Effect of Inspiratory Resistive Loading on Costal and Crural Diaphragm Electromyograms in Piglets

Abstract

ABSTRAff. We examined the effect of inspiratory resistive loaded breathing (IRL) on the electromyographic (EMG) activity of the costal and crural diaphragm in nine anesthetized spontaneously breathing piglets (age 10-23 days, weight 2.8-4.4 kg). Bipolar wire electrodes were inserted into the anterior paratendinous costal diaphragm and the midportion of the crural diaphragm. EMG activity was quantified in arbitrary units ( Experimental evidence from adult animal studies suggests that the costal and crural portions of the diaphragm may be two separate muscles (1 -4). Specifically, differences in the mechanical actions (I), fiber composition (2), embryologic development (3), and segmental innervation (4) of the costal and crural segments have been documented. Furthermore, investigators have recently reported differential costal and crural diaphragm EMG activity during periods of heightened respiratory drive (5, 6), suggesting that the neural control of the two diaphragmatic segments may be different.The effect of loaded breathing on costal and crural EMG activity has not been evaluated within a neonatal context. Developmental changes in 1) the diaphragmatic muscle (7), 2) the mechanical properties of the respiratory system (8), and 3) the chemosensory and mechanoreflex systems (9-1 1) of mammals are known to exist. Thus, one cannot assume that the EMG activity of the costal and crural segments of the developing diaphragm, in response to heightened respiratory drive, are similar to those of the adult. We therefore examined the effect of inspiratory resistive loaded breathing on the EMG activity of the costal and crural diaphragm in the piglet. We hypothesized that the inspiratory EMG activity of the diaphragm is differentially distributed between its costal and crural components during inspiratory resistive loaded breathing. METHODSFarm bred piglets obtained from the University of Washington vivarium served as our study animal. Experiments were performed on nine piglets of postnatal age 10-23 days (weight 2.8-4.4 kg). The animals were anesthetized with an intravenous combination of chloralose (50 mg/kg) and urethane (200 mg/ kg) and studied in the supine position. Subsequent infusions of anesthesia were given if the piglet developed jaw clonus. Only anesthetized piglets with a respiratory rate of 15 to 30 breaths per minute, a Pa02 of greater than 60 torr in room air, and a PaC02 of less than 50 torr were studied.The trachea was surgically exposed and cut horizontally. A metal tube (6.35 mm OD) was inserted in the distal trachea, secured with suture, and attached to a Hans-Rudolph miniature two-way nonrebreathing valve (no. 2384). A femoral artery and vein were cannulated to monitor blood gases and give anesthesia. A Corning 168 Blood Gas Analyzer (Corning Glass Works, Medfield, MA) was utilized to determine arterial blood gas tensions and pH. Rectal temperature was continuously monitored (YSI Tele-Thermometer 43TA, Yellow-Springs Instrument Co., Yellow-Springs, OH) and maintained between 38.5-39.5' C (12) by a radi...

Effect of Hypercapnia and Hypoxia on Costal and Crural Diaphragm Electromyograms in Piglets

“…In support of this concept, we have recently reported that the inspiratory EMG activity of the diaphragm is differentially distributed between its costal and crural components during inspiratory resistive loaded breathing in piglets (8). Specifically, we observed a greater augmentation in crural EMG activity when compared to its costal counterpart during the period of loaded breathing.…”

Ventilatory failure during resistive loaded breathing in the newborn primate

“…3 The crural diaphragm was selected for EMG recordings since it exhibits preferential augmentation during resistive loaded breathing. 6,7 The electrode placement was accomplished without laparotomy due to its potential adverse effects on diaphragmatic function. 8 A third electrode was placed subdermally at the base of the buttocks to provide an electrical ground.…”

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