Biomedical subjects

John Moxham

Publications and source records attributed to John Moxham.

At least 19 recordsLinked to original sources

PubMed2006

Quadriceps strength predicts mortality in patients with moderate to severe chronic obstructive pulmonary disease.

BACKGROUND: Prognosis in chronic obstructive pulmonary disease (COPD) is poorly predicted by indices of air flow obstruction, because other factors that reflect the systemic nature of the disease also influence prognosis. OBJECTIVE: To test the hypothesis that a reduction in quadriceps maximal voluntary contraction force (QMVC) is a useful predictor of mortality in patients with COPD. METHODS: A mortality questionnaire was sent to the primary care physician of 184 patients with COPD who had undergone quadriceps strength measurement over the past 5 years. QMVC was expressed as a percentage of the patient's body mass index. The end point measured was death or lung transplantation, and median (range) follow-up was 38 (1-54) months. RESULTS: Data were obtained for 162 patients (108 men and 54 women) with a mean (SD) percentage of forced expiratory volume in 1 s (FEV1) predicted of 35.6 (16.2), giving a response rate of 88%. Transplant-free survival of the cohort was 93.5% at 1 year and 87.1% at 2 years. Cox regression models showed that the mortality risk increased with increasing age and with reducing QMVC. Only age (HR 1.72 (95% CI 1.14 to 2.6); p = 0.01) and QMVC (HR 0.91 (95% CI 0.83 to 0.99); p = 0.036) continued to be significant predictors of mortality when controlled for other variables in the multivariate analysis. CONCLUSION: QMVC is simple and provides more powerful prognostic information on COPD than that provided by age, body mass index and forced expiratory volume in 1 s.

Disease-Free Survival↗

PubMed2006

Passive properties of the diaphragm in COPD.

Structural adaptations that occur in the diaphragm muscle of patients with chronic obstructive pulmonary disease (COPD), namely an increase in type I fibers and a decrease in type II fibers, have been explored in terms of the active contractile properties of the diaphragm. The aim of this study was to test the passive properties of the diaphragm by measuring the force response of relaxed diaphragm muscle fibers to stretching to determine the effect of COPD on these properties. Costal diaphragm biopsies were taken from patients with COPD and from controls with normal pulmonary function. From these biopsies, titin expression was assessed in diaphragm homogenates by gel electrophoresis, and the restoring force was measured by incremental stretching of single fibers in the relaxed state and measuring the force response to stretching. A quadratic model was used to illustrate the relationship between restoring force and muscle fiber length, and it revealed that COPD fibers generate significantly lower restoring forces than control fibers as judged by the area under the force-length curve. Furthermore, this finding applies to both type I and type II fibers. Gel electrophoresis revealed different titin isoforms in COPD and controls, consistent with the conclusion that COPD results not only in a change in muscle fiber-type distribution but in a structural change in the titin molecule in all muscle fiber types within the diaphragm. This may assist the muscle with the energetic changes in the length of the diaphragm required during breathing in COPD.

Adaptation, Physiological↗

PubMed2006

Exercise-induced depression of the diaphragm motor evoked potential is not affected by non-invasive ventilation.

Whole body exercise is followed by a depression of the diaphragm motor evoked potential (MEP). It is unknown whether the change is due to diaphragm activity or whole body exercise. To test the hypothesis that exercise-induced MEP depression was related to diaphragm activity, we performed two experiments. The first examined the effect of whole body exercise, performed with and without the use of non-invasive ventilation (NIV). NIV resulted in significant unloading of the diaphragm (pressure time product 101+/-68 cm H(2)O/s/min versus 278+/-95 cm H(2)O/s/min, p<0.001). Both conditions produced significant MEP depression compared to the control condition (% drop at 5 min, after exercise and exercise with NIV: 29 and 34%, p=0.77). Study 2 compared exercise with isocapnic hyperventilation. At 20 min the MEP had fallen by 29% in the exercise session versus 5% with hyperventilation (p=0.098). We conclude that the work of breathing during whole body exercise is not the primary driver of exercise-induced diaphragm MEP depression.

Adult↗

PubMed2006

+9/+9 Homozygosity of the bradykinin receptor gene polymorphism is associated with reduced fat-free mass in chronic obstructive pulmonary disease.

