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Biomedical subjects

M J Mador

Publications and source records attributed to M J Mador.

At least 19 recordsLinked to original sources
PubMed2005

A randomised trial to evaluate the self-administered standardised chronic respiratory questionnaire.

The original chronic respiratory questionnaire (CRQ), one of the most widely used measures of health-related quality of life (HRQL) in chronic respiratory disease (CRD), is traditionally interviewer administered (IA) and includes an individualised dyspnoea domain. The present authors studied the impact of self-administered (SA) and standardised dyspnoea questions on CRQ measurement properties. In a factorial design multicentre trial, 177 patients with CRD (mean age 67.7 yrs; mean forced expiratory volume in one second per cent predicted 44.6%) were randomised to CRQ-IA (n = 86) or CRQ-SA (n = 91), and to initially complete the standardised or individualised items before and after respiratory rehabilitation. While maintaining validity, the CRQ-SA proved more responsive to changes in HRQL than the CRQ-IA in all domains. Compared with the standardised dyspnoea domain, the individualised dyspnoea domain indicated greater responsiveness. The correlations of baseline scores and change scores with other HRQL instruments indicated good validity of the CRQ-SA. In conclusion, self-administration and standardisation of the chronic respiratory questionnaire maintains validity and responsiveness relative to the interviewer-administered chronic respiratory questionnaire. These results challenge the assumption that interviewer-administered questionnaires are superior to self-administered questionnaires in older patients with chronic respiratory disease.

Adaptation, Physiological↗
PubMed2002

Diaphragmatic function after intense exercise in congestive heart failure patients.

Respiratory muscle strength and endurance is reduced in patients with congestive heart failure, making these patients susceptible to diaphragmatic fatigue during exercise. In order to determine whether or not contractile fatigue of the diaphragm occurs in patients with congestive heart failure following intense exercise, twitch transdiaphragmatic pressures (twitch Ptdi) were measured during unpotentiated and potentiated cervical magnetic stimulation (CMS) of the phrenic nerves before and at intervals after cycle endurance exercise. Ten patients aged 65.7+/-6.0 yrs (mean+/-SD) with an ejection fraction of 31.2+/-9.8% performed a constant-load symptom-limited exercise test at 60% of their peak work capacity. Twitch Ptdi at baseline were 15.9+/-6.3 cmH2O (unpotentiated CMS) and 28.8+/-10.7 cmH2O (potentiated CMS) and at 10 min postexercise were 16.4+/-4.7 cmH2O (unpotentiated CMS) and 27.6+/-10.1 cmH2O (potentiated CMS). One patient demonstrated a sustained fall in twitch Ptdi of > or = 15%, considered potentially indicative of diaphragmatic fatigue. Contractile diaphragmatic fatigue is uncommon in untrained patients with congestive heart failure following high-intensity constant-workload cycle exercise. Therefore, diaphragmatic fatigue is an unlikely cause of exercise-limitation during activities of daily living in heart failure patients.

Activities of Daily Living↗
PubMed2001

Skeletal muscle dysfunction in chronic obstructive pulmonary disease.

It has become increasingly recognized that skeletal muscle dysfunction is common in patients with chronic obstructive pulmonary disease (COPD). Muscle strength and endurance are decreased, whereas muscle fatigability is increased. There is a reduced proportion of type I fibers and an increase in type II fibers. Muscle atrophy occurs with a reduction in fiber cross-sectional area. Oxidative enzyme activity is decreased, and measurement of muscle bioenergetics during exercise reveals a reduced aerobic capacity. Deconditioning is probably very important mechanistically. Other mechanisms that may be of varying importance in individual patients include chronic hypercapnia and/or hypoxia, nutritional depletion, steroid usage, and oxidative stress. Potential therapies include exercise training, oxygen supplementation, nutritional repletion, and administration of anabolic hormones.

Adrenal Cortex Hormones↗
PubMed2001

Effect of pulmonary rehabilitation on quadriceps fatiguability during exercise.

