Citations

To assess the relative contributions of the different groups of inspiratory intercostal muscles to the cranial motion of the ribs in the dog, we have measured the axial displacement of the fourth rib and recorded the electromyograms of the parasternal intercostal, external intercostal, and levator costae in the third interspace in 15 anesthetized animals breathing at rest. In eight animals, the parasternal intercostals were denervated in interspaces 1-5. This procedure caused a marked increase in the amount of external intercostal and levator costae inspiratory activity, and yet the inspiratory cranial motion of the rib was reduced by 55%. On the other hand, the external intercostals in interspaces 1-5 were sectioned in seven animals, and the reduction in the cranial rib motion was only 22%; the amount of parasternal and levator costae activity, however, was unchanged. When the parasternals in these animals were subsequently denervated, the levator costae inspiratory activity increased markedly, but the inspiratory cranial motion of the rib was abolished or reversed into an inspiratory caudal motion. These studies thus confirm that, in the dog breathing at rest, the parasternal intercostals have a larger role than the external intercostals and levator costae in causing the cranial motion of the ribs during inspiration. A quantitative analysis suggests that the parasternal contribution is approximately 80%.

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the α index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 ± 24 to 1,499 ± 84 ml and raised SBP from 118 ± 2 to 125 ± 3 mmHg, whereas RR decreased from 947 ± 18 to 855 ± 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 ± 1 to 9 ± 1 ms/mmHg, P < 0.001) and MSNA levels (by −37 ± 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.

The shortening of the canine parasternal intercostals during inspiration may have a passive component, and we have previously speculated that this might result from the actions of the levator costae and external intercostals (J. Appl. Physiol. 66: 1421-1429, 1989). The present studies were designed, therefore, to evaluate the pattern of activation of these muscles in the dog and to define their action on the rib cage during breathing. The results indicate that 1) the levator costae and external intercostals in the cranial part of the rib cage are active during inspiration, both in the supine and in the prone posture; 2) the inspiratory activation of the two muscles is increased after bilateral phrenicotomy; 3) it is increased even more when the parasternal intercostals in the different interspaces are also denervated; and 4) when the levator costae and external intercostals are the only muscles active during inspiration, the ribs continue to move cranially, and the sternum, rather than moving caudally as it does in the intact animal, moves cranially as well. Therefore, we conclude that the levator costae and external intercostals in the dog have a true inspiratory function. When needed, they are capable of causing a significant expansion of the rib cage and the lung during breathing.

When the parasternal intercostal in a single interspace is selectively denervated in dogs with diaphragmatic paralysis, it continues to shorten during both quiet and occluded inspiration. In the present studies, we have tested the hypothesis that this passive parasternal inspiratory shortening is due to the action of the other parasternal intercostals. Changes in length of the denervated third right parasternal were measured in eight supine phrenicotomized animals. We found that 1) the inspiratory muscle shortening increased after denervation of the third left parasternal but gradually decreased with denervation of the parasternals situated in the second, fourth, and fifth interspaces; 2) the muscle, however, always continued to shorten during inspiration, even after denervation of all the parasternals; 3) stimulating selectively the third left parasternal caused a muscle lengthening; and 4) bilateral stimulation of the parasternals in the second or the fourth interspace produced a muscle shortening. We conclude that 1) the two parasternals situated in the same interspace on both sides of the sternum are mechanically arranged in series, whereas the parasternals located in adjacent interspaces are mechanically arranged in parallel; and 2) if a denervated parasternal continues to shorten during inspiration, this is in part because of the action of the parasternals in the adjacent interspaces and in part because of other inspiratory muscles of the rib cage, possibly the external intercostals and the levator costae.

We have previously demonstrated that the shortening of the canine parasternal intercostals during inspiration results primarily from the muscles' own activation (J. Appl. Physiol. 64: 1546–1553, 1988). In the present studies, we have tested the hypothesis that other inspiratory rib cage muscles may contribute to the parasternal inspiratory shortening. Eight supine, spontaneously breathing dogs were studied. Changes in length of the third or fourth right parasternal intercostal were measured during quiet breathing and during single-breath airway occlusion first with the animal intact, then after selective denervation of the muscle, and finally after bilateral phrenicotomy. Denervating the parasternal virtually eliminated the muscle shortening during quiet inspiration and caused the muscle to lengthen during occluded breaths. After phrenicotomy, however, the parasternal, while being denervated, shortened again a significant amount during both quiet inspiration and occluded breaths. These data thus confirm that a component of the parasternal inspiratory shortening is not active and results from the action of other inspiratory rib cage muscles. Additional studies in four animals demonstrated that the scalene and serratus muscles do not play any role in this phenomenon; it must therefore result from the action of intrinsic rib cage muscles.

