Cardiorespiratory fitness fails to predict short-term postoperative mortality in patients undergoing elective open surgery for abdominal aortic aneurysm

INTRODUCTION

Preoperative cardiopulmonary exercise testing aids surgical risk stratification and is an established predictor of mid- to long-term survival in patients undergoing elective open abdominal aortic aneurysm repair. Whether cardiopulmonary exercise testing also predicts 30-day mortality in this population remains to be established.

MATERIALS AND METHODS

Data for 109 patients (mean age 72 years) who underwent cardiopulmonary exercise testing to assess risk for surgical abdominal aortic aneurysm repair was analysed. Patients were classified according to cardiopulmonary fitness as fit (peak oxygen uptake ≥ 15ml O₂.kg^-1.min^-1) or unfit (peak oxygen uptake less than 15ml O₂.kg^-1.min^-1) and further stratified according to clamp position (infrarenal or suprarenal). Between-group postoperative outcomes were compared for in-hospital 30-day mortality, postoperative morbidity scale scores (day 5) and hospital length of stay.

RESULTS

Seventy-nine patients underwent open surgery and 30 patients were treated conservatively. No deaths were recorded at 30 days post-surgery. Unfit patients with infrarenal clamping exhibited higher postoperative morbidity scale scores (64% vs 26%) and longer length of stay (four days) than fit patients (p < 0.05). Conversely, with suprarenal clamping, postoperative morbidity scale scores were similar and length of stay longer (three days) in fit compared with unfit patients (p < 0.05).

DISCUSSION AND CONCLUSION

Preoperative fitness level defined by peak oxygen uptake failed to identify patients at risk of 30-day mortality when undergoing elective abdominal aortic aneurysm repair. Postoperative morbidity and length of stay in patients with suprarenal clamping was high independent of cardiopulmonary fitness. These findings suggest that cardiopulmonary exercise testing may be a useful predictor of complications following infrarenal rather than suprarenal clamping but may not be a good predictor of 30-day mortality.

Cardiorespiratory fitness is impaired and predicts mid-term postoperative survival in patients with abdominal aortic aneurysm disease

NEW FINDINGS

What is the central question of this study? To what extent cardiorespiratory fitness is impaired in patients with abdominal aortic aneurysmal (AAA) disease and corresponding implications for postoperative survival requires further investigation. What is the main finding and its importance? Cardiorespiratory fitness is impaired in patients with AAA disease. Patients with peak oxygen uptake of <13.1 ml O₂  kg^-1  min^-1 and ventilatory equivalent for carbon dioxide at anaerobic threshold ≥34 are associated with increased risk of postoperative mortality at 2 years. These findings demonstrate that cardiorespiratory fitness can predict mid-term postoperative survival in AAA patients, which may help to direct care provision.

ABSTRACT

Preoperative cardiopulmonary exercise testing is a standard assessment of cardiorespiratory fitness (CRF) and risk stratification. However, to what extent CRF is impaired in patients undergoing surgical repair of abdominal aortic aneurysm (AAA) disease and the corresponding implications for postoperative outcome requires further investigation. We measured CRF during an incremental exercise test to exhaustion using online respiratory gas analysis in patients with AAA disease (n = 124, aged 72 ± 7 years) and healthy sedentary control subjects (n = 104, aged 70 ± 7 years). Postoperative survival was examined for association with CRF, and threshold values were calculated for independent predictors of mortality. Patients who underwent preoperative cardiopulmonary exercise testing before surgical repair had lower CRF [age-adjusted mean difference of 12.5 ml O₂  kg^-1  min^-1 for peak oxygen uptake ( V ̇ O 2 peak ), P < 0.001 versus control subjects]. After multivariable analysis, both V ̇ O 2 peak and the ventilatory equivalent for carbon dioxide at anaerobic threshold ( V ̇ E / V ̇ C O 2 - AT ) were independent predictors of mid-term postoperative survival (2 years). Hazard ratios of 5.27 (95% confidence interval 1.62-17.14, P = 0.006) and 3.26 (95% confidence interval 1.00-10.59, P = 0.049) were observed for V ̇ O 2 peak  < 13.1 ml O₂  kg^-1  min^-1 and V ̇ E / V ̇ C O 2 - AT ≥ 34, respectively. Thus, CRF is lower in patients with AAA, and those with a V ̇ O 2 peak  < 13.1 ml O₂  kg^-1  min^-1 and V ̇ E / V ̇ C O 2 - AT ≥ 34 are associated with a markedly increased risk of postoperative mortality. Collectively, our findings demonstrate that CRF can predict mid-term postoperative survival in AAA patients, which may help to direct care provision.

The cardiopulmonary exercise test grey zone; optimising fitness stratification by application of critical difference

BACKGROUND

Cardiorespiratory fitness can inform patient care, although to what extent natural variation in CRF influences clinical practice remains to be established. We calculated natural variation for cardiopulmonary exercise test (CPET) metrics, which may have implications for fitness stratification.

METHODS

In a two-armed experiment, critical difference comprising analytical imprecision and biological variation was calculated for cardiorespiratory fitness and thus defined the magnitude of change required to claim a clinically meaningful change. This metric was retrospectively applied to 213 patients scheduled for colorectal surgery. These patients underwent CPET and the potential for misclassification of fitness was calculated. We created a model with boundaries inclusive of natural variation [critical difference applied to oxygen uptake at anaerobic threshold (V˙O2-AT): 11 ml O2 kg-1 min-1, peak oxygen uptake (V˙O2 peak): 16 ml O2 kg-1 min-1, and ventilatory equivalent for carbon dioxide at AT (V̇E/V̇CO2-AT): 36].

