Respiratory mechanics evaluation of mice submitted to intravenous methacholine: Bolus vs. continuous infusion

Abstract

The application of a bronchoconstrictor, usually Methacholine (MCh), in respiratory mechanics studies is usually accompanied by the assessment of respiratory mechanics in a dose–response curve. The MCh used in the dose–response curve can be inhaled (i.h.) and intravenous (i.v.) and there are studies comparing i.v. bolus and i.h. MCh in both mice and rats. However, MCh i.v. can be injected at short time interval (bolus) or in continuous infusion. This comparison is relevant since the way MCh is applied influences the mathematical model. We chose an aging process scenario to compare both protocols. This study aims to compare respiratory mechanics of 3-, 6-, and 10-month SAMR1 mice and how both administration methods (continuous infusion and bolus) impact respiratory mechanics evaluation. Both protocols were capable of assessing the difference among ages and doses in: peak or plateau; and area under the curve analysis. The respiratory mechanics parameters were Rn, G, and H (two-way analysis of variance: groups and doses with a P < 0.05 for all). Also, the infusion protocol presented a higher sensitivity to dose increment. In conclusion, both protocols were able to discriminate intragroup and intergroup differences. In the bolus protocol, the highest value of each curve dose may not correspond to the highest real value, and the loss of this point may be a problematic factor in the sample size. These factors are not present in the infusion protocol. Additionally, at this lineage and age screening, the infusion protocol appeared to be more sensitive to differences among ages when compared to the bolus protocol. Impact statement Respiratory mechanics studies are associated with fundamental research and translational studies; the present work thus investigates this particular matter. Our current research describes differences and similarities between two different ways of administrating a very prevalent bronchoconstrictor (methacholine) in an aging process scenario. The core issue of our work is related with troubles we find with the bolus protocol and the application of the mathematical model used to assess the respiratory mechanics. Our findings reveal the continuous infusion as an alternative to these problems and we hope to provide the proper foundations to a more reliable assessment in the respiratory field.

Drug class effects on respiratory mechanics in animal models: access and applications

“…Considering the bolus and continuous infusion protocols, our group recently published a paper comparing the protocols in mice during normal aging process. 32 We found that the bolus and continuous infusion protocols could differentiate the CPM parameters among different ages with four (30, 100, 300, and 1000 µg·kg −1 for bolus) and three (48, 96, 192 µg·kg −1 ·min −1 for continuous infusion) doses of MCh (Table 2). Additionally, the main parameter affected by the aging process was the elastance, and the observed differences were similar in the two protocols.…”

“…This may increase the total experiment time because all the previous residual content (in the cannula connected to the pump) is injected into the animal to introduce the actual MCh content. 32 The volume of the dose solution must be controlled to avoid considerable increase in the animal’s volemia. The washout time depends on the cannula capacity and adjusted flow.…”

“…ketamine doses can range from 120 to 450 mg/kg. 31,32 Barbiturates These compounds induce sedative and hypnotic activities and act as non-selective CNS depressants. 33 Currently, they have been replaced by benzodiazepines, 33 which are more effective in promoting sedative and hypnotic actions.…”

“…It is common to use an intraperitoneal route to induce anesthesia with ketamine in association with xylazine. 27,28,32 Like ketamine, the dose of xylazine depends on the animal species, 26,28 time required for the procedure, 29 and association with other agents such as anesthetics and opioid analgesics. 30…”

“…This response was performed using data from a previous study. 32 The bolus protocol is not the sole protocol to present a rapid increase and decrease as a response after MCh administration; the MCh i.h. also presents the effect.…”