Identical and Nonidentical Twins: Risk and Factors Involved in Development of Islet Autoimmunity and Type 1 Diabetes

OBJECTIVE

There are variable reports of risk of concordance for progression to islet autoantibodies and type 1 diabetes in identical twins after one twin is diagnosed. We examined development of positive autoantibodies and type 1 diabetes and the effects of genetic factors and common environment on autoantibody positivity in identical twins, nonidentical twins, and full siblings.

RESEARCH DESIGN AND METHODS

Subjects from the TrialNet Pathway to Prevention Study (N = 48,026) were screened from 2004 to 2015 for islet autoantibodies (GAD antibody [GADA], insulinoma-associated antigen 2 [IA-2A], and autoantibodies against insulin [IAA]). Of these subjects, 17,226 (157 identical twins, 283 nonidentical twins, and 16,786 full siblings) were followed for autoantibody positivity or type 1 diabetes for a median of 2.1 years.

RESULTS

At screening, identical twins were more likely to have positive GADA, IA-2A, and IAA than nonidentical twins or full siblings (all P < 0.0001). Younger age, male sex, and genetic factors were significant factors for expression of IA-2A, IAA, one or more positive autoantibodies, and two or more positive autoantibodies (all P ≤ 0.03). Initially autoantibody-positive identical twins had a 69% risk of diabetes by 3 years compared with 1.5% for initially autoantibody-negative identical twins. In nonidentical twins, type 1 diabetes risk by 3 years was 72% for initially multiple autoantibody-positive, 13% for single autoantibody-positive, and 0% for initially autoantibody-negative nonidentical twins. Full siblings had a 3-year type 1 diabetes risk of 47% for multiple autoantibody-positive, 12% for single autoantibody-positive, and 0.5% for initially autoantibody-negative subjects.

CONCLUSIONS

Risk of type 1 diabetes at 3 years is high for initially multiple and single autoantibody-positive identical twins and multiple autoantibody-positive nonidentical twins. Genetic predisposition, age, and male sex are significant risk factors for development of positive autoantibodies in twins.

A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

A Study of Lobular Carcinoma of the Breast Based on the Third National Cancer Survey in the United States of America

Cases in in situ and infiltrating lobular carcinoma of the breast reported in the Third National Cancer Survey were reviewed according to age, sex, race, and geographic distribution. The age-specific incidence rates indicate that there are two peak age periods of risk for invasive lobular carcinoma, the first occurring in ages 40-50 years and the second after age 65. The incidence rates for lobular carcinoma were compared to the incidence rates for intraductal and infiltrating ductal carcinoma reported from the Third National Cancer Survey and for total breast cancer from the Miyagi prefecture in Japan. These comparisons indicate that factors which influence the geographic variation in breast cancer play important roles in the etiology of infiltrating ductal carcinoma, but may have little effect upon the incidence of lobular carcinoma and intraductal carcinoma. The limitations of large histological epidemiological surveys are discussed.

Obesity in Youth with Type 1 Diabetes in Germany, Austria, and the United States

OBJECTIVE

To examine the current extent of the obesity problem in 2 large pediatric clinical registries in the US and Europe and to examine the hypotheses that increased body mass index (BMI) z-scores (BMIz) are associated with greater hemoglobin A1c (HbA1c) and increased frequency of severe hypoglycemia in youth with type 1 diabetes (T1D).

STUDY DESIGN

International (World Health Organization) and national (Centers for Disease Control and Prevention/German Health Interview and Examination Survey for Children and Adolescents) BMI references were used to calculate BMIz in participants (age 2-<18 years and ≥ 1 year duration of T1D) enrolled in the T1D Exchange (n = 11,435) and the Diabetes Prospective Follow-up (n = 21,501). Associations between BMIz and HbA1c and severe hypoglycemia were assessed.

RESULTS

Participants in both registries had median BMI values that were greater than international and their respective national reference values. BMIz was significantly greater in the T1D Exchange vs the Diabetes Prospective Follow-up (P < .001). After stratification by age-group, no differences in BMI between registries existed for children 2-5 years, but differences were confirmed for 6- to 9-, 10- to 13-, and 14- to 17-year age groups (all P < .001). Greater BMIz were significantly related to greater HbA1c levels and more frequent occurrence of severe hypoglycemia across the registries, although these associations may not be clinically relevant.

CONCLUSIONS

Excessive weight is a common problem in children with T1D in Germany and Austria and, especially, in the US. Our data suggest that obesity contributes to the challenges in achieving optimal glycemic control in children and adolescents with T1D.

