Relationship between exercise tolerance and TV vs. RR relationship in patients with heart disease

Background: Although patients with heart disease sometimes complain of shortness of breath with rapid and shallow ventilation, its precise characteristics are unclear. We evaluated the relationship between exercise tolerance and the degree of rapidness and shallowness of breathing during exercise. Methods and results: Thirty-eight heart disease patients with shortness of breath during daily activity underwent pulmonary function test and cardiopulmonary exercise testing on the same day. Regression line relating tidal volume to respiratory rate (TV/RR slope) during a ramp protocol below the inflection point was regarded as an indicator of rapid ventilation. Tidal volume after the inflection point was regarded as an indicator of shallow ventilation (TV at plateau). TV/RR slope showed weak but significant positive correlation with anaerobic threshold (r=0.317) and peak (V)over dotO(2) (r=0.302). With (V)over dotE vs. (V)over dotCO(2) slope, it was negatively correlated (r=-0.528). TV at plateau was strongly correlated with inspiratory capacity (r=0.641). It also showed strong correlation with anaerobic threshold (r=0.594), peak (V)over dotO(2) (r=0.550), and (V)over dotE vs. (V)over dotCO(2) slope (r=-0.390). There was positive correlation between TV/RR slope and TV at plateau (r=0.647). Conclusions: It is suggested that both rapid breathing and shallow breathing are related to impaired exercise tolerance. Shallow breathing is partly determined by the ability of chest expansion. (C) 2008 Japanese College of Cardiology. Published by Elsevier Ireland Ltd. All rights reserved.