Risk stratification after acute myocardial infarction by Doppler stroke distance measurement.

OBJECTIVE: To establish the value of Doppler stroke distance measurement as a predictor of mortality risk following acute myocardial infarction. DESIGN: Follow up study. SETTING: Coronary care unit of a teaching and district general hospital. SUBJECTS: 378 patients (mean age 61 years) with acute myocardial infarction followed up for a mean of five years (range 2-7 years); 299 (79%) patients received thrombolysis. MAIN OUTCOME MEASURES: Stroke distance (the systolic velocity integral of blood flow in the aortic arch (percentage of age predicted normal value)); presence or absence of left ventricular failure on the admission chest radiograph; the codified admission ECG; death during follow up. RESULTS: Mean (SD) stroke distance was 81 (19)% and five year survival 76%. For patients with stroke distance > 100% (n = 60), 82-100% (n = 134), 63-81% (n = 122), and < 63% (n = 62), the one month mortality rates were 0%, 1.5%, 4%, and 18%, respectively; the corresponding estimates for mortality at five years were 17%, 19%, 24%, and 43%. Survival was independently related to age (p < 0.0001), stroke distance (p < 0.0001), and chest radiograph appearance (p = 0.002), but not to ECG codes (p = 0.31) or receipt of thrombolysis (p = 0.60). The areas under receiver operator characteristic plots for stroke distance measurements were 82%, 76%, 71%, and 65% for deaths within one month, six months, one year, and two years, respectively. CONCLUSIONS: The bedside measurement of stroke distance stratifies mortality risk after acute myocardial infarction. The predictive ability of this simple measure of left ventricular systolic function compares well with published accounts of the more complex measurement of ejection fraction.

Thrombolysis in peripheral general practices in Scotland: another rule of halves.

OBJECTIVE: To facilitate the adoption of thrombolysis by general practitioners in peripheral practices in Scotland. DESIGN: Survey of practice policies on the management of acute myocardial infarction before and after practice visits by a consultant physician acting as a facilitator; survey of hospital consultants' attitudes to thrombolysis by general practitioners. SETTING: One hundred and eighty-two practices, with an enlisted total of 550,000 patients, located at least 30 minutes from a district general hospital; 23 such hospitals serving these peripheral practices. MAIN OUTCOME MEASURES: Possession of electrocardiograph and defibrillator; adoption of a policy of giving thrombolytic therapy. RESULTS: The majority of practices possessed an electrocardiograph (87%) and a defibrillator (76%). At the time of the visits, 67 practices (37%) already had a policy of giving thrombolytic therapy. When contacted one year later 91 practices (50%) had such a policy. In the interval between visits and follow-up, few had received any encouragement from any source to use this treatment. Hospital consultants' attitudes to thrombolysis by general practitioners were generally negative, and support from local and national health authorities has been inadequate. CONCLUSIONS: Provision of timely thrombolytic therapy for the one tenth of the Scottish population living at least 30 minutes from a district general hospital is a major public health problem for which there is a ready solution: pre-hospital thrombolysis administered by general practitioners has been shown to be feasible, fast, safe, efficacious and cost-effective. To translate this evidence into practice requires a concerted effort from all the professionals involved, and must be directed and supported by local and national management of the National Health Service in Scotland.

Secondary prevention in coronary heart disease: baseline survey of provision in general practice.

