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Biomedical subjects

N L Jones

Publications and source records attributed to N L Jones.

At least 145 records · Page 8Linked to original sources
PubMed1985

Comparison of cardiac output during exercise by single-breath and CO2-rebreathing methods.

Cardiac output (Q) was estimated in supine rest and in upright cycling at several work rates up to 200 W in five male and one female subjects. At least four repetitions of both the CO2-rebreathing plateau method (Collier, J. Appl. Physiol. 9:25-29, 1956) and the Kim et al. (J. Appl. Physiol. 21: 1338-1344, 1966) single-breath method were performed at each work rate, in a steady state of O2 consumption and heart rate. At supine rest and low work rates, estimates of Q were similar by the two methods. However, at higher work rates, the single-breath method significantly (P less than 0.05) underestimated the value obtained by CO2 rebreathing. The reason for the difference in estimates of Q by the two methods was traced to the determination of arterial partial pressure of CO2 (PaCO2) and mixed venous partial pressure of CO2 (PvCO2). The estimate of PaCO2 from the single-breath method was approximately 88.5% of the estimate from end-tidal PCO2 used with the rebreathing method (P less than 0.001). The oxygenated PvCO2 calculated from the single-breath Q averaged approximately 92.5% of the PvCO2 from CO2 rebreathing (P less than 0.0001). The difference in estimates of Q was not eliminated by using a logarithmic form of the CO2 dissociation curve with the single-breath method.

Adult↗
PubMed1985

Inspiratory muscle forces and endurance in maximum resistive loading.

The ability of the respiratory muscles to sustain ventilation against increasing inspiratory resistive loads was measured in 10 normal subjects. All subjects reached a maximum rating of perceived respiratory effort and at maximum resistance showed signs of respiratory failure (CO2 retention, O2 desaturation, and rib cage and abdominal paradox). The maximum resistance achieved varied widely (range 73-660 cmH2O X l-1 X s). The increase in O2 uptake (delta Vo2) associated with loading was linearly related to the integrated mouth pressure (IMP): delta Vo2 = 0.028 X IMP + 19 ml/min (r = 0.88, P less than 0.001). Maximum delta Vo2 was 142 ml/min +/- SD 68 ml/min. There were significant (P less than 0.05) relationships between the maximum voluntary inspiratory pressure against an occluded airway (MIP) and both maximum IMP (r = 0.80) and maximum delta Vo2 (r = 0.76). In five subjects, three imposed breathing patterns were used to examine the effect of different patterns of respiratory muscle force deployment. Increasing inspiratory duration (TI) from 1.5 to 3.0 and 6.0 s, at the same frequency of breathing (5.5 breaths/min) reduced peak inspiratory pressure and increased the maximum resistance tolerated (190, 269, and 366 cmH2O X l-1 X s, respectively) and maximum IMP (2043, 2473, and 2913 cmH2O X s X min-1, but the effect on maximum delta Vo2 was less consistent (166, 237, and 180 ml/min). The ventilatory endurance capacity and the maximum O2 uptake of the respiratory muscles are related to the strength of the inspiratory muscles, but are also modified through the pattern of force deployment.

Adult↗
PubMed1985

Muscle performance and metabolism in maximal isokinetic cycling at slow and fast speeds.

To provide a description of the metabolic changes in muscle during maximal dynamic exercise, muscle biopsies were obtained in five healthy subjects before and after 30 s of isokinetic exercise at two pedaling frequencies (60 and 140 rpm) associated with contrasting fatigue characteristics. Higher peak power was attained at 140 rpm (1,473 + 185 W) (mean +/- SE) than at 60 rpm (1,122 +/- 70 W), but the decline in power during 30 s (fatigue index) was greater at 140 rpm (61.6 +/- 3.2 vs. 21.5 +/- 2.4%), total work in 30 s being similar (18.1 +/- 1.10 vs. 20.1 +/- 1.10 kJ). Changes in the concentration of muscle metabolites were similar; creatine phosphate concentration fell to approximately 50% of resting values, and the glycolytic intermediates glucose 6-phosphate, fructose 6-phosphate, and fructose 1,6-biphosphate increased up to 30-fold. Muscle lactate concentration ([La-]) was 29.0 +/- 3.98 and 31.0 +/- 4.31 mmol/kg wet wt immediately postexercise at 140 and 60 rpm, respectively. Even after only 10 s exercise (n = 2), large increases were measured in glycolytic intermediates and [La-]. In the two subjects, muscle [La-] increased to 17.2 and 15.1 mmol/kg at 140 rpm and to 14.3 and 14.2 mmol/kg at 60 rpm. In this type of exercise, glycogenolysis is activated very rapidly at both pedal speeds; the changes in glycolytic intermediates were consistent with rate-limiting steps at the phosphofructokinase and pyruvate dehydrogenase reactions. The greater fatigue at the higher speed is not accompanied by different biochemical changes than at 60 rpm.