Post-160-km race illness rates and decreases in granulocyte respiratory burst and salivary IgA output are not countered by quercetin ingestion

This study measured the influence of the flavonoid quercetin on immune changes and incidence rates of upper respiratory tract infections in ultramarathoners competing in the 160-km Western States Endurance Run. Sixty-three runners were randomized to quercetin and placebo groups, and under double-blinded methods ingested 1000 mg/day quercetin for 3 wks before, during, and 2 wks after the race. Thirty-nine of the 63 subjects (n = 18 for quercetin, n = 21 for placebo) finished the race and provided blood and saliva samples the morning before the race and 15 - 30 min postrace. Upper respiratory tract infections were assessed during the week before and the 2-wk period after the race using an illness symptom checklist. Race times did not differ significantly between quercetin and placebo groups. Significant pre- to postrace decreases were measured for natural killer cells (43 %), granulocyte respiratory burst activity (55 %), and salivary IgA output (48 %), and increases for neutrophil (288 %) and monocyte (211 %) cell counts, with no significant group differences. Postrace illness rates did not differ between groups. In conclusion, quercetin supplementation for 3 wks before and 2 wks after the Western States Endurance Run had no effect on illness rates, perturbations in leukocyte subset counts, or decreases in granulocyte respiratory burst activity and salivary IgA.

Effect of NSAID on Muscle Injury and Oxidative Stress

Indirect markers of muscle damage and delayed onset muscle soreness were examined and correlated to changes in oxidative stress, plasma antioxidant potential, and use or nonuse of non-steroidal anti-inflammatory drugs in 60 ultra-marathoners following the Western States Endurance Run. Blood was collected prior to and immediately following the race and analyzed for muscle damage by creatine phosphokinase and oxidative stress by F (2)-isoprostanes, protein carbonyls, and lipid hydroperoxides and antioxidant potential by the ferric reducing ability of plasma. Subjects recorded delayed onset muscle soreness during the week following the race. Lipid hydroperoxide concentrations were unchanged, but F (2)-isoprostanes, protein carbonyls, ferric reducing ability of plasma, creatine phosphokinase, and delayed onset muscle soreness increased significantly postrace. Protein carbonyls were significantly higher postrace in nonsteroidal anti-inflammatory drug users versus nonusers (p < 0.05). However, there was no difference between users and non-users for all other markers. Postrace creatine phosphokinase concentrations were not correlated with oxidative stress markers but were correlated with changes in delayed onset muscle soreness. Based upon these findings, caution should be used when consuming nonsteroidal anti-inflammatory drugs during ultra distance events.

Immune changes: 2 h of continuous vs. intermittent cycling

Immune changes following 2 h of intensive cycling with or without rest intervals were measured in trained cyclists (n = 12) who functioned as their own controls during two test sessions that were separated by two weeks. Subjects cycled for 2.0 h at approximately 64 % Watts(max) continuously (C) or with 3-min rest intervals (R) interspersed every 10 min (2.6 h total time), with the order of the sessions randomized. Blood samples were collected 30-min pre-exercise, and immediately and 1-h postexercise, and assayed for blood leukocyte subset counts, plasma IL-6, IL-10, IL-1ra, IL-8, PHA-induced lymphocyte proliferation, and natural killer cell activity (NKCA). Significant time effects were measured for all immune measures, but no significant differences in the pattern of change were found between C and R exercise trials. In conclusion, immune changes induced by 2 h of intense and prolonged exercise paralleled those measured when athletes rested 3 min every 10 min of exercise.

Psychological, nutritional, and energy expenditure differences in college females with anorexia nervosa vs. comparable-mass controls

This is the first study to examine psychological and behavioral variables in nonhospitalized college females with subclinical anorexia nervosa (AN) as compared to healthy college females of comparable body mass (i.e., body mass index (BMI)<19). Participants who met all DSM-IV [Diagnostic and statistical manual of mental disorders, 4th ed. (1994). Washington, DC: APA.] criteria for AN-restrictive type (except for BMI<17.5; n=11) and control participants (n=15) with comparable body mass completed psychological, nutritional, and exercise assessments. Results suggested that those with AN evidenced more general psychopathology, more eating disorder symptoms, more dieting, more compulsive exercise, and less consumption of calories compared to participants in the control group. There was no difference in macronutrient consumption. There was no significant difference in expenditure of energy, despite differences in reports of compulsive exercise. Given similar body mass, this suggests that the women with AN were experiencing an energy deficit consistent with the disorder's defining features of "fear of gaining weight or becoming fat" and provides us with more understanding of individuals with AN in their natural environment.

