Sonne and Davis found that resistive inspiratory training led to improved maximal exercise ventilation, oxygen uptake and work rate on a cycle ergometer, with no change in a sham training group. Jones et al, using a very similar program, with the addition of a third group who undertook simple physical exercises, found that all three groups improved equally. add comment
Many of these studies used inspiratory muscle training methods which left it open to the subjects to adopt an altered breathing strategy, and thereby avoid doing increased respiratory muscle work. The predictable performance of our threshold pressure valve allowed the prescription of a known inspiratory pressure.
The work done in decompressing inspired air across the valve (external work) could be altered only by the patient changing his minute ventilation. Minute ventilation during IMT in week 6 was no different from that in week 1. Pardy and Leith, reviewing the principles of skeletal muscle training as applied to the inspiratory muscles, noted that isocapneic hyperpnea is the form of training which most closely resembles exercise ventilation. It can be described as endurance training for high speed muscle changes at short length. However, this type of training is cumbersome and was found to be no more effective than intermittent positive pressure breathing. Our subjects trained with threshold pressure breathing which is a form of combined strength and endurance training, and which can be practiced at home.
The training led to decreased Ti/Ttot during resting breathing and during threshold pressure breathing. Reduction in Ti/Ttot may be beneficial in terms of diaphragmatic blood flow, leading to increase in oxygen supply to these important muscles of inspiration. If pressure-time integral is a better predictor of Vo2 resp than external work being done, then a shortening of Ti/Ttot might reduce Vo2 resp. Dyspnea has been found to correlate with mouth pressure and inspiratory time during breathing against both resistive and elastic loads, and so a shorter H/Ttot at a given Pm might reduce dyspnea.
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