"Second wind" during inspiratory loading.
Five human volunteers breathed through an inspiratory register to achieve a transdiaphragmatic pressure (Pdi) of 42-45% of the maximum, until fatigue. During the period of resistive breathing all subjects experienced at least one episode of a sudden feeling of relaxation and relief from dyspnea, i.e., "second wind." These episodes were accompanied by a sudden decrease in the neural stimulation to the diaphragm as reflected in the electromyogram (EMG). Changes in lung volume or chest configuration were eliminated as was recruitment of accessory muscles of inspiration during the "second wind"; thus, there appeared to be a change in the contractile function of the diaphragm such that the same force (Pdi) was achieved with less neural input. These results indicate that the phenomenon of "second wind" has physiologic correlates and may be subject to experimental verification and manipulation.
D000328:Adult; D003964:Diaphragm / Q000502:physiology; D004417:Dyspnea / Q000503:physiopathology; D004576:Electromyography; D006801:Humans; D007320:Inspiratory Capacity; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D005082:Physical Exertion; D011312:Pressure; D012119:Respiration; D013997:Time Factors