Randomised controlled trial of an integrated versus an optometric low vision rehabilitation service for patients with age-related macular degeneration: study design and methodology

A number of studies have measured the outcomes of low vision care but these have usually been longitudinal case series, thus constituting very low quality of evidence for effectiveness. To date, there have been no randomised controlled trials (RCTs) which have evaluated the effectiveness and cost effectiveness of different models of care in low vision. The size of the low vision population and the paucity of systematic evaluation have created a pressing need for evidence about cost-effectiveness in order to inform service developments for low vision rehabilitation. This paper describes the study design and methodology of a three-arm RCT currently under way in Manchester. The baseline population recruited is also described. A traditional hospital-based optometric service is being compared with an integrated service (comprising the addition of community-based rehabilitation officer input) and with more generic community input (which is non-integrated and is not vision specific). A wide range of outcome measures are being assessed at recruitment and 12 months post-intervention, including low vision specific and generic quality of life measures, patterns of low vision aid use, and task performance. The rationale for the trial is discussed and the main study outcomes are described.

The role of oxidative stress in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blind registration in the developed world, and yet its pathogenesis remains poorly understood. Oxidative stress, which refers to cellular damage caused by reactive oxygen intermediates (ROI), has been implicated in many disease processes, especially age-related disorders. ROIs include free radicals, hydrogen peroxide, and singlet oxygen, and they are often the byproducts of oxygen metabolism. The retina is particularly susceptible to oxidative stress because of its high consumption of oxygen, its high proportion of polyunsaturated fatty acids, and its exposure to visible light. In vitro studies have consistently shown that photochemical retinal injury is attributable to oxidative stress and that the antioxidant vitamins A, C, and E protect against this type of injury. Furthermore, there is strong evidence suggesting that lipofuscin is derived, at least in part, from oxidatively damaged photoreceptor outer segments and that it is itself a photoreactive substance. However, the relationships between dietary and serum levels of the antioxidant vitamins and age-related macular disease are less clear, although a protective effect of high plasma concentrations of alpha-tocopherol has been convincingly demonstrated. Macular pigment is also believed to limit retinal oxidative damage by absorbing incoming blue light and/or quenching ROIs. Many putative risk-factors for AMD have been linked to a lack of macular pigment, including female gender, lens density, tobacco use, light iris color, and reduced visual sensitivity. Moreover, the Eye Disease Case-Control Study found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular AMD. The concept that AMD can be attributed to cumulative oxidative stress is enticing, but remains unproven. With a view to reducing oxidative damage, the effect of nutritional antioxidant supplements on the onset and natural course of age-related macular disease is currently being evaluated.

Assessment of the diurnal variation in central corneal thickness and intraocular pressure for patients with suspected glaucoma

OBJECTIVE

To assess whether a single daily measurement using ultrasonic pachymetry gives a representative assessment of mean central corneal thickness (CCT) in patients with suspected glaucoma and whether diurnal changes in CCT are related to diurnal variations in intraocular pressure (IOP).

DESIGN

Cross-sectional study.

METHOD

Central CCT and IOP were measured by a single observer in 56 eyes of 28 patients with suspected glaucoma using an ultrasonic pachymeter and a Goldmann tonometer. Four measurements were made over a 24-hour period: at 8:00 AM, 12:00 PM, 4:00 PM, and 8:00 PM.

MAIN OUTCOME MEASURES

Intraocular pressure and pachymetry.

RESULTS

Mean IOP was 19.80 mmHg at 8:00 AM (95% confidence interval [CI], 18.95-20.66 mmHg), 20.38 mmHg at 12:00 PM (95% CI, 19.49-21.26 mmHg), 19.91 mmHg at 4:00 PM (95% CI, 19.99-21.83 mmHg), and 19.23 mmHg at 8:00 PM (95% CI, 18.35-20.11 mmHg). Mean CCT was 569.4 microm (95% CI, 560.2-578.7 microm), 567.6 microm (95% CI, 558.4-576.7 microm), 569.1 microm (95% CI, 559.5-578.6 microm), and 567.2 microm (95% CI, 557.9-576.4 microm) at the four respective time points. There was no significant correlation between IOP and CCT in any patient (Pearson rank correlation coefficient); nor was there any significant correlation between the mean diurnal variations of IOP and CCT.

CONCLUSIONS

In this group of patients with suspected glaucoma, there was no significant variation in CCT. Therefore, a single measurement of CCT is sufficient when assessing patients with suspected glaucoma. There was no correlation between change of IOP and change of CCT.

Relationship between corneal thickness and measured intraocular pressure in a general ophthalmology clinic

OBJECTIVE

To assess whether central corneal thickness (CCT) is a confounding factor in the classification of patients attending for glaucoma assessment in a district general hospital.

DESIGN

Cross-sectional study by a single observer.

PARTICIPANTS

Patients attending a general ophthalmic clinic: 235 clinically normal eyes, 52 eyes with normal-tension glaucoma (NTG), 335 eyes with primary open-angle glaucoma (POAG), 12 eyes with pseudoexfoliative glaucoma (PXE), 42 eyes with chronic angle closure glaucoma (CACG), and 232 glaucoma suspect (GS) eyes.

INTERVENTION

Central corneal thickness was measured using ultrasonic pachymetry.

