Biomedical subjects

N L Jones

Publications and source records attributed to N L Jones.

At least 127 records · Page 7Linked to original sources

PubMed1987

Measurement of cardiac output by CO2 rebreathing in unsteady state exercise.

The ability to determine cardiac output (Q) noninvasively during a nonsteady state (NSS) incremental exercise test was assessed. Seven healthy subjects performed two maximal incremental cycle ergometer exercise tests (100 kpm/min increments every minute), and also steady state exercise (SS) at 25, 50, and 75 percent of their maximum power output. The Q was determined by the indirect CO2 Fick method; mixed venous PCO2 was calculated using the exponential CO2 rebreathing method. No significant differences were observed for the cardiac output/oxygen uptake relationship (Q/VO2) obtained between the two incremental exercise tests. During NSS, the Q/VO2 was linear (r = .89; intercept = 5.69 L/min; slope = 5.39). During the SS, Q/VO2 was linear (r = .90; intercept = 5.47 L/min; slope = 4.87). No significant difference was observed between the SS and NSS Q/VO2 relationships (p greater than 0.05), and the NSS relationship was similar to Q/VO2 values previously reported in the literature. Accurate and reproducible measurements of Q can be obtained noninvasively in healthy subjects using the exponential CO2 rebreathing method during incremental progressive exercise tests, with similar values at comparable VO2 to those obtained in the steady state.

Adult↗

PubMed1987

Musical stimulation in the developmentally delayed child: a pilot study.

Music is a convenient way of bypassing barriers of communication and eliciting responses that may be helpful in the diagnoses and treatment of illness. The use of background music in elevators, in doctors' offices, and in stores are good examples of how music can be used to affect the subconscious mind. In this pilot study drums were used to better define the effects of particular elements of music and sound. When repetitive rhythms are presented as background music to a group of severely developmentally delayed children, three out of four subjects show a definite change in level of development in the unstructured task of free drawing. To discover more about the effects of the various elements of music and to better identify patterns in the environment that are conducive to optimal functioning, further studies are indicated.

Acoustic Stimulation↗

PubMed1986

Activation of human muscle pyruvate dehydrogenase with activity and immobilization.

The activity of pyruvate dehydrogenase (PDH) was measured in samples of triceps muscle obtained in 15 males, before and after immobilization for 5 weeks and 5 months of strength training carried out in random order with cross-over of treatment. Although the total PDH activity was unchanged at 300 nmol min-1 g-1, the proportion in the active form increased after strength training (62 +/- 10.1%) and decreased after immobilization (12 +/- 2.3%) compared with control (36 +/- 3.4%). In six subjects measurements were repeated after 10 min maximal exercise (arm ergometer). The proportion of PDH in the active form increased least after immobilization (to 52 +/- 13.6%), compared with control (95 +/- 11.7%) and post-training (98 +/- 6.6%). After exercise muscle glycogen fell to the greatest extent and lactate rose the least in the post-training state, with opposite findings post-immobilization, suggesting that PDH activation contributes to the control of lactate formation in muscle during heavy exercise, and that the effects of training and immobilization are mediated at least in part through changes in the activation of this regulatory enzyme.

Adult↗

PubMed1986

Influence of muscle power on aerobic performance and the effects of training.

This paper reviews briefly the authors' experience with a short (30 s) maximal isokinetic cycling test in which peak and average power, the decline in power during the test (fatigue index, FI), and the total work accomplished are measured by a computer assisted technique. In an untrained population, the power variables and total work were linearly related to height and lean thigh volume and decline with age; the FI was less in subjects who took part in regular leisure activity. A close linear relationship was found between the total work in 30 s and maximal oxygen intake (VO2 max). The method was applied to studies of the effects of endurance exercise in sedentary young and old men and in patients with coronary artery disease. In the young and old men training increased VO2 max by 28% and 38% respectively, with no change in isokinetic power measurements in the young, but increases of 12% in total work in 30 s in the old. In cardiac patients, reductions in initial VO2 max were greater than in the isokinetic test variables. Control subjects showed reductions in maximal 30 s performance after the study period (12 wk) with no change in VO2 max. Exercised subjects increased VO2 max by 18.5% with variable changes in 30 s performance. There is a close link between maximal short-term muscle capacity and VO2 max in healthy subjects. VO2 max may be increased by training, but this may or may not be accompanied by increases in maximal short-term capacity, presumably depending on the mechanisms that are limiting in any given case.