OBJECTIVE: To determine secondary preventive treatment and habits among patients with coronary heart disease in general practice. DESIGN: Process of care data on a random sample of patients were collected from medical records. Health and lifestyle data were collected by postal questionnaire (response rate 71%). SETTING: Stratified, random sample of general practices in Grampian. SUBJECTS: 1921 patients aged under 80 years with coronary heart disease identified from pre-existing registers of coronary heart disease and nitrate prescriptions. MAIN OUTCOME MEASURES: Treatment with aspirin, beta blockers, and angiotensin converting enzyme inhibitors. Management of lipid concentrations and hypertension according to local guidelines. Dietary habits (dietary instrument for nutritional evaluation score), physical activity (health practice indices), smoking, and body mass index. RESULTS: 825/1319 (63%) patients took aspirin. Of 414 patients with recent myocardial infarction, 131 (32%) took beta blockers, and of 257 with heart failure, 102 (40%) took angiotensin converting enzyme inhibitors. Blood pressure was managed according to current guidelines for 1566 (82%) patients but lipid concentrations for only 133 (17%). 673 of 1327 patients (51%) took little or no exercise, 245 of 1333 (18%) were current smokers, 808 of 1264 (64%) were overweight, and 627 of 1213 (52%) ate more fat than recommended. CONCLUSION: In terms of secondary prevention, half of patients had at least two aspects of their medical management that were suboptimal and nearly two thirds had at least two aspects of their health behaviour that would benefit from change. There seems to be considerable potential to increase secondary prevention of coronary heart disease in general practice.

Secondary prevention clinics for coronary heart disease: randomised trial of effect on health.

OBJECTIVE: To evaluate the effects of secondary prevention clinics run by nurses in general practice on the health of patients with coronary heart disease. DESIGN: Randomised controlled trial of clinics over one year with assessment by self completed postal questionnaires and audit of medical records at the start and end of the trial. SETTING: Random sample of 19 general practices in northeast Scotland. SUBJECTS: 1173 patients (685 men and 488 women) under 80 years with working diagnoses of coronary heart disease who did not have terminal illness or dementia and were not housebound. INTERVENTION: Clinic staff promoted medical and lifestyle aspects of secondary prevention and offered regular follow up. MAIN OUTCOME MEASURES: Health status measured by the SF-36 questionnaire, chest pain by the angina type specification, and anxiety and depression by the hospital anxiety and depression scale. Use of health services before and during the study. RESULTS: There were significant improvements in six of eight health status domains (all functioning scales, pain, and general health) among patients attending the clinic. Role limitations attributed to physical problems improved most (adjusted difference 8.52, 95% confidence interval 4.16 to 12. 9). Fewer patients reported worsening chest pain (odds ratio 0.59, 95% confidence interval 0.37 to 0.94). There were no significant effects on anxiety or depression. Fewer intervention group patients required hospital admissions (0.64, 0.48 to 0.86), but general practitioner consultation rates did not alter. CONCLUSIONS: Within their first year secondary prevention clinics improved patients' health and reduced hospital admissions.

Secondary prevention in coronary heart disease: a randomised trial of nurse led clinics in primary care.

OBJECTIVE: To evaluate whether nurse run clinics in general practice improve secondary prevention in patients with coronary heart disease. DESIGN: Randomised controlled trial. SETTING: A random sample of 19 general practices in northeast Scotland. PATIENTS: 1173 patients (685 men and 488 women) under 80 years with working diagnoses of coronary heart disease, but without terminal illness or dementia and not housebound. INTERVENTION: Nurse run clinics promoted medical and lifestyle aspects of secondary prevention and offered regular follow up. MAIN OUTCOME MEASURES: Components of secondary prevention assessed at baseline and one year were: aspirin use; blood pressure management; lipid management; physical activity; dietary fat; and smoking status. A cumulative score was generated by counting the number of appropriate components of secondary prevention for each patient. RESULTS: There were significant improvements in aspirin management (odds ratio 3.22, 95% confidence interval 2.15 to 4.80), blood pressure management (5.32, 3.01 to 9.41), lipid management (3.19, 2.39 to 4.26), physical activity (1.67, 1.23 to 2.26) and diet (1.47, 1.10 to 1.96). There was no effect on smoking cessation (0.78, 0.47 to 1.28). Of six possible components of secondary prevention, the baseline mean was 3.27. The adjusted mean improvement attributable to intervention was 0.55 of a component (0.44 to 0.67). Improvement was found regardless of practice baseline performance. CONCLUSIONS: Nurse run clinics proved practical to implement in general practice and effectively increased secondary prevention in coronary heart disease. Most patients gained at least one effective component of secondary prevention and, for them, future cardiovascular events and mortality could be reduced by up to a third.

