Biomedical subjects

T Cochrane

Publications and source records attributed to T Cochrane.

At least 19 recordsLinked to original sources

PubMed2005

Randomised controlled trial of the cost-effectiveness of water-based therapy for lower limb osteoarthritis.

OBJECTIVES: To determine the efficacy of community water-based therapy for the management of lower limb osteoarthritis (OA) in older patients. DESIGN: A pre-experimental matched-control study was used to estimate efficacy of water-based exercise treatment, to check design assumptions and delivery processes. The main study was a randomised controlled trial of the effectiveness of water-based exercise (treatment) compared with usual care (control) in older patients with hip and/or knee OA. The latter was accompanied by an economic evaluation comparing societal costs and consequences of the two treatments. SETTING: Water exercise was delivered in public swimming pools in the UK. Physical function assessments were carried out in established laboratory settings. PARTICIPANTS: 106 patients (93 women, 13 men) over the age of 60 years with confirmed hip and/or knee OA took part in the preliminary study. A similar, but larger, group of 312 patients (196 women, 116 men) took part in the main study, randomised into control (159) and water exercise (153) groups. INTERVENTIONS: Control group patients received usual care with quarterly semi-structured telephone interview follow-up only. The intervention in the main study lasted for 1 year, with a further follow-up period of 6 months. MAIN OUTCOME MEASURES: Pain score on the Western Ontario and McMaster Universities OA index (WOMAC). Additional outcome measures were included to evaluate effects on quality of life, cost-effectiveness and physical function measurements. RESULTS: Short-term efficacy of water exercise in the management of lower limb OA was confirmed, with effect sizes ranging from 0.44 [95% confidence interval (CI) 0.03 to 0.85] on WOMAC pain to 0.76 (95% CI 0.33 to 1.17) on WOMAC physical function. Of 153 patients randomised to treatment, 82 (53.5%) were estimated to have complied satisfactorily with their treatment at the 1-year point. This had declined to 28 (18%) by the end of the 6-month follow-up period, during which support for the intervention had been removed and those wishing to continue exercise had to pay their own costs for maintaining their exercise treatment. High levels of co-morbidity were recorded in both groups. Nearly two thirds of all patients had a significant other illness in addition to their OA. Fifty-four control and 53 exercise patients had hospital inpatient episodes during the study period. Water exercise remained effective in the main study but overall effect size was small, on WOMAC pain at 1 year, a reduction of about 10% in group mean pain score. This had declined, and was non-significant, at 18 months. Mean cost difference estimates showed a saving in the water exercise group of pound123--175 per patient per annum and incremental cost-effectiveness ratios ranged from pound3838 to pound5951 per quality-adjusted life-year (QALY). Net reduction in pain was achieved at a net saving of pound135--175 per patient per annum and the ceiling valuation of pound580--740 per unit of WOMAC pain reduction was favourably low. CONCLUSIONS: Group-based exercise in water over 1 year can produce significant reduction in pain and improvement in physical function in older adults with lower limb OA, and may be a useful adjunct in the management of hip and/or knee OA. The water-exercise programme produced a favourable cost--benefit outcome, using reduction in WOMAC pain as the measure of benefit. Further research is suggested into other similar public health interventions. Investigation is also needed into how general practice can best be supported to facilitate access to participants for research trials in healthcare, as well as an examination of the infrastructure and workforce capacities for physical activity delivery and the potential extent to which healthcare may be supported in this way. More detailed research is required to develop a better understanding of the types of exercise that will work for the different biomechanical subtypes of knee and hip OA and investigation is needed on access and environmental issues for physical activity programmes for older people, from both a provider and a participant perspective, the societal costs of the different approaches to the management of OA and longer term trends in outcome measures (costs and effects).

Aged↗

PubMed2004

Community rehabilitation for older adults with osteoarthritis of the lower limb: a controlled clinical trial.