Adult↗

PubMed1986

Preventive use of exercise rehabilitation after myocardial infarction.

Randomized controlled clinical trials of exercise after myocardial infarction, although difficult to compare, have not shown a reduction in mortality or morbidity. However, physiological and psychological improvements occur that enable patients to improve their quality of life. The effectiveness of exercise programmes is impaired by poor patient compliance. Some characteristics of poor compliers may be identified, but it is safer to assume all participants are potential non-compliers, and to apply compliance-improving strategies within exercise programmes. The authors' experience has indicated that a number of strategies may be followed at little cost. These include a spouse support programme, a written agreement to participate, self-control techniques including self-monitored exercise testing, and group discussion periods.

Evaluation Studies as Topic↗

PubMed1986

Acid-base and respiratory properties of a buffered bovine erythrocyte perfusion medium.

Current research in organ physiology often utilizes in situ or isolated perfused tissues. We have characterized a perfusion medium associated with excellent performance characteristics in perfused mammalian skeletal muscle. The perfusion medium consisting of Krebs-Henseleit buffer, bovine serum albumin, and fresh bovine erythrocytes was studied with respect to its gas-carrying relationships and its response to manipulation of acid-base state. Equilibration of the perfusion medium at base excess of -10, -5, 0, 5, and 10 mmol X L-1 to humidified gas mixtures varying in their CO2 and O2 content was followed by measurements of perfusate hematocrit, hemoglobin concentration, pH, Pco2, Cco2, Po2, and percent oxygen saturation. The oxygen dissociation curve was similar to that of mammalian bloods, having a P50 of 32 Torr (1 Torr = 133.3 Pa), Hill's constant n of 2.87 +/- 0.15, and a Bohr factor of -0.47, showing the typical Bohr shifts with respect to CO2 and pH. The oxygen capacity was calculated to be 190 mL X L-1 blood. The carbon dioxide dissociation curve was also similar to that of mammalian blood. The in vitro nonbicarbonate buffer capacity (delta [HCO3-] X delta pH-1) at zero base excess was -24.6 and -29.9 mmol X L-1 X pH-1 for the perfusate and buffer, respectively. The effects of reduced oxygen saturation on base excess and pH of the medium were quantified. The data were used to construct an acid-base alignment diagram for the medium, which may be used to quantify the flux of nonvolatile acid or base added to the venous effluent during tissue perfusions.

Acid-Base Equilibrium↗

PubMed1986

Effects of alkalosis on skeletal muscle metabolism and performance during exercise.

This study examined the effects of extracellular alkalosis on the metabolism and performance of perfused rat hindlimb muscles during electrical stimulation. Three acid-base conditions were used: control (C, normal acid-base state), metabolic alkalosis (MALK, increased bicarbonate concentration), and respiratory alkalosis (RALK, decreased PCO2). A one-pass system was used to perfuse the hindlimb via the femoral artery for 20 min at rest and during 5 min of tetanic stimulation via the sciatic nerve. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded. Arterial and venous perfusates were periodically sampled for substrate and metabolite measurements, and muscle samples were taken pre- and postperfusion. Peak isometric tensions in C, MALK, and RALK were similar: 3,367 +/- 107, 3,317 +/- 110, and 3,404 +/- 69 g, respectively. The rate of tension decay was also unaffected by alkalosis and represented 78 and 55% of the peak tension following 2 and 5 min of stimulation, respectively. Muscle O2 uptake, glycogen utilization, and total lactate (La-) production were similar following 5 min of stimulation in all conditions. However, alkalosis resulted in an enhanced La- release from working muscle (peak La- release: C, 15.5 +/- 1.1; MALK, 19.7 +/- 1.6; RALK, 18.3 +/- 2.2 mumol/min), and a 15-20% reduction in intramuscular La- accumulation. Alkalosis had no effect on muscle creatine phosphate and ATP concentrations. Thus, in the perfused rat hindlimb, alkalosis was not associated with changes in tetanic force or glycolysis, but La- release from the working muscle was enhanced by increased extracellular pH and bicarbonate.

