Effect of imposed inflation time on respiratory frequency and hyperinflation in patients with chronic obstructive pulmonary disease.
Decreases in ventilator inflation time (TI,vent) can cause tachypnea, probably as a response to lung inflation. The response may differ in chronic obstructive pulmonary disease (COPD) because time-constant inhomogeneities could foster overdistention of some lung units during early inflation, causing neural inspiratory time to be shorter than in healthy subjects. We tested the hypothesis that a decrease in TI,vent causes tachypnea, prolongation of exhalation, and a decrease in intrinsic positive end-expiratory pressure (PEEP(i)). Ten patients with stable COPD received assist-control ventilation through a mouthpiece. Decreases in TI,vent, achieved through increases in flow from 30 to 90 L/min, increased frequency, from 16.1 +/- 1.0 (SE) to 20.8 +/- 1.5 breaths/min (p < 0.001), time for exhalation, from 2.1 +/- 0.2 to 2.3 +/- 0.2 s (p < 0.025), and decreased PEEP(i), from 7.0 +/- 1.3 to 6.4 +/- 1.1 cm H(2)O (p < 0.01). Decreases in TI,vent, achieved by decreasing inspiratory pause from 2 to 0 s, increased frequency, from 12.9 +/- 0.8 to 18.1 +/- 1.6 breaths/min (p < 0.001), time for exhalation, from 2.0 +/- 0.2 to 2.6 +/- 0.3 s (p < 0.001), and decreased PEEP(i), from 6.4 +/- 1.1 to 5.5 +/- 0.9 cm H(2)O (p < 0.01). In both experiments, decreases in TI,vent reduced inspiratory effort (p < 0.01). In conclusion, strategies to reduce TI,vent in patients with COPD caused tachypnea, yet prolonged the time for exhalation with consequent decrease in PEEP(i).
Laghi
F
F
Division of Pulmonary and Critical Care Medicine, Edward Hines, Jr. Veterans Administration Hospital, 111N, 5th Avenue and Roosevelt Road, Hines, IL 60141, USA. flaghi@lumc.edu
Segal
J
J
Choe
W K
WK
Tobin
M J
MJ
D000368:Aged; D000403:Airway Resistance; D001784:Blood Gas Analysis; D005541:Forced Expiratory Volume; D005652:Functional Residual Capacity; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000145:classification / Q000150:complications / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy*; D008297:Male; D018467:Positive-Pressure Respiration, Intrinsic / Q000209:etiology*; D012121:Respiration, Artificial / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D015656:Respiratory Mechanics; D012720:Severity of Illness Index; D012815:Signal Processing, Computer-Assisted; D013990:Tidal Volume; D013997:Time Factors