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Effects of acute hypoxemia on force and surface EMG during sustained handgrip
Author(s) -
Dousset Erick,
Steinberg Jean Guillaume,
Balon Norbert,
Jammes Yves
Publication year - 2001
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/1097-4598(200103)24:3<364::aid-mus1007>3.0.co;2-b
Subject(s) - hypoxemia , stimulation , medicine , anesthesia , peripheral , electromyography , cardiology , muscle fatigue , physical medicine and rehabilitation
Data on the consequences of acute hypoxemia on the strength of contraction are often contradictory. In healthy subjects, we tested the effects of hypoxemia (PaO 2 = 56 mmHg), maintained for a 30‐min period, on static handgrip elicited by voluntary effort or direct electrical muscle stimulation, in order to separate the consequences of hypoxemia on central or peripheral factors, respectively. Force was measured during maximal voluntary contractions (MVCs), 60% MVCs sustained until exhaustion, and 1‐min periods of electrical muscle stimulation at 60 H Z . The evoked compound muscle action potential (M wave) was recorded in resting muscle and after each period of 60‐H Z stimulation or sustained 60% MVC. Power spectrum analysis of surface electromyogram (EMG) was performed during sustained 60% MVC. Compared to normoxemia, acute hypoxemia lowered MVC (−12%, P < 0.01) but enhanced (+38%, P < 0.01) the peak force elicited by electrical muscle stimulation. In resting muscle, hypoxemia had no influence on the M‐wave amplitude but lengthened the neuromuscular transmission time(+740 μs, P < 0.05). Hypoxemia did not alter the M wave measured after 60 H Z stimulation and 60% MVC. During sustained 60% MVC, hypoxemia markedly depressed the EMG changes, abolishing the leftward shift of power spectra. These data show that acute hypoxemia reduces MVC through depression of the central drive, whereas it improves the peripheral muscle response to electrical stimulation. In addition, hypoxemia reduces the recruitment of slow firing motor unit, which are highly oxygen‐dependent. This could constitute an adaptative muscle response to a reduced oxygen supply. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 364–371, 2001