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Biomedical subjects

M I Lewis

Publications and source records attributed to M I Lewis.

At least 19 recordsLinked to original sources
PubMed1992

Effect of corticosteroids on diaphragm fatigue, SDH activity, and muscle fiber size.

The influence of dexamethasone on diaphragm (DIA) fatigue, oxidative capacity, and fiber cross-sectional areas (CSA) was determined in growing hamsters. One group received dexamethasone by daily subcutaneous injection for 21 days (D animals), while pair-weight (P) and free-eating controls (CTL) received saline subcutaneously. Isometric contractile properties of the DIA were determined in vitro by supramaximal direct muscle stimulation in the presence of curare. DIA fatigue resistance was determined through repetitive stimulation at 40 pulses/s for 2 min. A computer-based image-processing system was used to histochemically determine muscle fiber-type proportions, CSA, and succinate dehydrogenase activities. The medial gastrocnemius muscle (MG) was used as a limb muscle control, with histochemical studies being performed on both the superficial (s) and deep/red (r) portions. Dexamethasone markedly attenuated the normal increment in body weight over the 3-wk period. DIA fatigue resistance was significantly reduced in the D compared with CTL and P animals. Dexamethasone had no effect on fiber-type proportions of the DIA or MGr (MGs contained only type II fibers). In the DIA, the CSA of type II fibers was reduced 33% in D and 18.5% in P animals compared with CTL. Although no significant atrophy was noted in the type I DIA fibers of either D or P animals, a trend toward significance was noted in D animals compared with CTL. In the MGs, the CSA of type II fibers was reduced 33% in D and 16.5% in P animals compared with CTL. Significant atrophy of type I and II fibers of the MGr was noted in D animals compared with CTL (33.8 and 35% reductions, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Adaptations of the diaphragm in emphysema.

In adult male hamsters the influence of emphysema (EMP) on the in vitro contractile and fatigue properties and the histochemical, morphometric, and metabolic properties of muscle fibers in the costal diaphragm was determined 6 mo after the administration of either elastase or saline (controls, CTL). Isometric contractile properties were determined in vitro using supramaximal direct muscle stimulation. Optimal fiber length for force generation was significantly shorter in the EMP than in the CTL diaphragm. Maximum specific force (i.e., force per unit area) was 25% lower than CTL. Fatigue resistance was significantly improved in the EMP diaphragm compared with CTL. Diaphragm muscle fibers were classified as type I or II on the basis of histochemical staining for myofibrillar adenosinetriphosphatase after alkaline preincubation. The proportions of type I and II fibers were similar between the two groups. Cross-sectional areas of type II fibers were 30% larger in EMP than in CTL diaphragms. Succinate dehydrogenase activities of both type I and II fibers were higher in EMP than in CTL diaphragms. The number of capillaries surrounding both type I and II fibers increased with EMP, but in proportion to the hypertrophy of these fibers. Thus, capillary density (number of capillaries per fiber cross-sectional area) remained unchanged. We postulate that these contractile, morphometric, and metabolic adaptations reflect an increased activation of the diaphragm in response to the loads imposed by EMP.

Adaptation, Physiological↗
PubMed1992

Effect of acute nutritional deprivation on diaphragm structure and function in adolescent rats.

The influence of 90 h of acute nutritional deprivation (ND; water ad libitum only) on in vitro contractile and fatigue properties, muscle fiber type proportions, and cross-sectional areas (CSA) of the adolescent rat diaphragm was determined. Diaphragm muscle properties in the ND rats were compared with those in control rats (CTL; food and water ad libitum). Acute ND resulted in a 32% reduction in body mass, whereas the body mass of CTL rats increased by 29%. Acute ND resulted in a significant reduction in the mass of the diaphragm (costal, 36%; crural, 43%), soleus (36%), and medial gastrocnemius (45%) muscles. Isometric twitch characteristics of the diaphragm muscle (contraction and half-relaxation times) were prolonged in the ND animals. Peak twitch and maximum tetanic forces were unaffected by ND. Fatigue resistance of the diaphragm muscle was improved in ND animals. Diaphragm muscle fiber type proportions were similar in ND and CTL groups. The CSA of type I and II diaphragm muscle fibers were reduced by 22 and 40%, respectively, in ND animals compared with CTL. We conclude that, whereas an identical protocol of acute ND had no significant effects on diaphragm muscle structure and function in adult rats, adolescent animals exhibit significantly less nutritional reserve. These differences may be due to curtailment of the rapid anabolic rate in growing animals.

Acute Disease↗
PubMed1992

Aging and mental health: primary care of the healthy older adult. A roundtable discussion: Part I.