We have recently shown that patients with chronic obstructive pulmonary disease (COPD) develop contractile fatigue of their quadriceps muscle following endurance exercise. Pulmonary rehabilitation can produce physiological adaptations in patients with COPD. We hypothesized that if pulmonary rehabilitation induces physiological adaptations in the exercising muscle, it should become more fatigue resistant. Twenty one patients with COPD, mean age 69.9 +/- 1.9 yr, FEV(1) 45 +/- 4% predicted, participated in an 8-wk outpatient, supervised pulmonary rehabilitation exercise program. Quadriceps contractile fatigue was detected by a fall in quadriceps twitch force postexercise. Twitch force was measured during magnetic stimulation of the femoral nerve. Because potentiated twitches may be more sensitive at detecting fatigue, both unpotentiated (TwQu) and potentiated (TwQp) twitches were obtained before and 10, 30, and 60 min after constant load cycle exercise. Prerehabilitation, during constant load exercise, patients exercised at 37 +/- 4 W for 11.2 +/- 1.8 min. Prerehabilitation, TwQu fell significantly postexercise down to a minimum value of 82.5 +/- 3.1% of the baseline preexercise value (p < 0.001). Similarly, prerehabilitation, TwQp fell significantly postexercise down to a minimum value of 73.9 +/- 3.9% of baseline (p < 0.001). Postrehabilitation, for the same intensity and duration of exercise, TwQu was not significantly different from baseline at any time postexercise. Postrehabilitation, TwQp fell significantly postexercise but the fall in TwQp with exercise was significantly less postrehabilitation compared with prerehabilitation (p < 0.001). In conclusion, pulmonary rehabilitation resulted in increased fatigue resistance of the quadriceps muscle in patients with COPD.

Aged↗
PubMed2000

Diaphragmatic fatigue and high-intensity exercise in patients with chronic obstructive pulmonary disease.

Patients with chronic obstructive pulmonary disease (COPD) are at a mechanical disadvantage and should be predisposed to the development of diaphragmatic fatigue when the ventilatory system is stressed by exercise. The purpose of this study was to determine whether patients with moderately severe COPD develop contractile fatigue of the diaphragm after cycle exercise to the limits of tolerance. Twelve male patients with COPD, age 61.4 +/- 3.0 yr, participated. Their forced expiratory volume in 1 s (FEV(1)) was 1.79 +/- 0.14 L, 49.6 +/- 3.4% of predicted. Patients cycled at 60-70% of their predetermined maximal work capacity until they had to stop because of intolerable symptoms. Twitch transdiaphragmatic pressure (Pdi,tw) was measured during cervical magnetic stimulation before and 10, 30, and 60 min after exercise. A persistent fall in Pdi,tw postexercise of >/= 10% was considered potentially indicative of contractile fatigue of the diaphragm. Patients cycled for 10.2 +/- 2.0 min at a workload of 59.9 +/- 4.3 W. Patients exercised maximally relative to their capacity reaching a peak oxygen consumption (V O(2)) of 108.1 +/- 2.8% of the peak V O(2) obtained during a preliminary maximal incremental exercise test. Pdi,tw was not significantly different from baseline at any time postexercise. Pdi,tw was 19.9 +/- 1.6 cm H(2)O at baseline, 19.6 +/- 2.0 cm H(2)O at 10 min postexercise, 18. 6 +/- 2.0 cm H(2)O at 30 min postexercise, and 19.5 +/- 1.7 cm H(2)O at 60 min postexercise. In the individual patients, two of the patients had a persistent >/= 10% fall in Pdi,tw postexercise, potentially indicative of contractile fatigue of the diaphragm. In conclusion, the majority of patients with moderately severe COPD do not develop contractile fatigue of the diaphragm after high-intensity constant workload cycle exercise to the limits of tolerance.

Diaphragm↗
PubMed1999

Validity of neural network in sleep apnea.

