Measurement of tidal volume by using transthoracic impedance variations in rats

Abstract

The application of impedance pneumography for monitoring respiration in small animals has been limited by problems with calibration. With improved instrumentation, we describe the calibration of tidal volume in anesthetized rats. The detection of changes in voltage, reflecting the electrical impedance variations associated with respiration, was optimized by using disposable adhesive silver-silver chloride electrodes, advanced circuitry, and analog-to-digital recording instrumentation. We found a linear relationship between change in impedance and tidal volume in individual rats (R2 >/= 98%), which was strongly influenced by rat weight. Consequently, a calibration equation incorporating change in impedance and rat weight was derived to predict tidal volume. Comparison of the predicted and true tidal volumes revealed a mean R2 >/= 98%, slopes of approximately 1, intercepts of approximately 0, and bias of approximately 0.07 ml. The predicted volumes were not significantly affected by either frequency of respiration or pulmonary edema. We conclude that impedance pneumography provides a valuable tool for the noninvasive measurement of tidal volume in anesthetized rats.

Lung function, permeability, and surfactant composition in oleic acid-induced acute lung injury in rats

“…Male Porton rats (200-330 g) were anesthetized with intraperitoneal methohexital sodium (60 mg/kg; Eli Lilly, Sydney, Australia) and pentobarbital sodium (40 mg/kg; Boehringer Ingelheim, Sydney, Australia) (12). The thorax and abdomen were shaved, and residual hair was removed (Veet hair removal cream, Reckitt and Colman Pharmaceuticals).…”

“…The thorax and abdomen were shaved, and residual hair was removed (Veet hair removal cream, Reckitt and Colman Pharmaceuticals). A caudal vein and artery at the base of the tail were catheterized (12). Lines were fixed in place (Loctite 406 cyanoacrylate ester, Loctite Australia, Sydney, Australia), and heparinized saline (0.15 M, 2 U/ml) was infused (1 ml/h) to maintain the patency of the arterial line.…”

“…Additional methohexital sodium (40 mg/kg) and pentobarbital sodium (25 mg/kg) were administered every ϳ45 min, providing a constant depth of anesthesia as monitored by the animal's cardiorespiratory and reflex responses. Body temperature was continuously monitored via a rectal probe and maintained at 37°C with a thermostatically controlled plate (12). Each OA-treated animal was matched with a saline control.…”

Electrical impedance plethysmography technique in estimating pulmonary function status

“…They found that transthoracic impedance in an open chest condition was greater in the expiratory state than in the inspiratory state. Researchers measured tidal volume (V T ) using transthoracic impedance variations in animals and found a linear relationship between change in impedance and V T [6,7]. Guha and Anand [8] investigated the EIP technique in comparison with electrical field plethysmography for evaluating cardiac and respiratory EIP pulses.…”

Thoracic impedance monitoring of respiratory rate during sedation – is it safe?

“…Impedance changes are a complex function of geometry and conductivity and studies have attempted to understand the relationship between impedance and physiological change [2]. The principle involved is based on the change in impedance that occurs across transthoracic electrodes during breathing [3].…”