Alkalosis↗

PubMed1986

Endogenous triacylglycerol utilization by rat skeletal muscle during tetanic stimulation.

An isolated perfused rat hindquarter preparation was used to examine the utilization of endogenous triacylglycerol (TG) during 20 min of electrical stimulation. The sciatic nerve was stimulated with maximal tetanic trains at 0.5 Hz. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and muscle samples were taken pre- and poststimulation. Twenty minutes of stimulation significantly reduced endogenous TG from 6.78 +/- 0.84 to 4.64 +/- 0.64 mumol X g dry wt-1 (32%) in the red gastrocnemius muscle and from 7.70 +/- 0.61 to 6.66 +/- 0.80 mumol X g dry wt-1 (13.5%) in the plantaris muscle. Although TG content decreased by 16% in the soleus (28.2 +/- 5.0 to 23.8 +/- 4.4 mumol X g-1), the change was not significant. Stimulation had no effect on white gastrocnemius TG concentration (6.84 +/- 1.22 to 6.25 +/- 1.41 mumol X g-1). Thus oxidation of TG occurred primarily in muscles with a large proportion of fast-twitch oxidative-glycolytic fibers. Calculations from measurements of muscle energy stores and fuel uptake indicated that up to 62% of the aerobic energy was provided by endogenous TG. Carbohydrate oxidation contributed up to 28% and the remaining 10% may be accounted for by the oxidation of exogenous free fatty acids originating in the perfusate or from hindquarter adipose tissue. The magnitude of the fall in TG concentration in a given muscle was inversely related to the fall in glycogen concentration.

Animals↗

PubMed1986

Muscle power and metabolism in maximal intermittent exercise.

Muscle power and the associated metabolic changes in muscle were investigated in eight male human subjects who performed four 30-s bouts of maximal isokinetic cycling at 100 rpm, with 4-min recovery intervals. In the first bout peak power and total work were (mean +/- SE) 1,626 +/- 102 W and 20.83 +/- 1.18 kJ, respectively; muscle glycogen decreased by 18.2 mmol/kg wet wt, lactate increased to 28.9 +/- 2.7 mmol/kg, and there were up to 10-fold increases in glycolytic intermediates. External power and work decreased by 20% in both the second and third exercise periods, but no further change occurred in the fourth bout. Muscle glycogen decreased by an additional 14.8 mmol/kg after the second exercise and thereafter remained constant. Muscle adenosine triphosphate (ATP) was reduced by 40% from resting after each exercise period; creatine phosphate (CP) decreased successively to less than 5% of resting; in the recovery periods ATP and CP increased to 76 and 95% of initial resting levels, respectively. Venous plasma glycerol increased linearly to 485% of resting; free fatty acids did not change. Changes in muscle glycogen, lactate, and glycolytic intermediates suggested rate limitation at phosphofructokinase during the first and second exercise periods, and phosphorylase in the third and fourth exercise periods. Despite minimal glycolytic flux in the third and fourth exercise periods, subjects generated 1,000 W peak power and sustained 400 W for 30 s, 60% of the values recorded in the first exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

PubMed1986

Breathlessness during exercise with and without resistive loading.

