Resistive loaded breathing changes the motor drive to arm and leg muscles in man.

Breathing through inspiratory or expiratory resistive loads activates respiratory afferents. In healthy individuals, we explored the recruitment of motor units in arm (adductor pollicis, AP and biceps branchialis, BB) and leg (vastus lateralis, VL) muscle groups during voluntary contractions sustained at 80% of maximal force. Quantitative EMG analysis consisted of measurement of energies in high (EH) and low (EL) frequency bands. EH and EL changes were measured at constant time, i.e. 10 and 20 s after the onset of plateau contraction. The resistive load was added to the inspiratory or the expiratory circuit for 10-min periods. Its value was high but not enough to induce changes in blood gases and blood pressure. Compared to muscle contractions performed during non-loaded breathing periods, inspiratory loading did not affect BB and VL contractions, whereas it induced significant changes in AP contraction, characterized by enhanced variations in EL value measured at 10 s. Expiratory loading affected solely the VP contraction. Then, EH decreased at 10 and 20 s while it increased always when VP contractions were executed during non-loaded breathing. Expiratory loading elevated the functional residual capacity (FRC), but the load-induced changes in VL contraction persisted when subjects adjusted their FRC to the control level. These data suggest that respiratory afferents influence the skeleto-motor drive. Thus, viscero-somatic reflex may be present in patients with severe obstructive pulmonary disease.

Association of oral almitrine and medroxyprogesterone acetate: effect on arterial blood gases in chronic obstructive pulmonary disease.

Almitrine (A) and medroxyprogesterone acetate (MA) given separately improve arterial blood gases in some patients with chronic obstructive pulmonary disease (COPD); the aim of this study was to assess the effect of the two drugs given together. Forty-eight patients with irreversible COPD and hypoxaemia were prospectively enrolled into a 14-day run-in period and received single-blind oral treatment with double placebo. Patients whose PaO2 remained stable (less than 10% change; n = 29, 25 males, mean age 65.6 years) were included in a 14-day active treatment period and randomly assigned to three groups. They received double-blind oral treatment with: A (50 mg bid, group A, n = 10); MA (20 mg tid, group MA, n = 9); A (50 mg bid) and MA (20 mg tid, group A+MA, n = 10). Anthropometric and spirometric measurements were similar in the three groups and so were the arterial blood gas values at the beginning and the end of the run-in period. At the end of the active treatment period, blood gas changes (mean+/-SE) were significantly different between groups (P<0.05, Kruskal-Wallis test), with improvement in both hypoxaemia and hypercapnia in group A+MA only: delta PaO2 = 7.4+/-1.9 mmHg, delta PaCO2 = -5.1+/-1.7 m mHg (P<0.05, Wilcoxon test). In short-term treatment, the association of A and MA is more efficient than either drug alone at improving arterial blood gases in COPD patients.

Supine hypoxemia following nebulizated salbutamol in patients with chronic airway obstruction.

Inhaled beta-adrenergic agonists can decrease arterial oxygen tension (PaO2). A decrease in PaO2 can also be observed with supine posture. We assessed the effect on PaO2 of supine posture following salbutamol nebulization inpatients with chronic airflow obstruction. Twelve patients (10 males, 2 females mean age 60 yr) with FEV1/FVC = 0.65 (mean 0.54) and resting PaO2 = 60 mm Hg while breathing room air (mean 76.5 mm Hg) were included in a prospective randomized double-blind double crossover study conducted for 2 consecutive days. On each study day, each patient successively underwent baseline PaO2 measurement; nebulization of either salbutamol (0.5% solution, 1 cm3) or saline; two supervised 30-min periods in the supine or seated posture, with PaO2 measurement at the end of each period. PaO2 values were compared with analysis of variance for repetitive measurements (6 values for each patient). PaO2 values (mean +/- SD; mm Hg) were similar at baseline (day 1: 76.5 +/- 8.1; day 2: 76.6 +/- 8.6), after saline + seated (74.8 +/- 7.2), after saline + supine (74.9 +/- 7.5), and after salbutamol + seated (74.3 +/- 7.3). In contrast, PaO2 after salbutamol + supine (70.8 +/- 10.1) was significantly lower than all other values (p <0.05), six patients exhibited large PaO2 decreases (from 9 to 21 mm Hg). Hypoxemia induced by the combination of nebulized salbutamol and supine posture may represent a potential hazard of bronchodilator therapy.

Fatigue-induced changes in diaphragmatic afferents and cortical activity in the cat.