BACKGROUND: The etiology of muscle wasting in chronic obstructive pulmonary disease (COPD) is incompletely understood. We previously showed that the D rather than the I polymorphic variant of the angiotensin-converting enzyme (ACE) gene is associated with preserved quadriceps strength in COPD. If the ACE D allele influences skeletal muscle through increased ACE-related kinin degradation [and reduced activity at the bradykinin type 2 receptor (BK(2)R)], we might expect a similar association with the +9 BK(2)R genotype in this population as well. OBJECTIVE: The objective was to test the hypothesis that the BK(2)R gene polymorphism is a determinant of fat-free mass and quadriceps strength in patients with COPD. DESIGN: In a cross-sectional design we determined BK(2)R genotype, fat-free mass, and quadriceps strength in 110 COPD patients with a mean (+/-SD) predicted forced expiratory volume in 1 s of 34.3 +/- 16.4% and in 104 healthy age-matched control subjects. RESULTS: The mean (+/-SD) fat-free mass index (in kg/m(2)) was significantly lower in 37 patients homozygous for the +9 allele than in carriers of the -9 allele (15.7 +/- 1.8 compared with 16.7 +/- 2.3; P = 0.038); the same pattern was true for quadriceps maximal voluntary force (30.8 +/- 10.4 and 36.4 +/- 12.8 kg; P = 0.02), respectively. No significant effect of BK(2)R genotype on inspiratory muscle strength or on any variable in control subjects was observed. There was no interaction between the effect of the BK(2)R and ACE genotypes on quadriceps strength. CONCLUSIONS: The genotype associated with reduced BK(2)R expression is associated with reduced fat-free mass and quadriceps strength in COPD. However, alterations in the activity at the BK(2)R do not seem to account for the previously identified association of quadriceps strength with ACE genotype.

Alleles↗

PubMed2005

Does symptom-limited cycle exercise cause low frequency diaphragm fatigue in patients with heart failure?

BACKGROUND: Reduced diaphragm contractility occurs in some healthy subjects when they exercise to exhaustion. This indicates low frequency fatigue, which may contribute to task failure. We hypothesised that patients with congestive heart failure (CHF) might be especially vulnerable to the development of low frequency diaphragm fatigue after exhaustive exercise. AIMS: To study the effect of exhaustive incremental cycle exercise on diaphragm contractility in patients with CHF. METHODS: 12 patients with CHF with an ejection fraction of 36.5 +/- 7.3% and 12 healthy age-matched control subjects performed an incremental cycle test to exhaustion. The unpotentiated twitch transdiaphragmatic pressure (twitch Pdi) in response to bilateral anterolateral magnetic phrenic nerve stimulation (BAMPS) was measured before and after exercise. RESULTS: Twitch Pdi at baseline was 20.2 +/- 6.7 cm H2O in the CHF group and 20.3 +/- .3 cm H2O in the controls (p = 0.957). 25 and 35 min post exercise the values were 19.9+/-5.4 and 20.0+/-5.1 cm H2O in the CHF group and 20.6 +/- 4.3 and 21.2 +/- 3.4 cm H2O in the control group; neither change was significant (F(2,27) = 0.007, p = 0.993; F(2,33) = 0.144, p = 0.866, respectively). CONCLUSION: When patients with CHF cycle to exhaustion, low frequency fatigue of the diaphragm does not occur, and this is unlikely to be an important factor limiting exercise capacity of such patients.

Diaphragm↗

PubMed2005

Twitch airway pressure elicited by magnetic phrenic nerve stimulation in anesthetized healthy children.

Children with diaphragm dysfunction may be unable to maintain adequate ventilation. Accurate diagnosis is important, but can only be achieved using an appropriate test and reference range. The aim of this study, therefore, was to measure diaphragm contractility and examine the influence of age and maturation, using magnetic phrenic nerve stimulation in healthy children. Anterolateral magnetic stimulation (MS) of the phrenic nerves was performed using a 43-mm figure-eight coil in 23 children (14 male; mean age, 7.8 years; range, 1.8-15.7) anesthetized for minor surgery with sevoflurane gas. The airway was maintained with a cuffed laryngeal mask airway (LMA) which was briefly occluded during MS. Diaphragm contractility was assessed by measuring the airway pressure (TwPaw) elicited by MS. TwPaw responses were obtained in all subjects, with mean (SD) TwPaw 18.2 (6.8) cm H2O bilateral, 7.3 (3.2) cm H2O left unilateral, and 8.6 (3.1) cm H2O right unilateral. Subgroup analysis was performed in 17 of the children who were prepubertal. Their mean (SD) TwPaw was 17.3 (6.8) cm H2O bilateral, 7.1 (3.7) cm H2O left unilateral, and 8.3 (3.3) right unilateral. The mean (SD) intrapatient coefficients of variation for bilateral and left and right unilateral TwPaw were 8.4% (5.2), 6.7% (3.5), and 11.7% (10.3), respectively. Bilateral and left and right unilateral TwPaw were significantly related to age (P < 0.05). In healthy prepubertal children, diaphragm contractility is primarily influenced by age.