MAIN OUTCOME MEASURE

Correlation of CCT and diagnosis.

RESULTS

Mean CCT was 553.9 microm (95% confidence intervals [CI] for the mean, 549.0-558.8 microm) in the clinically normal eyes, 550.1 microm (95% CI, 546.6-553.7 microm) in the POAG eyes, 514.0 microm (95% CI, 504.8-523.3 microm) in the NTG eyes, 530.7 microm (95% CI, 511.2-550.1 microm) in the PXE eyes, 559.9 microm (95% CI, 546.8-573.0 microm) in the CACG eyes, and 579.5 microm (95% CI, 574.8-584.1 microm) in the GS eyes. The differences of mean CCT between the groups were highly significant (P< 0.001 analysis of variance). Eighty-five percent of eyes with NTG and only 36% of eyes with POAG had a mean CCT of 540 microm or less. Thirteen percent of eyes with POAG and 42% of GS eyes had a mean CCT greater than 585 microm.

CONCLUSIONS

The CCT measurement is desirable in patients attending for glaucoma assessment in a district general hospital to avoid misclassification resulting from the relationship between CCT and tonometric pressure. Central corneal thickness alone is not an accurate predictor for the clinical diagnosis in this group of eyes. However, many eyes diagnosed as having NTG have thin corneas, which would tend to lower the tonometrically recorded intraocular pressure (IOP), so the finding of a less-than-normal thickness cornea introduces some doubt as to the diagnosis of NTG. For the GS eyes, most eyes had thick corneas, which would tend to increase the tonometrically recorded IOP. Thus, GS eyes with modest elevation of IOP and a thick cornea may be at low risk of progressing to POAG. Thus, many patients with "high IOPs" and a thick CCT do not necessarily have high IOPs and may not need to be followed as GS eyes.

Creatine depletion elicits structural, biochemical, and physiological adaptations in rat costal diaphragm

To elucidate adaptations elicited by creatine (Cr) depletion in the costal diaphragm (Dia), 16 12-wk-old male Fisher 344 rats had 2% beta-guanidinopropionic acid (beta-GPA), a competitive inhibitor of Cr transport into muscle, added to their food; a control group (Con) of 16 rats ate normal rat chow. After 18 wk, beta-GPA and Con Dia did not differ histochemically with respect to fiber-type distribution; however, the cross-sectional area of type II(b + x) fibers was 33% less in beta-GPA than Con Dia. Biochemically, the proportion of myosin heavy chain IIb in beta-GPA Dia was decreased 42% from Con Dia, whereas the proportions of myosin heavy chains I and IIa were increased. Physiologically, both peak twitch tension and tetanic tension in beta-GPA Dia were decreased 40% from Con. To assess fatigability, we used the protocol of Kelsen and Nochomovitz (J. Appl. Physiol. 53; 440-447, 1982) for 2-6 min duration; the percentage of initial force exhibited by beta-GPA Dia was approximately twice that of Con Dia. We conclude that these structural, biochemical, and physiological adaptations elicited by Cr depletion can all be explained by selective atrophy of IIb muscle fibers in the Dia.

The sensation of dyspnea during exercise is not determined by the work of breathing in patients with heart failure

OBJECTIVES

The present study sought to investigate whether the work of breathing was reduced after heart transplantation. Accordingly, the tension time index of the diaphragm was measured in patients with heart failure and in transplant recipients.

BACKGROUND

Patients with heart failure are frequently limited by exertional dyspnea that may be due to the increased work of breathing. After heart transplantation, exertional dyspnea is markedly diminished. Whether work of breathing is reduced in posttransplant recipients is unknown.

METHODS

Nine patients with heart failure, six normal subjects and six heart transplant recipients were studied. Transdiaphragmatic pressure was measured throughout exercise. Accessory respiratory muscle oxygenation was assessed using near-infrared spectroscopy. Peak oxygen consumption, time in inspiration, time per breath and maximal inspiratory and expiratory pressures were measured in all subjects.

RESULTS

The tension time index remained markedly abnormal after heart transplantation both at rest ([mean +/- SD] normal group 0.01 +/- 0.006, heart failure group 0.026 +/- 0.018, transplant group 0.058 +/- 0.015, p < 0.004) and at peak exercise (normal group 0.03 +/- 0.02, heart failure group 0.10 +/- 0.03, transplant group 0.10 +/- 0.04, p < 0.0001). Accessory respiratory muscle deoxygenation was present only in patients with heart failure (near-infrared absorbency changes [arbitrary units]: normal group -3 +/- 6, heart failure group 28 +/- 5, transplant group -3.5 +/- 4.4, p < 0.0001).

CONCLUSIONS

Although heart transplantation alleviates dyspnea in patients with heart failure, the work of breathing as assessed by the tension time index of the diaphragm is not decreased. Amelioration of exertional dyspnea is achieved by other mechanisms, such as improved respiratory muscle perfusion.