The purpose of this study was to quantify the intensity of breathlessness associated with exercise and respiratory resistive loading, with the specific purpose of isolating the quantitative contributions of inspiratory pressure, length, velocity, and frequency of inspiratory muscle shortening and duty cycle to breathlessness. The intensity of inspiratory pressure was quantified by measurement of estimated esophageal pressure (Pes = pressure at the mouth plus lung pressure), the extent of shortening by tidal volume (VT), and the velocity of shortening by inspiratory flow rate (VI). Six normal subjects underwent five incremental (100 kpm X min-1 X min-1) exercise tests on a cycle ergometer to maximum capacity. The first and last test were unloaded and the intervening tests were performed with external added resistances of 33, 57, and 73 cm H2O X l-1 X s in random order. The resistances were selected to provide a range of pressures, tidal volumes, flow rates, and patterns of breathing. At rest and at the end of each minute during exercise the subjects estimated the intensity of breathlessness (psi) by selecting a number ranging from 0 to 10 (Borg rating scale, 0 indicating no appreciable breathlessness and 10 the maximum tolerable sensation). Breathlessness was significantly and independently related to Pes (P less than 0.0001), VI (P less than 0.0001), frequency of breathing (fb) (P less than 0.01), and duty cycle [ratio of inspiratory duration to total breath duration (TI/TT)] (P less than 0.01): psi = 0.11 Pes + 0.61 VI + 1.99 TI/TT + 0.04 fb - 2.60 (r = 0.83). The results suggest that peak pressure (tension), VI (velocity of inspiratory muscle shortening), TI/TT, and fb contribute independently and collectively to breathlessness. The perception of respiratory muscle effort is ideally suited to subserve this sensation. The neurophysiological mechanism purported is a conscious awareness of the intensity of the outgoing motor command by means of corollary discharge within the central nervous system.

Adult↗

PubMed1986

Breathlessness and exercise in patients with cardiorespiratory disease.

Previous studies have led to the revival of the hypothesis that breathlessness is the perception of respiratory muscle effort and is present when the tension developed by muscles increases, when the muscles are weak, or when both conditions are present simultaneously. Using a category scale, the intensity of breathlessness was measured in 20 subjects (2 normal subjects and 18 patients) undergoing an incremental exercise test (50 to 100 kpm/min) to maximal capacity. The patients were selected to provide a heterogeneous group of pulmonary diseases, obesity, muscular weakness, and cardiac disease, with a wide variability in exercise capacity (250 to 1,900 kpm/min) and severity of dyspnea. Maximal inspiratory pressure (MIP), pleural pressure (Ppl), the extent of shortening of the inspiratory muscles as indicated by the tidal volume expressed as a percent of vital capacity (VT/VC), the rate of shortening as indicated by flow rate, the frequency of contraction as indicated by breathing frequency (fb), and the duty cycle (TI/Ttot) were measured throughout exercise to assess their relative contribution to the intensity of breathlessness. Using multifactorial analysis, the perception of breathlessness was significantly (p less than 0.01) related to the Ppl, inspiratory flow rate (VI), VT/VC, TI/Ttot, and fb. A multiple linear regression equation that included all these variables explained 69% of the variance, with no single factor being identified as uniquely predominant: Breathlessness = 3.0 (Ppl/MIP) + 1.2 (VI) + 4.5 (VT/VC) + 0.13 (fb) + 5.6 TI/Ttot) - 6.2 (R = 0.83). The intensity of effort required to produce a given pressure increases when the muscle is weak, when the velocity of contraction increases, or when the muscle shortens.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Cytoskeletal disruption during human cytomegalovirus infection of human lung fibroblasts.

Human cytomegalovirus (HCMV) infection causes a rapid, progressive disruption of the host cell cytoskeleton that correlates with actin depolymerization. Whole-mount (3D) electron microscopy was used to analyze the cytoskeleton of uninfected and HCMV-infected human lung fibroblast cells. Within 2 min of HCMV infection, localized areas of cytoskeletal disruption were observed. Disruption extended throughout the cytoplasm during the ensuing 45 to 90 min of infection and resulted in generalized cytoskeletal disorganization. Actin depolymerization occurred, as indicated by an increase in DNase I inhibition and alteration in the fluorescence pattern with rhodamine-conjugated phalloidin. Thus, actin appears to be the primary cytoskeletal target involved during HCMV infection. Fractionation of the virus seed inoculum showed that development of DNase I inhibitory activity in infected cells was associated only with the virus-containing fractions. Cytochalasin B treatment at early times of HCMV infection stimulated progeny virus production. This study demonstrates that rapid cytoskeletal disruption occurs during early periods of HCMV infection and indicates that actin depolymerization facilitates viral infectivity.