RESULTS

The critical difference for V˙O2-AT, V˙O2 peak, and V˙E/V˙CO2-AT was 19%, 13%, and 10%, respectively, resulting in false negative and false positive rates of up to 28% and 32% for unfit patients. Our model identified boundaries for unfit and fit patients: AT <9.2 and ≥13.6 ml O2 kg-1 min-1, V˙O2 peak <14.2 and ≥18.3 ml kg-1 min-1, V˙E/V˙CO2-AT ≥40.1 and <32.7, between which an area of indeterminate-fitness was established. With natural variation considered, up to 60% of patients presented with indeterminate-fitness.

CONCLUSIONS

These findings support a reappraisal of current clinical interpretation of cardiorespiratory fitness highlighting the potential for incorrect fitness stratification when natural variation is not accounted for.

Examination of fine-scale spatial-temporal overlap and segregation between two closely related congeners Gadus morhua and Gadus ogac in coastal Newfoundland

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high-resolution radio-acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (LT ) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 LT s(-1) , respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species.

Strategy for exploiting exotic germplasm using genetic, morphological, and environmental diversity: the Aegilops tauschii Coss. example

Hexaploid bread wheat evolved from a rare hybridisation, which resulted in a loss of genetic diversity in the wheat D-genome with respect to the ancestral donor, Aegilops tauschii. Novel genetic variation can be introduced into modern wheat by recreating the above hybridisation; however, the information associated with the Ae. tauschii accessions in germplasm collections is limited, making rational selection of accessions into a re-synthesis programme difficult. We describe methodologies to identify novel diversity from Ae. tauschii accessions that combines Bayesian analysis of genotypic data, sub-species diversity and geographic information that summarises variation in climate and habitat at the collection point for each accession. Comparisons were made between diversity discovered amongst a panel of Ae. tauschii accessions, bread wheat varieties and lines from the CIMMYT synthetic hexaploid wheat programme. The selection of Ae. tauschii accessions based on differing approaches had significant effect on diversity within each set. Our results suggest that a strategy that combines several criteria will be most effective in maximising the sampled variation across multiple parameters. The analysis of multiple layers of variation in ex situ Ae. tauschii collections allows for an informed and rational approach to the inclusion of wild relatives into crop breeding programmes.

Short, natural, and extended photoperiod response in BC2F4 lines of bread wheat with different photoperiod-1 (Ppd-1) alleles

Flowering is a critical period in the life cycle of flowering plant species, resulting in an irreversible commitment of significant resources. Wheat is photoperiod sensitive, flowering only when daylength surpasses a critical length; however, photoperiod insensitivity (PI) has been selected by plant breeders for >40 years to enhance yield in certain environments. Control of flowering time has been greatly facilitated by the development of molecular markers for the Photoperiod-1 (Ppd-1) homeoloci, on the group 2 chromosomes. In the current study, an allelic series of BC2F4 lines in the winter wheat cultivars 'Robigus' and 'Alchemy' was developed to elucidate the influence on flowering of eight gene variants from the B- and D-genomes of bread wheat and the A-genome of durum wheat. Allele effects were tested in short, natural, and extended photoperiods in the field and controlled environments. Across genetic background and treatment, the D-genome PI allele, Ppd-D1a, had a more potent effect on reducing flowering time than Ppd-B1a. However, there was significant donor allele effect for both Ppd-D1a and Ppd-B1a, suggesting the presence of linked modifier genes and/or additional sources of latent sensitivity. Development of Ppd-A1a BC2F4 lines derived from synthetic hexaploid wheat provided an opportunity to compare directly the flowering time effect of the A-genome allele from durum with the B- and D-genome variants from bread wheat for the first time. Analyses indicated that the reducing effect of Ppd-A1a is comparable with that of Ppd-D1a, confirming it as a useful alternative source of PI.

Morphometric analysis of miniature swine hearts as potential human xenografts

Miniature swine are considered to be potential donors for clinical cardiac transplantation. However, it is unclear how an appropriately sized porcine donor will be selected for a particular human recipient. To address this issue, we performed a morphometric study of the swine heart using transthoracic echocardiography (n = 26) to determine the diameters of the aortic annulus and root, pulmonary artery annulus, and mitral valve annulus. We also obtained direct ex vivo measurements of swine heart weight and linear dimensions (n = 71). Relationships between a swine's height, weight, length, chest circumference and these internal and external cardiac dimensions are described. The strongest correlations were found between a pig's body length and its aortic annulus and root diameters (r-values = 0.97). These relationships are accurately described by univariate linear regression models. By cross-relating our morphometric measurements of aortic annulus diameter in the miniature swine with normative human data, we were able to develop a nomogram, relating swine length and human height, which predicts which miniature swine would donate the best size-matched heart for a particular human recipient.