Quantification of the benefit of earlier thrombolytic therapy: five-year results of the Grampian Region Early Anistreplase Trial (GREAT).

OBJECTIVES: This report presents the 5-year results of the Grampian Region Early Anistreplase Trial (GREAT) and quantifies the benefit of earlier thrombolysis in terms that are generally applicable. BACKGROUND: Although it is accepted that the earlier thrombolytic therapy is given for acute myocardial infarction the greater the benefit, there are widely differing estimates of the magnitude of the time-related benefit of thrombolysis because of inappropriate trial design and analysis. METHODS: In a previously reported randomized trial, anistreplase (30 U) was given intravenously either before hospital admission or in the hospital, at a median time of 105 and 240 min, respectively, after onset of symptoms. Intention to treat and multivariate analyses of the 5-year results were performed. RESULTS: By 5 years, 41 (25%) of 163 patients had died in the prehospital treatment group compared with 53 (36%) of 148 in the hospital treatment group (log-rank test, p < 0.025). Delaying thrombolytic treatment by 1 h increases the hazard ratio of death by 20%, equivalent to the loss of 43/1,000 lives within the next 5 years (95% confidence interval 7 to 88, p = 0.012). Delaying thrombolytic treatment by 30 min reduces the average expectation of life by approximately 1 year. CONCLUSIONS: The magnitude of the benefit from earlier thrombolysis is such that giving thrombolytic therapy to patients with acute myocardial infarction should be accorded the same degree of urgency as treatment of cardiac arrest. Policies should be developed for giving thrombolytic therapy on-site if practicable and by the first qualified person to see the patient.

Myocardial salvage with early anistreplase treatment.

This randomized, double-blind trial in 311 patients with acute myocardial infarction has shown that very early therapy with anistreplase outside the hospital is not only feasible, but provides a major survival advantage. The difference in the median delay to treatment between the group treated in the hospital and those treated earlier was 2 1/4 h. After 30 months, mortality in the early group was less than half that in the later group, so that every hour of delay beyond 2 h resulted in almost 7 additional deaths per 100 patients treated. This is a greater percentage loss of life than would have resulted from a similar delay in the provision of resuscitation for the prehospital cardiac arrest. Multivariate analysis showed that age, treatment delay, and time of presentation were significant risk factors, with patients presenting at 1 h having more than twice the mortality of those presenting at 4 h; the sicker the patient, the earlier the presentation. By 5 years, prehospital administration of anistreplase, by saving 2 h, resulted in an additional 57% of a year's survival per patient. This compares favorably with the projected 14% of a year survival per patient reported with TPA versus streptokinase in GUSTO. Prehospital therapy with anistreplase was highly cost effective when compared with streptokinase given in hospital, and the marginal cost-effectiveness ratio was much lower than that for TPA versus streptokinase derived from GUSTO.

Cardiac rehabilitation in Scotland: is current provision satisfactory?

BACKGROUND: Cardiac rehabilitation is an effective intervention, lowering mortality following myocardial infarction and reducing morbidity in patients with coronary heart disease. However, its level of provision was unclear. This study aimed to provide a comprehensive description in Scotland. METHODS: A national survey of hospital, general practice and community sources was conducted in 1994 to identify cardiac rehabilitation programmes in Scotland. Detailed information about each programme was collected by computer-assisted telephone interviews. RESULTS: Sixty-nine programmes were identified, providing out-patient cardiac rehabilitation to 4980 patients and in-patient cardiac rehabilitation to 8920 patients. This represented 17 per cent and 30 per cent of patients admitted to hospital with coronary heart disease (excluding heart failure), respectively. There was considerable geographical variation in provision and dependence on sources outside the health service for much funding. CONCLUSIONS: Despite evidence of benefits from randomized trials, the overall provision of cardiac rehabilitation in Scotland was low. Considerable inequity was demonstrated between different health board areas. There is opportunity for better provision, which would improve care for many patients with coronary heart disease.