Benefit of selective respiratory muscle training on exercise capacity in patients with chronic congestive heart failure

BACKGROUND

Diminished respiratory muscle strength and endurance have been demonstrated in patients with heart failure. This may contribute to exertional dyspnea and reduced exercise capacity in these patients. The purpose of this study was to investigate whether selective respiratory muscle training could alleviate dyspnea and improve exercise performance in patients with chronic congestive heart failure.

METHODS AND RESULTS

Fourteen patients with chronic heart failure (left ventricular ejection fraction, 22 +/- 9%) were enrolled in a supervised respiratory muscle training program. This consisted of three weekly sessions of isocapnic hyperpnea at maximal sustainable ventilatory capacity, resistive breathing, and strength training. Maximum sustainable ventilatory capacity, maximum voluntary ventilation, maximal inspiratory and expiratory pressures, peak VO2, and the 6-minute walk test were measured before (pre) and after (post) 3 months of training. Eight patients completed the training program. Respiratory muscle endurance was improved with training, as evidenced by increases in maximal sustainable ventilatory capacity (pre, 48.6 +/- 10.7 versus post, 76.9 +/- 14.5 L/min; P < .05) and in maximal voluntary ventilation (pre, 100 +/- 36 versus post, 115 +/- 39 L/min; P < .05). Respiratory muscle strength was also increased with training as maximal inspiratory (pre, 64 +/- 31 versus post, 78 +/- 33 cm, H2O; P < .01) and expiratory (pre, 94 +/- 30 versus post, 133 +/- 53 cm H2O; P < .001) pressures rose. Submaximal and maximal exercise capacity were significantly improved with selective respiratory muscle training as the 6-minute walk (pre, 1101 +/- 351 versus post, 1421 +/- 328 ft; P < .001) and peak exercise VO2 (pre, 11.4 +/- 3.3 versus post, 13.3 +/- 2.7 mL.kg-1.min-1; P < .05) both significantly increased. Dyspnea during activities of daily living was subjectively improved in the majority of trained patients. Dyspnea quantified by the Borg scale was significantly reduced during progressive isocapnic hypernea but not during bicycle exercise. No statistically significant improvement in maximal sustainable ventilatory capacity, maximum voluntary ventilation, maximal inspiratory or expiratory mouth pressures, 6-minute walk, or peak VO2 was observed in the 6 patients who did not complete the training program.

CONCLUSIONS

Selective respiratory muscle training improves respiratory muscle endurance and strength, with an enhancement of submaximal and maximal exercise capacity in patients with heart failure. Dyspnea during activities of daily living was subjectively improved in the majority of trained patients.

Evidence of reduced respiratory muscle endurance in patients with heart failure

OBJECTIVES

We sought to investigate whether reduced respiratory muscle endurance contributes to increased dyspnea and decreased exercise capacity in patients with chronic heart failure.

BACKGROUND

In patients with heart failure, the sensation of dyspnea may be related to abnormalities of respiratory muscle function, such as diminished strength or endurance, or both.

METHODS

Respiratory muscle endurance was assessed by measuring maximal sustainable ventilatory capacity in 15 patients with congestive heart failure and 8 normal subjects using progressive isocapnic hyperpnea. Near-infrared spectroscopy of an accessory respiratory muscle, Borg scale recordings of perceived dyspnea, time in inspiration, time per breath and minute ventilation were measured. Exercise testing with measurement of oxygen consumption was also performed.

RESULTS

Maximal voluntary ventilation (normal subjects 167 +/- 40, heart failure group 89 +/- 31 liters/min) and maximal sustainable ventilatory capacity (normal subjects 90 +/- 23, heart failure group 53 +/- 22 liters/min) were significantly reduced in patients with heart failure (both p < 0.05). No significant accessory respiratory muscle deoxygenation was observed in either group. Borg scale recordings at maximal sustainable ventilatory capacity were comparable in both groups. At rest, the inspiratory duty cycle (i.e., time in inspiration divided by the time per breath) was comparable in the two groups (normal subjects 0.34 +/- 0.09, heart failure group 0.37 +/- 0.12, p = NS). However at maximal sustainable ventilatory capacity, only normal subjects had a significant increase in the inspiratory duty cycle (normal subjects 0.49 +/- 0.04, heart failure group 0.36 +/- 0.10, p < 0.05). This finding suggests obstruction to airflow in patients with congestive heart failure. Values for peak exercise minute ventilation did not differ significantly from values in maximal sustainable ventilatory capacity in either group and were significantly correlated (r = 0.84, p < 0.0001).

CONCLUSION

Respiratory muscle endurance as assessed by maximal sustainable ventilatory capacity is reduced in patients with heart failure.