Abnormal global left ventricular relaxation occurs early during the development of pharmacologically induced ischemia

In animal and human models, left ventricular (LV) diastolic function has been observed to be highly sensitive to myocardial ischemia. The response of LV diastolic parameters to pharmacologically induced ischemia, however, has not been characterized and might be important in the interpretation of dobutamine stress echocardiography. Eight mongrel dogs, in which were inserted a high-fidelity micromanometer LV catheter, coronary sinus sampling catheter, and ultrasonic coronary artery flow probe, underwent intravenous dobutamine infusion at escalating doses both before (control protocol) and after (ischemia protocol) creation of left anterior descending coronary artery stenosis with a hydraulic cuff occluder adjusted to maintain resting coronary artery flow but attenuate reactive hyperemia. At each dobutamine dose, epicardial short-axis 2-dimensional echocardiographic images and hemodynamic measurements were obtained. LV diastolic function was examined by calculation of peak (-)dP/dt and the time constant of isovolumic relaxation (tau). The dobutamine infusion protocol was terminated on the earliest recognition of an anterior wall motion abnormality. Peak (+)dP/dt normalized for developed isovolumetric pressure was calculated as a relatively load-independent index of global LV contractile function. Dobutamine infusion with and without ischemia resulted in comparable changes in heart rate and (+)dP/dt/IP, with no change in LV end-diastolic or -systolic pressure. The magnitude of peak (-)dP/dt increased less during the ischemia (1231 +/- 109 to 1791 +/- 200 mm Hg/sec) versus the control (1390 +/- 154 to 2432 +/- 320 mm Hg/sec) protocol (P <.05). Similarly, the observed decrease in tau was less during the ischemia (53 +/- 3 to 38 +/- 4 msec) than the control (51 +/- 5 to 23 +/- 3 msec) protocol, corresponding to a slower rate of relaxation (P <.05). In addition, the smaller decrease in tau was observed at the dobutamine dose before the dose at which an echocardiographic wall motion abnormality was first recognized. Dobutamine-induced ischemia is associated with abnormal LV diastolic function. In addition, these abnormalities seem to occur early in the development of ischemia. These observations extend to pharmacologically induced ischemia prior findings from other models of ischemia, suggesting the high sensitivity of LV diastolic function to the development of myocardial ischemia.

Coronary endothelial dysfunction in patients with acute-onset idiopathic dilated cardiomyopathy

OBJECTIVES

This study sought to determine whether coronary endothelial dysfunction exists in patients with acute-onset idiopathic dilated cardiomyopathy (DCM) and to explore its relation to recovery of left ventricular systolic function in this patient population.

BACKGROUND

Coronary endothelial dysfunction exists in chronic DCM, but its importance in the development and progression of ventricular dysfunction is not known. To address this issue we studied coronary endothelial function in patients with idiopathic DCM <6 months in duration and explored the relation between coronary endothelial function and subsequent changes in left ventricular ejection fraction (LVEF).

METHODS

Ten patients with acute-onset idiopathic DCM (duration of heart failure symptoms 2.0 +/- 0.4 months [mean +/- SEM]) and 11 control patients with normal left ventricular function underwent assessment of coronary endothelial function during intracoronary administration of the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator adenosine. Coronary cross-sectional area (CSA) was determined by quantitative coronary angiography and coronary blood flow (CBF) by the product of coronary CSA and CBF velocity measured by an intracoronary Doppler catheter. Patients with DCM underwent assessment of left ventricular function before and several months after the study.

RESULTS

Acetylcholine infusion produced no change in coronary CSA in control patients but significant epicardial constriction in patients with DCM (-36 +/- 11%, p < 0.01). These changes were associated with increases in CBF in control patients (+118 +/- 49%, p < 0.01) but no change in patients with DCM. Infusion of adenosine produced increases in coronary caliber and blood flow in both groups. Follow-up assessment of left ventricular function was obtained in nine patients with DCM 7.0 +/- 1.7 months after initial study, at which time LVEF had improved by > or =0.10 in four patients. Multiple linear regression revealed a positive correlation between both the coronary CSA (r2 = 0.57, p < 0.05) and CBF (r2 = 0.68, p < 0.01) response to acetylcholine and the subsequent improvement in LVEF.

CONCLUSIONS

Coronary endothelial dysfunction exists at both the microvascular and the epicardial level in patients with acute-onset idiopathic DCM. The preservation of coronary endothelial function in this population is associated with subsequent improvement in left ventricular function.

Accurate localization of mitral regurgitant defects using multiplane transesophageal echocardiography

BACKGROUND

Appropriate patient selection for surgical repair of the mitral valve depends on the specific location and mechanism of regurgitation, which, in turn, has necessitated a more detailed method to accurately describe mitral pathology. This study tests a strategy of using multiplane transesophageal echocardiography to systematically localize mitral regurgitant defects and compares these results with the surgical findings.

METHODS

Fifty patients with mitral regurgitation underwent intraoperative transesophageal echocardiography for the evaluation of mitral pathology and potential repair. Mitral regurgitant defects were localized using a systematic strategy and a simple nomenclature that divides each mitral valve into six sections (three sections per leaflet) and each prosthetic sewing ring into six sections (60 radial degrees = one section).

RESULTS

Thirty-nine patients with native mitral valves were studied, for a total of 234 sections evaluated. Eighty-seven of these sections contained regurgitant defects by transesophageal echocardiography (mean number of regurgitant defects per valve, 2.2; range, 1 through 6). There was agreement between the transesophageal echocardiographic and surgical localizations in 96% (224/234; p < 0.0001) of the sections. Eleven patients with prosthetic mitral valves were studied, for a total of 66 sections evaluated. Twenty-three of these sections contained paravalvular leaks by transesophageal echocardiography (mean number of leaks per prosthesis, 2.1; range, 1 through 6). There was agreement between the transesophageal echocardiographic and surgical localizations in 88% (58/66; p < 0.001) of the sections.

CONCLUSIONS

This transesophageal echocardiographic strategy provides a systematic method to accurately localize mitral regurgitant lesions and has the potential to improve the preoperative assessment of patients with significant mitral regurgitation.

