Am. J. Respir. Crit. Care Med., Vol 151, No. 3, 03 1995, 751-757.
Effect of inspiratory flow rate on respiratory sensation and pattern of breathing
HL Manning, EJ Molinary and JC Leiter
Department of Medicine and Physiology, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03756.
We examined the effect of inspiratory flow rate (IFR) on respiratory
sensation during mechanical ventilation in 10 normal subjects. We adjusted
the ventilator tidal volume (VT), frequency, and IFR until subjects
indicated that they were maximally comfortable ("comfort IFR"). Subjects
then rated breathing discomfort on a visual analog scale (VAS) while IFR
was varied among four levels: 70%, 100%, 200%, and 300% of the comfort IFR.
When compared with VAS ratings at the comfort IFR (4.4 +/- 1.2, mean +/-
SEM), VAS ratings were significantly greater at the lowest (i.e., 70%
comfort; 12.1 +/- 2.1) and highest (300% comfort; 8.2 +/- 0.9) IFR; there
was no difference in ratings between the comfort IFR and 200% comfort IFR.
At the lowest IFR, the breathing discomfort arose in the chest and had an
air hunger-like quality; at high IFR, the discomfort arose in the upper
airway. In the second portion of the study, subjects used open magnitude
estimation to rate breaths of five different sizes at three different IFR
(70%, 100%, and 200% of comfort rate). Neither the exponent nor intercept
for VT perception differed among the three IFR. Our results demonstrate
that although IFR does not alter magnitude estimation of breath size,
deviations of IFR from that desired by the subject may greatly affect
respiratory comfort.