Actins↗

PubMed1985

How should we measure function in patients with chronic heart and lung disease?

To elucidate the characteristics of measures of function in patients with chronic heart failure and chronic lung disease we administered four functional status questionnaires, a 6-min walk test and a cycle ergometer exercise test, to 43 patients limited in their day to day activities as a result of their underlying heart or lung disease. Correlations between these measures were calculated using Spearman's rank order correlation coefficient. The walk test correlated well with the cycle ergometer (r = 0.579), and almost as well with the four functional status questionnaires (r = 0.473-0.590) as the questionnaires did with one another (0.423-0.729). On the other hand, correlations between cycle ergometer results and the questionnaires was in each case 0.295 or lower, and none of these correlations reached statistical significance. These results suggest that exercise capacity in the laboratory can be differentiated from functional exercise capacity (the ability to undertake physically demanding activities of daily living) and that the walk test provides a good measure of function in patients with heart and lung disease.

Activities of Daily Living↗

PubMed1985

Measurement of mixed venous carbon dioxide pressure by rebreathing during exercise.

This study compared rebreathing methods currently used for the measurement of mixed venous PCO2 (PVCO2) during exercise. Four mathematical procedures were used to derive the asymptote of the exponential rise in end-tidal PCO2 during 15 sec rebreathing of low (2-6%) CO2 mixtures ('exponential' methods); the derived PVCO2 was compared to that obtained with an 'equilibrium' method, in which high CO2 mixtures were rebreathed to obtain an equilibrium of CO2 between the lungs and rebreathing bag. Precision was established by analysing duplicate rebreathings at each power output. The most precise of the four exponential procedures (coefficient of determination 0.98) used iterative statistical analysis to obtain an equation for the best fit curve of end-tidal PCO2 with time (t), solved for t = 20 sec. The PVCO2 derived by this procedure was similar to that obtained by the equilibrium method (r = 0.96), and both yielded estimates of cardiac output that were within the previously published expected range. Variations in the initial rebreathing bag volume and CO2 concentration, and in the breathing frequency during rebreathing had little effect on the derived PVCO2.

Adult↗

PubMed1985

Maximal short term exercise capacity in healthy subjects aged 15-70 years.

Fifty males and 50 females, 15-71 years of age, exercised maximally for 30 s on an isokinetic ergometer at a pedalling frequency of 60 rev./min. Results were compared with maximal oxygen uptake (VO2 max.) obtained in a progressive incremental exercise test. Total work in 30 s was higher in males than females, declined linearly by about 6% per decade of age (r = -0.65), and was related closely to height (r = 0.75) and to lean thigh volume estimated anthropometrically (r = 0.84). A close association with vital capacity (r = 0.86) was also found that accounted statistically for the combined effects of age and height. The percentage decline in power during 30 s (fatigue index) was lower in subjects reporting greater leisure activity. A close relationship was found between total work in 30 s and VO2max. (r = 0.86), with vital capacity and leisure activity exerting additional influences on VO2max. (P less than 0.001; multiple r = 0.93). The well-established reduction with age in VO2max. is associated with an apparent parallel reduction in the power output capacity of large muscle groups recruited in heavy dynamic leg exercise.

Adolescent↗

PubMed1985

Rat skeletal muscle triacylglycerol utilization during exhaustive swimming.