Experiences in Hong Kong with the theory and practice of the albumin column method of sperm separation for sex selection

Controversy still surrounds the human serum albumin (HSA) method for separation of X- and Y-bearing human spermatozoa. There is doubt about whether the procedure does enrich sperm samples for the chosen sex chromosome. We have applied the HSA separation method in a clinic in Hong Kong, using the method as described by Ericsson et al. [Nature, 246, 421-424 (1973)] taking care to keep the sperm recovery to <5% of the initial number. Aliquots of separated spermatozoa were examined for X- and Y-bearing spermatozoa by fluorescent in-situ hybridization (FISH) using appropriate DNA probes. Of 18 couples wanting boys, 13 had single boys, one had twin boys, and one had twins comprising one boy and one girl. Only three single girls were born. This success rate of 83% is significantly different (P < 0.001) from the usual expected ratio. There were four miscarriages, one in the third and one in the fourth week of pregnancy. The times of the others are not definitely known, but are thought to have occurred early in pregnancy. We lack information on three couples. The FISH procedure showed no change in the normal and equal numbers of X- and Y-bearing spermatozoa after the HSA separation procedure. This study confirmed that the HSA sperm separation method can bias the number of babies in favour of males. However, the theory that it does so by enriching the sperm samples with Y-bearing spermatozoa appears to be incorrect and some other theory has to be postulated. It is tentatively proposed that passage through the HSA inactivates X-bearing spermatozoa more than Y-bearing spermatozoa, even though this is not apparent simply on inspection of sperm motility.

Effects of prolonging peak dobutamine dose during stress echocardiography

OBJECTIVES

This study sought to test whether the physiologic advantage of a prolonged dobutamine stage during stress echocardiography can be effectively combined with a clinically practical infusion protocol.

BACKGROUND

Dobutamine has a half-life of 2 min and requires up to 10 min to achieve steady state. Despite these known pharmacodynamics, dobutamine stress echocardiography is routinely performed by advancing doses at 3-min intervals. Canine studies have shown that dobutamine stress echocardiography end points will occur at a lower dose if each stage is prolonged, but these findings have yet to be used in the clinical setting.

METHODS

The standard 3-min dobutamine dose stage during stress echocardiography was modified by extending the peak dose (40 micrograms/kg body weight per min) for an additional 2 min. Consecutive patients underwent this modified protocol to test whether the requirement for atropine could be reduced. According to this modified protocol, if a dobutamine stress echocardiographic end point (85% of maximal predicted heart rate, new wall motion abnormalities, hypotension, arrhythmia or intolerable symptoms) was not reached at 3 min of the peak dose, this dose was prolonged for an additional 2 min. If a doubtamine stress echocardiographic end point was still not attained, atropine (up to 1.0 mg intravenously) was administered.

RESULTS

The study included 84 patients, 22 of whom (26.2%) achieved a dobutamine stress echocardiographic end point using the standard 3-min stage. Of the 62 patients who did not reach an end point in the initial 3 min of peak dobutamine dose, the additional 2 min of dobutamine increased heart rate (from 99.6 +/- 23.8 to 107.2 +/- 23.2 beats/min, p < 0.01) and allowed 20 patients (32.3%, p < 0.01) to attain an end point. Of the remaining 42 patients, 23 never achieved a stress echocardiographic end point, despite 1.0 mg of atropine. One patient developed supraventricular tachycardia during the additional 2 min of dobutamine, and one developed nonsustained ventricular tachycardia after receiving atropine.

CONCLUSIONS

These data demonstrate that a significant number of patients (32%) who do not reach a dobutamine stress echocardiographic end point with the standard protocol can safely attain an end point solely by extending the duration of the peak dose. Adoption of this strategy may reduce the need for supplemental atropine and its potential adverse effects.

The role of angioplasty in acute myocardial infarction

The role of percutaneous transluminal coronary angioplasty (PTCA) in the management of acute myocardial infarction (AMI) has not yet been precisely defined. The longest experience with PTCA in this setting has been in patients who are not candidates for thrombolytic therapy and in patients in whom thrombolysis has failed. Clinical interest has recently focused on direct use of PTCA (instead of thrombolysis) as the initial approach to reperfusion in AMI. We review the conceptual bases for both thrombolytic therapy and PTCA in AMI, and we then detail the clinical experience with PTCA in a variety of patient populations with AMI to guide use of both therapies in this setting.

Social aspects of > 800 couples coming forward for gender selection of their children

The social characteristics of 809 couples attending a sex preselection clinic have been studied. Their ethnic origins were: Indian 57.8%, European 32.0%, Chinese 3.6% and others 6.8%. The average number of boys and girls per family was 0.09 and 2.70 respectively for couples wanting a boy, and 2.46 and 0.14 for those wanting a girl. The average age of the wives was 34.0 years. These figures were not significantly different in any ethnic subgroup. Out of all the couples, 80.6% stated that they would have had another baby even had sex preselection not been on offer; 37.5% of the couples interviewed have been treated so far. The figures among those treated are substantially the same as those for the whole group. Asian and Middle Eastern couples overwhelmingly wanted boys, whereas European couples showed a slight preference for girls. These results suggest that, given certain guidelines, sex selection is unlikely to lead to a serious distortion of the sex ratio in Britain and other Western societies, but may need careful monitoring in other parts of the world.

A clinical rule to predict preserved left ventricular ejection fraction in patients after myocardial infarction

OBJECTIVE

To derive and validate a clinical prediction rule that identifies patients after myocardial infarction who have preserved left ventricular systolic function.

DESIGN

Retrospective analysis of a prospective cohort study, with a derivation set to generate a clinical prediction rule and a validation set to test the prediction rule.

SETTING

Urban tertiary care hospital.