Adenosine Triphosphate↗
PubMed1985

Normal standards for an incremental progressive cycle ergometer test.

One hundred healthy subjects (50 male and 50 female), selected to provide an even distribution of age (15 to 71 yr) and height (165 to 194 cm in males and 152 to 176 cm in females), underwent a progressively incremental (100 kpm/min each min) exercise test to a symptom-limited maximum. Measurements were made of O2 intake and CO2 output, ventilation and breathing pattern, heart rate and blood pressure, and rating of perceived exertion. The ventilatory anaerobic threshold was identified. Predictive data were derived for measurements at maximal and submaximal exercise. Maximal power output (Wmax) and oxygen intake (VO2max) varied with sex (0, male; 1, female), age (yr), and height (Ht, cm): Wmax = 20.4 (Ht) - 8.74 (Age) - 288 (Sex) - 1,909 kpm/min (SEE, 216; r, 0.858); VO2max = 0.046 (Ht) - 0.021 (Age) - 0.62 (Sex) - 4.31 L/min (SEE, 0.458; r, 0.869). The extent of leisure time activity exerted a positive influence on VO2max (r, 0.47; p less than 0.001); VO2max was also related to lean thigh volume (r, 0.79). Maximal heart rate (HR) declined as a function of age: HRmax = 202 - 0.72 (Age) beats/min (SEE, 10.3; r, 0.72). Maximal O2 pulse (O2Pmax) was related to height and was systematically higher in males than in females: O2Pmax = 0.28 (Ht) - 3.3 (Sex) - 26.7 ml/beat (SEE, 2.8; r, 0.86). Ventilation was closely related to CO2 output, and the maximal tidal volume was related to vital capacity. The VO2 increased linearly with power throughout the test; in an individual subject, the intercept of this relationship was positively influenced by weight and height.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Rate of change of alveolar carbon dioxide and the control of ventilation during exercise.

The relationship between rate of change of alveolar PCO2 (delta PA, CO2/delta te), CO2 output (VCO2) and ventilation (VE) has been determined following a rapid increase in exercise intensity, to test the hypothesis that VE is related to VCO2 by a feed-forward control system responding to delta PA, CO2/delta te. There was a close relationship between delta PA, CO2/delta te and VCO2 (delta PA, CO2/delta te = 3.2 VCO2 + 0.85), but delta PA, CO2/delta te increased more rapidly than VCO2. Increases in mean inspiratory flow, an index of inspiratory drive, were more closely related to changes in delta PA, CO2/delta te than to changes in VCO2. Increases in VE during transient and steady-state conditions may be described by the equation: VE = 6.76 delta PA, CO2/delta te -3.50, a relationship which is consistent with a feed-forward control system.

Carbon Dioxide↗
PubMed1984

Effect of encouragement on walking test performance.

Walking tests, frequently used to document effects of treatment on exercise capacity, have never been standardised. We studied the effects of encouragement on walking test performance in a randomised study that controlled for the nature of the underlying disease, time of day, and order effects. We randomised 43 patients with chronic airflow limitation or chronic heart failure or both to receive or not receive encouragement as they performed serial two and six minute walks every fortnight for 10 weeks. Simple encouragement improved performance (p less than 0.02 for the six minute walk), and the magnitude of the effect was similar to that reported for patients in studies purporting to show beneficial effects of therapeutic manoeuvres. Age and test repetition also affected performance. These results demonstrate the need for careful standardisation of the performance of walking tests, and suggest caution in interpreting studies in which standardisation is not a major feature of the study design.

Chronic Disease↗
PubMed1984

Evaluation of a microprocessor-controlled exercise testing system.

