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Biomedical subjects

A W Jackson

Publications and source records attributed to A W Jackson.

At least 37 records · Page 2Linked to original sources
PubMed1989

Effects of pressure-demand respirator wear on physiological and perceptual variables during progressive exercise to maximal levels.

Current regulations governing the certification of respiratory protective devices are based on data published in the early 1950s. The limited data base of this early work and documented increases in the average height of the population underscore the need for additional information concerning the parameters of certification. In the present study, a protocol using an inclined treadmill (0.5% grade every 12 sec) was used to test a heterogeneous population (n = 38). Through submaximal up to and including maximal exercise levels with and without respirator wear, maximal oxygen uptake (VO2max) was significantly greater (p less than 0.01) with the respirator (44.11 +/- 1.3 mL/kg.min) than without the respirator (42.18 +/- 1.4 mL/kg.min) while maximal ventilation volumes (VEmax) were not significantly different (with = 118.7 +/- 4 L/min; without 119.6 +/- 5 L/min). While peak inspired flows (PFI) with the respirator (268 +/- 7 L/min) were less than without the respirator (281 +/- 9 L/min), p greater than 0.05, the lower peak expired flow (PFE) with the respirator (289 +/- 12 L/min) than without the respirator (324 +/- 13 L/min), p less than 0.01, indicated a significant blunting effect of the respiratory flows by the expired resistance during exercise to maximal levels. Peak inspired pressures (PPi) with and without the respirator were not significantly different (p greater than 0.05). The negative values obtained within the facepiece of the respirator (-7.65 +/- 0.8 cmH2O), however, indicate that the positive pressure within the facepiece was lost, and respiratory protection may be compromised. Peak expired pressure with the respirator (13.05 +/- 0.7 cmH2O) was significantly greater than without the respirator (10.7 +/- 0.5 cmH2O) indicating that, despite a lower PFE, greater force was required to overcome the resistances of the respirator on expiration. The dyspnea index, an index of physiological effort; suggests that the subjects were working at a higher percentage of their respiratory reserve with the respirator (p less than 0.05) than without. Perceptually, subjects also felt that breathing with the respirator was more difficult (p less than 0.05). The maximum heart rate and the ratings of perceived exertion were not significantly different between the two tests at maximal exercise levels. Maximum oxygen uptake was considered reached when subjects attained a respiratory exchange ratio of at least 1.15, when a heart rate response at or greater than age-predicted maximum was achieved, when ratings of perceived exertion indicated exhaustion, and/or when the measure of VO2 had plateaued during the final minute of exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Equipment Design↗
PubMed1989

Alterations in physiological and perceptual variables during exhaustive endurance work while wearing a pressure-demand respirator.

The purpose of this investigation was to describe the time course of changes in physiological and perceptual variables during exhaustive endurance work with and without an air-supplied, full-facepiece, pressure-demand respirator. Thirty-eight healthy subjects (24 to 51 years of age) volunteered for this study. Treadmill speed was set at 5.5 kph (3.4 mph) and elevation was set at a level calculated to elicit 70% of a previously determined maximal aerobic capacity (VO2max). Subjects continued at this rate to exhaustion. Despite a constant work rate, VO2 and %VO2max increased during exercise and were significantly greater with the respirator (34.4 +/- 1.1 mL/kg.min; 84% VO2max) than without the respirator (31.9 +/- 1.1 mL/kg.min; 76% VO2max) at the "final" measurement point prior to termination of exercise by each subject. The final values for ventilation volume (VE) also were significantly greater with the respirator (89.2 +/- 3.4 L/min) than without (73.4 +/- 3.7 L/min). At the conclusion of the endurance walk, dyspnea index (VE/MMV.25) remained well below maximal values (with = 58.6 +/- 2%; without = 44.6 +/- 2%; p less than 0.001). Also, at the final period, no significant differences occurred in the subjects' perceptual ratings of work of breathing, yet work performance time was significantly reduced (p less than 0.0001) from 69.1 +/- 4.4 min (without) to 55.6 +/- 3.8 min (with). A significantly greater swing in peak pressure (maximum pressure measured within the facepiece of respirator), however, from inspired (PPi) to expired (PPe) occurred with the respirator (13.42 cmH2O) than without the respirator (9.25 cmH2O).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

A method for predicting the cranio-caudal position of secondary embryonic structures.

The morphogenetic events that give rise to a specific body pattern have to date avoided extensive elucidation. Extant models of pattern formation have dealt almost exclusively with the "primary patterning" of structures in the embryo. These "universal" models fail to explain many morphological conditions, such as the simultaneous change in position of the limbs, celom, mesonephros, and umbilical artery relative to the somites as a result of a single mutation. In the present paper, we propose that the relation between two non-periodic waves may function to determine the position of "secondary structures", such as the limbs, in the embryo, relative to primary structures such as the somites. We propose that if two morphogenetic events are initiated at different times from the same region of the embryo, and are progressing in a cranio-caudal sequence at different rates, then the location of a given structure along the body axis can be described as a function of the two events. Applications and predictions based on the proposal are presented. Evidence from observations of morphogenetic events in the chick embryo, which tend to support the model, are also presented.