Adolescent↗

PubMed2005

Motor control of the costal and crural diaphragm--insights from transcranial magnetic stimulation in man.

The costal and crural parts of the diaphragm differ in their embryological development and physiological function. It is not known if this is reflected in differences in their motor cortical representation. We compared the response of the costal and crural diaphragms using varying intensities of transcranial magnetic stimulation of the motor cortex at rest and during submaximal and maximal inspiratory efforts. The costal and crural motor evoked potential recruitment curves during submaximal inspiratory efforts were similar. The response to stimulation before, during and at 10 and 30 min after 44 consecutive maximal inspiratory efforts was also the same. Using paired stimulations to investigate intra-cortical facilitatory and inhibitory circuits we found no difference between the costal and crural response with varying interstimulus intervals, or when conditioning and test stimulus intensity were varied. We conclude that supraspinal control of the costal and crural diaphragm is identical during inspiratory tasks.

Action Potentials↗

PubMed2005

Chest radiography cannot predict diaphragm function.

The finding of hemidiaphragm elevation on a chest radiograph, in absence of an ipsilateral lung disease, is assumed to indicate severe hemidiaphragm dysfunction. To test this hypothesis we retrospectively reviewed chest radiograph findings and corresponding twitch transdiaphragmatic pressure (T(W)P(DI)) results from 42 (17 female, age range 22-79 years) consecutive patients who underwent phrenic nerve stimulation studies. Chest radiographs were independently reviewed in a blind manner by two radiologists. The interobserver agreement was moderate, the kappa value ranging from 0.48 (left hemidiaphragm) to 0.59 (lung parenchyma). Hemidiaphragm dysfunction was diagnosed if T(W)P(DI) of corresponding hemidiaphragm was less than 3.5 cm H2O. The prevalence of patients with an elevated unilateral hemidiaphragm on chest radiograph was 64% and of patients with unilateral paralysis judged by T(W)P(DI) was 24%. Sensitivity, specificity, positive and negative predictive values for chest radiograph, as a diagnostic test for unilateral diaphragm dysfunction were 0.90, 0.44, 0.33 and 0.93, respectively. We conclude that the isolated elevation of hemidiaphragm on chest radiograph is of little value in the diagnosis of unilateral hemidiaphragm paralysis, though the condition is unlikely if diaphragm elevation is absent.

Adult↗

PubMed2004

Effect of bronchoscopic lung volume reduction on dynamic hyperinflation and exercise in emphysema.

Endobronchial valve placement improves pulmonary function in some patients with chronic obstructive pulmonary disease, but its effects on exercise physiology have not been investigated. In 19 patients with a mean (SD) FEV(1) of 28.4 (11.9)% predicted, studied before and 4 weeks after unilateral valve insertion, functional residual capacity decreased from 7.1 (1.5) to 6.6 (1.7) L (p = 0.03) and diffusing capacity rose from 3.3 (1.1) to 3.7 (1.2) mmol . minute(-1) . kPa(-1) (p = 0.03). Cycle endurance time at 80% of peak workload increased from 227 (129) to 315 (195) seconds (p = 0.03). This was associated with a reduction in end-expiratory lung volume at peak exercise from 7.6 (1.6) to 7.2 (1.7) L (p = 0.03). Using stepwise logistic regression analysis, a model containing changes in transfer factor and resting inspiratory capacity explained 81% of the variation in change in exercise time (p < 0.0001). The same variables were retained if the five patients with radiologic atelectasis were excluded from analysis. In a subgroup of patients in whom invasive measurements were performed, improvement in exercise capacity was associated with a reduction in lung compliance (r(2) = 0.43; p = 0.03) and isotime esophageal pressure-time product (r(2) = 0.47; p = 0.03). Endobronchial valve placement can improve lung volumes and gas transfer in patients with chronic obstructive pulmonary disease and prolong exercise time by reducing dynamic hyperinflation.

Bronchoscopy↗

PubMed2004

Community pulmonary rehabilitation after hospitalisation for acute exacerbations of chronic obstructive pulmonary disease: randomised controlled study.