PATIENTS

314 consecutive patients admitted with myocardial infarction who had one or more of the following tests to determine left ventricular ejection fraction: transthoracic echocardiography, contrast left ventriculography, or radionuclide ventriculography.

MEASUREMENTS

Left ventricular ejection fractions were determined by transthoracic echocardiography, contrast left ventriculography, and gated blood pool scan.

RESULTS

Multivariate analysis of patients in the derivation set yielded the following rule: The left ventricular ejection fraction is predicted to be 40% or more in patients who have 1) an interpretable electrocardiogram, 2) no previous Q-wave myocardial infarction, 3) no history of congestive heart failure, and 4) an index myocardial infarction that is not a Q-wave anterior infarction. In the derivation and the validation sets, the positive predictive value of the prediction rule was more than 0.98.

CONCLUSIONS

A simple clinical prediction rule using easily obtained historical and electrocardiographic data reliably identifies a substantial percentage of patients after myocardial infarction (40% in our hospital) who are likely to have preserved left ventricular systolic function. If validated in other patient populations, application of this prediction rule in clinical practice could result in a substantial decrease in the cost of treating uncomplicated myocardial infarction.

Recurrent infection stones with apparently negative cultures. The case for blind antibacterial treatment

Infection stones in the urinary tract are always associated with infection with a urease-producing, urea-splitting organism. The most common of these organisms are easy to culture and identify and can be treated early either with an appropriate antibiotic or with an anti-urease agent. Ureaplasma urealyticum and Corynebacterium urealyticum are urease-producing organisms which are difficult to grow; their presence and effects frequently go undetected and untreated. Other organisms, as yet unknown, may also be involved in the same process. We report the first series of 8 patients with recurrent infection-type stones likely to have been caused by a "hard to grow" organism. Five patients never had a positive culture; in 2 patients 1 of 10 urine cultures grew a coagulase-negative Staphylococcus and in 1 patient the same organism was grown from a stone but never in the urine. The clinical course of all of these patients was significantly improved after blind treatment with antibiotics and in one case with an anti-urease agent.

Metabolic balance studies of mineral supplementation in osteoporosis

1. We studied the effect of mineral supplementation and its duration in osteoporosis by analysing the calcium and phosphorus balances of 49 treated osteoporotic patients whose median length of calcium treatment was 19 weeks with a range of 8 days to over 4 years. Forty-four studies satisfied statistical criteria of reproducibility and included 35 women (10 also receiving oestrogen replacement therapy) and nine men. 2. Mean calcium balance was positive in women taking calcium supplements alone, +1.9 +/- 2.5 mmol daily (P less than 0.002), and was significantly more positive (P less than 0.05) in women also taking oestrogens, +4.2 +/- 2.1 mmol daily. Calcium balance was not significantly positive in men. 3. Calcium balance correlated negatively with duration of supplementation, but significantly, only when duration of supplementation was expressed logarithmically (r = -0.401, P less than 0.01) giving the regression equation y = 4.2-1.6 log x, where y = calcium balance in mol/day and x = duration of supplementation in weeks. Theoretical net calcium retention, without allowance for dermal loss, could be calculated by integration. 4. Mean phosphorus balance was significantly positive in both groups of women and in the whole population. Although its correlation with duration of supplementation did not reach statistical significance (P less than 0.1), the ratio of the regression slopes for calcium and phosphorus, 1.5:1, corresponded to their molar ratio in bone. 5. These statistics are, we believe, the first to describe an exponential decline in calcium balance during mineral treatment of osteoporosis, but they firmly suggest that such treatment, with or without oestrogen therapy, conveys temporary benefit.

Blood and urine analysis in patients with intestinal bladders

A group of 183 patients whose urine was stored in pouches formed either wholly or partly from bowel was reviewed to establish abnormal biochemical and haematological factors and to assess the risk of infection. Minimum follow-up was 1 year (range 1-28.5, mean 3 years 8 months) and the mean age of the patients at follow-up was 16.5 years (range 4-43). Pouches were augmentation and substitution cystoplasties and complete reconstructions with bowel. Bowel segments were ileum (55 patients), colon (100) and mixed (28). Anaemia was found in 15 patients, folate deficiency in 2 and folate excess in 2. Definite hyperchloraemic acidosis was found in 25 patients and borderline results in 40. Most of these patients had colon in the pouch but 5 definite and 13 borderline cases had ileum only. Troublesome urinary infections occurred in 27.9% of patients; 3 developed renal stones and 22 developed pouch/bladder stones. Stones were usually associated with infection and/or staples. Delayed linear growth occurred in 20% of children in spite of a normal increase in weight; there was no difference in any of the measurements between those who grew and those who did not.

Urinary oxalate and glycolate excretion and plasma oxalate concentration

The diagnosis of primary hyperoxaluria in young children is hampered by the lack of a reliable reference range for urinary oxalate excretion, especially in infants. We present data on urinary oxalate and glycolate excretion in 137 normal children, on the plasma oxalate concentration in 33 normal children and 53 with chronic renal failure, and on amniotic fluid oxalate concentration in 63 uncomplicated pregnancies. The urinary oxalate:creatinine molar ratios were log normally distributed: mean (range) values were less than 1 year 0.061 (0.015-0.26), 1-5 years 0.036 (0.011-0.12), 5-12 years 0.030 (0.0059-0.15), and greater than 12 years 0.013 (0.0021-0.083). Geometric mean (range) plasma oxalate concentration in the normal children was 1.53 (0.78-3.02) mumols/l and was independent of age. The mean (SD) plasma oxalate: creatinine molar ratio in these normal children and 50 with chronic renal failure was 0.033 (0.013), and was independent of age and renal function. Mean (SD) amniotic fluid oxalate concentration was 19.0 (4.3) mumols/l.

