John Rassulo

Dyssynchronous Breathing during Arm but Not Leg Exercise in Patients with Chronic Airflow Obstruction

Some patients with chronic airflow obstruction experience dyspnea with mild arm exercise but not with more-intense leg exercise. To investigate why these patients have limited endurance during arm exertion, we studied ventilatory responses to exercise with unsupported arms in 12 patients with chronic airflow obstruction (mean [+/- SD] forced expiratory volume in one second, 0.68 +/- 0.28 liters). Unloaded leg cycling was also studied for comparison. In the five patients who had the most severe airflow obstruction, arm exercise was limited by dyspnea after 3.3 +/- 0.7 minutes, and dyssynchronous thoracoabdominal breathing developed. In the other seven patients, arm exercise was limited by the sensation of muscle fatigue after 6.1 +/- 2.0 minutes (P less than 0.05), and dyssynchronous breathing did not occur. None of the 12 patients had dyssynchronous breathing during unloaded leg cycling. Maximal transdiaphragmatic pressure, a measure of diaphragmatic fatigue, declined similarly after arm and leg exercise in both groups. During unsupported arm work, the accessory muscles of inspiration help position the torso and arms. We hypothesize that the extra demand placed on these muscles during arm exertion leads to early fatigue, an increased load on the diaphragm, and dyssynchronous thoracoabdominal inspirations. This sequence may contribute to dyspnea and limited endurance during upper-extremity exercise.

Electromyographic validation of the mouth pressure-time index : a noninvasive assessment of inspiratory muscle load

The pressure-time index (PTI = Pmouth/Pi max x Ti/Ttot) has been validated by Ramonatxo (J. Appl. Physiol. 78 (1995) 646 and by Jabour (Am. Rev. Respir. Dis. 144 (1991) 531 as a noninvasive tool for the assessment of inspiratory muscles load. Nobody until now has evaluated the correlation between the PTI and diaphragmatic activity. Further, the PTI has not been compared with another measures of respiratory muscle load such as the transdiaphragmatic pressure index or TTdi. The purpose of our study was to test the hypothesis that the PTI measured at the mouth (PTIm) is a noninvasive reflection of TTdf and electromyographic activity of the diaphragm (EMGdf). We studied 6 patients with COPD and 5 normal individuals at rest and during a CO2 rebreathing trial and simultaneously measured PTIm, TTdi and EMGdi. The curves of PTIm and EMGdi follows the same trend during the CO2 rebreathing trial with strong and significant correlation between these parameters (r = 0.89 P < 0.05 and r = 0.82 P < 0.05 for PaCO2 of 45 and 53 mmHg respectively). We conclude that PTIm measured as Pmouth/Pi max x Ti/Ttot is an adequate noninvasive method that reflect not only the diaphragmatic activity but also the inspiratory muscles load.