OBJECTIVE: To evaluate the effects of an early community based pulmonary rehabilitation programme after hospitalisation for acute exacerbations of chronic obstructive pulmonary disease (COPD). DESIGN: A single centre, randomised controlled trial. SETTING: An inner city, secondary and tertiary care hospital in London. PARTICIPANTS: 42 patients admitted with an acute exacerbation of COPD. INTERVENTION: An eight week, pulmonary rehabilitation programme for outpatients, started within 10 days of hospital discharge, or usual care. MAIN OUTCOME MEASURES: Incremental shuttle walk distance, disease specific health status (St George's respiratory questionnaire, SGRQ; chronic respiratory questionnaire, CRQ) and generic health status (medical outcomes short form 36 questionnaire, SF-36) at three months after hospital discharge. RESULTS: Early pulmonary rehabilitation, compared with usual care, led to significant improvements in median incremental shuttle walk distance (60 metres, 95% confidence interval 26.6 metres to 93.4 metres, P = 0.0002), mean SGRQ total score (-12.7, -5.0 to -20.3, P = 0.002), all four domains of the CRQ (dyspnoea 5.5, 2.0 to 9.0, P = 0.003; fatigue 5.3, 1.9 to 8.8, P = 0.004; emotion 8.7, 2.4 to 15.0, P = 0.008; and mastery 7.5, 4.2 to 10.7, P < 0.001) and the mental component score of the SF-36 (20.1, 3.3 to 36.8, P = 0.02). Improvements in the physical component score of the SF-36 did not reach significance (10.6, -0.3 to 21.6, P = 0.057). CONCLUSION: Early pulmonary rehabilitation after admission to hospital for acute exacerbations of COPD is safe and leads to statistically and clinically significant improvements in exercise capacity and health status at three months.

Acute Disease↗

PubMed2004

Demonstration of a second rapidly conducting cortico-diaphragmatic pathway in humans.

Functional imaging studies in normal humans have shown that the supplementary motor area (SMA) and the primary motor cortex (PMC) are coactivated during various breathing tasks. It is not known whether a direct pathway from the SMA to the diaphragm exists, and if so what properties it has. Using transcranial magnetic stimulation (TMS) a site at the vertex, representing the diaphragm primary motor cortex, has been identified. TMS mapping revealed a second area 3 cm anterior to the vertex overlying the SMA, which had a rapidly conducting pathway to the diaphragm (mean latency 16.7 +/- 2.4 ms). In comparison to the vertex, the anterior position was characterized by a higher diaphragm motor threshold, a greater proportional increase in motor-evoked potential (MEP) amplitude with voluntary facilitation and a shorter silent period. Stimulus-response curves did not differ significantly between the vertex and anterior positions. Using paired TMS, we also compared intracortical inhibition/facilitation (ICI/ICF) curves. In comparison to the vertex, the MEP elicited from the anterior position was not inhibited at short interstimulus intervals (1-5 ms) and was more facilitated at long interstimulus intervals (9-20 ms). The patterns of response were identical for the costal and crural diaphragms. We conclude that the two coil positions represent discrete areas that are likely to be the PMC and SMA, with the latter wielding a more excitatory effect on the diaphragm.

Adult↗

PubMed2004

Corticospinal control of respiratory muscles in chronic obstructive pulmonary disease.

Patients with chronic obstructive pulmonary disease (COPD) face an increased respiratory load and in consequence have an elevated respiratory drive. We used transcranial magnetic stimulation (TMS) to investigate associated changes in corticospinal excitability both at rest and during voluntary facilitation at different levels of inspiratory effort. Diaphragm and abdominal motor thresholds were significantly lower in COPD than healthy controls, but the quadriceps response was the same. In patients there was a significant increase in diaphragm response from rest during 20% inspiratory efforts but no further increase with greater efforts. In controls there was a further stepwise increase at 40% and 60% of inspiratory effort. The cortical silent period was significantly shorter in COPD. Using paired stimulation to study intracortical inhibitory and excitatory circuits we found significantly less excitability of intracortical facilitatory circuits in patients at long (>7 ms) interstimulus intervals. These results suggest that there is a ceiling effect in motor control output to the respiratory muscles of patients with COPD.

Abdominal Muscles↗

PubMed2004

Angiotensin converting enzyme genotype and strength in chronic obstructive pulmonary disease.