We evaluated a new exercise-testing system (Beckman Horizon MMC), incorporating a microprocessor that controls the acquisition of data, corrects for time delays, applies calibration factors, ensures quality control, and presents results in a variety of formats. Precision of measurements of ventilation (VE) and mixed expired gas concentrations was high. In steady-state exercise (n = 100) VO2 was measured with a precision (+/- SD) of 66 ml/min (4.3%), (r = 0.991); there was a small (4.62%) systematic underestimation of VCO2, but precision was comparable with VO2, with SD being 67 ml/min (4.55%) (r = 0.993). Good agreement was obtained between measurements made in progressive incremental exercise in healthy subjects with correlation coefficients of 0.997 for VE, 0.995 for VO2, and 0.994 for VCO2. Agreement in patients with cardiorespiratory disorders (n = 10) was similar, except in three patients in whom a variable pattern of breathing limited strict comparisons. Comparison with a breath-by-breath analysis system (n = 5) showed that rapid changes in VE, VCO2, and VO2 were followed accurately; the half time for a change in VO2 was not systematically different between the two systems (SD, 3.34 s, r = 0.951). The incorporation of microprocessor-controlled calibration procedures, which are simple to carry out frequently, was judged to be an important feature of this system.

Exercise Test↗
PubMed1984

Effect of pH on metabolic and cardiorespiratory responses during progressive exercise.

Six healthy male subjects performed three exercise tests in which the power output was increased by 100 kpm/min each minute until exhaustion. The studies were carried out after oral administration of CaCO3 (control), NH4Cl (metabolic acidosis), and NaHCO3 (metabolic alkalosis). Ventilation (VE), O2 intake (VO2), and CO2 output (VCO2) were monitored continuously. Arterialized-venous blood samples were drawn at specific times and analyzed for pH, PCO2, and lactate concentration. Resting pH (mean +/- SE) was lowest in acidosis (7.29 +/- 0.01) and highest in alkalosis (7.46 +/- 0.02). A lower peak power output (kpm/min) was achieved in acidosis (1,717 +/- 95) compared with control (1,867 +/- 120) alkalosis (1,867 +/- 125). Submaximal VO2 and VCO2 were similar, but peak VO2 and VCO2 were lower in acidosis. Plasma lactate concentration was lower at rest and during exercise in acidosis. Although lactate accumulation was reduced in acidosis, increases in hydrogen ion concentration were similar in the three conditions. We conclude that acid-base changes influence the maximum power output that may be sustained in incremental dynamic exercise and modify plasma lactate appearance, but have little effect on hydrogen ion appearance in plasma.

Acid-Base Equilibrium↗
PubMed1984

Alveolar gas exchange during exercise: a single-breath analysis.

Changes in expired alveolar O2 and CO2 were measured breath-by-breath in six healthy male subjects (mean age 30 yr, mean weight 80 kg) at rest, 600 kpm/min, and 1,200 kpm/min. Changes were expressed in relation to expired volume (liters) and time (s) and separated into an initial dead-space component using the Fowler method applied to expired CO2 and O2, and alveolar slope. The alveolar slopes with respect to time (dPACO2, dPAO2, Torr/s) increased in relation to CO2 output (VCO2, 1/min, STPD) and O2 intake (VO2, 1/min, STPD) but were reduced by increasing tidal volume (VT, liters, BTPS): dPACO2 = 2.7 + 4.6(VCO2) - 1.9(VT) (r = 0.97); and dPAO2 = 2.3 + 5.5(VO2) - 1.9(VT) (r = 0.96). From the alveolar slopes, tidal volume, and airway dead-space volume, mean expired alveolar PO2 and PCO2 (PAO2, PACO2) were calculated. There was no change in arterialized capillary PCO2 (PaCO2) between rest (38.9 +/- 0.66 Torr) and heavy exercise (38.2 +/- 2.18 Torr), but mean PACO2 rose from 36.7 +/- 0.55 to 40.8 +/- 1.67 Torr during heavy exercise. There was no change in arterialized capillary (mean = 84.3 +/- 0.7 Torr) or alveolar (mean = 107.2 +/- 1.03 Torr) PO2. Exercise increases the fluctuations in alveolar gas composition leading to discrepancies between the PCO2 in mean alveolar gas and arterial blood to an extent that is dependent on VCO2 and VT.

Adult↗
PubMed1984

Dyspnea in exercise.

