Pectoralis Major Muscle

The muscle activations estimated from the musculoskeletal model during the upper-extremity isometric force task were used to calculate synergies. The muscle activations from all force directions were combined into an m × t matrix, V, where m was the number of muscles (i.e., 30) and t was the number of force directions (i.e., 1000). The activations for each muscle were normalized to unit-variance to ensure that the synergies were not biased toward high-variance muscles (Roh et al., 2012 (link)). NNMF was used to calculate synergies (Lee and Seung, 1999 (link); Tresch et al., 1999 (link), 2006 (link)) such that V = W^*C where W is the m × n matrix with n synergies and C is the n × t matrix of synergy activation coefficients. Thus, each column of W represents the weights of each muscle for one synergy, and each row of C represents how much the corresponding synergy was activated or used to generate force in each direction. The number of synergies, n, was set at four to compare to the prior experimental study. The NNMF algorithm was implemented within an iterative optimization which tested random initial estimates of W and C and selected the muscle weights and activation timings that minimized the sum of squared error between V and the muscle activations.
To demonstrate that our simulation was consistent with experimental observation, we first compared the synergies estimated from the musculoskeletal model to the synergies from the experimental protocol reported by Roh et al. (2012 (link)). The experimental protocol included EMG from eight muscles: the brachioradialis, biceps brachii, triceps brachii (long and lateral heads), deltoid (anterior, medial, and posterior fibers), and pectoralis major (clavicular fibers). Thus, for this comparison, we used the activations from the musculoskeletal model for the eight muscles with EMG to calculate synergies using NNMF. We compared the synergies from the musculoskeletal model to the experimental synergies from eight unimpaired subjects. We calculated the similarity of the synergies as the average correlation coefficient. To evaluate if the synergies from the simulation were within the inter-subject variability, we compared the synergies from the musculoskeletal model to the experimental synergies of each subject. We calculated the similarity of the experimental synergies from each subject to one another to evaluate the inter-subject variability. Each subject's synergies were then compared to the simulated synergies to evaluate the similarity between the experimental and simulated synergies. We used an equivalence test to determine if the similarity of the experimental and simulated synergies were within the inter-subject similarity with a significance level of 0.05. For both the inter-subject similarity and similarity between experimental and simulated, we report the 95% confidence intervals.

Body composition analyses for abdominal fat and muscles were performed from the reconstructed water and fat images, using the commercially available service AMRA^® Profiler (Advanced MR Analytics AB, Linköping, Sweden). The methods used in AMRA^® Profiler have been thoroughly described in earlier publications [10 (link), 11 (link), 15 (link), 33 ] but briefly the analysis consisted of the following steps: (1) image calibration to fat referenced images, (2) labels of fat and muscle compartments registered to the acquired volumes, (3) quality control of labels performed by trained analysis engineers at Advanced MR Analytics (Linköping, Sweden), and (4) quantification of fat and muscle volumes based on the calibrated images by integrating over the quality controlled labels. This process was described in detail in [11 (link)]. The included fat and muscle compartments were visceral adipose tissue (VAT), abdominal subcutaneous adipose tissue (ASAT), posterior thigh muscles, anterior thigh muscles, lower leg muscles, and abdominal muscles, detailed definitions of the anatomical regions used for compartmental fat and muscle segmentations and quality control are listed in Table 1. Finally, the individual muscles latissimus dorsi, pectoralis major, and rhomboideus were included.
Muscle fat infiltration was measured for each muscle. The MFI measurements were defined as the average PDFF of the muscle tissue, i.e. muscle tissue with an adipose tissue concentration of less than 50%. As the calibrated fat images are T1-corrected [20 (link)], and represent the adipose tissue concentration of the tissue, the MFI was calculated by scaling the adipose tissue concentration with the PDFF of adipose tissue. In this study a constant PDFF of 93.7% was assumed for adipose tissue to convert adipose tissue concentration to PDFF.
Based on water-fat images acquired with a 5° flip angle, the liver-fat was measured as the average PDFF of three 22x22x28 mm³ regions of interest (ROI) manually placed in right liver lobe, avoiding major vessels and bile ducts. The liver test and re-test scans were pooled and analysed in randomized order.