Metabolism of pyridoxine in mild metabolic hyperoxaluria and primary hyperoxaluria (type 1)

Plasma pyridoxine metabolites in plasma and 4-pyridoxic acid excretions in urine were measured in normal subjects, in 7 patients with type-1 hyperoxaluria and in 8 patients with mild metabolic hyperoxaluria, while receiving various doses of pyridoxine. Compliance with ingestion of pyridoxine was verified by measuring urinary 4-pyridoxic acid. In the normal subjects the maximum level of pyridoxal phosphate was obtained after only 10 mg/day of pyridoxine. The patients were divided into nonresponders, good responders and poor responders to pyridoxine according to the fall in urinary oxalate and glycollate excretions. In patients taking pyridoxine, the plasma pyridoxal phosphate levels were as for normal subjects in primary hyperoxaluria, lower than for normal subjects in mild metabolic hyperoxaluria (p less than 0.01), and in the latter group lower in partial responders than in good responders (p = 0.04). Hence in mild metabolic hyperoxaluria there may be difficulty in converting pyridoxine to pyridoxal phosphate.

Effects of oral pyridoxine upon plasma and 24-hour urinary oxalate levels in normal subjects and stone formers with idiopathic hypercalciuria

The effect of pyridoxine hydrochloride, 200 mg/day (0.97 mmol/day) for 3 weeks, upon plasma and urinary oxalate has been determined in ten normal subjects and seven patients with idiopathic hypercalciuria while both groups were on low-oxalate diets. Patients had higher basal urinary oxalate levels than normal subjects. In normal subjects pyridoxine administration decreased plasma oxalate levels and raised urinary oxalate. The patients showed no change in either plasma or urinary oxalate.

Excessive urinary oxalate excretion after combined renal and hepatic transplantation for correction of hyperoxaluria type 1

A 4.5-year-old boy received a combined liver and kidney transplant for correction of hyperoxaluria type 1. Both organs were from the same donor and functioned primarily. Three months after transplantation, urine oxalate excretion reached a maximum of 10,500 mumol/24 h and remained above 2300 mumol/24 h for the next 2 months. Two months later, oxalate excretion decreased to about 565 mumol/24 h, indicating exhaustion of a large oxalate pool. Six months after transplantation plasma oxalate is near normal (4.9 mumol/l). With the exception of one episode of acute rejection of the renal transplant, both organs were tolerated well and continue to have a unimpaired function 9 months after transplantation. However, there is increased echogenity on renal ultrasound, indicating oxalate deposits in the grafted kidney. This case illustrates that successful combined transplantation of both liver and kidney can be performed in infants, resulting in cure of the metabolic defect. The prolonged or acute excretion of oxalate may lead to oxalate deposition in the grafted kidney without impaired graft function or early graft loss.

Plasma oxalate and creatinine and oxalate/creatinine clearance ratios in normal subjects and in primary hyperoxaluria. Evidence for renal hyperoxaluria

Plasma oxalate and creatinine were measured repeatedly in healthy individuals and in 12 patients with type 1 primary hyperoxaluria unresponsive to pyridoxine. The mean ratios were 0.025 (SD 0.006) and 0.120 (SD 0.048), respectively. One patient repeatedly had normal plasma oxalate despite markedly raised urinary oxalate and it seems unlikely that this excess oxalate could have come from the liver. Oxalate/creatinine clearance ratios in the normal group had an overall mean of 0.59 (SD 0.27) in 24 h urine collections and 0.741 (SD 0.297) in repeated short clearance periods. Both renal tubular absorption and secretion of oxalate apparently occurred on different days, but this did not depend upon urinary flow rate. Oxalate/creatinine clearance ratios in type 1 primary hyperoxaluria had a mean of 2.88 (SD 3.11). The raised oxalate/creatinine clearance ratios in the patients were not correlated with either plasma oxalate or creatinine. A few patients showed much higher clearance ratios and in some were sufficiently high to indicate that oxalate was generated and secreted in the kidneys.

Hyperoxaluria or hypercalciuria in nephrolithiasis: the importance of renal tubular functions

The role of the kidney in states of hyperoxaluria and hypercalciuria was investigated in seven patients with hyperoxaluria after jejunoileal bypass (JIB) and six patients with idiopathic hypercalciuria (IHC). Eight apparently healthy persons formed a control group. Besides hyperoxaluria, the patients with JIB displayed an elevated plasma concentration of oxalate and the oxalate clearance was increased and higher than creatinine clearance, indicating a net tubular secretion of oxalate. The JIB patients had lower 24-h urinary excretions of calcium, phosphate, magnesium and citrate and higher serum parathyroid hormone (PTH) than controls, indicating increased secretion of PTH to compensate for calcium malabsorption. IHC patients exhibited increased fasting urinary calcium even though their serum values were similar to those in the controls. These results indicate a reduced tubular calcium reabsorption, which was most pronounced in patients with highest PTH values. We conclude that hyperoxaluria in JIB patients is associated both with intestinal hyperabsorption and with enhanced tubular secretion of oxalate, and that in some patients with IHC hypercalciuria is due to reduced tubular reabsorption of calcium.