OBJECTIVE: To examine the effectiveness of a 12-month community-based water exercise programme on measures of self-reported health and physical function in people aged over 60 years old with knee-hip osteoarthritis (OA). DESIGN: A quasi-experimental design consisting of an exercise group and an age-matched control group. SETTING: Public community swimming pool in Sheffield, UK. SUBJECTS: One hundred and six community-dwelling sedentary older people, with confirmed knee-hip osteoarthritis, enrolled in an experimental controlled trial for 12 months. Sixty-six subjects in the exercise group were offered a water-exercise programme. Forty age-matched, nonexercising, 'control' subjects received monthly education material and quarterly telephone calls. INTERVENTIONS: Participants in the exercise group were asked to attend two exercise sessions a week of 1 hour duration led by specially trained swimming instructors. MAIN MEASURES: Primary outcome measure was the disease-specific Western Ontario and McMaster University Osteoarthritis Index (WOMAC). Secondary outcomes included a battery of performance-based physical function tests. RESULTS: Adherence to exercise averaged 70% (+/- 14%) over the year: 77% of the exercising subjects and 89% control subjects completed both pre- and post-outcome measures. After one year, participants in the exercise group experienced a significant improvement in physical function (4.0 +/- 9.1 versus -0.4 +/- 7.3 units; 95% confidence interval (CI) 0.96-7.96, p < 0.05) and reduction in the perception of pain (1.3 +/- 3.7 versus 0.2 +/- 2.5 units; 95% CI -0.19-2.52, p < 0.05) compared with the control group, as measured by the WOMAC Osteoarthritis Index. In addition, the exercise group performed significantly better in the ascending and descending stairs tests (p < 0.05), had significantly greater improvements in knee range of movement (p < 0.01) and hip range of movements (p < 0.005). There were no significant differences in the two groups for quadriceps muscle strength and psychosocial well-being (Arthritis Impact Measurement Scales 2 questionnaire). CONCLUSIONS: Older people with knee/hip osteoarthritis gained modest improvements in measures of physical function, pain, general mobility and flexibility after participating in 12 months of community-based water exercise.

Aged↗

PubMed2001

Tests for physical function of the elderly with knee and hip osteoarthritis.

This study reports the results of a battery of physical function tests used to assess physical function of older patients with clinical knee and/or hip osteoarthritis (OA), and the correlation to the WOMAC Index (disease-specific questionnaire). A total of 106 sedentary subjects, aged >60 years (mean 69.4, S.D. 5.9) with hip and/or knee OA (mean 12.2 yrs, S.D. 11.0) participated in the study. Mobility, joint flexibility and muscle strength were evaluated by recording time to: walk a distance of 8', ascend/descend 4 stairs, rise from/sit down from a chair (5 times). Hip/knee flexion and isometric quadriceps strength were also measured. Categories of performance were formed by dividing data into quartiles for each test (1=highest, 4=lowest score, 5=unable to complete) and, by summing the category scores, a total summary score (TSS) was obtained. The battery of physical function tests showed an acceptable test-retest reliability (ICC of all tasks > or =0.80) and internal consistency (Cronbach's alpha > or =0.80). Performance scores on walking, stair climb, chair-rise and ROM of affected OA joints were significantly correlated with each other, and with the WOMAC Index (P<0.05, Spearman's correlation). Lower scores on the TSS were associated with lower scores on all the WOMAC Index items (P<0.001). This study shows that a simple battery of physical function tests in combination with the WOMAC Index are reliable and may be useful outcome measures in the evaluation of therapeutic interventions and geriatric rehabilitation.

Aged↗

PubMed2001

A descriptive epidemiological study of shoulder injury in top level English male volleyball players.

The aims of this study were to estimate the prevalence and incidence of shoulder sports injuries, to discover the main shoulder injury, and to survey outcome of treatment or injuries in top level male volleyball athletes. Furthermore, the actions which most commonly cause injuries and the differences of physical characteristics between injured and healthy players were also investigated. Fifty-nine English Volleyball Federation division one athletes were recruited in the 1997/98 and 1998/99 seasons. All subjects completed two different questionnaires; a First recruitment and monthly Follow-up questionnaire throughout the period in question. Twenty-seven of the fifty-nine athletes had a history of shoulder sports injury, with a total of 29 injuries reported. The results of the First recruitment showed that overuse type injuries (19/29) were the main shoulder injuries. Cuff muscle tendinitis was predominant in these injuries (14/29). Furthermore, spiking was the major action during which a shoulder injury (23/29) first occurred. In the follow-up phase the incidences of shoulder chronic injury (or pain), re-injury, and new injury in these twenty-seven players were 3.0, 9.3 and 1.0 injuries/1,000 hours of exposure respectively. The mean duration of chronic injury or pain was 2.3 +/- 1.3 (+/- SD) months. The distribution of history of regular training, between injured and healthy subject groups, was significantly different (p = 0.008). This study has identified rotator cuff muscle/tendon injuries or involved lesions as the main shoulder injuries in top level English male volleyball athletes. These injuries result in prolonged shoulder pain symptoms.