Dementia, depression, alcoholism, and suicide are some of the most important mental health issues for the aging population. Among the factors that affect the physician's ability to evaluate and manage these disorders are drug-induced side effects, the ability and willingness of patients to communicate their feelings, the level of caregiver cooperation, and limitations imposed by federal regulations and reimbursement policies. In this first of three installments of a panel discussion, experts in geriatrics and geropsychiatry discuss healthy aging, age-related memory and sensory loss, changes in mentation postanesthesia, sexuality in the elderly, and side effects of common psychoactive medications.

Aged↗
PubMed1992

Aging and mental health: diagnosis of dementia and depression.

In this second segment of a panel discussion on aging and mental health, panelists focus on the primary care evaluation and management of the patient with dementia, including differential diagnosis of depression. Other topics of discussion include the roles of psychiatric referral and psychotherapy in patient management, suicide prevention, and alcoholism in elderly patients.

Aged↗
PubMed1990

Effect of acute nutritional deprivation on diaphragm structure and function.

The influence of 90 h of acute nutritional deprivation (ND) on the cross-sectional areas of muscle fibers and the contractile and fatigue properties of the adult rat diaphragm were determined. Isometric contractile properties and fatigue resistance of the diaphragm were measured by means of an in vitro nerve-muscle strip preparation. Contractions were evoked by using phrenic nerve stimulation (left hemidiaphragm) or direct muscle stimulation (right hemidiaphragm) in the presence of curare. Acute ND resulted in a 20% reduction in body weight. No significant decrements in diaphragm or soleus weights were noted in the ND animals compared with controls (CTL), whereas the weight of the medial gastrocnemius was reduced by 20% in the ND animals. Peak twitch and tetanic tensions (normalized for the weight of the diaphragm strip) were not reduced in ND compared with CTL animals after either nerve or muscle stimulation. The fatigue index of the diaphragm was significantly reduced in ND animals only after nerve stimulation. After the fatigue test, there was rapid recovery of the additional fatigue noted with nerve stimulation. The proportions of type I and II muscle fibers of the diaphragm were similar in the CTL and ND animals. No differences in diaphragm cross-sectional areas were noted for either type I or II muscle fibers in the CTL and ND animals. It is concluded that acute ND has no effect on diaphragm contractility or morphometry and only an inconsequential influence on diaphragm fatigue.

Animals↗
PubMed1989

Effects of undernutrition on diaphragm fiber size, SDH activity, and fatigue resistance.

The influence of prolonged nutritional deprivation on the succinate dehydrogenase (SDH) activity and cross-sectional areas of individual fibers in the rat diaphragm and deep portion of the medial gastrocnemius (MGr) muscles was determined. Fatigue resistance of the diaphragm was measured by means of an in vitro nerve-muscle strip preparation. Fiber SDH activity and cross-sectional area were quantified by means of an image processing system. Diaphragm fatigue resistance was significantly improved in the nutritionally deprived (ND) group. In both muscles, nutritional deprivation resulted in a significant decrease in fiber cross-sectional area (both type I and II), type II fibers showing greater atrophy. The SDH activities of type I and II fibers in the diaphragm were not affected by nutritional deprivation. This contrasted with a significant decrease in the SDH activity of both type I and II fibers in the MGr of ND animals. An assessment of the interrelationships between fiber atrophy and fiber SDH activity revealed a greater effect of malnutrition on those diaphragm type II fibers that had the lowest relative SDH activities and the largest cross-sectional areas. By comparison, the effect of malnutrition on type I and II fibers in the MGr was nonselective with regard to fiber SDH activity. We conclude that the enhanced diaphragm fatigue resistance in the ND animals does not result from an increase in the oxidative capacity of muscle fibers and is best explained by the pattern of diaphragm muscle fiber atrophy.

Animals↗
PubMed1988

The value of bronchial washings and bronchoalveolar lavage in the diagnosis of lymphangitic carcinomatosis.

This study examines the value of bronchoalveolar lavage (BAL) in diagnosing lymphangitic carcinomatosis. A retrospective analysis of fiberoptic bronchoscopic records at a tertiary referral hospital was performed. Twelve patients with neoplastic disease and diffuse pulmonary infiltrates compatible with lymphangitic carcinomatosis who underwent diagnostic fiberoptic bronchoscopy were identified. Bronchoalveolar lavage correctly identified five (100 percent) out of five patients, bronchial washings identified four (57 percent) of seven patients and either procedure identified nine (75 percent) of 12 patients. Bronchial brushings were positive in two (40 percent) of five patients, and transbronchial lung biopsy confirmed the diagnosis in only four (44 percent) of nine patients. Transbronchial lung biopsy was uniquely positive in only one patient. One patient had a significant pulmonary hemorrhage following transbronchial lung biopsy, while no complications of BAL occurred. Two patients had significant coagulopathy, and one patient was severely agitated precluding transbronchial lung biopsy, and all three were positive by BAL. This study suggests that BAL should be performed to confirm the diagnosis of lymphangitic carcinomatosis before proceeding to a biopsy, especially when the risks of pneumothorax and hemorrhage are excessive.