Respiratory muscle function and dyspnea in patients with chronic congestive heart failure

BACKGROUND

Patients with heart failure (HF) frequently experience exertional dyspnea. Using near-infrared spectroscopy, we have previously demonstrated accessory respiratory muscle deoxygenation during exercise in these patients by monitoring changes in light absorption at 760-800 nm.

METHODS AND RESULTS

To investigate whether low-frequency respiratory muscle fatigue occurs, we performed supramaximal bilateral transcutaneous phrenic nerve stimulation before and after maximal bicycle exercise in 10 patients with HF (age, 62 +/- 10 years; ejection fraction, 18 +/- 7%) and six normal subjects (age, 50 +/- 8 years). Maximal rates of contraction and relaxation, peak twitch tension, and maximal transdiaphragmatic pressure (Pdi) were derived before and after exercise from analysis of six to 12 twitches obtained at functional residual capacity. Pdi, time in inspiration (Ti), time per breath (TTOT), respiratory gases, ratings of perceived dyspnea and fatigue, and 760-800 nm near-infrared spectroscopy absorbency changes of the serratus anterior muscle were measured throughout exercise. The tension time index (TTdi) of the diaphragm was derived. In both normal and HF subjects, all parameters of diaphragmatic function (i.e., maximal rates of contraction and relaxation, peak twitch tension, and maximal Pdi) were unchanged before and after exercise. Mean Pdi was comparable at rest (normal, 3.7 +/- 1; HF, 5.8 +/- 2.9 cm H2O; p = NS) but significantly greater in patients with HF at peak exercise (normal, 12.1 +/- 3; HF, 18.3 +/- 6.6 cm H2O; p less than 0.05). Ti/TTOT of both groups was similar at rest and throughout exercise. TTdi was significantly greater at rest (normal, 0.01 +/- 0.01; HF, 0.03 +/- 0.02; p less than 0.05) and at peak exercise (normal, 0.03 +/- 0.02; HF, 0.10 +/- 0.03; p less than 0.04) in patients with HF. Significant accessory respiration muscle deoxygenation was noted only in patients with HF (peak exercise; normal, -1 +/- 13; HF, 28 +/- 15 arbitrary units; p less than 0.01). Linear correlation analysis was performed between ratings of perceived dyspnea and parameters of pulmonary and diaphragmatic function. Significant correlations were observed between ratings of perceived dyspnea and maximal inspiratory and expiratory pressure, the TTdi of the diaphragm, near-infrared absorption changes, and forced expiratory volume in 1 second (FEV1) (all r greater than 0.5; p less than 0.05). Thus, respiratory muscle strength, work, and oxygenation were significantly correlated with the degree of dyspnea.

CONCLUSIONS

We conclude that low-frequency diaphragmatic muscle fatigue does not occur despite accessory respiratory muscle deoxygenation during exercise in patients with HF. However, diaphragmatic work as assessed by the TTdi is dramatically increased in patients with HF and approaches levels previously shown to generate fatigue. The sensation of dyspnea appears closely related to respiratory muscle function.

Use of a triaxial magnetometer for respiratory measurements

We describe a triaxial magnetometer (Tri-mag) system, which consists of a transmitter, four sensors, a processing unit, and a personal computer (PC). The Tri-mag processing unit outputs the position of each sensor relative to the transmitter in three orthogonal coordinates, and this information is communicated to the PC. First, we demonstrated that within a defined octant of a sphere in which the center is the transmitter, we can measure radial distances with an accuracy of +/- 1 mm over a range extending from 10 to 70 cm from the transmitter. Second, we recorded the three-dimensional movement of sensors on the anterior and posterior surfaces of the chest wall during maximum voluntary ventilation in four normal men; all sensors were placed in the midsagittal plane of the body. Anterior sensors were located on the sternum at the level of the third intercostal space and at 2 cm above the umbilicus, whereas posterior sensors were located on the posterior spine at the same vertical levels as the anterior sensors. In all subjects the following was found. 1) Both anterior sensors moved anterior and cephalad during inspiration. The anterior thoracic sensor showed greater vertical than anteroposterior (A-P) movement, whereas the anterior abdominal sensor showed greater A-P than vertical movement. 2) Inspiration was associated with spinal extension, whereas expiration was associated with spinal flexion. Third, we used Tri-mag information to 1) measure tidal volume (VT) over a range extending from 500 ml to inspiratory capacity and 2) measure the change in end-expiratory lung volume (EELV) over a range extending from FRC to FRC plus a minimum of 1.5 liters. Our results indicate that greater than 96% of the changes in VT and greater than 82% of the changes in EELV can be accounted for by changes in A-P, vertical, and lateral dimensions of the chest wall.