The utilization of triacylglycerol in slow oxidative, fast oxidative-glycolytic, and fast glycolytic skeletal muscle fiber types was examined in rats subjected to a prolonged exhaustive swim. Significant reductions of intramuscular triacylglycerol occurred following 2 h and 40 min of swimming in all muscles containing a predominance of slow oxidative and fast oxidative-glycolytic fibers, which possess a high capacity for free fatty acid oxidation. Triacylglycerol content in the soleus decreased by 48%, and reductions of 41, 29, and 27% were measured in the red vastus lateralis, red gastrocnemius, and plantaris muscles, respectively. In the white vastus lateralis and white gastrocnemius muscles (fast glycolytic fibers) triacylglycerol concentrations were unaffected. In all muscles the variability of intramuscular triacylglycerol measurements between animals was 20-50% and the within animal variance (right vs. left hindlimb) was similar. Analytical repeatability was approximately 10% in all muscles and significantly less than the between- and within-animal variances. It was concluded that a real biological variation exists in the triacylglycerol content of all rat skeletal muscles and that intramuscular triacylglycerol is an important energy source during prolonged exercise of moderate intensity.

Animals↗

PubMed1985

Muscle metabolism and performance in perfused rat hindquarter during heavy exercise.

An isolated perfused rat hindquarter model was used to examine muscle metabolism and performance during heavy muscular contraction. A one-pass system was used to perfuse the hindquarter for 30 min at rest and 20 min while electrically stimulated at 0.5 Hz with tetanic stimuli (100 Hz). The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded continuously, and muscle biopsies were taken pre- and postperfusion. Peak tension was 2,648 +/- 55 g, decreasing to 69.3 and 51.6% of peak following 5 and 20 min of stimulation, respectively. Hindquarter O2 uptake increased from 0.56 mumol X min-1 X g perfused muscle-1 to 2.60 mumol X min-1 X g working muscle-1 after 3 min of stimulation and declined slightly thereafter. Lactate release by the hindquarter increased at the onset of stimulation, peaked at 2-4 min (23.4 +/- 1.4 mumol X min-1), and decreased to a constant amount in the final 10 min. Five minutes of stimulation produced large decreases in glycogen, creatine phosphate (CP), and ATP levels and increased lactate concentrations in all muscles sampled except the soleus. An additional 15 min of stimulation further decreased glycogen concentrations while lactate concentrations decreased in all muscles. Calculations based on the measured amounts of O2 and CP consumed and the amount of lactate produced revealed a heavy glycolytic contribution to energy production during the initial 5 min of stimulation (23%) and an aerobic domination during the final 15 min (90%). With this model heavy muscular contraction can be sustained to permit the measurement of uptake and release of substrates and products of the main energy-yielding pathways.

Animals↗

PubMed1985

Effects of acidosis on rat muscle metabolism and performance during heavy exercise.

The metabolism and performance of a perfused rat hindquarter preparation was examined during heavy exercise in three conditions: control (C), metabolic acidosis (MA, decreased bicarbonate concentration), and respiratory acidosis (RA, increased CO2 tension). A one-pass system was used to perfuse the hindquarters for 30 min at rest and 20 min during tetanic stimulation via the sciatic nerve. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and biopsies were taken pre- and postperfusion. Initial isometric tensions were similar in all conditions, but the rate of tension decay was largest in acidosis; the 5-min tensions for C, MA, and RA were 1,835 +/- 63, 1,534 +/- 63, and 1,434 +/- 73 g, respectively. O2 uptake in C was greater than in MA and RA (23.4 +/- 1.3 vs. 17.0 +/- 1.4 and 16.5 +/- 2.3 mumol X min-1), paralleling the tension findings. Hindquarter lactate release was greatest in C, least in MA, and intermediate in RA. Acidosis resulted in less muscle glycogen utilization and lactate accumulation than during control. Muscle creatine phosphate utilization and ATP levels were unaffected by acidosis. Acidosis decreased the muscle's ability to generate isometric tension and depressed both aerobic and anaerobic metabolism. During stimulation in this model lactate left the muscle mainly as a function of the production rate, although a low plasma bicarbonate concentration at pH 7.15 depressed muscle lactate release.

Acidosis↗