Respiratory muscle dynamics and control during exercise with externally imposed expiratory flow limitation.
To determine how decreasing velocity of shortening (U) of expiratory muscles affects breathing during exercise, six normal men performed incremental exercise with externally imposed expiratory flow limitation (EFLe) at approximately 1 l/s. We measured volumes of chest wall, lung- and diaphragm-apposed rib cage (Vrc,p and Vrc,a, respectively), and abdomen (Vab) by optoelectronic plethysmography; esophageal, gastric, and transdiaphragmatic pressures (Pdi); and end-tidal CO2 concentration. From these, we calculated velocity of shortening and power (W) of diaphragm, rib cage, and abdominal muscles (di, rcm, ab, respectively). EFLe forced a decrease in Uab, which increased Pab and which lasted well into inspiration. This imposed a load, overcome by preinspiratory diaphragm contraction. Udi and inspiratory Urcm increased, reducing their ability to generate pressure. Pdi, Prcm, and Wab increased, indicating an increased central drive to all muscle groups secondary to hypercapnia, which developed in all subjects. These results suggest a vicious cycle in which EFLe decreases Uab, increasing Pab and exacerbating the hypercapnia, which increases central drive increasing Pab even more, leading to further CO2 retention, and so forth.
Aliverti
Andrea
A
Centro di Bioingegneria, Fondazione Don Gnocchi e Politecnico I-20148 Milano, Italy. aliverti@mail.cbi.polimi.it
Iandelli
Iacopo
I
Duranti
Roberto
R
Cala
Stephen J
SJ
Kayser
Bengt
B
Kelly
Susan
S
Misuri
Gianni
G
Pedotti
Antonio
A
Scano
Giorgio
G
Sliwinski
Pawel
P
Yan
Sheng
S
Macklem
Peter T
PT
D000009:Abdominal Muscles / Q000502:physiology; D000328:Adult; D002245:Carbon Dioxide / Q000032:analysis / Q000502:physiology; D003964:Diaphragm / Q000502:physiology; D004417:Dyspnea / Q000150:complications / Q000503:physiopathology; D005080:Exercise Test; D006801:Humans; D006935:Hypercapnia / Q000209:etiology / Q000503:physiopathology; D007366:Intercostal Muscles / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D010366:Peak Expiratory Flow Rate / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011312:Pressure; D012123:Pulmonary Ventilation / Q000502:physiology*; D012016:Reference Values; D012132:Respiratory Muscles / Q000502:physiology*; D013909:Thorax / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology; D014939:Work of Breathing / Q000502:physiology
D002245:Carbon Dioxide