Clinical assessment of obstructive sleep apnea (OSA) is poor. Overnight polysomnography (OPG) is the standard reference test, but it is expensive and time-consuming. We developed an artificial neural network (ANN) using anthropomorphic measurements and clinical information to predict the apnea-hypopnea index (AHI). All patients completed a questionnaire about sleep symptoms, sleep behavior, and demographic information prior to undergoing OPG. Neck circumference, height, and weight were obtained on presentation to the sleep center. Twelve variables were used as inputs. The output was an estimate of the AHI. The network was trained with a back-propagation algorithm on 189 patients and validated prospectively on 80 additional patients. Data from the derivation group was used to calculate the 95% confidence interval of the estimated AHI. Predictive accuracy at different AHI thresholds was assessed by the c-index, which is equivalent to the area under the receiver operator characteristic curve. The c-index for predicting OSA in the validation set was 0.96 +/- 0.0191 SE, 0.951 +/- 0.0203 SE, and 0.935 +/- 0.0274 SE, using thresholds of > 10, > 15, and > 20/hour respectively. The actual AHI of the 80 patients in the validation data set fell within the 95% confidence limits of the values predicted by the ANN. This study suggests that ANN may be useful as a predictive tool for OSA.

Adolescent↗
PubMed1997

Effect of acute hypercapnia on diaphragmatic and limb muscle contractility.

The purpose of this study was to determine whether acute hypercapnia depresses limb muscle and diaphragmatic contractility. Twelve subjects breathed 8% CO2 for 20 min on two separate occasions. On one occasion, twitch transdiaphragmatic pressure (Pdi) was obtained during both cervical magnetic and transcutaneous stimulation before and 2, 10, and 30 min after CO2 breathing. In addition, twitch Pdi was obtained during CO2 breathing in five subjects using cervical magnetic stimulation. On the other occasion, adductor pollicis twitch force was measured during transcutaneous supramaximal ulnar nerve stimulation and arterialized venous blood gas determinations were obtained before, during, and after CO2 breathing. Twitch Pdi was not significantly different from baseline at any time after CO2 breathing. Similarly, twitch Pdi did not significantly change from the beginning to the end of the period of CO2 breathing. In contrast, adductor pollicis twitch force was significantly less than baseline 2 min after CO2 breathing (p < 0.01). Furthermore, during CO2 breathing, adductor pollicis twitch force fell significantly, reaching statistical significance at 8 min, decreasing still further by 13 min, and then plateauing. During the final 2 min of CO2 breathing, adductor pollicis twitch force averaged 86.5 +/- 2.7% of the baseline value (p < 0.0007). During CO2 breathing, Pco2 rose to 60.1 +/- 0.5 mm Hg, whereas pH fell to 7.27 +/- 0.004 units. Breathing 8% CO2 elicited a moderate hyperpnea, and minute ventilation during the final minute of CO2 breathing averaged 54.74 +/- 4.90 L/min. To ensure that this hyperpnea did not augment diaphragmatic activity enough to potentiate the twitch, five subjects voluntarily mimicked their CO2 hyperpnea on a separate occasion. Twitch Pdi was not significantly different from baseline at any time after voluntary mimicking. To ensure that changes in diaphragmatic contractility were not missed by our twitch measurements, Pdi was measured during bilateral transcutaneous phrenic nerve stimulation at 10 Hz in four subjects. Again, Pdi during 10 Hz stimulation was not significantly different from baseline at any time after CO2 breathing. In conclusion, (1) acute moderate hypercapnia mildly depresses limb muscle contractility, and (2) acute moderate hypercapnia did not produce significant changes in diaphragmatic contractility.

Acute Disease↗
PubMed1996

Comparison of cervical magnetic and transcutaneous phrenic nerve stimulation before and after threshold loading.