Adult↗
PubMed1988

Nutrition and the respiratory muscles.

Malnutrition may be an important complicating factor in acute and chronic lung disease. Animal studies have demonstrated significant atrophy of diaphragm muscle fibers following prolonged undernutrition resulting in a marked reduction in diaphragm muscle strength as well as alteration in other contractile and fatigue properties of the muscle. In severe chronic obstructive pulmonary disease (COPD), malnutrition is common and may, in conjunction with the influences of hyperinflation on diaphragm performance, predispose to respiratory muscle fatigue and failure. The course of progressive weight loss in patients with COPD is not known but may, in part, be related to a "hypermetabolic" state arising from an increased oxygen consumption of the respiratory muscles secondary to enhanced resistive loads and impaired mechanical efficiency of the respiratory muscles. Reports of the impact of nutritional repletion on respiratory muscle performance in critically ill patients, as well as in patients with COPD, are preliminary. Further studies are necessary to establish whether such measures impact meaningfully on both the morbidity and mortality of these patients.

Animals↗
PubMed1987

Nutritional supplementation in ambulatory patients with chronic obstructive pulmonary disease.

We examined the effect of nutritional supplementation for 8 wk on respiratory muscle function (RMF) in 21 malnourished patients with COPD. Patients were randomized to a fed group or to a control group. Patients in the fed group were provided with an enteral formula in addition to their usual diet. Daily calorie and protein intake and weekly anthropometric measures were made. Pulmonary function tests were measured on Weeks 1, 4, and 8. Respiratory muscle strength was measured by means of maximal inspiratory and expiratory pressures (MIP), (MEP), and respiratory muscle endurance was measured by the maximal sustained ventilatory capacity (MSVC). The mean weight of the fed group increased from 52.2 +/- 6.4 to 53.3 +/- 6.9 kg (NS). The mean daily caloric intake of the fed group was significantly increased during the study (p less than 0.02). The mean calorie intake during the study of the fed group was 174 +/- 17% of the estimated basal energy expenditure. During the study period, no change was observed in anthropometric measures, pulmonary function studies, or RMF. Because patients tend to decrease their own food intake while receiving enteral formulas, it is difficult to provide sufficient calories and protein needed to effect changes in nutritional status and RMF in an outpatient COPD population. In addition, we compared RMF in 12 poorly nourished male patients (87.6 +/- 6.1% of ideal body weight) and 13 well-nourished male patients with severe COPD. Both groups had comparable degrees of air-flow limitation and hyperinflation. No difference was noted between the groups in either MIP, MEP, or MSVC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Oxygen conservation and oxygen-conserving devices in chronic lung disease. A review.

The efficacy of long-term oxygen therapy for hypoxemic COPD patients is well established. However, oxygen is expensive and the portability of home oxygen is limited by the weight and bulk of the oxygen source. As a result, there has been a recent surge of interest in creating oxygen-conserving devices and methods. The efficiency of oxygen therapy can be improved over steady flow delivery by focusing oxygen delivery to early inspiration. Three methods for improving oxygen delivery efficiency--transtracheal catheter, reservoir cannula and demand-pulse oxygen delivery--are currently available for patient use. Each has its own set of advantages and disadvantages. By using oxygen conservation methods, the oxygen required to achieve adequate blood oxygenation can be reduced by a factor of 2:1 to 7:1 compared to steady flow. Thus, the cost of oxygen can be substantially reduced while increasing the portability and range of home oxygen therapy.

Costs and Cost Analysis↗
PubMed1986

Subjective comfort vote and air temperature as predictors of performance in factory workers.

Volunteer factory workers performed a series of tests in a mobile climate laboratory. The tests simulated factory skills and were performed at 6 degrees, 12 degrees, 18 degrees or 24 degrees C at low vapour pressures. At each temperature four groups of about 30 workers were tested: black men, and women and white men and women. A first order polynomial was used to fit the data for temperature and comfort vote. The comfort vote predicted about 6% of performance, temperature about 11%. On some manual tasks air temperature predicted more than 40% of performance. There were few differences between the groups.

Climate↗
PubMed1986

Effect of nutritional deprivation on diaphragm contractility and muscle fiber size.