Outpatient cardiac rehabilitation: are the potential benefits being realised?

OBJECTIVE: to give a comprehensive description of the practice of outpatient cardiac rehabilitation in Scotland. DESIGN: an identifying survey of 1,270 individuals in hospital, general practice and community sources nationally, followed by computer-assisted telephone interviews about programme characteristics with key personnel from identified cardiac rehabilitation schemes. OUTCOME MEASURES: patient provision, referral criteria and programme features. RESULTS: 65 programmes provided outpatient cardiac rehabilitation for 4,980 patients in one year, representing 17% of the 29,180 patients who survived admission to hospital with coronary heart disease. Cardiac rehabilitation practice varied widely: 53 (82%) programmes included exercise, although only 19 (29%) at the most beneficial level; 40 (62%) included relaxation training, although only three (5%) at a level shown to give benefit; 47 (72%) included education, although only 16 (25%) in a manner with reported benefits in randomised trials. CONCLUSIONS: outpatient cardiac rehabilitation was provided to a minority of patients with coronary heart disease. Programmes varied widely, and were often more limited than those reporting mortality and morbidity benefits in randomised trials. There is a substantial gap between current provision and practice of cardiac rehabilitation and that advocated in published guidelines.

Seasonal variation in coronary heart disease in Scotland.

STUDY OBJECTIVE: Seasonality of coronary heart disease (CHD) was examined to determine whether fatal and non-fatal disease have the same annual rhythm. DESIGN: Time series analysis was carried out on retrospective data over a 10 year period and analysed by age groups ( < 45 to > 75 years) and gender. SETTING: Data by month were obtained for the years 1962-71. The Registrar General provided information on deaths and the Research and Intelligence Unit of the Scottish Home and Health Department on hospital admissions. SUBJECTS: In Scotland, between 1962 and 1971, 123 000 patients were admitted to hospital for CHD, of whom 29 000 died. There were a further 97 000 CHD deaths outside hospital. These two groups were also examined as one (coronary incidence) - that is, all coronary deaths and coronary admissions discharged alive. STATISTICAL ANALYSIS AND MAIN RESULTS: Where there was a single annual peak, the sine curve was analysed by cosinor analysis. When there were two peaks the analysis was by normal approximation to Poisson distribution. In younger men (under 45 years) admitted to hospital there was a dominant spring peak and an autumn trough. A bimodal pattern of spring and winter peaks was evident for hospital admissions in older male age groups: with increasing age the spring peak diminished and the winter peak increased. In contrast, female hospital admissions showed a dominant winter/summer pattern of seasonal variation. In male and female CHD deaths seasonal variation showed a dominant pattern of winter peaks and summer troughs, with the winter peak spreading into spring in the two youngest male age groups. CHD incidence in women showed a winter/summer rhythm, but in men the spring peak was dominant up to the age of 55. CONCLUSION: The male, age related spring peak in CHD hospital admissions suggests there is an androgenic risk factor for myocardial infarction operating through an unknown effector mechanism. As age advances and reproduction becomes less important, the well defined winter/summer pattern of seasonal variation of CHD is superimposed, and shows a close relationship with the environment, especially temperature, or the autumn and early winter fall in temperature.

Delay between the onset of symptoms of acute myocardial infarction and seeking medical assistance is influenced by left ventricular function at presentation.