Quadriceps muscle weakness is an important contributor to exercise limitation in patients with chronic obstructive pulmonary disease. The deletion allele of the angiotensin converting enzyme gene polymorphism has previously been associated with a greater response to strength training in healthy subjects and might, therefore, protect against detraining in these patients. In 103 stable outpatients (mean [SD] FEV(1) 34.4 [16.5] % predicted), the angiotensin deletion allele was associated with greater isometric quadriceps strength; mean (SD) 31.4 (10.8) kg for insertion homozygotes, 34.1 (13.0) kg for heterozygotes, and 38.3 (11.6) kg for deletion homozygotes (p = 0.04 linear trend). Adjusted for fat-free mass, the relationship was stronger (linear trend p = 0.007). There was no correlation between strength and genotype in a group of 101 age-matched healthy control subjects. Twitch quadriceps force in response to magnetic femoral nerve stimulation, measured in 39 patients, was also genotype dependent; 8.3 (2.6) kg for insertion homozygotes, 10.1 (3.6) kg for heterozygotes, and 12.4 (3.5) kg for deletion homozygotes (p = 0.002 linear trend). Body mass index and fat-free mass did not differ significantly between genotypes in either group. There was no association in either patients or control subjects between genotype and inspiratory muscle strength. In chronic obstructive pulmonary disease the deletion allele is associated with greater quadriceps strength independent of confounding factors.

Cohort Studies↗

PubMed2004

Depression of diaphragm motor cortex excitability during mechanical ventilation.

The effect of mechanical ventilation on the diaphragm motor cortex remains unknown. We assessed the effect of mechanical ventilation on diaphragm motor cortex excitability by measuring the costal and crural diaphragm motor-evoked potential (MEP) elicited by single and paired transcranial magnetic stimulation. In six healthy subjects, MEP recruitment curves of the costal and crural diaphragms were assessed at relaxed end expiration during spontaneous breathing [baseline tidal volume (Vt(baseline))] and isocapnic volume cycled ventilation delivered noninvasively (NIV) at three different levels of tidal volume (Vt(baseline), Vt(baseline) + 5 ml/kg liters, and Vt(baseline) + 10 ml/kg liters). The costal and crural diaphragm response to peripheral stimulation of the right phrenic nerve was not reduced by NIV. NIV reduced the costal and crural MEP amplitude during NIV (P < 0.0001) with the maximal reduction at Vt(baseline) + 5 ml/kg. Response to paired TMS showed that NIV (Vt(baseline) + 5 ml/kg) significantly increased the sensitivity of the cortical motoneurons to facilitatory (>9 ms) interstimulus intervals (P = 0.002), suggesting that the diaphragm MEP amplitude depression during NIV is related to neuromechanical inhibition at the level of motor cortex. Our results demonstrate that mechanical ventilation directly inhibits central projections to the diaphragm.

Abdomen↗

PubMed2003

Measurement of diaphragm loading during pressure support ventilation.

OBJECTIVE: The diaphragmatic pressure-time product (PTPdi) has been used to quantify the loading and unloading of the diaphragm. The validity of the relationship between PTPdi and diaphragm electrical activity (EMGdi) during pressure-support ventilation (PSV) is unclear. We examined this relationship. DESIGN AND SETTING: Physiological study in a physiology laboratory. SUBJECTS: Six healthy adults. INTERVENTIONS: Spontaneous breathing (SB) and two levels of PSV (6 and 12 cmH(2)O), breathing room air and incremental concentrations of carbon dioxide, sufficient to achieve an EMGdi signal of approximately 200% of baseline value. MEASUREMENTS AND RESULTS: We measured the electrical (EMGdi) and mechanical (PTPdi) activity of the diaphragm using oesophageal electrode and oesophageal and gastric balloon catheters. The relationship between EMGdi and PTPdi during SB was linear in five subjects and curvilinear in one. However, with PSV 12 cmH(2)O we observed that the relationship between EMGdi and PTPdi was 'left shifted'; specifically, for any given level of EMGdi the PTPdi was smaller with PSV 12 cmH(2)O than during SB. However, when PTPdi was converted to power (the product of pressure and flow) the tendency to left shift was largely reversed. CONCLUSIONS: We conclude that when assessing of diaphragm unloading during PSV flow measurements are required. Where flow is constant, PTPdi is a valid measure of diaphragm unloading, but if not these data may be used to make an appropriate correction.

Airway Resistance↗

PubMed2003

Effects of exhaustive incremental treadmill exercise on diaphragm and quadriceps motor potentials evoked by transcranial magnetic stimulation.