Brief supramaximal stimulation of the phrenic nerves (twitch) is considered a promising technique to detect diaphragmatic fatigue in humans. However, the most commonly employed methodology (transcutaneous stimulation) is technically difficult. Cervical magnetic stimulation is a recently described technique that is potentially simpler and may obviate some of the problems inherent with transcutaneous stimulation. The purpose of this study was to determine the ability of cervical magnetic stimulation to evaluate diaphragmatic function. Accordingly, we measured transdiaphragmatic pressure (Pdi) during transcutaneous and cervical magnetic stimulation of the phrenic nerves before and after a potentially fatiguing task; inspiratory threshold loading to task failure. During threshold loading, subjects generated approximately 60% of their maximal esophageal pressure with each breath until they could no longer reach the target pressure. At least 10 twitches were obtained during both transcutaneous and magnetic stimulation before and 10, 30, 60, and 120 min after threshold loading. Control twitch Pdi was significantly larger during magnetic stimulation compared with transcutaneous stimulation: 39.3 +/- 3.0 (mean +/- SE) versus 27.4 +/- 2.3 cm H2O, p < 0.0005. This increase in twitch Pdi was solely due to the esophageal component. Following threshold loading, a significant reduction in transcutaneous twitch Pdi was seen in only three of the 10 subjects. Mean transcutaneous twitch Pdi fell only slightly from 27.4 +/- 2.3 during control to 25.1 +/- 2.2 cm H2O at 10 min after loading (p < 0.004). In contrast, magnetic twitch Pdi was significantly reduced in nine of the 10 subjects following threshold loading. Mean magnetic twitch Pdi fell from 39.3 +/- 3.0 during control to 31.1 +/- 3.0 cm H2O at 10 min after loading (p < 0.0001). The average fall in twitch Pdi post-loading (expressed as a percentage of the control value) was significantly greater for magnetic stimulation compared with transcutaneous stimulation: 21.0 +/- 3.1 versus 7.8 +/- 2.9%, p < 0.0001. In summary: (1) in the fresh state, twitch Pdi is larger with magnetic stimulation compared with transcutaneous stimulation, and (2) transcutaneous and cervical magnetic twitch Pdi are affected differently by threshold loading to task failure.

Adult↗
PubMed1996

Mechanisms for diaphragmatic fatigue following high-intensity leg exercise.

Diaphragmatic fatigue can occur following high-intensity leg exercise to exhaustion. Exercise-induced diaphragmatic fatigue may be due to changes in the milieu to which the diaphragm is exposed (i.e., acidosis, etc.) and/or to increases in diaphragmatic activity during exercise. The purpose of this study was to determine whether changes in milieu are responsible for exercise-induced diaphragmatic fatigue. Fourteen subjects exercised at 70 to 75% of their maximal work capacity until volitional exhaustion. Transdiaphragmatic twitch pressure (Pdi) was measured during bilateral transcutaneous supramaximal phrenic nerve stimulation and adductor pollicis twitch force was measured during transcutaneous supramaximal ulnar nerve stimulation before and 10 to 15, 30, and 60 min after exercise. On a separate day, arterialized venous blood samples were obtained for lactate measurements at baseline and 5, 15, 30, and 60 min postexercise. Nine subjects demonstrated a > or = 10% decrease in twitch Pdi postexercise, which was considered indicative of diaphragmatic fatigue (fatigue group). In these subjects, twitch Pdi fell from 24.3 +/- 1.6 at baseline to 19.7 +/- 1.6 cm H2O at 10 min postexercise (p < 0.0001, ANOVA). Adductor pollicis twitch force was not significantly different from baseline at any time postexercise in either the fatiguers or nonfatiguers. In both groups, a significant lactic acidosis developed during exercise and the magnitude of this acidosis was similar for the two groups. The adductor pollicis muscle (a nonexercising muscle during cycle exercise) is exposed to the same milieu as the diaphragm. Because adductor pollicis twitch force was unchanged postexercise while twitch Pdi fell, changes in milieu cannot be solely responsible for exercise-induced diaphragmatic fatigue.

Adult↗
PubMed1995

Reproducibility of Borg scale measurements of dyspnea during exercise in patients with COPD.

The purpose of this study was to evaluate the moderate term (5 weeks) reproducibility of Borg scale ratings of the effort to breathe (Borge) and the degree of discomfort evoked by breathing (Borgd) in patients with COPD during exercise. Six subjects with moderately severe COPD (FEV1, 1.42 +/- 0.50 L) underwent progressive incremental exercise (15 W/min) on a cycle ergometer to a symptom-limited maximum every week for 6 weeks (first week used as practice session). Minute ventilation (VE), oxygen consumption (VO2), and Borg ratings were obtained every minute during exercise. Borge and Borgd were highly correlated in each subject (r = 0.99 +/- 0.01). Borg scores were not significantly different across study days during both maximal and submaximal exercise. The within-subject coefficient of variation (CV) for Borge during maximal exercise was 13.9 +/- 9.0% (range, 6 to 31%) which was not significantly different from that observed for the physiological indices: 8.2 +/- 4.1% (range, 4 to 15%) for VE and 5.2 +/- 3.4% (range, 1 to 10%) for VO2. In contrast, at 66% of the maximum workload, the within-subject CV for Borge was 25.0 +/- 13.6% (range, 12 to 50%) which was significantly greater than that observed for the physiologic indices: 5.8 +/- 2.0% (range, 3 to 9%) for VE and 4.6 +/- 1.1% (range, 3 to 6%) for VO2. In every subject, Borge was linearly correlated with VE, VO2, and workload. However, within an individual subject, the slope of these relationships varied between trials; within-subject CV for the slope of the Borge/VE relationship was 20.2 +/- 8.0% (range, 12 to 32%). In conclusion, during incremental exercise Borg ratings of dyspnea are not as reproducible as physiologic indices in patients with COPD.