OBJECTIVE: To determine whether the interval between the onset of symptoms of acute myocardial infarction and the patient's call for medical assistance (patient delay) is related to left ventricular function at the time of presentation. DESIGN: Prospective observational study. SETTING: Coronary care unit of Aberdeen Royal Infirmary. PATIENTS: 93 consecutive patients with acute myocardial infarction. MAIN OUTCOME MEASURES: Left ventricular stroke distance, expressed as a percentage of the age predicted normal value, measured first on admission, and then daily for 10 days or until discharge. Patients were questioned at admission to determine the time of onset of symptoms and the time of their call for medical assistance. RESULTS: Median (range) patient delay was 30 (1-360) min. Mean (SD) stroke distance on admission was 70(18)%, rising to 77(19)% on the second recording, and to 84(18)% on the day of discharge. Linear regression of log(e)(patient delay) against first, second, and last measurements of stroke distance gave correlation coefficients of 0.28 (P < 0.01), 0.18 (not significant), and 0.11 (not significant), respectively. CONCLUSIONS: Patient delay within the first 4 h after the onset of symptoms of acute myocardial infarction is positively related to left ventricular function on admission. A possible explanation is that deteriorating left ventricular function influences the patient's decision to call for help. This tendency for patients with more severe infarction to call for help sooner is an added reason for giving thrombolytic treatment at the first opportunity: those who call early have most to gain from prompt management.

Women and myocardial infarction: agism rather than sexism?

OBJECTIVE: To determine whether women with myocardial infarction are treated differently from men of the same age and to assess the effect of changes in the coronary care unit admission policy. DESIGN: Clinical audit. SETTING: The coronary care unit and general medical wards of a teaching hospital. In 1990 the age limit for admission to coronary care was 65 years. This age limit was removed in 1991. PATIENTS: 539 female and 977 male patients admitted with myocardial infarction between 1990 and 1992. MAIN OUTCOMES: Admission to the coronary care unit, administration of thrombolysis, and in-hospital mortality. RESULTS: 409 men and 254 women were admitted with myocardial infarction in 1990 and 568 men and 285 women in 1992. Removal of the age limit for admission to the coronary care unit resulted in an increase in the numbers of both sexes admitted with myocardial infarction. In both years, however, proportionately more men with infarction were admitted to coronary care: 226 men (55%) and 96 women (38%) (P < 0.01) (95% CI 7 to 28) in 1990 and 459 men (81%) and 200 women (70%) (P < 0.01) (%CI 2 to 19) in 1992. Some 246 men (60%) and 133 women (52%) with infarction (P < 0.01) received thrombolytic treatment in 1990 compared with 319 men (56%) and 130 women (46%) (P < 0.01) in 1992. The mean age of women sustaining a myocardial infarction was significantly greater in both years studied. In 1992 a total of 78 men (7%) and 34 women (4%) (P < 0.05) admitted with chest pain underwent cardiac catheterisation before discharge from hospital. CONCLUSIONS: Differences in admission rates to the coronary care unit and the rate of thrombolysis between the sexes can be explained by the older age of women sustaining infarction. The application of age limits for admission to coronary care or administration of thrombolysis places elderly patients at a disadvantage. As women sustain myocardial infarctions at an older age they are placed at a greater disadvantage.

A quantitative magnetic resonance imaging study of changes in brain morphology from infancy to late adulthood.

