Biomedical subjects

W H Martin

Publications and source records attributed to W H Martin.

At least 55 records · Page 3Linked to original sources

PubMed1994

New techniques of hearing assessment.

This article reviews current literature in the areas of otoacoustic emissions and auditory brain stem responses (ABRs) and their application to the evaluation of peripheral auditory function in infants and children. The different types of otoacoustic emissions are described along with their incidence, development, clinical applications, and interpretation in the pediatric group. The development of the auditory system, reflected by ABRs, is presented in detail with previously unpublished results from three-channel Lissajous' trajectory studies performed in infants. Clinical application of frequency-specific ABRs, both air and bone conducted, are presented. Finally, a discussion of the need to develop objective estimators of signal quality and threshold detection for otoacoustic emissions and ABRs in infants and children is presented, which includes previously unpublished results evaluating a new technique.

Auditory Perception↗

PubMed1993

Triiodothyronine, beta-adrenergic receptors, agonist responses, and exercise capacity.

Although thyroid hormone excess results in increased beta-adrenergic receptor density or agonist responses in some cells of experimental animals, the role of these effects in contributing to clinical manifestations of hyperthyroidism in human subjects is unclear. To shed further light on this issue, we characterized the effect of 2 weeks of excess triiodothyronine administration on cardiac and metabolic responses to graded-dose isoproterenol infusion, skeletal muscle beta-adrenergic receptor density, and physiologic determinants of exercise capacity in young healthy subjects. The slope of the heart rate response to isoproterenol was 36% greater (p < 0.05) after triiodothyronine administration. In addition, beta-adrenergic receptor density was increased (p < 0.01) in all types of skeletal muscle fibers. Maximal oxygen uptake during treadmill exercise declined 5% (p < 0.001) after triiodothyronine administration because of a decrease in the arteriovenous oxygen difference (p < 0.05). The plasma lactate response to submaximal exercise was 25% greater (p < 0.01) in the hyperthyroid state. These effects were paralleled by a decrement in skeletal muscle oxidative capacity and a decrease in cross-sectional area of type 2A skeletal myocytes. Thus, thyroid hormone excess enhances cardiac beta-adrenergic sensitivity under in vivo conditions in human subjects. Nevertheless, exercise capacity is diminished in the hyperthyroid state, an effect that may be related to reduced skeletal muscle oxidative capacity and type 2A fiber atrophy.

Adult↗

PubMed1993

Noninvasive detection of Chlamydia trachomatis in men: a comparison of two immunoassay tests.

This investigation compared a rapid enzyme immunoassay test and an enzyme-amplified immunoassay test with culture for the noninvasive detection of Chlamydia trachomatis urethritis in men. Urine specimens from 108 male subjects were evaluated for the presence of C trachomatis antigen, using the Kodak Surecell Chlamydia rapid enzyme immunoassay test and IDEIA Chlamydia enzyme-amplified immunoassay test. The test results were then compared with urethral C trachomatis culture and urethral Gram's stain analyses. Performance characteristics of the two tests were similar. The rapid chlamydial enzyme immunoassay test demonstrated several clinical advantages. Appropriate use of these tests may decrease patient morbidity and clarify organism etiology for enhanced specific medical care of urethritis in men.

Adult↗

PubMed1993

Effect of endurance training on plasma free fatty acid turnover and oxidation during exercise.

Plasma free fatty acid (FFA) levels tend to be lower and the plasma lipolytic hormone response to prolonged exercise of the same intensity is blunted after endurance exercise training. To determine whether training elicits a corresponding decrease in plasma FFA turnover and metabolism during prolonged exercise, we measured plasma [1-13C]palmitate kinetics and oxidation and respiratory gas exchange in 13 subjects during the latter portion of a 90- to 120-min bout of cycle ergometer work performed before and after 12 wk of alternate-day cycling and running. Training increased total fat oxidation during prolonged exercise by 41% (P < 0.005). However, for the final 30-60 min of the cycle ergometer protocol, the rate of 13CO2 production from [1-13C]palmitate oxidation was 27% lower (P < 0.05), the rate of palmitate turnover was 33% less (P < 0.05), and plasma FFA and glycerol concentrations were 32 and 20% lower (P < 0.05), respectively, than in the untrained state. Thus endurance exercise training results in decreased plasma FFA turnover and oxidation during a 90- to 120-min bout of submaximal exercise because of a slower rate of FFA release from adipose tissue.

