Patterns of inspiratory muscle shortening during hypoxia and hypercapnia in dogs

Abstract

The shortening of parasternal intercostal muscles (Para) and crural (Cru) and costal diaphragms (Cos) are not precisely understood. We therefore examined shortening patterns of these inspiratory muscles by using chronically implanted sonomicrometers in dogs.To avoid acute effects of surgery, measurements were performed 3 weeks after implanting the sonomicrometers. Patterns of length changes of Para, Cru, and Cos were measured during hypoxia and hypercapnia under two levels of anaesthesia.Respiratory length change (∆L) was assessed as a percentage change relative to the resting length at functional residual capacity (LFRC). Peak tidal shortening was defined as the maximal change from LFRC (∆L/LFRC). Under light anesthesia, the ∆L/LFRC was the same among the three muscle groups at all tidal volumes (VT). Under deep anaesthesia, the ∆L/LFRC both of Cru and Cos exceeded that of Para. Under light anaesthesia, the maximal shortening velocity ((∆L/LFRC)/∆t ) of Cru was greater than that of Para. Under deep anaesthesia, the (∆L/LFRC)/∆t of Para was exceeded by that both of Cru and Cos. Furthermore, the (∆L/LFRC)/∆t of each inspiratory muscle was greater during hypoxia than during hypercapnia at equal volume.We conclude that: 1) the contribution of the diaphragm to ventilation increases during deep anaesthesia; 2) the muscle shortening velocity during hypoxia or hypercapnia is lower in parasternal intercostal muscles than in the diaphragm; and 3) there is no difference in the shortening pattern between crural and costal diaphragms. Eur Respir J 1997; 10: 430-436 Among the respiratory muscles of the chest wall, the intercostal muscles and the diaphragm act as the major respiratory muscles for breathing. Several reports have suggested that parasternal intercostal muscles (Para) are the primary muscles responsible for expanding the upper rib cage during inspiration [1,2]. The diaphragm is anatomically divided into two muscles, the crural (Cru) and costal parts (Cos) [3]. In animals, the activities of the inspiratory muscles have been studied mainly by electromyography (EMG) [4,5]. These studies have demonstrated that the intercostal muscles, Cru, and Cos are activated differently. On the other hand, studies on the mechanical activities of the inspiratory muscles have focused primarily on their overall movements, i.e. the rib cage and abdominal movements, by inductive plethysmography [6], or the volume-pressure relationships of the rib cage and the diaphragm-abdomen [7]. These studies have suggested that the contribution of the rib cage and diaphragm to ventilation is altered by the magnitude of ventilation or by anaesthesia.Recently, direct measurements of the changes in the lengths of the respiratory muscles have been reported by the use of sonomicrometry [8,9]. This technique allows an accurate measurement of any change in the length of respiratory muscles in vivo. However, EASTON and co-workers [10] found that there was a transient inhibition of diaphragmatic shortening after the upper abdominal surgery require...

Two-dimensional strain ultrasound speckle tracking as a novel approach for the evaluation of right hemidiaphragmatic longitudinal deformation

“…However, Suzuki et al examined the shortening of the parasternal intercostal muscles, crural diaphragm and costal diaphragm in dogs through implanted sonomicrometers. The authors identified no difference in the shortening pattern between crural and costal diaphragms (20). The advantage of right diaphragm strain imaging using non-Doppler 2D speckle tracking is that it tracks in two dimensions, along the direction of the longitudinal shortening and extension of the diaphragm, not along the US beam, and since it is not based on tissue Doppler measurements, it is angle-independent (18).…”