Chronic dehydration stone disease

A study was made of 819 patients attending a metabolic stone clinic. A firm diagnosis was made in 708 (86%) and in 132 of these (19%) the diagnosis was thought to be chronic dehydration. The records were available for study for 87 males and 11 females in the chronic dehydration group. The mean age at presentation was 43 years. The causes of chronic dehydration were hot climate (62%), with hot occupation and low water intake almost equal in second place. In patients with a single cause of chronic dehydration, 57% also had a dietary risk factor for urolithiasis and this was most commonly high oxalate intake. Following dietary advice, the mean urinary volume increased from 1720 to 2475 ml/24 h. This was accompanied by a rise in mean urinary calcium from 6.02 to 6.96 mmol/24 h, presumably due to the calcium in the additional water drunk. Urinary oxalate did not change significantly. The mean follow-up time was 4.85 years and the stone recurrence rate was low. It was concluded that chronic dehydration is a common cause of urolithiasis; this can be treated satisfactorily by increasing water intake plus dietary advice in certain cases.

Experience with a transfusion recipient education program about hepatitis C

Shortly after test kits for antibodies to the hepatitis C virus (HCV) were licensed in May of 1990, our medical community undertook a public education program encouraging previous transfusion recipients to see their physicians about the wisdom of being tested for anti-HCV. In response, 1034 samples were received for testing. All samples repeatably reactive (RR) with anti-HCV enzyme-linked immunoassay (EIA) were tested further with a research recombinant immunoblot assay (RIBA). Overall, 76 of the 1034 (7.4%) recipient samples were RR and 64 of these (84.2%) were reactive with RIBA. Recipients transfused prior to surrogate testing (alanine aminotransferase [ALT] and anti-hepatitis B core [anti-HBc]) in 1986 showed a 8.6 percent reactivity with RIBA and those transfused after surrogate testing showed a 4.8 percent reactivity, a 44 percent reduction. Of the 57 recipient samples reactive with RIBA and suitable for assay, 11 (19.3%) had an elevated ALT. Among 76 randomly selected blood donors with RR EIAs studied for comparison with recipients, 20 (26.3%) were reactive with RIBA, 9 of which had an abnormal surrogate test that would have disqualified them. ALT concentrations were abnormal in 6 (30%) of the donors who were reactive on RIBA. We conclude that an education program that encourages previous transfusion recipients to seek medical advice about anti-HCV testing is practical from the standpoint of the blood center. We believe more widespread implementation of similar programs should be considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Liquid chromatographic studies of vitamin B6 metabolism in man

The effects of increased intake of pyridoxine hydrochloride on plasma vitamin B6 metabolism within therapeutic limits (up to 800 mg/day) were investigated. Maximum plasma concentrations of pyridoxal phosphate were attained at relatively low intakes of pyridoxine hydrochloride. Two metabolism thought to be unidentified forms of vitamin B6 were present in subjects taking more than 200 mg of pyridoxine hydrochloride per day as have recently been described. We investigated the possibility that these were isomeric forms of vitamin B6. However, 'Peak 2' metabolite was shown to be probably 4-pyridoxolactone. The metabolism of isopyridoxal has not previously been investigated in man. We demonstrated that it is an active vitamer of the B6 complex in humans. The main fluorescent metabolite of isopyridoxal present in plasma and urine had a similar retention time to 'Peak 1' metabolite. Isopyridoxal was incapable of being directly phosphorylated in rat liver extract and it is therefore unlikely that peak 1 is isopyridoxal phosphate. Its nature remains unknown.

Fluoride therapy and parathyroid hormone activity in osteoporosis

1. To determine the relationships between parathyroid hormone activity and long-term sodium fluoride therapy in osteoporosis, cytochemical bioassays (for biologically active parathyroid hormone) were performed in 22 osteoporotic control patients and in 18 patients after 15 +/- 10 months of treatment (60 mg of sodium fluoride daily). Ten patients were studied longitudinally by repeated metabolic balances and were therefore common to both groups. All patients were receiving mineral supplements. 2. Cross-sectional data showed a fourfold mean increase in biologically active parathyroid hormone on fluoride treatment (P less than 0.005) together with a 51% increase in serum alkaline phosphatase (P less than 0.005). Longitudinal data showed, in addition, a significant increase in the calcium balance of 2.4 +/- 1.2 (SEM) mmol daily (P less than 0.05) and the development of a positive phosphorus balance (P less than 0.02). 3. Fluoride-treated patients were then analysed in two groups according to the level of biologically active parathyroid hormone. Thirty-two per cent of values were above the upper limit of normal (18 pg/ml). The mean serum alkaline phosphatase level in this group showed no elevation above that of the control patients, the overall rise being accounted for entirely by patients with normal levels of biologically active parathyroid hormone. High levels of biologically active parathyroid hormone were also associated with relative hypophosphataemia (P less than 0.01), relative hypercalciuria (P less than 0.05) and an increased urine/faecal calcium ratio (P less than 0.025). 4. Results show that long-term fluoride and calcium therapy increase biologically active parathyroid hormone in osteoporosis and that excessive parathyroid hormone activity may account for certain features of the refractory state.

Chemical measurement of calcium oxalate crystalluria: results in various causes of calcium urolithiasis

Calcium oxalate and calcium phosphate crystalluria have been measured chemically in 1,173 urine samples whose chemical compositions were also analysed. The importance of urinary oxalate as a determinant for calcium oxalate crystalluria was confirmed. Significant concentrations of calcium oxalate crystals may be present in urine even though the crystals are too small for detection by light microscopy or by many particle-counting methods. Calcium phosphate crystals in urine always contain a small proportion of calcium oxalate. Results in various clinical situations are reviewed.