Adult↗

PubMed1993

Differences in cardiovascular adaptations to endurance exercise training between older men and women.

Recent studies have shown that people in their seventh decade are able to adapt to exercise training with an increase in maximal O2 uptake (VO2max) similar in relative magnitude to that observed in young people. The purpose of this study was to determine the relative contributions of increases in stroke volume and O2 extraction to the training-induced increase in VO2max in older men and women. Fifteen men [63 +/- 3 (SE) yr] and 16 women (64 +/- 3 yr), in good health, participated in 9-12 mo of endurance exercise training at 70 to 85% of maximal heart rate for 45 min/day, 4 days/wk. VO2max increased 19% (2.35 +/- 0.1 to 2.8 +/- 0.1 l/min; P < 0.01) in the men and 22% (1.36 +/- 0.1 to 1.66 +/- 0.1 l/min; P < 0.01) in the women in response to training. In the men, stroke volume during maximal exercise was 15% higher after training, and this increase accounted for 66% of the increase in VO2max. The remainder of the increase in VO2max was accounted for by a 7% greater arteriovenous O2 content difference during maximal exercise. In contrast, training resulted in no change in stroke volume in women, in whom the entire increase in VO2max was accounted for by a greater arteriovenous O2 content difference (12.2 +/- 0.4 before vs. 14.4 +/- 0.4 ml O2/100 ml blood after; P < 0.01) during maximal exercise. There were no changes in these variables in the control subjects. The mechanisms responsible for the training-induced increase in VO2max in the older men were similar to those found in young people.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1993

Salicylate-induced changes in cat auditory nerve activity.

The purpose of this study was to measure, in the cat, spontaneous auditory nerve (AN) activity before and after injection with sodium salicylate. Ten cats were anesthetized, and the AN and round window (RW) were surgically exposed. Electrodes were applied to allow recording from three channels, including bipolar electrodes and monopolar electrodes located directly on the auditory nerve, in addition to an RW electrode. Spectral averaging of the spontaneous activity was performed before and during salicylate treatment. An increase in spectral activity near 200 Hz was noted in all cats by 3 hours after salicylate injection. This activity was present in bipolar, monopolar, and RW records, and was temporarily diminished or eliminated by injection of lidocaine. No such spectral changes were found in saline-injected control animals. These results show promise of developing a noninvasive, objective, quantitative measure of tinnitus for studies in animals and in man.

Animals↗

PubMed1993

Bipolar cochlear nerve recording technique: a preliminary report.

To preserve hearing during vestibular neurectomy and acoustic neuroma removal, the cochlear nerve must be identified. Present techniques, including monitoring eighth nerve action potentials, help the surgeon identify those maneuvers that increase the risk of nerve injury but do not help in the anatomic identification of the cochlear nerve or the cochlear-vestibular cleavage plane. The purpose of this study was to demonstrate an electrophysiologic method of identifying the cochlear portion of the eighth cranial nerve. A flush-tipped, bipolar electrode recording probe was used to directly record responses to monaural click stimuli from the cochlear nerve but not from surrounding tissue. It was also used to delineate the cochlear-vestibular cleavage plane. Stimulus intensity levels over 25 dB sensation level tended to reduce the accuracy of nerve identification, and lower levels prolonged recording time. This technique and its application to posterior fossa surgery is discussed.

Adolescent↗

PubMed1992

Contralateral effects of cerebello-pontine angle exposure on human auditory brain-stem evoked potentials.

Auditory brain-stem evoked potentials (ABEPs) were recorded during surgical procedures which exposed the cerebello-pontine angle (CPA) in humans. Recordings made with the CPA contralateral to stimulus exposed were compared with those obtained with the skin sutured at the end of surgery. Single-channel as well as 3-channel Lissajous' trajectory (3-CLT) analyses were used to evaluate the effect of the surgical exposure on ABEP. The results suggest that exposure of the CPA contralateral to the stimulated ear did not affect dipole equivalent orientation nor magnitude, but did affect timing of the recorded activity being more pronounced for segments 'd'-'e' (corresponding to waves IV-V) than for 'a'-'b' (waves I-II). The results imply that the effects of disrupting the volume conductor may have been overwhelmed by other effects, such as local temperature changes. These changes, although not associated with clinical sequella, should be accounted for when analyzing subtle quantitative changes involving surgical exposures.

