Response of ventilator dependent patients to different levels of
proportional assist (pav).
Marantz, S., W. Patrick, K. Webster, D. Roberts, L. Oppenheimer, and
M. Younes.
Respiratory and Critical Care Sections, Health Sciences Centre,
Winnipeg, Manitoba, Canada R3A 1R8
APStracts 2:0416A, 1995.
Proportional assist ventilation (PAV) is a form of ventilatory support
with which airway pressure increases in proportion to patient effort.
Because it effectively reduces the mechanical load to an adjustable
extent, PAV permits the study of pattern of breathing in patients
with respiratory disease when unconstrained by abnormal respiratory
mechanics. We studied eleven patients with assorted medical problems
requiring ventilatory support. The patients were switched to PAV and
level of support was varied from near maximal levels to the lowest
tolerable level. Each level was maintained for several minutes while
ventilation (VE), tidal volume (VT) and respiratory rate (f) were
monitored. The breathing pattern observed with the highest assist
varied substantially among patients. The range, (and means) of VE, VT
and f were 5.6 to 18.7 (12.8) l/min, 203 to 844 (517) ml and 18 to 33
(25)min-1, respectively. The correlation between VT and VE at the
highest assist was very high (r = 0.91) suggesting that ventilatory
demand is the most important determinant of VT variability. There
were no systematic changes in breathing pattern as the level of
assist was altered; at the highest and lowest levels of support VE,
VT, and f were, respectively, 12.8+5.4 (S.D.) vs 11.6+4.3 l/min,
517+217 vs 459+175 ml and 25.0 +4.2 vs 25.7+3.9 min-1. These results
indicate that within each patient, in a given state, there exist
unique values for desired VE, VT and f that are largely independent
of the mechanical load; if assist is increased, patient effort is
decreased in order to maintain the desired ventilatory targets.
Received 13 January 1995; accepted in final form 10 July 1995.
APS Manuscript Number A50-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95