Negative-pressure ventilation

In this review, we make the following major points: (1) Canine experiments indicate that in an experimental model of ARDS, cyclic NPV plus NEEP is as effective as cyclic PPV plus PEEP in treating arterial hypoxemia. Because cyclic NPV plus NEEP does not depress cardiac output as much as cyclic PPV plus PEEP, further study of this potential therapy is warranted. (2) At the present time, NPV has little use in neonatal medicine. (3) However, in adult medicine, NPV is efficacious for providing chronic ventilatory support in patients with neuromuscular and chest wall diseases. Additionally, the role of NPV in postoperative weaning warrants further study. (4) Some data in the literature suggest that some subsets of patients with CAL may benefit from chronic intermittent NPV therapy. However, criteria for identifying these patients have not been established. (5) Some investigators have recently demonstrated that PPV delivered via the nares can elicit VMR. Because this technique provides us with the opportunity to elicit VMR by a method other than NPV, nasal PPV provides us with a method to directly validate our presumption that improvements in COPD patients are related to VMR per se.

Inspiratory pressure generation: comparison of subjects with COPD and age-matched normals

We continuously monitored esophageal (Pes) and gastric (Pga) pressures and used these measurements in a three-component model to estimate instantaneous diaphragmatic (DIA), inspiratory accessory muscle (IAM), and postexpiratory recoil (PER) pressures at various times during inspiration. We validated our model both by volume-pressure relationships of the respiratory system (Vrc-Pga and Vab-Pga, where Vrc and Vab are the rib cage and abdominal volumes, respectively) as well as electromyography of the respiratory muscles. Measurements were carried out at rest and during graded treadmill exercise in 11 subjects with chronic obstructive pulmonary disease (COPDs) and 8 age-matched normal subjects (AMNs). AMNs were 59 +/- 2 (SE) yr and had a forced expiratory volume at 1 s (FEV1.0) of 3.6 +/- 0.2 liters; COPDs were 66 +/- 2 yr and had a FEV1.0 of 1.0 +/- 0.1 liters. We noted the following. At rest, both AMNs and COPDs exhibited an increasing DIA pressure (PDIA) across inspiratory time (TI) at rest. As expired minute ventilation increased with exercise intensity, AMNs continued to maintain this PDIA ramp across inspiration; in contrast, COPDs exhibited higher values of PDIA during the first half of TI than during the second half. At all intensities of exercise, COPDs exhibited higher IAM and PER pressures than the AMNs.

Respiratory muscle rest therapy

This article discusses the role of respiratory muscle rest therapy in hypercapnic ventilatory failure and/or inspiratory muscle fatigue associated with primary lung disease, diseases of the chest wall, and neuromuscular diseases. Some animal data on the role of ventilatory muscle rest therapy in states characterized by a low cardiac output and arterial hypotension are also reviewed. Additionally, a method for quantitating the degree of respiratory muscle rest elicited by negative pressure ventilation devices is presented.

Low-frequency diaphragmatic fatigue in spontaneously breathing humans

We used transdiaphragmatic peak twitch tension (PTT) elicited by bilateral phrenic nerve stimulation to ascertain whether low-frequency (LF) diaphragmatic fatigue (DF) can be induced in spontaneously breathing humans by a combination of an inspiratory resistive load (IRL) and graded treadmill exercise (GXT). Our subjects were 10 young males with normal cardiopulmonary function. Before exercise we measured PTT in each subject by administering supramaximal electrical pulses of 100-microseconds duration at a frequency of 1 Hz to each phrenic nerve with the subjects breath holding at functional residual capacity at a given thoracoabdominal configuration. A minimum of six satisfactory PTT measurements were made in each subject, and we computed the 95% confidence limits (CL) for each subject. The subjects then inspired through a resistive load of 38 cmH2O.1(-1).s-1 while carrying out the GXT until exhaustion. After the GXT, PTT was remeasured in all subjects. In five of the subjects, the post-GXT mean PTT fell below the 95% CL of the pre-GXT mean PTT. However, post-GXT PTT means for the other five subjects were within the 95% CL of the pre-GXT means. In conclusion, using PTT as a measure of LFDF, these results demonstrate that LFDF can be produced in 50% of spontaneously breathing young normal males.

Selection factors in clinical trials: results from the Community Clinical Oncology Program Physician's Patient Log

Between August 1984 and November 1985, data concerning 44,156 newly diagnosed cancer patients were entered in the Community Clinical Oncology Program Physician's Patient Log. Forty percent (17,773 patients) had a National Cancer Institute-approved protocol available for site and stage of disease. Fifty-six percent of patients with a protocol available were clinically eligible and 19% were entered on protocol. Thus, one-third of clinically eligible patients were entered in the study. Age was a major factor influencing eligibility and entry on study. Eighty percent of patients less than 25 years of age with a protocol available were clinically eligible for clinical trials participation, and 58% were placed on protocol. Patients greater than or equal to 65 years of age with a protocol available were less likely to be clinically eligible (48%) or placed on study (14%). A physician's preference for an alternate treatment and patient refusal for protocol treatment were also important reasons that clinically eligible patients were not registered on protocol. Selection for clinical trials participation affects the characteristics of patients under study and may have an impact on the ability to generalize the results of clinical trials.