It is unknown whether changes in corticomotor excitability follow exercise in healthy humans. We hypothesized that a fall in the diaphragm and quadriceps motor-evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation of the motor cortex would occur after an incremental exercise task. In 11 healthy subjects, we measured transdiaphragmatic pressure and isometric quadriceps tension in response to supramaximal peripheral magnetic nerve stimulation. MEPs were recorded from these muscles in response to transcranial magnetic stimulation. After baseline measurements, subjects performed a period of submaximal exercise (gentle walking). Measurements were repeated 5 and 20 min after this. The subjects then exercised on a treadmill with an incremental protocol to exhaustion. Transcranial magnetic stimulation was performed at baseline and at 5, 20, 40, and 60 min after exhaustive exercise, and force measurements were obtained at baseline, 20 min, and 60 min. Mean exercise duration was 18 +/- 4 min, and mean maximum heart rate was 172 +/- 10 beats/min. Twitch transdiaphragmatic pressure and twitch isometric quadriceps tension were not different from baseline after exercise, but a significant decrease was observed in diaphragm MEP amplitude 5 and 20 min after exercise (60 +/- 38 and 45 +/- 24%, respectively, of baseline, P = 0.0001). At the same times, the mean quadriceps MEPs were 59 +/- 39 and 74 +/- 32% of baseline (P < 0.0001 and P < 0.01, respectively). Studies using paired stimuli confirmed a likely intracortical mechanism for this depression. Our data confirm significant depression of both diaphragm and quadriceps MEPs after incremental treadmill exercise.

Adult↗

PubMed2003

Cough gastric pressure and maximum expiratory mouth pressure in humans.

Maximal expiratory mouth pressure is a well established test that is used to assess expiratory muscle strength. However, low values are difficult to interpret, as they may result from technical difficulties in performing the test, particularly in patients with facial muscle weakness or bulbar dysfunction. We hypothesized that measuring the gastric pressure during a cough, a natural maneuver recruiting the expiratory muscles, might prove to be a useful additional test in the assessment of expiratory muscle function. Mouth expiratory and cough gastric pressures were measured in 99 healthy volunteers to obtain normal values and in 293 patients referred for respiratory muscle assessment to compare the two measurements. Between-occasion within-subject coefficient of variation, assessed in 24 healthy volunteers, was 10.3% for mouth pressure and 6.9% for cough. Mean +/- SD cough gastric pressure for normal males was 214.4 +/- 42.2 and 165.1 +/- 34.8 cm H2O for females. In 171 patients deemed weak by a low mouth expiratory pressure, 42% had a normal cough gastric pressure. In 105 patients deemed weak by a low cough gastric pressure, 5.7% had a normal expiratory mouth pressure. Low maximal expiratory mouth pressures do not always indicate expiratory muscle weakness. Cough gastric pressure provides a useful complementary test for the assessment of expiratory muscle strength.

Case-Control Studies↗

PubMed2003

Symptoms and quadriceps fatigability after walking and cycling in chronic obstructive pulmonary disease.

Patients with chronic obstructive pulmonary disease (COPD) may stop cycling due to leg effort rather than breathlessness. However, cycling is not relevant to many patients, although walking may be more familiar. A total of 84 patients with COPD were asked to name the predominant symptom limiting incremental shuttle walking, endurance shuttle walking, incremental cycle ergometry, and endurance cycle ergometry, performed to exhaustion on four separate days. Furthermore, quadriceps fatigability was evaluated in 12 patients by measuring unpotentiated and potentiated twitch quadriceps tensions before and 30 minutes after incremental walking and cycling. Breathlessness alone was a more commonly cited limiting symptom after incremental walking compared with incremental cycling (81 vs. 34%; p < 0.001) and after endurance walking compared with endurance cycling (75 vs. 29%; p < 0.001). In addition, there was no significant change in mean pre- and postwalking twitch quadriceps tensions. However, cycling produced a significant reduction (unpotentiated 7.42 +/- 2.22 vs. 6.48 +/- 2.09 kg [p < 0.001]; potentiated 10.19 +/- 3.99 vs. 8.45 +/- 3.18 kg [p < 0.001]). Pre- to postexercise changes were significantly greater during cycling compared with walking (unpotentiated p = 0.01; potentiated p = 0.003). Leg effort is an infrequent symptom after walking in COPD, and low frequency fatigue of the quadriceps is an infrequent feature of incremental walking.

Aged↗