title: Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise.
abstract: The purpose of this study was to elucidate the influence of inspiratory muscle fatigue on muscle sympathetic nerve activity (MSNA) and blood pressure (BP) response during submaximal exercise. We hypothesized that inspiratory muscle fatigue would elicit increases in sympathetic vasoconstrictor outflow and BP during dynamic leg exercise. The subjects carried out four submaximal exercise tests: two were maximal inspiratory pressure (PI(max)) tests and two were MSNA tests. In the PI(max) tests, the subjects performed two 10-min exercises at 40% peak oxygen uptake using a cycle ergometer in a semirecumbent position [spontaneous breathing for 5 min and with or without inspiratory resistive breathing for 5 min (breathing frequency: 60 breaths/min, inspiratory and expiratory times were each set at 0.5 s)]. Before and immediately after exercise, PI(max) was estimated. In MSNA tests, the subjects performed two 15-min exercises (spontaneous breathing for 5 min, with or without inspiratory resistive breathing for 5 min, and spontaneous breathing for 5 min). MSNA was recorded via microneurography of the right median nerve at the elbow. PI(max) decreased following exercise with resistive breathing, whereas no change was found without resistance. The time-dependent increase in MSNA burst frequency (BF) appeared during exercise with inspiratory resistive breathing, accompanied by an augmentation of diastolic BP (DBP) (with resistance: MSNA, BF +83.4%; DBP, +23.8%; without resistance: MSNA BF, +19.2%; DBP, -0.4%, from spontaneous breathing during exercise). These results suggest that inspiratory muscle fatigue induces increases in muscle sympathetic vasomotor outflow and BP during dynamic leg exercise at mild intensity.
authors.affiliation: Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan. katayama@htc.nagoya-u.ac.jp
authors.forename: Keisho
authors.initials: K
authors.lastname: Katayama
authors.forename: Erika
authors.initials: E
authors.lastname: Iwamoto
authors.forename: Koji
authors.initials: K
authors.lastname: Ishida
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Koike
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Saito
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D013997:Time Factors; D014666:Vasomotor System / Q000502:physiology*; D055815:Young Adult