The influence of nutritional deprivation on the contractile and fatigue properties of the diaphragm was studied in adult rats. Food access was restricted to one-third of normal daily intake until the body weight of nutritionally deprived (ND) animals was approximately 50% of controls (CTL). Isometric contractile properties were studied in an in vitro nerve muscle strip preparation. Both twitch (Pt) and tetanic (Po) tensions of diaphragms from the ND animals were markedly reduced compared with CTL; however, Pt/Po was higher for the ND group. The shape of the force-frequency curve (normalized to Po) was generally similar between the two groups, except at 5 and 10 pulses/s stimulation, where greater relative tensions were produced in diaphragms from the ND animals. Diaphragm fatigue was induced by repetitive stimulation at either 20 or 100 pulses/s. Endurance time (defined as the time required for tension to fall to 50% of initial) of diaphragms from ND animals was prolonged at both 20 and 100 pulses/s. Immediately after induction of fatigue, force-frequency curves for both ND and CTL diaphragms were shifted to the right. However, this rightward shift was attenuated in the ND group compared with CTL. Nutritional deprivation had no effect on the proportions of different fiber types within the diaphragm but did result in a significant decrease in the cross-sectional area of both fast-and slow-twitch fibers. This decrease in cross-sectional area was significantly greater for fast-twitch fibers. We conclude that these changes in diaphragm contractile and fatigue properties occur as a result of the influence of malnutrition on muscle fiber cross-sectional area.

Animals↗
PubMed1986

Aminophylline and fatigue of the sternomastoid muscle.

We examined the influence of intravenously infused aminophylline on the contractility of the sternomastoid muscle in 8 subjects. The muscle was stimulated directly using bipolar surface electrodes at 1, 10, 20, and 50 pulses per second (pps), and the force response was recorded. The ratio of force produced at 20 pps and 50 pps (20/50 ratio) was calculated. The effect of aminophylline on the 20/50 ratio was assessed at 2 dosages producing different blood serum levels (10.7 mg/L and 15.3 mg/L). At the lower dosage of aminophylline the potential prophylactic and curative influence of aminophylline was tested using 3 different experimental paradigms performed on separate days: (1) Baseline force frequency responses were determined before and 15 and 35 min after a headlifting maneuver; headlifting resulted in a decrease in the 20/50 ratio (low frequency fatigue). (2) The same sequence as in (1), with the addition of a continuous infusion of aminophylline started after the baseline force frequency responses. (3) The same sequence as in (1) except that the aminophylline infusion was begun only after the headlifting maneuver. After the fatiguing maneuvers, there were comparable and significant falls in the 20/50 ratio on all experimental days. The infusion of aminophylline did not significantly affect the baseline 20/50 ratio. In addition, aminophylline did not prevent the fatigue-related decrease in the 20/50 ratio or enhance its recovery. Experimental paradigms 1 and 2 were repeated at the higher aminophylline levels. Again, aminophylline did not prevent or reverse sternomastoid fatigue. We conclude that aminophylline in therapeutic dosages does not prevent or reverse low frequency fatigue of the sternomastoid muscle.

Adult↗
PubMed1986

Resistive breathing training in patients with chronic obstructive pulmonary disease.

In order to investigate the effect of resistive breathing training on ventilatory muscular endurance, we examined the maximal sustained ventilatory capacity in ten patients with chronic obstructive pulmonary disease (COPD) before and after a six-week program of resistive breathing training. In addition, we investigated the effect of altered breathing strategy on resistive breathing performance. The patients performed two 15-minute sessions of resistive breathing daily for six weeks using an inspiratory resistive device (Pflex). Before and after the training, we found no significant change in spirometric data, pulmonary volumes, maximal inspiratory pressure, and maximal expiratory pressure. Of the ten patients, seven failed to show an improvement in their performance of resistive breathing. Furthermore, the maximal sustained ventilatory capacity was unchanged after the resistive breathing training. After the completion of the training program, seven of the patients participated in an additional experiment in which they were instructed to take long slow inspirations while breathing through the resistive device. With this change in breathing pattern, five of the seven were able to improve their performance of resistive breathing. Analysis of the breathing strategy showed that a reduction in the peak mouth pressure, breathing frequency, and external resistive work with a longer inspiratory time was beneficial. We conclude that neither resistive breathing performance nor ventilatory muscular endurance, as measured by sustained hyperpnea, is improved by resistive breathing training performed according to the current instructions with the resistive device, and alterations in breathing strategy have a profound effect on the performance of resistive breathing. The lack of details of breathing strategy in previous studies of resistive breathing makes it difficult to determine if previously demonstrated improvements were due to a real enhancement of ventilatory muscular performance or merely secondary to a different strategy.

Aged↗