title: Respiratory muscle dynamics and control during exercise with externally imposed expiratory flow limitation.
abstract: 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.
authors.affiliation: Centro di Bioingegneria, Fondazione Don Gnocchi e Politecnico I-20148 Milano, Italy. aliverti@mail.cbi.polimi.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Aliverti
authors.forename: Iacopo
authors.initials: I
authors.lastname: Iandelli
authors.forename: Roberto
authors.initials: R
authors.lastname: Duranti
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Cala
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
authors.forename: Susan
authors.initials: S
authors.lastname: Kelly
authors.forename: Gianni
authors.initials: G
authors.lastname: Misuri
authors.forename: Antonio
authors.initials: A
authors.lastname: Pedotti
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scano
authors.forename: Pawel
authors.initials: P
authors.lastname: Sliwinski
authors.forename: Sheng
authors.initials: S
authors.lastname: Yan
authors.forename: Peter T
authors.initials: PT
authors.lastname: Macklem
mesh_terms: 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
chemical_list: D002245:Carbon Dioxide