Importance of visual field score and asymmetry in the detection of glaucoma

The visual fields and intraocular pressures (IOP's) of 115 normal volunteers and 107 suspect/diagnosed early glaucoma subjects were recorded by Friedmann static perimetry and noncontact tonometry or applanation tonometry. The visual field data were analyzed statistically and quantified numerically by a microcomputer. The readings obtained from the suspect/diagnosed early glaucoma subjects were compared to those from an age-matched control group according to four criteria: highest field score; field score asymmetry; highest IOP; and IOP asymmetry. A combined field score and asymmetry analysis was found to be more sensitive, 86%, than a combined IOP and IOP asymmetry analysis, 56%. The combined field score and field score asymmetry analysis also gave a clear bimodal separation of subjects with early visual field defects from those with normal visual function.

Micropachometry: a technique for measuring the thickness of the corneal epithelium

A micropachometer was developed for the measurement of epithelial thickness in the living human cornea. The technique requires no contact with the eye and will be of value in studies of the anterior cornea and the physiological effects of contact lenses. The design is described, and results are presented from measurements of epithelial thickness.

An epidemiologic study of cancer of the cervix, vagina, and vulva based on the Third National Cancer Survey in the United States

Cases of invasive and in situ carcinoma of the lower female genital tract as reported in the Third National Cancer Survey in the United States were analyzed according to age, race, and geographic distribution. Results indicate that the incidence rates of in situ and invasive carcinoma of the cervix were greater in black than in white women, with a relative risk rate for black women of approximately two for both types of cervical carcinoma. For white women, the age-specific rates for invasive carcinoma of the cervix remained relatively constant after age 45, while for black women the age-specific rates for invasive carcinoma continued to increase after age 45. For both races, the patterns of age-specific incidence rates for in situ and invasive carcinoma of the cervix were not similar to those for carcinoma of the vagina or vulva. The pattern of age-specific incidence rates of adenocarcinoma of the cervix did not resemble those for in situ or invasive squamous cell carcinoma of the cervix. The rates for adenocarcinoma of the cervix demonstrated patterns similar to those for intraductal carcinoma of the breast. Results of the study are discussed in relationship to the field theory of carcinogenesis as developed for the lower female genital tract.

Mouse cytomegalovirus. Necrosis of infected and morphologically normal submaxillary gland acinar cells during termination of chronic infection

The ultrastructural lesions in the submaxillary glands of C(3)H mice chronically infected with the murine cytomegalovirus are reported. Virus was synthesized in the nucleus of acinar glandular cells. After passage into the cytoplasm, virus was located in large vesicles which were derived from the Golgi apparatus. These vesicles, which were periodic acid-Schiff positive, migrated to the apex of the cell and released virus into the acinar lumen or canaliculi. Eventually, lymphocytes infiltrated the interstitium and surrounded the basal lamina of acini which contained infected cells. In acini encompassed by lymphocytes, both infected cells and morphologically normal acinar cells simultaneously degenerated, producing a small focus of necrosis. Physical contact between lymphocytes and necrotic cells did not occur for an intact basal lamina was always found interposed between them. Degeneration of infected cells coincided with a decrease in virus titer in the salivary glands. Degeneration of infected and normal acinar cells also occurred in DBA 2 mice which lack the fifth component of complement. In mice conditioned with cortisone to suppress inflammation, neither infected nor normal acinar cells degenerated. We concluded from the electron microscope observations that lymphocytes terminate chronic MCMV infection, that MCMV infection of acinar epithelium is not cytolytic and that normal cells also undergo necrosis during termination of chronic MCMV infection. It is postulated that lymphocytes in responding to infection release a cytotoxic substance which diffuses into the acini and causes indiscriminate necrosis of acinar cells.

Chronic infection of the rabbit central nervous system by a slowly growing equine herpesvirus

The spinal cords of rabbits were chronically infected by a slowly growing horse herpesvirus (a "cytomegalovirus") inoculated directly therein. Virus was recovered from the central nervous systems of some of such animals after more than 1 year. The virus could be reisolated from all the animals killed during the first few weeks after its injection; acute focal meningomyelitis was present with involvement of gray and white matter of the cervical, thoracic, and lumbar levels of the spinal cords of these rabbits, though the nerve cells themselves remained undamaged. Thereafter, reisolation of the virus became sporadic, and no damage to the spinal cord could be histologically discerned even in animals from which the virus was recovered. No paralytic or other clinical effects could be attributed to the infection.

Pathogenesis of chronic mouse cytomegalovirus infection in submaxillary glands of C3H mice

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