Aged↗
PubMed1994

Twitch potentiation following voluntary diaphragmatic contraction.

The purpose of this study was to determine whether twitch potentiation (a transient augmentation of twitch tension following vigorous muscular contraction) occurs in the human diaphragm in vivo. Six healthy subjects were studied. To determine whether twitch potentiation occurs, the subjects attempted to maximally activate their diaphragm by performing the combined Mueller-expulsive maneuver with visual feedback (Pdi max maneuver). Twitches were obtained before, at 10 s after the transdiaphragmatic pressure (Pdi) maneuver, and at intervals over the ensuing 10 min. We also determined whether twitch potentiation would occur following submaximal voluntary diaphragmatic contractions (33 and 66% of Pdi max). In addition, we examined whether repeated voluntary contractions would result in greater twitch potentiation compared with that observed after a single voluntary contraction. Twitch potentiation was observed in every subject. The number of maximal voluntary contractions (MVC) (one, two, or four) had no significant effect on the degree of twitch potentiation. The increase in twitch amplitude (expressed as a percentage of the control value) averaged 63 +/- 35% (SD)(pooled data from one, two, and four contraction trials). Twitch potentiation decayed in a monoexponential fashion (r = 0.99) with a time constant of 125 s (95% Cl = 100 to 160 s). Twitch potentiation was also observed after submaximal voluntary diaphragmatic contractions. Again, the number of voluntary contractions (one or four) had no significant effect on the degree of twitch potentiation. After submaximal diaphragmatic contractions of 66% of Pdi max, the degree of twitch potentiation was not significantly different, 61 +/- 36% (pooled data from one and four contraction trials) from that observed following the maximal voluntary contraction maneuvers.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Effect of nebulized lidocaine on ventilatory response to CO2 in healthy subjects.

Partial vagal blockade produced by inhalation of a local anesthetic aerosol has enhanced CO2 responsiveness in some studies but not in others. The effect of inhaled local anesthetic may depend on the amount of drug depositing in the central airways, i.e., the degree of airway anesthesia. We examined the ventilatory response to CO2 rebreathing in 11 healthy subjects before and after inhalation of 4% lidocaine and a normal saline control solution. Lidocaine and control solutions were aerosolized via two different nebulizers: one produced particles with a mass median aerodynamic diameter of 5.28 microns, and the other produced particles with a mass median aerodynamic diameter of 1.76 microns. The ventilatory response to CO2 was not affected by the control solution. In contrast, the ventilatory response to CO2 was significantly increased after aerosolized lidocaine when administered via the moderate-particle-size nebulizer (2.13 +/- 0.66 vs. 1.83 +/- 0.54 l.min-1.Torr-1 during control, P = 0.01) but not via the small-particle-size nebulizer (1.96 +/- 0.82 vs. 1.94 +/- 0.84 l.min-1.Torr-1 during control, P = NS). The increase in ventilation was achieved predominantly by an increase in frequency (P = 0.01) while tidal volume was unchanged. In conclusion, airway receptors accessible to inhaled local anesthetic play a role in the control of breathing during CO2 rebreathing. Previous negative studies may be due to differences in nebulizer technique, affecting the amount of drug depositing within the central airways.

Administration, Inhalation↗
PubMed1993

Diaphragmatic fatigue after exercise in healthy human subjects.

