Περίληψη:
Peak expiratory flow (PEF) has previously been considered an
effort-dependent, non flow-limited parameter that is constrained by the
force-velocity relationship of the respiratory muscles. It has also been
assumed that, if the muscles were able to augment the expiratory
pressure, the PEF would increase. We tested the validity of this notion
in normal volunteers who were able to enhance their expiratory pressure
with maneuvers utilizing the stretch-shortening cycle (greater force
when contractions were immediately preceded by eccentric contractions).
Five healthy volunteers [35 (2) years] performed two successive
maximal expiratory flow-volume maneuvers (MEFV) in rapid sequence. MEFV1
was a standard maneuver, whereas MEFV2 included a forceful inspiration
to total lung capacity; a strategy designed to augment expiratory
pressure via the stretch-shortening cycle. Neither maneuver included a
post-inspiratory pause. We measured PEF, esophageal pressure (P-es), and
the electromyographic activity of the abdominal muscles. Compared to
MEFV1, MEFV2 produced greater activation of the abdominal muscles during
inspiration (eccentric contraction), greater peak expiratory P-es,
greater rate of rise of P-es, shorter time to PEF, but similar PEF. Our
findings directly demonstrate the inability of the augmented expiratory
effort to in-crease PEF and thus support the notion that PEF is
determined by a flow-limiting mechanism and not by the velocity of
muscle shortening.
Συγγραφείς:
Tzelepis, GE
Pavleas, I
Altarifi, A
Omran, Q
McCool, FD