Adult↗

PubMed2001

Knee flexor strength following anterior cruciate ligament reconstruction with the semitendinosus and gracilis tendons.

Knee flexor strength recovery following anterior cruciate ligament reconstruction with the doubled semitendinosus and gracilis tendons was assessed for up to 12 months post-surgery. Twelve patients were followed up, four at 3 months, five at 6 months and three at 12 months post-surgery. Knee flexor moment was recorded using the Biodex System-3 isokinetic dynamometer. Three sets of five repetitions of reciprocal eccentric/ concentric knee flexion contractions were carried out with each set at 1.05, 2.09 or 3.14 rad x s(-1). T-tests were used to test for significant differences between and within groups. The uninjured leg produced greater average peak moments than the injured leg; significant differences (p < 0.05) were seen between the legs at 1.05 rad x s(-1) for the 3-month group concentrically, and all three groups eccentrically. There was no significant difference (p > 0.05) between groups for the percentage deficit between legs. On average, a 23% deficit in average peak moment was still evident at 12 months both eccentrically and concentrically at 1.05 rad x s(-1). Taken as a whole this evidence suggests that there is a deficit in knee flexor strength up to at least 12 months post-surgery following doubled semitendinosus and gracilis tendon graft reconstruction even after a full rehabilitation protocol.

Adult↗

PubMed2001

Mobility impairment, muscle imbalance, muscle weakness, scapular asymmetry and shoulder injury in elite volleyball athletes.

BACKGROUND: The aim of this study was to evaluate the relationship between shoulder mobility, rotator muscles' strength and scapular symmetry, and shoulder injuries and/or pain in elite volleyball athletes. METHODS: An isokinetic shoulder muscle strength test, which was performed at speeds of 60/sec and 180/sec, and shoulder mobility and scapula lateral slide tests were conducted bilaterally on 16 subjects, who represented the England elite volleyball players. The subjects also prospectively completed monthly questionnaires during the competition season to report on their shoulder condition. RESULTS: The results showed that the active range of shoulder internal rotation and concentric external rotators' strength in the dominant arm were significantly less, than in the non-dominant arms, but the internal rotators were significantly stronger in both concentric and eccentric tests at both testing speeds. Seven of 16 subjects indicated overt shoulder injury or pain during their training season, nine subjects had shoulder mobility impairment, seven had muscle imbalance, 13 had relative muscle weakness and five had scapular asymmetry. The association between shoulder muscle strength imbalance (eccentric external < concentric internal) of rotators in the dominant arm and shoulder injuries was statistically significant (Fisher's exact test, p<0.05). CONCLUSIONS: We conclude that rotator muscle strength imbalance may play an important role in shoulder injuries in high-level volleyball players.

Adult↗

PubMed2000

Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency.

The hamstrings:quadriceps muscle strength ratio has been used as an indicator of normal balance between the knee flexors and extensors. A more functional approach to this strength ratio would be to compare opposite muscle actions of antagonistic muscle groups. The dynamic strength control ratio (DSCR) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. Effects of ACL deficiency on isokinetic peak torque for eccentric and concentric muscle actions of the quadriceps and hamstrings, in conjunction with isometric peak torque, were examined in 10 patients awaiting reconstructive surgery (male = 8, female = 2 ; age = 32.8 +/- 8.3 years; height = 1.77 +/- 0.08 m; mass = 72.1 +/- 12.5 kg). These variables were assessed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured using a knee ligament arthrometer to confirm clinical diagnosis of ACL rupture. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s(-1) (60 degrees s(-1)). Significant strength deficits were apparent between normal and injured sides for: concentric isokinetic quadriceps action (p < 0.05); isometric quadriceps action at 70 degrees of knee flexion (p < 0.05); isometric quadriceps action at 40 degrees of knee flexion (p<0.01); eccentric isokinetic hamstrings action (p < 0.05). With bilateral comparison, the conventional strength ratios showed no significant difference, as did the DSCR. The bilateral comparison of isometric strength ratios revealed significant losses in quadriceps strength for the injured side (p < 0.05) but no significant losses in hamstring strength (p > 0.05). Thus, differences can be seen in conventional ratios and DSCR for ACL-deficient subjects. This is an area of clinical interest with the increasing frequency of ACL reconstruction using hamstrings tendons.

Adult↗

PubMed2000

Isokinetic performance and shoulder mobility in elite volleyball athletes from the United Kingdom.