The purpose of this study was to determine whether diaphragmatic fatigue occurs after high-intensity constant-load whole-body exercise to volitional exhaustion. Ten sedentary subjects with a maximal oxygen uptake of 2.52 +/- 0.47 L/min were studied. Subjects exercised on a bicycle ergometer at 80% of their maximal working capacity until volitional exhaustion. Minute ventilation during the last minute of exercise was 89.9 +/- 13.6 L/min, which represented 50 +/- 6% of the subjects' 12-s maximal voluntary ventilation. During the last minute of exercise, mean inspiratory esophageal pressure was 18.1 +/- 5.3 cm H2O, which represented only 15 +/- 4% of the subjects' maximal static inspiratory pressure. Bilateral transcutaneous supramaximal phrenic nerve stimulation was performed before and 10, 30, 45 and 60 min after exercise. Twitch diaphragmatic pressure (twitch Pdi) was significantly decreased after exercise in seven of the 10 subjects. For the group as a whole, twitch Pdi fell from 28.9 +/- 3.7 cm H2O during control to 23.9 +/- 5.1 cm H2O at 10 min after exercise (p < 0.005). The fall in twitch Pdi was due to a significant decrease in twitch esophageal pressure from 19.6 +/- 4.3 cm H2O during control to 15.5 +/- 4.9 cm H2O (p < 0.001). Twitch gastric pressure was not significantly different: 8.7 +/- 4.0 cm H2O, compared with 9.2 +/- 3.8 cm H2O during control. Twitch Pdi recovered to 93 +/- 7% of control values at 60 min after exercise. The fall in twitch Pdi after exercise indicates that diaphragmatic fatigue can occur following heavy endurance exercise in sedentary healthy persons.

Adult↗
PubMed1992

The effect of inspiratory muscle fatigue on breathing pattern and ventilatory response to CO2.

1. The effects of inducing inspiratory muscle fatigue on the subsequent breathing pattern were examined during resting unstimulated breathing and during CO2 rebreathing. In addition, we examined whether induction of inspiratory muscle fatigue alters CO2 responsiveness. 2. Global inspiratory muscle fatigue and diaphragmatic fatigue were achieved by having subjects breathe against an inspiratory resistive load while generating a predetermined fraction of either their maximal mouth pressure or maximal transdiaphragmatic pressure until they were unable to generate the target pressure. 3. Induction of inspiratory muscle fatigue had no effect on the subsequent breathing pattern during either unstimulated breathing or during CO2 rebreathing. 4. Following induction of inspiratory muscle fatigue, the slope of the ventilatory response to CO2 was significantly decreased from 18.8 +/- 3.3 during control to 13.8 +/- 2.1 l min-1 (% end-tidal CO2 concentration)-1 with fatigue (P < 0.02).

Adult↗
PubMed1992

Reproducibility of visual analog scale measurements of dyspnea in patients with chronic obstructive pulmonary disease.

The purpose of this study was to evaluate the reproducibility of visual analog scale ratings of the effort to breathe (VASe) and the degree of discomfort evoked by breathing (VASd) in patients with chronic obstructive pulmonary disease (COPD) during exercise. Six subjects with moderately severe COPD (FEV1 = 1.12 +/- 0.29 L, FEV1/FVC = 44 +/- 4%) underwent progressive incremental exercise testing to a symptom-limited maximum every week for 8 wk. VASe and VASd were highly correlated in each subject (r = 0.99 +/- 0.01). The slope of the VASd/VASe relationship for all trials in all subjects was not significantly different from 1, indicating that our subjects were rating a common sensation with the two scales. VASe at maximal exercise was reproducible in every subject; the within-subject coefficient of variation (CV) was 6% (range, 2 to 10%) and compared favorably with physiologic indices: 7% (range, 3 to 12%) for oxygen consumption and 10% (range, 5 to 16%) for minute ventilation (VI). In contrast, submaximal VAS ratings were highly variable. At 66% of the maximal work load, the within-subject CV for VASe was 21% (range, 11 to 28%) compared with 6% (range, 4 to 7%) for VO2 (p less than 0.003) and 10% (range, 5 to 16%) for VI (p less than 0.01). VASe correlated linearly with VI and VO2 in all subjects in all trials. However, within an individual subject the slope and position of these relationships varied widely between trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