Risk factors for urinary calcium oxalate crystals as revealed by their specific enzymatic assay

Calcium oxalate crystal concentrations were assayed by a new highly specific enzymatic method in 1200 urine samples from normal subjects and stone formers. Examination of the crystals was also carried out by light microscopy and urines were analysed for oxalate, calcium, magnesium, citrate, urate, pH and osmolality. A striking positive correlation was established between urinary oxalate concentration and calcium oxalate crystal concentration as well as incidence of calcium oxalate crystals and aggregates seen by microscopy. A less striking relationship, also supported by light microscopy, was found between calcium oxalate crystal concentration and urinary calcium concentration. A small rise in calcium oxalate crystalluria was seen with increasing osmolality, but no relationship found between concentration or urinary urate, citrate or magnesium and that of calcium oxalate crystals. Higher levels of calcium oxalate crystal concentration appeared in alkaline urines in association with calcium phosphates. The dominance of urinary oxalate as a risk factor for calcium oxalate crystalluria is confirmed.

Measurement of calcium phosphate crystalluria: influence of pH and osmolality and invariable presence of oxalate

Calcium phosphate and calcium oxalate urinary crystal concentrations in normal and stone-forming subjects were measured. The urinary crystals were examined by light microscopy and urine samples were analysed for oxalate, pH and osmolality. Calcium phosphate crystal concentrations were clearly related to urine pH but unrelated to urine osmolality. An unexpected finding was co-precipitation of oxalate with calcium phosphate. Consequently, precipitated invariable oxalate increased with rising urinary pH. Possible explanations and implications are discussed.

Failure of allopurinol to modify urinary composition in enteric hyperoxaluria

Conventional treatment of enteric hyperoxaluria (EHO) consists of dietary restriction of oxalate and fat and correction of its underlying cause whenever possible. Recent work suggests that allopurinol reduces the incidence of urolithiasis and the urinary excretion of both oxalate and uric acid in patients without intestinal disease. We have assessed the effect of allopurinol, 300 mg daily for 2 weeks, on urine biochemistry in patients with EHO due to small bowel Crohn's disease and/or resections. Compliance with treatment was confirmed by a fall in plasma uric acid in every patient. Allopurinol failed to alter 24 h urinary oxalate excretion or oxalate concentration. There were also no significant changes in the urinary excretion of glycollate (like oxalate, a breakdown product of glyoxylate), citrate, magnesium or calcium, each of which was at the lower end of the normal range before and during treatment with allopurinol. It appears unlikely that allopurinol will prove useful in the prevention of urolithiasis in patients with EHO.

Determination of plasma pyridoxal phosphate levels using a modified apotryptophanase assay

The development of a simple non-isotopic enzymatic assay for plasma pyridoxal phosphate (PLP) using a modified apotryptophanase procedure is reported. Recovery of added PLP from plasma was 86% and the within-run precision of the assay was 6.5%. Between-run precision was 7.5%. Concentrations of cupric ions as low as 20 mumol/L severely inhibited apotryptophanase activity and this effect of copper was almost completely prevented by the addition of EDTA. The reference plasma PLP range obtained by the apotryptophanase method was found to be between 5 and 50 micrograms/L plasma, with a mean of 17 +/- 10 micrograms/L plasma. The assay requires minimum technical skill and, with the aid of a multisample reaction rate analyser, more than 50 samples could easily be handled within a working day.

A simple liquid-chromatographic method for measuring vitamin B6 compounds in plasma

This relatively simple high-performance liquid chromatographic (HPLC) method for measuring all seven known forms of vitamin B6 in plasma from individuals supplemented with pyridoxine hydrochloride shows good analytical recovery (85-98%) and precision. Within-run and between-run CVs for plasmas supplemented with standards were 4% and 7%, respectively. The major forms of B6 found in unsupplemented plasma from normal subjects were pyridoxal phosphate and 4-pyridoxic acid, with pyridoxal just detectable. The HPLC procedure correlated well (r = 0.94) with a modification of an enzymatic method involving apotryptophanase (Anal Biochem 1972;45:567-76) for measuring plasma pyridoxal phosphate, and also (r = 0.94) with a routine method for determining 4-pyridoxic acid in urine (Clin Chem 1964;10:479-89). Elimination of pyridoxine from the plasma of both normal and hyperoxaluric individuals was shown to be very rapid, with half-lives (t1/2) of 45 and 40 min, respectively. Finally, we present evidence for the existence of two other forms of B6 and discuss the possibility of a new metabolic pathway in vitamin B6 metabolism.

A simple liquid-chromatographic method for measuring vitamin B6 compounds in plasma

This relatively simple high-performance liquid chromatographic (HPLC) method for measuring all seven known forms of vitamin B6 in plasma from individuals supplemented with pyridoxine hydrochloride shows good analytical recovery (85-98%) and precision. Within-run and between-run CVs for plasmas supplemented with standards were 4% and 7%, respectively. The major forms of B6 found in unsupplemented plasma from normal subjects were pyridoxal phosphate and 4-pyridoxic acid, with pyridoxal just detectable. The HPLC procedure correlated well (r = 0.94) with a modification of an enzymatic method involving apotryptophanase (Anal Biochem 1972;45:567-76) for measuring plasma pyridoxal phosphate, and also (r = 0.94) with a routine method for determining 4-pyridoxic acid in urine (Clin Chem 1964;10:479-89). Elimination of pyridoxine from the plasma of both normal and hyperoxaluric individuals was shown to be very rapid, with half-lives (t1/2) of 45 and 40 min, respectively. Finally, we present evidence for the existence of two other forms of B6 and discuss the possibility of a new metabolic pathway in vitamin B6 metabolism.