Effects of the inspiratory pressure waveform during patient-triggered ventilation on pulmonary stretch receptor and phrenic nerve activity in cats.
OBJECTIVE
To examine the effects of square wave, sinusoidal, and linear inspiratory pressure waveforms during pressure-controlled assist/control ventilation on the firing pattern of pulmonary stretch receptors and phrenic nerve activity.


METHODS
Experimental, comparative study.


METHODS
Research laboratory at a university biomedical center.


METHODS
Nine anesthetized, endotracheally intubated young cats (2.5-3.4 kg).


METHODS
With interposed periods of continuous positive airway pressure (0.2 kPa), each cat was exposed to periods of assist/control ventilation with three different pressure waveforms, where the peak inspiratory pressure (0.74 +/- 0.13 kPa), end-expiratory pressure (0.2 +/- 0.02 kPa), and tidal volume (14.9 +/- 5.22 mL/kg) were kept constant. Preset controlled ventilator rate was set below the rate of spontaneous breathing, and the mechanical inflation time equaled the inspiratory time during spontaneous breathing on continuous positive airway pressure.


RESULTS
Respiratory rate and arterial blood gases did not change between the three pressure waveforms during assist/control ventilation. Peak pulmonary stretch receptor activity was lower and mean phrenic nerve activity higher during continuous positive airway pressure than during assist/control ventilation (p <.05). Peak inspiratory pulmonary stretch receptor activity was the same with all three pressure waveforms (82 +/- 17 impulses.sec-1) but occurred earlier with square wave than with sinusoidal or linear pressure waveforms (p <.05). The total number of impulses in the phrenic nerve activity burst was smaller with square wave than with the other two pressure waveforms (0.21 +/- 0.17 vs. 0.33 +/- 0.27 and 0.42 +/- 0.30 arbitrary units; p <.05), and the phrenic nerve activity burst duration was shorter with square wave (1.10 +/- 0.45 vs. 1.54 +/- 0.36 and 1.64 +/- 0.25 secs; p <.05).


CONCLUSIONS
Square wave pressure waveform during pressure-controlled assist/control ventilation strongly inhibits spontaneous inspiratory activity in cats. One mechanism for this inhibition is earlier and sustained peak pulmonary stretch receptor activity during inspiration. These findings show that differences in inspiratory pressure waveforms influence the spontaneous breathing effort during assist/control ventilation in cats.
Ehrhardt
H
H
Department of Women's and Children's Health, Uppsala University, Children's University Hospital, 751 85 Uppsala, Sweden.
Sindelar
R
R
Jonzon
A
A
Rieger-Fackeldey
E
E
Schaller
P
P
Schulze
A
A
Sedin
G
G
D000222:Adaptation, Physiological; D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D007384:Intermittent Positive-Pressure Breathing; D010791:Phrenic Nerve / Q000502:physiology*; D011661:Pulmonary Stretch Receptors / Q000502:physiology*; D015656:Respiratory Mechanics; D012815:Signal Processing, Computer-Assisted; D013990:Tidal Volume