The rationale for the present study was to test the hypothesis that changes in phrenic sensory activity during diaphragmatic fatigue may modify the transmission of phrenic afferent action potentials to the cortex and also the spontaneous EEG activity. This was performed in anesthetized cats. Diaphragmatic fatigue was produced by intermittent direct muscle stimulation for a 30 min period. Diaphragmatic metaboreceptors (tonically active afferents) and mechanoreceptors (phasic phrenic activity) were identified by their activation by intraarterial lactic acid injection or their discharge in phase with diaphragmatic contraction, respectively. Cortical phrenic evoked potentials (CPEPs) and spontaneous EEG activity were recorded from the left sensorimotor area. Diaphragmatic failure was shown from the 10th minute of stimulation. Then, the activity of tonic phrenic afferents increased markedly whereas, in parallel, the phasic discharge of mechanoreceptors decreased progressively. This was associated with progressive lengthening in onset and peak latencies of CPEPs. The main EEG changes (visual and fast Fourier transform analysis) were characterized by a transient increased energy in the delta frequency band during the first minutes of the fatigue run, followed by decreased energy in the theta frequency band after 11-25 min of stimulation. Denervation of the diaphragm suppressed the EEG changes during the fatigue run. The present observations suggest that the cortical integration of sensory information from the diaphragm may be altered during fatigue.

EMG changes in respiratory and skeletal muscles during isometric contraction under normoxic, hypoxemic, or ischemic conditions.

The consequences of general hypoxemia (PaO2 = 51 mmHg) on two muscle groups (adductor pollicis and diaphragm) sustaining 80% maximal isometric voluntary contraction were studied in healthy individuals. For adductor pollicis, contractions were also executed after 10-s or 3-min rest ischemia. Compared to control, i.e., normoxic, sustained isometric workloads, significant shortening of endurance time occurred only when adductor pollicis contracted under hypoxemic conditions. In both muscle groups, a 3-min ischemia test as well as hypoxemia reduced the rate of changes in integrated surface EMG in a low frequency band and lowered, or did not modify, the rate of change in the high above low frequency ratio. Recovery of normal patterns of EMG changes was prolonged only after the adductor pollicis contracted under hypoxemic conditions. The present data show that both hypoxemia and prolonged rest ischemia reduced the rate of changes in quantitative EMG activity, with the more significant effects being measured under hypoxemia.

Comparative effects of ischemia and acute hypoxemia on muscle afferents from tibialis anterior in cats.

Comparative effects of ischemia and acute hypoxemia (PaO2 = 24 mm Hg) were studied in anesthetized cats on afferents from the tibialis anterior limb muscle. Metaboreceptors (groups III and IV fibers) and mechanoreceptors were identified by their activation by an intraarterial injection of lactic acid (LA) or high-frequency vibrations (HFV) applied to the extremity of the muscle tendon, respectively. Ischemia and hypoxemia exerted opposite influences on the two categories of muscle afferents: they depressed the response of mechanoreceptors to HFV, but markedly enhanced the spontaneous tonic activity of metaboreceptors. The effects of hypoxemia were delayed but slightly greater and lasted longer during the recovery period than those exerted by ischemia. The inhibitory action on mechanoreceptors exerted by a reduced oxygen supply to muscle is interpreted as a result from local acidosis. Indeed, under normoxic conditions, a LA bolus injection during the HFV test also reduced the firing rate of these receptors.

EMG power spectrum of respiratory and skeletal muscles during static contraction in healthy man.

Changes in EMG power spectrum during isometric voluntary contraction maintained until exhaustion in the range of 20-80% MVC were studied in three skeletal muscles (adductor pollicis or AP, vastus lateralis, and medialis) and two respiratory muscles (diaphragm and rectus abdominis). Quantitative EMG analysis consisted of computation of the median frequency (MF) of power spectra and also the continuous measurement of EMG power in two bands of high (EH) and low (EL) frequencies using bandpass filters. This allowed the calculation of the H/L ratio and its time constant of decay rate (TC delta H/L) throughout the sustained static contraction. The main results were: (1) highly significant, positive correlations between TC delta H/L and the maximal MF changes and also the endurance time to fatigue; (2) EMG changes were determined early, within the first 10-20 s of contraction; and (3) EL always increased throughout the fatiguing isometric contraction, but EH changes markedly varied within the five muscle groups studied. These observations are discussed in terms of the differences in muscle fiber composition and also the variations in motor unit recruitment.