Respiratory muscle training in multiple sclerosis: a pilot study.

We assessed the effects of respiratory muscle training (RMT) in patients with multiple sclerosis (MS) on vital capacity (VC), maximal static inspiratory (PImax) and expiratory (PEmax) pressures and maximal voluntary ventilation (MVV). Eight patients (mean age 53, range 42 to 65 years) with stable disease and respiratory muscle weakness (RMW; VC = 83%, PImax = 64%, PEmax = 41%, MVV = 62% of predicted value) underwent a 4 +/- 1 week RMT program using inspiratory and/or expiratory resistive loads. Results showed changes in PImax (+31%, p less than 0.02), PEmax (+31%, p less than 0.05), and MVV (+21%, p less than 0.05); VC was unchanged (+1%). Thus in these patients, RMT improved respiratory muscle strength and ventilatory capacity. RMT may be an additional method of rehabilitation in selected patients with MS, in whom RMW contributes to exercise intolerance, coughing and talking impairment.

Increased energy cost of walking in multiple sclerosis: effect of spasticity, ataxia, and weakness.

Multiple sclerosis patients with motor involvement of the lower extremities and the trunk often experience exertional dyspnea and generalized or leg fatigue on walking, and their walking performance is reduced. It has recently been suggested that a high energy cost of walking (Cw) may be an important contributing factor to the observed dyspnea and fatigue. The purpose of this study was to determine which factors influence Cw. Clinical tests were used to assess the major alterations of the motor system. Thirty-three patients (mean age 41 years, mean maximal speed 2.8 km/h, range 1.2 to 6.2 km/h) in a stable phase of their disease were examined. Cost of walking (mean +/- SE) at 1.8 km/h was 0.287 +/- 0.018 ml 02.kg-1.m-1 (normal value 0.163 +/- 0.007, p less than 0.001). A multivariate regression analysis showed that Cw was significantly related to spasticity of the lower extremities, whereas lower extremity and truncal weakness did not contribute to the observed high Cw.

Energy cost of walking and exertional dyspnea in multiple sclerosis.

Pulmonary functions at rest and cardiorespiratory responses to low speed treadmill walking were investigated in 24 patients (P), (mean age, 38 years; range, 20 to 56 yr) with multiple sclerosis and compared with a control group (C). The following parameters were significantly (p less than 0.01) different in P from those in C. At rest in P, the residual volume to TLC ratio was 21% greater, respiratory muscle strength index was 28% lower, and heart rate (HR) was 11 beats/min-1 higher. During treadmill walking at a given speed, HR, minute ventilation (VE), and O2 consumption (VO2) were all elevated (37 to 119%). In addition, the energy cost of walking, per unit distance, above resting, was 2 to 3 times greater, with mean +/- SEM values for P of 0.299 +/- 0.019 and C of 0.147 +/- 0.006 at 2 km/h and 0.275 +/- 0.042 and 0.110 +/- 0.005 (for P and C, respectively) ml O2 kg-1 m-1 at 4 km/h; the HR and VE/VO2, also when referred to a given VO2, were higher. We conclude that a high energy cost of walking may be an important contributing factor to breathlessness and leg fatigue in patients with multiple sclerosis. Poor conditioning, altered cardiovascular control, and respiratory muscle weakness may play additional roles.

Effects of induced bronchoconstriction on pulmonary blood flow.

Allergic bronchoconstriction may be associated with hemodynamic alterations due to changes in respiratory mechanics (or the associated changes in arterial blood gas composition) or the cardiovascular effects of chemical mediators. In an attempt to differentiate between these two possible mechanisms, we obtained measurements of hemodynamics, respiratory mechanics, and O2 consumption (VO2) in nine asymptomatic adult ragweed asthmatics before and after inhalation challenge with either ragweed extract or methacholine. We measured specific airway conductance (sGaw) by body plethysmography, pleural pressure with an esophageal balloon catheter, pulmonary blood flow (Q) and VO2 by a rebreathing technique, and heart rate. For a similar degree of bronchoconstriction after the two types of challenge (mean +/- SD sGaw 0.06 +/- 0.03 and 0.05 +/- 0.02 cmH2O-1 . s-1, P = NS), mean Q increased by 29 and 29%, and mean VO2 by 33 and 37% 15-20 min after ragweed and methacholine, respectively. Since heart rate did not change, there was a concomitant increase in mean stroke volume by 25 and 35%, respectively (P less than 0.05). The respiratory pleural pressure swings during quiet breathing and the rebreathing maneuver and the work of breathing during rebreathing also increased to a similar degree after the two types of challenge. These observations suggest that, if chemical mediators are released into the circulation during antigen-induced bronchoconstriction, their blood concentrations are too low for appreciable cardiovascular effects. The increase in rebreathing cardiac output during allergic and nonallergic bronchoconstriction is probably due to increases in intrathoracic pressure swings and in the work of breathing.