OBJECTIVES: To evaluate the differences in strength and mobility of shoulder rotator muscles in the dominant and non-dominant shoulders of elite volleyball players. METHODS: Isokinetic muscle strength tests were performed at speeds of 60 and 120 degrees/s, and shoulder mobility was examined in ten players from the England national men's volleyball squad. The subjects also completed a questionnaire that included a visual prompt and analogue pain scale. RESULTS: The range of motion of internal rotation on the dominant side was less than that on the non-dominant side (p < 0.01). The average peak strength at 60 degrees/s external eccentric contraction was lower than that of internal concentric contraction in the dominant arm, but was higher in the non-dominant arm. Six of the ten subjects reported a shoulder problem, described as a diffuse pain located laterally on the dominant shoulder. CONCLUSIONS: These elite volleyball players had a lower range of motion (internal rotation) and relative muscle imbalance in the dominant compared with the non-dominant shoulder.

Adult↗

PubMed1997

Altered ventricular repolarization during hypoglycaemia in patients with diabetes.

There is circumstantial evidence implicating hypoglycaemia in the sudden overnight death of young patients with insulin-dependent (Type 1) diabetes mellitus (IDDM), the mechanism of which is unknown. We have investigated the effects of hypoglycaemia on the electrocardiogram in 15 patients with diabetes (8 with IDDM and 7 with NIDDM) using a high resolution computer-based system. Patients were randomized to either 2 h of euglycaemia or hypoglycaemia (at around 3 mmol l(-1)) during the afternoon, using hyperinsulinaemic glucose clamps, the two visits separated by a period of at least 4 weeks. Corrected QT interval (QTc), plasma potassium, and adrenaline were measured at baseline and at 0, 60, and 120 min. The degree of QTc lengthening (from baseline) during clamped hypoglycaemia was greater compared to the euglycaemic control period in patients with IDDM (median[range] at 60 min, 156[8 to 258] vs 6[-3 to 28] ms, p <0.02) and NIDDM (120 min, 128[16 to 166] vs 4[-3 to 169] ms, p <0.05). The fall in plasma potassium was greater during clamped hypoglycaemia compared to euglycaemia in those with NIDDM (p <0.03) but not in those with IDDM (p> 0.06). The rise in plasma adrenaline was greater during clamped hypoglycaemia in both groups (IDDM p <0.02, NIDDM p <0.02) and there was a strong relationship between the rise in adrenaline and increase in QTc (r = 0.73, p <0.0001). These data demonstrate alteration of ventricular repolarization with lengthening of the QT interval during hypoglycaemia and suggest a possible mechanism by which hypoglycaemia could cause ventricular arrhythmias.

Adult↗

PubMed1996

Low calcium dialysate and hyperparathyroidism.

A low calcium dialysate reduces hypercalcemia from calcium-containing phosphate binders and makes phosphate control possible without the use of aluminum salts. We asked whether this might, however, lead to hyperparathyroidism. We prospectively studied serum concentrations of parathyroid hormone levels (by an immunoreactive intact molecule assay) in 173 patients on continuous ambulatory peritoneal dialysis (CAPD) who were started on a low calcium dialysate (Ca2+ 1.25 or 1.00 mmol/L) because of hypercalcemia. Median follow-up was 13.2 months (range 1-28). Initial serum parathyroid hormone was [median(range)]: 70(5-1043) ng/L pre low calcium dialysate, and this rose to 130(5-914) ng/L at 0-6 months; 130(5-1030) ng/L at 6-12 months; 170(170-1400) ng/L at 12-18 months; and 130(5-1200) ng/L at 18-24 months (p = 0.0006). Twenty-two patients required a parathyroidectomy because of a sustained rise in parathyroid hormone that was not responsive to alfacalcidol and hypercalcemia. Initial serum parathyroid hormone was significantly higher in these patients at 359 (5-1073) ng/L as compared to a level of 69.5 (6-1147) ng/L in patients who did not have a parathyroidectomy (p = 0.0009). There was a significant sustained fall in mean serum corrected calcium from 2.77 (2.37-3.51) mmol/L to 2.53 (1.39-3.20) mmol/L at three months (p = 0.0006), a nonsignificant rise in mean serum alkaline phosphate from 179 (47-1858) mmol/L to 191 (55-1821) mmol/L (p = 0.15), and a fall in mean serum phosphate levels from 1.87 (0.59-3.18) mmol/L to 1.68 (0.45-3.6) mmol/L (p = 0.76). Our data suggest that the benefits of a low calcium dialysate in CAPD patients are balanced by an increased risk of hyperparathyroidism, and that this risk is higher in patients with an initially high serum parathyroid hormone level.