All patients underwent volumetric, thin-section, chest CT at full inspiration and expiration in the supine position. CT images were acuqired using a first-generation, dual-source CT scanner (Somatom Definition; Siemens Healthcare, Forchheim, Germany) in a caudocranial direction using the following parameters: 140 kVp, 100 mA, 0.9–1 beam pitch and slice thickness 0.6 mm and 3 mm. CT data were reconstructed using a soft convolution kernel (B30f). The pectoralis muscle was evaluated using mediastinal window images [width, 400 Hounsfield units (HU); level, 20 HU].
PMA and PMD were measured on a single axial slice of the chest CT scan above the aortic arch at baseline CT (Fig. 2) [12 (link)]. The pectoralis muscle was segmented by drawing a region of interest (ROI) that traced along the edge of the right and left pectoralis major and minor muscles; COPD severity was blinded during the analyses. PMA (in cm²) was evaluated as the sum of the left and right pectoralis major and minor muscles. PMD (in HU) was defined as the mean attenuation within the ROI that segmented the pectoralis muscle.
Fig. 2

Computed tomography (CT) scans were used to assess the pectoralis muscle area and density. a, the CT axial slice above the aortic arch level shows the pectoralis muscle segmentation (red, pectoralis major muscle; blue, pectoralis minor muscle). b and c, differences between pectoralis muscle densities are depicted in CT images

Using in-house software, whole-lung images were automatically extracted from the chest wall, mediastinum and large airways to quantitatively assess emphysema and bronchial wall thickness. Subsequently, the attenuation coefficients of pixels in these images were measured. The emphysema index (EI) was defined as the volume fraction (%) of the lung below − 950 HU at full inspiration [21 (link)]. Airway dimensions, including wall area (WA), lumen area, and WA% [defined as WA/(WA + lumen area) × 100], were measured near the origin of the right apical and left apicoposterior segmental bronchi [22 (link)]. Furthermore, WA% was used to assess airway thicknesses and the mean values of segmental bronchi in the statistical analyses; these CT measurements were performed on each participant at baseline.

After generally anesthetized under tracheal incubation, the patient was placed in a supine position on a pad positioner, with the neck gently extended using a mildly sloping pillow under the shoulder and neck. Place the operated side body close to the edge of the surgical bed (Figure 1A), and the arm was naturally abducted at about 90 degrees at the arm board (Figure 1B), which could be adjusted if the clavicle is higher than the thyroid isthmus. The monitor was placed contralateral, and the surgeon and assistant were seated on either side of the patient's arm (Figure 1C).
For the classical design (5 (link)), the main oblique incision (about 3.5–4.5 cm in length) was made along the armpit's first or second natural skin fold. It should not exceed the anterior axillary line, whereby the endoscope and surgical instrument were placed. In addition, we made a 0.5 cm small incision at the intersection of the axillary front line and the upper edge of the breast; the location was 3.0–4.0 cm underneath the main incision, whereby a 5 mm trocar, and the cannula was then inserted (Figures 2A,B). For the zero-line design, an oblique incision (about 3.5–4.5 cm in length) parallel to the armpit stripes was made about 2 cm from the axillary top. The front end should not exceed the anterior axillary line. Define the line connecting the intersection of the incision with the lateral border of the pectoralis major and the highest point of the clavicle as the zero-line. After that, define the intersection of the reverse extension line of zero-line and the anterior midline of the chest (midline of the sternum) as the apex point, then draw a straight line along a 30-degree counterclockwise angle. A 0.5 cm trocar incision is then made at the intersection of this line and the lateral border of the pectoralis major; the 30-degree angle could be slightly different due to right-handed habit. When choosing the site of the trocar incision for a female patient, the breast should be retracted inferiorly, and kept the chest skin flattened (Figures 2D,E).

Skeletal muscle and adipose tissue parameters were retrieved from routinely obtained chest CT scans at ED presentation or admission. All CT scans were obtained without the application of IV contrast. Total cross-sectional area (CSA) of the pectoralis major and minor muscles was measured bilaterally at the level of the fourth thoracic vertebra. Additionally, CSA of skeletal muscle, VAT, and SAT was demarcated at the level of the first lumbar vertebra (L1). The muscles analyzed at the L1 level included the psoas, erector, spinae, quadratus lumborum, transversus abdominis, external and internal oblique, and rectus abdominis. At both levels, following previously described methods, a single transverse image at the most cranial slide with both vertebral transverse processes clearly visible was used (Fig 1).^{12 ,13} (link) If the selected image was of poor quality, had artefacts, or did not fully depict tissue of interest, the specific slice or missing tissue was considered as a missing value and was not analyzed. CSA of these structures were quantified by one trained assessor, blinded to clinical outcomes, based on pre-established Hounsfield units (HU) thresholds (skeletal muscle, –29 to 150 HU; SAT, –190 to –30 HU; and VAT, –150 to –50 HU).²⁰ (link)^,21 (link) Boundaries were corrected manually when necessary. All analyses were performed with Slice-O-Matic software version 5.0 (Tomovision).Figure 1

A-D, Representative examples of selected CT scan slices at the fourth thoracic vertebra level (A) with demarcated pectoralis major and minor muscle (B) and at first lumbar vertebra (L1) level (C) with demarcated L1 muscle, visceral, and subcutaneous adipose tissue (D).