To assess the mechanical coupling between the parasternal and external intercostals in the cranial portion of the rib cage, we measured the respiratory changes in length and the electromyograms of the two muscles in the same third or fourth intercostal space in 24 spontaneously breathing dogs. We found that 1) the amount of inspiratory shortening of the external intercostal was considerably smaller than the amount of shortening of the parasternal; 2) after selective denervation of the parasternal, the inspiratory shortening of both the parasternal and the external intercostal was almost abolished; 3) on the other hand, after selective denervation of the external intercostal, the inspiratory shortening of the parasternal was unchanged, and the inspiratory shortening of the external intercostal was reduced but not suppressed; and 4) this persistent shortening of the external intercostal was reversed into a clear-cut inspiratory lengthening when the parasternal was subsequently denervated. We conclude that in the dog 1) the inspiratory contraction of the external intercostals in the cranial portion of the rib cage is agonistic in nature as is the contraction of the parasternals; 2) during resting breathing, however, the changes in length of these external intercostals are largely determined by the action of the parasternals. These observations are consistent with the idea that in the dog, the parasternals play a larger role than the external intercostals in elevating the ribs during resting inspiratio

Abdominal surgery has a marked inhibitory influence on the diaphragm, but its effect on the expiratory muscles is not known. Therefore, we have recorded the electromyograms of the triangularis sterni, abdominal external oblique, and transversus abdominis before and after a midline laparotomy in 10 anesthetized, spontaneously breathing dogs. Measurements were obtained during quiet breathing in the supine posture, during breathing against expiratory threshold loads, during head-up tilting, and during hyperoxic hypercapnia. Expiratory activation of the transversus abdominis in all conditions was considerably reduced after laparotomy. This reduction was real, as no change in the compound muscle action potential during single pulse stimulation was observed. In contrast, expiratory recruitment of either the triangularis sterni or the abdominal external oblique was maintained or increased. We therefore conclude that laparotomy inhibits not only activation of the diaphragm during inspiration but also activation of the transversus abdominis during expiration. Visceral afferents thus affect in concert the two respiratory muscles lining the peritoneum. The present findings also emphasize the important fact that the pattern of activation of a particular abdominal muscle is not necessarily representative of the entire abdominal musculature.

Changes over time in the presenting features and clinical course of patients with primary biliary cholangitis are poorly described. We sought to describe temporal trends in patient and disease characteristics over a 44‐year period across a large international primary biliary cholangitis cohort of 4,805 patients diagnosed between 1970 and 2014, from 17 centers across Europe and North America. Patients were divided into five cohorts according to their year of diagnosis: 1970‐1979 (n = 143), 1980‐1989 (n = 858), 1990‐1999 (n = 1,754), 2000‐2009 (n = 1,815), and ≥2010 (n = 235). Age at diagnosis, disease stage, response to ursodeoxycholic acid, and clinical outcomes were compared. Mean age at diagnosis increased incrementally by 2‐3 years per decade from 46.9 ± 10.1 years in the 1970s to 57.0 ± 12.1 years from 2010 onward (P < 0.001). The female to male ratio (9:1) and antimitochondrial antibody positivity (90%) were not significantly variable. The proportion of patients presenting with mild biochemical disease (according to Rotterdam staging) increased from 41.3% in the 1970s to 72.2% in the 1990s (P < 0.001) and remained relatively stable thereafter. Patients with a mild histological stage at diagnosis increased from 60.4% (1970‐1989) to 76.5% (1990‐2014) (P < 0.001). Correspondingly, response to ursodeoxycholic acid according to Paris‐I criteria increased; 51.7% in the 1970s and 70.5% in the 1990s (P < 0.001). Recent decades were also characterized by lower decompensation rates (18.5% in the 1970s to 5.8% in the 2000s, P < 0.001) and higher 10‐year transplant‐free survival (48.4%, 68.7%, 79.7%, and 80.1% for each respective cohort; P < 0.001). Conclusion: In recent decades, a pattern of primary biliary cholangitis presentation consistent with an older age at diagnosis alongside reduced disease severity has been noted; the observed trends may be explained by an increase in routine testing of liver function and/or a changing environmental trigger. (Hepatology 2018;67:1920‐1930).

Familial interstitial lung disease (ILD) is defined as presence of ILD in 2 or more family members. Surfactant protein C (SFTPC) gene mutations are rare, but well-known cause of familial ILD. We reported a 20-year-old male, who was referred for lung transplantation. He was symptomatic at age 3 and underwent surgical lung biopsy at age 6, which revealed a nonspecific interstitial pneumonia (NSIP) pattern. Genetic workup revealed a novel SFTPC mutation in the first intron with a C to A transversion. At age 21, he underwent bilateral lung transplantation. Explanted lung histology suggested NSIP. In addition there was pulmonary neuroendocrine cell (PNEC) hyperplasia and carcinoid tumorlets. His mother had undergone lung transplantation several years earlier, and her explanted lung showed similar pathology. SFTPC mutations are inherited in an autosomal dominant pattern. Various types of ILD have been associated with SFTPC mutation including NSIP, usual interstitial pneumonia (UIP), and desquamative interstitial pneumonia (DIP). PNEC hyperplasia has been described to occur in association with lung inflammation but has not been previously described with familial ILD associated with SFTPC mutation.