Animals↗
PubMed1988

Institutional screening for the fragile X syndrome.

Cytogenetic screening of mentally retarded patients for the fragile X (fra[X]) chromosome is helpful in identifying individuals who could benefit from genetic counseling and treatment. Previous studies have demonstrated a prevalence of the fra(X) syndrome as high as 6% in institutionalized retarded males. The physical and behavioral predictors of positive findings from cytogenetic testing have not been clarified, since many features of the fra(X) syndrome are found in other retarded populations. We performed physical and cytogenetic examinations on 440 patients at the Wheat Ridge (Colo) Regional Center. Twenty-eight (6.3%) demonstrated abnormal karyotypes. Seventeen of these were autosomal abnormalities or sex chromosome aneuploidies and 11 demonstrated the fra(X) chromosome (seven males, four females). In males, the physical features that were predictive of the fra(X) syndrome included the combination of ear lengths of 7.0 cm or greater, macroorchidism of 30 mL or greater, and the presence of hand calluses or lesions secondary to hand biting. The fra(X) chromosome was not seen in spastic quadriplegic patients. All seven males with the fra(X) syndrome were detected among the 141 ambulatory males who resided in the highest functioning units at this institution.

Adolescent↗
PubMed1986

Autism, mental retardation, and chromosomal abnormalities.

There are reports of sex chromosomal abnormalities including XXY, XYY, and fragile X karyotypes in autistic individuals, but structural autosomal defects have rarely been reported. This paper presents four patients with autism, mental retardation, minor dysmorphic features, and structural autosomal defects. These patients shared autistic features including fascination with inanimate objects, catastrophic reactions to changes in their environment or their daily routine, echolalia, and poor relatedness; IQ scores indicate mild to severe retardation. Their autosomal abnormalities included inversion/duplications of 3p and 16q, 5p+, and 17p-. Parental chromosomes were all normal. Chromosomal analysis should be performed on mentally retarded, autistic individuals, especially those with minor physical anomalies and no specific etiology for their retardation.

Adolescent↗
PubMed1981

The physiological responses of mild pulmonary impaired subjects while using a "demand" respirator during rest and work.

This investigation determined the cardiorespiratory responses of subjects with normal lung function and exercise tolerance and compared them with subjects with moderate and severe impairment of lung function and exercise tolerance. Comparisons were made during work while wearing an industrial respirator. The respirator was a full-face mask (MSA-ultravue) "demand" breathing type equipped with an inspiratory resistance of 85 mm H2O at 85 L/min air flow and an expiratory resistance of 25 mm H2O at 85 L/min air flow. Physiologically and subjectively the response of the normal and moderately impaired subjects to respirator wear during rest, 35%, 50% and 63% of their maximal workloads were not different. However, when the moderately impaired worked at 63% of their maximum the workload was equivalent to 50% of maximum of the normal subject. Significant differences in the peak flow/pressure ratio of the severely impaired compared to the normals and moderately impaired were found. By relating work performance to the dyspnea index (VI/MBC) it was suggested that the relationship between maximal lung function and maximal work performance needs to be identified both with and without respirators. This relationship may prove suitable in predicting performance during respirator wear.

Adult↗
PubMed1975

The steepness of the dose response curve both for tumor cure and normal tissue injury.

At the Christie Hospital in Manchester, 4 MeV radiation was introduced in 1955. In consequence of a lack of knowledge of absolute dose definition and R.B.E. factor, patients were treated over a range of dosage. Three hundred fourteen patients with laryngeal cancer, treated over a time interval of three weeks, received doses over a range of 5,000 rad to 5,800 rads. Recurrence, morbidity and necrosis rates are plotted against dose. In T1 tumors there is very little variation in recurrence rate, and such tumors may be safely treated at the lower doses thus avoiding morbidity and necrosis. T3 tumors, however, show a considerable variation in recurrence rate being 68 percent at the lower end of the range, dropping to 30 percent at the high end. Necrosis nil at the lower end rises to some 8 percent at the high end. The balance of advantage of tumor sterilization versus the disadvantage of normal tissue damage is discussed.

Dose-Response Relationship, Radiation↗
PubMedDate not supplied

Speech disturbances (cluttering) in mildly impaired males with the Martin-Bell/fragile X syndrome.

The language characteristics of fra(X) males (n = 10) with an IQ greater than or equal to 70 were evaluated. Language testing demonstrated relatively stronger receptive vocabulary skills compared to weak auditory memory and processing skills. A characteristic speech and language disturbance, cluttering, was present in 9 of the 10 study patients. Their speech was characterized by a fast and fluctuating rate of speech, and repetitions of sounds, words or phrases. Other aspects of cluttering including attentional problems, hyperactivity, motor delays and reading difficulties are commonly seen in the fra(X) syndrome. Cluttering may be helpful in identifying the fra(X) syndrome in a male who is not retarded.

Child↗