OBJECTIVE: To model in vivo the dynamic interrelations of head size, gray matter, white matter, and cerebrospinal fluid (CSF) volumes from infancy to old age using magnetic resonance imaging (MRI). DESIGN: Cross-sectional, between-subjects using an age-regression model. SETTING: A Veterans Affairs medical center and community hospitals. PARTICIPANTS: There were 88 male and female subjects aged 3 months to 30 years whose clinical MRI film had been read as normal and 73 healthy male volunteers aged 21 to 70 years who had an MRI performed specifically for this study. MAIN OUTCOME MEASURES: These MRI data were quantified using a semiautomated computer technique for segmenting images into gray matter, white matter, and CSF compartments. The cortex was defined geometrically as the outer 45% on each analyzed slice, and the volumes of cortical white matter, gray matter, and CSF were computed. Subcortical (ventricular) CSF volume was computed for the inner 55% of each analyzed slice. RESULTS: In the younger sample, intracranial volume increased by about 300 mL from 3 months to 10 years. The same patterns of change in volume of each compartment across the age range were seen in both sexes: cortical gray matter volume peaked around age 4 years and decreased thereafter; cortical white matter volume increased steadily until about age 20 years; cortical and ventricular CSF volumes remained constant. In the older sample, brain volumes were statistically adjusted for normal variation in head size through a regression procedure and revealed the following pattern: cortical gray matter volume decreased curvilin-early, showing an average volume loss of 0.7 mL/y, while cortical white matter volume remained constant during the five decades; complementary to the cortical gray matter decrease, cortical CSF volume increased by 0.6 mL/y and ventricular volumes increased by 0.3 mL/y. CONCLUSIONS: These patterns of growth and change seen in vivo with MRI are largely consistent with neuropathological studies, as well as animal models of development, and may reflect neuronal progressive and regressive processes, including cell growth, myelination, cell death, and atrophy.

Effect of respiration on the QT interval.

This clinical study was undertaken to investigate the effect of respiration on the QT interval. The QT interval is affected by a variety of factors, including steady changes in heart rate, instantaneous changes in heart rate as in atrial fibrillation, and changes in autonomic tone. Respiration gives rise to cyclical changes in the instantaneous heart rate and autonomic tone. The effect of respiration on the QT interval was analyzed in 25 subjects in sinus rhythm. Cosinor analysis was used to estimate the amplitude of its change from the mean value, its statistical significance, and the timing of the maximum change. Thirteen (52%) subjects revealed significant respiratory change in the QT interval, being the shortest during inspiration in 10 of them. Its amplitude correlated positively with respiratory cycle length (r = .58, P < .01), but not with age, mean heart rate, or the amplitude of change in the RR interval. The mean amplitude of change in the QT interval was 0.8% compared to a change of 2.6% in the RR interval. There is a respiratory variation in the QT interval in subjects in sinus rhythm that is more prominent during slower respirations. However, the amplitude of change in the QT interval is small compared to the change in the RR interval.

Patients with suspected myocardial infarction who present with ST depression.

Patients with suspected myocardial infarction who present with ST depression have a high mortality which is not reduced by thrombolytic therapy. Despite this, there are few data on these patients. We studied the electrocardiographic and clinical characteristics of these patients, the diagnostic and prognostic value of the presenting electrocardiogram (ECG), and the reasons for the high mortality and apparent lack of thrombolytic efficacy. We studied all patients with suspected infarction admitted during 1990 with ST depression. Of the 136 patients (84 men, mean [SD] age 68 [11] years), 74 (54%) had confirmed infarction and 73 (54%) had previous infarction. 1-year mortality was 26% for all patients, 31% for those with confirmed infarcts, and 19% for those in whom infarction was subsequently excluded. Patients with infarction had more severe ST depression (mean 2.5 mm [SD 1.5]) and more ECG leads with ST depression (mean 4.7 leads [1.8]) compared with patients without infarction (1.4 mm [0.8], p < 0.001; 3.6 leads [1.7], p < 0.001). Sensitivity and specificity for the subsequent diagnosis of infarction with ST depression were 20% and 97%, respectively, for at least 4 mm; and 21% and 95%, respectively, for at least 7 leads. 1-year mortality was low in patients with 1 mm ST depression (14%) or no more than 2 leads (11%), but high in patients with at least 2 mm ST depression (39%, p < 0.001) and at least 3 leads (30%, p = 0.08). Patients with suspected infarction and ST depression had a high mean age, high incidence of previous infarction, and poor prognosis. The presenting ECG is helpful in predicting prognosis, and ST depression of at least 4 mm or involving at least 7 leads is highly specific for diagnosis of infarction.

Recovery of left ventricular function after acute myocardial infarction: efficacy of domiciliary thrombolysis in the Grampian Region Early Anistreplase Trial.

