Ataxia telangiectasia. Case report of a benign variant with telangiectasia recurrent infection and low IgA.
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Adult↗
Biomedical subjects
F M Bennett
Publications and source records attributed to F M Bennett.
Sociomedical study of patients over 75 in general practice.
In a survey of people of 75 years and over in a general practice situated in the north-west of England a total of 297 patients was examined. Among the many previously unreported medical conditions and social needs were seven unknown malignant conditions, 28 patients with heart failure, five with diabetes, and one with myxoedema. A high incidence of nutritional anaemia was also found. It is concluded that such a survey can detect much hidden illness and disability and that general practice is the right setting for it.
Aged↗
Influence of autoregressive model parameter uncertainty on spectral estimates of heart rate dynamics.
Linear autoregressive (AR) model-based heart rate (HR) spectral analysis has been widely used to study HR dynamics. Owing to system and measurement noise, the parameters of an AR model have intrinsic statistical uncertainty. In this study, we evaluate how this AR parameter uncertainty can translate to uncertainty in HR power spectra. HR time series, obtained from seven subjects in supine and standing positions, were fitted to AR models by least squares minimization via singular value decomposition. Spectral uncertainty due to inexact parameter estimation was assessed through a Monte Carlo study in which the AR model parameters were varied randomly according to their Gaussian distributions. Histogram techniques were used to evaluate the distribution of 50,000 AR spectral estimates of each HR time series. These Monte Carlo uncertainties were found to exceed those predicted by previous theoretical approximations. It was determined that the uncertainty of AR HR spectral estimates, particularly the locations and magnitudes of spectral peaks, can often be large. The same Monte Carlo analysis was applied to synthetic AR time series and found levels of spectral uncertainty similar to that of the HR data, thus suggesting that the results of this study are not specific to experimental HR data. Therefore, AR spectra may be unreliable, and one must be careful in assigning pathophysiological origins to specific spectral features of any one spectrum.
Adult↗
Special issue introduction: in honor of Fred S. Grodins.
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History, 20th Century↗
Regulation of PaCO2 during rest and exercise: a modeling study.
A nonlinear mathematical model of the CO2 control system was used to examine a number of issues concerning the regulation of PaCO2 during rest and exercise. To gain insight to the regulatory properties of the respiratory system, the open loop gain (GL) and closed loop sensitivities SI = delta PaCO2/delta PICO2 and SV = delta PaCO2/delta VCO2 were calculated. GL indicates the ability of a control system to regulate the controlled variable, PaCO2 in the model. SI and SV represent the change in PaCO2 to unit changes in PICO2 and VCO2, respectively. Model predications were obtained for rest and various intensities of exercise for the following challenges to the respiratory system: (a) CO2 inhalation, (b) i.v. CO2 loading, (c) application of an external dead space, and (d) a shift in the resting operating point. Increasing exercise intensity produced a substantial decrease in GL and increase in SI consistent with the hypothesis that exercise degrades the ability of the respiratory system to regulate PaCO2. However, SV decreased indicating that the respiratory system would actually be better able to regulate PaCO2 if there were fluctuations in VCO2. Thus, GL does not completely describe the regulatory characteristics of the respiratory control system. It is demonstrated that the regulatory characteristics of the respiratory system as described by GL, SI, and SV are complex and depend on the nature of the challenge. Techniques for systematically describing the regulatory properties of the CO2 control system are described.
Carbon Dioxide↗
Analysis of heart rate dynamics as a measure of autonomic tone in obstetrical patients undergoing epidural or spinal anesthesia.
BACKGROUND AND OBJECTIVES: The purpose of this study is to determine if spectral analysis of beat-to-beat heart rate variability will provide important data on autonomic nervous system function during either spinal or epidural anesthesia that is not apparent from the monitoring of mean heart rate and blood pressure. METHODS: Twelve ASA I patients presenting for elective cesarean delivery (7 epidural and 5 spinal anesthetics) were prospectively selected for study. Control and postblock 10-minute segments of instantaneous heart rates were analyzed for each patient. The total spectral power (Ps, 0.02-0.5 Hz), low frequency spectral power (PLF, 0.02-0.12 Hz), and high frequency spectral power (PHF, 0.12-0.5 Hz) were calculated for each data segment. The complexity of the heart rate time series was estimated by calculating the approximate entropy. RESULTS: Neither spinal or epidural anesthesia had any effect on heart rate or blood pressure. Both spinal and epidural anesthesia did produce a significant decrease in PS, PLF, and PHF. Although there were significant decreases in both the PLF and PHF, there was no change in the PLF/PHF ratio. There was a significant reduction in approximate entropy with spinal and epidural anesthesia, indicating a decrease in complexity of the heart rate dynamics. CONCLUSIONS: These data suggest that autonomic tone decreased with spinal and epidural anesthesia but the sympathetic-parasympathetic balance (expressed as PLF/PHF) did not change. Spectral measures, as well as approximate entropy, provide an independent evaluation of the integrity of the autonomic nervous system and cardiovascular control mechanisms that cannot be discerned from mean heart rate and blood pressure.
Adult↗
Cocaine effects on neonatal heart rate dynamics: preliminary findings and methodological problems.
Cocaine use by pregnant women has been reported to cause fetal and neonatal morbidity and mortality. We hypothesized that human neonates exposed to cocaine via maternal use during pregnancy might manifest changes in beat-to-beat heart rate variability, similar to those described in experimental animals. In this preliminary report, we present findings from the first systematic analysis of heart rate dynamics in a small group of (n = 5) neonates exposed in utero to cocaine compared to gestationally age matched controls (n = 6) without known drug exposure. Overall heart rate spectral power during ten minute periods of quiescent sleep was significantly reduced (p < 0.01) in the cocaine-exposed group, reminiscent of the changes recently reported in an animal model. In two other cocaine-exposed newborns, a quiescent sleep period could not be found. We discuss the special methodological problems associated with collection and interpretation of such data.
Cocaine↗