A novel, non-invasive method of respiratory monitoring for use with stereotactic procedures

Abstract

Accurate monitoring of respiration is often needed for neurophysiological studies, as either a dependent experimental variable or an indicator of physiological state. Current options for respiratory monitoring of animals held in a stereotaxic frame include EMG recordings, pneumotachograph measurements, inductance-plethysmography, whole-body plethysmography (WBP), and visual monitoring. While powerful, many of these methods prevent access to the animal’s body, interfere with experimental manipulations, or require deep anesthesia and additional surgery. For experiments where these issues may be problematic, we developed a non-invasive method of recording respiratory parameters specifically for use with animals held in a stereotaxic frame. This system, ventilation pressure transduction (VPT), measures variations in pressure at the animal’s nostril from inward and outward airflow during breathing. These pressure changes are detected by a sensitive pressure transducer, then filtered and amplified. The output is an analog signal representing each breath. VPT was validated against WBP using 10% carbon dioxide and systemic morphine (4 mg/kg) challenges in lightly anesthetized animals. VPT accurately represented breathing rate and tidal volume changes under both baseline and challenge conditions. This novel technique can therefore be used to measure respiratory rate and relative tidal volume when stereotaxic procedures are needed for neuronal manipulations and recording.

Parabrachial complex links pain transmission to descending pain modulation

“…Heart rate was monitored using EKG, and respiratory rate using a ventilation pressure transducer. 16 Body temperature was monitored and maintained at 36–37 °C with a heating pad. When preparatory surgeries were complete, rats were placed on a continuous methohexital infusion.…”

Adaptations in responsiveness of brainstem pain-modulating neurons in acute compared with chronic inflammation

“…Room temperature was kept around 25 °C, and body temperature maintained between 36 and 37 °C using a heating pad. Heart rate was monitored using EKG, and respiratory rate was monitored by recording changes in air pressure at the nares, as described in detail elsewhere [7]. The experimental protocol was started once heart rate, core temperature, and respiratory rate were stable and methohexital flow rate not adjusted for a minimum of 45 min.…”

Pain-facilitating medullary neurons contribute to opioid-induced respiratory depression

“…Breathing was monitored by using two different noninvasive methods, both of which provide accurate measurements of breathing rate and relative tidal volume compared with whole body plethysmography (Cleary et al 2012). Initial experiments used accelerometry-based plethysmography (Devonshire et al 2009), where an accelerometer was attached to the chest wall of the animal to detect movements associated with breathing.…”

“…Initial experiments used accelerometry-based plethysmography (Devonshire et al 2009), where an accelerometer was attached to the chest wall of the animal to detect movements associated with breathing. In later experiments, respiration was monitored by ventilation pressure transduction (Cleary et al 2012), which measures small changes in pressure just outside the animal's nose resulting from inhalation and exhalation. The respiratory signals were amplified, filtered, and recorded for off-line analysis (Spike2; CED, Cambridge, UK).…”

“…Respiratory rate was determined by averaging the interbreath interval over the 60-s period before each TF. Relative respiratory amplitude was determined by expressing peak-to-peak amplitude, a correlate of tidal volume (Cleary et al 2012), as a percentage of the predrug baseline. Heart rate was derived from the electrocardiogram.…”