[Effect of physical exercise on adaptation to energy expenditure in multiple sclerosis]. / Effet de l'exercice physique sur l'adaptation à l'effort dans la sclérose en plaques.

The ability to walk and the activities of daily life in patients with multiple sclerosis may be impaired by metabolic and cardiorespiratory factors, since an energy cost of walking (Cw) more than twice the normal value has recently been demonstrated. In 12 clinically stable patients (9 men, 3 women, age 38 +/- 7 years) resting pulmonary functions, walking performance and cardiorespiratory response to walking on a treadmill at slow speed were examined before and after a 24 +/- 6 days period of rehabilitation. There was a significant improvement (p less than 0.01) in walking distance (+31%), endurance time (+26%), maximal speed (+15%) and oxygen pulse at the maximal speed (+18%). The heart rate/oxygen consumption and minute ventilation/oxygen consumption ratios and Cw were above normal and were unchanged after the period of rehabilitation. The respiratory muscle strength was decreased by 38% (p less than 0.05 from a control group) and did not change. From these preliminary results it is concluded that a 3-4 week period of rehabilitation improves walking performance. This improvement is probably the result of improved cardiorespiratory fitness due to the training effect.

Hemodynamic effects of resistive breathing.

To examine the acute hemodynamic effects induced by large swings in intrathoracic pressure such as may be generated by obstructive lung disease, airway obstruction was simulated by means of two different fixed external alinear resistances and the results were compared with those for unobstructed breathing (C). Eight normal subjects breathed through external resistances during inspiration (I), expiration (E), or both (IE) at rest (Re) and exercise (Ex). The resistances were chosen to induce similar mouth pressure (Pm) swings at Re and Ex. Pleural pressures (Ppl) were found to correlate closely with Pm. During IE resistive breathing mean swings in Pm were -31 and +19 cmH2O at Re and -38 and +22 cmH2O at Ex, with a corresponding decrease in minute ventilation (-30 and -18%) and an increase in end-tidal PCO2 (+5.6 and +4.2 Torr); these were associated with an increase in heart rate (delta HR = 4 and 6 beats/min) and systolic systemic arterial pressure (delta Psas = 10 and 14 Torr at Re and Ex, respectively). O2 consumption and cardiac output did not change. The myocardial O2 consumption, estimated from the product HR X (Psas--Ppl), increased by 17 and 20% at Re and Ex, respectively. Changes in mechanics, gas exchange, and hemodynamics were less pronounced during I or E resistive loading. It is concluded that breathing through a tight external resistance during IE at Re and Ex increases the metabolic load on the myocardium.

Diffusing capacity in idiopathic scoliosis and its interpretation regarding alveolar development.

We measured lung volumes, diffusing capacity by the single breath method (DL), membrane permeability (DM), and capillary blood volume (Vc) in 22 subjects with idiopathic scoliosis (mean angle of curvature, 66 degrees). Compared with an age-matched group, vital capacity, total lung capacity, and functional residual capacity were respectively, 21% (p less than 0.0001), 18% (p less than 0.01), and 15% (p less than 0.05) lower. The DL was 17% lower (p less than 0.01), but specific DL (DL divided by alveolar volume = DLVA) was the same. For both groups, DLVA was inversely correlated with VA. The same qualitative relationship existed between DM, Vc, their specific values, and VA except for a larger spread of Vc in the scoliotic group. The data show that DL and its components, DM and Vc, are normal in idiopathic scoliosis when reduced lung volumes are allowed for. These findings are consistent with partial failure of alveolar enlargement as a result of the thoracic deformity rather than any atrophy of the alveoli or pulmonary vasculature. Thus scoliosis results in a delay of lung development, such that in a group of symptomatic patients with moderate degrees of deformity (mean angle of curvature, 66 degrees), lung volumes and DL are about 80% of that of an age-matched control group; the alveolar characteristics of a 12-yr-old with scoliosis are therefore similar to those of a 9-yr-old normal child.

Differential effects of methacholine and antigen challenge on gas exchange in allergic subjects.

In order to better characterize the differential effects of nonspecific and specific (antigen) bronchial challenge on gas exchange, seven ragweed-sensitive subjects with a history of asthma underwent progressive inhalation challenge with methacholine and ragweed extract on two different days. For comparable severity of bronchospasm (mean specific airway conductance 0.05 sec-1cm-1H2O for methacholine and 0.06 sec-1cm-1H2O for ragweed), there was a greater decrease in mean arterial oxygen saturation after ragweed (4.7%) than after methacholine challenge (2.7%) (p less than 0.05). While this was not accompanied by differences in static lung volumes, the density-dependent index decreased by 19% after ragweed (p less than 0.001) but remained unchanged after methacholine challenge. These results suggest that a greater involvement of peripheral airways in the bronchospastic response is, at least in part, responsible for the greater decrease in arterial oxygen saturation after ragweed challenge.