Acoustic Stimulation↗

PubMed1992

Effect of hyperthyroidism of short duration on cardiac sensitivity to beta-adrenergic stimulation.

The effect of hyperthyroidism on cardiac sensitivity to beta-adrenergic stimulation in humans is controversial. To determine whether heart rate and left ventricular contractile sensitivity to beta-adrenergic stimulation are altered by hyperthyroidism in human subjects, the frequency, velocity and extent of left ventricular shortening at rest and during a 4-stage graded dose isoproterenol infusion were characterized in eight young healthy subjects before and after 2 weeks of daily administration of 100 micrograms of triiodothyronine (T3). The rate and extent of left ventricular shortening were determined by Doppler and two-dimensionally guided M-mode echocardiography. In the hyperthyroid state, heart rate at rest was faster (57 +/- 3 vs. 68 +/- 4 beats/min; p less than 0.001) and the slope of the relation of heart rate to the rate of isoproterenol infusion was 36% steeper (1,538 +/- 126 vs. 1,131 +/- 95; p less than 0.05). The left ventricular ejection time was shorter and the mean velocity of left ventricular circumferential fiber shortening (mVcf) was greater during all stages of isoproterenol infusion in the hyperthyroid versus the euthyroid state (p less than 0.01). After adjustment for the faster heart rate after T3 administration, left ventricular ejection time and mVcf were similar in the euthyroid and hyperthyroid states at baseline and during maximal beta-adrenergic stimulation but shortened and enhanced, respectively, during stages 1 and 2 of isoproterenol infusion (p less than 0.05). There was no effect of T3 administration on left ventricular mass, dimensions, end-systolic wall stress or stroke volume at rest or during any stage of isoproterenol infusion. These results indicate that in human subjects hyperthyroidism of short duration increases the sensitivity of heart rate and left ventricular shortening velocity to beta-adrenergic stimulation in the absence of changes in left ventricular mass, loading conditions or extent of shortening.

Administration, Oral↗

PubMed1992

Skeletal muscle beta-adrenoceptor distribution and responses to isoproterenol in hyperthyroidism.

To determine whether hyperthyroidism selectively increases beta-adrenergic receptor density in vessels or fibers of human skeletal muscle, we characterized beta-receptor distribution autoradiographically in muscle biopsies of 18 subjects aged 26 +/- 1 yr before and after daily administration of 100 micrograms 3,5,3'-triiodothyronine (T3) for 2 wk. To establish whether vascular and metabolic responses to beta-adrenergic stimulation are concomitantly altered, we quantified calf blood flow and plasma concentrations of glucose, lactate, glycerol, free fatty acids (FFA), insulin, and C-peptide during graded-dose isoproterenol infusion in eight of these individuals. Differences in beta-adrenergic receptor density among muscle fiber types and vascular components were highly significant (type I greater than type IIa greater than type IIb muscle fibers, P less than 0.001; and type I muscle fibers greater than resistance arterioles, P less than 0.05). Hyperthyroidism increased beta-adrenergic receptor density in all types of muscle fibers (+31-50%; P less than 0.01) but not in resistance arterioles. There was no change in calf blood flow or plasma glucose, glycerol, FFA, insulin, or C-peptide responses to isoproterenol. A rise in lactate during stages 3 and 4 of isoproterenol infusion (P less than 0.01) was observed before but not after T3 administration. Thus hyperthyroidism increases beta-adrenergic receptor density in fibers but not vessels of human skeletal muscle without increasing either metabolic or vascular responses to selective beta-adrenergic stimulation.

Adult↗

PubMed1992

Exercise training prevents decline in stroke volume during exercise in young healthy subjects.

