title: Effects of exercise-induced arterial hypoxaemia and work rate on diaphragmatic fatigue in highly trained endurance athletes.
abstract: Diaphragmatic fatigue occurs in highly trained athletes during exhaustive exercise. Since approximately half of them also exhibit exercise-induced arterial hypoxaemia (EIAH) during high-intensity exercise, the present study sought to test the hypothesis that arterial hypoxaemia contributes to exercise-induced diaphragmatic fatigue in this population. Ten cyclists ( : 70.0 +/- 1.6 ml kg(-1) min(-1); mean +/-s.e.m.) completed, in a balanced ordering sequence, one normoxic (end-exercise arterial O(2) saturation (S(a,O(2))): 92 +/- 1%) and one hyperoxic (F(I,O(2)): 0.5% O(2); S(a,O(2)) : 97 +/- 1%) 5 min exercise test at intensities equal to 80 +/- 3 and 90 +/- 3% of maximal work rate (WR(max)), respectively, producing the same tidal volume (V(T)) and breathing frequency (f) throughout exercise. Cervical magnetic stimulation was used to determine reduction in twitch transdiaphragmatic pressure (P(di,tw)) during recovery. Hyperoxic exercise at 90% WR(max) induced significantly (P= 0.022) greater post-exercise reduction in P(di,tw) (15 +/- 2%) than did normoxic exercise at 80% WR(max) (9 +/- 2%), despite the similar mean ventilation (123 +/- 8 and 119 +/- 8 l min(-1), respectively), breathing pattern (V(T): 2.53 +/- 0.05 and 2.61 +/- 0.05 l, f: 49 +/- 2 and 46 +/- 2 breaths min(-1), respectively), mean changes in P(di) during exercise (37.1 +/- 2.4 and 38.2 +/- 2.8 cmH(2)O, respectively) and end-exercise arterial lactate (12.1 +/- 1.4 and 10.8 +/- 1.1 mmol l(-1), respectively). The difference found in diaphragmatic fatigue between the hyperoxic (at higher leg work rate) and the normoxic (at lower leg work rate) tests suggests that neither EIAH nor lactic acidosis per se are likely predominant causative factors in diaphragmatic fatigue in this population, at least at the level of S(a,O(2)) tested. Rather, this result leads us to hypothesize that blood flow competition with the legs is an important contributor to diaphragmatic fatigue in heavy exercise, assuming that higher leg work required greater leg blood flow.
authors.affiliation: Department of Critical Care Medicine and Pulmonary Services, Evangelismos Hospital, M. Simou and GP Livanos Laboratories, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Vogiatzis
authors.forename: Olga
authors.initials: O
authors.lastname: Georgiadou
authors.forename: Ifigenia
authors.initials: I
authors.lastname: Giannopoulou
authors.forename: Maria
authors.initials: M
authors.lastname: Koskolou
authors.forename: Spyros
authors.initials: S
authors.lastname: Zakynthinos
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Kostikas
authors.forename: Epaminondas
authors.initials: E
authors.lastname: Kosmas
authors.forename: Harrieth
authors.initials: H
authors.lastname: Wagner
authors.forename: Eleni
authors.initials: E
authors.lastname: Peraki
authors.forename: Antonia
authors.initials: A
authors.lastname: Koutsoukou
authors.forename: Nickolaos
authors.initials: N
authors.lastname: Koulouris
authors.forename: Peter D
authors.initials: PD
authors.lastname: Wagner
authors.forename: Charis
authors.initials: C
authors.lastname: Roussos
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D003964:Diaphragm / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D007773:Lactates / Q000097:blood; D007866:Leg / Q000098:blood supply / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness; D012123:Pulmonary Ventilation / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D012119:Respiration; D013990:Tidal Volume; D013997:Time Factors
chemical_list: D007773:Lactates; D010100:Oxygen