Extensive psychophysical experiments have established that the sense of respiratory effort bears a power function relationship to the force generated by respiratory muscles and the frequency and duration of their contraction, and an inverse relationship to respiratory muscle strength. Using this information an approach to the assessment of dyspnea is developed which has several components. First, the response to exercise, in terms of the metabolic and gas exchange demands is established. Second, the ventilatory responses are analyzed in terms of total ventilation, the pattern of breathing (tidal volume and breathing frequency), and the timing of breathing (inspiratory and expiratory times). Third, the exercise measurements are considered in relation to the elastic and resistive components of the respiratory system that impede volume and flow, as reflected in measurements of static lung volume and the flow:volume characteristic. Finally, measurement of the maximum inspiratory pressure against an occluded airway reflects respiratory muscle strength. Dyspnea, the sensation of increased respiratory effort, is usually due to a combination of abnormalities--increased metabolic demand, increased ventilatory response, increased impedance to breathing, and reduced respiratory muscle power. Management of abnormality in each of these components is distinctly separate.

Carbon Dioxide↗
PubMed1984

The use of exercise testing and other methods in the investigation of dyspnea.

The sensation of effort is increased when the tension developed by active muscle is increased or when the muscle is weak; similar factors contribute to the sense of respiratory effort that constitute the symptoms of dyspnea. Exercise testing enables systematic loading of the respiratory muscles to be studied; the components of the ventilatory responses to exercise may be quantified in terms of the pattern and timing of breathing and of inspiratory flow and volume. The associated sensation of respiratory effort may then be related to the tension developed by respiratory muscles and to their strength.

Dyspnea↗
PubMed1983

Characteristics that predicted recurrence of infarction within 3 years in the Ontario Exercise-Heart Collaborative Study.

Data on 13 baseline characteristics of 618 patients who had previously had a myocardial infarction and who had entered the Ontario Exercise-Heart Collaborative Study were analysed for their ability to predict recurrence of infarction within 3 years. These characteristics were age, serum levels of cholesterol and triglycerides, systolic and diastolic blood pressure, number of hours of competitive sports per week, number of hours of jogging per week, angina, type of occupation, smoking, cough and phlegm production, personality type and the number of previous infarctions. The characteristics showing independent statistical significance (p less than 0.05) were smoking and blue-collar occupation, with estimated adjusted relative odds of 2.3 and 2.1 respectively.

Adult↗
PubMed1983

Predictors of dropout from cardiac exercise rehabilitation. Ontario Exercise-Heart Collaborative Study.

The Ontario Exercise-Heart Collaborative Study was a multicenter randomized clinical trial of high intensity exercise for the prevention of recurrent myocardial infarction in 733 men. Of the 678 subjects who could have participated for at least 3 years, 315 (46.5%) dropped out. Stepwise multiple linear logistic regression analysis was carried out to examine the relation between subject characteristics and the probability of dropping out during the study. Analysis was performed on the entry group as a whole by considering those subjects who had reinfarction while complying with the program and also by excluding all subjects with reinfarctions. The consistent and statistically significant predictors of dropout in both analyses were smoking and a blue collar occupation. Angina was significantly associated with dropout only when reinfarctions were excluded. It may be important to consider these factors when investigating the potential for compliance-improving strategies in reducing dropout from exercise rehabilitation programs.

Adult↗
PubMed1983

The CO2 responsiveness and ventilatory response to leg and arm exercise in female swimmers.

The primary purpose of this study was to compare the ventilatory response to CO2 during rebreathing (delta VI/delta PCO2) among 8 competitive synchronized swimmers (SS), 8 competitive speed swimmers (CS) and 8 recreation swimmers (RS) who acted as controls. A secondary purpose was to study the relationship between delta VI/delta PCO2 and the ventilatory equivalent to the metabolic CO2 output (delta VE/delta VCO2) during graded exercise consisting of treadmill walking and arm cranking. No significant difference was observed amongst the groups in either the intercept or slope of the ventilatory response to increasing alveolar PCO2 was 1.48 +/- 0.33, 2.04 +/- 0.13 and 1.87 +/- 0.18 (mean +/- SEM) in the SS, CS and RS, respectively. The delta VI/delta PCO2 during rebreathing; delta VI/delta PCO2 during rebreathing was not significantly related to the delta VE/delta VCO2 obtained during either treadmill walking or arm cranking. The delta VE/delta VCO2 achieved during treadmill walking was similar for the 3 groups. However, during arm cranking, the delta VE/delta VCO2 was similar for the SS and CS, but both values were significantly lower than the delta VE/delta VCO2 achieved by the RS. It appears that the training regime experienced by the SS and CS did not alter their responsiveness to CO2 during rebreathing. The reduced delta VE/delta VCO2 observed during exercise with the trained limbs (arms) in the SS and CS compared to RS cannot be explained by altered responsiveness to CO2 secondary to training.

Adolescent↗