Stroke volume (SV) increases above the resting level during exercise and then declines at higher intensities of exercise in sedentary subjects. The purpose of this study was to determine whether an attenuation of the decline in SV at higher exercise intensities contributes to the increase in maximal cardiac output (Qmax) that occurs in response to endurance training. We studied six men and six women, 25 +/- 1 (SE) yr old, before and after 12 wk of endurance training (3 days/wk running for 40 min, 3 days/wk interval training). Cardiac output was measured at rest and during exercise at 50 and 100% of maximal O2 uptake (Vo2max) by the C2H2-rebreathing method. VO2max was increased by 19% (from 2.7 +/- 0.2 to 3.2 +/- 0.3 l/min, P less than 0.001) in response to the training program. Qmax was increased by 12% (from 18.1 +/- 1 to 20.2 +/- 1 l/min, P less than 0.01), SV at maximal exercise was increased by 16% (from 97 +/- 6 to 113 +/- 8 ml/beat, P less than 0.001) and maximal heart rate was decreased by 3% (from 185 +/- 2 to 180 +/- 2 beats/min, P less than 0.01) after training. The calculated arteriovenous O2 content difference at maximal exercise was increased by 7% (14.4 +/- 0.4 to 15.4 +/- 0.4 ml O2/100 ml blood) after training. Before training, SV at VO2max was 9% lower than during exercise at 50% VO2max (P less than 0.05). In contrast, after training, the decline in SV between 50 and 100% VO2max was only 2% (P = NS). Furthermore, SV was significantly higher (P less than 0.01) at 50% VO2max after training than it was before. Left ventricular hypertrophy was evident, as determined by two-dimensional echocardiography at the completion of training. The results indicate that in young healthy subjects the training-induced increase in Qmax is due in part to attenuation of the decrease in SV as exercise intensity is increased.

Adult↗

PubMed1992

Effects of aging, sex, and physical training on cardiovascular responses to exercise.

BACKGROUND: The relative contributions of decreases in maximal heart rate, stroke volume, and oxygen extraction and of changes in body weight and composition to the age-related decline in maximal oxygen uptake (VO2max) are unclear and may be influenced by sex and level of physical activity. METHODS AND RESULTS: To investigate mechanisms by which aging, sex, and physical activity influence VO2max, we quantified VO2, cardiac output, and heart rate during submaximal and maximal treadmill exercise and assessed weight and fat-free mass in healthy younger and older sedentary and endurance exercise-trained men and women. For results expressed in milliliters per kilogram per minute, a three-to-four-decade greater age was associated with a 40-41% lower VO2max in sedentary subjects and a 25-32% lower VO2max in trained individuals (p less than 0.001). A smaller stroke volume accounted for nearly 50% of these age-related differences, and the remainder was explained by a lower maximal heart rate and reduced oxygen extraction (all p less than 0.001). Age-related effects on maximal heart rate and oxygen extraction were attenuated in trained subjects (p less than 0.05). After normalization of VO2max and maximal cardiac output to fat-free mass, age- and training-related differences were reduced by 24-47% but remained significant (p less than 0.05). For trained but not sedentary subjects, maximal cardiac output and stroke volume normalized to fat-free mass were greater in men than in women (p less than 0.05). CONCLUSIONS: A lower stroke volume, heart rate, and arteriovenous oxygen difference at maximal exercise all contribute to the age-related decline in VO2max. Effects of age and training on VO2max, maximal cardiac output, and stroke volume cannot be fully explained by differences in body composition. In sedentary subjects, however, the sex difference in maximal cardiac output and stroke volume can be accounted for by the greater percentage of body fat in women than in men.

Adult↗

PubMed1992

A comparison of three rapid chlamydial tests in pregnant and nonpregnant women.

BACKGROUND: The purpose of this investigation was to evaluate the performance characteristics of three rapid immunoassay tests to detect Chlamydia trachomatis cervicitis. METHODS: Endocervical samples from 506 women were evaluated using the three rapid immunoassay tests and the results were compared with those obtained by an endocervical chlamydial culture. RESULTS: The prevalence of C trachomatis cervicitis was 9.3%. Overall sensitivity and specificity of the Abbott TestPack Chlamydia test were 66.0% and 99.8%, respectively, of the Kodak Surecell Chlamydia test were 85.1% and 99.3%, respectively, and of the Unipath Clearview Chlamydia test were 85.1% and 98.5%, respectively. Pregnancy did not affect test specificity, but did influence sensitivity. The tests ranged from 5% to 22% less sensitive in nonpregnant women. CONCLUSIONS: The results of the investigation establish that the Clearview and Surecell chlamydial immunoassay tests performed well, particularly for pregnant women.