Adult↗

PubMed1993

Blocks in choice responding as a function of age and physical fitness.

Although both physical fitness and aspects of cognitive functioning are known to be poorer among older people, there is conflicting evidence about the interaction between age and fitness. Is greater age more strongly associated with impaired cognition among less fit people than it is among more fit people? In a sample of employed men aged 17-63 years, it is shown that this interaction is significant with respect to the occurrence of exceptionally slow responses but is not significant for mean reaction time. Multiple regression analyses suggest that the former measure may be interpreted as an inability to maintain concentration over time rather than as an index of response speed.

Adolescent↗

PubMed1992

Continuity equation and Gorlin formula compared with directly observed orifice area in native and prosthetic aortic valves.

Orifice areas calculated by the continuity and Gorlin equations have been shown to correlate well in vivo. The continuity equation, however, gives underestimates compared with the Gorlin formula and it is not clear which is the more accurate. Both equations have therefore been tested against maximal orifice area measured by planimetry in eight prepared native aortic valves and four bioprostheses. A computer controlled, ventricular flow simulator (cycled at 70 beats/min) was used at five different stroke volumes that gave cardiac outputs of 2.8 to 7.0 l/min. The mean difference between measured and estimated orifice area was zero for the continuity equation, but -0.14 cm2 for the conventional Gorlin formula. Thus the Gorlin formula tended to give overestimates compared with both measured area and area estimated by the continuity equation, probably because of the effect of pressure recovery. When predictive equations derived from these data were tested, residual standard deviations were around 0.3 cm2 at all stroke volumes for the continuity equation, around 0.2 cm2 for the invasive Gorlin formula, and between 0.2 and 0.4 cm2 for the modified Gorlin formula. These results suggest that estimates of orifice area in an individual valve as judged by any of the equations tested should be seen as a guide to rather than as a precise measure of actual orific area.

Anthropometry↗

PubMed1991

Simple model of circulatory system dynamics including heart valve mechanics.

This paper describes an extension of the Windkessel model of circulatory system dynamics, which takes into account the opening action of the mitral and aortic valves, including stenotic and regurgitant orifices. The starting point for the model is the ventricular emptying/filling curve which is taken from a quasi-physiological ventricular flow relationship which incorporates variation of systolic and diastolic intervals with cycle rate. The valves are assumed to open with a linear rise in area up to maximum orifice, followed by a period at maximum orifice and then a linear fall-off in area to the closed position (which may allow regurgitation). Flow through the valves is assumed to be governed by the Gorlin equation. Peripheral resistance and compliance are considered as fixed parameters of the arterial system. The model is useful in helping to understand the complex interaction between valvular mechanics and the rest of the cardiovascular system. Applications of the model are illustrated by considering isolated aortic stenosis, isolated aortic regurgitation, cardiac adaptation in the presence of these two abnormalities and the effects of variation of peripheral resistance on pressures within the cardiovascular system.

Adaptation, Physiological↗

PubMed1991

Validation of the orifice formula for estimating effective heart valve opening area.

Interest in the Gorlin formula for estimating heart valve effective orifice area (EOA) has recently been rekindled and the formula itself has been challenged. In this validation study, explanted native heart valves, unimplanted mechanical prostheses, unimplanted bioprostheses and explanted bioprostheses have been tested in vitro in a pulsatile flow simulator. Pressures have been measured 30 mm upstream and 100 mm downstream from the plane of the valve sewing ring (to give pressure drop, pd in kPa). Flow (Q in 1 min-1) has been measured directly by electromagnetic flowmeter and orifice areas have either been taken from manufacturer supplied data (mechanical valves) or have been digitised from video images at maximum orifice (biological valves). The formula EOA = Q/(6.96 x pd 1/2) - 0.7 fitted the data with good correlation, r = 0.96 (n = 179). The orifice assumption on which this formula is based (cf. Gorlin formula) is confirmed though it is recommended that the formula should be modified to account for (i) the pressure recovery phenomenon and (ii) the fact that forward flow through a valve only occurs over a portion of the cycle in pulsatile flow. Heart rates used in the study ranged from 40 to 140 min-1, stroke volumes ranged from 20 to 114.3 ml, cardiac outputs from 2.0 to 8.0 1 min-1 and peripheral resistance from 0.1 to 1.6 kPa 1-1 min (1 - 12 mmHg l-1 min). Application of the formula was independent of the flow conditions.

