Neural Respiratory Drive In Healthy Young And Elderly Subjects At Rest And During Exercise

Part 1 Lung Function and Neural Respiratory DriveObjective Lung function deceases with age. It is not sure whether the reduction of lung function in healthy elderly subjects is related to neural respiratory drive. The aim of this study is to compare neural respiratory drive and lung function in healthy elderly subjects with those in young subjects.Methods 8 healthy elderly subjects (mean±SD age, 57.3±5.0 years; FEV₁, 102.2%±10.9% pred ) and 8 sex-matched healthy young subjects (age, 28.3±3.4 years; FEV₁, 104.0%±6.7% pred) were studied. Conventional lung function tests were performed in all the subjects. Neural respiratory drive was assessed by Diaphragm EMG recorded from a multipair esophageal electrode.Results Maximal diaphragm EMG was similar between healthy elderly subjects and healthy young subjects (172.2±54.6μV vs 175.0±55.7μV, P=0.921) although VC in the elderly subjects was much smaller than that in the young subjects . Neural respiratory drive at rest in the healthy elderly subjects (27.8%±12.9%) was higher than that in the healthy young subjects(16.4%±7.2%, P <0.05). Conclusion The fact that lung function decreases with age is not due to reduction of neural respiratory drive. Part 2 Neural Respiratory Drive and Its Efficiency during exercise in healthy young and elderly subjects【Abstract】Objective It is unknown whether neural respiratory drive and its efficiency expressed as a ratio of ventilation to diaphragm electromyogram (EMGdi) during exercise in healthy young subjects differ from those in the elderly.Methods 9 healthy elderly subjects (mean±SD age, 59.3±7.8years; FEV₁, 99.9%±12.4%pred ) and 9 sex-matched healthy young subjects (age, 27.6±3.0 years; FEV₁, 102.3%±8.3%pred) were studied. Neural respiratory drive was assessed by diaphragm EMG recorded from a multipair esophageal electrode. We recorded minute ventilation, oxygen consumption and diaphragm EMG during exercise.Results Maximal root mean square (RMS) of EMGdi was similar between healthy elderly subjects and healthy young subjects (218.2±54.3μV vs 220.2±48.6μV, P=0.935). Maximal esophageal pressure ( Pes ) obtained by the maximal voluntary inspiratory efforts was 62.5±17.2 cmH₂O in the health elderly subjects and was lower than that in the young subjects(79.5±8.1 cmH₂0, P<0.05). EMGdi increased gradually and reached a sub-maximal drive during incremental cycle exercise in both young and elderly subjects. Neural respiratory drive expressed as a percentage of maximal drive at the end of exercise was 64.9%±7.8% in the elderly subjects and was higher than that in the healthy young subjects(55.7%±8.9%, P <0.05). The ratio of ventilation to EMGdi at the end of exercise in the elderly subjects is lower than that in the young subjects (101%±19% vs 158%±35%,P<0.01).Conclusions The reserve of neural respiratory drive in the elderly was lower than that in the young. Exercise limitation in the elderly may be related to a reduction of reserve of neural respiratory drive. The reduction of Efficiency of neural drive in the elderly subjects may be related to the reduction of function of respiratory system.