Adult↗

PubMed1991

Effects of chronic and acute exercise on cardiovascular beta-adrenergic responses.

beta-Adrenergic receptor density and responsiveness may be increased in experimental animals by physical conditioning, and the opposite effects have been observed after a single bout of exercise. To determine whether the chronic and acute effects of exercise include similar alterations in cardiovascular function in humans, we characterized heart rate, blood pressure, and distal lower extremity blood flow responses to graded-dose isoproterenol infusion in 15 young healthy subjects before and after exercise training and with and without a single preceding bout of prolonged exercise of either low or high intensity (61 +/- 1 or 82 +/- 1% maximal heart rate). VO2max was increased 18% after exercise training (43.2 +/- 2.7 to 51.1 +/- 3.3 ml.kg-1.min-1; P less than 0.001). Despite a concomitant fall in resting heart rate (59 +/- 3 to 50 +/- 2 beats/min; P less than 0.001), chronotropic and lower extremity blood flow responses to isoproterenol remained unchanged. Similarly, 1 h of acute high-intensity treadmill exercise altered baseline heart rate (58 +/- 4 to 74 +/- 5 beats/min; P less than 0.02), but neither low- nor high-intensity acute exercise influenced heart rate or lower extremity blood flow responses to isoproterenol. In contrast, the systolic pressure response to isoproterenol was blunted after high- but not low-intensity prolonged exercise (P less than 0.02). These data indicate that cardiac chronotropic (primarily beta 1) and vascular (beta 2) adrenergic agonist responses are not altered in humans by training or acute exercise. The systolic blood pressure response to beta-adrenergic stimulation is decreased by a single bout of high-intensity prolonged exercise by mechanisms that remain to be defined.

Adult↗

PubMed1991

Effects of gender, age, and fitness level on response of VO2max to training in 60-71 yr olds.

The adaptive response of maximal aerobic power (VO2max) to endurance exercise training was compared in 53 men and 57 women, aged 60-71 yr. The subjects were healthy and had been sedentary for at least 2 yr. Pretraining VO2max was measured during graded treadmill walking on two occasions. These values were reproducible (24.4 +/- 4.7 vs. 24.4 +/- 4.6 (SD) ml.min-l.kg-1; r = 0.96). Subjects trained primarily by walking and running for 9-12 mo, averaging 3.9 +/- 0.6 days/wk and 45 +/- 5 min/day at 80 +/- 5% of maximal heart rate (HRmax). Average improvement in VO2max (ml.min-1.kg-1) was 24 +/- 12% (range 0-58%). Relative improvement was not significantly different in men and women (26 +/- 12 vs. 23 +/- 12%, ml.min-1.kg-1; 21 +/- 10 vs 19 +/- 10%, l/min). When subjects were divided into three groups by age (60-62, 63-66, 67-71 yr), there were no significant differences among the groups in the relative increase in VO2max (21% vs. 19% vs. 18%, 1/min). Correlation analysis also yielded a nonsignificant relationship between improvement and age (r = -0.13). To examine the effect of initial fitness level on the adaptive response to exercise, pretraining VO2max was correlated with the absolute improvement in VO2max. This relationship was not significant in either men (r = 0.04) or women (r = -0.23). In conclusion, in healthy people aged 60-71 yr, VO2max adapts to endurance exercise training to the same relative extent as in young people, and this adaptation is independent of gender, age, and initial level of fitness.

Adaptation, Physiological↗

PubMed1991

Effects of aging, gender, and physical training on peripheral vascular function.