Adult↗

PubMed1990

Ventricular stroke work loss: validation of a method of quantifying the severity of aortic stenosis and derivation of an orifice formula.

Because aortic stenosis results in the loss of left ventricular stroke work (due to resistance to flow through the valve and turbulence in the aorta), the percentage of stroke work that is lost may reflect the severity of stenosis. This index can be calculated from pressure data alone. The relation between percent stroke work loss and anatomic aortic valve orifice area (measured by planimetry from videotape) was investigated in a pulsatile flow model. Thirteen valves were studied (nine human aortic valves obtained at necropsy and four bioprosthetic valves) at stroke volumes of 40 to 100 ml, giving 57 data points. Valve area ranged from 0.3 to 2.8 cm2 and mean systolic pressure gradient from 3 to 84 mm Hg. Percent stroke work loss, calculated as mean systolic pressure gradient divided by mean ventricular systolic pressure x 100%, ranged from 7 to 68%. It was closely related to anatomic orifice area with an inverse exponential relation and was not significantly related to flow (r = -0.15). An orifice formula was derived that predicted anatomic orifice area with a 95% confidence interval of +/- 0.5 cm2 (orifice area [cm2] = 4.82 [2.39 x log percent stroke work loss], r = -0.94, SEE = 0.029). These results support the clinical use of percent stroke work loss as an easily obtained index of the severity of aortic stenosis.

Aortic Valve↗

PubMed1989

Efficacy of aortic balloon valvoplasty: direct measurement of orificial area in a model with pulsatile flow.

The efficacy of balloon valvoplasty of calcific aortic stenosis remains controversial. We studied, therefore, 5 human aortic valves obtained at necropsy in a positive-displacement pulse duplicator which delivered stroke volumes of 40-100 ml with a quasiphysiological waveform of flow. All valves had three leaflets without commissural fusion and were preserved in antibiotic solution before study. Orificial area was planimetered from videotape of opening of the valve and varied with flow in all cases. Valvoplasty with a 20 mm diameter balloon had no effect on the orifice of the normal valve but increased the orifice of 2 mildly calcified valves from 0.70-1.77 cm2 (range) at baseline to 1.06-1.95 cm2. In 2 valves with severe calcification of the leaflets, the orifice was increased from 0.31-0.82 cm2 to 0.73-1.07 cm2. Dual balloon valvoplasty achieved a variable but small further increase in orificial area. No valve showed tears of the leaflets or fracture of calcific deposits after valvoplasty. We conclude that balloon valvoplasty can acutely increase orificial area, independently of any change in stroke volume. In valves without commissural fusion, its mechanism appears to be an increase in the pliability of the leaflets which does not require macroscopic fracture of calcific deposits.

Adult↗

PubMed1989

Doppler spectral waveform generation in vitro: an aid to diagnosis of vascular disease.

This paper describes a microcomputer controlled pump which generates pulsatile flows similar to those found in the human peripheral circulation. Continuous wave Doppler ultrasound was used to investigate the flows generated by the pump and the behaviour of diagnostic indices derived from the spectra was examined. Sonograms were recorded from elastic and rigid tubes with various degrees of axisymmetric constriction. Heart rate, stroke volume, severity of vessel constriction, vessel wall elasticity, distal resistance, and systemic peripheral impedance were varied in turn and the resulting Doppler spectra compared. Indices considered were the pulsatility index, spectral broadening index and peck Doppler frequency. In general, the indices lacked the sensitivity to detect low to moderate levels of disease.

Humans↗

PubMed1989

The Gorlin formula validated against directly observed orifice area in porcine mitral bioprostheses.

To assess the effect of fluid flow on orifice area and to test the Gorlin formula, six Carpentier-Edwards mitral valve prostheses were studied in a positive displacement pulse duplicator at 20 different rate-stroke volume combinations. Peak transvalvular velocity (V max) was measured by continuous wave Doppler ultrasound, and orifice area was determined from hard copy of video images. Orifice area was directly related to mean flow (Q), although cusp opening behavior was asymmetric and complex and varied among the individual valves. There was a strong correlation between measured orifice area (OA) and the modified Gorlin relation, Q/V max (r = 0.88; p less than 0.00001) given by the regression formula OA = 0.18 x Q/V max - 0.15. There was also a good correlation between measured orifice area and the conventional Gorlin relation, Q/root mean pressure drop. The derived empiric Gorlin constant did not vary significantly with flow.

Bioprosthesis↗