on arterial blood flow. The increment of oxygen extraction after drug administration correlated negatively with the walking distance of the patients (r = 0.69, p less than 0.01). Systolic and diastolic blood pressure decreased significantly by 10% and 6%, respectively, whereas heart rate remained unchanged after the administration of verapamil. The results suggest that verapamil might be beneficial in the treatment of patients with intermittent claudication, despite the fact that no vasodilatation was seen after the drug.