BACKGROUND: Blood pressure and total peripheral resistance increase with age. However, the effect of age on vasodilatory capacity has not been characterized. METHODS AND RESULTS: To delineate the effects of aging, gender, and physical training on peripheral vascular function, we measured blood pressure during submaximal and maximal treadmill exercise and measured blood pressure, calf blood flow, and calf conductance (blood flow/mean blood pressure) at rest and during maximal hyperemia in 58 healthy sedentary subjects (men aged 25 +/- 5 and 65 +/- 3 years and women aged 27 +/- 5 and 65 +/- 4 years) and in 52 endurance exercise-trained subjects (men aged 30 +/- 3 and 65 +/- 4 years and women aged 27 +/- 3 and 65 +/- 3 years). Systolic and mean blood pressures were higher at rest, during maximal calf hyperemia, and during submaximal exercise of the same intensity in the older than in the younger subjects of the same gender and exercise training status (p less than 0.01). The magnitude of the age-related effect on blood pressure during exercise was greater in women than in men (p less than 0.01). Diastolic blood pressure during submaximal exercise was also higher in the older than in the younger subjects (p less than 0.05) but not in women treated with estrogen replacement. In contrast, systolic and mean blood pressures during submaximal work were lower in physically conditioned subjects than in sedentary age- and gender-matched subjects (p less than 0.05) but not in older women. Increased age was associated with reduced maximal calf conductance in women (p less than 0.01) but not in men. However, calf vasodilatory capacity was higher in trained than in untrained subjects (p less than 0.01), regardless of age and gender. There was a significant inverse relation between maximal calf conductance and systolic, diastolic, and mean blood pressures during submaximal exercise (r = -0.31 to -0.53, p less than 0.01) and a direct relation between maximal calf conductance and maximal oxygen uptake (r = 0.66, p less than 0.0001). CONCLUSIONS: Thus, for healthy subjects between the ages of 25 and 65 years, there is an interactive effect between age and gender and an independent effect of physical training on peripheral vascular function.

Adult↗

PubMed1991

Mechanisms of impaired exercise capacity in short duration experimental hyperthyroidism.

To investigate the mechanism of reduced exercise tolerance in hyperthyroidism, we characterized cardiovascular function and determinants of skeletal muscle metabolism in 18 healthy subjects aged 26 +/- 1 yr (mean +/- SE) before and after 2 wk of daily ingestion of 100 micrograms of triiodothyronine (T3). Resting oxygen uptake, heart rate, and cardiac output increased and heart rate and cardiac output at the same submaximal exercise intensity were higher in the hyperthyroid state (P less than 0.05). However, maximal oxygen uptake decreased after T3 administration (3.08 +/- 0.17 vs. 2.94 +/- 0.19 l/min; P less than 0.001) despite increased heart rate and cardiac output at maximal exercise (P less than 0.05). Plasma lactic acid concentration at an equivalent submaximal exercise intensity was elevated 25% (P less than 0.01) and the arteriovenous oxygen difference at maximal effort was reduced (P less than 0.05) in the hyperthyroid state. These effects were associated with a 21-37% decline in activities of oxidative (P less than 0.001) and glycolytic (P less than 0.05) enzymes in skeletal muscle and a 15% decrease in type IIA muscle fiber cross-sectional area (P less than 0.05). Lean body mass was reduced (P less than 0.001) and the rates of whole body leucine oxidation and protein breakdown were enhanced (P less than 0.05). Thus, exercise tolerance is impaired in short duration hyperthyroidism because of decreased skeletal muscle mass and oxidative capacity related to accelerated protein catabolism but cardiac pump function is not reduced.

Adult↗

PubMed1991

Noninvasive detection of Chlamydia trachomatis urethritis in men by a rapid enzyme immunoassay test.

BACKGROUND: The purpose of this investigation was to evaluate the ability of a rapid enzyme immunoassay test to noninvasively detect Chlamydia trachomatis urethritis in men from a urine specimen. METHODS: Urethral samples and urine from 207 patients were evaluated. Urethral and urine sediment Gram stains, leukocyte esterase dipstick tests, and enzyme immunoassay analyses of centrifuged and uncentrifuged urine were compared with urethral C trachomatis culture. RESULTS: The prevalence of infection in this population was 10.3%. Sensitivity and specificity of the enzyme immunoassay on the centrifuged urine specimen were 70% and 96%, respectively. The positive and negative predictive values were 67% and 97%, respectively. The uncentrifuged urine enzyme immunoassay sensitivity was 35.7% and specificity was 98.9%. Leukocyte esterase test sensitivity compared with that of the Neisseria gonorrhoeae and/or C trachomatis cultures was 83.3%, and specificity was 52%. CONCLUSIONS: The rapid enzyme immunoassay clinically complemented the screening urine sediment Gram stain and the leukocyte esterase test. The judicious use of a noninvasive C trachomatis rapid enzyme immunoassay test to identify organism-specific urethritis may improve patient management of sexually transmitted disease.

Adult↗