BACKGROUND: The objective was to compare the effect of thrombolytic therapy given either at home or in hospital on the recovery of left ventricular function after acute myocardial infarction. METHODS: In a randomized double-blind trial, 311 patients with suspected acute myocardial infarction were given 30 units anistreplase intravenously either at home, or later, in hospital. The median time-saving made with domiciliary thrombolysis was 130 min. All patients were admitted to hospital where left ventricular stroke distance was measured daily using a simple bedside ultrasound technique, and expressed as a percentage of the age-predicted normal value. The last recorded inpatient stroke distance measurement was used to assess residual left ventricular function after recovery from myocardial infarction. RESULTS: The mean stroke distance in patients with confirmed myocardial infarction was 74% on the day of admission, rising to 83% on the last inpatient day; it did not change between discharge and 3 months after admission. For 180 patients assigned randomly to treatment within 2 h of the onset of symptoms, mean stroke distance was greater by 6.8% in those given active anistreplase at home rather than in hospital (95% confidence interval 1.0 to 12.7%, P = 0.02), but there was no significant difference in stroke distance following home or hospital thrombolysis in 111 patients assigned treatment after that time (difference -2.0%, 95% confidence interval -8.4 to 4.5%, P = 0.54). CONCLUSIONS: The efficacy of thrombolytic therapy is enhanced when administered within 2 h of the onset of symptoms.

Correction for head size in brain-imaging measurements.

Structural brain-imaging measurements based on computed tomography (CT) or magnetic resonance imaging (MRI) are often corrected or adjusted for normal variation in head size. Some methods of head-size correction, such as the ventricle-brain ratio (VBR), are based on taking the brain structure size as a proportion of the estimated head size, while other methods have used a regression model to obtain head-size residualized structure measures. Recently, head-size correction was shown to result in less reliable volumetric measures of brain structures (Arndt et al., 1991). In the present study, MRI was used to examine the effects of head-size correction on the interrater reliability of volumetric measures of gray matter, white matter, and cerebrospinal fluid. Four raters independently scored MRI brain images from 26 subjects, generating separate estimates of head size and region of interest (ROI) size. Two methods were used to correct MRI values for differences in head size, one based on proportions and the other based on linear regression. Results confirmed that head-size correction did produce measures with lower reliability; however, further analysis based on classical measurement theory showed that the lower reliability was attributable not only to increased measurement error variance, but also to reduced true score variance. Subsequent analyses of criterion validity compared the raw (uncorrected) and head-size-corrected ROI measures in terms of their correlations with age in a sample of 43 normal control subjects, and in terms of their ability to differentiate schizophrenic patients (n = 22) from normal control subjects (n = 20). Results indicated that head-size correction often improved criterion validity, producing higher correlations with age and with diagnostic status than those produced by the raw measures. These findings suggest that head-size correction removes irrelevant true-score variance which reduces reliability yet improves the correlations with validity criteria such as age and diagnostic status.

Mutual interactions of respiratory sinus arrhythmia and the carotid baroreceptor-heart rate reflex.

1. In six healthy subjects the amplitude and phase of respiratory sinus arrhythmia were determined at five different respiratory cycle lengths ranging from 3 to 9.5 s. 2. At each respiratory cycle length the carotid baroreceptor-heart rate reflex response was determined by cyclical neck suction at -40 mmHg at five different cycle lengths covering the same range of 3-9.5 s. 3. The application of cyclical neck suction increased the amplitude of respiratory sinus arrhythmia in all but the longest respiratory cycle lengths. 4. With increasing respiratory cycle length the amplitude of sinus arrhythmia increased, and R-R intervals were at their longest at an earlier phase of the respiratory cycle. Similarly, with increasing suction cycle length the amplitude of the cardiac interval response increased and the phase angle decreased. 5. The cardiac interval responses to respiration and to neck suction at different frequencies were independent of each other, the heart rate at any moment resulting from the algebraic summation of the two responses.